63#include <forward_list>
69#define LLE_OPTION "loop-load-elim"
70#define DEBUG_TYPE LLE_OPTION
73 "runtime-check-per-loop-load-elim",
cl::Hidden,
74 cl::desc(
"Max number of memchecks allowed per eliminated load on average"),
79 cl::desc(
"The maximum number of SCEV checks allowed for Loop "
82STATISTIC(NumLoopLoadEliminted,
"Number of loads eliminated by LLE");
87struct StoreToLoadForwardingCandidate {
92 : Load(Load), Store(Store) {}
98 Value *LoadPtr =
Load->getPointerOperand();
101 auto &
DL =
Load->getParent()->getModule()->getDataLayout();
105 DL.getTypeSizeInBits(LoadType) ==
107 "Should be a known dependence");
112 if (
getPtrStride(PSE, LoadType, LoadPtr, L).value_or(0) != 1 ||
113 getPtrStride(PSE, LoadType, StorePtr, L).value_or(0) != 1)
116 unsigned TypeByteSize =
DL.getTypeAllocSize(
const_cast<Type *
>(LoadType));
118 auto *LoadPtrSCEV = cast<SCEVAddRecExpr>(PSE.
getSCEV(LoadPtr));
119 auto *StorePtrSCEV = cast<SCEVAddRecExpr>(PSE.
getSCEV(StorePtr));
123 auto *Dist = cast<SCEVConstant>(
125 const APInt &Val = Dist->getAPInt();
126 return Val == TypeByteSize;
129 Value *getLoadPtr()
const {
return Load->getPointerOperand(); }
133 const StoreToLoadForwardingCandidate &Cand) {
134 OS << *Cand.Store <<
" -->\n";
148 L->getLoopLatches(Latches);
156 return Load->getParent() != L->getHeader();
162class LoadEliminationForLoop {
167 :
L(
L), LI(LI), LAI(LAI), DT(DT),
BFI(
BFI), PSI(PSI), PSE(LAI.getPSE()) {}
174 std::forward_list<StoreToLoadForwardingCandidate>
176 std::forward_list<StoreToLoadForwardingCandidate> Candidates;
188 for (
const auto &Dep : *Deps) {
190 Instruction *Destination = Dep.getDestination(LAI);
193 if (isa<LoadInst>(Source))
194 LoadsWithUnknownDepedence.
insert(Source);
195 if (isa<LoadInst>(Destination))
196 LoadsWithUnknownDepedence.
insert(Destination);
200 if (Dep.isBackward())
206 assert(Dep.isForward() &&
"Needs to be a forward dependence");
208 auto *
Store = dyn_cast<StoreInst>(Source);
211 auto *
Load = dyn_cast<LoadInst>(Destination);
218 Store->getParent()->getModule()->getDataLayout()))
221 Candidates.emplace_front(Load, Store);
224 if (!LoadsWithUnknownDepedence.
empty())
225 Candidates.remove_if([&](
const StoreToLoadForwardingCandidate &
C) {
226 return LoadsWithUnknownDepedence.
count(
C.Load);
234 auto I = InstOrder.find(Inst);
235 assert(
I != InstOrder.end() &&
"No index for instruction");
258 void removeDependencesFromMultipleStores(
259 std::forward_list<StoreToLoadForwardingCandidate> &Candidates) {
262 using LoadToSingleCandT =
264 LoadToSingleCandT LoadToSingleCand;
266 for (
const auto &Cand : Candidates) {
268 LoadToSingleCandT::iterator Iter;
270 std::tie(Iter, NewElt) =
271 LoadToSingleCand.
insert(std::make_pair(Cand.Load, &Cand));
273 const StoreToLoadForwardingCandidate *&OtherCand = Iter->second;
275 if (OtherCand ==
nullptr)
281 if (Cand.Store->getParent() == OtherCand->Store->getParent() &&
282 Cand.isDependenceDistanceOfOne(PSE, L) &&
283 OtherCand->isDependenceDistanceOfOne(PSE, L)) {
285 if (getInstrIndex(OtherCand->Store) < getInstrIndex(Cand.Store))
292 Candidates.remove_if([&](
const StoreToLoadForwardingCandidate &Cand) {
293 if (LoadToSingleCand[Cand.Load] != &Cand) {
295 dbgs() <<
"Removing from candidates: \n"
297 <<
" The load may have multiple stores forwarding to "
310 bool needsChecking(
unsigned PtrIdx1,
unsigned PtrIdx2,
317 return ((PtrsWrittenOnFwdingPath.
count(Ptr1) && CandLoadPtrs.
count(Ptr2)) ||
318 (PtrsWrittenOnFwdingPath.
count(Ptr2) && CandLoadPtrs.
count(Ptr1)));
345 std::max_element(Candidates.
begin(), Candidates.
end(),
346 [&](
const StoreToLoadForwardingCandidate &
A,
347 const StoreToLoadForwardingCandidate &
B) {
348 return getInstrIndex(A.Load) < getInstrIndex(B.Load);
352 std::min_element(Candidates.
begin(), Candidates.
end(),
353 [&](
const StoreToLoadForwardingCandidate &
A,
354 const StoreToLoadForwardingCandidate &
B) {
355 return getInstrIndex(A.Store) <
356 getInstrIndex(B.Store);
366 if (
auto *S = dyn_cast<StoreInst>(
I))
367 PtrsWrittenOnFwdingPath.
insert(S->getPointerOperand());
370 std::for_each(MemInstrs.begin() + getInstrIndex(FirstStore) + 1,
371 MemInstrs.end(), InsertStorePtr);
372 std::for_each(MemInstrs.begin(), &MemInstrs[getInstrIndex(LastLoad)],
375 return PtrsWrittenOnFwdingPath;
384 findPointersWrittenOnForwardingPath(Candidates);
388 for (
const auto &Candidate : Candidates)
389 CandLoadPtrs.
insert(Candidate.getLoadPtr());
394 copy_if(AllChecks, std::back_inserter(Checks),
396 for (
auto PtrIdx1 :
Check.first->Members)
397 for (
auto PtrIdx2 :
Check.second->Members)
398 if (needsChecking(PtrIdx1, PtrIdx2, PtrsWrittenOnFwdingPath,
413 propagateStoredValueToLoadUsers(
const StoreToLoadForwardingCandidate &Cand,
430 Value *
Ptr = Cand.Load->getPointerOperand();
431 auto *PtrSCEV = cast<SCEVAddRecExpr>(PSE.
getSCEV(
Ptr));
432 auto *PH =
L->getLoopPreheader();
433 assert(PH &&
"Preheader should exist!");
434 Value *InitialPtr =
SEE.expandCodeFor(PtrSCEV->getStart(),
Ptr->getType(),
435 PH->getTerminator());
437 Cand.Load->getType(), InitialPtr,
"load_initial",
438 false, Cand.Load->getAlign(), PH->getTerminator());
441 &
L->getHeader()->front());
442 PHI->addIncoming(Initial, PH);
445 Type *StoreType = Cand.Store->getValueOperand()->getType();
449 assert(
DL.getTypeSizeInBits(LoadType) ==
DL.getTypeSizeInBits(StoreType) &&
450 "The type sizes should match!");
452 Value *StoreValue = Cand.Store->getValueOperand();
453 if (LoadType != StoreType)
455 StoreValue, LoadType,
"store_forward_cast", Cand.Store);
457 PHI->addIncoming(StoreValue,
L->getLoopLatch());
459 Cand.Load->replaceAllUsesWith(
PHI);
465 LLVM_DEBUG(
dbgs() <<
"\nIn \"" <<
L->getHeader()->getParent()->getName()
466 <<
"\" checking " << *L <<
"\n");
487 auto StoreToLoadDependences = findStoreToLoadDependences(LAI);
488 if (StoreToLoadDependences.empty())
497 removeDependencesFromMultipleStores(StoreToLoadDependences);
498 if (StoreToLoadDependences.empty())
503 for (
const StoreToLoadForwardingCandidate &Cand : StoreToLoadDependences) {
519 if (!Cand.isDependenceDistanceOfOne(PSE, L))
522 assert(isa<SCEVAddRecExpr>(PSE.
getSCEV(Cand.Load->getPointerOperand())) &&
523 "Loading from something other than indvar?");
525 isa<SCEVAddRecExpr>(PSE.
getSCEV(Cand.Store->getPointerOperand())) &&
526 "Storing to something other than indvar?");
532 <<
". Valid store-to-load forwarding across the loop backedge\n");
534 if (Candidates.
empty())
553 if (!
L->isLoopSimplifyForm()) {
561 "convergent calls\n");
565 auto *HeaderBB =
L->getHeader();
566 auto *
F = HeaderBB->getParent();
567 bool OptForSize =
F->hasOptSize() ||
569 PGSOQueryType::IRPass);
572 dbgs() <<
"Versioning is needed but not allowed when optimizing "
585 auto NoLongerGoodCandidate = [
this](
586 const StoreToLoadForwardingCandidate &Cand) {
587 return !isa<SCEVAddRecExpr>(
588 PSE.
getSCEV(Cand.Load->getPointerOperand())) ||
589 !isa<SCEVAddRecExpr>(
590 PSE.
getSCEV(Cand.Store->getPointerOperand()));
599 for (
const auto &Cand : Candidates)
600 propagateStoredValueToLoadUsers(Cand,
SEE);
601 NumLoopLoadEliminted += Candidates.size();
637 bool Changed =
false;
639 for (
Loop *TopLevelLoop : LI)
641 Changed |=
simplifyLoop(L, &DT, &LI, SE, AC,
nullptr,
false);
643 if (L->isInnermost())
648 for (
Loop *L : Worklist) {
650 if (!L->isRotatedForm() || !L->getExitingBlock())
653 LoadEliminationForLoop LEL(L, &LI, LAIs.
getInfo(*L), &DT, BFI, PSI);
654 Changed |= LEL.processLoop();
673 auto *BFI = (PSI && PSI->hasProfileSummary()) ?
MachineBasicBlock MachineBasicBlock::iterator DebugLoc DL
This file implements a class to represent arbitrary precision integral constant values and operations...
static GCRegistry::Add< OcamlGC > B("ocaml", "ocaml 3.10-compatible GC")
static GCRegistry::Add< ErlangGC > A("erlang", "erlang-compatible garbage collector")
This file defines the DenseMap class.
This file builds on the ADT/GraphTraits.h file to build generic depth first graph iterator.
This is the interface for a simple mod/ref and alias analysis over globals.
This header provides classes for managing per-loop analyses.
static bool eliminateLoadsAcrossLoops(Function &F, LoopInfo &LI, DominatorTree &DT, BlockFrequencyInfo *BFI, ProfileSummaryInfo *PSI, ScalarEvolution *SE, AssumptionCache *AC, LoopAccessInfoManager &LAIs)
static cl::opt< unsigned > LoadElimSCEVCheckThreshold("loop-load-elimination-scev-check-threshold", cl::init(8), cl::Hidden, cl::desc("The maximum number of SCEV checks allowed for Loop " "Load Elimination"))
static bool isLoadConditional(LoadInst *Load, Loop *L)
Return true if the load is not executed on all paths in the loop.
static bool doesStoreDominatesAllLatches(BasicBlock *StoreBlock, Loop *L, DominatorTree *DT)
Check if the store dominates all latches, so as long as there is no intervening store this value will...
static cl::opt< unsigned > CheckPerElim("runtime-check-per-loop-load-elim", cl::Hidden, cl::desc("Max number of memchecks allowed per eliminated load on average"), cl::init(1))
This header defines the LoopLoadEliminationPass object.
Module.h This file contains the declarations for the Module class.
This header defines various interfaces for pass management in LLVM.
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
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)
Class for arbitrary precision integers.
A container for analyses that lazily runs them and caches their results.
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs... ExtraArgs)
Get the result of an analysis pass for a given IR unit.
A function analysis which provides an AssumptionCache.
A cache of @llvm.assume calls within a function.
LLVM Basic Block Representation.
Analysis pass which computes BlockFrequencyInfo.
BlockFrequencyInfo pass uses BlockFrequencyInfoImpl implementation to estimate IR basic block frequen...
static CastInst * CreateBitOrPointerCast(Value *S, Type *Ty, const Twine &Name="", Instruction *InsertBefore=nullptr)
Create a BitCast, a PtrToInt, or an IntToPTr cast instruction.
static bool isBitOrNoopPointerCastable(Type *SrcTy, Type *DestTy, const DataLayout &DL)
Check whether a bitcast, inttoptr, or ptrtoint cast between these types is valid and a no-op.
std::pair< iterator, bool > insert(const std::pair< KeyT, ValueT > &KV)
Analysis pass which computes a DominatorTree.
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree.
bool dominates(const BasicBlock *BB, const Use &U) const
Return true if the (end of the) basic block BB dominates the use U.
An instruction for reading from memory.
This analysis provides dependence information for the memory accesses of a loop.
const LoopAccessInfo & getInfo(Loop &L)
Drive the analysis of memory accesses in the loop.
const MemoryDepChecker & getDepChecker() const
the Memory Dependence Checker which can determine the loop-independent and loop-carried dependences b...
const RuntimePointerChecking * getRuntimePointerChecking() const
const PredicatedScalarEvolution & getPSE() const
Used to add runtime SCEV checks.
bool hasConvergentOp() const
Return true if there is a convergent operation in the loop.
Analysis pass that exposes the LoopInfo for a function.
This class emits a version of the loop where run-time checks ensure that may-alias pointers can't ove...
Represents a single loop in the control flow graph.
const MachineFunction * getParent() const
Return the MachineFunction containing this basic block.
const DataLayout & getDataLayout() const
Return the DataLayout attached to the Module associated to this MF.
const SmallVectorImpl< Instruction * > & getMemoryInstructions() const
The vector of memory access instructions.
const SmallVectorImpl< Dependence > * getDependences() const
Returns the memory dependences.
DenseMap< Instruction *, unsigned > generateInstructionOrderMap() const
Generate a mapping between the memory instructions and their indices according to program order.
An analysis over an "inner" IR unit that provides access to an analysis manager over a "outer" IR uni...
static PHINode * Create(Type *Ty, unsigned NumReservedValues, const Twine &NameStr="", Instruction *InsertBefore=nullptr)
Constructors - NumReservedValues is a hint for the number of incoming edges that this phi node will h...
An interface layer with SCEV used to manage how we see SCEV expressions for values in the context of ...
ScalarEvolution * getSE() const
Returns the ScalarEvolution analysis used.
const SCEVPredicate & getPredicate() const
const SCEV * getSCEV(Value *V)
Returns the SCEV expression of V, in the context of the current SCEV predicate.
A set of analyses that are preserved following a run of a transformation pass.
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
An analysis pass based on the new PM to deliver ProfileSummaryInfo.
Analysis providing profile information.
void printChecks(raw_ostream &OS, const SmallVectorImpl< RuntimePointerCheck > &Checks, unsigned Depth=0) const
Print Checks.
const SmallVectorImpl< RuntimePointerCheck > & getChecks() const
Returns the checks that generateChecks created.
const PointerInfo & getPointerInfo(unsigned PtrIdx) const
Return PointerInfo for pointer at index PtrIdx.
This class uses information about analyze scalars to rewrite expressions in canonical form.
virtual unsigned getComplexity() const
Returns the estimated complexity of this predicate.
virtual bool isAlwaysTrue() const =0
Returns true if the predicate is always true.
Analysis pass that exposes the ScalarEvolution for a function.
The main scalar evolution driver.
const SCEV * getMinusSCEV(const SCEV *LHS, const SCEV *RHS, SCEV::NoWrapFlags Flags=SCEV::FlagAnyWrap, unsigned Depth=0)
Return LHS-RHS.
A templated base class for SmallPtrSet which provides the typesafe interface that is common across al...
size_type count(ConstPtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements.
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
void push_back(const T &Elt)
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
An instruction for storing to memory.
The instances of the Type class are immutable: once they are created, they are never changed.
unsigned getPointerAddressSpace() const
Get the address space of this pointer or pointer vector type.
LLVM Value Representation.
Type * getType() const
All values are typed, get the type of this value.
This class implements an extremely fast bulk output stream that can only output to a stream.
raw_ostream & indent(unsigned NumSpaces)
indent - Insert 'NumSpaces' spaces.
@ C
The default llvm calling convention, compatible with C.
initializer< Ty > init(const Ty &Val)
This is an optimization pass for GlobalISel generic memory operations.
bool simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, ScalarEvolution *SE, AssumptionCache *AC, MemorySSAUpdater *MSSAU, bool PreserveLCSSA)
Simplify each loop in a loop nest recursively.
bool all_of(R &&range, UnaryPredicate P)
Provide wrappers to std::all_of which take ranges instead of having to pass begin/end explicitly.
std::pair< const RuntimeCheckingPtrGroup *, const RuntimeCheckingPtrGroup * > RuntimePointerCheck
A memcheck which made up of a pair of grouped pointers.
std::optional< int64_t > getPtrStride(PredicatedScalarEvolution &PSE, Type *AccessTy, Value *Ptr, const Loop *Lp, const ValueToValueMap &StridesMap=ValueToValueMap(), bool Assume=false, bool ShouldCheckWrap=true)
If the pointer has a constant stride return it in units of the access type size.
bool shouldOptimizeForSize(const MachineFunction *MF, ProfileSummaryInfo *PSI, const MachineBlockFrequencyInfo *BFI, PGSOQueryType QueryType=PGSOQueryType::Other)
Returns true if machine function MF is suggested to be size-optimized based on the profile.
OutputIt copy_if(R &&Range, OutputIt Out, UnaryPredicate P)
Provide wrappers to std::copy_if which take ranges instead of having to pass begin/end explicitly.
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
raw_ostream & operator<<(raw_ostream &OS, const APFixedPoint &FX)
void erase_if(Container &C, UnaryPredicate P)
Provide a container algorithm similar to C++ Library Fundamentals v2's erase_if which is equivalent t...
iterator_range< df_iterator< T > > depth_first(const T &G)
Type * getLoadStoreType(Value *I)
A helper function that returns the type of a load or store instruction.
void swap(llvm::BitVector &LHS, llvm::BitVector &RHS)
Implement std::swap in terms of BitVector swap.
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
TrackingVH< Value > PointerValue
Holds the pointer value that we need to check.