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+//===- MemCpyOptimizer.cpp - Optimize use of memcpy and friends -----------===//
+//
+// 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 pass performs various transformations related to eliminating memcpy
+// calls, or transforming sets of stores into memset's.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar/MemCpyOptimizer.h"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/None.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/iterator_range.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/GlobalsModRef.h"
+#include "llvm/Analysis/Loads.h"
+#include "llvm/Analysis/MemoryDependenceAnalysis.h"
+#include "llvm/Analysis/MemoryLocation.h"
+#include "llvm/Analysis/MemorySSA.h"
+#include "llvm/Analysis/MemorySSAUpdater.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/Argument.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/GetElementPtrTypeIterator.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/InstrTypes.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Operator.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/IR/Type.h"
+#include "llvm/IR/User.h"
+#include "llvm/IR/Value.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/MathExtras.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include <algorithm>
+#include <cassert>
+#include <cstdint>
+#include <utility>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "memcpyopt"
+
+static cl::opt<bool>
+ EnableMemorySSA("enable-memcpyopt-memoryssa", cl::init(false), cl::Hidden,
+ cl::desc("Use MemorySSA-backed MemCpyOpt."));
+
+STATISTIC(NumMemCpyInstr, "Number of memcpy instructions deleted");
+STATISTIC(NumMemSetInfer, "Number of memsets inferred");
+STATISTIC(NumMoveToCpy, "Number of memmoves converted to memcpy");
+STATISTIC(NumCpyToSet, "Number of memcpys converted to memset");
+STATISTIC(NumCallSlot, "Number of call slot optimizations performed");
+
+namespace {
+
+/// Represents a range of memset'd bytes with the ByteVal value.
+/// This allows us to analyze stores like:
+/// store 0 -> P+1
+/// store 0 -> P+0
+/// store 0 -> P+3
+/// store 0 -> P+2
+/// which sometimes happens with stores to arrays of structs etc. When we see
+/// the first store, we make a range [1, 2). The second store extends the range
+/// to [0, 2). The third makes a new range [2, 3). The fourth store joins the
+/// two ranges into [0, 3) which is memset'able.
+struct MemsetRange {
+ // Start/End - A semi range that describes the span that this range covers.
+ // The range is closed at the start and open at the end: [Start, End).
+ int64_t Start, End;
+
+ /// StartPtr - The getelementptr instruction that points to the start of the
+ /// range.
+ Value *StartPtr;
+
+ /// Alignment - The known alignment of the first store.
+ unsigned Alignment;
+
+ /// TheStores - The actual stores that make up this range.
+ SmallVector<Instruction*, 16> TheStores;
+
+ bool isProfitableToUseMemset(const DataLayout &DL) const;
+};
+
+} // end anonymous namespace
+
+bool MemsetRange::isProfitableToUseMemset(const DataLayout &DL) const {
+ // If we found more than 4 stores to merge or 16 bytes, use memset.
+ if (TheStores.size() >= 4 || End-Start >= 16) return true;
+
+ // If there is nothing to merge, don't do anything.
+ if (TheStores.size() < 2) return false;
+
+ // If any of the stores are a memset, then it is always good to extend the
+ // memset.
+ for (Instruction *SI : TheStores)
+ if (!isa<StoreInst>(SI))
+ return true;
+
+ // Assume that the code generator is capable of merging pairs of stores
+ // together if it wants to.
+ if (TheStores.size() == 2) return false;
+
+ // If we have fewer than 8 stores, it can still be worthwhile to do this.
+ // For example, merging 4 i8 stores into an i32 store is useful almost always.
+ // However, merging 2 32-bit stores isn't useful on a 32-bit architecture (the
+ // memset will be split into 2 32-bit stores anyway) and doing so can
+ // pessimize the llvm optimizer.
+ //
+ // Since we don't have perfect knowledge here, make some assumptions: assume
+ // the maximum GPR width is the same size as the largest legal integer
+ // size. If so, check to see whether we will end up actually reducing the
+ // number of stores used.
+ unsigned Bytes = unsigned(End-Start);
+ unsigned MaxIntSize = DL.getLargestLegalIntTypeSizeInBits() / 8;
+ if (MaxIntSize == 0)
+ MaxIntSize = 1;
+ unsigned NumPointerStores = Bytes / MaxIntSize;
+
+ // Assume the remaining bytes if any are done a byte at a time.
+ unsigned NumByteStores = Bytes % MaxIntSize;
+
+ // If we will reduce the # stores (according to this heuristic), do the
+ // transformation. This encourages merging 4 x i8 -> i32 and 2 x i16 -> i32
+ // etc.
+ return TheStores.size() > NumPointerStores+NumByteStores;
+}
+
+namespace {
+
+class MemsetRanges {
+ using range_iterator = SmallVectorImpl<MemsetRange>::iterator;
+
+ /// A sorted list of the memset ranges.
+ SmallVector<MemsetRange, 8> Ranges;
+
+ const DataLayout &DL;
+
+public:
+ MemsetRanges(const DataLayout &DL) : DL(DL) {}
+
+ using const_iterator = SmallVectorImpl<MemsetRange>::const_iterator;
+
+ const_iterator begin() const { return Ranges.begin(); }
+ const_iterator end() const { return Ranges.end(); }
+ bool empty() const { return Ranges.empty(); }
+
+ void addInst(int64_t OffsetFromFirst, Instruction *Inst) {
+ if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
+ addStore(OffsetFromFirst, SI);
+ else
+ addMemSet(OffsetFromFirst, cast<MemSetInst>(Inst));
+ }
+
+ void addStore(int64_t OffsetFromFirst, StoreInst *SI) {
+ int64_t StoreSize = DL.getTypeStoreSize(SI->getOperand(0)->getType());
+
+ addRange(OffsetFromFirst, StoreSize, SI->getPointerOperand(),
+ SI->getAlign().value(), SI);
+ }
+
+ void addMemSet(int64_t OffsetFromFirst, MemSetInst *MSI) {
+ int64_t Size = cast<ConstantInt>(MSI->getLength())->getZExtValue();
+ addRange(OffsetFromFirst, Size, MSI->getDest(), MSI->getDestAlignment(), MSI);
+ }
+
+ void addRange(int64_t Start, int64_t Size, Value *Ptr,
+ unsigned Alignment, Instruction *Inst);
+};
+
+} // end anonymous namespace
+
+/// Add a new store to the MemsetRanges data structure. This adds a
+/// new range for the specified store at the specified offset, merging into
+/// existing ranges as appropriate.
+void MemsetRanges::addRange(int64_t Start, int64_t Size, Value *Ptr,
+ unsigned Alignment, Instruction *Inst) {
+ int64_t End = Start+Size;
+
+ range_iterator I = partition_point(
+ Ranges, [=](const MemsetRange &O) { return O.End < Start; });
+
+ // We now know that I == E, in which case we didn't find anything to merge
+ // with, or that Start <= I->End. If End < I->Start or I == E, then we need
+ // to insert a new range. Handle this now.
+ if (I == Ranges.end() || End < I->Start) {
+ MemsetRange &R = *Ranges.insert(I, MemsetRange());
+ R.Start = Start;
+ R.End = End;
+ R.StartPtr = Ptr;
+ R.Alignment = Alignment;
+ R.TheStores.push_back(Inst);
+ return;
+ }
+
+ // This store overlaps with I, add it.
+ I->TheStores.push_back(Inst);
+
+ // At this point, we may have an interval that completely contains our store.
+ // If so, just add it to the interval and return.
+ if (I->Start <= Start && I->End >= End)
+ return;
+
+ // Now we know that Start <= I->End and End >= I->Start so the range overlaps
+ // but is not entirely contained within the range.
+
+ // See if the range extends the start of the range. In this case, it couldn't
+ // possibly cause it to join the prior range, because otherwise we would have
+ // stopped on *it*.
+ if (Start < I->Start) {
+ I->Start = Start;
+ I->StartPtr = Ptr;
+ I->Alignment = Alignment;
+ }
+
+ // Now we know that Start <= I->End and Start >= I->Start (so the startpoint
+ // is in or right at the end of I), and that End >= I->Start. Extend I out to
+ // End.
+ if (End > I->End) {
+ I->End = End;
+ range_iterator NextI = I;
+ while (++NextI != Ranges.end() && End >= NextI->Start) {
+ // Merge the range in.
+ I->TheStores.append(NextI->TheStores.begin(), NextI->TheStores.end());
+ if (NextI->End > I->End)
+ I->End = NextI->End;
+ Ranges.erase(NextI);
+ NextI = I;
+ }
+ }
+}
+
+//===----------------------------------------------------------------------===//
+// MemCpyOptLegacyPass Pass
+//===----------------------------------------------------------------------===//
+
+namespace {
+
+class MemCpyOptLegacyPass : public FunctionPass {
+ MemCpyOptPass Impl;
+
+public:
+ static char ID; // Pass identification, replacement for typeid
+
+ MemCpyOptLegacyPass() : FunctionPass(ID) {
+ initializeMemCpyOptLegacyPassPass(*PassRegistry::getPassRegistry());
+ }
+
+ bool runOnFunction(Function &F) override;
+
+private:
+ // This transformation requires dominator postdominator info
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.setPreservesCFG();
+ AU.addRequired<AssumptionCacheTracker>();
+ AU.addRequired<DominatorTreeWrapperPass>();
+ AU.addPreserved<DominatorTreeWrapperPass>();
+ AU.addPreserved<GlobalsAAWrapperPass>();
+ AU.addRequired<TargetLibraryInfoWrapperPass>();
+ if (!EnableMemorySSA)
+ AU.addRequired<MemoryDependenceWrapperPass>();
+ AU.addPreserved<MemoryDependenceWrapperPass>();
+ AU.addRequired<AAResultsWrapperPass>();
+ AU.addPreserved<AAResultsWrapperPass>();
+ if (EnableMemorySSA)
+ AU.addRequired<MemorySSAWrapperPass>();
+ AU.addPreserved<MemorySSAWrapperPass>();
+ }
+};
+
+} // end anonymous namespace
+
+char MemCpyOptLegacyPass::ID = 0;
+
+/// The public interface to this file...
+FunctionPass *llvm::createMemCpyOptPass() { return new MemCpyOptLegacyPass(); }
+
+INITIALIZE_PASS_BEGIN(MemCpyOptLegacyPass, "memcpyopt", "MemCpy Optimization",
+ false, false)
+INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
+INITIALIZE_PASS_END(MemCpyOptLegacyPass, "memcpyopt", "MemCpy Optimization",
+ false, false)
+
+// Check that V is either not accessible by the caller, or unwinding cannot
+// occur between Start and End.
+static bool mayBeVisibleThroughUnwinding(Value *V, Instruction *Start,
+ Instruction *End) {
+ assert(Start->getParent() == End->getParent() && "Must be in same block");
+ if (!Start->getFunction()->doesNotThrow() &&
+ !isa<AllocaInst>(getUnderlyingObject(V))) {
+ for (const Instruction &I :
+ make_range(Start->getIterator(), End->getIterator())) {
+ if (I.mayThrow())
+ return true;
+ }
+ }
+ return false;
+}
+
+void MemCpyOptPass::eraseInstruction(Instruction *I) {
+ if (MSSAU)
+ MSSAU->removeMemoryAccess(I);
+ if (MD)
+ MD->removeInstruction(I);
+ I->eraseFromParent();
+}
+
+// Check for mod or ref of Loc between Start and End, excluding both boundaries.
+// Start and End must be in the same block
+static bool accessedBetween(AliasAnalysis &AA, MemoryLocation Loc,
+ const MemoryUseOrDef *Start,
+ const MemoryUseOrDef *End) {
+ assert(Start->getBlock() == End->getBlock() && "Only local supported");
+ for (const MemoryAccess &MA :
+ make_range(++Start->getIterator(), End->getIterator())) {
+ if (isModOrRefSet(AA.getModRefInfo(cast<MemoryUseOrDef>(MA).getMemoryInst(),
+ Loc)))
+ return true;
+ }
+ return false;
+}
+
+// Check for mod of Loc between Start and End, excluding both boundaries.
+// Start and End can be in different blocks.
+static bool writtenBetween(MemorySSA *MSSA, MemoryLocation Loc,
+ const MemoryUseOrDef *Start,
+ const MemoryUseOrDef *End) {
+ // TODO: Only walk until we hit Start.
+ MemoryAccess *Clobber = MSSA->getWalker()->getClobberingMemoryAccess(
+ End->getDefiningAccess(), Loc);
+ return !MSSA->dominates(Clobber, Start);
+}
+
+/// When scanning forward over instructions, we look for some other patterns to
+/// fold away. In particular, this looks for stores to neighboring locations of
+/// memory. If it sees enough consecutive ones, it attempts to merge them
+/// together into a memcpy/memset.
+Instruction *MemCpyOptPass::tryMergingIntoMemset(Instruction *StartInst,
+ Value *StartPtr,
+ Value *ByteVal) {
+ const DataLayout &DL = StartInst->getModule()->getDataLayout();
+
+ // Okay, so we now have a single store that can be splatable. Scan to find
+ // all subsequent stores of the same value to offset from the same pointer.
+ // Join these together into ranges, so we can decide whether contiguous blocks
+ // are stored.
+ MemsetRanges Ranges(DL);
+
+ BasicBlock::iterator BI(StartInst);
+
+ // Keeps track of the last memory use or def before the insertion point for
+ // the new memset. The new MemoryDef for the inserted memsets will be inserted
+ // after MemInsertPoint. It points to either LastMemDef or to the last user
+ // before the insertion point of the memset, if there are any such users.
+ MemoryUseOrDef *MemInsertPoint = nullptr;
+ // Keeps track of the last MemoryDef between StartInst and the insertion point
+ // for the new memset. This will become the defining access of the inserted
+ // memsets.
+ MemoryDef *LastMemDef = nullptr;
+ for (++BI; !BI->isTerminator(); ++BI) {
+ if (MSSAU) {
+ auto *CurrentAcc = cast_or_null<MemoryUseOrDef>(
+ MSSAU->getMemorySSA()->getMemoryAccess(&*BI));
+ if (CurrentAcc) {
+ MemInsertPoint = CurrentAcc;
+ if (auto *CurrentDef = dyn_cast<MemoryDef>(CurrentAcc))
+ LastMemDef = CurrentDef;
+ }
+ }
+
+ if (!isa<StoreInst>(BI) && !isa<MemSetInst>(BI)) {
+ // If the instruction is readnone, ignore it, otherwise bail out. We
+ // don't even allow readonly here because we don't want something like:
+ // A[1] = 2; strlen(A); A[2] = 2; -> memcpy(A, ...); strlen(A).
+ if (BI->mayWriteToMemory() || BI->mayReadFromMemory())
+ break;
+ continue;
+ }
+
+ if (StoreInst *NextStore = dyn_cast<StoreInst>(BI)) {
+ // If this is a store, see if we can merge it in.
+ if (!NextStore->isSimple()) break;
+
+ Value *StoredVal = NextStore->getValueOperand();
+
+ // Don't convert stores of non-integral pointer types to memsets (which
+ // stores integers).
+ if (DL.isNonIntegralPointerType(StoredVal->getType()->getScalarType()))
+ break;
+
+ // Check to see if this stored value is of the same byte-splattable value.
+ Value *StoredByte = isBytewiseValue(StoredVal, DL);
+ if (isa<UndefValue>(ByteVal) && StoredByte)
+ ByteVal = StoredByte;
+ if (ByteVal != StoredByte)
+ break;
+
+ // Check to see if this store is to a constant offset from the start ptr.
+ Optional<int64_t> Offset =
+ isPointerOffset(StartPtr, NextStore->getPointerOperand(), DL);
+ if (!Offset)
+ break;
+
+ Ranges.addStore(*Offset, NextStore);
+ } else {
+ MemSetInst *MSI = cast<MemSetInst>(BI);
+
+ if (MSI->isVolatile() || ByteVal != MSI->getValue() ||
+ !isa<ConstantInt>(MSI->getLength()))
+ break;
+
+ // Check to see if this store is to a constant offset from the start ptr.
+ Optional<int64_t> Offset = isPointerOffset(StartPtr, MSI->getDest(), DL);
+ if (!Offset)
+ break;
+
+ Ranges.addMemSet(*Offset, MSI);
+ }
+ }
+
+ // If we have no ranges, then we just had a single store with nothing that
+ // could be merged in. This is a very common case of course.
+ if (Ranges.empty())
+ return nullptr;
+
+ // If we had at least one store that could be merged in, add the starting
+ // store as well. We try to avoid this unless there is at least something
+ // interesting as a small compile-time optimization.
+ Ranges.addInst(0, StartInst);
+
+ // If we create any memsets, we put it right before the first instruction that
+ // isn't part of the memset block. This ensure that the memset is dominated
+ // by any addressing instruction needed by the start of the block.
+ IRBuilder<> Builder(&*BI);
+
+ // Now that we have full information about ranges, loop over the ranges and
+ // emit memset's for anything big enough to be worthwhile.
+ Instruction *AMemSet = nullptr;
+ for (const MemsetRange &Range : Ranges) {
+ if (Range.TheStores.size() == 1) continue;
+
+ // If it is profitable to lower this range to memset, do so now.
+ if (!Range.isProfitableToUseMemset(DL))
+ continue;
+
+ // Otherwise, we do want to transform this! Create a new memset.
+ // Get the starting pointer of the block.
+ StartPtr = Range.StartPtr;
+
+ AMemSet = Builder.CreateMemSet(StartPtr, ByteVal, Range.End - Range.Start,
+ MaybeAlign(Range.Alignment));
+ LLVM_DEBUG(dbgs() << "Replace stores:\n"; for (Instruction *SI
+ : Range.TheStores) dbgs()
+ << *SI << '\n';
+ dbgs() << "With: " << *AMemSet << '\n');
+ if (!Range.TheStores.empty())
+ AMemSet->setDebugLoc(Range.TheStores[0]->getDebugLoc());
+
+ if (MSSAU) {
+ assert(LastMemDef && MemInsertPoint &&
+ "Both LastMemDef and MemInsertPoint need to be set");
+ auto *NewDef =
+ cast<MemoryDef>(MemInsertPoint->getMemoryInst() == &*BI
+ ? MSSAU->createMemoryAccessBefore(
+ AMemSet, LastMemDef, MemInsertPoint)
+ : MSSAU->createMemoryAccessAfter(
+ AMemSet, LastMemDef, MemInsertPoint));
+ MSSAU->insertDef(NewDef, /*RenameUses=*/true);
+ LastMemDef = NewDef;
+ MemInsertPoint = NewDef;
+ }
+
+ // Zap all the stores.
+ for (Instruction *SI : Range.TheStores)
+ eraseInstruction(SI);
+
+ ++NumMemSetInfer;
+ }
+
+ return AMemSet;
+}
+
+// This method try to lift a store instruction before position P.
+// It will lift the store and its argument + that anything that
+// may alias with these.
+// The method returns true if it was successful.
+bool MemCpyOptPass::moveUp(StoreInst *SI, Instruction *P, const LoadInst *LI) {
+ // If the store alias this position, early bail out.
+ MemoryLocation StoreLoc = MemoryLocation::get(SI);
+ if (isModOrRefSet(AA->getModRefInfo(P, StoreLoc)))
+ return false;
+
+ // Keep track of the arguments of all instruction we plan to lift
+ // so we can make sure to lift them as well if appropriate.
+ DenseSet<Instruction*> Args;
+ if (auto *Ptr = dyn_cast<Instruction>(SI->getPointerOperand()))
+ if (Ptr->getParent() == SI->getParent())
+ Args.insert(Ptr);
+
+ // Instruction to lift before P.
+ SmallVector<Instruction *, 8> ToLift{SI};
+
+ // Memory locations of lifted instructions.
+ SmallVector<MemoryLocation, 8> MemLocs{StoreLoc};
+
+ // Lifted calls.
+ SmallVector<const CallBase *, 8> Calls;
+
+ const MemoryLocation LoadLoc = MemoryLocation::get(LI);
+
+ for (auto I = --SI->getIterator(), E = P->getIterator(); I != E; --I) {
+ auto *C = &*I;
+
+ // Make sure hoisting does not perform a store that was not guaranteed to
+ // happen.
+ if (!isGuaranteedToTransferExecutionToSuccessor(C))
+ return false;
+
+ bool MayAlias = isModOrRefSet(AA->getModRefInfo(C, None));
+
+ bool NeedLift = false;
+ if (Args.erase(C))
+ NeedLift = true;
+ else if (MayAlias) {
+ NeedLift = llvm::any_of(MemLocs, [C, this](const MemoryLocation &ML) {
+ return isModOrRefSet(AA->getModRefInfo(C, ML));
+ });
+
+ if (!NeedLift)
+ NeedLift = llvm::any_of(Calls, [C, this](const CallBase *Call) {
+ return isModOrRefSet(AA->getModRefInfo(C, Call));
+ });
+ }
+
+ if (!NeedLift)
+ continue;
+
+ if (MayAlias) {
+ // Since LI is implicitly moved downwards past the lifted instructions,
+ // none of them may modify its source.
+ if (isModSet(AA->getModRefInfo(C, LoadLoc)))
+ return false;
+ else if (const auto *Call = dyn_cast<CallBase>(C)) {
+ // If we can't lift this before P, it's game over.
+ if (isModOrRefSet(AA->getModRefInfo(P, Call)))
+ return false;
+
+ Calls.push_back(Call);
+ } else if (isa<LoadInst>(C) || isa<StoreInst>(C) || isa<VAArgInst>(C)) {
+ // If we can't lift this before P, it's game over.
+ auto ML = MemoryLocation::get(C);
+ if (isModOrRefSet(AA->getModRefInfo(P, ML)))
+ return false;
+
+ MemLocs.push_back(ML);
+ } else
+ // We don't know how to lift this instruction.
+ return false;
+ }
+
+ ToLift.push_back(C);
+ for (unsigned k = 0, e = C->getNumOperands(); k != e; ++k)
+ if (auto *A = dyn_cast<Instruction>(C->getOperand(k))) {
+ if (A->getParent() == SI->getParent()) {
+ // Cannot hoist user of P above P
+ if(A == P) return false;
+ Args.insert(A);
+ }
+ }
+ }
+
+ // Find MSSA insertion point. Normally P will always have a corresponding
+ // memory access before which we can insert. However, with non-standard AA
+ // pipelines, there may be a mismatch between AA and MSSA, in which case we
+ // will scan for a memory access before P. In either case, we know for sure
+ // that at least the load will have a memory access.
+ // TODO: Simplify this once P will be determined by MSSA, in which case the
+ // discrepancy can no longer occur.
+ MemoryUseOrDef *MemInsertPoint = nullptr;
+ if (MSSAU) {
+ if (MemoryUseOrDef *MA = MSSAU->getMemorySSA()->getMemoryAccess(P)) {
+ MemInsertPoint = cast<MemoryUseOrDef>(--MA->getIterator());
+ } else {
+ const Instruction *ConstP = P;
+ for (const Instruction &I : make_range(++ConstP->getReverseIterator(),
+ ++LI->getReverseIterator())) {
+ if (MemoryUseOrDef *MA = MSSAU->getMemorySSA()->getMemoryAccess(&I)) {
+ MemInsertPoint = MA;
+ break;
+ }
+ }
+ }
+ }
+
+ // We made it, we need to lift.
+ for (auto *I : llvm::reverse(ToLift)) {
+ LLVM_DEBUG(dbgs() << "Lifting " << *I << " before " << *P << "\n");
+ I->moveBefore(P);
+ if (MSSAU) {
+ assert(MemInsertPoint && "Must have found insert point");
+ if (MemoryUseOrDef *MA = MSSAU->getMemorySSA()->getMemoryAccess(I)) {
+ MSSAU->moveAfter(MA, MemInsertPoint);
+ MemInsertPoint = MA;
+ }
+ }
+ }
+
+ return true;
+}
+
+bool MemCpyOptPass::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
+ if (!SI->isSimple()) return false;
+
+ // Avoid merging nontemporal stores since the resulting
+ // memcpy/memset would not be able to preserve the nontemporal hint.
+ // In theory we could teach how to propagate the !nontemporal metadata to
+ // memset calls. However, that change would force the backend to
+ // conservatively expand !nontemporal memset calls back to sequences of
+ // store instructions (effectively undoing the merging).
+ if (SI->getMetadata(LLVMContext::MD_nontemporal))
+ return false;
+
+ const DataLayout &DL = SI->getModule()->getDataLayout();
+
+ Value *StoredVal = SI->getValueOperand();
+
+ // Not all the transforms below are correct for non-integral pointers, bail
+ // until we've audited the individual pieces.
+ if (DL.isNonIntegralPointerType(StoredVal->getType()->getScalarType()))
+ return false;
+
+ // Load to store forwarding can be interpreted as memcpy.
+ if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
+ if (LI->isSimple() && LI->hasOneUse() &&
+ LI->getParent() == SI->getParent()) {
+
+ auto *T = LI->getType();
+ if (T->isAggregateType()) {
+ MemoryLocation LoadLoc = MemoryLocation::get(LI);
+
+ // We use alias analysis to check if an instruction may store to
+ // the memory we load from in between the load and the store. If
+ // such an instruction is found, we try to promote there instead
+ // of at the store position.
+ // TODO: Can use MSSA for this.
+ Instruction *P = SI;
+ for (auto &I : make_range(++LI->getIterator(), SI->getIterator())) {
+ if (isModSet(AA->getModRefInfo(&I, LoadLoc))) {
+ P = &I;
+ break;
+ }
+ }
+
+ // We found an instruction that may write to the loaded memory.
+ // We can try to promote at this position instead of the store
+ // position if nothing alias the store memory after this and the store
+ // destination is not in the range.
+ if (P && P != SI) {
+ if (!moveUp(SI, P, LI))
+ P = nullptr;
+ }
+
+ // If a valid insertion position is found, then we can promote
+ // the load/store pair to a memcpy.
+ if (P) {
+ // If we load from memory that may alias the memory we store to,
+ // memmove must be used to preserve semantic. If not, memcpy can
+ // be used.
+ bool UseMemMove = false;
+ if (!AA->isNoAlias(MemoryLocation::get(SI), LoadLoc))
+ UseMemMove = true;
+
+ uint64_t Size = DL.getTypeStoreSize(T);
+
+ IRBuilder<> Builder(P);
+ Instruction *M;
+ if (UseMemMove)
+ M = Builder.CreateMemMove(
+ SI->getPointerOperand(), SI->getAlign(),
+ LI->getPointerOperand(), LI->getAlign(), Size);
+ else
+ M = Builder.CreateMemCpy(
+ SI->getPointerOperand(), SI->getAlign(),
+ LI->getPointerOperand(), LI->getAlign(), Size);
+
+ LLVM_DEBUG(dbgs() << "Promoting " << *LI << " to " << *SI << " => "
+ << *M << "\n");
+
+ if (MSSAU) {
+ auto *LastDef =
+ cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(SI));
+ auto *NewAccess =
+ MSSAU->createMemoryAccessAfter(M, LastDef, LastDef);
+ MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
+ }
+
+ eraseInstruction(SI);
+ eraseInstruction(LI);
+ ++NumMemCpyInstr;
+
+ // Make sure we do not invalidate the iterator.
+ BBI = M->getIterator();
+ return true;
+ }
+ }
+
+ // Detect cases where we're performing call slot forwarding, but
+ // happen to be using a load-store pair to implement it, rather than
+ // a memcpy.
+ CallInst *C = nullptr;
+ if (EnableMemorySSA) {
+ if (auto *LoadClobber = dyn_cast<MemoryUseOrDef>(
+ MSSA->getWalker()->getClobberingMemoryAccess(LI))) {
+ // The load most post-dom the call. Limit to the same block for now.
+ // TODO: Support non-local call-slot optimization?
+ if (LoadClobber->getBlock() == SI->getParent())
+ C = dyn_cast_or_null<CallInst>(LoadClobber->getMemoryInst());
+ }
+ } else {
+ MemDepResult ldep = MD->getDependency(LI);
+ if (ldep.isClobber() && !isa<MemCpyInst>(ldep.getInst()))
+ C = dyn_cast<CallInst>(ldep.getInst());
+ }
+
+ if (C) {
+ // Check that nothing touches the dest of the "copy" between
+ // the call and the store.
+ MemoryLocation StoreLoc = MemoryLocation::get(SI);
+ if (EnableMemorySSA) {
+ if (accessedBetween(*AA, StoreLoc, MSSA->getMemoryAccess(C),
+ MSSA->getMemoryAccess(SI)))
+ C = nullptr;
+ } else {
+ for (BasicBlock::iterator I = --SI->getIterator(),
+ E = C->getIterator();
+ I != E; --I) {
+ if (isModOrRefSet(AA->getModRefInfo(&*I, StoreLoc))) {
+ C = nullptr;
+ break;
+ }
+ }
+ }
+ }
+
+ if (C) {
+ bool changed = performCallSlotOptzn(
+ LI, SI, SI->getPointerOperand()->stripPointerCasts(),
+ LI->getPointerOperand()->stripPointerCasts(),
+ DL.getTypeStoreSize(SI->getOperand(0)->getType()),
+ commonAlignment(SI->getAlign(), LI->getAlign()), C);
+ if (changed) {
+ eraseInstruction(SI);
+ eraseInstruction(LI);
+ ++NumMemCpyInstr;
+ return true;
+ }
+ }
+ }
+ }
+
+ // There are two cases that are interesting for this code to handle: memcpy
+ // and memset. Right now we only handle memset.
+
+ // Ensure that the value being stored is something that can be memset'able a
+ // byte at a time like "0" or "-1" or any width, as well as things like
+ // 0xA0A0A0A0 and 0.0.
+ auto *V = SI->getOperand(0);
+ if (Value *ByteVal = isBytewiseValue(V, DL)) {
+ if (Instruction *I = tryMergingIntoMemset(SI, SI->getPointerOperand(),
+ ByteVal)) {
+ BBI = I->getIterator(); // Don't invalidate iterator.
+ return true;
+ }
+
+ // If we have an aggregate, we try to promote it to memset regardless
+ // of opportunity for merging as it can expose optimization opportunities
+ // in subsequent passes.
+ auto *T = V->getType();
+ if (T->isAggregateType()) {
+ uint64_t Size = DL.getTypeStoreSize(T);
+ IRBuilder<> Builder(SI);
+ auto *M = Builder.CreateMemSet(SI->getPointerOperand(), ByteVal, Size,
+ SI->getAlign());
+
+ LLVM_DEBUG(dbgs() << "Promoting " << *SI << " to " << *M << "\n");
+
+ if (MSSAU) {
+ assert(isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(SI)));
+ auto *LastDef =
+ cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(SI));
+ auto *NewAccess = MSSAU->createMemoryAccessAfter(M, LastDef, LastDef);
+ MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
+ }
+
+ eraseInstruction(SI);
+ NumMemSetInfer++;
+
+ // Make sure we do not invalidate the iterator.
+ BBI = M->getIterator();
+ return true;
+ }
+ }
+
+ return false;
+}
+
+bool MemCpyOptPass::processMemSet(MemSetInst *MSI, BasicBlock::iterator &BBI) {
+ // See if there is another memset or store neighboring this memset which
+ // allows us to widen out the memset to do a single larger store.
+ if (isa<ConstantInt>(MSI->getLength()) && !MSI->isVolatile())
+ if (Instruction *I = tryMergingIntoMemset(MSI, MSI->getDest(),
+ MSI->getValue())) {
+ BBI = I->getIterator(); // Don't invalidate iterator.
+ return true;
+ }
+ return false;
+}
+
+/// Takes a memcpy and a call that it depends on,
+/// and checks for the possibility of a call slot optimization by having
+/// the call write its result directly into the destination of the memcpy.
+bool MemCpyOptPass::performCallSlotOptzn(Instruction *cpyLoad,
+ Instruction *cpyStore, Value *cpyDest,
+ Value *cpySrc, uint64_t cpyLen,
+ Align cpyAlign, CallInst *C) {
+ // The general transformation to keep in mind is
+ //
+ // call @func(..., src, ...)
+ // memcpy(dest, src, ...)
+ //
+ // ->
+ //
+ // memcpy(dest, src, ...)
+ // call @func(..., dest, ...)
+ //
+ // Since moving the memcpy is technically awkward, we additionally check that
+ // src only holds uninitialized values at the moment of the call, meaning that
+ // the memcpy can be discarded rather than moved.
+
+ // Lifetime marks shouldn't be operated on.
+ if (Function *F = C->getCalledFunction())
+ if (F->isIntrinsic() && F->getIntrinsicID() == Intrinsic::lifetime_start)
+ return false;
+
+ // Require that src be an alloca. This simplifies the reasoning considerably.
+ AllocaInst *srcAlloca = dyn_cast<AllocaInst>(cpySrc);
+ if (!srcAlloca)
+ return false;
+
+ ConstantInt *srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize());
+ if (!srcArraySize)
+ return false;
+
+ const DataLayout &DL = cpyLoad->getModule()->getDataLayout();
+ uint64_t srcSize = DL.getTypeAllocSize(srcAlloca->getAllocatedType()) *
+ srcArraySize->getZExtValue();
+
+ if (cpyLen < srcSize)
+ return false;
+
+ // Check that accessing the first srcSize bytes of dest will not cause a
+ // trap. Otherwise the transform is invalid since it might cause a trap
+ // to occur earlier than it otherwise would.
+ if (!isDereferenceableAndAlignedPointer(cpyDest, Align(1), APInt(64, cpyLen),
+ DL, C, DT))
+ return false;
+
+ // Make sure that nothing can observe cpyDest being written early. There are
+ // a number of cases to consider:
+ // 1. cpyDest cannot be accessed between C and cpyStore as a precondition of
+ // the transform.
+ // 2. C itself may not access cpyDest (prior to the transform). This is
+ // checked further below.
+ // 3. If cpyDest is accessible to the caller of this function (potentially
+ // captured and not based on an alloca), we need to ensure that we cannot
+ // unwind between C and cpyStore. This is checked here.
+ // 4. If cpyDest is potentially captured, there may be accesses to it from
+ // another thread. In this case, we need to check that cpyStore is
+ // guaranteed to be executed if C is. As it is a non-atomic access, it
+ // renders accesses from other threads undefined.
+ // TODO: This is currently not checked.
+ if (mayBeVisibleThroughUnwinding(cpyDest, C, cpyStore))
+ return false;
+
+ // Check that dest points to memory that is at least as aligned as src.
+ Align srcAlign = srcAlloca->getAlign();
+ bool isDestSufficientlyAligned = srcAlign <= cpyAlign;
+ // If dest is not aligned enough and we can't increase its alignment then
+ // bail out.
+ if (!isDestSufficientlyAligned && !isa<AllocaInst>(cpyDest))
+ return false;
+
+ // Check that src is not accessed except via the call and the memcpy. This
+ // guarantees that it holds only undefined values when passed in (so the final
+ // memcpy can be dropped), that it is not read or written between the call and
+ // the memcpy, and that writing beyond the end of it is undefined.
+ SmallVector<User *, 8> srcUseList(srcAlloca->users());
+ while (!srcUseList.empty()) {
+ User *U = srcUseList.pop_back_val();
+
+ if (isa<BitCastInst>(U) || isa<AddrSpaceCastInst>(U)) {
+ append_range(srcUseList, U->users());
+ continue;
+ }
+ if (GetElementPtrInst *G = dyn_cast<GetElementPtrInst>(U)) {
+ if (!G->hasAllZeroIndices())
+ return false;
+
+ append_range(srcUseList, U->users());
+ continue;
+ }
+ if (const IntrinsicInst *IT = dyn_cast<IntrinsicInst>(U))
+ if (IT->isLifetimeStartOrEnd())
+ continue;
+
+ if (U != C && U != cpyLoad)
+ return false;
+ }
+
+ // Check that src isn't captured by the called function since the
+ // transformation can cause aliasing issues in that case.
+ for (unsigned ArgI = 0, E = C->arg_size(); ArgI != E; ++ArgI)
+ if (C->getArgOperand(ArgI) == cpySrc && !C->doesNotCapture(ArgI))
+ return false;
+
+ // Since we're changing the parameter to the callsite, we need to make sure
+ // that what would be the new parameter dominates the callsite.
+ if (!DT->dominates(cpyDest, C)) {
+ // Support moving a constant index GEP before the call.
+ auto *GEP = dyn_cast<GetElementPtrInst>(cpyDest);
+ if (GEP && GEP->hasAllConstantIndices() &&
+ DT->dominates(GEP->getPointerOperand(), C))
+ GEP->moveBefore(C);
+ else
+ return false;
+ }
+
+ // In addition to knowing that the call does not access src in some
+ // unexpected manner, for example via a global, which we deduce from
+ // the use analysis, we also need to know that it does not sneakily
+ // access dest. We rely on AA to figure this out for us.
+ ModRefInfo MR = AA->getModRefInfo(C, cpyDest, LocationSize::precise(srcSize));
+ // If necessary, perform additional analysis.
+ if (isModOrRefSet(MR))
+ MR = AA->callCapturesBefore(C, cpyDest, LocationSize::precise(srcSize), DT);
+ if (isModOrRefSet(MR))
+ return false;
+
+ // We can't create address space casts here because we don't know if they're
+ // safe for the target.
+ if (cpySrc->getType()->getPointerAddressSpace() !=
+ cpyDest->getType()->getPointerAddressSpace())
+ return false;
+ for (unsigned ArgI = 0; ArgI < C->arg_size(); ++ArgI)
+ if (C->getArgOperand(ArgI)->stripPointerCasts() == cpySrc &&
+ cpySrc->getType()->getPointerAddressSpace() !=
+ C->getArgOperand(ArgI)->getType()->getPointerAddressSpace())
+ return false;
+
+ // All the checks have passed, so do the transformation.
+ bool changedArgument = false;
+ for (unsigned ArgI = 0; ArgI < C->arg_size(); ++ArgI)
+ if (C->getArgOperand(ArgI)->stripPointerCasts() == cpySrc) {
+ Value *Dest = cpySrc->getType() == cpyDest->getType() ? cpyDest
+ : CastInst::CreatePointerCast(cpyDest, cpySrc->getType(),
+ cpyDest->getName(), C);
+ changedArgument = true;
+ if (C->getArgOperand(ArgI)->getType() == Dest->getType())
+ C->setArgOperand(ArgI, Dest);
+ else
+ C->setArgOperand(ArgI, CastInst::CreatePointerCast(
+ Dest, C->getArgOperand(ArgI)->getType(),
+ Dest->getName(), C));
+ }
+
+ if (!changedArgument)
+ return false;
+
+ // If the destination wasn't sufficiently aligned then increase its alignment.
+ if (!isDestSufficientlyAligned) {
+ assert(isa<AllocaInst>(cpyDest) && "Can only increase alloca alignment!");
+ cast<AllocaInst>(cpyDest)->setAlignment(srcAlign);
+ }
+
+ // Drop any cached information about the call, because we may have changed
+ // its dependence information by changing its parameter.
+ if (MD)
+ MD->removeInstruction(C);
+
+ // Update AA metadata
+ // FIXME: MD_tbaa_struct and MD_mem_parallel_loop_access should also be
+ // handled here, but combineMetadata doesn't support them yet
+ unsigned KnownIDs[] = {LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
+ LLVMContext::MD_noalias,
+ LLVMContext::MD_invariant_group,
+ LLVMContext::MD_access_group};
+ combineMetadata(C, cpyLoad, KnownIDs, true);
+
+ ++NumCallSlot;
+ return true;
+}
+
+/// We've found that the (upward scanning) memory dependence of memcpy 'M' is
+/// the memcpy 'MDep'. Try to simplify M to copy from MDep's input if we can.
+bool MemCpyOptPass::processMemCpyMemCpyDependence(MemCpyInst *M,
+ MemCpyInst *MDep) {
+ // We can only transforms memcpy's where the dest of one is the source of the
+ // other.
+ if (M->getSource() != MDep->getDest() || MDep->isVolatile())
+ return false;
+
+ // If dep instruction is reading from our current input, then it is a noop
+ // transfer and substituting the input won't change this instruction. Just
+ // ignore the input and let someone else zap MDep. This handles cases like:
+ // memcpy(a <- a)
+ // memcpy(b <- a)
+ if (M->getSource() == MDep->getSource())
+ return false;
+
+ // Second, the length of the memcpy's must be the same, or the preceding one
+ // must be larger than the following one.
+ ConstantInt *MDepLen = dyn_cast<ConstantInt>(MDep->getLength());
+ ConstantInt *MLen = dyn_cast<ConstantInt>(M->getLength());
+ if (!MDepLen || !MLen || MDepLen->getZExtValue() < MLen->getZExtValue())
+ return false;
+
+ // Verify that the copied-from memory doesn't change in between the two
+ // transfers. For example, in:
+ // memcpy(a <- b)
+ // *b = 42;
+ // memcpy(c <- a)
+ // It would be invalid to transform the second memcpy into memcpy(c <- b).
+ //
+ // TODO: If the code between M and MDep is transparent to the destination "c",
+ // then we could still perform the xform by moving M up to the first memcpy.
+ if (EnableMemorySSA) {
+ // TODO: It would be sufficient to check the MDep source up to the memcpy
+ // size of M, rather than MDep.
+ if (writtenBetween(MSSA, MemoryLocation::getForSource(MDep),
+ MSSA->getMemoryAccess(MDep), MSSA->getMemoryAccess(M)))
+ return false;
+ } else {
+ // NOTE: This is conservative, it will stop on any read from the source loc,
+ // not just the defining memcpy.
+ MemDepResult SourceDep =
+ MD->getPointerDependencyFrom(MemoryLocation::getForSource(MDep), false,
+ M->getIterator(), M->getParent());
+ if (!SourceDep.isClobber() || SourceDep.getInst() != MDep)
+ return false;
+ }
+
+ // If the dest of the second might alias the source of the first, then the
+ // source and dest might overlap. We still want to eliminate the intermediate
+ // value, but we have to generate a memmove instead of memcpy.
+ bool UseMemMove = false;
+ if (!AA->isNoAlias(MemoryLocation::getForDest(M),
+ MemoryLocation::getForSource(MDep)))
+ UseMemMove = true;
+
+ // If all checks passed, then we can transform M.
+ LLVM_DEBUG(dbgs() << "MemCpyOptPass: Forwarding memcpy->memcpy src:\n"
+ << *MDep << '\n' << *M << '\n');
+
+ // TODO: Is this worth it if we're creating a less aligned memcpy? For
+ // example we could be moving from movaps -> movq on x86.
+ IRBuilder<> Builder(M);
+ Instruction *NewM;
+ if (UseMemMove)
+ NewM = Builder.CreateMemMove(M->getRawDest(), M->getDestAlign(),
+ MDep->getRawSource(), MDep->getSourceAlign(),
+ M->getLength(), M->isVolatile());
+ else
+ NewM = Builder.CreateMemCpy(M->getRawDest(), M->getDestAlign(),
+ MDep->getRawSource(), MDep->getSourceAlign(),
+ M->getLength(), M->isVolatile());
+
+ if (MSSAU) {
+ assert(isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(M)));
+ auto *LastDef = cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(M));
+ auto *NewAccess = MSSAU->createMemoryAccessAfter(NewM, LastDef, LastDef);
+ MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
+ }
+
+ // Remove the instruction we're replacing.
+ eraseInstruction(M);
+ ++NumMemCpyInstr;
+ return true;
+}
+
+/// We've found that the (upward scanning) memory dependence of \p MemCpy is
+/// \p MemSet. Try to simplify \p MemSet to only set the trailing bytes that
+/// weren't copied over by \p MemCpy.
+///
+/// In other words, transform:
+/// \code
+/// memset(dst, c, dst_size);
+/// memcpy(dst, src, src_size);
+/// \endcode
+/// into:
+/// \code
+/// memcpy(dst, src, src_size);
+/// memset(dst + src_size, c, dst_size <= src_size ? 0 : dst_size - src_size);
+/// \endcode
+bool MemCpyOptPass::processMemSetMemCpyDependence(MemCpyInst *MemCpy,
+ MemSetInst *MemSet) {
+ // We can only transform memset/memcpy with the same destination.
+ if (MemSet->getDest() != MemCpy->getDest())
+ return false;
+
+ // Check that src and dst of the memcpy aren't the same. While memcpy
+ // operands cannot partially overlap, exact equality is allowed.
+ if (!AA->isNoAlias(MemoryLocation(MemCpy->getSource(),
+ LocationSize::precise(1)),
+ MemoryLocation(MemCpy->getDest(),
+ LocationSize::precise(1))))
+ return false;
+
+ if (EnableMemorySSA) {
+ // We know that dst up to src_size is not written. We now need to make sure
+ // that dst up to dst_size is not accessed. (If we did not move the memset,
+ // checking for reads would be sufficient.)
+ if (accessedBetween(*AA, MemoryLocation::getForDest(MemSet),
+ MSSA->getMemoryAccess(MemSet),
+ MSSA->getMemoryAccess(MemCpy))) {
+ return false;
+ }
+ } else {
+ // We have already checked that dst up to src_size is not accessed. We
+ // need to make sure that there are no accesses up to dst_size either.
+ MemDepResult DstDepInfo = MD->getPointerDependencyFrom(
+ MemoryLocation::getForDest(MemSet), false, MemCpy->getIterator(),
+ MemCpy->getParent());
+ if (DstDepInfo.getInst() != MemSet)
+ return false;
+ }
+
+ // Use the same i8* dest as the memcpy, killing the memset dest if different.
+ Value *Dest = MemCpy->getRawDest();
+ Value *DestSize = MemSet->getLength();
+ Value *SrcSize = MemCpy->getLength();
+
+ if (mayBeVisibleThroughUnwinding(Dest, MemSet, MemCpy))
+ return false;
+
+ // By default, create an unaligned memset.
+ unsigned Align = 1;
+ // If Dest is aligned, and SrcSize is constant, use the minimum alignment
+ // of the sum.
+ const unsigned DestAlign =
+ std::max(MemSet->getDestAlignment(), MemCpy->getDestAlignment());
+ if (DestAlign > 1)
+ if (ConstantInt *SrcSizeC = dyn_cast<ConstantInt>(SrcSize))
+ Align = MinAlign(SrcSizeC->getZExtValue(), DestAlign);
+
+ IRBuilder<> Builder(MemCpy);
+
+ // If the sizes have different types, zext the smaller one.
+ if (DestSize->getType() != SrcSize->getType()) {
+ if (DestSize->getType()->getIntegerBitWidth() >
+ SrcSize->getType()->getIntegerBitWidth())
+ SrcSize = Builder.CreateZExt(SrcSize, DestSize->getType());
+ else
+ DestSize = Builder.CreateZExt(DestSize, SrcSize->getType());
+ }
+
+ Value *Ule = Builder.CreateICmpULE(DestSize, SrcSize);
+ Value *SizeDiff = Builder.CreateSub(DestSize, SrcSize);
+ Value *MemsetLen = Builder.CreateSelect(
+ Ule, ConstantInt::getNullValue(DestSize->getType()), SizeDiff);
+ Instruction *NewMemSet = Builder.CreateMemSet(
+ Builder.CreateGEP(Dest->getType()->getPointerElementType(), Dest,
+ SrcSize),
+ MemSet->getOperand(1), MemsetLen, MaybeAlign(Align));
+
+ if (MSSAU) {
+ assert(isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(MemCpy)) &&
+ "MemCpy must be a MemoryDef");
+ // The new memset is inserted after the memcpy, but it is known that its
+ // defining access is the memset about to be removed which immediately
+ // precedes the memcpy.
+ auto *LastDef =
+ cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(MemCpy));
+ auto *NewAccess = MSSAU->createMemoryAccessBefore(
+ NewMemSet, LastDef->getDefiningAccess(), LastDef);
+ MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
+ }
+
+ eraseInstruction(MemSet);
+ return true;
+}
+
+/// Determine whether the instruction has undefined content for the given Size,
+/// either because it was freshly alloca'd or started its lifetime.
+static bool hasUndefContents(Instruction *I, ConstantInt *Size) {
+ if (isa<AllocaInst>(I))
+ return true;
+
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
+ if (II->getIntrinsicID() == Intrinsic::lifetime_start)
+ if (ConstantInt *LTSize = dyn_cast<ConstantInt>(II->getArgOperand(0)))
+ if (LTSize->getZExtValue() >= Size->getZExtValue())
+ return true;
+
+ return false;
+}
+
+static bool hasUndefContentsMSSA(MemorySSA *MSSA, AliasAnalysis *AA, Value *V,
+ MemoryDef *Def, ConstantInt *Size) {
+ if (MSSA->isLiveOnEntryDef(Def))
+ return isa<AllocaInst>(getUnderlyingObject(V));
+
+ if (IntrinsicInst *II =
+ dyn_cast_or_null<IntrinsicInst>(Def->getMemoryInst())) {
+ if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
+ ConstantInt *LTSize = cast<ConstantInt>(II->getArgOperand(0));
+ if (AA->isMustAlias(V, II->getArgOperand(1)) &&
+ LTSize->getZExtValue() >= Size->getZExtValue())
+ return true;
+ }
+ }
+
+ return false;
+}
+
+/// Transform memcpy to memset when its source was just memset.
+/// In other words, turn:
+/// \code
+/// memset(dst1, c, dst1_size);
+/// memcpy(dst2, dst1, dst2_size);
+/// \endcode
+/// into:
+/// \code
+/// memset(dst1, c, dst1_size);
+/// memset(dst2, c, dst2_size);
+/// \endcode
+/// When dst2_size <= dst1_size.
+///
+/// The \p MemCpy must have a Constant length.
+bool MemCpyOptPass::performMemCpyToMemSetOptzn(MemCpyInst *MemCpy,
+ MemSetInst *MemSet) {
+ // Make sure that memcpy(..., memset(...), ...), that is we are memsetting and
+ // memcpying from the same address. Otherwise it is hard to reason about.
+ if (!AA->isMustAlias(MemSet->getRawDest(), MemCpy->getRawSource()))
+ return false;
+
+ // A known memset size is required.
+ ConstantInt *MemSetSize = dyn_cast<ConstantInt>(MemSet->getLength());
+ if (!MemSetSize)
+ return false;
+
+ // Make sure the memcpy doesn't read any more than what the memset wrote.
+ // Don't worry about sizes larger than i64.
+ ConstantInt *CopySize = cast<ConstantInt>(MemCpy->getLength());
+ if (CopySize->getZExtValue() > MemSetSize->getZExtValue()) {
+ // If the memcpy is larger than the memset, but the memory was undef prior
+ // to the memset, we can just ignore the tail. Technically we're only
+ // interested in the bytes from MemSetSize..CopySize here, but as we can't
+ // easily represent this location, we use the full 0..CopySize range.
+ MemoryLocation MemCpyLoc = MemoryLocation::getForSource(MemCpy);
+ bool CanReduceSize = false;
+ if (EnableMemorySSA) {
+ MemoryUseOrDef *MemSetAccess = MSSA->getMemoryAccess(MemSet);
+ MemoryAccess *Clobber = MSSA->getWalker()->getClobberingMemoryAccess(
+ MemSetAccess->getDefiningAccess(), MemCpyLoc);
+ if (auto *MD = dyn_cast<MemoryDef>(Clobber))
+ if (hasUndefContentsMSSA(MSSA, AA, MemCpy->getSource(), MD, CopySize))
+ CanReduceSize = true;
+ } else {
+ MemDepResult DepInfo = MD->getPointerDependencyFrom(
+ MemCpyLoc, true, MemSet->getIterator(), MemSet->getParent());
+ if (DepInfo.isDef() && hasUndefContents(DepInfo.getInst(), CopySize))
+ CanReduceSize = true;
+ }
+
+ if (!CanReduceSize)
+ return false;
+ CopySize = MemSetSize;
+ }
+
+ IRBuilder<> Builder(MemCpy);
+ Instruction *NewM =
+ Builder.CreateMemSet(MemCpy->getRawDest(), MemSet->getOperand(1),
+ CopySize, MaybeAlign(MemCpy->getDestAlignment()));
+ if (MSSAU) {
+ auto *LastDef =
+ cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(MemCpy));
+ auto *NewAccess = MSSAU->createMemoryAccessAfter(NewM, LastDef, LastDef);
+ MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
+ }
+
+ return true;
+}
+
+/// Perform simplification of memcpy's. If we have memcpy A
+/// which copies X to Y, and memcpy B which copies Y to Z, then we can rewrite
+/// B to be a memcpy from X to Z (or potentially a memmove, depending on
+/// circumstances). This allows later passes to remove the first memcpy
+/// altogether.
+bool MemCpyOptPass::processMemCpy(MemCpyInst *M, BasicBlock::iterator &BBI) {
+ // We can only optimize non-volatile memcpy's.
+ if (M->isVolatile()) return false;
+
+ // If the source and destination of the memcpy are the same, then zap it.
+ if (M->getSource() == M->getDest()) {
+ ++BBI;
+ eraseInstruction(M);
+ return true;
+ }
+
+ // If copying from a constant, try to turn the memcpy into a memset.
+ if (GlobalVariable *GV = dyn_cast<GlobalVariable>(M->getSource()))
+ if (GV->isConstant() && GV->hasDefinitiveInitializer())
+ if (Value *ByteVal = isBytewiseValue(GV->getInitializer(),
+ M->getModule()->getDataLayout())) {
+ IRBuilder<> Builder(M);
+ Instruction *NewM =
+ Builder.CreateMemSet(M->getRawDest(), ByteVal, M->getLength(),
+ MaybeAlign(M->getDestAlignment()), false);
+ if (MSSAU) {
+ auto *LastDef =
+ cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(M));
+ auto *NewAccess =
+ MSSAU->createMemoryAccessAfter(NewM, LastDef, LastDef);
+ MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
+ }
+
+ eraseInstruction(M);
+ ++NumCpyToSet;
+ return true;
+ }
+
+ if (EnableMemorySSA) {
+ MemoryUseOrDef *MA = MSSA->getMemoryAccess(M);
+ MemoryAccess *AnyClobber = MSSA->getWalker()->getClobberingMemoryAccess(MA);
+ MemoryLocation DestLoc = MemoryLocation::getForDest(M);
+ const MemoryAccess *DestClobber =
+ MSSA->getWalker()->getClobberingMemoryAccess(AnyClobber, DestLoc);
+
+ // Try to turn a partially redundant memset + memcpy into
+ // memcpy + smaller memset. We don't need the memcpy size for this.
+ // The memcpy most post-dom the memset, so limit this to the same basic
+ // block. A non-local generalization is likely not worthwhile.
+ if (auto *MD = dyn_cast<MemoryDef>(DestClobber))
+ if (auto *MDep = dyn_cast_or_null<MemSetInst>(MD->getMemoryInst()))
+ if (DestClobber->getBlock() == M->getParent())
+ if (processMemSetMemCpyDependence(M, MDep))
+ return true;
+
+ // The optimizations after this point require the memcpy size.
+ ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength());
+ if (!CopySize) return false;
+
+ MemoryAccess *SrcClobber = MSSA->getWalker()->getClobberingMemoryAccess(
+ AnyClobber, MemoryLocation::getForSource(M));
+
+ // There are four possible optimizations we can do for memcpy:
+ // a) memcpy-memcpy xform which exposes redundance for DSE.
+ // b) call-memcpy xform for return slot optimization.
+ // c) memcpy from freshly alloca'd space or space that has just started
+ // its lifetime copies undefined data, and we can therefore eliminate
+ // the memcpy in favor of the data that was already at the destination.
+ // d) memcpy from a just-memset'd source can be turned into memset.
+ if (auto *MD = dyn_cast<MemoryDef>(SrcClobber)) {
+ if (Instruction *MI = MD->getMemoryInst()) {
+ if (auto *C = dyn_cast<CallInst>(MI)) {
+ // The memcpy must post-dom the call. Limit to the same block for now.
+ // Additionally, we need to ensure that there are no accesses to dest
+ // between the call and the memcpy. Accesses to src will be checked
+ // by performCallSlotOptzn().
+ // TODO: Support non-local call-slot optimization?
+ if (C->getParent() == M->getParent() &&
+ !accessedBetween(*AA, DestLoc, MD, MA)) {
+ // FIXME: Can we pass in either of dest/src alignment here instead
+ // of conservatively taking the minimum?
+ Align Alignment = std::min(M->getDestAlign().valueOrOne(),
+ M->getSourceAlign().valueOrOne());
+ if (performCallSlotOptzn(M, M, M->getDest(), M->getSource(),
+ CopySize->getZExtValue(), Alignment, C)) {
+ LLVM_DEBUG(dbgs() << "Performed call slot optimization:\n"
+ << " call: " << *C << "\n"
+ << " memcpy: " << *M << "\n");
+ eraseInstruction(M);
+ ++NumMemCpyInstr;
+ return true;
+ }
+ }
+ }
+ if (auto *MDep = dyn_cast<MemCpyInst>(MI))
+ return processMemCpyMemCpyDependence(M, MDep);
+ if (auto *MDep = dyn_cast<MemSetInst>(MI)) {
+ if (performMemCpyToMemSetOptzn(M, MDep)) {
+ LLVM_DEBUG(dbgs() << "Converted memcpy to memset\n");
+ eraseInstruction(M);
+ ++NumCpyToSet;
+ return true;
+ }
+ }
+ }
+
+ if (hasUndefContentsMSSA(MSSA, AA, M->getSource(), MD, CopySize)) {
+ LLVM_DEBUG(dbgs() << "Removed memcpy from undef\n");
+ eraseInstruction(M);
+ ++NumMemCpyInstr;
+ return true;
+ }
+ }
+ } else {
+ MemDepResult DepInfo = MD->getDependency(M);
+
+ // Try to turn a partially redundant memset + memcpy into
+ // memcpy + smaller memset. We don't need the memcpy size for this.
+ if (DepInfo.isClobber())
+ if (MemSetInst *MDep = dyn_cast<MemSetInst>(DepInfo.getInst()))
+ if (processMemSetMemCpyDependence(M, MDep))
+ return true;
+
+ // The optimizations after this point require the memcpy size.
+ ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength());
+ if (!CopySize) return false;
+
+ // There are four possible optimizations we can do for memcpy:
+ // a) memcpy-memcpy xform which exposes redundance for DSE.
+ // b) call-memcpy xform for return slot optimization.
+ // c) memcpy from freshly alloca'd space or space that has just started
+ // its lifetime copies undefined data, and we can therefore eliminate
+ // the memcpy in favor of the data that was already at the destination.
+ // d) memcpy from a just-memset'd source can be turned into memset.
+ if (DepInfo.isClobber()) {
+ if (CallInst *C = dyn_cast<CallInst>(DepInfo.getInst())) {
+ // FIXME: Can we pass in either of dest/src alignment here instead
+ // of conservatively taking the minimum?
+ Align Alignment = std::min(M->getDestAlign().valueOrOne(),
+ M->getSourceAlign().valueOrOne());
+ if (performCallSlotOptzn(M, M, M->getDest(), M->getSource(),
+ CopySize->getZExtValue(), Alignment, C)) {
+ eraseInstruction(M);
+ ++NumMemCpyInstr;
+ return true;
+ }
+ }
+ }
+
+ MemoryLocation SrcLoc = MemoryLocation::getForSource(M);
+ MemDepResult SrcDepInfo = MD->getPointerDependencyFrom(
+ SrcLoc, true, M->getIterator(), M->getParent());
+
+ if (SrcDepInfo.isClobber()) {
+ if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(SrcDepInfo.getInst()))
+ return processMemCpyMemCpyDependence(M, MDep);
+ } else if (SrcDepInfo.isDef()) {
+ if (hasUndefContents(SrcDepInfo.getInst(), CopySize)) {
+ eraseInstruction(M);
+ ++NumMemCpyInstr;
+ return true;
+ }
+ }
+
+ if (SrcDepInfo.isClobber())
+ if (MemSetInst *MDep = dyn_cast<MemSetInst>(SrcDepInfo.getInst()))
+ if (performMemCpyToMemSetOptzn(M, MDep)) {
+ eraseInstruction(M);
+ ++NumCpyToSet;
+ return true;
+ }
+ }
+
+ return false;
+}
+
+/// Transforms memmove calls to memcpy calls when the src/dst are guaranteed
+/// not to alias.
+bool MemCpyOptPass::processMemMove(MemMoveInst *M) {
+ if (!TLI->has(LibFunc_memmove))
+ return false;
+
+ // See if the pointers alias.
+ if (!AA->isNoAlias(MemoryLocation::getForDest(M),
+ MemoryLocation::getForSource(M)))
+ return false;
+
+ LLVM_DEBUG(dbgs() << "MemCpyOptPass: Optimizing memmove -> memcpy: " << *M
+ << "\n");
+
+ // If not, then we know we can transform this.
+ Type *ArgTys[3] = { M->getRawDest()->getType(),
+ M->getRawSource()->getType(),
+ M->getLength()->getType() };
+ M->setCalledFunction(Intrinsic::getDeclaration(M->getModule(),
+ Intrinsic::memcpy, ArgTys));
+
+ // For MemorySSA nothing really changes (except that memcpy may imply stricter
+ // aliasing guarantees).
+
+ // MemDep may have over conservative information about this instruction, just
+ // conservatively flush it from the cache.
+ if (MD)
+ MD->removeInstruction(M);
+
+ ++NumMoveToCpy;
+ return true;
+}
+
+/// This is called on every byval argument in call sites.
+bool MemCpyOptPass::processByValArgument(CallBase &CB, unsigned ArgNo) {
+ const DataLayout &DL = CB.getCaller()->getParent()->getDataLayout();
+ // Find out what feeds this byval argument.
+ Value *ByValArg = CB.getArgOperand(ArgNo);
+ Type *ByValTy = cast<PointerType>(ByValArg->getType())->getElementType();
+ uint64_t ByValSize = DL.getTypeAllocSize(ByValTy);
+ MemoryLocation Loc(ByValArg, LocationSize::precise(ByValSize));
+ MemCpyInst *MDep = nullptr;
+ if (EnableMemorySSA) {
+ MemoryUseOrDef *CallAccess = MSSA->getMemoryAccess(&CB);
+ MemoryAccess *Clobber = MSSA->getWalker()->getClobberingMemoryAccess(
+ CallAccess->getDefiningAccess(), Loc);
+ if (auto *MD = dyn_cast<MemoryDef>(Clobber))
+ MDep = dyn_cast_or_null<MemCpyInst>(MD->getMemoryInst());
+ } else {
+ MemDepResult DepInfo = MD->getPointerDependencyFrom(
+ Loc, true, CB.getIterator(), CB.getParent());
+ if (!DepInfo.isClobber())
+ return false;
+ MDep = dyn_cast<MemCpyInst>(DepInfo.getInst());
+ }
+
+ // If the byval argument isn't fed by a memcpy, ignore it. If it is fed by
+ // a memcpy, see if we can byval from the source of the memcpy instead of the
+ // result.
+ if (!MDep || MDep->isVolatile() ||
+ ByValArg->stripPointerCasts() != MDep->getDest())
+ return false;
+
+ // The length of the memcpy must be larger or equal to the size of the byval.
+ ConstantInt *C1 = dyn_cast<ConstantInt>(MDep->getLength());
+ if (!C1 || C1->getValue().getZExtValue() < ByValSize)
+ return false;
+
+ // Get the alignment of the byval. If the call doesn't specify the alignment,
+ // then it is some target specific value that we can't know.
+ MaybeAlign ByValAlign = CB.getParamAlign(ArgNo);
+ if (!ByValAlign) return false;
+
+ // If it is greater than the memcpy, then we check to see if we can force the
+ // source of the memcpy to the alignment we need. If we fail, we bail out.
+ MaybeAlign MemDepAlign = MDep->getSourceAlign();
+ if ((!MemDepAlign || *MemDepAlign < *ByValAlign) &&
+ getOrEnforceKnownAlignment(MDep->getSource(), ByValAlign, DL, &CB, AC,
+ DT) < *ByValAlign)
+ return false;
+
+ // The address space of the memcpy source must match the byval argument
+ if (MDep->getSource()->getType()->getPointerAddressSpace() !=
+ ByValArg->getType()->getPointerAddressSpace())
+ return false;
+
+ // Verify that the copied-from memory doesn't change in between the memcpy and
+ // the byval call.
+ // memcpy(a <- b)
+ // *b = 42;
+ // foo(*a)
+ // It would be invalid to transform the second memcpy into foo(*b).
+ if (EnableMemorySSA) {
+ if (writtenBetween(MSSA, MemoryLocation::getForSource(MDep),
+ MSSA->getMemoryAccess(MDep), MSSA->getMemoryAccess(&CB)))
+ return false;
+ } else {
+ // NOTE: This is conservative, it will stop on any read from the source loc,
+ // not just the defining memcpy.
+ MemDepResult SourceDep = MD->getPointerDependencyFrom(
+ MemoryLocation::getForSource(MDep), false,
+ CB.getIterator(), MDep->getParent());
+ if (!SourceDep.isClobber() || SourceDep.getInst() != MDep)
+ return false;
+ }
+
+ Value *TmpCast = MDep->getSource();
+ if (MDep->getSource()->getType() != ByValArg->getType()) {
+ BitCastInst *TmpBitCast = new BitCastInst(MDep->getSource(), ByValArg->getType(),
+ "tmpcast", &CB);
+ // Set the tmpcast's DebugLoc to MDep's
+ TmpBitCast->setDebugLoc(MDep->getDebugLoc());
+ TmpCast = TmpBitCast;
+ }
+
+ LLVM_DEBUG(dbgs() << "MemCpyOptPass: Forwarding memcpy to byval:\n"
+ << " " << *MDep << "\n"
+ << " " << CB << "\n");
+
+ // Otherwise we're good! Update the byval argument.
+ CB.setArgOperand(ArgNo, TmpCast);
+ ++NumMemCpyInstr;
+ return true;
+}
+
+/// Executes one iteration of MemCpyOptPass.
+bool MemCpyOptPass::iterateOnFunction(Function &F) {
+ bool MadeChange = false;
+
+ // Walk all instruction in the function.
+ for (BasicBlock &BB : F) {
+ // Skip unreachable blocks. For example processStore assumes that an
+ // instruction in a BB can't be dominated by a later instruction in the
+ // same BB (which is a scenario that can happen for an unreachable BB that
+ // has itself as a predecessor).
+ if (!DT->isReachableFromEntry(&BB))
+ continue;
+
+ for (BasicBlock::iterator BI = BB.begin(), BE = BB.end(); BI != BE;) {
+ // Avoid invalidating the iterator.
+ Instruction *I = &*BI++;
+
+ bool RepeatInstruction = false;
+
+ if (StoreInst *SI = dyn_cast<StoreInst>(I))
+ MadeChange |= processStore(SI, BI);
+ else if (MemSetInst *M = dyn_cast<MemSetInst>(I))
+ RepeatInstruction = processMemSet(M, BI);
+ else if (MemCpyInst *M = dyn_cast<MemCpyInst>(I))
+ RepeatInstruction = processMemCpy(M, BI);
+ else if (MemMoveInst *M = dyn_cast<MemMoveInst>(I))
+ RepeatInstruction = processMemMove(M);
+ else if (auto *CB = dyn_cast<CallBase>(I)) {
+ for (unsigned i = 0, e = CB->arg_size(); i != e; ++i)
+ if (CB->isByValArgument(i))
+ MadeChange |= processByValArgument(*CB, i);
+ }
+
+ // Reprocess the instruction if desired.
+ if (RepeatInstruction) {
+ if (BI != BB.begin())
+ --BI;
+ MadeChange = true;
+ }
+ }
+ }
+
+ return MadeChange;
+}
+
+PreservedAnalyses MemCpyOptPass::run(Function &F, FunctionAnalysisManager &AM) {
+ auto *MD = !EnableMemorySSA ? &AM.getResult<MemoryDependenceAnalysis>(F)
+ : AM.getCachedResult<MemoryDependenceAnalysis>(F);
+ auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
+ auto *AA = &AM.getResult<AAManager>(F);
+ auto *AC = &AM.getResult<AssumptionAnalysis>(F);
+ auto *DT = &AM.getResult<DominatorTreeAnalysis>(F);
+ auto *MSSA = EnableMemorySSA ? &AM.getResult<MemorySSAAnalysis>(F)
+ : AM.getCachedResult<MemorySSAAnalysis>(F);
+
+ bool MadeChange =
+ runImpl(F, MD, &TLI, AA, AC, DT, MSSA ? &MSSA->getMSSA() : nullptr);
+ if (!MadeChange)
+ return PreservedAnalyses::all();
+
+ PreservedAnalyses PA;
+ PA.preserveSet<CFGAnalyses>();
+ PA.preserve<GlobalsAA>();
+ if (MD)
+ PA.preserve<MemoryDependenceAnalysis>();
+ if (MSSA)
+ PA.preserve<MemorySSAAnalysis>();
+ return PA;
+}
+
+bool MemCpyOptPass::runImpl(Function &F, MemoryDependenceResults *MD_,
+ TargetLibraryInfo *TLI_, AliasAnalysis *AA_,
+ AssumptionCache *AC_, DominatorTree *DT_,
+ MemorySSA *MSSA_) {
+ bool MadeChange = false;
+ MD = MD_;
+ TLI = TLI_;
+ AA = AA_;
+ AC = AC_;
+ DT = DT_;
+ MSSA = MSSA_;
+ MemorySSAUpdater MSSAU_(MSSA_);
+ MSSAU = MSSA_ ? &MSSAU_ : nullptr;
+ // If we don't have at least memset and memcpy, there is little point of doing
+ // anything here. These are required by a freestanding implementation, so if
+ // even they are disabled, there is no point in trying hard.
+ if (!TLI->has(LibFunc_memset) || !TLI->has(LibFunc_memcpy))
+ return false;
+
+ while (true) {
+ if (!iterateOnFunction(F))
+ break;
+ MadeChange = true;
+ }
+
+ if (MSSA_ && VerifyMemorySSA)
+ MSSA_->verifyMemorySSA();
+
+ MD = nullptr;
+ return MadeChange;
+}
+
+/// This is the main transformation entry point for a function.
+bool MemCpyOptLegacyPass::runOnFunction(Function &F) {
+ if (skipFunction(F))
+ return false;
+
+ auto *MDWP = !EnableMemorySSA
+ ? &getAnalysis<MemoryDependenceWrapperPass>()
+ : getAnalysisIfAvailable<MemoryDependenceWrapperPass>();
+ auto *TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
+ auto *AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
+ auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
+ auto *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ auto *MSSAWP = EnableMemorySSA
+ ? &getAnalysis<MemorySSAWrapperPass>()
+ : getAnalysisIfAvailable<MemorySSAWrapperPass>();
+
+ return Impl.runImpl(F, MDWP ? & MDWP->getMemDep() : nullptr, TLI, AA, AC, DT,
+ MSSAWP ? &MSSAWP->getMSSA() : nullptr);
+}
generated by cgit v1.2.3 (git 2.25.1) at 2025-10-10 08:46:56 +0000