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+//===- MemCpyOptimizer.cpp - Optimize use of memcpy and friends -----------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass performs various transformations related to eliminating memcpy
+// calls, or transforming sets of stores into memset's.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "memcpyopt"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/IntrinsicInst.h"
+#include "llvm/Instructions.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/MemoryDependenceAnalysis.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/GetElementPtrTypeIterator.h"
+#include "llvm/Target/TargetData.h"
+#include <list>
+using namespace llvm;
+
+STATISTIC(NumMemCpyInstr, "Number of memcpy instructions deleted");
+STATISTIC(NumMemSetInfer, "Number of memsets inferred");
+
+/// isBytewiseValue - If the specified value can be set by repeating the same
+/// byte in memory, return the i8 value that it is represented with. This is
+/// true for all i8 values obviously, but is also true for i32 0, i32 -1,
+/// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated
+/// byte store (e.g. i16 0x1234), return null.
+static Value *isBytewiseValue(Value *V) {
+ // All byte-wide stores are splatable, even of arbitrary variables.
+ if (V->getType() == Type::Int8Ty) return V;
+
+ // Constant float and double values can be handled as integer values if the
+ // corresponding integer value is "byteable". An important case is 0.0.
+ if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) {
+ if (CFP->getType() == Type::FloatTy)
+ V = ConstantExpr::getBitCast(CFP, Type::Int32Ty);
+ if (CFP->getType() == Type::DoubleTy)
+ V = ConstantExpr::getBitCast(CFP, Type::Int64Ty);
+ // Don't handle long double formats, which have strange constraints.
+ }
+
+ // We can handle constant integers that are power of two in size and a
+ // multiple of 8 bits.
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
+ unsigned Width = CI->getBitWidth();
+ if (isPowerOf2_32(Width) && Width > 8) {
+ // We can handle this value if the recursive binary decomposition is the
+ // same at all levels.
+ APInt Val = CI->getValue();
+ APInt Val2;
+ while (Val.getBitWidth() != 8) {
+ unsigned NextWidth = Val.getBitWidth()/2;
+ Val2 = Val.lshr(NextWidth);
+ Val2.trunc(Val.getBitWidth()/2);
+ Val.trunc(Val.getBitWidth()/2);
+
+ // If the top/bottom halves aren't the same, reject it.
+ if (Val != Val2)
+ return 0;
+ }
+ return ConstantInt::get(Val);
+ }
+ }
+
+ // Conceptually, we could handle things like:
+ // %a = zext i8 %X to i16
+ // %b = shl i16 %a, 8
+ // %c = or i16 %a, %b
+ // but until there is an example that actually needs this, it doesn't seem
+ // worth worrying about.
+ return 0;
+}
+
+static int64_t GetOffsetFromIndex(const GetElementPtrInst *GEP, unsigned Idx,
+ bool &VariableIdxFound, TargetData &TD) {
+ // Skip over the first indices.
+ gep_type_iterator GTI = gep_type_begin(GEP);
+ for (unsigned i = 1; i != Idx; ++i, ++GTI)
+ /*skip along*/;
+
+ // Compute the offset implied by the rest of the indices.
+ int64_t Offset = 0;
+ for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
+ ConstantInt *OpC = dyn_cast<ConstantInt>(GEP->getOperand(i));
+ if (OpC == 0)
+ return VariableIdxFound = true;
+ if (OpC->isZero()) continue; // No offset.
+
+ // Handle struct indices, which add their field offset to the pointer.
+ if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
+ Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
+ continue;
+ }
+
+ // Otherwise, we have a sequential type like an array or vector. Multiply
+ // the index by the ElementSize.
+ uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType());
+ Offset += Size*OpC->getSExtValue();
+ }
+
+ return Offset;
+}
+
+/// IsPointerOffset - Return true if Ptr1 is provably equal to Ptr2 plus a
+/// constant offset, and return that constant offset. For example, Ptr1 might
+/// be &A[42], and Ptr2 might be &A[40]. In this case offset would be -8.
+static bool IsPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
+ TargetData &TD) {
+ // Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical
+ // base. After that base, they may have some number of common (and
+ // potentially variable) indices. After that they handle some constant
+ // offset, which determines their offset from each other. At this point, we
+ // handle no other case.
+ GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(Ptr1);
+ GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(Ptr2);
+ if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0))
+ return false;
+
+ // Skip any common indices and track the GEP types.
+ unsigned Idx = 1;
+ for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx)
+ if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx))
+ break;
+
+ bool VariableIdxFound = false;
+ int64_t Offset1 = GetOffsetFromIndex(GEP1, Idx, VariableIdxFound, TD);
+ int64_t Offset2 = GetOffsetFromIndex(GEP2, Idx, VariableIdxFound, TD);
+ if (VariableIdxFound) return false;
+
+ Offset = Offset2-Offset1;
+ return true;
+}
+
+
+/// MemsetRange - 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.
+namespace {
+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<StoreInst*, 16> TheStores;
+
+ bool isProfitableToUseMemset(const TargetData &TD) const;
+
+};
+} // end anon namespace
+
+bool MemsetRange::isProfitableToUseMemset(const TargetData &TD) const {
+ // If we found more than 8 stores to merge or 64 bytes, use memset.
+ if (TheStores.size() >= 8 || End-Start >= 64) 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 pointer size and assume that
+ // this width can be stored. If so, check to see whether we will end up
+ // actually reducing the number of stores used.
+ unsigned Bytes = unsigned(End-Start);
+ unsigned NumPointerStores = Bytes/TD.getPointerSize();
+
+ // Assume the remaining bytes if any are done a byte at a time.
+ unsigned NumByteStores = Bytes - NumPointerStores*TD.getPointerSize();
+
+ // 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 {
+ /// Ranges - A sorted list of the memset ranges. We use std::list here
+ /// because each element is relatively large and expensive to copy.
+ std::list<MemsetRange> Ranges;
+ typedef std::list<MemsetRange>::iterator range_iterator;
+ TargetData &TD;
+public:
+ MemsetRanges(TargetData &td) : TD(td) {}
+
+ typedef std::list<MemsetRange>::const_iterator const_iterator;
+ const_iterator begin() const { return Ranges.begin(); }
+ const_iterator end() const { return Ranges.end(); }
+ bool empty() const { return Ranges.empty(); }
+
+ void addStore(int64_t OffsetFromFirst, StoreInst *SI);
+};
+
+} // end anon namespace
+
+
+/// addStore - 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::addStore(int64_t Start, StoreInst *SI) {
+ int64_t End = Start+TD.getTypeStoreSize(SI->getOperand(0)->getType());
+
+ // Do a linear search of the ranges to see if this can be joined and/or to
+ // find the insertion point in the list. We keep the ranges sorted for
+ // simplicity here. This is a linear search of a linked list, which is ugly,
+ // however the number of ranges is limited, so this won't get crazy slow.
+ range_iterator I = Ranges.begin(), E = Ranges.end();
+
+ while (I != E && Start > I->End)
+ ++I;
+
+ // 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 == E || End < I->Start) {
+ MemsetRange &R = *Ranges.insert(I, MemsetRange());
+ R.Start = Start;
+ R.End = End;
+ R.StartPtr = SI->getPointerOperand();
+ R.Alignment = SI->getAlignment();
+ R.TheStores.push_back(SI);
+ return;
+ }
+
+ // This store overlaps with I, add it.
+ I->TheStores.push_back(SI);
+
+ // 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 = SI->getPointerOperand();
+ }
+
+ // 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 != E && 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;
+ }
+ }
+}
+
+//===----------------------------------------------------------------------===//
+// MemCpyOpt Pass
+//===----------------------------------------------------------------------===//
+
+namespace {
+
+ class VISIBILITY_HIDDEN MemCpyOpt : public FunctionPass {
+ bool runOnFunction(Function &F);
+ public:
+ static char ID; // Pass identification, replacement for typeid
+ MemCpyOpt() : FunctionPass(&ID) {}
+
+ private:
+ // This transformation requires dominator postdominator info
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesCFG();
+ AU.addRequired<DominatorTree>();
+ AU.addRequired<MemoryDependenceAnalysis>();
+ AU.addRequired<AliasAnalysis>();
+ AU.addRequired<TargetData>();
+ AU.addPreserved<AliasAnalysis>();
+ AU.addPreserved<MemoryDependenceAnalysis>();
+ AU.addPreserved<TargetData>();
+ }
+
+ // Helper fuctions
+ bool processStore(StoreInst *SI, BasicBlock::iterator& BBI);
+ bool processMemCpy(MemCpyInst* M);
+ bool performCallSlotOptzn(MemCpyInst* cpy, CallInst* C);
+ bool iterateOnFunction(Function &F);
+ };
+
+ char MemCpyOpt::ID = 0;
+}
+
+// createMemCpyOptPass - The public interface to this file...
+FunctionPass *llvm::createMemCpyOptPass() { return new MemCpyOpt(); }
+
+static RegisterPass<MemCpyOpt> X("memcpyopt",
+ "MemCpy Optimization");
+
+
+
+/// processStore - When GVN is 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 consequtive ones
+/// (currently 4) it attempts to merge them together into a memcpy/memset.
+bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator& BBI) {
+ if (SI->isVolatile()) return false;
+
+ // 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.
+ Value *ByteVal = isBytewiseValue(SI->getOperand(0));
+ if (!ByteVal)
+ return false;
+
+ TargetData &TD = getAnalysis<TargetData>();
+ AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
+
+ // 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(TD);
+
+ Value *StartPtr = SI->getPointerOperand();
+
+ BasicBlock::iterator BI = SI;
+ for (++BI; !isa<TerminatorInst>(BI); ++BI) {
+ if (isa<CallInst>(BI) || isa<InvokeInst>(BI)) {
+ // If the call 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 (AA.getModRefBehavior(CallSite::get(BI)) ==
+ AliasAnalysis::DoesNotAccessMemory)
+ continue;
+
+ // TODO: If this is a memset, try to join it in.
+
+ break;
+ } else if (isa<VAArgInst>(BI) || isa<LoadInst>(BI))
+ break;
+
+ // If this is a non-store instruction it is fine, ignore it.
+ StoreInst *NextStore = dyn_cast<StoreInst>(BI);
+ if (NextStore == 0) continue;
+
+ // If this is a store, see if we can merge it in.
+ if (NextStore->isVolatile()) break;
+
+ // Check to see if this stored value is of the same byte-splattable value.
+ if (ByteVal != isBytewiseValue(NextStore->getOperand(0)))
+ break;
+
+ // Check to see if this store is to a constant offset from the start ptr.
+ int64_t Offset;
+ if (!IsPointerOffset(StartPtr, NextStore->getPointerOperand(), Offset, TD))
+ break;
+
+ Ranges.addStore(Offset, NextStore);
+ }
+
+ // 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 false;
+
+ // 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.addStore(0, SI);
+
+
+ Function *MemSetF = 0;
+
+ // Now that we have full information about ranges, loop over the ranges and
+ // emit memset's for anything big enough to be worthwhile.
+ bool MadeChange = false;
+ for (MemsetRanges::const_iterator I = Ranges.begin(), E = Ranges.end();
+ I != E; ++I) {
+ const MemsetRange &Range = *I;
+
+ if (Range.TheStores.size() == 1) continue;
+
+ // If it is profitable to lower this range to memset, do so now.
+ if (!Range.isProfitableToUseMemset(TD))
+ continue;
+
+ // Otherwise, we do want to transform this! Create a new memset. We put
+ // the memset right before the first instruction that isn't part of this
+ // memset block. This ensure that the memset is dominated by any addressing
+ // instruction needed by the start of the block.
+ BasicBlock::iterator InsertPt = BI;
+
+ if (MemSetF == 0) {
+ const Type *Tys[] = {Type::Int64Ty};
+ MemSetF = Intrinsic::getDeclaration(SI->getParent()->getParent()
+ ->getParent(), Intrinsic::memset,
+ Tys, 1);
+ }
+
+ // Get the starting pointer of the block.
+ StartPtr = Range.StartPtr;
+
+ // Cast the start ptr to be i8* as memset requires.
+ const Type *i8Ptr = PointerType::getUnqual(Type::Int8Ty);
+ if (StartPtr->getType() != i8Ptr)
+ StartPtr = new BitCastInst(StartPtr, i8Ptr, StartPtr->getNameStart(),
+ InsertPt);
+
+ Value *Ops[] = {
+ StartPtr, ByteVal, // Start, value
+ ConstantInt::get(Type::Int64Ty, Range.End-Range.Start), // size
+ ConstantInt::get(Type::Int32Ty, Range.Alignment) // align
+ };
+ Value *C = CallInst::Create(MemSetF, Ops, Ops+4, "", InsertPt);
+ DEBUG(cerr << "Replace stores:\n";
+ for (unsigned i = 0, e = Range.TheStores.size(); i != e; ++i)
+ cerr << *Range.TheStores[i];
+ cerr << "With: " << *C); C=C;
+
+ // Don't invalidate the iterator
+ BBI = BI;
+
+ // Zap all the stores.
+ for (SmallVector<StoreInst*, 16>::const_iterator SI = Range.TheStores.begin(),
+ SE = Range.TheStores.end(); SI != SE; ++SI)
+ (*SI)->eraseFromParent();
+ ++NumMemSetInfer;
+ MadeChange = true;
+ }
+
+ return MadeChange;
+}
+
+
+/// performCallSlotOptzn - 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 MemCpyOpt::performCallSlotOptzn(MemCpyInst *cpy, 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.
+
+ // Deliberately get the source and destination with bitcasts stripped away,
+ // because we'll need to do type comparisons based on the underlying type.
+ Value* cpyDest = cpy->getDest();
+ Value* cpySrc = cpy->getSource();
+ CallSite CS = CallSite::get(C);
+
+ // We need to be able to reason about the size of the memcpy, so we require
+ // that it be a constant.
+ ConstantInt* cpyLength = dyn_cast<ConstantInt>(cpy->getLength());
+ if (!cpyLength)
+ return false;
+
+ // Require that src be an alloca. This simplifies the reasoning considerably.
+ AllocaInst* srcAlloca = dyn_cast<AllocaInst>(cpySrc);
+ if (!srcAlloca)
+ return false;
+
+ // Check that all of src is copied to dest.
+ TargetData& TD = getAnalysis<TargetData>();
+
+ ConstantInt* srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize());
+ if (!srcArraySize)
+ return false;
+
+ uint64_t srcSize = TD.getTypeAllocSize(srcAlloca->getAllocatedType()) *
+ srcArraySize->getZExtValue();
+
+ if (cpyLength->getZExtValue() < 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 (AllocaInst* A = dyn_cast<AllocaInst>(cpyDest)) {
+ // The destination is an alloca. Check it is larger than srcSize.
+ ConstantInt* destArraySize = dyn_cast<ConstantInt>(A->getArraySize());
+ if (!destArraySize)
+ return false;
+
+ uint64_t destSize = TD.getTypeAllocSize(A->getAllocatedType()) *
+ destArraySize->getZExtValue();
+
+ if (destSize < srcSize)
+ return false;
+ } else if (Argument* A = dyn_cast<Argument>(cpyDest)) {
+ // If the destination is an sret parameter then only accesses that are
+ // outside of the returned struct type can trap.
+ if (!A->hasStructRetAttr())
+ return false;
+
+ const Type* StructTy = cast<PointerType>(A->getType())->getElementType();
+ uint64_t destSize = TD.getTypeAllocSize(StructTy);
+
+ if (destSize < srcSize)
+ return false;
+ } else {
+ 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->use_begin(),
+ srcAlloca->use_end());
+ while (!srcUseList.empty()) {
+ User* UI = srcUseList.back();
+ srcUseList.pop_back();
+
+ if (isa<BitCastInst>(UI)) {
+ for (User::use_iterator I = UI->use_begin(), E = UI->use_end();
+ I != E; ++I)
+ srcUseList.push_back(*I);
+ } else if (GetElementPtrInst* G = dyn_cast<GetElementPtrInst>(UI)) {
+ if (G->hasAllZeroIndices())
+ for (User::use_iterator I = UI->use_begin(), E = UI->use_end();
+ I != E; ++I)
+ srcUseList.push_back(*I);
+ else
+ return false;
+ } else if (UI != C && UI != cpy) {
+ 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.
+ DominatorTree& DT = getAnalysis<DominatorTree>();
+ if (Instruction* cpyDestInst = dyn_cast<Instruction>(cpyDest))
+ if (!DT.dominates(cpyDestInst, C))
+ 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.
+ AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
+ if (AA.getModRefInfo(C, cpy->getRawDest(), srcSize) !=
+ AliasAnalysis::NoModRef)
+ return false;
+
+ // All the checks have passed, so do the transformation.
+ bool changedArgument = false;
+ for (unsigned i = 0; i < CS.arg_size(); ++i)
+ if (CS.getArgument(i)->stripPointerCasts() == cpySrc) {
+ if (cpySrc->getType() != cpyDest->getType())
+ cpyDest = CastInst::CreatePointerCast(cpyDest, cpySrc->getType(),
+ cpyDest->getName(), C);
+ changedArgument = true;
+ if (CS.getArgument(i)->getType() != cpyDest->getType())
+ CS.setArgument(i, CastInst::CreatePointerCast(cpyDest,
+ CS.getArgument(i)->getType(), cpyDest->getName(), C));
+ else
+ CS.setArgument(i, cpyDest);
+ }
+
+ if (!changedArgument)
+ return false;
+
+ // Drop any cached information about the call, because we may have changed
+ // its dependence information by changing its parameter.
+ MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
+ MD.removeInstruction(C);
+
+ // Remove the memcpy
+ MD.removeInstruction(cpy);
+ cpy->eraseFromParent();
+ NumMemCpyInstr++;
+
+ return true;
+}
+
+/// processMemCpy - perform simplication 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 MemCpyOpt::processMemCpy(MemCpyInst* M) {
+ MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
+
+ // The are two possible optimizations we can do for memcpy:
+ // a) memcpy-memcpy xform which exposes redundance for DSE
+ // b) call-memcpy xform for return slot optimization
+ MemDepResult dep = MD.getDependency(M);
+ if (!dep.isClobber())
+ return false;
+ if (!isa<MemCpyInst>(dep.getInst())) {
+ if (CallInst* C = dyn_cast<CallInst>(dep.getInst()))
+ return performCallSlotOptzn(M, C);
+ return false;
+ }
+
+ MemCpyInst* MDep = cast<MemCpyInst>(dep.getInst());
+
+ // We can only transforms memcpy's where the dest of one is the source of the
+ // other
+ if (M->getSource() != MDep->getDest())
+ return false;
+
+ // Second, the length of the memcpy's must be the same, or the preceeding one
+ // must be larger than the following one.
+ ConstantInt* C1 = dyn_cast<ConstantInt>(MDep->getLength());
+ ConstantInt* C2 = dyn_cast<ConstantInt>(M->getLength());
+ if (!C1 || !C2)
+ return false;
+
+ uint64_t DepSize = C1->getValue().getZExtValue();
+ uint64_t CpySize = C2->getValue().getZExtValue();
+
+ if (DepSize < CpySize)
+ return false;
+
+ // Finally, we have to make sure that the dest of the second does not
+ // alias the source of the first
+ AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
+ if (AA.alias(M->getRawDest(), CpySize, MDep->getRawSource(), DepSize) !=
+ AliasAnalysis::NoAlias)
+ return false;
+ else if (AA.alias(M->getRawDest(), CpySize, M->getRawSource(), CpySize) !=
+ AliasAnalysis::NoAlias)
+ return false;
+ else if (AA.alias(MDep->getRawDest(), DepSize, MDep->getRawSource(), DepSize)
+ != AliasAnalysis::NoAlias)
+ return false;
+
+ // If all checks passed, then we can transform these memcpy's
+ const Type *Tys[1];
+ Tys[0] = M->getLength()->getType();
+ Function* MemCpyFun = Intrinsic::getDeclaration(
+ M->getParent()->getParent()->getParent(),
+ M->getIntrinsicID(), Tys, 1);
+
+ Value *Args[4] = {
+ M->getRawDest(), MDep->getRawSource(), M->getLength(), M->getAlignmentCst()
+ };
+
+ CallInst* C = CallInst::Create(MemCpyFun, Args, Args+4, "", M);
+
+
+ // If C and M don't interfere, then this is a valid transformation. If they
+ // did, this would mean that the two sources overlap, which would be bad.
+ if (MD.getDependency(C) == dep) {
+ MD.removeInstruction(M);
+ M->eraseFromParent();
+ NumMemCpyInstr++;
+ return true;
+ }
+
+ // Otherwise, there was no point in doing this, so we remove the call we
+ // inserted and act like nothing happened.
+ MD.removeInstruction(C);
+ C->eraseFromParent();
+ return false;
+}
+
+// MemCpyOpt::runOnFunction - This is the main transformation entry point for a
+// function.
+//
+bool MemCpyOpt::runOnFunction(Function& F) {
+
+ bool changed = false;
+ bool shouldContinue = true;
+
+ while (shouldContinue) {
+ shouldContinue = iterateOnFunction(F);
+ changed |= shouldContinue;
+ }
+
+ return changed;
+}
+
+
+// MemCpyOpt::iterateOnFunction - Executes one iteration of GVN
+bool MemCpyOpt::iterateOnFunction(Function &F) {
+ bool changed_function = false;
+
+ // Walk all instruction in the function
+ for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {
+ for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
+ BI != BE;) {
+ // Avoid invalidating the iterator
+ Instruction* I = BI++;
+
+ if (StoreInst *SI = dyn_cast<StoreInst>(I))
+ changed_function |= processStore(SI, BI);
+ else if (MemCpyInst* M = dyn_cast<MemCpyInst>(I)) {
+ changed_function |= processMemCpy(M);
+ }
+ }
+ }
+
+ return changed_function;
+}
generated by cgit v1.2.3 (git 2.25.1) at 2025-11-04 07:34:02 +0000