LLVM 20.0.0git
DeadStoreElimination.cpp
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1//===- DeadStoreElimination.cpp - MemorySSA Backed Dead Store Elimination -===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// The code below implements dead store elimination using MemorySSA. It uses
10// the following general approach: given a MemoryDef, walk upwards to find
11// clobbering MemoryDefs that may be killed by the starting def. Then check
12// that there are no uses that may read the location of the original MemoryDef
13// in between both MemoryDefs. A bit more concretely:
14//
15// For all MemoryDefs StartDef:
16// 1. Get the next dominating clobbering MemoryDef (MaybeDeadAccess) by walking
17// upwards.
18// 2. Check that there are no reads between MaybeDeadAccess and the StartDef by
19// checking all uses starting at MaybeDeadAccess and walking until we see
20// StartDef.
21// 3. For each found CurrentDef, check that:
22// 1. There are no barrier instructions between CurrentDef and StartDef (like
23// throws or stores with ordering constraints).
24// 2. StartDef is executed whenever CurrentDef is executed.
25// 3. StartDef completely overwrites CurrentDef.
26// 4. Erase CurrentDef from the function and MemorySSA.
27//
28//===----------------------------------------------------------------------===//
29
31#include "llvm/ADT/APInt.h"
32#include "llvm/ADT/DenseMap.h"
33#include "llvm/ADT/MapVector.h"
35#include "llvm/ADT/SetVector.h"
38#include "llvm/ADT/Statistic.h"
39#include "llvm/ADT/StringRef.h"
52#include "llvm/IR/Argument.h"
53#include "llvm/IR/BasicBlock.h"
54#include "llvm/IR/Constant.h"
55#include "llvm/IR/Constants.h"
56#include "llvm/IR/DataLayout.h"
57#include "llvm/IR/DebugInfo.h"
58#include "llvm/IR/Dominators.h"
59#include "llvm/IR/Function.h"
60#include "llvm/IR/IRBuilder.h"
62#include "llvm/IR/InstrTypes.h"
63#include "llvm/IR/Instruction.h"
66#include "llvm/IR/Module.h"
67#include "llvm/IR/PassManager.h"
69#include "llvm/IR/Value.h"
72#include "llvm/Support/Debug.h"
79#include <algorithm>
80#include <cassert>
81#include <cstdint>
82#include <iterator>
83#include <map>
84#include <optional>
85#include <utility>
86
87using namespace llvm;
88using namespace PatternMatch;
89
90#define DEBUG_TYPE "dse"
91
92STATISTIC(NumRemainingStores, "Number of stores remaining after DSE");
93STATISTIC(NumRedundantStores, "Number of redundant stores deleted");
94STATISTIC(NumFastStores, "Number of stores deleted");
95STATISTIC(NumFastOther, "Number of other instrs removed");
96STATISTIC(NumCompletePartials, "Number of stores dead by later partials");
97STATISTIC(NumModifiedStores, "Number of stores modified");
98STATISTIC(NumCFGChecks, "Number of stores modified");
99STATISTIC(NumCFGTries, "Number of stores modified");
100STATISTIC(NumCFGSuccess, "Number of stores modified");
101STATISTIC(NumGetDomMemoryDefPassed,
102 "Number of times a valid candidate is returned from getDomMemoryDef");
103STATISTIC(NumDomMemDefChecks,
104 "Number iterations check for reads in getDomMemoryDef");
105
106DEBUG_COUNTER(MemorySSACounter, "dse-memoryssa",
107 "Controls which MemoryDefs are eliminated.");
108
109static cl::opt<bool>
110EnablePartialOverwriteTracking("enable-dse-partial-overwrite-tracking",
111 cl::init(true), cl::Hidden,
112 cl::desc("Enable partial-overwrite tracking in DSE"));
113
114static cl::opt<bool>
115EnablePartialStoreMerging("enable-dse-partial-store-merging",
116 cl::init(true), cl::Hidden,
117 cl::desc("Enable partial store merging in DSE"));
118
120 MemorySSAScanLimit("dse-memoryssa-scanlimit", cl::init(150), cl::Hidden,
121 cl::desc("The number of memory instructions to scan for "
122 "dead store elimination (default = 150)"));
124 "dse-memoryssa-walklimit", cl::init(90), cl::Hidden,
125 cl::desc("The maximum number of steps while walking upwards to find "
126 "MemoryDefs that may be killed (default = 90)"));
127
129 "dse-memoryssa-partial-store-limit", cl::init(5), cl::Hidden,
130 cl::desc("The maximum number candidates that only partially overwrite the "
131 "killing MemoryDef to consider"
132 " (default = 5)"));
133
135 "dse-memoryssa-defs-per-block-limit", cl::init(5000), cl::Hidden,
136 cl::desc("The number of MemoryDefs we consider as candidates to eliminated "
137 "other stores per basic block (default = 5000)"));
138
140 "dse-memoryssa-samebb-cost", cl::init(1), cl::Hidden,
141 cl::desc(
142 "The cost of a step in the same basic block as the killing MemoryDef"
143 "(default = 1)"));
144
146 MemorySSAOtherBBStepCost("dse-memoryssa-otherbb-cost", cl::init(5),
148 cl::desc("The cost of a step in a different basic "
149 "block than the killing MemoryDef"
150 "(default = 5)"));
151
153 "dse-memoryssa-path-check-limit", cl::init(50), cl::Hidden,
154 cl::desc("The maximum number of blocks to check when trying to prove that "
155 "all paths to an exit go through a killing block (default = 50)"));
156
157// This flags allows or disallows DSE to optimize MemorySSA during its
158// traversal. Note that DSE optimizing MemorySSA may impact other passes
159// downstream of the DSE invocation and can lead to issues not being
160// reproducible in isolation (i.e. when MemorySSA is built from scratch). In
161// those cases, the flag can be used to check if DSE's MemorySSA optimizations
162// impact follow-up passes.
163static cl::opt<bool>
164 OptimizeMemorySSA("dse-optimize-memoryssa", cl::init(true), cl::Hidden,
165 cl::desc("Allow DSE to optimize memory accesses."));
166
167//===----------------------------------------------------------------------===//
168// Helper functions
169//===----------------------------------------------------------------------===//
170using OverlapIntervalsTy = std::map<int64_t, int64_t>;
172
173/// Returns true if the end of this instruction can be safely shortened in
174/// length.
176 // Don't shorten stores for now
177 if (isa<StoreInst>(I))
178 return false;
179
180 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
181 switch (II->getIntrinsicID()) {
182 default: return false;
183 case Intrinsic::memset:
184 case Intrinsic::memcpy:
185 case Intrinsic::memcpy_element_unordered_atomic:
186 case Intrinsic::memset_element_unordered_atomic:
187 // Do shorten memory intrinsics.
188 // FIXME: Add memmove if it's also safe to transform.
189 return true;
190 }
191 }
192
193 // Don't shorten libcalls calls for now.
194
195 return false;
196}
197
198/// Returns true if the beginning of this instruction can be safely shortened
199/// in length.
201 // FIXME: Handle only memset for now. Supporting memcpy/memmove should be
202 // easily done by offsetting the source address.
203 return isa<AnyMemSetInst>(I);
204}
205
206static std::optional<TypeSize> getPointerSize(const Value *V,
207 const DataLayout &DL,
208 const TargetLibraryInfo &TLI,
209 const Function *F) {
211 ObjectSizeOpts Opts;
213
214 if (getObjectSize(V, Size, DL, &TLI, Opts))
215 return TypeSize::getFixed(Size);
216 return std::nullopt;
217}
218
219namespace {
220
221enum OverwriteResult {
222 OW_Begin,
223 OW_Complete,
224 OW_End,
225 OW_PartialEarlierWithFullLater,
226 OW_MaybePartial,
227 OW_None,
228 OW_Unknown
229};
230
231} // end anonymous namespace
232
233/// Check if two instruction are masked stores that completely
234/// overwrite one another. More specifically, \p KillingI has to
235/// overwrite \p DeadI.
236static OverwriteResult isMaskedStoreOverwrite(const Instruction *KillingI,
237 const Instruction *DeadI,
238 BatchAAResults &AA) {
239 const auto *KillingII = dyn_cast<IntrinsicInst>(KillingI);
240 const auto *DeadII = dyn_cast<IntrinsicInst>(DeadI);
241 if (KillingII == nullptr || DeadII == nullptr)
242 return OW_Unknown;
243 if (KillingII->getIntrinsicID() != DeadII->getIntrinsicID())
244 return OW_Unknown;
245 if (KillingII->getIntrinsicID() == Intrinsic::masked_store) {
246 // Type size.
247 VectorType *KillingTy =
248 cast<VectorType>(KillingII->getArgOperand(0)->getType());
249 VectorType *DeadTy = cast<VectorType>(DeadII->getArgOperand(0)->getType());
250 if (KillingTy->getScalarSizeInBits() != DeadTy->getScalarSizeInBits())
251 return OW_Unknown;
252 // Element count.
253 if (KillingTy->getElementCount() != DeadTy->getElementCount())
254 return OW_Unknown;
255 // Pointers.
256 Value *KillingPtr = KillingII->getArgOperand(1)->stripPointerCasts();
257 Value *DeadPtr = DeadII->getArgOperand(1)->stripPointerCasts();
258 if (KillingPtr != DeadPtr && !AA.isMustAlias(KillingPtr, DeadPtr))
259 return OW_Unknown;
260 // Masks.
261 // TODO: check that KillingII's mask is a superset of the DeadII's mask.
262 if (KillingII->getArgOperand(3) != DeadII->getArgOperand(3))
263 return OW_Unknown;
264 return OW_Complete;
265 }
266 return OW_Unknown;
267}
268
269/// Return 'OW_Complete' if a store to the 'KillingLoc' location completely
270/// overwrites a store to the 'DeadLoc' location, 'OW_End' if the end of the
271/// 'DeadLoc' location is completely overwritten by 'KillingLoc', 'OW_Begin'
272/// if the beginning of the 'DeadLoc' location is overwritten by 'KillingLoc'.
273/// 'OW_PartialEarlierWithFullLater' means that a dead (big) store was
274/// overwritten by a killing (smaller) store which doesn't write outside the big
275/// store's memory locations. Returns 'OW_Unknown' if nothing can be determined.
276/// NOTE: This function must only be called if both \p KillingLoc and \p
277/// DeadLoc belong to the same underlying object with valid \p KillingOff and
278/// \p DeadOff.
279static OverwriteResult isPartialOverwrite(const MemoryLocation &KillingLoc,
280 const MemoryLocation &DeadLoc,
281 int64_t KillingOff, int64_t DeadOff,
282 Instruction *DeadI,
284 const uint64_t KillingSize = KillingLoc.Size.getValue();
285 const uint64_t DeadSize = DeadLoc.Size.getValue();
286 // We may now overlap, although the overlap is not complete. There might also
287 // be other incomplete overlaps, and together, they might cover the complete
288 // dead store.
289 // Note: The correctness of this logic depends on the fact that this function
290 // is not even called providing DepWrite when there are any intervening reads.
292 KillingOff < int64_t(DeadOff + DeadSize) &&
293 int64_t(KillingOff + KillingSize) >= DeadOff) {
294
295 // Insert our part of the overlap into the map.
296 auto &IM = IOL[DeadI];
297 LLVM_DEBUG(dbgs() << "DSE: Partial overwrite: DeadLoc [" << DeadOff << ", "
298 << int64_t(DeadOff + DeadSize) << ") KillingLoc ["
299 << KillingOff << ", " << int64_t(KillingOff + KillingSize)
300 << ")\n");
301
302 // Make sure that we only insert non-overlapping intervals and combine
303 // adjacent intervals. The intervals are stored in the map with the ending
304 // offset as the key (in the half-open sense) and the starting offset as
305 // the value.
306 int64_t KillingIntStart = KillingOff;
307 int64_t KillingIntEnd = KillingOff + KillingSize;
308
309 // Find any intervals ending at, or after, KillingIntStart which start
310 // before KillingIntEnd.
311 auto ILI = IM.lower_bound(KillingIntStart);
312 if (ILI != IM.end() && ILI->second <= KillingIntEnd) {
313 // This existing interval is overlapped with the current store somewhere
314 // in [KillingIntStart, KillingIntEnd]. Merge them by erasing the existing
315 // intervals and adjusting our start and end.
316 KillingIntStart = std::min(KillingIntStart, ILI->second);
317 KillingIntEnd = std::max(KillingIntEnd, ILI->first);
318 ILI = IM.erase(ILI);
319
320 // Continue erasing and adjusting our end in case other previous
321 // intervals are also overlapped with the current store.
322 //
323 // |--- dead 1 ---| |--- dead 2 ---|
324 // |------- killing---------|
325 //
326 while (ILI != IM.end() && ILI->second <= KillingIntEnd) {
327 assert(ILI->second > KillingIntStart && "Unexpected interval");
328 KillingIntEnd = std::max(KillingIntEnd, ILI->first);
329 ILI = IM.erase(ILI);
330 }
331 }
332
333 IM[KillingIntEnd] = KillingIntStart;
334
335 ILI = IM.begin();
336 if (ILI->second <= DeadOff && ILI->first >= int64_t(DeadOff + DeadSize)) {
337 LLVM_DEBUG(dbgs() << "DSE: Full overwrite from partials: DeadLoc ["
338 << DeadOff << ", " << int64_t(DeadOff + DeadSize)
339 << ") Composite KillingLoc [" << ILI->second << ", "
340 << ILI->first << ")\n");
341 ++NumCompletePartials;
342 return OW_Complete;
343 }
344 }
345
346 // Check for a dead store which writes to all the memory locations that
347 // the killing store writes to.
348 if (EnablePartialStoreMerging && KillingOff >= DeadOff &&
349 int64_t(DeadOff + DeadSize) > KillingOff &&
350 uint64_t(KillingOff - DeadOff) + KillingSize <= DeadSize) {
351 LLVM_DEBUG(dbgs() << "DSE: Partial overwrite a dead load [" << DeadOff
352 << ", " << int64_t(DeadOff + DeadSize)
353 << ") by a killing store [" << KillingOff << ", "
354 << int64_t(KillingOff + KillingSize) << ")\n");
355 // TODO: Maybe come up with a better name?
356 return OW_PartialEarlierWithFullLater;
357 }
358
359 // Another interesting case is if the killing store overwrites the end of the
360 // dead store.
361 //
362 // |--dead--|
363 // |-- killing --|
364 //
365 // In this case we may want to trim the size of dead store to avoid
366 // generating stores to addresses which will definitely be overwritten killing
367 // store.
369 (KillingOff > DeadOff && KillingOff < int64_t(DeadOff + DeadSize) &&
370 int64_t(KillingOff + KillingSize) >= int64_t(DeadOff + DeadSize)))
371 return OW_End;
372
373 // Finally, we also need to check if the killing store overwrites the
374 // beginning of the dead store.
375 //
376 // |--dead--|
377 // |-- killing --|
378 //
379 // In this case we may want to move the destination address and trim the size
380 // of dead store to avoid generating stores to addresses which will definitely
381 // be overwritten killing store.
383 (KillingOff <= DeadOff && int64_t(KillingOff + KillingSize) > DeadOff)) {
384 assert(int64_t(KillingOff + KillingSize) < int64_t(DeadOff + DeadSize) &&
385 "Expect to be handled as OW_Complete");
386 return OW_Begin;
387 }
388 // Otherwise, they don't completely overlap.
389 return OW_Unknown;
390}
391
392/// Returns true if the memory which is accessed by the second instruction is not
393/// modified between the first and the second instruction.
394/// Precondition: Second instruction must be dominated by the first
395/// instruction.
396static bool
398 BatchAAResults &AA, const DataLayout &DL,
399 DominatorTree *DT) {
400 // Do a backwards scan through the CFG from SecondI to FirstI. Look for
401 // instructions which can modify the memory location accessed by SecondI.
402 //
403 // While doing the walk keep track of the address to check. It might be
404 // different in different basic blocks due to PHI translation.
405 using BlockAddressPair = std::pair<BasicBlock *, PHITransAddr>;
407 // Keep track of the address we visited each block with. Bail out if we
408 // visit a block with different addresses.
410
411 BasicBlock::iterator FirstBBI(FirstI);
412 ++FirstBBI;
413 BasicBlock::iterator SecondBBI(SecondI);
414 BasicBlock *FirstBB = FirstI->getParent();
415 BasicBlock *SecondBB = SecondI->getParent();
416 MemoryLocation MemLoc;
417 if (auto *MemSet = dyn_cast<MemSetInst>(SecondI))
418 MemLoc = MemoryLocation::getForDest(MemSet);
419 else
420 MemLoc = MemoryLocation::get(SecondI);
421
422 auto *MemLocPtr = const_cast<Value *>(MemLoc.Ptr);
423
424 // Start checking the SecondBB.
425 WorkList.push_back(
426 std::make_pair(SecondBB, PHITransAddr(MemLocPtr, DL, nullptr)));
427 bool isFirstBlock = true;
428
429 // Check all blocks going backward until we reach the FirstBB.
430 while (!WorkList.empty()) {
431 BlockAddressPair Current = WorkList.pop_back_val();
432 BasicBlock *B = Current.first;
433 PHITransAddr &Addr = Current.second;
434 Value *Ptr = Addr.getAddr();
435
436 // Ignore instructions before FirstI if this is the FirstBB.
437 BasicBlock::iterator BI = (B == FirstBB ? FirstBBI : B->begin());
438
440 if (isFirstBlock) {
441 // Ignore instructions after SecondI if this is the first visit of SecondBB.
442 assert(B == SecondBB && "first block is not the store block");
443 EI = SecondBBI;
444 isFirstBlock = false;
445 } else {
446 // It's not SecondBB or (in case of a loop) the second visit of SecondBB.
447 // In this case we also have to look at instructions after SecondI.
448 EI = B->end();
449 }
450 for (; BI != EI; ++BI) {
451 Instruction *I = &*BI;
452 if (I->mayWriteToMemory() && I != SecondI)
453 if (isModSet(AA.getModRefInfo(I, MemLoc.getWithNewPtr(Ptr))))
454 return false;
455 }
456 if (B != FirstBB) {
457 assert(B != &FirstBB->getParent()->getEntryBlock() &&
458 "Should not hit the entry block because SI must be dominated by LI");
459 for (BasicBlock *Pred : predecessors(B)) {
460 PHITransAddr PredAddr = Addr;
461 if (PredAddr.needsPHITranslationFromBlock(B)) {
462 if (!PredAddr.isPotentiallyPHITranslatable())
463 return false;
464 if (!PredAddr.translateValue(B, Pred, DT, false))
465 return false;
466 }
467 Value *TranslatedPtr = PredAddr.getAddr();
468 auto Inserted = Visited.insert(std::make_pair(Pred, TranslatedPtr));
469 if (!Inserted.second) {
470 // We already visited this block before. If it was with a different
471 // address - bail out!
472 if (TranslatedPtr != Inserted.first->second)
473 return false;
474 // ... otherwise just skip it.
475 continue;
476 }
477 WorkList.push_back(std::make_pair(Pred, PredAddr));
478 }
479 }
480 }
481 return true;
482}
483
484static void shortenAssignment(Instruction *Inst, Value *OriginalDest,
485 uint64_t OldOffsetInBits, uint64_t OldSizeInBits,
486 uint64_t NewSizeInBits, bool IsOverwriteEnd) {
487 const DataLayout &DL = Inst->getDataLayout();
488 uint64_t DeadSliceSizeInBits = OldSizeInBits - NewSizeInBits;
489 uint64_t DeadSliceOffsetInBits =
490 OldOffsetInBits + (IsOverwriteEnd ? NewSizeInBits : 0);
491 auto SetDeadFragExpr = [](auto *Assign,
492 DIExpression::FragmentInfo DeadFragment) {
493 // createFragmentExpression expects an offset relative to the existing
494 // fragment offset if there is one.
495 uint64_t RelativeOffset = DeadFragment.OffsetInBits -
496 Assign->getExpression()
497 ->getFragmentInfo()
498 .value_or(DIExpression::FragmentInfo(0, 0))
499 .OffsetInBits;
501 Assign->getExpression(), RelativeOffset, DeadFragment.SizeInBits)) {
502 Assign->setExpression(*NewExpr);
503 return;
504 }
505 // Failed to create a fragment expression for this so discard the value,
506 // making this a kill location.
508 DIExpression::get(Assign->getContext(), std::nullopt),
509 DeadFragment.OffsetInBits, DeadFragment.SizeInBits);
510 Assign->setExpression(Expr);
511 Assign->setKillLocation();
512 };
513
514 // A DIAssignID to use so that the inserted dbg.assign intrinsics do not
515 // link to any instructions. Created in the loop below (once).
516 DIAssignID *LinkToNothing = nullptr;
517 LLVMContext &Ctx = Inst->getContext();
518 auto GetDeadLink = [&Ctx, &LinkToNothing]() {
519 if (!LinkToNothing)
520 LinkToNothing = DIAssignID::getDistinct(Ctx);
521 return LinkToNothing;
522 };
523
524 // Insert an unlinked dbg.assign intrinsic for the dead fragment after each
525 // overlapping dbg.assign intrinsic. The loop invalidates the iterators
526 // returned by getAssignmentMarkers so save a copy of the markers to iterate
527 // over.
528 auto LinkedRange = at::getAssignmentMarkers(Inst);
529 SmallVector<DbgVariableRecord *> LinkedDVRAssigns =
531 SmallVector<DbgAssignIntrinsic *> Linked(LinkedRange.begin(),
532 LinkedRange.end());
533 auto InsertAssignForOverlap = [&](auto *Assign) {
534 std::optional<DIExpression::FragmentInfo> NewFragment;
535 if (!at::calculateFragmentIntersect(DL, OriginalDest, DeadSliceOffsetInBits,
536 DeadSliceSizeInBits, Assign,
537 NewFragment) ||
538 !NewFragment) {
539 // We couldn't calculate the intersecting fragment for some reason. Be
540 // cautious and unlink the whole assignment from the store.
541 Assign->setKillAddress();
542 Assign->setAssignId(GetDeadLink());
543 return;
544 }
545 // No intersect.
546 if (NewFragment->SizeInBits == 0)
547 return;
548
549 // Fragments overlap: insert a new dbg.assign for this dead part.
550 auto *NewAssign = static_cast<decltype(Assign)>(Assign->clone());
551 NewAssign->insertAfter(Assign);
552 NewAssign->setAssignId(GetDeadLink());
553 if (NewFragment)
554 SetDeadFragExpr(NewAssign, *NewFragment);
555 NewAssign->setKillAddress();
556 };
557 for_each(Linked, InsertAssignForOverlap);
558 for_each(LinkedDVRAssigns, InsertAssignForOverlap);
559}
560
561static bool tryToShorten(Instruction *DeadI, int64_t &DeadStart,
562 uint64_t &DeadSize, int64_t KillingStart,
563 uint64_t KillingSize, bool IsOverwriteEnd) {
564 auto *DeadIntrinsic = cast<AnyMemIntrinsic>(DeadI);
565 Align PrefAlign = DeadIntrinsic->getDestAlign().valueOrOne();
566
567 // We assume that memet/memcpy operates in chunks of the "largest" native
568 // type size and aligned on the same value. That means optimal start and size
569 // of memset/memcpy should be modulo of preferred alignment of that type. That
570 // is it there is no any sense in trying to reduce store size any further
571 // since any "extra" stores comes for free anyway.
572 // On the other hand, maximum alignment we can achieve is limited by alignment
573 // of initial store.
574
575 // TODO: Limit maximum alignment by preferred (or abi?) alignment of the
576 // "largest" native type.
577 // Note: What is the proper way to get that value?
578 // Should TargetTransformInfo::getRegisterBitWidth be used or anything else?
579 // PrefAlign = std::min(DL.getPrefTypeAlign(LargestType), PrefAlign);
580
581 int64_t ToRemoveStart = 0;
582 uint64_t ToRemoveSize = 0;
583 // Compute start and size of the region to remove. Make sure 'PrefAlign' is
584 // maintained on the remaining store.
585 if (IsOverwriteEnd) {
586 // Calculate required adjustment for 'KillingStart' in order to keep
587 // remaining store size aligned on 'PerfAlign'.
588 uint64_t Off =
589 offsetToAlignment(uint64_t(KillingStart - DeadStart), PrefAlign);
590 ToRemoveStart = KillingStart + Off;
591 if (DeadSize <= uint64_t(ToRemoveStart - DeadStart))
592 return false;
593 ToRemoveSize = DeadSize - uint64_t(ToRemoveStart - DeadStart);
594 } else {
595 ToRemoveStart = DeadStart;
596 assert(KillingSize >= uint64_t(DeadStart - KillingStart) &&
597 "Not overlapping accesses?");
598 ToRemoveSize = KillingSize - uint64_t(DeadStart - KillingStart);
599 // Calculate required adjustment for 'ToRemoveSize'in order to keep
600 // start of the remaining store aligned on 'PerfAlign'.
601 uint64_t Off = offsetToAlignment(ToRemoveSize, PrefAlign);
602 if (Off != 0) {
603 if (ToRemoveSize <= (PrefAlign.value() - Off))
604 return false;
605 ToRemoveSize -= PrefAlign.value() - Off;
606 }
607 assert(isAligned(PrefAlign, ToRemoveSize) &&
608 "Should preserve selected alignment");
609 }
610
611 assert(ToRemoveSize > 0 && "Shouldn't reach here if nothing to remove");
612 assert(DeadSize > ToRemoveSize && "Can't remove more than original size");
613
614 uint64_t NewSize = DeadSize - ToRemoveSize;
615 if (auto *AMI = dyn_cast<AtomicMemIntrinsic>(DeadI)) {
616 // When shortening an atomic memory intrinsic, the newly shortened
617 // length must remain an integer multiple of the element size.
618 const uint32_t ElementSize = AMI->getElementSizeInBytes();
619 if (0 != NewSize % ElementSize)
620 return false;
621 }
622
623 LLVM_DEBUG(dbgs() << "DSE: Remove Dead Store:\n OW "
624 << (IsOverwriteEnd ? "END" : "BEGIN") << ": " << *DeadI
625 << "\n KILLER [" << ToRemoveStart << ", "
626 << int64_t(ToRemoveStart + ToRemoveSize) << ")\n");
627
628 Value *DeadWriteLength = DeadIntrinsic->getLength();
629 Value *TrimmedLength = ConstantInt::get(DeadWriteLength->getType(), NewSize);
630 DeadIntrinsic->setLength(TrimmedLength);
631 DeadIntrinsic->setDestAlignment(PrefAlign);
632
633 Value *OrigDest = DeadIntrinsic->getRawDest();
634 if (!IsOverwriteEnd) {
635 Value *Indices[1] = {
636 ConstantInt::get(DeadWriteLength->getType(), ToRemoveSize)};
638 Type::getInt8Ty(DeadIntrinsic->getContext()), OrigDest, Indices, "",
639 DeadI->getIterator());
640 NewDestGEP->setDebugLoc(DeadIntrinsic->getDebugLoc());
641 DeadIntrinsic->setDest(NewDestGEP);
642 }
643
644 // Update attached dbg.assign intrinsics. Assume 8-bit byte.
645 shortenAssignment(DeadI, OrigDest, DeadStart * 8, DeadSize * 8, NewSize * 8,
646 IsOverwriteEnd);
647
648 // Finally update start and size of dead access.
649 if (!IsOverwriteEnd)
650 DeadStart += ToRemoveSize;
651 DeadSize = NewSize;
652
653 return true;
654}
655
657 int64_t &DeadStart, uint64_t &DeadSize) {
658 if (IntervalMap.empty() || !isShortenableAtTheEnd(DeadI))
659 return false;
660
661 OverlapIntervalsTy::iterator OII = --IntervalMap.end();
662 int64_t KillingStart = OII->second;
663 uint64_t KillingSize = OII->first - KillingStart;
664
665 assert(OII->first - KillingStart >= 0 && "Size expected to be positive");
666
667 if (KillingStart > DeadStart &&
668 // Note: "KillingStart - KillingStart" is known to be positive due to
669 // preceding check.
670 (uint64_t)(KillingStart - DeadStart) < DeadSize &&
671 // Note: "DeadSize - (uint64_t)(KillingStart - DeadStart)" is known to
672 // be non negative due to preceding checks.
673 KillingSize >= DeadSize - (uint64_t)(KillingStart - DeadStart)) {
674 if (tryToShorten(DeadI, DeadStart, DeadSize, KillingStart, KillingSize,
675 true)) {
676 IntervalMap.erase(OII);
677 return true;
678 }
679 }
680 return false;
681}
682
685 int64_t &DeadStart, uint64_t &DeadSize) {
687 return false;
688
689 OverlapIntervalsTy::iterator OII = IntervalMap.begin();
690 int64_t KillingStart = OII->second;
691 uint64_t KillingSize = OII->first - KillingStart;
692
693 assert(OII->first - KillingStart >= 0 && "Size expected to be positive");
694
695 if (KillingStart <= DeadStart &&
696 // Note: "DeadStart - KillingStart" is known to be non negative due to
697 // preceding check.
698 KillingSize > (uint64_t)(DeadStart - KillingStart)) {
699 // Note: "KillingSize - (uint64_t)(DeadStart - DeadStart)" is known to
700 // be positive due to preceding checks.
701 assert(KillingSize - (uint64_t)(DeadStart - KillingStart) < DeadSize &&
702 "Should have been handled as OW_Complete");
703 if (tryToShorten(DeadI, DeadStart, DeadSize, KillingStart, KillingSize,
704 false)) {
705 IntervalMap.erase(OII);
706 return true;
707 }
708 }
709 return false;
710}
711
712static Constant *
714 int64_t KillingOffset, int64_t DeadOffset,
715 const DataLayout &DL, BatchAAResults &AA,
716 DominatorTree *DT) {
717
718 if (DeadI && isa<ConstantInt>(DeadI->getValueOperand()) &&
719 DL.typeSizeEqualsStoreSize(DeadI->getValueOperand()->getType()) &&
720 KillingI && isa<ConstantInt>(KillingI->getValueOperand()) &&
721 DL.typeSizeEqualsStoreSize(KillingI->getValueOperand()->getType()) &&
722 memoryIsNotModifiedBetween(DeadI, KillingI, AA, DL, DT)) {
723 // If the store we find is:
724 // a) partially overwritten by the store to 'Loc'
725 // b) the killing store is fully contained in the dead one and
726 // c) they both have a constant value
727 // d) none of the two stores need padding
728 // Merge the two stores, replacing the dead store's value with a
729 // merge of both values.
730 // TODO: Deal with other constant types (vectors, etc), and probably
731 // some mem intrinsics (if needed)
732
733 APInt DeadValue = cast<ConstantInt>(DeadI->getValueOperand())->getValue();
734 APInt KillingValue =
735 cast<ConstantInt>(KillingI->getValueOperand())->getValue();
736 unsigned KillingBits = KillingValue.getBitWidth();
737 assert(DeadValue.getBitWidth() > KillingValue.getBitWidth());
738 KillingValue = KillingValue.zext(DeadValue.getBitWidth());
739
740 // Offset of the smaller store inside the larger store
741 unsigned BitOffsetDiff = (KillingOffset - DeadOffset) * 8;
742 unsigned LShiftAmount =
743 DL.isBigEndian() ? DeadValue.getBitWidth() - BitOffsetDiff - KillingBits
744 : BitOffsetDiff;
745 APInt Mask = APInt::getBitsSet(DeadValue.getBitWidth(), LShiftAmount,
746 LShiftAmount + KillingBits);
747 // Clear the bits we'll be replacing, then OR with the smaller
748 // store, shifted appropriately.
749 APInt Merged = (DeadValue & ~Mask) | (KillingValue << LShiftAmount);
750 LLVM_DEBUG(dbgs() << "DSE: Merge Stores:\n Dead: " << *DeadI
751 << "\n Killing: " << *KillingI
752 << "\n Merged Value: " << Merged << '\n');
753 return ConstantInt::get(DeadI->getValueOperand()->getType(), Merged);
754 }
755 return nullptr;
756}
757
758namespace {
759// Returns true if \p I is an intrinsic that does not read or write memory.
760bool isNoopIntrinsic(Instruction *I) {
761 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
762 switch (II->getIntrinsicID()) {
763 case Intrinsic::lifetime_start:
764 case Intrinsic::lifetime_end:
765 case Intrinsic::invariant_end:
766 case Intrinsic::launder_invariant_group:
767 case Intrinsic::assume:
768 return true;
769 case Intrinsic::dbg_declare:
770 case Intrinsic::dbg_label:
771 case Intrinsic::dbg_value:
772 llvm_unreachable("Intrinsic should not be modeled in MemorySSA");
773 default:
774 return false;
775 }
776 }
777 return false;
778}
779
780// Check if we can ignore \p D for DSE.
781bool canSkipDef(MemoryDef *D, bool DefVisibleToCaller) {
782 Instruction *DI = D->getMemoryInst();
783 // Calls that only access inaccessible memory cannot read or write any memory
784 // locations we consider for elimination.
785 if (auto *CB = dyn_cast<CallBase>(DI))
786 if (CB->onlyAccessesInaccessibleMemory())
787 return true;
788
789 // We can eliminate stores to locations not visible to the caller across
790 // throwing instructions.
791 if (DI->mayThrow() && !DefVisibleToCaller)
792 return true;
793
794 // We can remove the dead stores, irrespective of the fence and its ordering
795 // (release/acquire/seq_cst). Fences only constraints the ordering of
796 // already visible stores, it does not make a store visible to other
797 // threads. So, skipping over a fence does not change a store from being
798 // dead.
799 if (isa<FenceInst>(DI))
800 return true;
801
802 // Skip intrinsics that do not really read or modify memory.
803 if (isNoopIntrinsic(DI))
804 return true;
805
806 return false;
807}
808
809struct DSEState {
810 Function &F;
811 AliasAnalysis &AA;
813
814 /// The single BatchAA instance that is used to cache AA queries. It will
815 /// not be invalidated over the whole run. This is safe, because:
816 /// 1. Only memory writes are removed, so the alias cache for memory
817 /// locations remains valid.
818 /// 2. No new instructions are added (only instructions removed), so cached
819 /// information for a deleted value cannot be accessed by a re-used new
820 /// value pointer.
821 BatchAAResults BatchAA;
822
823 MemorySSA &MSSA;
824 DominatorTree &DT;
826 const TargetLibraryInfo &TLI;
827 const DataLayout &DL;
828 const LoopInfo &LI;
829
830 // Whether the function contains any irreducible control flow, useful for
831 // being accurately able to detect loops.
832 bool ContainsIrreducibleLoops;
833
834 // All MemoryDefs that potentially could kill other MemDefs.
836 // Any that should be skipped as they are already deleted
838 // Keep track whether a given object is captured before return or not.
839 DenseMap<const Value *, bool> CapturedBeforeReturn;
840 // Keep track of all of the objects that are invisible to the caller after
841 // the function returns.
842 DenseMap<const Value *, bool> InvisibleToCallerAfterRet;
843 // Keep track of blocks with throwing instructions not modeled in MemorySSA.
844 SmallPtrSet<BasicBlock *, 16> ThrowingBlocks;
845 // Post-order numbers for each basic block. Used to figure out if memory
846 // accesses are executed before another access.
847 DenseMap<BasicBlock *, unsigned> PostOrderNumbers;
848
849 /// Keep track of instructions (partly) overlapping with killing MemoryDefs per
850 /// basic block.
852 // Check if there are root nodes that are terminated by UnreachableInst.
853 // Those roots pessimize post-dominance queries. If there are such roots,
854 // fall back to CFG scan starting from all non-unreachable roots.
855 bool AnyUnreachableExit;
856
857 // Whether or not we should iterate on removing dead stores at the end of the
858 // function due to removing a store causing a previously captured pointer to
859 // no longer be captured.
860 bool ShouldIterateEndOfFunctionDSE;
861
862 /// Dead instructions to be removed at the end of DSE.
864
865 // Class contains self-reference, make sure it's not copied/moved.
866 DSEState(const DSEState &) = delete;
867 DSEState &operator=(const DSEState &) = delete;
868
869 DSEState(Function &F, AliasAnalysis &AA, MemorySSA &MSSA, DominatorTree &DT,
870 PostDominatorTree &PDT, const TargetLibraryInfo &TLI,
871 const LoopInfo &LI)
872 : F(F), AA(AA), EI(DT, &LI), BatchAA(AA, &EI), MSSA(MSSA), DT(DT),
873 PDT(PDT), TLI(TLI), DL(F.getDataLayout()), LI(LI) {
874 // Collect blocks with throwing instructions not modeled in MemorySSA and
875 // alloc-like objects.
876 unsigned PO = 0;
877 for (BasicBlock *BB : post_order(&F)) {
878 PostOrderNumbers[BB] = PO++;
879 for (Instruction &I : *BB) {
880 MemoryAccess *MA = MSSA.getMemoryAccess(&I);
881 if (I.mayThrow() && !MA)
882 ThrowingBlocks.insert(I.getParent());
883
884 auto *MD = dyn_cast_or_null<MemoryDef>(MA);
885 if (MD && MemDefs.size() < MemorySSADefsPerBlockLimit &&
886 (getLocForWrite(&I) || isMemTerminatorInst(&I)))
887 MemDefs.push_back(MD);
888 }
889 }
890
891 // Treat byval or inalloca arguments the same as Allocas, stores to them are
892 // dead at the end of the function.
893 for (Argument &AI : F.args())
894 if (AI.hasPassPointeeByValueCopyAttr())
895 InvisibleToCallerAfterRet.insert({&AI, true});
896
897 // Collect whether there is any irreducible control flow in the function.
898 ContainsIrreducibleLoops = mayContainIrreducibleControl(F, &LI);
899
900 AnyUnreachableExit = any_of(PDT.roots(), [](const BasicBlock *E) {
901 return isa<UnreachableInst>(E->getTerminator());
902 });
903 }
904
905 static void pushMemUses(MemoryAccess *Acc,
908 for (Use &U : Acc->uses()) {
909 auto *MA = cast<MemoryAccess>(U.getUser());
910 if (Visited.insert(MA).second)
911 WorkList.push_back(MA);
912 }
913 };
914
915 LocationSize strengthenLocationSize(const Instruction *I,
916 LocationSize Size) const {
917 if (auto *CB = dyn_cast<CallBase>(I)) {
918 LibFunc F;
919 if (TLI.getLibFunc(*CB, F) && TLI.has(F) &&
920 (F == LibFunc_memset_chk || F == LibFunc_memcpy_chk)) {
921 // Use the precise location size specified by the 3rd argument
922 // for determining KillingI overwrites DeadLoc if it is a memset_chk
923 // instruction. memset_chk will write either the amount specified as 3rd
924 // argument or the function will immediately abort and exit the program.
925 // NOTE: AA may determine NoAlias if it can prove that the access size
926 // is larger than the allocation size due to that being UB. To avoid
927 // returning potentially invalid NoAlias results by AA, limit the use of
928 // the precise location size to isOverwrite.
929 if (const auto *Len = dyn_cast<ConstantInt>(CB->getArgOperand(2)))
930 return LocationSize::precise(Len->getZExtValue());
931 }
932 }
933 return Size;
934 }
935
936 /// Return 'OW_Complete' if a store to the 'KillingLoc' location (by \p
937 /// KillingI instruction) completely overwrites a store to the 'DeadLoc'
938 /// location (by \p DeadI instruction).
939 /// Return OW_MaybePartial if \p KillingI does not completely overwrite
940 /// \p DeadI, but they both write to the same underlying object. In that
941 /// case, use isPartialOverwrite to check if \p KillingI partially overwrites
942 /// \p DeadI. Returns 'OR_None' if \p KillingI is known to not overwrite the
943 /// \p DeadI. Returns 'OW_Unknown' if nothing can be determined.
944 OverwriteResult isOverwrite(const Instruction *KillingI,
945 const Instruction *DeadI,
946 const MemoryLocation &KillingLoc,
947 const MemoryLocation &DeadLoc,
948 int64_t &KillingOff, int64_t &DeadOff) {
949 // AliasAnalysis does not always account for loops. Limit overwrite checks
950 // to dependencies for which we can guarantee they are independent of any
951 // loops they are in.
952 if (!isGuaranteedLoopIndependent(DeadI, KillingI, DeadLoc))
953 return OW_Unknown;
954
955 LocationSize KillingLocSize =
956 strengthenLocationSize(KillingI, KillingLoc.Size);
957 const Value *DeadPtr = DeadLoc.Ptr->stripPointerCasts();
958 const Value *KillingPtr = KillingLoc.Ptr->stripPointerCasts();
959 const Value *DeadUndObj = getUnderlyingObject(DeadPtr);
960 const Value *KillingUndObj = getUnderlyingObject(KillingPtr);
961
962 // Check whether the killing store overwrites the whole object, in which
963 // case the size/offset of the dead store does not matter.
964 if (DeadUndObj == KillingUndObj && KillingLocSize.isPrecise() &&
965 isIdentifiedObject(KillingUndObj)) {
966 std::optional<TypeSize> KillingUndObjSize =
967 getPointerSize(KillingUndObj, DL, TLI, &F);
968 if (KillingUndObjSize && *KillingUndObjSize == KillingLocSize.getValue())
969 return OW_Complete;
970 }
971
972 // FIXME: Vet that this works for size upper-bounds. Seems unlikely that we'll
973 // get imprecise values here, though (except for unknown sizes).
974 if (!KillingLocSize.isPrecise() || !DeadLoc.Size.isPrecise()) {
975 // In case no constant size is known, try to an IR values for the number
976 // of bytes written and check if they match.
977 const auto *KillingMemI = dyn_cast<MemIntrinsic>(KillingI);
978 const auto *DeadMemI = dyn_cast<MemIntrinsic>(DeadI);
979 if (KillingMemI && DeadMemI) {
980 const Value *KillingV = KillingMemI->getLength();
981 const Value *DeadV = DeadMemI->getLength();
982 if (KillingV == DeadV && BatchAA.isMustAlias(DeadLoc, KillingLoc))
983 return OW_Complete;
984 }
985
986 // Masked stores have imprecise locations, but we can reason about them
987 // to some extent.
988 return isMaskedStoreOverwrite(KillingI, DeadI, BatchAA);
989 }
990
991 const TypeSize KillingSize = KillingLocSize.getValue();
992 const TypeSize DeadSize = DeadLoc.Size.getValue();
993 // Bail on doing Size comparison which depends on AA for now
994 // TODO: Remove AnyScalable once Alias Analysis deal with scalable vectors
995 const bool AnyScalable =
996 DeadSize.isScalable() || KillingLocSize.isScalable();
997
998 if (AnyScalable)
999 return OW_Unknown;
1000 // Query the alias information
1001 AliasResult AAR = BatchAA.alias(KillingLoc, DeadLoc);
1002
1003 // If the start pointers are the same, we just have to compare sizes to see if
1004 // the killing store was larger than the dead store.
1005 if (AAR == AliasResult::MustAlias) {
1006 // Make sure that the KillingSize size is >= the DeadSize size.
1007 if (KillingSize >= DeadSize)
1008 return OW_Complete;
1009 }
1010
1011 // If we hit a partial alias we may have a full overwrite
1012 if (AAR == AliasResult::PartialAlias && AAR.hasOffset()) {
1013 int32_t Off = AAR.getOffset();
1014 if (Off >= 0 && (uint64_t)Off + DeadSize <= KillingSize)
1015 return OW_Complete;
1016 }
1017
1018 // If we can't resolve the same pointers to the same object, then we can't
1019 // analyze them at all.
1020 if (DeadUndObj != KillingUndObj) {
1021 // Non aliasing stores to different objects don't overlap. Note that
1022 // if the killing store is known to overwrite whole object (out of
1023 // bounds access overwrites whole object as well) then it is assumed to
1024 // completely overwrite any store to the same object even if they don't
1025 // actually alias (see next check).
1026 if (AAR == AliasResult::NoAlias)
1027 return OW_None;
1028 return OW_Unknown;
1029 }
1030
1031 // Okay, we have stores to two completely different pointers. Try to
1032 // decompose the pointer into a "base + constant_offset" form. If the base
1033 // pointers are equal, then we can reason about the two stores.
1034 DeadOff = 0;
1035 KillingOff = 0;
1036 const Value *DeadBasePtr =
1037 GetPointerBaseWithConstantOffset(DeadPtr, DeadOff, DL);
1038 const Value *KillingBasePtr =
1039 GetPointerBaseWithConstantOffset(KillingPtr, KillingOff, DL);
1040
1041 // If the base pointers still differ, we have two completely different
1042 // stores.
1043 if (DeadBasePtr != KillingBasePtr)
1044 return OW_Unknown;
1045
1046 // The killing access completely overlaps the dead store if and only if
1047 // both start and end of the dead one is "inside" the killing one:
1048 // |<->|--dead--|<->|
1049 // |-----killing------|
1050 // Accesses may overlap if and only if start of one of them is "inside"
1051 // another one:
1052 // |<->|--dead--|<-------->|
1053 // |-------killing--------|
1054 // OR
1055 // |-------dead-------|
1056 // |<->|---killing---|<----->|
1057 //
1058 // We have to be careful here as *Off is signed while *.Size is unsigned.
1059
1060 // Check if the dead access starts "not before" the killing one.
1061 if (DeadOff >= KillingOff) {
1062 // If the dead access ends "not after" the killing access then the
1063 // dead one is completely overwritten by the killing one.
1064 if (uint64_t(DeadOff - KillingOff) + DeadSize <= KillingSize)
1065 return OW_Complete;
1066 // If start of the dead access is "before" end of the killing access
1067 // then accesses overlap.
1068 else if ((uint64_t)(DeadOff - KillingOff) < KillingSize)
1069 return OW_MaybePartial;
1070 }
1071 // If start of the killing access is "before" end of the dead access then
1072 // accesses overlap.
1073 else if ((uint64_t)(KillingOff - DeadOff) < DeadSize) {
1074 return OW_MaybePartial;
1075 }
1076
1077 // Can reach here only if accesses are known not to overlap.
1078 return OW_None;
1079 }
1080
1081 bool isInvisibleToCallerAfterRet(const Value *V) {
1082 if (isa<AllocaInst>(V))
1083 return true;
1084 auto I = InvisibleToCallerAfterRet.insert({V, false});
1085 if (I.second) {
1086 if (!isInvisibleToCallerOnUnwind(V)) {
1087 I.first->second = false;
1088 } else if (isNoAliasCall(V)) {
1089 I.first->second = !PointerMayBeCaptured(V, true, false);
1090 }
1091 }
1092 return I.first->second;
1093 }
1094
1095 bool isInvisibleToCallerOnUnwind(const Value *V) {
1096 bool RequiresNoCaptureBeforeUnwind;
1097 if (!isNotVisibleOnUnwind(V, RequiresNoCaptureBeforeUnwind))
1098 return false;
1099 if (!RequiresNoCaptureBeforeUnwind)
1100 return true;
1101
1102 auto I = CapturedBeforeReturn.insert({V, true});
1103 if (I.second)
1104 // NOTE: This could be made more precise by PointerMayBeCapturedBefore
1105 // with the killing MemoryDef. But we refrain from doing so for now to
1106 // limit compile-time and this does not cause any changes to the number
1107 // of stores removed on a large test set in practice.
1108 I.first->second = PointerMayBeCaptured(V, false, true);
1109 return !I.first->second;
1110 }
1111
1112 std::optional<MemoryLocation> getLocForWrite(Instruction *I) const {
1113 if (!I->mayWriteToMemory())
1114 return std::nullopt;
1115
1116 if (auto *CB = dyn_cast<CallBase>(I))
1117 return MemoryLocation::getForDest(CB, TLI);
1118
1120 }
1121
1122 /// Assuming this instruction has a dead analyzable write, can we delete
1123 /// this instruction?
1124 bool isRemovable(Instruction *I) {
1125 assert(getLocForWrite(I) && "Must have analyzable write");
1126
1127 // Don't remove volatile/atomic stores.
1128 if (StoreInst *SI = dyn_cast<StoreInst>(I))
1129 return SI->isUnordered();
1130
1131 if (auto *CB = dyn_cast<CallBase>(I)) {
1132 // Don't remove volatile memory intrinsics.
1133 if (auto *MI = dyn_cast<MemIntrinsic>(CB))
1134 return !MI->isVolatile();
1135
1136 // Never remove dead lifetime intrinsics, e.g. because they are followed
1137 // by a free.
1138 if (CB->isLifetimeStartOrEnd())
1139 return false;
1140
1141 return CB->use_empty() && CB->willReturn() && CB->doesNotThrow() &&
1142 !CB->isTerminator();
1143 }
1144
1145 return false;
1146 }
1147
1148 /// Returns true if \p UseInst completely overwrites \p DefLoc
1149 /// (stored by \p DefInst).
1150 bool isCompleteOverwrite(const MemoryLocation &DefLoc, Instruction *DefInst,
1151 Instruction *UseInst) {
1152 // UseInst has a MemoryDef associated in MemorySSA. It's possible for a
1153 // MemoryDef to not write to memory, e.g. a volatile load is modeled as a
1154 // MemoryDef.
1155 if (!UseInst->mayWriteToMemory())
1156 return false;
1157
1158 if (auto *CB = dyn_cast<CallBase>(UseInst))
1159 if (CB->onlyAccessesInaccessibleMemory())
1160 return false;
1161
1162 int64_t InstWriteOffset, DepWriteOffset;
1163 if (auto CC = getLocForWrite(UseInst))
1164 return isOverwrite(UseInst, DefInst, *CC, DefLoc, InstWriteOffset,
1165 DepWriteOffset) == OW_Complete;
1166 return false;
1167 }
1168
1169 /// Returns true if \p Def is not read before returning from the function.
1170 bool isWriteAtEndOfFunction(MemoryDef *Def, const MemoryLocation &DefLoc) {
1171 LLVM_DEBUG(dbgs() << " Check if def " << *Def << " ("
1172 << *Def->getMemoryInst()
1173 << ") is at the end the function \n");
1176
1177 pushMemUses(Def, WorkList, Visited);
1178 for (unsigned I = 0; I < WorkList.size(); I++) {
1179 if (WorkList.size() >= MemorySSAScanLimit) {
1180 LLVM_DEBUG(dbgs() << " ... hit exploration limit.\n");
1181 return false;
1182 }
1183
1184 MemoryAccess *UseAccess = WorkList[I];
1185 if (isa<MemoryPhi>(UseAccess)) {
1186 // AliasAnalysis does not account for loops. Limit elimination to
1187 // candidates for which we can guarantee they always store to the same
1188 // memory location.
1189 if (!isGuaranteedLoopInvariant(DefLoc.Ptr))
1190 return false;
1191
1192 pushMemUses(cast<MemoryPhi>(UseAccess), WorkList, Visited);
1193 continue;
1194 }
1195 // TODO: Checking for aliasing is expensive. Consider reducing the amount
1196 // of times this is called and/or caching it.
1197 Instruction *UseInst = cast<MemoryUseOrDef>(UseAccess)->getMemoryInst();
1198 if (isReadClobber(DefLoc, UseInst)) {
1199 LLVM_DEBUG(dbgs() << " ... hit read clobber " << *UseInst << ".\n");
1200 return false;
1201 }
1202
1203 if (MemoryDef *UseDef = dyn_cast<MemoryDef>(UseAccess))
1204 pushMemUses(UseDef, WorkList, Visited);
1205 }
1206 return true;
1207 }
1208
1209 /// If \p I is a memory terminator like llvm.lifetime.end or free, return a
1210 /// pair with the MemoryLocation terminated by \p I and a boolean flag
1211 /// indicating whether \p I is a free-like call.
1212 std::optional<std::pair<MemoryLocation, bool>>
1213 getLocForTerminator(Instruction *I) const {
1214 uint64_t Len;
1215 Value *Ptr;
1216 if (match(I, m_Intrinsic<Intrinsic::lifetime_end>(m_ConstantInt(Len),
1217 m_Value(Ptr))))
1218 return {std::make_pair(MemoryLocation(Ptr, Len), false)};
1219
1220 if (auto *CB = dyn_cast<CallBase>(I)) {
1221 if (Value *FreedOp = getFreedOperand(CB, &TLI))
1222 return {std::make_pair(MemoryLocation::getAfter(FreedOp), true)};
1223 }
1224
1225 return std::nullopt;
1226 }
1227
1228 /// Returns true if \p I is a memory terminator instruction like
1229 /// llvm.lifetime.end or free.
1230 bool isMemTerminatorInst(Instruction *I) const {
1231 auto *CB = dyn_cast<CallBase>(I);
1232 return CB && (CB->getIntrinsicID() == Intrinsic::lifetime_end ||
1233 getFreedOperand(CB, &TLI) != nullptr);
1234 }
1235
1236 /// Returns true if \p MaybeTerm is a memory terminator for \p Loc from
1237 /// instruction \p AccessI.
1238 bool isMemTerminator(const MemoryLocation &Loc, Instruction *AccessI,
1239 Instruction *MaybeTerm) {
1240 std::optional<std::pair<MemoryLocation, bool>> MaybeTermLoc =
1241 getLocForTerminator(MaybeTerm);
1242
1243 if (!MaybeTermLoc)
1244 return false;
1245
1246 // If the terminator is a free-like call, all accesses to the underlying
1247 // object can be considered terminated.
1248 if (getUnderlyingObject(Loc.Ptr) !=
1249 getUnderlyingObject(MaybeTermLoc->first.Ptr))
1250 return false;
1251
1252 auto TermLoc = MaybeTermLoc->first;
1253 if (MaybeTermLoc->second) {
1254 const Value *LocUO = getUnderlyingObject(Loc.Ptr);
1255 return BatchAA.isMustAlias(TermLoc.Ptr, LocUO);
1256 }
1257 int64_t InstWriteOffset = 0;
1258 int64_t DepWriteOffset = 0;
1259 return isOverwrite(MaybeTerm, AccessI, TermLoc, Loc, InstWriteOffset,
1260 DepWriteOffset) == OW_Complete;
1261 }
1262
1263 // Returns true if \p Use may read from \p DefLoc.
1264 bool isReadClobber(const MemoryLocation &DefLoc, Instruction *UseInst) {
1265 if (isNoopIntrinsic(UseInst))
1266 return false;
1267
1268 // Monotonic or weaker atomic stores can be re-ordered and do not need to be
1269 // treated as read clobber.
1270 if (auto SI = dyn_cast<StoreInst>(UseInst))
1271 return isStrongerThan(SI->getOrdering(), AtomicOrdering::Monotonic);
1272
1273 if (!UseInst->mayReadFromMemory())
1274 return false;
1275
1276 if (auto *CB = dyn_cast<CallBase>(UseInst))
1277 if (CB->onlyAccessesInaccessibleMemory())
1278 return false;
1279
1280 return isRefSet(BatchAA.getModRefInfo(UseInst, DefLoc));
1281 }
1282
1283 /// Returns true if a dependency between \p Current and \p KillingDef is
1284 /// guaranteed to be loop invariant for the loops that they are in. Either
1285 /// because they are known to be in the same block, in the same loop level or
1286 /// by guaranteeing that \p CurrentLoc only references a single MemoryLocation
1287 /// during execution of the containing function.
1288 bool isGuaranteedLoopIndependent(const Instruction *Current,
1289 const Instruction *KillingDef,
1290 const MemoryLocation &CurrentLoc) {
1291 // If the dependency is within the same block or loop level (being careful
1292 // of irreducible loops), we know that AA will return a valid result for the
1293 // memory dependency. (Both at the function level, outside of any loop,
1294 // would also be valid but we currently disable that to limit compile time).
1295 if (Current->getParent() == KillingDef->getParent())
1296 return true;
1297 const Loop *CurrentLI = LI.getLoopFor(Current->getParent());
1298 if (!ContainsIrreducibleLoops && CurrentLI &&
1299 CurrentLI == LI.getLoopFor(KillingDef->getParent()))
1300 return true;
1301 // Otherwise check the memory location is invariant to any loops.
1302 return isGuaranteedLoopInvariant(CurrentLoc.Ptr);
1303 }
1304
1305 /// Returns true if \p Ptr is guaranteed to be loop invariant for any possible
1306 /// loop. In particular, this guarantees that it only references a single
1307 /// MemoryLocation during execution of the containing function.
1308 bool isGuaranteedLoopInvariant(const Value *Ptr) {
1309 Ptr = Ptr->stripPointerCasts();
1310 if (auto *GEP = dyn_cast<GEPOperator>(Ptr))
1311 if (GEP->hasAllConstantIndices())
1312 Ptr = GEP->getPointerOperand()->stripPointerCasts();
1313
1314 if (auto *I = dyn_cast<Instruction>(Ptr)) {
1315 return I->getParent()->isEntryBlock() ||
1316 (!ContainsIrreducibleLoops && !LI.getLoopFor(I->getParent()));
1317 }
1318 return true;
1319 }
1320
1321 // Find a MemoryDef writing to \p KillingLoc and dominating \p StartAccess,
1322 // with no read access between them or on any other path to a function exit
1323 // block if \p KillingLoc is not accessible after the function returns. If
1324 // there is no such MemoryDef, return std::nullopt. The returned value may not
1325 // (completely) overwrite \p KillingLoc. Currently we bail out when we
1326 // encounter an aliasing MemoryUse (read).
1327 std::optional<MemoryAccess *>
1328 getDomMemoryDef(MemoryDef *KillingDef, MemoryAccess *StartAccess,
1329 const MemoryLocation &KillingLoc, const Value *KillingUndObj,
1330 unsigned &ScanLimit, unsigned &WalkerStepLimit,
1331 bool IsMemTerm, unsigned &PartialLimit) {
1332 if (ScanLimit == 0 || WalkerStepLimit == 0) {
1333 LLVM_DEBUG(dbgs() << "\n ... hit scan limit\n");
1334 return std::nullopt;
1335 }
1336
1337 MemoryAccess *Current = StartAccess;
1338 Instruction *KillingI = KillingDef->getMemoryInst();
1339 LLVM_DEBUG(dbgs() << " trying to get dominating access\n");
1340
1341 // Only optimize defining access of KillingDef when directly starting at its
1342 // defining access. The defining access also must only access KillingLoc. At
1343 // the moment we only support instructions with a single write location, so
1344 // it should be sufficient to disable optimizations for instructions that
1345 // also read from memory.
1346 bool CanOptimize = OptimizeMemorySSA &&
1347 KillingDef->getDefiningAccess() == StartAccess &&
1348 !KillingI->mayReadFromMemory();
1349
1350 // Find the next clobbering Mod access for DefLoc, starting at StartAccess.
1351 std::optional<MemoryLocation> CurrentLoc;
1352 for (;; Current = cast<MemoryDef>(Current)->getDefiningAccess()) {
1353 LLVM_DEBUG({
1354 dbgs() << " visiting " << *Current;
1355 if (!MSSA.isLiveOnEntryDef(Current) && isa<MemoryUseOrDef>(Current))
1356 dbgs() << " (" << *cast<MemoryUseOrDef>(Current)->getMemoryInst()
1357 << ")";
1358 dbgs() << "\n";
1359 });
1360
1361 // Reached TOP.
1362 if (MSSA.isLiveOnEntryDef(Current)) {
1363 LLVM_DEBUG(dbgs() << " ... found LiveOnEntryDef\n");
1364 if (CanOptimize && Current != KillingDef->getDefiningAccess())
1365 // The first clobbering def is... none.
1366 KillingDef->setOptimized(Current);
1367 return std::nullopt;
1368 }
1369
1370 // Cost of a step. Accesses in the same block are more likely to be valid
1371 // candidates for elimination, hence consider them cheaper.
1372 unsigned StepCost = KillingDef->getBlock() == Current->getBlock()
1375 if (WalkerStepLimit <= StepCost) {
1376 LLVM_DEBUG(dbgs() << " ... hit walker step limit\n");
1377 return std::nullopt;
1378 }
1379 WalkerStepLimit -= StepCost;
1380
1381 // Return for MemoryPhis. They cannot be eliminated directly and the
1382 // caller is responsible for traversing them.
1383 if (isa<MemoryPhi>(Current)) {
1384 LLVM_DEBUG(dbgs() << " ... found MemoryPhi\n");
1385 return Current;
1386 }
1387
1388 // Below, check if CurrentDef is a valid candidate to be eliminated by
1389 // KillingDef. If it is not, check the next candidate.
1390 MemoryDef *CurrentDef = cast<MemoryDef>(Current);
1391 Instruction *CurrentI = CurrentDef->getMemoryInst();
1392
1393 if (canSkipDef(CurrentDef, !isInvisibleToCallerOnUnwind(KillingUndObj))) {
1394 CanOptimize = false;
1395 continue;
1396 }
1397
1398 // Before we try to remove anything, check for any extra throwing
1399 // instructions that block us from DSEing
1400 if (mayThrowBetween(KillingI, CurrentI, KillingUndObj)) {
1401 LLVM_DEBUG(dbgs() << " ... skip, may throw!\n");
1402 return std::nullopt;
1403 }
1404
1405 // Check for anything that looks like it will be a barrier to further
1406 // removal
1407 if (isDSEBarrier(KillingUndObj, CurrentI)) {
1408 LLVM_DEBUG(dbgs() << " ... skip, barrier\n");
1409 return std::nullopt;
1410 }
1411
1412 // If Current is known to be on path that reads DefLoc or is a read
1413 // clobber, bail out, as the path is not profitable. We skip this check
1414 // for intrinsic calls, because the code knows how to handle memcpy
1415 // intrinsics.
1416 if (!isa<IntrinsicInst>(CurrentI) && isReadClobber(KillingLoc, CurrentI))
1417 return std::nullopt;
1418
1419 // Quick check if there are direct uses that are read-clobbers.
1420 if (any_of(Current->uses(), [this, &KillingLoc, StartAccess](Use &U) {
1421 if (auto *UseOrDef = dyn_cast<MemoryUseOrDef>(U.getUser()))
1422 return !MSSA.dominates(StartAccess, UseOrDef) &&
1423 isReadClobber(KillingLoc, UseOrDef->getMemoryInst());
1424 return false;
1425 })) {
1426 LLVM_DEBUG(dbgs() << " ... found a read clobber\n");
1427 return std::nullopt;
1428 }
1429
1430 // If Current does not have an analyzable write location or is not
1431 // removable, skip it.
1432 CurrentLoc = getLocForWrite(CurrentI);
1433 if (!CurrentLoc || !isRemovable(CurrentI)) {
1434 CanOptimize = false;
1435 continue;
1436 }
1437
1438 // AliasAnalysis does not account for loops. Limit elimination to
1439 // candidates for which we can guarantee they always store to the same
1440 // memory location and not located in different loops.
1441 if (!isGuaranteedLoopIndependent(CurrentI, KillingI, *CurrentLoc)) {
1442 LLVM_DEBUG(dbgs() << " ... not guaranteed loop independent\n");
1443 CanOptimize = false;
1444 continue;
1445 }
1446
1447 if (IsMemTerm) {
1448 // If the killing def is a memory terminator (e.g. lifetime.end), check
1449 // the next candidate if the current Current does not write the same
1450 // underlying object as the terminator.
1451 if (!isMemTerminator(*CurrentLoc, CurrentI, KillingI)) {
1452 CanOptimize = false;
1453 continue;
1454 }
1455 } else {
1456 int64_t KillingOffset = 0;
1457 int64_t DeadOffset = 0;
1458 auto OR = isOverwrite(KillingI, CurrentI, KillingLoc, *CurrentLoc,
1459 KillingOffset, DeadOffset);
1460 if (CanOptimize) {
1461 // CurrentDef is the earliest write clobber of KillingDef. Use it as
1462 // optimized access. Do not optimize if CurrentDef is already the
1463 // defining access of KillingDef.
1464 if (CurrentDef != KillingDef->getDefiningAccess() &&
1465 (OR == OW_Complete || OR == OW_MaybePartial))
1466 KillingDef->setOptimized(CurrentDef);
1467
1468 // Once a may-aliasing def is encountered do not set an optimized
1469 // access.
1470 if (OR != OW_None)
1471 CanOptimize = false;
1472 }
1473
1474 // If Current does not write to the same object as KillingDef, check
1475 // the next candidate.
1476 if (OR == OW_Unknown || OR == OW_None)
1477 continue;
1478 else if (OR == OW_MaybePartial) {
1479 // If KillingDef only partially overwrites Current, check the next
1480 // candidate if the partial step limit is exceeded. This aggressively
1481 // limits the number of candidates for partial store elimination,
1482 // which are less likely to be removable in the end.
1483 if (PartialLimit <= 1) {
1484 WalkerStepLimit -= 1;
1485 LLVM_DEBUG(dbgs() << " ... reached partial limit ... continue with next access\n");
1486 continue;
1487 }
1488 PartialLimit -= 1;
1489 }
1490 }
1491 break;
1492 };
1493
1494 // Accesses to objects accessible after the function returns can only be
1495 // eliminated if the access is dead along all paths to the exit. Collect
1496 // the blocks with killing (=completely overwriting MemoryDefs) and check if
1497 // they cover all paths from MaybeDeadAccess to any function exit.
1499 KillingDefs.insert(KillingDef->getMemoryInst());
1500 MemoryAccess *MaybeDeadAccess = Current;
1501 MemoryLocation MaybeDeadLoc = *CurrentLoc;
1502 Instruction *MaybeDeadI = cast<MemoryDef>(MaybeDeadAccess)->getMemoryInst();
1503 LLVM_DEBUG(dbgs() << " Checking for reads of " << *MaybeDeadAccess << " ("
1504 << *MaybeDeadI << ")\n");
1505
1508 pushMemUses(MaybeDeadAccess, WorkList, Visited);
1509
1510 // Check if DeadDef may be read.
1511 for (unsigned I = 0; I < WorkList.size(); I++) {
1512 MemoryAccess *UseAccess = WorkList[I];
1513
1514 LLVM_DEBUG(dbgs() << " " << *UseAccess);
1515 // Bail out if the number of accesses to check exceeds the scan limit.
1516 if (ScanLimit < (WorkList.size() - I)) {
1517 LLVM_DEBUG(dbgs() << "\n ... hit scan limit\n");
1518 return std::nullopt;
1519 }
1520 --ScanLimit;
1521 NumDomMemDefChecks++;
1522
1523 if (isa<MemoryPhi>(UseAccess)) {
1524 if (any_of(KillingDefs, [this, UseAccess](Instruction *KI) {
1525 return DT.properlyDominates(KI->getParent(),
1526 UseAccess->getBlock());
1527 })) {
1528 LLVM_DEBUG(dbgs() << " ... skipping, dominated by killing block\n");
1529 continue;
1530 }
1531 LLVM_DEBUG(dbgs() << "\n ... adding PHI uses\n");
1532 pushMemUses(UseAccess, WorkList, Visited);
1533 continue;
1534 }
1535
1536 Instruction *UseInst = cast<MemoryUseOrDef>(UseAccess)->getMemoryInst();
1537 LLVM_DEBUG(dbgs() << " (" << *UseInst << ")\n");
1538
1539 if (any_of(KillingDefs, [this, UseInst](Instruction *KI) {
1540 return DT.dominates(KI, UseInst);
1541 })) {
1542 LLVM_DEBUG(dbgs() << " ... skipping, dominated by killing def\n");
1543 continue;
1544 }
1545
1546 // A memory terminator kills all preceeding MemoryDefs and all succeeding
1547 // MemoryAccesses. We do not have to check it's users.
1548 if (isMemTerminator(MaybeDeadLoc, MaybeDeadI, UseInst)) {
1549 LLVM_DEBUG(
1550 dbgs()
1551 << " ... skipping, memterminator invalidates following accesses\n");
1552 continue;
1553 }
1554
1555 if (isNoopIntrinsic(cast<MemoryUseOrDef>(UseAccess)->getMemoryInst())) {
1556 LLVM_DEBUG(dbgs() << " ... adding uses of intrinsic\n");
1557 pushMemUses(UseAccess, WorkList, Visited);
1558 continue;
1559 }
1560
1561 if (UseInst->mayThrow() && !isInvisibleToCallerOnUnwind(KillingUndObj)) {
1562 LLVM_DEBUG(dbgs() << " ... found throwing instruction\n");
1563 return std::nullopt;
1564 }
1565
1566 // Uses which may read the original MemoryDef mean we cannot eliminate the
1567 // original MD. Stop walk.
1568 if (isReadClobber(MaybeDeadLoc, UseInst)) {
1569 LLVM_DEBUG(dbgs() << " ... found read clobber\n");
1570 return std::nullopt;
1571 }
1572
1573 // If this worklist walks back to the original memory access (and the
1574 // pointer is not guarenteed loop invariant) then we cannot assume that a
1575 // store kills itself.
1576 if (MaybeDeadAccess == UseAccess &&
1577 !isGuaranteedLoopInvariant(MaybeDeadLoc.Ptr)) {
1578 LLVM_DEBUG(dbgs() << " ... found not loop invariant self access\n");
1579 return std::nullopt;
1580 }
1581 // Otherwise, for the KillingDef and MaybeDeadAccess we only have to check
1582 // if it reads the memory location.
1583 // TODO: It would probably be better to check for self-reads before
1584 // calling the function.
1585 if (KillingDef == UseAccess || MaybeDeadAccess == UseAccess) {
1586 LLVM_DEBUG(dbgs() << " ... skipping killing def/dom access\n");
1587 continue;
1588 }
1589
1590 // Check all uses for MemoryDefs, except for defs completely overwriting
1591 // the original location. Otherwise we have to check uses of *all*
1592 // MemoryDefs we discover, including non-aliasing ones. Otherwise we might
1593 // miss cases like the following
1594 // 1 = Def(LoE) ; <----- DeadDef stores [0,1]
1595 // 2 = Def(1) ; (2, 1) = NoAlias, stores [2,3]
1596 // Use(2) ; MayAlias 2 *and* 1, loads [0, 3].
1597 // (The Use points to the *first* Def it may alias)
1598 // 3 = Def(1) ; <---- Current (3, 2) = NoAlias, (3,1) = MayAlias,
1599 // stores [0,1]
1600 if (MemoryDef *UseDef = dyn_cast<MemoryDef>(UseAccess)) {
1601 if (isCompleteOverwrite(MaybeDeadLoc, MaybeDeadI, UseInst)) {
1602 BasicBlock *MaybeKillingBlock = UseInst->getParent();
1603 if (PostOrderNumbers.find(MaybeKillingBlock)->second <
1604 PostOrderNumbers.find(MaybeDeadAccess->getBlock())->second) {
1605 if (!isInvisibleToCallerAfterRet(KillingUndObj)) {
1607 << " ... found killing def " << *UseInst << "\n");
1608 KillingDefs.insert(UseInst);
1609 }
1610 } else {
1612 << " ... found preceeding def " << *UseInst << "\n");
1613 return std::nullopt;
1614 }
1615 } else
1616 pushMemUses(UseDef, WorkList, Visited);
1617 }
1618 }
1619
1620 // For accesses to locations visible after the function returns, make sure
1621 // that the location is dead (=overwritten) along all paths from
1622 // MaybeDeadAccess to the exit.
1623 if (!isInvisibleToCallerAfterRet(KillingUndObj)) {
1624 SmallPtrSet<BasicBlock *, 16> KillingBlocks;
1625 for (Instruction *KD : KillingDefs)
1626 KillingBlocks.insert(KD->getParent());
1627 assert(!KillingBlocks.empty() &&
1628 "Expected at least a single killing block");
1629
1630 // Find the common post-dominator of all killing blocks.
1631 BasicBlock *CommonPred = *KillingBlocks.begin();
1632 for (BasicBlock *BB : llvm::drop_begin(KillingBlocks)) {
1633 if (!CommonPred)
1634 break;
1635 CommonPred = PDT.findNearestCommonDominator(CommonPred, BB);
1636 }
1637
1638 // If the common post-dominator does not post-dominate MaybeDeadAccess,
1639 // there is a path from MaybeDeadAccess to an exit not going through a
1640 // killing block.
1641 if (!PDT.dominates(CommonPred, MaybeDeadAccess->getBlock())) {
1642 if (!AnyUnreachableExit)
1643 return std::nullopt;
1644
1645 // Fall back to CFG scan starting at all non-unreachable roots if not
1646 // all paths to the exit go through CommonPred.
1647 CommonPred = nullptr;
1648 }
1649
1650 // If CommonPred itself is in the set of killing blocks, we're done.
1651 if (KillingBlocks.count(CommonPred))
1652 return {MaybeDeadAccess};
1653
1654 SetVector<BasicBlock *> WorkList;
1655 // If CommonPred is null, there are multiple exits from the function.
1656 // They all have to be added to the worklist.
1657 if (CommonPred)
1658 WorkList.insert(CommonPred);
1659 else
1660 for (BasicBlock *R : PDT.roots()) {
1661 if (!isa<UnreachableInst>(R->getTerminator()))
1662 WorkList.insert(R);
1663 }
1664
1665 NumCFGTries++;
1666 // Check if all paths starting from an exit node go through one of the
1667 // killing blocks before reaching MaybeDeadAccess.
1668 for (unsigned I = 0; I < WorkList.size(); I++) {
1669 NumCFGChecks++;
1670 BasicBlock *Current = WorkList[I];
1671 if (KillingBlocks.count(Current))
1672 continue;
1673 if (Current == MaybeDeadAccess->getBlock())
1674 return std::nullopt;
1675
1676 // MaybeDeadAccess is reachable from the entry, so we don't have to
1677 // explore unreachable blocks further.
1678 if (!DT.isReachableFromEntry(Current))
1679 continue;
1680
1681 for (BasicBlock *Pred : predecessors(Current))
1682 WorkList.insert(Pred);
1683
1684 if (WorkList.size() >= MemorySSAPathCheckLimit)
1685 return std::nullopt;
1686 }
1687 NumCFGSuccess++;
1688 }
1689
1690 // No aliasing MemoryUses of MaybeDeadAccess found, MaybeDeadAccess is
1691 // potentially dead.
1692 return {MaybeDeadAccess};
1693 }
1694
1695 /// Delete dead memory defs and recursively add their operands to ToRemove if
1696 /// they became dead.
1697 void
1700 MemorySSAUpdater Updater(&MSSA);
1701 SmallVector<Instruction *, 32> NowDeadInsts;
1702 NowDeadInsts.push_back(SI);
1703 --NumFastOther;
1704
1705 while (!NowDeadInsts.empty()) {
1706 Instruction *DeadInst = NowDeadInsts.pop_back_val();
1707 ++NumFastOther;
1708
1709 // Try to preserve debug information attached to the dead instruction.
1710 salvageDebugInfo(*DeadInst);
1711 salvageKnowledge(DeadInst);
1712
1713 // Remove the Instruction from MSSA.
1714 MemoryAccess *MA = MSSA.getMemoryAccess(DeadInst);
1715 bool IsMemDef = MA && isa<MemoryDef>(MA);
1716 if (MA) {
1717 if (IsMemDef) {
1718 auto *MD = cast<MemoryDef>(MA);
1719 SkipStores.insert(MD);
1720 if (Deleted)
1721 Deleted->insert(MD);
1722 if (auto *SI = dyn_cast<StoreInst>(MD->getMemoryInst())) {
1723 if (SI->getValueOperand()->getType()->isPointerTy()) {
1724 const Value *UO = getUnderlyingObject(SI->getValueOperand());
1725 if (CapturedBeforeReturn.erase(UO))
1726 ShouldIterateEndOfFunctionDSE = true;
1727 InvisibleToCallerAfterRet.erase(UO);
1728 }
1729 }
1730 }
1731
1732 Updater.removeMemoryAccess(MA);
1733 }
1734
1735 auto I = IOLs.find(DeadInst->getParent());
1736 if (I != IOLs.end())
1737 I->second.erase(DeadInst);
1738 // Remove its operands
1739 for (Use &O : DeadInst->operands())
1740 if (Instruction *OpI = dyn_cast<Instruction>(O)) {
1741 O.set(PoisonValue::get(O->getType()));
1742 if (isInstructionTriviallyDead(OpI, &TLI))
1743 NowDeadInsts.push_back(OpI);
1744 }
1745
1746 EI.removeInstruction(DeadInst);
1747 // Remove memory defs directly if they don't produce results, but only
1748 // queue other dead instructions for later removal. They may have been
1749 // used as memory locations that have been cached by BatchAA. Removing
1750 // them here may lead to newly created instructions to be allocated at the
1751 // same address, yielding stale cache entries.
1752 if (IsMemDef && DeadInst->getType()->isVoidTy())
1753 DeadInst->eraseFromParent();
1754 else
1755 ToRemove.push_back(DeadInst);
1756 }
1757 }
1758
1759 // Check for any extra throws between \p KillingI and \p DeadI that block
1760 // DSE. This only checks extra maythrows (those that aren't MemoryDef's).
1761 // MemoryDef that may throw are handled during the walk from one def to the
1762 // next.
1763 bool mayThrowBetween(Instruction *KillingI, Instruction *DeadI,
1764 const Value *KillingUndObj) {
1765 // First see if we can ignore it by using the fact that KillingI is an
1766 // alloca/alloca like object that is not visible to the caller during
1767 // execution of the function.
1768 if (KillingUndObj && isInvisibleToCallerOnUnwind(KillingUndObj))
1769 return false;
1770
1771 if (KillingI->getParent() == DeadI->getParent())
1772 return ThrowingBlocks.count(KillingI->getParent());
1773 return !ThrowingBlocks.empty();
1774 }
1775
1776 // Check if \p DeadI acts as a DSE barrier for \p KillingI. The following
1777 // instructions act as barriers:
1778 // * A memory instruction that may throw and \p KillingI accesses a non-stack
1779 // object.
1780 // * Atomic stores stronger that monotonic.
1781 bool isDSEBarrier(const Value *KillingUndObj, Instruction *DeadI) {
1782 // If DeadI may throw it acts as a barrier, unless we are to an
1783 // alloca/alloca like object that does not escape.
1784 if (DeadI->mayThrow() && !isInvisibleToCallerOnUnwind(KillingUndObj))
1785 return true;
1786
1787 // If DeadI is an atomic load/store stronger than monotonic, do not try to
1788 // eliminate/reorder it.
1789 if (DeadI->isAtomic()) {
1790 if (auto *LI = dyn_cast<LoadInst>(DeadI))
1791 return isStrongerThanMonotonic(LI->getOrdering());
1792 if (auto *SI = dyn_cast<StoreInst>(DeadI))
1793 return isStrongerThanMonotonic(SI->getOrdering());
1794 if (auto *ARMW = dyn_cast<AtomicRMWInst>(DeadI))
1795 return isStrongerThanMonotonic(ARMW->getOrdering());
1796 if (auto *CmpXchg = dyn_cast<AtomicCmpXchgInst>(DeadI))
1797 return isStrongerThanMonotonic(CmpXchg->getSuccessOrdering()) ||
1798 isStrongerThanMonotonic(CmpXchg->getFailureOrdering());
1799 llvm_unreachable("other instructions should be skipped in MemorySSA");
1800 }
1801 return false;
1802 }
1803
1804 /// Eliminate writes to objects that are not visible in the caller and are not
1805 /// accessed before returning from the function.
1806 bool eliminateDeadWritesAtEndOfFunction() {
1807 bool MadeChange = false;
1808 LLVM_DEBUG(
1809 dbgs()
1810 << "Trying to eliminate MemoryDefs at the end of the function\n");
1811 do {
1812 ShouldIterateEndOfFunctionDSE = false;
1813 for (MemoryDef *Def : llvm::reverse(MemDefs)) {
1814 if (SkipStores.contains(Def))
1815 continue;
1816
1817 Instruction *DefI = Def->getMemoryInst();
1818 auto DefLoc = getLocForWrite(DefI);
1819 if (!DefLoc || !isRemovable(DefI)) {
1820 LLVM_DEBUG(dbgs() << " ... could not get location for write or "
1821 "instruction not removable.\n");
1822 continue;
1823 }
1824
1825 // NOTE: Currently eliminating writes at the end of a function is
1826 // limited to MemoryDefs with a single underlying object, to save
1827 // compile-time. In practice it appears the case with multiple
1828 // underlying objects is very uncommon. If it turns out to be important,
1829 // we can use getUnderlyingObjects here instead.
1830 const Value *UO = getUnderlyingObject(DefLoc->Ptr);
1831 if (!isInvisibleToCallerAfterRet(UO))
1832 continue;
1833
1834 if (isWriteAtEndOfFunction(Def, *DefLoc)) {
1835 // See through pointer-to-pointer bitcasts
1836 LLVM_DEBUG(dbgs() << " ... MemoryDef is not accessed until the end "
1837 "of the function\n");
1839 ++NumFastStores;
1840 MadeChange = true;
1841 }
1842 }
1843 } while (ShouldIterateEndOfFunctionDSE);
1844 return MadeChange;
1845 }
1846
1847 /// If we have a zero initializing memset following a call to malloc,
1848 /// try folding it into a call to calloc.
1849 bool tryFoldIntoCalloc(MemoryDef *Def, const Value *DefUO) {
1850 Instruction *DefI = Def->getMemoryInst();
1851 MemSetInst *MemSet = dyn_cast<MemSetInst>(DefI);
1852 if (!MemSet)
1853 // TODO: Could handle zero store to small allocation as well.
1854 return false;
1855 Constant *StoredConstant = dyn_cast<Constant>(MemSet->getValue());
1856 if (!StoredConstant || !StoredConstant->isNullValue())
1857 return false;
1858
1859 if (!isRemovable(DefI))
1860 // The memset might be volatile..
1861 return false;
1862
1863 if (F.hasFnAttribute(Attribute::SanitizeMemory) ||
1864 F.hasFnAttribute(Attribute::SanitizeAddress) ||
1865 F.hasFnAttribute(Attribute::SanitizeHWAddress) ||
1866 F.getName() == "calloc")
1867 return false;
1868 auto *Malloc = const_cast<CallInst *>(dyn_cast<CallInst>(DefUO));
1869 if (!Malloc)
1870 return false;
1871 auto *InnerCallee = Malloc->getCalledFunction();
1872 if (!InnerCallee)
1873 return false;
1874 LibFunc Func;
1875 if (!TLI.getLibFunc(*InnerCallee, Func) || !TLI.has(Func) ||
1876 Func != LibFunc_malloc)
1877 return false;
1878 // Gracefully handle malloc with unexpected memory attributes.
1879 auto *MallocDef = dyn_cast_or_null<MemoryDef>(MSSA.getMemoryAccess(Malloc));
1880 if (!MallocDef)
1881 return false;
1882
1883 auto shouldCreateCalloc = [](CallInst *Malloc, CallInst *Memset) {
1884 // Check for br(icmp ptr, null), truebb, falsebb) pattern at the end
1885 // of malloc block
1886 auto *MallocBB = Malloc->getParent(),
1887 *MemsetBB = Memset->getParent();
1888 if (MallocBB == MemsetBB)
1889 return true;
1890 auto *Ptr = Memset->getArgOperand(0);
1891 auto *TI = MallocBB->getTerminator();
1892 BasicBlock *TrueBB, *FalseBB;
1893 if (!match(TI, m_Br(m_SpecificICmp(ICmpInst::ICMP_EQ, m_Specific(Ptr),
1894 m_Zero()),
1895 TrueBB, FalseBB)))
1896 return false;
1897 if (MemsetBB != FalseBB)
1898 return false;
1899 return true;
1900 };
1901
1902 if (Malloc->getOperand(0) != MemSet->getLength())
1903 return false;
1904 if (!shouldCreateCalloc(Malloc, MemSet) ||
1905 !DT.dominates(Malloc, MemSet) ||
1906 !memoryIsNotModifiedBetween(Malloc, MemSet, BatchAA, DL, &DT))
1907 return false;
1908 IRBuilder<> IRB(Malloc);
1909 Type *SizeTTy = Malloc->getArgOperand(0)->getType();
1910 auto *Calloc = emitCalloc(ConstantInt::get(SizeTTy, 1),
1911 Malloc->getArgOperand(0), IRB, TLI);
1912 if (!Calloc)
1913 return false;
1914
1915 MemorySSAUpdater Updater(&MSSA);
1916 auto *NewAccess =
1917 Updater.createMemoryAccessAfter(cast<Instruction>(Calloc), nullptr,
1918 MallocDef);
1919 auto *NewAccessMD = cast<MemoryDef>(NewAccess);
1920 Updater.insertDef(NewAccessMD, /*RenameUses=*/true);
1921 Malloc->replaceAllUsesWith(Calloc);
1923 return true;
1924 }
1925
1926 // Check if there is a dominating condition, that implies that the value
1927 // being stored in a ptr is already present in the ptr.
1928 bool dominatingConditionImpliesValue(MemoryDef *Def) {
1929 auto *StoreI = cast<StoreInst>(Def->getMemoryInst());
1930 BasicBlock *StoreBB = StoreI->getParent();
1931 Value *StorePtr = StoreI->getPointerOperand();
1932 Value *StoreVal = StoreI->getValueOperand();
1933
1934 DomTreeNode *IDom = DT.getNode(StoreBB)->getIDom();
1935 if (!IDom)
1936 return false;
1937
1938 auto *BI = dyn_cast<BranchInst>(IDom->getBlock()->getTerminator());
1939 if (!BI || !BI->isConditional())
1940 return false;
1941
1942 // In case both blocks are the same, it is not possible to determine
1943 // if optimization is possible. (We would not want to optimize a store
1944 // in the FalseBB if condition is true and vice versa.)
1945 if (BI->getSuccessor(0) == BI->getSuccessor(1))
1946 return false;
1947
1948 Instruction *ICmpL;
1950 if (!match(BI->getCondition(),
1951 m_c_ICmp(Pred,
1952 m_CombineAnd(m_Load(m_Specific(StorePtr)),
1953 m_Instruction(ICmpL)),
1954 m_Specific(StoreVal))) ||
1955 !ICmpInst::isEquality(Pred))
1956 return false;
1957
1958 // In case the else blocks also branches to the if block or the other way
1959 // around it is not possible to determine if the optimization is possible.
1960 if (Pred == ICmpInst::ICMP_EQ &&
1961 !DT.dominates(BasicBlockEdge(BI->getParent(), BI->getSuccessor(0)),
1962 StoreBB))
1963 return false;
1964
1965 if (Pred == ICmpInst::ICMP_NE &&
1966 !DT.dominates(BasicBlockEdge(BI->getParent(), BI->getSuccessor(1)),
1967 StoreBB))
1968 return false;
1969
1970 MemoryAccess *LoadAcc = MSSA.getMemoryAccess(ICmpL);
1971 MemoryAccess *ClobAcc =
1972 MSSA.getSkipSelfWalker()->getClobberingMemoryAccess(Def, BatchAA);
1973
1974 return MSSA.dominates(ClobAcc, LoadAcc);
1975 }
1976
1977 /// \returns true if \p Def is a no-op store, either because it
1978 /// directly stores back a loaded value or stores zero to a calloced object.
1979 bool storeIsNoop(MemoryDef *Def, const Value *DefUO) {
1980 Instruction *DefI = Def->getMemoryInst();
1981 StoreInst *Store = dyn_cast<StoreInst>(DefI);
1982 MemSetInst *MemSet = dyn_cast<MemSetInst>(DefI);
1983 Constant *StoredConstant = nullptr;
1984 if (Store)
1985 StoredConstant = dyn_cast<Constant>(Store->getOperand(0));
1986 else if (MemSet)
1987 StoredConstant = dyn_cast<Constant>(MemSet->getValue());
1988 else
1989 return false;
1990
1991 if (!isRemovable(DefI))
1992 return false;
1993
1994 if (StoredConstant) {
1995 Constant *InitC =
1996 getInitialValueOfAllocation(DefUO, &TLI, StoredConstant->getType());
1997 // If the clobbering access is LiveOnEntry, no instructions between them
1998 // can modify the memory location.
1999 if (InitC && InitC == StoredConstant)
2000 return MSSA.isLiveOnEntryDef(
2001 MSSA.getSkipSelfWalker()->getClobberingMemoryAccess(Def, BatchAA));
2002 }
2003
2004 if (!Store)
2005 return false;
2006
2007 if (dominatingConditionImpliesValue(Def))
2008 return true;
2009
2010 if (auto *LoadI = dyn_cast<LoadInst>(Store->getOperand(0))) {
2011 if (LoadI->getPointerOperand() == Store->getOperand(1)) {
2012 // Get the defining access for the load.
2013 auto *LoadAccess = MSSA.getMemoryAccess(LoadI)->getDefiningAccess();
2014 // Fast path: the defining accesses are the same.
2015 if (LoadAccess == Def->getDefiningAccess())
2016 return true;
2017
2018 // Look through phi accesses. Recursively scan all phi accesses by
2019 // adding them to a worklist. Bail when we run into a memory def that
2020 // does not match LoadAccess.
2022 MemoryAccess *Current =
2023 MSSA.getWalker()->getClobberingMemoryAccess(Def, BatchAA);
2024 // We don't want to bail when we run into the store memory def. But,
2025 // the phi access may point to it. So, pretend like we've already
2026 // checked it.
2027 ToCheck.insert(Def);
2028 ToCheck.insert(Current);
2029 // Start at current (1) to simulate already having checked Def.
2030 for (unsigned I = 1; I < ToCheck.size(); ++I) {
2031 Current = ToCheck[I];
2032 if (auto PhiAccess = dyn_cast<MemoryPhi>(Current)) {
2033 // Check all the operands.
2034 for (auto &Use : PhiAccess->incoming_values())
2035 ToCheck.insert(cast<MemoryAccess>(&Use));
2036 continue;
2037 }
2038
2039 // If we found a memory def, bail. This happens when we have an
2040 // unrelated write in between an otherwise noop store.
2041 assert(isa<MemoryDef>(Current) &&
2042 "Only MemoryDefs should reach here.");
2043 // TODO: Skip no alias MemoryDefs that have no aliasing reads.
2044 // We are searching for the definition of the store's destination.
2045 // So, if that is the same definition as the load, then this is a
2046 // noop. Otherwise, fail.
2047 if (LoadAccess != Current)
2048 return false;
2049 }
2050 return true;
2051 }
2052 }
2053
2054 return false;
2055 }
2056
2057 bool removePartiallyOverlappedStores(InstOverlapIntervalsTy &IOL) {
2058 bool Changed = false;
2059 for (auto OI : IOL) {
2060 Instruction *DeadI = OI.first;
2061 MemoryLocation Loc = *getLocForWrite(DeadI);
2062 assert(isRemovable(DeadI) && "Expect only removable instruction");
2063
2064 const Value *Ptr = Loc.Ptr->stripPointerCasts();
2065 int64_t DeadStart = 0;
2066 uint64_t DeadSize = Loc.Size.getValue();
2067 GetPointerBaseWithConstantOffset(Ptr, DeadStart, DL);
2068 OverlapIntervalsTy &IntervalMap = OI.second;
2069 Changed |= tryToShortenEnd(DeadI, IntervalMap, DeadStart, DeadSize);
2070 if (IntervalMap.empty())
2071 continue;
2072 Changed |= tryToShortenBegin(DeadI, IntervalMap, DeadStart, DeadSize);
2073 }
2074 return Changed;
2075 }
2076
2077 /// Eliminates writes to locations where the value that is being written
2078 /// is already stored at the same location.
2079 bool eliminateRedundantStoresOfExistingValues() {
2080 bool MadeChange = false;
2081 LLVM_DEBUG(dbgs() << "Trying to eliminate MemoryDefs that write the "
2082 "already existing value\n");
2083 for (auto *Def : MemDefs) {
2084 if (SkipStores.contains(Def) || MSSA.isLiveOnEntryDef(Def))
2085 continue;
2086
2087 Instruction *DefInst = Def->getMemoryInst();
2088 auto MaybeDefLoc = getLocForWrite(DefInst);
2089 if (!MaybeDefLoc || !isRemovable(DefInst))
2090 continue;
2091
2092 MemoryDef *UpperDef;
2093 // To conserve compile-time, we avoid walking to the next clobbering def.
2094 // Instead, we just try to get the optimized access, if it exists. DSE
2095 // will try to optimize defs during the earlier traversal.
2096 if (Def->isOptimized())
2097 UpperDef = dyn_cast<MemoryDef>(Def->getOptimized());
2098 else
2099 UpperDef = dyn_cast<MemoryDef>(Def->getDefiningAccess());
2100 if (!UpperDef || MSSA.isLiveOnEntryDef(UpperDef))
2101 continue;
2102
2103 Instruction *UpperInst = UpperDef->getMemoryInst();
2104 auto IsRedundantStore = [&]() {
2105 if (DefInst->isIdenticalTo(UpperInst))
2106 return true;
2107 if (auto *MemSetI = dyn_cast<MemSetInst>(UpperInst)) {
2108 if (auto *SI = dyn_cast<StoreInst>(DefInst)) {
2109 // MemSetInst must have a write location.
2110 auto UpperLoc = getLocForWrite(UpperInst);
2111 if (!UpperLoc)
2112 return false;
2113 int64_t InstWriteOffset = 0;
2114 int64_t DepWriteOffset = 0;
2115 auto OR = isOverwrite(UpperInst, DefInst, *UpperLoc, *MaybeDefLoc,
2116 InstWriteOffset, DepWriteOffset);
2117 Value *StoredByte = isBytewiseValue(SI->getValueOperand(), DL);
2118 return StoredByte && StoredByte == MemSetI->getOperand(1) &&
2119 OR == OW_Complete;
2120 }
2121 }
2122 return false;
2123 };
2124
2125 if (!IsRedundantStore() || isReadClobber(*MaybeDefLoc, DefInst))
2126 continue;
2127 LLVM_DEBUG(dbgs() << "DSE: Remove No-Op Store:\n DEAD: " << *DefInst
2128 << '\n');
2129 deleteDeadInstruction(DefInst);
2130 NumRedundantStores++;
2131 MadeChange = true;
2132 }
2133 return MadeChange;
2134 }
2135};
2136
2137static bool eliminateDeadStores(Function &F, AliasAnalysis &AA, MemorySSA &MSSA,
2139 const TargetLibraryInfo &TLI,
2140 const LoopInfo &LI) {
2141 bool MadeChange = false;
2142
2143 DSEState State(F, AA, MSSA, DT, PDT, TLI, LI);
2144 // For each store:
2145 for (unsigned I = 0; I < State.MemDefs.size(); I++) {
2146 MemoryDef *KillingDef = State.MemDefs[I];
2147 if (State.SkipStores.count(KillingDef))
2148 continue;
2149 Instruction *KillingI = KillingDef->getMemoryInst();
2150
2151 std::optional<MemoryLocation> MaybeKillingLoc;
2152 if (State.isMemTerminatorInst(KillingI)) {
2153 if (auto KillingLoc = State.getLocForTerminator(KillingI))
2154 MaybeKillingLoc = KillingLoc->first;
2155 } else {
2156 MaybeKillingLoc = State.getLocForWrite(KillingI);
2157 }
2158
2159 if (!MaybeKillingLoc) {
2160 LLVM_DEBUG(dbgs() << "Failed to find analyzable write location for "
2161 << *KillingI << "\n");
2162 continue;
2163 }
2164 MemoryLocation KillingLoc = *MaybeKillingLoc;
2165 assert(KillingLoc.Ptr && "KillingLoc should not be null");
2166 const Value *KillingUndObj = getUnderlyingObject(KillingLoc.Ptr);
2167 LLVM_DEBUG(dbgs() << "Trying to eliminate MemoryDefs killed by "
2168 << *KillingDef << " (" << *KillingI << ")\n");
2169
2170 unsigned ScanLimit = MemorySSAScanLimit;
2171 unsigned WalkerStepLimit = MemorySSAUpwardsStepLimit;
2172 unsigned PartialLimit = MemorySSAPartialStoreLimit;
2173 // Worklist of MemoryAccesses that may be killed by KillingDef.
2175 // Track MemoryAccesses that have been deleted in the loop below, so we can
2176 // skip them. Don't use SkipStores for this, which may contain reused
2177 // MemoryAccess addresses.
2179 [[maybe_unused]] unsigned OrigNumSkipStores = State.SkipStores.size();
2180 ToCheck.insert(KillingDef->getDefiningAccess());
2181
2182 bool Shortend = false;
2183 bool IsMemTerm = State.isMemTerminatorInst(KillingI);
2184 // Check if MemoryAccesses in the worklist are killed by KillingDef.
2185 for (unsigned I = 0; I < ToCheck.size(); I++) {
2186 MemoryAccess *Current = ToCheck[I];
2187 if (Deleted.contains(Current))
2188 continue;
2189
2190 std::optional<MemoryAccess *> MaybeDeadAccess = State.getDomMemoryDef(
2191 KillingDef, Current, KillingLoc, KillingUndObj, ScanLimit,
2192 WalkerStepLimit, IsMemTerm, PartialLimit);
2193
2194 if (!MaybeDeadAccess) {
2195 LLVM_DEBUG(dbgs() << " finished walk\n");
2196 continue;
2197 }
2198
2199 MemoryAccess *DeadAccess = *MaybeDeadAccess;
2200 LLVM_DEBUG(dbgs() << " Checking if we can kill " << *DeadAccess);
2201 if (isa<MemoryPhi>(DeadAccess)) {
2202 LLVM_DEBUG(dbgs() << "\n ... adding incoming values to worklist\n");
2203 for (Value *V : cast<MemoryPhi>(DeadAccess)->incoming_values()) {
2204 MemoryAccess *IncomingAccess = cast<MemoryAccess>(V);
2205 BasicBlock *IncomingBlock = IncomingAccess->getBlock();
2206 BasicBlock *PhiBlock = DeadAccess->getBlock();
2207
2208 // We only consider incoming MemoryAccesses that come before the
2209 // MemoryPhi. Otherwise we could discover candidates that do not
2210 // strictly dominate our starting def.
2211 if (State.PostOrderNumbers[IncomingBlock] >
2212 State.PostOrderNumbers[PhiBlock])
2213 ToCheck.insert(IncomingAccess);
2214 }
2215 continue;
2216 }
2217 auto *DeadDefAccess = cast<MemoryDef>(DeadAccess);
2218 Instruction *DeadI = DeadDefAccess->getMemoryInst();
2219 LLVM_DEBUG(dbgs() << " (" << *DeadI << ")\n");
2220 ToCheck.insert(DeadDefAccess->getDefiningAccess());
2221 NumGetDomMemoryDefPassed++;
2222
2223 if (!DebugCounter::shouldExecute(MemorySSACounter))
2224 continue;
2225
2226 MemoryLocation DeadLoc = *State.getLocForWrite(DeadI);
2227
2228 if (IsMemTerm) {
2229 const Value *DeadUndObj = getUnderlyingObject(DeadLoc.Ptr);
2230 if (KillingUndObj != DeadUndObj)
2231 continue;
2232 LLVM_DEBUG(dbgs() << "DSE: Remove Dead Store:\n DEAD: " << *DeadI
2233 << "\n KILLER: " << *KillingI << '\n');
2234 State.deleteDeadInstruction(DeadI, &Deleted);
2235 ++NumFastStores;
2236 MadeChange = true;
2237 } else {
2238 // Check if DeadI overwrites KillingI.
2239 int64_t KillingOffset = 0;
2240 int64_t DeadOffset = 0;
2241 OverwriteResult OR = State.isOverwrite(
2242 KillingI, DeadI, KillingLoc, DeadLoc, KillingOffset, DeadOffset);
2243 if (OR == OW_MaybePartial) {
2244 auto Iter = State.IOLs.insert(
2245 std::make_pair<BasicBlock *, InstOverlapIntervalsTy>(
2246 DeadI->getParent(), InstOverlapIntervalsTy()));
2247 auto &IOL = Iter.first->second;
2248 OR = isPartialOverwrite(KillingLoc, DeadLoc, KillingOffset,
2249 DeadOffset, DeadI, IOL);
2250 }
2251
2252 if (EnablePartialStoreMerging && OR == OW_PartialEarlierWithFullLater) {
2253 auto *DeadSI = dyn_cast<StoreInst>(DeadI);
2254 auto *KillingSI = dyn_cast<StoreInst>(KillingI);
2255 // We are re-using tryToMergePartialOverlappingStores, which requires
2256 // DeadSI to dominate KillingSI.
2257 // TODO: implement tryToMergeParialOverlappingStores using MemorySSA.
2258 if (DeadSI && KillingSI && DT.dominates(DeadSI, KillingSI)) {
2260 KillingSI, DeadSI, KillingOffset, DeadOffset, State.DL,
2261 State.BatchAA, &DT)) {
2262
2263 // Update stored value of earlier store to merged constant.
2264 DeadSI->setOperand(0, Merged);
2265 ++NumModifiedStores;
2266 MadeChange = true;
2267
2268 Shortend = true;
2269 // Remove killing store and remove any outstanding overlap
2270 // intervals for the updated store.
2271 State.deleteDeadInstruction(KillingSI, &Deleted);
2272 auto I = State.IOLs.find(DeadSI->getParent());
2273 if (I != State.IOLs.end())
2274 I->second.erase(DeadSI);
2275 break;
2276 }
2277 }
2278 }
2279
2280 if (OR == OW_Complete) {
2281 LLVM_DEBUG(dbgs() << "DSE: Remove Dead Store:\n DEAD: " << *DeadI
2282 << "\n KILLER: " << *KillingI << '\n');
2283 State.deleteDeadInstruction(DeadI, &Deleted);
2284 ++NumFastStores;
2285 MadeChange = true;
2286 }
2287 }
2288 }
2289
2290 assert(State.SkipStores.size() - OrigNumSkipStores == Deleted.size() &&
2291 "SkipStores and Deleted out of sync?");
2292
2293 // Check if the store is a no-op.
2294 if (!Shortend && State.storeIsNoop(KillingDef, KillingUndObj)) {
2295 LLVM_DEBUG(dbgs() << "DSE: Remove No-Op Store:\n DEAD: " << *KillingI
2296 << '\n');
2297 State.deleteDeadInstruction(KillingI);
2298 NumRedundantStores++;
2299 MadeChange = true;
2300 continue;
2301 }
2302
2303 // Can we form a calloc from a memset/malloc pair?
2304 if (!Shortend && State.tryFoldIntoCalloc(KillingDef, KillingUndObj)) {
2305 LLVM_DEBUG(dbgs() << "DSE: Remove memset after forming calloc:\n"
2306 << " DEAD: " << *KillingI << '\n');
2307 State.deleteDeadInstruction(KillingI);
2308 MadeChange = true;
2309 continue;
2310 }
2311 }
2312
2314 for (auto &KV : State.IOLs)
2315 MadeChange |= State.removePartiallyOverlappedStores(KV.second);
2316
2317 MadeChange |= State.eliminateRedundantStoresOfExistingValues();
2318 MadeChange |= State.eliminateDeadWritesAtEndOfFunction();
2319
2320 while (!State.ToRemove.empty()) {
2321 Instruction *DeadInst = State.ToRemove.pop_back_val();
2322 DeadInst->eraseFromParent();
2323 }
2324
2325 return MadeChange;
2326}
2327} // end anonymous namespace
2328
2329//===----------------------------------------------------------------------===//
2330// DSE Pass
2331//===----------------------------------------------------------------------===//
2336 MemorySSA &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
2338 LoopInfo &LI = AM.getResult<LoopAnalysis>(F);
2339
2340 bool Changed = eliminateDeadStores(F, AA, MSSA, DT, PDT, TLI, LI);
2341
2342#ifdef LLVM_ENABLE_STATS
2344 for (auto &I : instructions(F))
2345 NumRemainingStores += isa<StoreInst>(&I);
2346#endif
2347
2348 if (!Changed)
2349 return PreservedAnalyses::all();
2350
2354 PA.preserve<LoopAnalysis>();
2355 return PA;
2356}
This file implements a class to represent arbitrary precision integral constant values and operations...
ReachingDefAnalysis InstSet & ToRemove
MachineBasicBlock MachineBasicBlock::iterator DebugLoc DL
Expand Atomic instructions
static GCRegistry::Add< OcamlGC > B("ocaml", "ocaml 3.10-compatible GC")
static GCRegistry::Add< StatepointGC > D("statepoint-example", "an example strategy for statepoint")
This file contains the declarations for the subclasses of Constant, which represent the different fla...
static void shortenAssignment(Instruction *Inst, Value *OriginalDest, uint64_t OldOffsetInBits, uint64_t OldSizeInBits, uint64_t NewSizeInBits, bool IsOverwriteEnd)
static bool isShortenableAtTheEnd(Instruction *I)
Returns true if the end of this instruction can be safely shortened in length.
static cl::opt< bool > EnablePartialStoreMerging("enable-dse-partial-store-merging", cl::init(true), cl::Hidden, cl::desc("Enable partial store merging in DSE"))
static bool tryToShortenBegin(Instruction *DeadI, OverlapIntervalsTy &IntervalMap, int64_t &DeadStart, uint64_t &DeadSize)
std::map< int64_t, int64_t > OverlapIntervalsTy
static bool isShortenableAtTheBeginning(Instruction *I)
Returns true if the beginning of this instruction can be safely shortened in length.
static cl::opt< unsigned > MemorySSADefsPerBlockLimit("dse-memoryssa-defs-per-block-limit", cl::init(5000), cl::Hidden, cl::desc("The number of MemoryDefs we consider as candidates to eliminated " "other stores per basic block (default = 5000)"))
static Constant * tryToMergePartialOverlappingStores(StoreInst *KillingI, StoreInst *DeadI, int64_t KillingOffset, int64_t DeadOffset, const DataLayout &DL, BatchAAResults &AA, DominatorTree *DT)
static bool memoryIsNotModifiedBetween(Instruction *FirstI, Instruction *SecondI, BatchAAResults &AA, const DataLayout &DL, DominatorTree *DT)
Returns true if the memory which is accessed by the second instruction is not modified between the fi...
static OverwriteResult isMaskedStoreOverwrite(const Instruction *KillingI, const Instruction *DeadI, BatchAAResults &AA)
Check if two instruction are masked stores that completely overwrite one another.
static cl::opt< unsigned > MemorySSAOtherBBStepCost("dse-memoryssa-otherbb-cost", cl::init(5), cl::Hidden, cl::desc("The cost of a step in a different basic " "block than the killing MemoryDef" "(default = 5)"))
static bool tryToShorten(Instruction *DeadI, int64_t &DeadStart, uint64_t &DeadSize, int64_t KillingStart, uint64_t KillingSize, bool IsOverwriteEnd)
static cl::opt< unsigned > MemorySSAScanLimit("dse-memoryssa-scanlimit", cl::init(150), cl::Hidden, cl::desc("The number of memory instructions to scan for " "dead store elimination (default = 150)"))
static cl::opt< unsigned > MemorySSASameBBStepCost("dse-memoryssa-samebb-cost", cl::init(1), cl::Hidden, cl::desc("The cost of a step in the same basic block as the killing MemoryDef" "(default = 1)"))
static cl::opt< bool > EnablePartialOverwriteTracking("enable-dse-partial-overwrite-tracking", cl::init(true), cl::Hidden, cl::desc("Enable partial-overwrite tracking in DSE"))
static OverwriteResult isPartialOverwrite(const MemoryLocation &KillingLoc, const MemoryLocation &DeadLoc, int64_t KillingOff, int64_t DeadOff, Instruction *DeadI, InstOverlapIntervalsTy &IOL)
Return 'OW_Complete' if a store to the 'KillingLoc' location completely overwrites a store to the 'De...
static cl::opt< unsigned > MemorySSAPartialStoreLimit("dse-memoryssa-partial-store-limit", cl::init(5), cl::Hidden, cl::desc("The maximum number candidates that only partially overwrite the " "killing MemoryDef to consider" " (default = 5)"))
static std::optional< TypeSize > getPointerSize(const Value *V, const DataLayout &DL, const TargetLibraryInfo &TLI, const Function *F)
static bool tryToShortenEnd(Instruction *DeadI, OverlapIntervalsTy &IntervalMap, int64_t &DeadStart, uint64_t &DeadSize)
static cl::opt< unsigned > MemorySSAUpwardsStepLimit("dse-memoryssa-walklimit", cl::init(90), cl::Hidden, cl::desc("The maximum number of steps while walking upwards to find " "MemoryDefs that may be killed (default = 90)"))
static cl::opt< bool > OptimizeMemorySSA("dse-optimize-memoryssa", cl::init(true), cl::Hidden, cl::desc("Allow DSE to optimize memory accesses."))
static cl::opt< unsigned > MemorySSAPathCheckLimit("dse-memoryssa-path-check-limit", cl::init(50), cl::Hidden, cl::desc("The maximum number of blocks to check when trying to prove that " "all paths to an exit go through a killing block (default = 50)"))
This file provides an implementation of debug counters.
#define DEBUG_COUNTER(VARNAME, COUNTERNAME, DESC)
Definition: DebugCounter.h:190
#define LLVM_DEBUG(X)
Definition: Debug.h:101
This file defines the DenseMap class.
uint64_t Addr
uint64_t Size
This is the interface for a simple mod/ref and alias analysis over globals.
Hexagon Common GEP
IRTranslator LLVM IR MI
static void deleteDeadInstruction(Instruction *I)
#define F(x, y, z)
Definition: MD5.cpp:55
#define I(x, y, z)
Definition: MD5.cpp:58
This file implements a map that provides insertion order iteration.
This file provides utility analysis objects describing memory locations.
This file exposes an interface to building/using memory SSA to walk memory instructions using a use/d...
Module.h This file contains the declarations for the Module class.
Contains a collection of routines for determining if a given instruction is guaranteed to execute if ...
uint64_t IntrinsicInst * II
This header defines various interfaces for pass management in LLVM.
This file builds on the ADT/GraphTraits.h file to build a generic graph post order iterator.
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
This file implements a set that has insertion order iteration characteristics.
This file defines the SmallPtrSet class.
This file defines the SmallVector class.
This file defines the 'Statistic' class, which is designed to be an easy way to expose various metric...
#define STATISTIC(VARNAME, DESC)
Definition: Statistic.h:166
A manager for alias analyses.
Class for arbitrary precision integers.
Definition: APInt.h:77
APInt zext(unsigned width) const
Zero extend to a new width.
Definition: APInt.cpp:981
static APInt getBitsSet(unsigned numBits, unsigned loBit, unsigned hiBit)
Get a value with a block of bits set.
Definition: APInt.h:235
unsigned getBitWidth() const
Return the number of bits in the APInt.
Definition: APInt.h:1445
The possible results of an alias query.
Definition: AliasAnalysis.h:77
@ NoAlias
The two locations do not alias at all.
Definition: AliasAnalysis.h:95
@ PartialAlias
The two locations alias, but only due to a partial overlap.
@ MustAlias
The two locations precisely alias each other.
constexpr int32_t getOffset() const
constexpr bool hasOffset() const
A container for analyses that lazily runs them and caches their results.
Definition: PassManager.h:253
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs... ExtraArgs)
Get the result of an analysis pass for a given IR unit.
Definition: PassManager.h:405
This class represents an incoming formal argument to a Function.
Definition: Argument.h:31
LLVM Basic Block Representation.
Definition: BasicBlock.h:61
const Function * getParent() const
Return the enclosing method, or null if none.
Definition: BasicBlock.h:219
InstListType::iterator iterator
Instruction iterators...
Definition: BasicBlock.h:177
const Instruction * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.h:239
This class is a wrapper over an AAResults, and it is intended to be used only when there are no IR ch...
AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB)
bool isMustAlias(const MemoryLocation &LocA, const MemoryLocation &LocB)
ModRefInfo getModRefInfo(const Instruction *I, const std::optional< MemoryLocation > &OptLoc)
Represents analyses that only rely on functions' control flow.
Definition: Analysis.h:72
This class represents a function call, abstracting a target machine's calling convention.
Predicate
This enumeration lists the possible predicates for CmpInst subclasses.
Definition: InstrTypes.h:757
This is an important base class in LLVM.
Definition: Constant.h:42
bool isNullValue() const
Return true if this is the value that would be returned by getNullValue.
Definition: Constants.cpp:90
Assignment ID.
static DIAssignID * getDistinct(LLVMContext &Context)
static std::optional< DIExpression * > createFragmentExpression(const DIExpression *Expr, unsigned OffsetInBits, unsigned SizeInBits)
Create a DIExpression to describe one part of an aggregate variable that is fragmented across multipl...
PreservedAnalyses run(Function &F, FunctionAnalysisManager &FAM)
A parsed version of the target data layout string in and methods for querying it.
Definition: DataLayout.h:63
static bool shouldExecute(unsigned CounterName)
Definition: DebugCounter.h:87
iterator find(const_arg_type_t< KeyT > Val)
Definition: DenseMap.h:155
bool erase(const KeyT &Val)
Definition: DenseMap.h:336
std::pair< iterator, bool > insert(const std::pair< KeyT, ValueT > &KV)
Definition: DenseMap.h:211
DomTreeNodeBase * getIDom() const
NodeT * getBlock() const
Analysis pass which computes a DominatorTree.
Definition: Dominators.h:279
NodeT * findNearestCommonDominator(NodeT *A, NodeT *B) const
Find nearest common dominator basic block for basic block A and B.
iterator_range< root_iterator > roots()
DomTreeNodeBase< NodeT > * getNode(const NodeT *BB) const
getNode - return the (Post)DominatorTree node for the specified basic block.
bool properlyDominates(const DomTreeNodeBase< NodeT > *A, const DomTreeNodeBase< NodeT > *B) const
properlyDominates - Returns true iff A dominates B and A != B.
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree.
Definition: Dominators.h:162
bool isReachableFromEntry(const Use &U) const
Provide an overload for a Use.
Definition: Dominators.cpp:321
bool dominates(const BasicBlock *BB, const Use &U) const
Return true if the (end of the) basic block BB dominates the use U.
Definition: Dominators.cpp:122
Context-sensitive CaptureInfo provider, which computes and caches the earliest common dominator closu...
void removeInstruction(Instruction *I)
const BasicBlock & getEntryBlock() const
Definition: Function.h:807
static GetElementPtrInst * CreateInBounds(Type *PointeeType, Value *Ptr, ArrayRef< Value * > IdxList, const Twine &NameStr="", InsertPosition InsertBefore=nullptr)
Create an "inbounds" getelementptr.
Definition: Instructions.h:961
bool isEquality() const
Return true if this predicate is either EQ or NE.
This provides a uniform API for creating instructions and inserting them into a basic block: either a...
Definition: IRBuilder.h:2686
bool mayThrow(bool IncludePhaseOneUnwind=false) const LLVM_READONLY
Return true if this instruction may throw an exception.
bool mayWriteToMemory() const LLVM_READONLY
Return true if this instruction may modify memory.
bool isAtomic() const LLVM_READONLY
Return true if this instruction has an AtomicOrdering of unordered or higher.
InstListType::iterator eraseFromParent()
This method unlinks 'this' from the containing basic block and deletes it.
Definition: Instruction.cpp:92
bool mayReadFromMemory() const LLVM_READONLY
Return true if this instruction may read memory.
bool isIdenticalTo(const Instruction *I) const LLVM_READONLY
Return true if the specified instruction is exactly identical to the current one.
void setDebugLoc(DebugLoc Loc)
Set the debug location information for this instruction.
Definition: Instruction.h:463
const DataLayout & getDataLayout() const
Get the data layout of the module this instruction belongs to.
Definition: Instruction.cpp:74
const_iterator begin() const
Definition: IntervalMap.h:1146
bool empty() const
empty - Return true when no intervals are mapped.
Definition: IntervalMap.h:1101
const_iterator end() const
Definition: IntervalMap.h:1158
A wrapper class for inspecting calls to intrinsic functions.
Definition: IntrinsicInst.h:48
This is an important class for using LLVM in a threaded context.
Definition: LLVMContext.h:67
static LocationSize precise(uint64_t Value)
bool isScalable() const
TypeSize getValue() const
bool isPrecise() const
Analysis pass that exposes the LoopInfo for a function.
Definition: LoopInfo.h:566
LoopT * getLoopFor(const BlockT *BB) const
Return the inner most loop that BB lives in.
Represents a single loop in the control flow graph.
Definition: LoopInfo.h:39
This class implements a map that also provides access to all stored values in a deterministic order.
Definition: MapVector.h:36
iterator end()
Definition: MapVector.h:71
iterator find(const KeyT &Key)
Definition: MapVector.h:167
Value * getLength() const
Value * getValue() const
This class wraps the llvm.memset and llvm.memset.inline intrinsics.
BasicBlock * getBlock() const
Definition: MemorySSA.h:161
Represents a read-write access to memory, whether it is a must-alias, or a may-alias.
Definition: MemorySSA.h:369
void setOptimized(MemoryAccess *MA)
Definition: MemorySSA.h:389
Representation for a specific memory location.
static MemoryLocation get(const LoadInst *LI)
Return a location with information about the memory reference by the given instruction.
LocationSize Size
The maximum size of the location, in address-units, or UnknownSize if the size is not known.
static MemoryLocation getAfter(const Value *Ptr, const AAMDNodes &AATags=AAMDNodes())
Return a location that may access any location after Ptr, while remaining within the underlying objec...
MemoryLocation getWithNewPtr(const Value *NewPtr) const
const Value * Ptr
The address of the start of the location.
static MemoryLocation getForDest(const MemIntrinsic *MI)
Return a location representing the destination of a memory set or transfer.
static std::optional< MemoryLocation > getOrNone(const Instruction *Inst)
An analysis that produces MemorySSA for a function.
Definition: MemorySSA.h:924
MemoryAccess * getClobberingMemoryAccess(const Instruction *I, BatchAAResults &AA)
Given a memory Mod/Ref/ModRef'ing instruction, calling this will give you the nearest dominating Memo...
Definition: MemorySSA.h:1041
Encapsulates MemorySSA, including all data associated with memory accesses.
Definition: MemorySSA.h:697
MemorySSAWalker * getSkipSelfWalker()
Definition: MemorySSA.cpp:1603
bool dominates(const MemoryAccess *A, const MemoryAccess *B) const
Given two memory accesses in potentially different blocks, determine whether MemoryAccess A dominates...
Definition: MemorySSA.cpp:2173
MemorySSAWalker * getWalker()
Definition: MemorySSA.cpp:1590
MemoryUseOrDef * getMemoryAccess(const Instruction *I) const
Given a memory Mod/Ref'ing instruction, get the MemorySSA access associated with it.
Definition: MemorySSA.h:715
bool isLiveOnEntryDef(const MemoryAccess *MA) const
Return true if MA represents the live on entry value.
Definition: MemorySSA.h:735
MemoryAccess * getDefiningAccess() const
Get the access that produces the memory state used by this Use.
Definition: MemorySSA.h:259
Instruction * getMemoryInst() const
Get the instruction that this MemoryUse represents.
Definition: MemorySSA.h:256
PHITransAddr - An address value which tracks and handles phi translation.
Definition: PHITransAddr.h:35
Value * translateValue(BasicBlock *CurBB, BasicBlock *PredBB, const DominatorTree *DT, bool MustDominate)
translateValue - PHI translate the current address up the CFG from CurBB to Pred, updating our state ...
bool isPotentiallyPHITranslatable() const
isPotentiallyPHITranslatable - If this needs PHI translation, return true if we have some hope of doi...
bool needsPHITranslationFromBlock(BasicBlock *BB) const
needsPHITranslationFromBlock - Return true if moving from the specified BasicBlock to its predecessor...
Definition: PHITransAddr.h:62
Value * getAddr() const
Definition: PHITransAddr.h:58
static PoisonValue * get(Type *T)
Static factory methods - Return an 'poison' object of the specified type.
Definition: Constants.cpp:1852
Analysis pass which computes a PostDominatorTree.
PostDominatorTree Class - Concrete subclass of DominatorTree that is used to compute the post-dominat...
bool dominates(const Instruction *I1, const Instruction *I2) const
Return true if I1 dominates I2.
A set of analyses that are preserved following a run of a transformation pass.
Definition: Analysis.h:111
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: Analysis.h:117
void preserveSet()
Mark an analysis set as preserved.
Definition: Analysis.h:146
void preserve()
Mark an analysis as preserved.
Definition: Analysis.h:131
A vector that has set insertion semantics.
Definition: SetVector.h:57
size_type size() const
Determine the number of elements in the SetVector.
Definition: SetVector.h:98
bool insert(const value_type &X)
Insert a new element into the SetVector.
Definition: SetVector.h:162
A templated base class for SmallPtrSet which provides the typesafe interface that is common across al...
Definition: SmallPtrSet.h:346
size_type count(ConstPtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
Definition: SmallPtrSet.h:435
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:367
iterator begin() const
Definition: SmallPtrSet.h:455
bool contains(ConstPtrType Ptr) const
Definition: SmallPtrSet.h:441
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements.
Definition: SmallPtrSet.h:502
A SetVector that performs no allocations if smaller than a certain size.
Definition: SetVector.h:370
bool empty() const
Definition: SmallVector.h:94
size_t size() const
Definition: SmallVector.h:91
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: SmallVector.h:586
void push_back(const T &Elt)
Definition: SmallVector.h:426
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
Definition: SmallVector.h:1209
An instruction for storing to memory.
Definition: Instructions.h:290
Value * getValueOperand()
Definition: Instructions.h:374
Analysis pass providing the TargetLibraryInfo.
Provides information about what library functions are available for the current target.
bool has(LibFunc F) const
Tests whether a library function is available.
bool getLibFunc(StringRef funcName, LibFunc &F) const
Searches for a particular function name.
static constexpr TypeSize getFixed(ScalarTy ExactSize)
Definition: TypeSize.h:345
The instances of the Type class are immutable: once they are created, they are never changed.
Definition: Type.h:45
static IntegerType * getInt8Ty(LLVMContext &C)
bool isVoidTy() const
Return true if this is 'void'.
Definition: Type.h:139
A Use represents the edge between a Value definition and its users.
Definition: Use.h:43
op_range operands()
Definition: User.h:242
LLVM Value Representation.
Definition: Value.h:74
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:255
const Value * stripPointerCasts() const
Strip off pointer casts, all-zero GEPs and address space casts.
Definition: Value.cpp:694
LLVMContext & getContext() const
All values hold a context through their type.
Definition: Value.cpp:1075
iterator_range< use_iterator > uses()
Definition: Value.h:376
constexpr bool isScalable() const
Returns whether the quantity is scaled by a runtime quantity (vscale).
Definition: TypeSize.h:171
const ParentTy * getParent() const
Definition: ilist_node.h:32
self_iterator getIterator()
Definition: ilist_node.h:132
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
bool match(Val *V, const Pattern &P)
Definition: PatternMatch.h:49
bind_ty< Instruction > m_Instruction(Instruction *&I)
Match an instruction, capturing it if we match.
Definition: PatternMatch.h:816
specificval_ty m_Specific(const Value *V)
Match if we have a specific specified value.
Definition: PatternMatch.h:875
class_match< ConstantInt > m_ConstantInt()
Match an arbitrary ConstantInt and ignore it.
Definition: PatternMatch.h:168
match_combine_and< LTy, RTy > m_CombineAnd(const LTy &L, const RTy &R)
Combine two pattern matchers matching L && R.
Definition: PatternMatch.h:245
OneOps_match< OpTy, Instruction::Load > m_Load(const OpTy &Op)
Matches LoadInst.
brc_match< Cond_t, bind_ty< BasicBlock >, bind_ty< BasicBlock > > m_Br(const Cond_t &C, BasicBlock *&T, BasicBlock *&F)
CmpClass_match< LHS, RHS, ICmpInst, ICmpInst::Predicate, true > m_c_ICmp(ICmpInst::Predicate &Pred, const LHS &L, const RHS &R)
Matches an ICmp with a predicate over LHS and RHS in either order.
SpecificCmpClass_match< LHS, RHS, ICmpInst, ICmpInst::Predicate > m_SpecificICmp(ICmpInst::Predicate MatchPred, const LHS &L, const RHS &R)
class_match< Value > m_Value()
Match an arbitrary value and ignore it.
Definition: PatternMatch.h:92
is_zero m_Zero()
Match any null constant or a vector with all elements equal to 0.
Definition: PatternMatch.h:612
AssignmentMarkerRange getAssignmentMarkers(DIAssignID *ID)
Return a range of dbg.assign intrinsics which use \ID as an operand.
Definition: DebugInfo.cpp:1825
SmallVector< DbgVariableRecord * > getDVRAssignmentMarkers(const Instruction *Inst)
Definition: DebugInfo.h:240
bool calculateFragmentIntersect(const DataLayout &DL, const Value *Dest, uint64_t SliceOffsetInBits, uint64_t SliceSizeInBits, const DbgAssignIntrinsic *DbgAssign, std::optional< DIExpression::FragmentInfo > &Result)
Calculate the fragment of the variable in DAI covered from (Dest + SliceOffsetInBits) to to (Dest + S...
Definition: DebugInfo.cpp:1920
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:443
NodeAddr< DefNode * > Def
Definition: RDFGraph.h:384
NodeAddr< FuncNode * > Func
Definition: RDFGraph.h:393
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
auto drop_begin(T &&RangeOrContainer, size_t N=1)
Return a range covering RangeOrContainer with the first N elements excluded.
Definition: STLExtras.h:329
UnaryFunction for_each(R &&Range, UnaryFunction F)
Provide wrappers to std::for_each which take ranges instead of having to pass begin/end explicitly.
Definition: STLExtras.h:1715
Constant * getInitialValueOfAllocation(const Value *V, const TargetLibraryInfo *TLI, Type *Ty)
If this is a call to an allocation function that initializes memory to a fixed value,...
bool isStrongerThanMonotonic(AtomicOrdering AO)
bool isAligned(Align Lhs, uint64_t SizeInBytes)
Checks that SizeInBytes is a multiple of the alignment.
Definition: Alignment.h:145
void salvageDebugInfo(const MachineRegisterInfo &MRI, MachineInstr &MI)
Assuming the instruction MI is going to be deleted, attempt to salvage debug users of MI by writing t...
Definition: Utils.cpp:1678
Value * emitCalloc(Value *Num, Value *Size, IRBuilderBase &B, const TargetLibraryInfo &TLI)
Emit a call to the calloc function.
Value * GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset, const DataLayout &DL, bool AllowNonInbounds=true)
Analyze the specified pointer to see if it can be expressed as a base pointer plus a constant offset.
const Value * getUnderlyingObject(const Value *V, unsigned MaxLookup=6)
This method strips off any GEP address adjustments, pointer casts or llvm.threadlocal....
iterator_range< po_iterator< T > > post_order(const T &G)
bool isNoAliasCall(const Value *V)
Return true if this pointer is returned by a noalias function.
bool any_of(R &&range, UnaryPredicate P)
Provide wrappers to std::any_of which take ranges instead of having to pass begin/end explicitly.
Definition: STLExtras.h:1729
bool isInstructionTriviallyDead(Instruction *I, const TargetLibraryInfo *TLI=nullptr)
Return true if the result produced by the instruction is not used, and the instruction will return.
Definition: Local.cpp:400
bool getObjectSize(const Value *Ptr, uint64_t &Size, const DataLayout &DL, const TargetLibraryInfo *TLI, ObjectSizeOpts Opts={})
Compute the size of the object pointed by Ptr.
auto reverse(ContainerTy &&C)
Definition: STLExtras.h:419
bool isModSet(const ModRefInfo MRI)
Definition: ModRef.h:48
bool PointerMayBeCaptured(const Value *V, bool ReturnCaptures, bool StoreCaptures, unsigned MaxUsesToExplore=0)
PointerMayBeCaptured - Return true if this pointer value may be captured by the enclosing function (w...
bool NullPointerIsDefined(const Function *F, unsigned AS=0)
Check whether null pointer dereferencing is considered undefined behavior for a given function or an ...
Definition: Function.cpp:2132
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:163
bool AreStatisticsEnabled()
Check if statistics are enabled.
Definition: Statistic.cpp:139
bool isNotVisibleOnUnwind(const Value *Object, bool &RequiresNoCaptureBeforeUnwind)
Return true if Object memory is not visible after an unwind, in the sense that program semantics cann...
uint64_t offsetToAlignment(uint64_t Value, Align Alignment)
Returns the offset to the next integer (mod 2**64) that is greater than or equal to Value and is a mu...
Definition: Alignment.h:197
bool salvageKnowledge(Instruction *I, AssumptionCache *AC=nullptr, DominatorTree *DT=nullptr)
Calls BuildAssumeFromInst and if the resulting llvm.assume is valid insert if before I.
Value * getFreedOperand(const CallBase *CB, const TargetLibraryInfo *TLI)
If this if a call to a free function, return the freed operand.
Value * isBytewiseValue(Value *V, const DataLayout &DL)
If the specified value can be set by repeating the same byte in memory, return the i8 value that it i...
auto predecessors(const MachineBasicBlock *BB)
bool mayContainIrreducibleControl(const Function &F, const LoopInfo *LI)
bool isIdentifiedObject(const Value *V)
Return true if this pointer refers to a distinct and identifiable object.
bool isStrongerThan(AtomicOrdering AO, AtomicOrdering Other)
Returns true if ao is stronger than other as defined by the AtomicOrdering lattice,...
bool isRefSet(const ModRefInfo MRI)
Definition: ModRef.h:51
This struct is a compact representation of a valid (non-zero power of two) alignment.
Definition: Alignment.h:39
uint64_t value() const
This is a hole in the type system and should not be abused.
Definition: Alignment.h:85
Various options to control the behavior of getObjectSize.
bool NullIsUnknownSize
If this is true, null pointers in address space 0 will be treated as though they can't be evaluated.