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llvm-mirror/lib/Transforms/Scalar/LoopLoadElimination.cpp
Max Kazantsev 262e4a75c1 [LoopLoadElim] Pass ScalarEvolution in old pass manager. PR49141 
Loop canonicalization may end up deleting blocks from CFG. And
Scalar Evolution may still keep cached referenced to those blocks
unless updated properly.
2021-02-15 18:08:23 +07:00

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//===- LoopLoadElimination.cpp - Loop Load Elimination Pass ---------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implement a loop-aware load elimination pass.
//
// It uses LoopAccessAnalysis to identify loop-carried dependences with a
// distance of one between stores and loads. These form the candidates for the
// transformation. The source value of each store then propagated to the user
// of the corresponding load. This makes the load dead.
//
// The pass can also version the loop and add memchecks in order to prove that
// may-aliasing stores can't change the value in memory before it's read by the
// load.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/LoopLoadElimination.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/LazyBlockFrequencyInfo.h"
#include "llvm/Analysis/LoopAccessAnalysis.h"
#include "llvm/Analysis/LoopAnalysisManager.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/MemorySSA.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Value.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils.h"
#include "llvm/Transforms/Utils/LoopSimplify.h"
#include "llvm/Transforms/Utils/LoopVersioning.h"
#include "llvm/Transforms/Utils/ScalarEvolutionExpander.h"
#include "llvm/Transforms/Utils/SizeOpts.h"
#include <algorithm>
#include <cassert>
#include <forward_list>
#include <set>
#include <tuple>
#include <utility>
using namespace llvm;
#define LLE_OPTION "loop-load-elim"
#define DEBUG_TYPE LLE_OPTION
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));
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"));
STATISTIC(NumLoopLoadEliminted, "Number of loads eliminated by LLE");
namespace {
/// Represent a store-to-forwarding candidate.
struct StoreToLoadForwardingCandidate {
LoadInst *Load;
StoreInst *Store;
StoreToLoadForwardingCandidate(LoadInst *Load, StoreInst *Store)
: Load(Load), Store(Store) {}
/// Return true if the dependence from the store to the load has a
/// distance of one. E.g. A[i+1] = A[i]
bool isDependenceDistanceOfOne(PredicatedScalarEvolution &PSE,
Loop *L) const {
Value *LoadPtr = Load->getPointerOperand();
Value *StorePtr = Store->getPointerOperand();
Type *LoadPtrType = LoadPtr->getType();
Type *LoadType = LoadPtrType->getPointerElementType();
assert(LoadPtrType->getPointerAddressSpace() ==
StorePtr->getType()->getPointerAddressSpace() &&
LoadType == StorePtr->getType()->getPointerElementType() &&
"Should be a known dependence");
// Currently we only support accesses with unit stride. FIXME: we should be
// able to handle non unit stirde as well as long as the stride is equal to
// the dependence distance.
if (getPtrStride(PSE, LoadPtr, L) != 1 ||
getPtrStride(PSE, StorePtr, L) != 1)
return false;
auto &DL = Load->getParent()->getModule()->getDataLayout();
unsigned TypeByteSize = DL.getTypeAllocSize(const_cast<Type *>(LoadType));
auto *LoadPtrSCEV = cast<SCEVAddRecExpr>(PSE.getSCEV(LoadPtr));
auto *StorePtrSCEV = cast<SCEVAddRecExpr>(PSE.getSCEV(StorePtr));
// We don't need to check non-wrapping here because forward/backward
// dependence wouldn't be valid if these weren't monotonic accesses.
auto *Dist = cast<SCEVConstant>(
PSE.getSE()->getMinusSCEV(StorePtrSCEV, LoadPtrSCEV));
const APInt &Val = Dist->getAPInt();
return Val == TypeByteSize;
}
Value *getLoadPtr() const { return Load->getPointerOperand(); }
#ifndef NDEBUG
friend raw_ostream &operator<<(raw_ostream &OS,
const StoreToLoadForwardingCandidate &Cand) {
OS << *Cand.Store << " -->\n";
OS.indent(2) << *Cand.Load << "\n";
return OS;
}
#endif
};
} // end anonymous namespace
/// Check if the store dominates all latches, so as long as there is no
/// intervening store this value will be loaded in the next iteration.
static bool doesStoreDominatesAllLatches(BasicBlock *StoreBlock, Loop *L,
DominatorTree *DT) {
SmallVector<BasicBlock *, 8> Latches;
L->getLoopLatches(Latches);
return llvm::all_of(Latches, [&](const BasicBlock *Latch) {
return DT->dominates(StoreBlock, Latch);
});
}
/// Return true if the load is not executed on all paths in the loop.
static bool isLoadConditional(LoadInst *Load, Loop *L) {
return Load->getParent() != L->getHeader();
}
namespace {
/// The per-loop class that does most of the work.
class LoadEliminationForLoop {
public:
LoadEliminationForLoop(Loop *L, LoopInfo *LI, const LoopAccessInfo &LAI,
DominatorTree *DT, BlockFrequencyInfo *BFI,
ProfileSummaryInfo* PSI)
: L(L), LI(LI), LAI(LAI), DT(DT), BFI(BFI), PSI(PSI), PSE(LAI.getPSE()) {}
/// Look through the loop-carried and loop-independent dependences in
/// this loop and find store->load dependences.
///
/// Note that no candidate is returned if LAA has failed to analyze the loop
/// (e.g. if it's not bottom-tested, contains volatile memops, etc.)
std::forward_list<StoreToLoadForwardingCandidate>
findStoreToLoadDependences(const LoopAccessInfo &LAI) {
std::forward_list<StoreToLoadForwardingCandidate> Candidates;
const auto *Deps = LAI.getDepChecker().getDependences();
if (!Deps)
return Candidates;
// Find store->load dependences (consequently true dep). Both lexically
// forward and backward dependences qualify. Disqualify loads that have
// other unknown dependences.
SmallPtrSet<Instruction *, 4> LoadsWithUnknownDepedence;
for (const auto &Dep : *Deps) {
Instruction *Source = Dep.getSource(LAI);
Instruction *Destination = Dep.getDestination(LAI);
if (Dep.Type == MemoryDepChecker::Dependence::Unknown) {
if (isa<LoadInst>(Source))
LoadsWithUnknownDepedence.insert(Source);
if (isa<LoadInst>(Destination))
LoadsWithUnknownDepedence.insert(Destination);
continue;
}
if (Dep.isBackward())
// Note that the designations source and destination follow the program
// order, i.e. source is always first. (The direction is given by the
// DepType.)
std::swap(Source, Destination);
else
assert(Dep.isForward() && "Needs to be a forward dependence");
auto *Store = dyn_cast<StoreInst>(Source);
if (!Store)
continue;
auto *Load = dyn_cast<LoadInst>(Destination);
if (!Load)
continue;
// Only progagate the value if they are of the same type.
if (Store->getPointerOperandType() != Load->getPointerOperandType())
continue;
Candidates.emplace_front(Load, Store);
}
if (!LoadsWithUnknownDepedence.empty())
Candidates.remove_if([&](const StoreToLoadForwardingCandidate &C) {
return LoadsWithUnknownDepedence.count(C.Load);
});
return Candidates;
}
/// Return the index of the instruction according to program order.
unsigned getInstrIndex(Instruction *Inst) {
auto I = InstOrder.find(Inst);
assert(I != InstOrder.end() && "No index for instruction");
return I->second;
}
/// If a load has multiple candidates associated (i.e. different
/// stores), it means that it could be forwarding from multiple stores
/// depending on control flow. Remove these candidates.
///
/// Here, we rely on LAA to include the relevant loop-independent dependences.
/// LAA is known to omit these in the very simple case when the read and the
/// write within an alias set always takes place using the *same* pointer.
///
/// However, we know that this is not the case here, i.e. we can rely on LAA
/// to provide us with loop-independent dependences for the cases we're
/// interested. Consider the case for example where a loop-independent
/// dependece S1->S2 invalidates the forwarding S3->S2.
///
/// A[i] = ... (S1)
/// ... = A[i] (S2)
/// A[i+1] = ... (S3)
///
/// LAA will perform dependence analysis here because there are two
/// *different* pointers involved in the same alias set (&A[i] and &A[i+1]).
void removeDependencesFromMultipleStores(
std::forward_list<StoreToLoadForwardingCandidate> &Candidates) {
// If Store is nullptr it means that we have multiple stores forwarding to
// this store.
using LoadToSingleCandT =
DenseMap<LoadInst *, const StoreToLoadForwardingCandidate *>;
LoadToSingleCandT LoadToSingleCand;
for (const auto &Cand : Candidates) {
bool NewElt;
LoadToSingleCandT::iterator Iter;
std::tie(Iter, NewElt) =
LoadToSingleCand.insert(std::make_pair(Cand.Load, &Cand));
if (!NewElt) {
const StoreToLoadForwardingCandidate *&OtherCand = Iter->second;
// Already multiple stores forward to this load.
if (OtherCand == nullptr)
continue;
// Handle the very basic case when the two stores are in the same block
// so deciding which one forwards is easy. The later one forwards as
// long as they both have a dependence distance of one to the load.
if (Cand.Store->getParent() == OtherCand->Store->getParent() &&
Cand.isDependenceDistanceOfOne(PSE, L) &&
OtherCand->isDependenceDistanceOfOne(PSE, L)) {
// They are in the same block, the later one will forward to the load.
if (getInstrIndex(OtherCand->Store) < getInstrIndex(Cand.Store))
OtherCand = &Cand;
} else
OtherCand = nullptr;
}
}
Candidates.remove_if([&](const StoreToLoadForwardingCandidate &Cand) {
if (LoadToSingleCand[Cand.Load] != &Cand) {
LLVM_DEBUG(
dbgs() << "Removing from candidates: \n"
<< Cand
<< " The load may have multiple stores forwarding to "
<< "it\n");
return true;
}
return false;
});
}
/// Given two pointers operations by their RuntimePointerChecking
/// indices, return true if they require an alias check.
///
/// We need a check if one is a pointer for a candidate load and the other is
/// a pointer for a possibly intervening store.
bool needsChecking(unsigned PtrIdx1, unsigned PtrIdx2,
const SmallPtrSetImpl<Value *> &PtrsWrittenOnFwdingPath,
const SmallPtrSetImpl<Value *> &CandLoadPtrs) {
Value *Ptr1 =
LAI.getRuntimePointerChecking()->getPointerInfo(PtrIdx1).PointerValue;
Value *Ptr2 =
LAI.getRuntimePointerChecking()->getPointerInfo(PtrIdx2).PointerValue;
return ((PtrsWrittenOnFwdingPath.count(Ptr1) && CandLoadPtrs.count(Ptr2)) ||
(PtrsWrittenOnFwdingPath.count(Ptr2) && CandLoadPtrs.count(Ptr1)));
}
/// Return pointers that are possibly written to on the path from a
/// forwarding store to a load.
///
/// These pointers need to be alias-checked against the forwarding candidates.
SmallPtrSet<Value *, 4> findPointersWrittenOnForwardingPath(
const SmallVectorImpl<StoreToLoadForwardingCandidate> &Candidates) {
// From FirstStore to LastLoad neither of the elimination candidate loads
// should overlap with any of the stores.
//
// E.g.:
//
// st1 C[i]
// ld1 B[i] <-------,
// ld0 A[i] <----, | * LastLoad
// ... | |
// st2 E[i] | |
// st3 B[i+1] -- | -' * FirstStore
// st0 A[i+1] ---'
// st4 D[i]
//
// st0 forwards to ld0 if the accesses in st4 and st1 don't overlap with
// ld0.
LoadInst *LastLoad =
std::max_element(Candidates.begin(), Candidates.end(),
[&](const StoreToLoadForwardingCandidate &A,
const StoreToLoadForwardingCandidate &B) {
return getInstrIndex(A.Load) < getInstrIndex(B.Load);
})
->Load;
StoreInst *FirstStore =
std::min_element(Candidates.begin(), Candidates.end(),
[&](const StoreToLoadForwardingCandidate &A,
const StoreToLoadForwardingCandidate &B) {
return getInstrIndex(A.Store) <
getInstrIndex(B.Store);
})
->Store;
// We're looking for stores after the first forwarding store until the end
// of the loop, then from the beginning of the loop until the last
// forwarded-to load. Collect the pointer for the stores.
SmallPtrSet<Value *, 4> PtrsWrittenOnFwdingPath;
auto InsertStorePtr = [&](Instruction *I) {
if (auto *S = dyn_cast<StoreInst>(I))
PtrsWrittenOnFwdingPath.insert(S->getPointerOperand());
};
const auto &MemInstrs = LAI.getDepChecker().getMemoryInstructions();
std::for_each(MemInstrs.begin() + getInstrIndex(FirstStore) + 1,
MemInstrs.end(), InsertStorePtr);
std::for_each(MemInstrs.begin(), &MemInstrs[getInstrIndex(LastLoad)],
InsertStorePtr);
return PtrsWrittenOnFwdingPath;
}
/// Determine the pointer alias checks to prove that there are no
/// intervening stores.
SmallVector<RuntimePointerCheck, 4> collectMemchecks(
const SmallVectorImpl<StoreToLoadForwardingCandidate> &Candidates) {
SmallPtrSet<Value *, 4> PtrsWrittenOnFwdingPath =
findPointersWrittenOnForwardingPath(Candidates);
// Collect the pointers of the candidate loads.
SmallPtrSet<Value *, 4> CandLoadPtrs;
for (const auto &Candidate : Candidates)
CandLoadPtrs.insert(Candidate.getLoadPtr());
const auto &AllChecks = LAI.getRuntimePointerChecking()->getChecks();
SmallVector<RuntimePointerCheck, 4> Checks;
copy_if(AllChecks, std::back_inserter(Checks),
[&](const RuntimePointerCheck &Check) {
for (auto PtrIdx1 : Check.first->Members)
for (auto PtrIdx2 : Check.second->Members)
if (needsChecking(PtrIdx1, PtrIdx2, PtrsWrittenOnFwdingPath,
CandLoadPtrs))
return true;
return false;
});
LLVM_DEBUG(dbgs() << "\nPointer Checks (count: " << Checks.size()
<< "):\n");
LLVM_DEBUG(LAI.getRuntimePointerChecking()->printChecks(dbgs(), Checks));
return Checks;
}
/// Perform the transformation for a candidate.
void
propagateStoredValueToLoadUsers(const StoreToLoadForwardingCandidate &Cand,
SCEVExpander &SEE) {
// loop:
// %x = load %gep_i
// = ... %x
// store %y, %gep_i_plus_1
//
// =>
//
// ph:
// %x.initial = load %gep_0
// loop:
// %x.storeforward = phi [%x.initial, %ph] [%y, %loop]
// %x = load %gep_i <---- now dead
// = ... %x.storeforward
// store %y, %gep_i_plus_1
Value *Ptr = Cand.Load->getPointerOperand();
auto *PtrSCEV = cast<SCEVAddRecExpr>(PSE.getSCEV(Ptr));
auto *PH = L->getLoopPreheader();
assert(PH && "Preheader should exist!");
Value *InitialPtr = SEE.expandCodeFor(PtrSCEV->getStart(), Ptr->getType(),
PH->getTerminator());
Value *Initial = new LoadInst(
Cand.Load->getType(), InitialPtr, "load_initial",
/* isVolatile */ false, Cand.Load->getAlign(), PH->getTerminator());
PHINode *PHI = PHINode::Create(Initial->getType(), 2, "store_forwarded",
&L->getHeader()->front());
PHI->addIncoming(Initial, PH);
PHI->addIncoming(Cand.Store->getOperand(0), L->getLoopLatch());
Cand.Load->replaceAllUsesWith(PHI);
}
/// Top-level driver for each loop: find store->load forwarding
/// candidates, add run-time checks and perform transformation.
bool processLoop() {
LLVM_DEBUG(dbgs() << "\nIn \"" << L->getHeader()->getParent()->getName()
<< "\" checking " << *L << "\n");
// Look for store-to-load forwarding cases across the
// backedge. E.g.:
//
// loop:
// %x = load %gep_i
// = ... %x
// store %y, %gep_i_plus_1
//
// =>
//
// ph:
// %x.initial = load %gep_0
// loop:
// %x.storeforward = phi [%x.initial, %ph] [%y, %loop]
// %x = load %gep_i <---- now dead
// = ... %x.storeforward
// store %y, %gep_i_plus_1
// First start with store->load dependences.
auto StoreToLoadDependences = findStoreToLoadDependences(LAI);
if (StoreToLoadDependences.empty())
return false;
// Generate an index for each load and store according to the original
// program order. This will be used later.
InstOrder = LAI.getDepChecker().generateInstructionOrderMap();
// To keep things simple for now, remove those where the load is potentially
// fed by multiple stores.
removeDependencesFromMultipleStores(StoreToLoadDependences);
if (StoreToLoadDependences.empty())
return false;
// Filter the candidates further.
SmallVector<StoreToLoadForwardingCandidate, 4> Candidates;
for (const StoreToLoadForwardingCandidate &Cand : StoreToLoadDependences) {
LLVM_DEBUG(dbgs() << "Candidate " << Cand);
// Make sure that the stored values is available everywhere in the loop in
// the next iteration.
if (!doesStoreDominatesAllLatches(Cand.Store->getParent(), L, DT))
continue;
// If the load is conditional we can't hoist its 0-iteration instance to
// the preheader because that would make it unconditional. Thus we would
// access a memory location that the original loop did not access.
if (isLoadConditional(Cand.Load, L))
continue;
// Check whether the SCEV difference is the same as the induction step,
// thus we load the value in the next iteration.
if (!Cand.isDependenceDistanceOfOne(PSE, L))
continue;
assert(isa<SCEVAddRecExpr>(PSE.getSCEV(Cand.Load->getPointerOperand())) &&
"Loading from something other than indvar?");
assert(
isa<SCEVAddRecExpr>(PSE.getSCEV(Cand.Store->getPointerOperand())) &&
"Storing to something other than indvar?");
Candidates.push_back(Cand);
LLVM_DEBUG(
dbgs()
<< Candidates.size()
<< ". Valid store-to-load forwarding across the loop backedge\n");
}
if (Candidates.empty())
return false;
// Check intervening may-alias stores. These need runtime checks for alias
// disambiguation.
SmallVector<RuntimePointerCheck, 4> Checks = collectMemchecks(Candidates);
// Too many checks are likely to outweigh the benefits of forwarding.
if (Checks.size() > Candidates.size() * CheckPerElim) {
LLVM_DEBUG(dbgs() << "Too many run-time checks needed.\n");
return false;
}
if (LAI.getPSE().getUnionPredicate().getComplexity() >
LoadElimSCEVCheckThreshold) {
LLVM_DEBUG(dbgs() << "Too many SCEV run-time checks needed.\n");
return false;
}
if (!L->isLoopSimplifyForm()) {
LLVM_DEBUG(dbgs() << "Loop is not is loop-simplify form");
return false;
}
if (!Checks.empty() || !LAI.getPSE().getUnionPredicate().isAlwaysTrue()) {
if (LAI.hasConvergentOp()) {
LLVM_DEBUG(dbgs() << "Versioning is needed but not allowed with "
"convergent calls\n");
return false;
}
auto *HeaderBB = L->getHeader();
auto *F = HeaderBB->getParent();
bool OptForSize = F->hasOptSize() ||
llvm::shouldOptimizeForSize(HeaderBB, PSI, BFI,
PGSOQueryType::IRPass);
if (OptForSize) {
LLVM_DEBUG(
dbgs() << "Versioning is needed but not allowed when optimizing "
"for size.\n");
return false;
}
// Point of no-return, start the transformation. First, version the loop
// if necessary.
LoopVersioning LV(LAI, Checks, L, LI, DT, PSE.getSE());
LV.versionLoop();
// After versioning, some of the candidates' pointers could stop being
// SCEVAddRecs. We need to filter them out.
auto NoLongerGoodCandidate = [this](
const StoreToLoadForwardingCandidate &Cand) {
return !isa<SCEVAddRecExpr>(
PSE.getSCEV(Cand.Load->getPointerOperand())) ||
!isa<SCEVAddRecExpr>(
PSE.getSCEV(Cand.Store->getPointerOperand()));
};
llvm::erase_if(Candidates, NoLongerGoodCandidate);
}
// Next, propagate the value stored by the store to the users of the load.
// Also for the first iteration, generate the initial value of the load.
SCEVExpander SEE(*PSE.getSE(), L->getHeader()->getModule()->getDataLayout(),
"storeforward");
for (const auto &Cand : Candidates)
propagateStoredValueToLoadUsers(Cand, SEE);
NumLoopLoadEliminted += Candidates.size();
return true;
}
private:
Loop *L;
/// Maps the load/store instructions to their index according to
/// program order.
DenseMap<Instruction *, unsigned> InstOrder;
// Analyses used.
LoopInfo *LI;
const LoopAccessInfo &LAI;
DominatorTree *DT;
BlockFrequencyInfo *BFI;
ProfileSummaryInfo *PSI;
PredicatedScalarEvolution PSE;
};
} // end anonymous namespace
static bool
eliminateLoadsAcrossLoops(Function &F, LoopInfo &LI, DominatorTree &DT,
BlockFrequencyInfo *BFI, ProfileSummaryInfo *PSI,
ScalarEvolution *SE, AssumptionCache *AC,
function_ref<const LoopAccessInfo &(Loop &)> GetLAI) {
// Build up a worklist of inner-loops to transform to avoid iterator
// invalidation.
// FIXME: This logic comes from other passes that actually change the loop
// nest structure. It isn't clear this is necessary (or useful) for a pass
// which merely optimizes the use of loads in a loop.
SmallVector<Loop *, 8> Worklist;
bool Changed = false;
for (Loop *TopLevelLoop : LI)
for (Loop *L : depth_first(TopLevelLoop)) {
Changed |= simplifyLoop(L, &DT, &LI, SE, AC, /*MSSAU*/ nullptr, false);
// We only handle inner-most loops.
if (L->isInnermost())
Worklist.push_back(L);
}
// Now walk the identified inner loops.
for (Loop *L : Worklist) {
// Match historical behavior
if (!L->isRotatedForm() || !L->getExitingBlock())
continue;
// The actual work is performed by LoadEliminationForLoop.
LoadEliminationForLoop LEL(L, &LI, GetLAI(*L), &DT, BFI, PSI);
Changed |= LEL.processLoop();
}
return Changed;
}
namespace {
/// The pass. Most of the work is delegated to the per-loop
/// LoadEliminationForLoop class.
class LoopLoadElimination : public FunctionPass {
public:
static char ID;
LoopLoadElimination() : FunctionPass(ID) {
initializeLoopLoadEliminationPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override {
if (skipFunction(F))
return false;
auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
auto &LAA = getAnalysis<LoopAccessLegacyAnalysis>();
auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
auto *PSI = &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
auto *BFI = (PSI && PSI->hasProfileSummary()) ?
&getAnalysis<LazyBlockFrequencyInfoPass>().getBFI() :
nullptr;
auto *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
// Process each loop nest in the function.
return eliminateLoadsAcrossLoops(
F, LI, DT, BFI, PSI, SE, /*AC*/ nullptr,
[&LAA](Loop &L) -> const LoopAccessInfo & { return LAA.getInfo(&L); });
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequiredID(LoopSimplifyID);
AU.addRequired<LoopInfoWrapperPass>();
AU.addPreserved<LoopInfoWrapperPass>();
AU.addRequired<LoopAccessLegacyAnalysis>();
AU.addRequired<ScalarEvolutionWrapperPass>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addPreserved<GlobalsAAWrapperPass>();
AU.addRequired<ProfileSummaryInfoWrapperPass>();
LazyBlockFrequencyInfoPass::getLazyBFIAnalysisUsage(AU);
}
};
} // end anonymous namespace
char LoopLoadElimination::ID;
static const char LLE_name[] = "Loop Load Elimination";
INITIALIZE_PASS_BEGIN(LoopLoadElimination, LLE_OPTION, LLE_name, false, false)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopAccessLegacyAnalysis)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LazyBlockFrequencyInfoPass)
INITIALIZE_PASS_END(LoopLoadElimination, LLE_OPTION, LLE_name, false, false)
FunctionPass *llvm::createLoopLoadEliminationPass() {
return new LoopLoadElimination();
}
PreservedAnalyses LoopLoadEliminationPass::run(Function &F,
FunctionAnalysisManager &AM) {
auto &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
auto &LI = AM.getResult<LoopAnalysis>(F);
auto &TTI = AM.getResult<TargetIRAnalysis>(F);
auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
auto &AA = AM.getResult<AAManager>(F);
auto &AC = AM.getResult<AssumptionAnalysis>(F);
auto &MAMProxy = AM.getResult<ModuleAnalysisManagerFunctionProxy>(F);
auto *PSI = MAMProxy.getCachedResult<ProfileSummaryAnalysis>(*F.getParent());
auto *BFI = (PSI && PSI->hasProfileSummary()) ?
&AM.getResult<BlockFrequencyAnalysis>(F) : nullptr;
MemorySSA *MSSA = EnableMSSALoopDependency
? &AM.getResult<MemorySSAAnalysis>(F).getMSSA()
: nullptr;
auto &LAM = AM.getResult<LoopAnalysisManagerFunctionProxy>(F).getManager();
bool Changed = eliminateLoadsAcrossLoops(
F, LI, DT, BFI, PSI, &SE, &AC, [&](Loop &L) -> const LoopAccessInfo & {
LoopStandardAnalysisResults AR = {AA, AC, DT, LI, SE,
TLI, TTI, nullptr, MSSA};
return LAM.getResult<LoopAccessAnalysis>(L, AR);
});
if (!Changed)
return PreservedAnalyses::all();
PreservedAnalyses PA;
return PA;
}
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