LLVM  9.0.0svn
WebAssemblyCFGStackify.cpp
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1 //===-- WebAssemblyCFGStackify.cpp - CFG Stackification -------------------===//
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 /// \file
10 /// This file implements a CFG stacking pass.
11 ///
12 /// This pass inserts BLOCK, LOOP, and TRY markers to mark the start of scopes,
13 /// since scope boundaries serve as the labels for WebAssembly's control
14 /// transfers.
15 ///
16 /// This is sufficient to convert arbitrary CFGs into a form that works on
17 /// WebAssembly, provided that all loops are single-entry.
18 ///
19 /// In case we use exceptions, this pass also fixes mismatches in unwind
20 /// destinations created during transforming CFG into wasm structured format.
21 ///
22 //===----------------------------------------------------------------------===//
23 
24 #include "WebAssembly.h"
27 #include "WebAssemblySubtarget.h"
28 #include "WebAssemblyUtilities.h"
29 #include "llvm/ADT/Statistic.h"
32 #include "llvm/MC/MCAsmInfo.h"
33 using namespace llvm;
34 
35 #define DEBUG_TYPE "wasm-cfg-stackify"
36 
37 STATISTIC(NumUnwindMismatches, "Number of EH pad unwind mismatches found");
38 
39 namespace {
40 class WebAssemblyCFGStackify final : public MachineFunctionPass {
41  StringRef getPassName() const override { return "WebAssembly CFG Stackify"; }
42 
43  void getAnalysisUsage(AnalysisUsage &AU) const override {
48  }
49 
50  bool runOnMachineFunction(MachineFunction &MF) override;
51 
52  // For each block whose label represents the end of a scope, record the block
53  // which holds the beginning of the scope. This will allow us to quickly skip
54  // over scoped regions when walking blocks.
56 
57  // Placing markers.
58  void placeMarkers(MachineFunction &MF);
59  void placeBlockMarker(MachineBasicBlock &MBB);
60  void placeLoopMarker(MachineBasicBlock &MBB);
61  void placeTryMarker(MachineBasicBlock &MBB);
62  void removeUnnecessaryInstrs(MachineFunction &MF);
63  bool fixUnwindMismatches(MachineFunction &MF);
64  void rewriteDepthImmediates(MachineFunction &MF);
65  void fixEndsAtEndOfFunction(MachineFunction &MF);
66 
67  // For each BLOCK|LOOP|TRY, the corresponding END_(BLOCK|LOOP|TRY).
69  // For each END_(BLOCK|LOOP|TRY), the corresponding BLOCK|LOOP|TRY.
71  // <TRY marker, EH pad> map
73  // <EH pad, TRY marker> map
75 
76  // There can be an appendix block at the end of each function, shared for:
77  // - creating a correct signature for fallthrough returns
78  // - target for rethrows that need to unwind to the caller, but are trapped
79  // inside another try/catch
80  MachineBasicBlock *AppendixBB = nullptr;
81  MachineBasicBlock *getAppendixBlock(MachineFunction &MF) {
82  if (!AppendixBB) {
83  AppendixBB = MF.CreateMachineBasicBlock();
84  // Give it a fake predecessor so that AsmPrinter prints its label.
85  AppendixBB->addSuccessor(AppendixBB);
86  MF.push_back(AppendixBB);
87  }
88  return AppendixBB;
89  }
90 
91  // Helper functions to register / unregister scope information created by
92  // marker instructions.
93  void registerScope(MachineInstr *Begin, MachineInstr *End);
94  void registerTryScope(MachineInstr *Begin, MachineInstr *End,
95  MachineBasicBlock *EHPad);
96  void unregisterScope(MachineInstr *Begin);
97 
98 public:
99  static char ID; // Pass identification, replacement for typeid
100  WebAssemblyCFGStackify() : MachineFunctionPass(ID) {}
101  ~WebAssemblyCFGStackify() override { releaseMemory(); }
102  void releaseMemory() override;
103 };
104 } // end anonymous namespace
105 
107 INITIALIZE_PASS(WebAssemblyCFGStackify, DEBUG_TYPE,
108  "Insert BLOCK/LOOP/TRY markers for WebAssembly scopes", false,
109  false)
110 
112  return new WebAssemblyCFGStackify();
113 }
114 
115 /// Test whether Pred has any terminators explicitly branching to MBB, as
116 /// opposed to falling through. Note that it's possible (eg. in unoptimized
117 /// code) for a branch instruction to both branch to a block and fallthrough
118 /// to it, so we check the actual branch operands to see if there are any
119 /// explicit mentions.
121  MachineBasicBlock *MBB) {
122  for (MachineInstr &MI : Pred->terminators())
123  for (MachineOperand &MO : MI.explicit_operands())
124  if (MO.isMBB() && MO.getMBB() == MBB)
125  return true;
126  return false;
127 }
128 
129 // Returns an iterator to the earliest position possible within the MBB,
130 // satisfying the restrictions given by BeforeSet and AfterSet. BeforeSet
131 // contains instructions that should go before the marker, and AfterSet contains
132 // ones that should go after the marker. In this function, AfterSet is only
133 // used for sanity checking.
136  const SmallPtrSet<const MachineInstr *, 4> &BeforeSet,
137  const SmallPtrSet<const MachineInstr *, 4> &AfterSet) {
138  auto InsertPos = MBB->end();
139  while (InsertPos != MBB->begin()) {
140  if (BeforeSet.count(&*std::prev(InsertPos))) {
141 #ifndef NDEBUG
142  // Sanity check
143  for (auto Pos = InsertPos, E = MBB->begin(); Pos != E; --Pos)
144  assert(!AfterSet.count(&*std::prev(Pos)));
145 #endif
146  break;
147  }
148  --InsertPos;
149  }
150  return InsertPos;
151 }
152 
153 // Returns an iterator to the latest position possible within the MBB,
154 // satisfying the restrictions given by BeforeSet and AfterSet. BeforeSet
155 // contains instructions that should go before the marker, and AfterSet contains
156 // ones that should go after the marker. In this function, BeforeSet is only
157 // used for sanity checking.
160  const SmallPtrSet<const MachineInstr *, 4> &BeforeSet,
161  const SmallPtrSet<const MachineInstr *, 4> &AfterSet) {
162  auto InsertPos = MBB->begin();
163  while (InsertPos != MBB->end()) {
164  if (AfterSet.count(&*InsertPos)) {
165 #ifndef NDEBUG
166  // Sanity check
167  for (auto Pos = InsertPos, E = MBB->end(); Pos != E; ++Pos)
168  assert(!BeforeSet.count(&*Pos));
169 #endif
170  break;
171  }
172  ++InsertPos;
173  }
174  return InsertPos;
175 }
176 
177 void WebAssemblyCFGStackify::registerScope(MachineInstr *Begin,
178  MachineInstr *End) {
179  BeginToEnd[Begin] = End;
180  EndToBegin[End] = Begin;
181 }
182 
183 void WebAssemblyCFGStackify::registerTryScope(MachineInstr *Begin,
184  MachineInstr *End,
185  MachineBasicBlock *EHPad) {
186  registerScope(Begin, End);
187  TryToEHPad[Begin] = EHPad;
188  EHPadToTry[EHPad] = Begin;
189 }
190 
191 void WebAssemblyCFGStackify::unregisterScope(MachineInstr *Begin) {
192  assert(BeginToEnd.count(Begin));
193  MachineInstr *End = BeginToEnd[Begin];
194  assert(EndToBegin.count(End));
195  BeginToEnd.erase(Begin);
196  EndToBegin.erase(End);
197  MachineBasicBlock *EHPad = TryToEHPad.lookup(Begin);
198  if (EHPad) {
199  assert(EHPadToTry.count(EHPad));
200  TryToEHPad.erase(Begin);
201  EHPadToTry.erase(EHPad);
202  }
203 }
204 
205 /// Insert a BLOCK marker for branches to MBB (if needed).
206 // TODO Consider a more generalized way of handling block (and also loop and
207 // try) signatures when we implement the multi-value proposal later.
208 void WebAssemblyCFGStackify::placeBlockMarker(MachineBasicBlock &MBB) {
209  assert(!MBB.isEHPad());
210  MachineFunction &MF = *MBB.getParent();
211  auto &MDT = getAnalysis<MachineDominatorTree>();
212  const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
213  const auto &MFI = *MF.getInfo<WebAssemblyFunctionInfo>();
214 
215  // First compute the nearest common dominator of all forward non-fallthrough
216  // predecessors so that we minimize the time that the BLOCK is on the stack,
217  // which reduces overall stack height.
218  MachineBasicBlock *Header = nullptr;
219  bool IsBranchedTo = false;
220  bool IsBrOnExn = false;
221  MachineInstr *BrOnExn = nullptr;
222  int MBBNumber = MBB.getNumber();
223  for (MachineBasicBlock *Pred : MBB.predecessors()) {
224  if (Pred->getNumber() < MBBNumber) {
225  Header = Header ? MDT.findNearestCommonDominator(Header, Pred) : Pred;
226  if (explicitlyBranchesTo(Pred, &MBB)) {
227  IsBranchedTo = true;
228  if (Pred->getFirstTerminator()->getOpcode() == WebAssembly::BR_ON_EXN) {
229  IsBrOnExn = true;
230  assert(!BrOnExn && "There should be only one br_on_exn per block");
231  BrOnExn = &*Pred->getFirstTerminator();
232  }
233  }
234  }
235  }
236  if (!Header)
237  return;
238  if (!IsBranchedTo)
239  return;
240 
241  assert(&MBB != &MF.front() && "Header blocks shouldn't have predecessors");
242  MachineBasicBlock *LayoutPred = MBB.getPrevNode();
243 
244  // If the nearest common dominator is inside a more deeply nested context,
245  // walk out to the nearest scope which isn't more deeply nested.
246  for (MachineFunction::iterator I(LayoutPred), E(Header); I != E; --I) {
247  if (MachineBasicBlock *ScopeTop = ScopeTops[I->getNumber()]) {
248  if (ScopeTop->getNumber() > Header->getNumber()) {
249  // Skip over an intervening scope.
250  I = std::next(ScopeTop->getIterator());
251  } else {
252  // We found a scope level at an appropriate depth.
253  Header = ScopeTop;
254  break;
255  }
256  }
257  }
258 
259  // Decide where in Header to put the BLOCK.
260 
261  // Instructions that should go before the BLOCK.
263  // Instructions that should go after the BLOCK.
265  for (const auto &MI : *Header) {
266  // If there is a previously placed LOOP marker and the bottom block of the
267  // loop is above MBB, it should be after the BLOCK, because the loop is
268  // nested in this BLOCK. Otherwise it should be before the BLOCK.
269  if (MI.getOpcode() == WebAssembly::LOOP) {
270  auto *LoopBottom = BeginToEnd[&MI]->getParent()->getPrevNode();
271  if (MBB.getNumber() > LoopBottom->getNumber())
272  AfterSet.insert(&MI);
273 #ifndef NDEBUG
274  else
275  BeforeSet.insert(&MI);
276 #endif
277  }
278 
279  // All previously inserted BLOCK/TRY markers should be after the BLOCK
280  // because they are all nested blocks.
281  if (MI.getOpcode() == WebAssembly::BLOCK ||
282  MI.getOpcode() == WebAssembly::TRY)
283  AfterSet.insert(&MI);
284 
285 #ifndef NDEBUG
286  // All END_(BLOCK|LOOP|TRY) markers should be before the BLOCK.
287  if (MI.getOpcode() == WebAssembly::END_BLOCK ||
288  MI.getOpcode() == WebAssembly::END_LOOP ||
289  MI.getOpcode() == WebAssembly::END_TRY)
290  BeforeSet.insert(&MI);
291 #endif
292 
293  // Terminators should go after the BLOCK.
294  if (MI.isTerminator())
295  AfterSet.insert(&MI);
296  }
297 
298  // Local expression tree should go after the BLOCK.
299  for (auto I = Header->getFirstTerminator(), E = Header->begin(); I != E;
300  --I) {
301  if (std::prev(I)->isDebugInstr() || std::prev(I)->isPosition())
302  continue;
303  if (WebAssembly::isChild(*std::prev(I), MFI))
304  AfterSet.insert(&*std::prev(I));
305  else
306  break;
307  }
308 
309  // Add the BLOCK.
310 
311  // 'br_on_exn' extracts except_ref object and pushes variable number of values
312  // depending on its tag. For C++ exception, its a single i32 value, and the
313  // generated code will be in the form of:
314  // block i32
315  // br_on_exn 0, $__cpp_exception
316  // rethrow
317  // end_block
319  if (IsBrOnExn) {
320  const char *TagName = BrOnExn->getOperand(1).getSymbolName();
321  if (std::strcmp(TagName, "__cpp_exception") != 0)
322  llvm_unreachable("Only C++ exception is supported");
323  ReturnType = WebAssembly::ExprType::I32;
324  }
325 
326  auto InsertPos = getLatestInsertPos(Header, BeforeSet, AfterSet);
327  MachineInstr *Begin =
328  BuildMI(*Header, InsertPos, Header->findDebugLoc(InsertPos),
329  TII.get(WebAssembly::BLOCK))
330  .addImm(int64_t(ReturnType));
331 
332  // Decide where in Header to put the END_BLOCK.
333  BeforeSet.clear();
334  AfterSet.clear();
335  for (auto &MI : MBB) {
336 #ifndef NDEBUG
337  // END_BLOCK should precede existing LOOP and TRY markers.
338  if (MI.getOpcode() == WebAssembly::LOOP ||
339  MI.getOpcode() == WebAssembly::TRY)
340  AfterSet.insert(&MI);
341 #endif
342 
343  // If there is a previously placed END_LOOP marker and the header of the
344  // loop is above this block's header, the END_LOOP should be placed after
345  // the BLOCK, because the loop contains this block. Otherwise the END_LOOP
346  // should be placed before the BLOCK. The same for END_TRY.
347  if (MI.getOpcode() == WebAssembly::END_LOOP ||
348  MI.getOpcode() == WebAssembly::END_TRY) {
349  if (EndToBegin[&MI]->getParent()->getNumber() >= Header->getNumber())
350  BeforeSet.insert(&MI);
351 #ifndef NDEBUG
352  else
353  AfterSet.insert(&MI);
354 #endif
355  }
356  }
357 
358  // Mark the end of the block.
359  InsertPos = getEarliestInsertPos(&MBB, BeforeSet, AfterSet);
360  MachineInstr *End = BuildMI(MBB, InsertPos, MBB.findPrevDebugLoc(InsertPos),
361  TII.get(WebAssembly::END_BLOCK));
362  registerScope(Begin, End);
363 
364  // Track the farthest-spanning scope that ends at this point.
365  int Number = MBB.getNumber();
366  if (!ScopeTops[Number] ||
367  ScopeTops[Number]->getNumber() > Header->getNumber())
368  ScopeTops[Number] = Header;
369 }
370 
371 /// Insert a LOOP marker for a loop starting at MBB (if it's a loop header).
372 void WebAssemblyCFGStackify::placeLoopMarker(MachineBasicBlock &MBB) {
373  MachineFunction &MF = *MBB.getParent();
374  const auto &MLI = getAnalysis<MachineLoopInfo>();
375  const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
376 
377  MachineLoop *Loop = MLI.getLoopFor(&MBB);
378  if (!Loop || Loop->getHeader() != &MBB)
379  return;
380 
381  // The operand of a LOOP is the first block after the loop. If the loop is the
382  // bottom of the function, insert a dummy block at the end.
384  auto Iter = std::next(Bottom->getIterator());
385  if (Iter == MF.end()) {
386  getAppendixBlock(MF);
387  Iter = std::next(Bottom->getIterator());
388  }
389  MachineBasicBlock *AfterLoop = &*Iter;
390 
391  // Decide where in Header to put the LOOP.
394  for (const auto &MI : MBB) {
395  // LOOP marker should be after any existing loop that ends here. Otherwise
396  // we assume the instruction belongs to the loop.
397  if (MI.getOpcode() == WebAssembly::END_LOOP)
398  BeforeSet.insert(&MI);
399 #ifndef NDEBUG
400  else
401  AfterSet.insert(&MI);
402 #endif
403  }
404 
405  // Mark the beginning of the loop.
406  auto InsertPos = getEarliestInsertPos(&MBB, BeforeSet, AfterSet);
407  MachineInstr *Begin = BuildMI(MBB, InsertPos, MBB.findDebugLoc(InsertPos),
408  TII.get(WebAssembly::LOOP))
409  .addImm(int64_t(WebAssembly::ExprType::Void));
410 
411  // Decide where in Header to put the END_LOOP.
412  BeforeSet.clear();
413  AfterSet.clear();
414 #ifndef NDEBUG
415  for (const auto &MI : MBB)
416  // Existing END_LOOP markers belong to parent loops of this loop
417  if (MI.getOpcode() == WebAssembly::END_LOOP)
418  AfterSet.insert(&MI);
419 #endif
420 
421  // Mark the end of the loop (using arbitrary debug location that branched to
422  // the loop end as its location).
423  InsertPos = getEarliestInsertPos(AfterLoop, BeforeSet, AfterSet);
424  DebugLoc EndDL = AfterLoop->pred_empty()
425  ? DebugLoc()
426  : (*AfterLoop->pred_rbegin())->findBranchDebugLoc();
427  MachineInstr *End =
428  BuildMI(*AfterLoop, InsertPos, EndDL, TII.get(WebAssembly::END_LOOP));
429  registerScope(Begin, End);
430 
431  assert((!ScopeTops[AfterLoop->getNumber()] ||
432  ScopeTops[AfterLoop->getNumber()]->getNumber() < MBB.getNumber()) &&
433  "With block sorting the outermost loop for a block should be first.");
434  if (!ScopeTops[AfterLoop->getNumber()])
435  ScopeTops[AfterLoop->getNumber()] = &MBB;
436 }
437 
438 void WebAssemblyCFGStackify::placeTryMarker(MachineBasicBlock &MBB) {
439  assert(MBB.isEHPad());
440  MachineFunction &MF = *MBB.getParent();
441  auto &MDT = getAnalysis<MachineDominatorTree>();
442  const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
443  const auto &WEI = getAnalysis<WebAssemblyExceptionInfo>();
444  const auto &MFI = *MF.getInfo<WebAssemblyFunctionInfo>();
445 
446  // Compute the nearest common dominator of all unwind predecessors
447  MachineBasicBlock *Header = nullptr;
448  int MBBNumber = MBB.getNumber();
449  for (auto *Pred : MBB.predecessors()) {
450  if (Pred->getNumber() < MBBNumber) {
451  Header = Header ? MDT.findNearestCommonDominator(Header, Pred) : Pred;
452  assert(!explicitlyBranchesTo(Pred, &MBB) &&
453  "Explicit branch to an EH pad!");
454  }
455  }
456  if (!Header)
457  return;
458 
459  // If this try is at the bottom of the function, insert a dummy block at the
460  // end.
461  WebAssemblyException *WE = WEI.getExceptionFor(&MBB);
462  assert(WE);
464 
465  auto Iter = std::next(Bottom->getIterator());
466  if (Iter == MF.end()) {
467  getAppendixBlock(MF);
468  Iter = std::next(Bottom->getIterator());
469  }
470  MachineBasicBlock *Cont = &*Iter;
471 
472  assert(Cont != &MF.front());
473  MachineBasicBlock *LayoutPred = Cont->getPrevNode();
474 
475  // If the nearest common dominator is inside a more deeply nested context,
476  // walk out to the nearest scope which isn't more deeply nested.
477  for (MachineFunction::iterator I(LayoutPred), E(Header); I != E; --I) {
478  if (MachineBasicBlock *ScopeTop = ScopeTops[I->getNumber()]) {
479  if (ScopeTop->getNumber() > Header->getNumber()) {
480  // Skip over an intervening scope.
481  I = std::next(ScopeTop->getIterator());
482  } else {
483  // We found a scope level at an appropriate depth.
484  Header = ScopeTop;
485  break;
486  }
487  }
488  }
489 
490  // Decide where in Header to put the TRY.
491 
492  // Instructions that should go before the TRY.
494  // Instructions that should go after the TRY.
496  for (const auto &MI : *Header) {
497  // If there is a previously placed LOOP marker and the bottom block of the
498  // loop is above MBB, it should be after the TRY, because the loop is nested
499  // in this TRY. Otherwise it should be before the TRY.
500  if (MI.getOpcode() == WebAssembly::LOOP) {
501  auto *LoopBottom = BeginToEnd[&MI]->getParent()->getPrevNode();
502  if (MBB.getNumber() > LoopBottom->getNumber())
503  AfterSet.insert(&MI);
504 #ifndef NDEBUG
505  else
506  BeforeSet.insert(&MI);
507 #endif
508  }
509 
510  // All previously inserted BLOCK/TRY markers should be after the TRY because
511  // they are all nested trys.
512  if (MI.getOpcode() == WebAssembly::BLOCK ||
513  MI.getOpcode() == WebAssembly::TRY)
514  AfterSet.insert(&MI);
515 
516 #ifndef NDEBUG
517  // All END_(BLOCK/LOOP/TRY) markers should be before the TRY.
518  if (MI.getOpcode() == WebAssembly::END_BLOCK ||
519  MI.getOpcode() == WebAssembly::END_LOOP ||
520  MI.getOpcode() == WebAssembly::END_TRY)
521  BeforeSet.insert(&MI);
522 #endif
523 
524  // Terminators should go after the TRY.
525  if (MI.isTerminator())
526  AfterSet.insert(&MI);
527  }
528 
529  // Local expression tree should go after the TRY.
530  for (auto I = Header->getFirstTerminator(), E = Header->begin(); I != E;
531  --I) {
532  if (std::prev(I)->isDebugInstr() || std::prev(I)->isPosition())
533  continue;
534  if (WebAssembly::isChild(*std::prev(I), MFI))
535  AfterSet.insert(&*std::prev(I));
536  else
537  break;
538  }
539 
540  // If Header unwinds to MBB (= Header contains 'invoke'), the try block should
541  // contain the call within it. So the call should go after the TRY. The
542  // exception is when the header's terminator is a rethrow instruction, in
543  // which case that instruction, not a call instruction before it, is gonna
544  // throw.
545  if (MBB.isPredecessor(Header)) {
546  auto TermPos = Header->getFirstTerminator();
547  if (TermPos == Header->end() ||
548  TermPos->getOpcode() != WebAssembly::RETHROW) {
549  for (const auto &MI : reverse(*Header)) {
550  if (MI.isCall()) {
551  AfterSet.insert(&MI);
552  // Possibly throwing calls are usually wrapped by EH_LABEL
553  // instructions. We don't want to split them and the call.
554  if (MI.getIterator() != Header->begin() &&
555  std::prev(MI.getIterator())->isEHLabel())
556  AfterSet.insert(&*std::prev(MI.getIterator()));
557  break;
558  }
559  }
560  }
561  }
562 
563  // Add the TRY.
564  auto InsertPos = getLatestInsertPos(Header, BeforeSet, AfterSet);
565  MachineInstr *Begin =
566  BuildMI(*Header, InsertPos, Header->findDebugLoc(InsertPos),
567  TII.get(WebAssembly::TRY))
568  .addImm(int64_t(WebAssembly::ExprType::Void));
569 
570  // Decide where in Header to put the END_TRY.
571  BeforeSet.clear();
572  AfterSet.clear();
573  for (const auto &MI : *Cont) {
574 #ifndef NDEBUG
575  // END_TRY should precede existing LOOP and BLOCK markers.
576  if (MI.getOpcode() == WebAssembly::LOOP ||
577  MI.getOpcode() == WebAssembly::BLOCK)
578  AfterSet.insert(&MI);
579 
580  // All END_TRY markers placed earlier belong to exceptions that contains
581  // this one.
582  if (MI.getOpcode() == WebAssembly::END_TRY)
583  AfterSet.insert(&MI);
584 #endif
585 
586  // If there is a previously placed END_LOOP marker and its header is after
587  // where TRY marker is, this loop is contained within the 'catch' part, so
588  // the END_TRY marker should go after that. Otherwise, the whole try-catch
589  // is contained within this loop, so the END_TRY should go before that.
590  if (MI.getOpcode() == WebAssembly::END_LOOP) {
591  // For a LOOP to be after TRY, LOOP's BB should be after TRY's BB; if they
592  // are in the same BB, LOOP is always before TRY.
593  if (EndToBegin[&MI]->getParent()->getNumber() > Header->getNumber())
594  BeforeSet.insert(&MI);
595 #ifndef NDEBUG
596  else
597  AfterSet.insert(&MI);
598 #endif
599  }
600 
601  // It is not possible for an END_BLOCK to be already in this block.
602  }
603 
604  // Mark the end of the TRY.
605  InsertPos = getEarliestInsertPos(Cont, BeforeSet, AfterSet);
606  MachineInstr *End =
607  BuildMI(*Cont, InsertPos, Bottom->findBranchDebugLoc(),
608  TII.get(WebAssembly::END_TRY));
609  registerTryScope(Begin, End, &MBB);
610 
611  // Track the farthest-spanning scope that ends at this point. We create two
612  // mappings: (BB with 'end_try' -> BB with 'try') and (BB with 'catch' -> BB
613  // with 'try'). We need to create 'catch' -> 'try' mapping here too because
614  // markers should not span across 'catch'. For example, this should not
615  // happen:
616  //
617  // try
618  // block --| (X)
619  // catch |
620  // end_block --|
621  // end_try
622  for (int Number : {Cont->getNumber(), MBB.getNumber()}) {
623  if (!ScopeTops[Number] ||
624  ScopeTops[Number]->getNumber() > Header->getNumber())
625  ScopeTops[Number] = Header;
626  }
627 }
628 
629 void WebAssemblyCFGStackify::removeUnnecessaryInstrs(MachineFunction &MF) {
630  const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
631 
632  // When there is an unconditional branch right before a catch instruction and
633  // it branches to the end of end_try marker, we don't need the branch, because
634  // it there is no exception, the control flow transfers to that point anyway.
635  // bb0:
636  // try
637  // ...
638  // br bb2 <- Not necessary
639  // bb1:
640  // catch
641  // ...
642  // bb2:
643  // end
644  for (auto &MBB : MF) {
645  if (!MBB.isEHPad())
646  continue;
647 
648  MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
650  MachineBasicBlock *EHPadLayoutPred = MBB.getPrevNode();
651  MachineBasicBlock *Cont = BeginToEnd[EHPadToTry[&MBB]]->getParent();
652  bool Analyzable = !TII.analyzeBranch(*EHPadLayoutPred, TBB, FBB, Cond);
653  if (Analyzable && ((Cond.empty() && TBB && TBB == Cont) ||
654  (!Cond.empty() && FBB && FBB == Cont)))
655  TII.removeBranch(*EHPadLayoutPred);
656  }
657 
658  // When there are block / end_block markers that overlap with try / end_try
659  // markers, and the block and try markers' return types are the same, the
660  // block /end_block markers are not necessary, because try / end_try markers
661  // also can serve as boundaries for branches.
662  // block <- Not necessary
663  // try
664  // ...
665  // catch
666  // ...
667  // end
668  // end <- Not necessary
670  for (auto &MBB : MF) {
671  for (auto &MI : MBB) {
672  if (MI.getOpcode() != WebAssembly::TRY)
673  continue;
674 
675  MachineInstr *Try = &MI, *EndTry = BeginToEnd[Try];
676  MachineBasicBlock *TryBB = Try->getParent();
677  MachineBasicBlock *Cont = EndTry->getParent();
678  int64_t RetType = Try->getOperand(0).getImm();
679  for (auto B = Try->getIterator(), E = std::next(EndTry->getIterator());
680  B != TryBB->begin() && E != Cont->end() &&
681  std::prev(B)->getOpcode() == WebAssembly::BLOCK &&
682  E->getOpcode() == WebAssembly::END_BLOCK &&
683  std::prev(B)->getOperand(0).getImm() == RetType;
684  --B, ++E) {
685  ToDelete.push_back(&*std::prev(B));
686  ToDelete.push_back(&*E);
687  }
688  }
689  }
690  for (auto *MI : ToDelete) {
691  if (MI->getOpcode() == WebAssembly::BLOCK)
692  unregisterScope(MI);
693  MI->eraseFromParent();
694  }
695 }
696 
697 bool WebAssemblyCFGStackify::fixUnwindMismatches(MachineFunction &MF) {
698  const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
700 
701  // Linearizing the control flow by placing TRY / END_TRY markers can create
702  // mismatches in unwind destinations. There are two kinds of mismatches we
703  // try to solve here.
704 
705  // 1. When an instruction may throw, but the EH pad it will unwind to can be
706  // different from the original CFG.
707  //
708  // Example: we have the following CFG:
709  // bb0:
710  // call @foo (if it throws, unwind to bb2)
711  // bb1:
712  // call @bar (if it throws, unwind to bb3)
713  // bb2 (ehpad):
714  // catch
715  // ...
716  // bb3 (ehpad)
717  // catch
718  // handler body
719  //
720  // And the CFG is sorted in this order. Then after placing TRY markers, it
721  // will look like: (BB markers are omitted)
722  // try $label1
723  // try
724  // call @foo
725  // call @bar (if it throws, unwind to bb3)
726  // catch <- ehpad (bb2)
727  // ...
728  // end_try
729  // catch <- ehpad (bb3)
730  // handler body
731  // end_try
732  //
733  // Now if bar() throws, it is going to end up ip in bb2, not bb3, where it
734  // is supposed to end up. We solve this problem by
735  // a. Split the target unwind EH pad (here bb3) so that the handler body is
736  // right after 'end_try', which means we extract the handler body out of
737  // the catch block. We do this because this handler body should be
738  // somewhere branch-eable from the inner scope.
739  // b. Wrap the call that has an incorrect unwind destination ('call @bar'
740  // here) with a nested try/catch/end_try scope, and within the new catch
741  // block, branches to the handler body.
742  // c. Place a branch after the newly inserted nested end_try so it can bypass
743  // the handler body, which is now outside of a catch block.
744  //
745  // The result will like as follows. (new: a) means this instruction is newly
746  // created in the process of doing 'a' above.
747  //
748  // block $label0 (new: placeBlockMarker)
749  // try $label1
750  // try
751  // call @foo
752  // try (new: b)
753  // call @bar
754  // catch (new: b)
755  // local.set n / drop (new: b)
756  // br $label1 (new: b)
757  // end_try (new: b)
758  // catch <- ehpad (bb2)
759  // end_try
760  // br $label0 (new: c)
761  // catch <- ehpad (bb3)
762  // end_try (hoisted: a)
763  // handler body
764  // end_block (new: placeBlockMarker)
765  //
766  // Note that the new wrapping block/end_block will be generated later in
767  // placeBlockMarker.
768  //
769  // TODO Currently local.set and local.gets are generated to move except_ref
770  // value created by catches. That's because we don't support yielding values
771  // from a block in LLVM machine IR yet, even though it is supported by wasm.
772  // Delete unnecessary local.get/local.sets once yielding values from a block
773  // is supported. The full EH spec requires multi-value support to do this, but
774  // for C++ we don't yet need it because we only throw a single i32.
775  //
776  // ---
777  // 2. The same as 1, but in this case an instruction unwinds to a caller
778  // function and not another EH pad.
779  //
780  // Example: we have the following CFG:
781  // bb0:
782  // call @foo (if it throws, unwind to bb2)
783  // bb1:
784  // call @bar (if it throws, unwind to caller)
785  // bb2 (ehpad):
786  // catch
787  // ...
788  //
789  // And the CFG is sorted in this order. Then after placing TRY markers, it
790  // will look like:
791  // try
792  // call @foo
793  // call @bar (if it throws, unwind to caller)
794  // catch <- ehpad (bb2)
795  // ...
796  // end_try
797  //
798  // Now if bar() throws, it is going to end up ip in bb2, when it is supposed
799  // throw up to the caller.
800  // We solve this problem by
801  // a. Create a new 'appendix' BB at the end of the function and put a single
802  // 'rethrow' instruction (+ local.get) in there.
803  // b. Wrap the call that has an incorrect unwind destination ('call @bar'
804  // here) with a nested try/catch/end_try scope, and within the new catch
805  // block, branches to the new appendix block.
806  //
807  // block $label0 (new: placeBlockMarker)
808  // try
809  // call @foo
810  // try (new: b)
811  // call @bar
812  // catch (new: b)
813  // local.set n (new: b)
814  // br $label0 (new: b)
815  // end_try (new: b)
816  // catch <- ehpad (bb2)
817  // ...
818  // end_try
819  // ...
820  // end_block (new: placeBlockMarker)
821  // local.get n (new: a) <- appendix block
822  // rethrow (new: a)
823  //
824  // In case there are multiple calls in a BB that may throw to the caller, they
825  // can be wrapped together in one nested try scope. (In 1, this couldn't
826  // happen, because may-throwing instruction there had an unwind destination,
827  // i.e., it was an invoke before, and there could be only one invoke within a
828  // BB.)
829 
831  // Range of intructions to be wrapped in a new nested try/catch
832  using TryRange = std::pair<MachineInstr *, MachineInstr *>;
833  // In original CFG, <unwind destionation BB, a vector of try ranges>
835  // In new CFG, <destination to branch to, a vector of try ranges>
837  // In new CFG, <destination to branch to, register containing except_ref>
839 
840  // Gather possibly throwing calls (i.e., previously invokes) whose current
841  // unwind destination is not the same as the original CFG.
842  for (auto &MBB : reverse(MF)) {
843  bool SeenThrowableInstInBB = false;
844  for (auto &MI : reverse(MBB)) {
845  if (MI.getOpcode() == WebAssembly::TRY)
846  EHPadStack.pop_back();
847  else if (MI.getOpcode() == WebAssembly::CATCH)
848  EHPadStack.push_back(MI.getParent());
849 
850  // In this loop we only gather calls that have an EH pad to unwind. So
851  // there will be at most 1 such call (= invoke) in a BB, so after we've
852  // seen one, we can skip the rest of BB. Also if MBB has no EH pad
853  // successor or MI does not throw, this is not an invoke.
854  if (SeenThrowableInstInBB || !MBB.hasEHPadSuccessor() ||
856  continue;
857  SeenThrowableInstInBB = true;
858 
859  // If the EH pad on the stack top is where this instruction should unwind
860  // next, we're good.
861  MachineBasicBlock *UnwindDest = nullptr;
862  for (auto *Succ : MBB.successors()) {
863  if (Succ->isEHPad()) {
864  UnwindDest = Succ;
865  break;
866  }
867  }
868  if (EHPadStack.back() == UnwindDest)
869  continue;
870 
871  // If not, record the range.
872  UnwindDestToTryRanges[UnwindDest].push_back(TryRange(&MI, &MI));
873  }
874  }
875 
876  assert(EHPadStack.empty());
877 
878  // Gather possibly throwing calls that are supposed to unwind up to the caller
879  // if they throw, but currently unwind to an incorrect destination. Unlike the
880  // loop above, there can be multiple calls within a BB that unwind to the
881  // caller, which we should group together in a range.
882  bool NeedAppendixBlock = false;
883  for (auto &MBB : reverse(MF)) {
884  MachineInstr *RangeBegin = nullptr, *RangeEnd = nullptr; // inclusive
885  for (auto &MI : reverse(MBB)) {
886  if (MI.getOpcode() == WebAssembly::TRY)
887  EHPadStack.pop_back();
888  else if (MI.getOpcode() == WebAssembly::CATCH)
889  EHPadStack.push_back(MI.getParent());
890 
891  // If MBB has an EH pad successor, this inst does not unwind to caller.
892  if (MBB.hasEHPadSuccessor())
893  continue;
894 
895  // We wrap up the current range when we see a marker even if we haven't
896  // finished a BB.
897  if (RangeEnd && WebAssembly::isMarker(MI)) {
898  NeedAppendixBlock = true;
899  // Record the range. nullptr here means the unwind destination is the
900  // caller.
901  UnwindDestToTryRanges[nullptr].push_back(
902  TryRange(RangeBegin, RangeEnd));
903  RangeBegin = RangeEnd = nullptr; // Reset range pointers
904  }
905 
906  // If EHPadStack is empty, that means it is correctly unwind to caller if
907  // it throws, so we're good. If MI does not throw, we're good too.
908  if (EHPadStack.empty() || !WebAssembly::mayThrow(MI))
909  continue;
910 
911  // We found an instruction that unwinds to the caller but currently has an
912  // incorrect unwind destination. Create a new range or increment the
913  // currently existing range.
914  if (!RangeEnd)
915  RangeBegin = RangeEnd = &MI;
916  else
917  RangeBegin = &MI;
918  }
919 
920  if (RangeEnd) {
921  NeedAppendixBlock = true;
922  // Record the range. nullptr here means the unwind destination is the
923  // caller.
924  UnwindDestToTryRanges[nullptr].push_back(TryRange(RangeBegin, RangeEnd));
925  RangeBegin = RangeEnd = nullptr; // Reset range pointers
926  }
927  }
928 
929  assert(EHPadStack.empty());
930  // We don't have any unwind destination mismatches to resolve.
931  if (UnwindDestToTryRanges.empty())
932  return false;
933 
934  // If we found instructions that should unwind to the caller but currently
935  // have incorrect unwind destination, we create an appendix block at the end
936  // of the function with a local.get and a rethrow instruction.
937  if (NeedAppendixBlock) {
938  auto *AppendixBB = getAppendixBlock(MF);
939  unsigned ExnReg =
940  MRI.createVirtualRegister(&WebAssembly::EXCEPT_REFRegClass);
941  BuildMI(AppendixBB, DebugLoc(), TII.get(WebAssembly::RETHROW))
942  .addReg(ExnReg);
943  // These instruction ranges should branch to this appendix BB.
944  for (auto Range : UnwindDestToTryRanges[nullptr])
945  BrDestToTryRanges[AppendixBB].push_back(Range);
946  BrDestToExnReg[AppendixBB] = ExnReg;
947  }
948 
949  // We loop through unwind destination EH pads that are targeted from some
950  // inner scopes. Because these EH pads are destination of more than one scope
951  // now, we split them so that the handler body is after 'end_try'.
952  // - Before
953  // ehpad:
954  // catch
955  // local.set n / drop
956  // handler body
957  // ...
958  // cont:
959  // end_try
960  //
961  // - After
962  // ehpad:
963  // catch
964  // local.set n / drop
965  // brdest: (new)
966  // end_try (hoisted from 'cont' BB)
967  // handler body (taken from 'ehpad')
968  // ...
969  // cont:
970  for (auto &P : UnwindDestToTryRanges) {
971  NumUnwindMismatches++;
972 
973  // This means the destination is the appendix BB, which was separately
974  // handled above.
975  if (!P.first)
976  continue;
977 
978  MachineBasicBlock *EHPad = P.first;
979 
980  // Find 'catch' and 'local.set' or 'drop' instruction that follows the
981  // 'catch'. If -wasm-disable-explicit-locals is not set, 'catch' should be
982  // always followed by either 'local.set' or a 'drop', because 'br_on_exn' is
983  // generated after 'catch' in LateEHPrepare and we don't support blocks
984  // taking values yet.
985  MachineInstr *Catch = nullptr;
986  unsigned ExnReg = 0;
987  for (auto &MI : *EHPad) {
988  switch (MI.getOpcode()) {
989  case WebAssembly::CATCH:
990  Catch = &MI;
991  ExnReg = Catch->getOperand(0).getReg();
992  break;
993  }
994  }
995  assert(Catch && "EH pad does not have a catch");
996  assert(ExnReg != 0 && "Invalid register");
997 
998  auto SplitPos = std::next(Catch->getIterator());
999 
1000  // Create a new BB that's gonna be the destination for branches from the
1001  // inner mismatched scope.
1002  MachineInstr *BeginTry = EHPadToTry[EHPad];
1003  MachineInstr *EndTry = BeginToEnd[BeginTry];
1004  MachineBasicBlock *Cont = EndTry->getParent();
1005  auto *BrDest = MF.CreateMachineBasicBlock();
1006  MF.insert(std::next(EHPad->getIterator()), BrDest);
1007  // Hoist up the existing 'end_try'.
1008  BrDest->insert(BrDest->end(), EndTry->removeFromParent());
1009  // Take out the handler body from EH pad to the new branch destination BB.
1010  BrDest->splice(BrDest->end(), EHPad, SplitPos, EHPad->end());
1011  // Fix predecessor-successor relationship.
1012  BrDest->transferSuccessors(EHPad);
1013  EHPad->addSuccessor(BrDest);
1014 
1015  // All try ranges that were supposed to unwind to this EH pad now have to
1016  // branch to this new branch dest BB.
1017  for (auto Range : UnwindDestToTryRanges[EHPad])
1018  BrDestToTryRanges[BrDest].push_back(Range);
1019  BrDestToExnReg[BrDest] = ExnReg;
1020 
1021  // In case we fall through to the continuation BB after the catch block, we
1022  // now have to add a branch to it.
1023  // - Before
1024  // try
1025  // ...
1026  // (falls through to 'cont')
1027  // catch
1028  // handler body
1029  // end
1030  // <-- cont
1031  //
1032  // - After
1033  // try
1034  // ...
1035  // br %cont (new)
1036  // catch
1037  // end
1038  // handler body
1039  // <-- cont
1040  MachineBasicBlock *EHPadLayoutPred = &*std::prev(EHPad->getIterator());
1041  MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
1043  bool Analyzable = !TII.analyzeBranch(*EHPadLayoutPred, TBB, FBB, Cond);
1044  if (Analyzable && !TBB && !FBB) {
1045  DebugLoc DL = EHPadLayoutPred->empty()
1046  ? DebugLoc()
1047  : EHPadLayoutPred->rbegin()->getDebugLoc();
1048  BuildMI(EHPadLayoutPred, DL, TII.get(WebAssembly::BR)).addMBB(Cont);
1049  }
1050  }
1051 
1052  // For possibly throwing calls whose unwind destinations are currently
1053  // incorrect because of CFG linearization, we wrap them with a nested
1054  // try/catch/end_try, and within the new catch block, we branch to the correct
1055  // handler.
1056  // - Before
1057  // mbb:
1058  // call @foo <- Unwind destination mismatch!
1059  // ehpad:
1060  // ...
1061  //
1062  // - After
1063  // mbb:
1064  // try (new)
1065  // call @foo
1066  // nested-ehpad: (new)
1067  // catch (new)
1068  // local.set n / drop (new)
1069  // br %brdest (new)
1070  // nested-end: (new)
1071  // end_try (new)
1072  // ehpad:
1073  // ...
1074  for (auto &P : BrDestToTryRanges) {
1075  MachineBasicBlock *BrDest = P.first;
1076  auto &TryRanges = P.second;
1077  unsigned ExnReg = BrDestToExnReg[BrDest];
1078 
1079  for (auto Range : TryRanges) {
1080  MachineInstr *RangeBegin = nullptr, *RangeEnd = nullptr;
1081  std::tie(RangeBegin, RangeEnd) = Range;
1082  auto *MBB = RangeBegin->getParent();
1083 
1084  // Include possible EH_LABELs in the range
1085  if (RangeBegin->getIterator() != MBB->begin() &&
1086  std::prev(RangeBegin->getIterator())->isEHLabel())
1087  RangeBegin = &*std::prev(RangeBegin->getIterator());
1088  if (std::next(RangeEnd->getIterator()) != MBB->end() &&
1089  std::next(RangeEnd->getIterator())->isEHLabel())
1090  RangeEnd = &*std::next(RangeEnd->getIterator());
1091 
1092  MachineBasicBlock *EHPad = nullptr;
1093  for (auto *Succ : MBB->successors()) {
1094  if (Succ->isEHPad()) {
1095  EHPad = Succ;
1096  break;
1097  }
1098  }
1099 
1100  // Create the nested try instruction.
1101  MachineInstr *NestedTry =
1102  BuildMI(*MBB, *RangeBegin, RangeBegin->getDebugLoc(),
1103  TII.get(WebAssembly::TRY))
1104  .addImm(int64_t(WebAssembly::ExprType::Void));
1105 
1106  // Create the nested EH pad and fill instructions in.
1107  MachineBasicBlock *NestedEHPad = MF.CreateMachineBasicBlock();
1108  MF.insert(std::next(MBB->getIterator()), NestedEHPad);
1109  NestedEHPad->setIsEHPad();
1110  NestedEHPad->setIsEHScopeEntry();
1111  BuildMI(NestedEHPad, RangeEnd->getDebugLoc(), TII.get(WebAssembly::CATCH),
1112  ExnReg);
1113  BuildMI(NestedEHPad, RangeEnd->getDebugLoc(), TII.get(WebAssembly::BR))
1114  .addMBB(BrDest);
1115 
1116  // Create the nested continuation BB and end_try instruction.
1117  MachineBasicBlock *NestedCont = MF.CreateMachineBasicBlock();
1118  MF.insert(std::next(NestedEHPad->getIterator()), NestedCont);
1119  MachineInstr *NestedEndTry =
1120  BuildMI(*NestedCont, NestedCont->begin(), RangeEnd->getDebugLoc(),
1121  TII.get(WebAssembly::END_TRY));
1122  // In case MBB has more instructions after the try range, move them to the
1123  // new nested continuation BB.
1124  NestedCont->splice(NestedCont->end(), MBB,
1125  std::next(RangeEnd->getIterator()), MBB->end());
1126  registerTryScope(NestedTry, NestedEndTry, NestedEHPad);
1127 
1128  // Fix predecessor-successor relationship.
1129  NestedCont->transferSuccessors(MBB);
1130  if (EHPad)
1131  NestedCont->removeSuccessor(EHPad);
1132  MBB->addSuccessor(NestedEHPad);
1133  MBB->addSuccessor(NestedCont);
1134  NestedEHPad->addSuccessor(BrDest);
1135  }
1136  }
1137 
1138  // Renumber BBs and recalculate ScopeTop info because new BBs might have been
1139  // created and inserted above.
1140  MF.RenumberBlocks();
1141  ScopeTops.clear();
1142  ScopeTops.resize(MF.getNumBlockIDs());
1143  for (auto &MBB : reverse(MF)) {
1144  for (auto &MI : reverse(MBB)) {
1145  if (ScopeTops[MBB.getNumber()])
1146  break;
1147  switch (MI.getOpcode()) {
1149  case WebAssembly::END_LOOP:
1150  case WebAssembly::END_TRY:
1151  ScopeTops[MBB.getNumber()] = EndToBegin[&MI]->getParent();
1152  break;
1153  case WebAssembly::CATCH:
1154  ScopeTops[MBB.getNumber()] = EHPadToTry[&MBB]->getParent();
1155  break;
1156  }
1157  }
1158  }
1159 
1160  // Recompute the dominator tree.
1161  getAnalysis<MachineDominatorTree>().runOnMachineFunction(MF);
1162 
1163  // Place block markers for newly added branches.
1165  for (auto &P : BrDestToTryRanges)
1166  BrDests.push_back(P.first);
1167  llvm::sort(BrDests,
1168  [&](const MachineBasicBlock *A, const MachineBasicBlock *B) {
1169  auto ANum = A->getNumber();
1170  auto BNum = B->getNumber();
1171  return ANum < BNum;
1172  });
1173  for (auto *Dest : BrDests)
1174  placeBlockMarker(*Dest);
1175 
1176  return true;
1177 }
1178 
1179 static unsigned
1181  const MachineBasicBlock *MBB) {
1182  unsigned Depth = 0;
1183  for (auto X : reverse(Stack)) {
1184  if (X == MBB)
1185  break;
1186  ++Depth;
1187  }
1188  assert(Depth < Stack.size() && "Branch destination should be in scope");
1189  return Depth;
1190 }
1191 
1192 /// In normal assembly languages, when the end of a function is unreachable,
1193 /// because the function ends in an infinite loop or a noreturn call or similar,
1194 /// it isn't necessary to worry about the function return type at the end of
1195 /// the function, because it's never reached. However, in WebAssembly, blocks
1196 /// that end at the function end need to have a return type signature that
1197 /// matches the function signature, even though it's unreachable. This function
1198 /// checks for such cases and fixes up the signatures.
1199 void WebAssemblyCFGStackify::fixEndsAtEndOfFunction(MachineFunction &MF) {
1200  const auto &MFI = *MF.getInfo<WebAssemblyFunctionInfo>();
1201  assert(MFI.getResults().size() <= 1);
1202 
1203  if (MFI.getResults().empty())
1204  return;
1205 
1206  WebAssembly::ExprType RetType;
1207  switch (MFI.getResults().front().SimpleTy) {
1208  case MVT::i32:
1209  RetType = WebAssembly::ExprType::I32;
1210  break;
1211  case MVT::i64:
1212  RetType = WebAssembly::ExprType::I64;
1213  break;
1214  case MVT::f32:
1215  RetType = WebAssembly::ExprType::F32;
1216  break;
1217  case MVT::f64:
1218  RetType = WebAssembly::ExprType::F64;
1219  break;
1220  case MVT::v16i8:
1221  case MVT::v8i16:
1222  case MVT::v4i32:
1223  case MVT::v2i64:
1224  case MVT::v4f32:
1225  case MVT::v2f64:
1226  RetType = WebAssembly::ExprType::V128;
1227  break;
1228  case MVT::ExceptRef:
1230  break;
1231  default:
1232  llvm_unreachable("unexpected return type");
1233  }
1234 
1235  for (MachineBasicBlock &MBB : reverse(MF)) {
1236  for (MachineInstr &MI : reverse(MBB)) {
1237  if (MI.isPosition() || MI.isDebugInstr())
1238  continue;
1239  if (MI.getOpcode() == WebAssembly::END_BLOCK) {
1240  EndToBegin[&MI]->getOperand(0).setImm(int32_t(RetType));
1241  continue;
1242  }
1243  if (MI.getOpcode() == WebAssembly::END_LOOP) {
1244  EndToBegin[&MI]->getOperand(0).setImm(int32_t(RetType));
1245  continue;
1246  }
1247  // Something other than an `end`. We're done.
1248  return;
1249  }
1250  }
1251 }
1252 
1253 // WebAssembly functions end with an end instruction, as if the function body
1254 // were a block.
1256  const WebAssemblyInstrInfo &TII) {
1257  BuildMI(MF.back(), MF.back().end(),
1258  MF.back().findPrevDebugLoc(MF.back().end()),
1259  TII.get(WebAssembly::END_FUNCTION));
1260 }
1261 
1262 /// Insert LOOP/TRY/BLOCK markers at appropriate places.
1263 void WebAssemblyCFGStackify::placeMarkers(MachineFunction &MF) {
1264  // We allocate one more than the number of blocks in the function to
1265  // accommodate for the possible fake block we may insert at the end.
1266  ScopeTops.resize(MF.getNumBlockIDs() + 1);
1267  // Place the LOOP for MBB if MBB is the header of a loop.
1268  for (auto &MBB : MF)
1269  placeLoopMarker(MBB);
1270 
1271  const MCAsmInfo *MCAI = MF.getTarget().getMCAsmInfo();
1272  for (auto &MBB : MF) {
1273  if (MBB.isEHPad()) {
1274  // Place the TRY for MBB if MBB is the EH pad of an exception.
1276  MF.getFunction().hasPersonalityFn())
1277  placeTryMarker(MBB);
1278  } else {
1279  // Place the BLOCK for MBB if MBB is branched to from above.
1280  placeBlockMarker(MBB);
1281  }
1282  }
1283  // Fix mismatches in unwind destinations induced by linearizing the code.
1284  fixUnwindMismatches(MF);
1285 }
1286 
1287 void WebAssemblyCFGStackify::rewriteDepthImmediates(MachineFunction &MF) {
1288  // Now rewrite references to basic blocks to be depth immediates.
1290  for (auto &MBB : reverse(MF)) {
1291  for (auto I = MBB.rbegin(), E = MBB.rend(); I != E; ++I) {
1292  MachineInstr &MI = *I;
1293  switch (MI.getOpcode()) {
1294  case WebAssembly::BLOCK:
1295  case WebAssembly::TRY:
1296  assert(ScopeTops[Stack.back()->getNumber()]->getNumber() <=
1297  MBB.getNumber() &&
1298  "Block/try marker should be balanced");
1299  Stack.pop_back();
1300  break;
1301 
1302  case WebAssembly::LOOP:
1303  assert(Stack.back() == &MBB && "Loop top should be balanced");
1304  Stack.pop_back();
1305  break;
1306 
1308  case WebAssembly::END_TRY:
1309  Stack.push_back(&MBB);
1310  break;
1311 
1312  case WebAssembly::END_LOOP:
1313  Stack.push_back(EndToBegin[&MI]->getParent());
1314  break;
1315 
1316  default:
1317  if (MI.isTerminator()) {
1318  // Rewrite MBB operands to be depth immediates.
1320  while (MI.getNumOperands() > 0)
1321  MI.RemoveOperand(MI.getNumOperands() - 1);
1322  for (auto MO : Ops) {
1323  if (MO.isMBB())
1324  MO = MachineOperand::CreateImm(getDepth(Stack, MO.getMBB()));
1325  MI.addOperand(MF, MO);
1326  }
1327  }
1328  break;
1329  }
1330  }
1331  }
1332  assert(Stack.empty() && "Control flow should be balanced");
1333 }
1334 
1335 void WebAssemblyCFGStackify::releaseMemory() {
1336  ScopeTops.clear();
1337  BeginToEnd.clear();
1338  EndToBegin.clear();
1339  TryToEHPad.clear();
1340  EHPadToTry.clear();
1341  AppendixBB = nullptr;
1342 }
1343 
1344 bool WebAssemblyCFGStackify::runOnMachineFunction(MachineFunction &MF) {
1345  LLVM_DEBUG(dbgs() << "********** CFG Stackifying **********\n"
1346  "********** Function: "
1347  << MF.getName() << '\n');
1348  const MCAsmInfo *MCAI = MF.getTarget().getMCAsmInfo();
1349 
1350  releaseMemory();
1351 
1352  // Liveness is not tracked for VALUE_STACK physreg.
1354 
1355  // Place the BLOCK/LOOP/TRY markers to indicate the beginnings of scopes.
1356  placeMarkers(MF);
1357 
1358  // Remove unnecessary instructions possibly introduced by try/end_trys.
1359  if (MCAI->getExceptionHandlingType() == ExceptionHandling::Wasm &&
1361  removeUnnecessaryInstrs(MF);
1362 
1363  // Convert MBB operands in terminators to relative depth immediates.
1364  rewriteDepthImmediates(MF);
1365 
1366  // Fix up block/loop/try signatures at the end of the function to conform to
1367  // WebAssembly's rules.
1368  fixEndsAtEndOfFunction(MF);
1369 
1370  // Add an end instruction at the end of the function body.
1371  const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
1373  .getTargetTriple()
1374  .isOSBinFormatELF())
1375  appendEndToFunction(MF, TII);
1376 
1377  MF.getInfo<WebAssemblyFunctionInfo>()->setCFGStackified();
1378  return true;
1379 }
static GCMetadataPrinterRegistry::Add< ErlangGCPrinter > X("erlang", "erlang-compatible garbage collector")
DILocation * get() const
Get the underlying DILocation.
Definition: DebugLoc.cpp:21
static void appendEndToFunction(MachineFunction &MF, const WebAssemblyInstrInfo &TII)
This class represents lattice values for constants.
Definition: AllocatorList.h:23
void RenumberBlocks(MachineBasicBlock *MBBFrom=nullptr)
RenumberBlocks - This discards all of the MachineBasicBlock numbers and recomputes them...
static bool explicitlyBranchesTo(MachineBasicBlock *Pred, MachineBasicBlock *MBB)
Test whether Pred has any terminators explicitly branching to MBB, as opposed to falling through...
bool isOSBinFormatELF() const
Tests whether the OS uses the ELF binary format.
Definition: Triple.h:615
unsigned getNumBlockIDs() const
getNumBlockIDs - Return the number of MBB ID&#39;s allocated.
bool mayThrow(const MachineInstr &MI)
const DebugLoc & getDebugLoc() const
Returns the debug location id of this MachineInstr.
Definition: MachineInstr.h:382
unsigned getReg() const
getReg - Returns the register number.
void transferSuccessors(MachineBasicBlock *FromMBB)
Transfers all the successors from MBB to this machine basic block (i.e., copies all the successors Fr...
STATISTIC(NumFunctions, "Total number of functions")
A debug info location.
Definition: DebugLoc.h:33
iterator_range< mop_iterator > operands()
Definition: MachineInstr.h:458
This file contains the entry points for global functions defined in the LLVM WebAssembly back-end...
iterator_range< succ_iterator > successors()
bool analyzeBranch(MachineBasicBlock &MBB, MachineBasicBlock *&TBB, MachineBasicBlock *&FBB, SmallVectorImpl< MachineOperand > &Cond, bool AllowModify) const override
Analyze the branching code at the end of MBB, returning true if it cannot be understood (e...
AnalysisUsage & addRequired()
MachineFunctionPass - This class adapts the FunctionPass interface to allow convenient creation of pa...
const HexagonInstrInfo * TII
unsigned getNumOperands() const
Retuns the total number of operands.
Definition: MachineInstr.h:411
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: APFloat.h:41
bool isTerminator(QueryType Type=AnyInBundle) const
Returns true if this instruction part of the terminator for a basic block.
Definition: MachineInstr.h:648
iterator_range< iterator > terminators()
unsigned getOpcode() const
Returns the opcode of this MachineInstr.
Definition: MachineInstr.h:408
const char * getSymbolName() const
BlockT * getHeader() const
Definition: LoopInfo.h:100
#define DEBUG_TYPE
auto reverse(ContainerTy &&C, typename std::enable_if< has_rbegin< ContainerTy >::value >::type *=nullptr) -> decltype(make_range(C.rbegin(), C.rend()))
Definition: STLExtras.h:266
DebugLoc findPrevDebugLoc(instr_iterator MBBI)
Find the previous valid DebugLoc preceding MBBI, skipping and DBG_VALUE instructions.
static MachineBasicBlock::iterator getEarliestInsertPos(MachineBasicBlock *MBB, const SmallPtrSet< const MachineInstr *, 4 > &BeforeSet, const SmallPtrSet< const MachineInstr *, 4 > &AfterSet)
bool hasPersonalityFn() const
Check whether this function has a personality function.
Definition: Function.h:707
int getNumber() const
MachineBasicBlocks are uniquely numbered at the function level, unless they&#39;re not in a MachineFuncti...
This file implements WebAssemblyException information analysis.
reverse_iterator rend()
INITIALIZE_PASS(WebAssemblyCFGStackify, DEBUG_TYPE, "Insert BLOCK/LOOP/TRY markers for WebAssembly scopes", false, false) FunctionPass *llvm
MachineBasicBlock * CreateMachineBasicBlock(const BasicBlock *bb=nullptr)
CreateMachineBasicBlock - Allocate a new MachineBasicBlock.
reverse_iterator rbegin()
StringRef getName() const
getName - Return the name of the corresponding LLVM function.
WebAssembly Exception Handling.
This class is intended to be used as a base class for asm properties and features specific to the tar...
Definition: MCAsmInfo.h:55
This file contains the declaration of the WebAssembly-specific utility functions. ...
MachineInstrBuilder BuildMI(MachineFunction &MF, const DebugLoc &DL, const MCInstrDesc &MCID)
Builder interface. Specify how to create the initial instruction itself.
#define P(N)
Control flow instructions. These all have token chains.
Definition: ISDOpcodes.h:652
static GCRegistry::Add< OcamlGC > B("ocaml", "ocaml 3.10-compatible GC")
unsigned const MachineRegisterInfo * MRI
const TargetSubtargetInfo & getSubtarget() const
getSubtarget - Return the subtarget for which this machine code is being compiled.
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - Subclasses that override getAnalysisUsage must call this.
const Triple & getTargetTriple() const
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
const MCAsmInfo * getMCAsmInfo() const
Return target specific asm information.
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:370
bool isPredecessor(const MachineBasicBlock *MBB) const
Return true if the specified MBB is a predecessor of this block.
Represent the analysis usage information of a pass.
Ty * getInfo()
getInfo - Keep track of various per-function pieces of information for backends that would like to do...
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:284
size_type count(ConstPtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
Definition: SmallPtrSet.h:381
self_iterator getIterator()
Definition: ilist_node.h:81
iterator_range< pred_iterator > predecessors()
size_t size() const
Definition: SmallVector.h:52
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
void sort(IteratorTy Start, IteratorTy End)
Definition: STLExtras.h:1115
This file declares the WebAssembly-specific subclass of TargetSubtarget.
Iterator for intrusive lists based on ilist_node.
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:417
void addSuccessor(MachineBasicBlock *Succ, BranchProbability Prob=BranchProbability::getUnknown())
Add Succ as a successor of this MachineBasicBlock.
void addOperand(MachineFunction &MF, const MachineOperand &Op)
Add the specified operand to the instruction.
MachineOperand class - Representation of each machine instruction operand.
This is a &#39;vector&#39; (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:841
static unsigned getDepth(const SmallVectorImpl< const MachineBasicBlock *> &Stack, const MachineBasicBlock *MBB)
ExprType
This is used to indicate block signatures.
void invalidateLiveness()
invalidateLiveness - Indicates that register liveness is no longer being tracked accurately.
int64_t getImm() const
const Function & getFunction() const
Return the LLVM function that this machine code represents.
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:132
unsigned removeBranch(MachineBasicBlock &MBB, int *BytesRemoved=nullptr) const override
Remove the branching code at the end of the specific MBB.
DebugLoc findBranchDebugLoc()
Find and return the merged DebugLoc of the branch instructions of the block.
const MachineBasicBlock * getParent() const
Definition: MachineInstr.h:253
MachineRegisterInfo - Keep track of information for virtual and physical registers, including vreg register classes, use/def chains for registers, etc.
Representation of each machine instruction.
Definition: MachineInstr.h:63
This class is derived from MachineFunctionInfo and contains private WebAssembly-specific information ...
const MachineFunction * getParent() const
Return the MachineFunction containing this basic block.
void splice(iterator Where, MachineBasicBlock *Other, iterator From)
Take an instruction from MBB &#39;Other&#39; at the position From, and insert it into this MBB right before &#39;...
MachineRegisterInfo & getRegInfo()
getRegInfo - Return information about the registers currently in use.
bool isEHPad() const
Returns true if the block is a landing pad.
LLVM_NODISCARD bool empty() const
Definition: SmallVector.h:55
Represents a single loop in the control flow graph.
Definition: LoopInfo.h:465
static MachineOperand CreateImm(int64_t Val)
#define I(x, y, z)
Definition: MD5.cpp:58
bool isMarker(const MachineInstr &MI)
This file declares WebAssembly-specific per-machine-function information.
const MachineBasicBlock & back() const
const LLVMTargetMachine & getTarget() const
getTarget - Return the target machine this machine code is compiled with
size_type count(const_arg_type_t< KeyT > Val) const
Return 1 if the specified key is in the map, 0 otherwise.
Definition: DenseMap.h:171
MachineInstr * removeFromParent()
Unlink &#39;this&#39; from the containing basic block, and return it without deleting it. ...
void removeSuccessor(MachineBasicBlock *Succ, bool NormalizeSuccProbs=false)
Remove successor from the successors list of this MachineBasicBlock.
ValueT lookup(const_arg_type_t< KeyT > Val) const
lookup - Return the entry for the specified key, or a default constructed value if no such entry exis...
Definition: DenseMap.h:211
FunctionPass * createWebAssemblyCFGStackify()
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
void insert(iterator MBBI, MachineBasicBlock *MBB)
static MachineBasicBlock::iterator getLatestInsertPos(MachineBasicBlock *MBB, const SmallPtrSet< const MachineInstr *, 4 > &BeforeSet, const SmallPtrSet< const MachineInstr *, 4 > &AfterSet)
MachineBasicBlock * getBottom(const T *Unit)
Return the "bottom" block of an entity, which can be either a MachineLoop or WebAssemblyException.
void push_back(MachineBasicBlock *MBB)
static const Function * getParent(const Value *V)
ExceptionHandling getExceptionHandlingType() const
Definition: MCAsmInfo.h:569
IRTranslator LLVM IR MI
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:48
void RemoveOperand(unsigned OpNo)
Erase an operand from an instruction, leaving it with one fewer operand than it started with...
#define LLVM_DEBUG(X)
Definition: Debug.h:122
bool isChild(const MachineInstr &MI, const WebAssemblyFunctionInfo &MFI)
Test whether MI is a child of some other node in an expression tree.
const MachineOperand & getOperand(unsigned i) const
Definition: MachineInstr.h:413
DominatorTree Class - Concrete subclass of DominatorTreeBase that is used to compute a normal dominat...
unsigned createVirtualRegister(const TargetRegisterClass *RegClass, StringRef Name="")
createVirtualRegister - Create and return a new virtual register in the function with the specified r...
void resize(size_type N)
Definition: SmallVector.h:344