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Factor a bunch of functionality related to memcpy and memset transforms out of 

GVN and into its own pass.

llvm-svn: 49419
This commit is contained in:
Owen Anderson 2008-04-09 08:23:16 +00:00
parent 8ee792d1b6
commit ef9a6fd5c2
13 changed files with 790 additions and 628 deletions
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1
llvm/include/llvm/LinkAllPasses.h
View File

@ -112,6 +112,7 @@ namespace {
(void) llvm::createPredicateSimplifierPass();
(void) llvm::createCodeGenPreparePass();
(void) llvm::createGVNPass();
(void) llvm::createMemCpyOptPass();
(void)new llvm::IntervalPartition();
(void)new llvm::FindUsedTypes();

7
llvm/include/llvm/Transforms/Scalar.h
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@ -303,6 +303,13 @@ FunctionPass *createGVNPREPass();
//
FunctionPass *createGVNPass();
//===----------------------------------------------------------------------===//
//
// MemCpyOpt - This pass performs optimizations related to eliminating memcpy
// calls and/or combining multiple stores into memset's.
//
FunctionPass *createMemCpyOptPass();
//===----------------------------------------------------------------------===//
//
// CodeGenPrepare - This pass prepares a function for instruction selection.

620
llvm/lib/Transforms/Scalar/GVN.cpp
View File

@ -42,14 +42,6 @@ using namespace llvm;
STATISTIC(NumGVNInstr, "Number of instructions deleted");
STATISTIC(NumGVNLoad, "Number of loads deleted");
STATISTIC(NumMemSetInfer, "Number of memsets inferred");
namespace {
cl::opt<bool>
FormMemSet("form-memset-from-stores",
cl::desc("Transform straight-line stores to memsets"),
cl::init(true), cl::Hidden);
}
//===----------------------------------------------------------------------===//
// ValueTable Class
@ -668,17 +660,12 @@ namespace {
bool processLoad(LoadInst* L,
DenseMap<Value*, LoadInst*> &lastLoad,
SmallVectorImpl<Instruction*> &toErase);
bool processStore(StoreInst *SI, SmallVectorImpl<Instruction*> &toErase);
bool processInstruction(Instruction* I,
ValueNumberedSet& currAvail,
DenseMap<Value*, LoadInst*>& lastSeenLoad,
SmallVectorImpl<Instruction*> &toErase);
bool processNonLocalLoad(LoadInst* L,
SmallVectorImpl<Instruction*> &toErase);
bool processMemCpy(MemCpyInst* M, MemCpyInst* MDep,
SmallVectorImpl<Instruction*> &toErase);
bool performCallSlotOptzn(MemCpyInst* cpy, CallInst* C,
SmallVectorImpl<Instruction*> &toErase);
Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig,
DenseMap<BasicBlock*, Value*> &Phis,
bool top_level = false);
@ -983,593 +970,6 @@ bool GVN::processLoad(LoadInst *L, DenseMap<Value*, LoadInst*> &lastLoad,
return deletedLoad;
}
/// 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.getABITypeSize(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;
}
}
}
/// 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 GVN::processStore(StoreInst *SI, SmallVectorImpl<Instruction*> &toErase) {
if (!FormMemSet) return false;
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)
MemSetF = Intrinsic::getDeclaration(SI->getParent()->getParent()
->getParent(), Intrinsic::memset_i64);
// 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;
// Zap all the stores.
toErase.append(Range.TheStores.begin(), Range.TheStores.end());
++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 GVN::performCallSlotOptzn(MemCpyInst *cpy, CallInst *C,
SmallVectorImpl<Instruction*> &toErase) {
// 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.getABITypeSize(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.getABITypeSize(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.getABITypeSize(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<GetElementPtrInst>(UI) || isa<BitCastInst>(UI)) {
for (User::use_iterator I = UI->use_begin(), E = UI->use_end();
I != E; ++I)
srcUseList.push_back(*I);
} 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.
for (unsigned i = 0; i < CS.arg_size(); ++i)
if (CS.getArgument(i) == cpySrc) {
if (cpySrc->getType() != cpyDest->getType())
cpyDest = CastInst::createPointerCast(cpyDest, cpySrc->getType(),
cpyDest->getName(), C);
CS.setArgument(i, cpyDest);
}
// Drop any cached information about the call, because we may have changed
// its dependence information by changing its parameter.
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
MD.dropInstruction(C);
// Remove the memcpy
MD.removeInstruction(cpy);
toErase.push_back(cpy);
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 GVN::processMemCpy(MemCpyInst* M, MemCpyInst* MDep,
SmallVectorImpl<Instruction*> &toErase) {
// 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
Function* MemCpyFun = Intrinsic::getDeclaration(
M->getParent()->getParent()->getParent(),
M->getIntrinsicID());
std::vector<Value*> args;
args.push_back(M->getRawDest());
args.push_back(MDep->getRawSource());
args.push_back(M->getLength());
args.push_back(M->getAlignment());
CallInst* C = CallInst::Create(MemCpyFun, args.begin(), args.end(), "", M);
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
if (MD.getDependency(C) == MDep) {
MD.dropInstruction(M);
toErase.push_back(M);
return true;
}
MD.removeInstruction(C);
toErase.push_back(C);
return false;
}
/// processInstruction - When calculating availability, handle an instruction
/// by inserting it into the appropriate sets
bool GVN::processInstruction(Instruction *I, ValueNumberedSet &currAvail,
@ -1578,31 +978,11 @@ bool GVN::processInstruction(Instruction *I, ValueNumberedSet &currAvail,
if (LoadInst* L = dyn_cast<LoadInst>(I))
return processLoad(L, lastSeenLoad, toErase);
if (StoreInst *SI = dyn_cast<StoreInst>(I))
return processStore(SI, toErase);
// Allocations are always uniquely numbered, so we can save time and memory
// by fast failing them.
if (isa<AllocationInst>(I))
return false;
if (MemCpyInst* M = dyn_cast<MemCpyInst>(I)) {
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
Instruction* dep = MD.getDependency(M);
if (dep == MemoryDependenceAnalysis::None ||
dep == MemoryDependenceAnalysis::NonLocal)
return false;
if (MemCpyInst *MemCpy = dyn_cast<MemCpyInst>(dep))
return processMemCpy(M, MemCpy, toErase);
if (CallInst* C = dyn_cast<CallInst>(dep))
return performCallSlotOptzn(M, C, toErase);
return false;
}
unsigned num = VN.lookup_or_add(I);
// Collapse PHI nodes

769
llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp Normal file
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@ -0,0 +1,769 @@
//===- 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/BasicBlock.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Instructions.h"
#include "llvm/ParameterAttributes.h"
#include "llvm/Value.h"
#include "llvm/ADT/DepthFirstIterator.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/CFG.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.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");
namespace {
cl::opt<bool>
FormMemSet("form-memset-from-stores",
cl::desc("Transform straight-line stores to memsets"),
cl::init(true), cl::Hidden);
}
/// 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.getABITypeSize(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((intptr_t)&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 processInstruction(Instruction* I,
SmallVectorImpl<Instruction*> &toErase);
bool processStore(StoreInst *SI, SmallVectorImpl<Instruction*> &toErase);
bool processMemCpy(MemCpyInst* M, MemCpyInst* MDep,
SmallVectorImpl<Instruction*> &toErase);
bool performCallSlotOptzn(MemCpyInst* cpy, CallInst* C,
SmallVectorImpl<Instruction*> &toErase);
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, SmallVectorImpl<Instruction*> &toErase) {
if (!FormMemSet) return false;
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)
MemSetF = Intrinsic::getDeclaration(SI->getParent()->getParent()
->getParent(), Intrinsic::memset_i64);
// 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;
// Zap all the stores.
toErase.append(Range.TheStores.begin(), Range.TheStores.end());
++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,
SmallVectorImpl<Instruction*> &toErase) {
// 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.getABITypeSize(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.getABITypeSize(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.getABITypeSize(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<GetElementPtrInst>(UI) || isa<BitCastInst>(UI)) {
for (User::use_iterator I = UI->use_begin(), E = UI->use_end();
I != E; ++I)
srcUseList.push_back(*I);
} 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.
for (unsigned i = 0; i < CS.arg_size(); ++i)
if (CS.getArgument(i) == cpySrc) {
if (cpySrc->getType() != cpyDest->getType())
cpyDest = CastInst::createPointerCast(cpyDest, cpySrc->getType(),
cpyDest->getName(), C);
CS.setArgument(i, cpyDest);
}
// Drop any cached information about the call, because we may have changed
// its dependence information by changing its parameter.
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
MD.dropInstruction(C);
// Remove the memcpy
MD.removeInstruction(cpy);
toErase.push_back(cpy);
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, MemCpyInst* MDep,
SmallVectorImpl<Instruction*> &toErase) {
// 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
Function* MemCpyFun = Intrinsic::getDeclaration(
M->getParent()->getParent()->getParent(),
M->getIntrinsicID());
std::vector<Value*> args;
args.push_back(M->getRawDest());
args.push_back(MDep->getRawSource());
args.push_back(M->getLength());
args.push_back(M->getAlignment());
CallInst* C = CallInst::Create(MemCpyFun, args.begin(), args.end(), "", M);
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
if (MD.getDependency(C) == MDep) {
MD.dropInstruction(M);
toErase.push_back(M);
return true;
}
MD.removeInstruction(C);
toErase.push_back(C);
return false;
}
/// processInstruction - When calculating availability, handle an instruction
/// by inserting it into the appropriate sets
bool MemCpyOpt::processInstruction(Instruction *I,
SmallVectorImpl<Instruction*> &toErase) {
if (StoreInst *SI = dyn_cast<StoreInst>(I))
return processStore(SI, toErase);
if (MemCpyInst* M = dyn_cast<MemCpyInst>(I)) {
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
Instruction* dep = MD.getDependency(M);
if (dep == MemoryDependenceAnalysis::None ||
dep == MemoryDependenceAnalysis::NonLocal)
return false;
if (MemCpyInst *MemCpy = dyn_cast<MemCpyInst>(dep))
return processMemCpy(M, MemCpy, toErase);
if (CallInst* C = dyn_cast<CallInst>(dep))
return performCallSlotOptzn(M, C, toErase);
return false;
}
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;
DominatorTree &DT = getAnalysis<DominatorTree>();
SmallVector<Instruction*, 8> toErase;
// Top-down walk of the dominator tree
for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()),
E = df_end(DT.getRootNode()); DI != E; ++DI) {
BasicBlock* BB = DI->getBlock();
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
BI != BE;) {
changed_function |= processInstruction(BI, toErase);
if (toErase.empty()) {
++BI;
continue;
}
// If we need some instructions deleted, do it now.
NumMemCpyInstr += toErase.size();
// Avoid iterator invalidation.
bool AtStart = BI == BB->begin();
if (!AtStart)
--BI;
for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
E = toErase.end(); I != E; ++I)
(*I)->eraseFromParent();
if (AtStart)
BI = BB->begin();
else
++BI;
toErase.clear();
}
}
return changed_function;
}

2
llvm/test/Transforms/GVN/2008-02-24-MultipleUseofSRet.ll → llvm/test/Transforms/MemCpyOpt/2008-02-24-MultipleUseofSRet.ll
View File

@ -1,4 +1,4 @@
; RUN: llvm-as < %s | opt -gvn -dse | llvm-dis | grep {call.*initialize} | not grep memtmp
; RUN: llvm-as < %s | opt -memcpyopt -dse | llvm-dis | grep {call.*initialize} | not grep memtmp
; PR2077
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32"

2
llvm/test/Transforms/GVN/2008-03-13-ReturnSlotBitcast.ll → llvm/test/Transforms/MemCpyOpt/2008-03-13-ReturnSlotBitcast.ll
View File

@ -1,4 +1,4 @@
; RUN: llvm-as < %s | opt -gvn | llvm-dis | not grep {call.*memcpy.}
; RUN: llvm-as < %s | opt -memcpyopt | llvm-dis | not grep {call.*memcpy.}
%a = type { i32 }
%b = type { float }

3
llvm/test/Transforms/MemCpyOpt/dg.exp Normal file
View File

@ -0,0 +1,3 @@
load_lib llvm.exp
RunLLVMTests [lsort [glob -nocomplain $srcdir/$subdir/*.{ll,llx,c,cpp,tr}]]

4
llvm/test/Transforms/GVN/form-memset.ll → llvm/test/Transforms/MemCpyOpt/form-memset.ll
View File

@ -1,5 +1,5 @@
; RUN: llvm-as < %s | opt -gvn -form-memset-from-stores | llvm-dis | not grep store
; RUN: llvm-as < %s | opt -gvn -form-memset-from-stores | llvm-dis | grep {call.*llvm.memset}
; RUN: llvm-as < %s | opt -memcpyopt -form-memset-from-stores | llvm-dis | not grep store
; RUN: llvm-as < %s | opt -memcpyopt -form-memset-from-stores | llvm-dis | grep {call.*llvm.memset}
; All the stores in this example should be merged into a single memset.

4
llvm/test/Transforms/GVN/form-memset2.ll → llvm/test/Transforms/MemCpyOpt/form-memset2.ll
View File

@ -1,5 +1,5 @@
; RUN: llvm-as < %s | opt -gvn -form-memset-from-stores | llvm-dis | not grep store
; RUN: llvm-as < %s | opt -gvn -form-memset-from-stores | llvm-dis | grep {call.*llvm.memset} | count 3
; RUN: llvm-as < %s | opt -memcpyopt -form-memset-from-stores | llvm-dis | not grep store
; RUN: llvm-as < %s | opt -memcpyopt -form-memset-from-stores | llvm-dis | grep {call.*llvm.memset} | count 3
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
target triple = "i386-apple-darwin8"

2
llvm/test/Transforms/GVN/memcpy.ll → llvm/test/Transforms/MemCpyOpt/memcpy.ll
View File

@ -1,4 +1,4 @@
; RUN: llvm-as < %s | opt -gvn -dse | llvm-dis | grep {call.*memcpy} | count 1
; RUN: llvm-as < %s | opt -memcpyopt -dse | llvm-dis | grep {call.*memcpy} | count 1
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
target triple = "i686-apple-darwin9"

2
llvm/test/Transforms/GVN/sret.ll → llvm/test/Transforms/MemCpyOpt/sret.ll
View File

@ -1,4 +1,4 @@
; RUN: llvm-as < %s | opt -gvn | llvm-dis | not grep {call.*memcpy}
; RUN: llvm-as < %s | opt -memcpyopt | llvm-dis | not grep {call.*memcpy}
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
target triple = "i686-apple-darwin9"

1
llvm/tools/llvm-ld/Optimize.cpp
View File

@ -169,6 +169,7 @@ void Optimize(Module* M) {
addPass(Passes, createGlobalsModRefPass()); // IP alias analysis
addPass(Passes, createLICMPass()); // Hoist loop invariants
addPass(Passes, createMemCpyOptPass()); // Remove dead memcpy's
addPass(Passes, createGVNPass()); // Remove redundancies
addPass(Passes, createDeadStoreEliminationPass()); // Nuke dead stores

1
llvm/tools/opt/opt.cpp
View File

@ -282,6 +282,7 @@ void AddStandardCompilePasses(PassManager &PM) {
addPass(PM, createIndVarSimplifyPass()); // Canonicalize indvars
addPass(PM, createLoopUnrollPass()); // Unroll small loops
addPass(PM, createInstructionCombiningPass()); // Clean up after the unroller
addPass(PM, createMemCpyOptPass()); // Remove unneeded memcpy's
addPass(PM, createGVNPass()); // Remove redundancies
addPass(PM, createSCCPPass()); // Constant prop with SCCP