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llvm-mirror/lib/Transforms/Scalar/ScalarReplAggregates.cpp

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//===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This transformation implements the well known scalar replacement of
// aggregates transformation. This xform breaks up alloca instructions of
// aggregate type (structure or array) into individual alloca instructions for
// each member (if possible). Then, if possible, it transforms the individual
// alloca instructions into nice clean scalar SSA form.
//
// This combines a simple SRoA algorithm with the Mem2Reg algorithm because
// often interact, especially for C++ programs. As such, iterating between
// SRoA, then Mem2Reg until we run out of things to promote works well.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "scalarrepl"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/LLVMContext.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/IRBuilder.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumReplaced, "Number of allocas broken up");
STATISTIC(NumPromoted, "Number of allocas promoted");
STATISTIC(NumConverted, "Number of aggregates converted to scalar");
STATISTIC(NumGlobals, "Number of allocas copied from constant global");
namespace {
struct SROA : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
explicit SROA(signed T = -1) : FunctionPass(ID) {
initializeSROAPass(*PassRegistry::getPassRegistry());
if (T == -1)
SRThreshold = 128;
else
SRThreshold = T;
}
bool runOnFunction(Function &F);
bool performScalarRepl(Function &F);
bool performPromotion(Function &F);
// getAnalysisUsage - This pass does not require any passes, but we know it
// will not alter the CFG, so say so.
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<DominatorTree>();
AU.addRequired<DominanceFrontier>();
AU.setPreservesCFG();
}
private:
TargetData *TD;
/// DeadInsts - Keep track of instructions we have made dead, so that
/// we can remove them after we are done working.
SmallVector<Value*, 32> DeadInsts;
/// AllocaInfo - When analyzing uses of an alloca instruction, this captures
/// information about the uses. All these fields are initialized to false
/// and set to true when something is learned.
struct AllocaInfo {
/// isUnsafe - This is set to true if the alloca cannot be SROA'd.
bool isUnsafe : 1;
/// isMemCpySrc - This is true if this aggregate is memcpy'd from.
bool isMemCpySrc : 1;
/// isMemCpyDst - This is true if this aggregate is memcpy'd into.
bool isMemCpyDst : 1;
AllocaInfo()
: isUnsafe(false), isMemCpySrc(false), isMemCpyDst(false) {}
};
unsigned SRThreshold;
void MarkUnsafe(AllocaInfo &I) { I.isUnsafe = true; }
bool isSafeAllocaToScalarRepl(AllocaInst *AI);
void isSafeForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
AllocaInfo &Info);
void isSafeGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t &Offset,
AllocaInfo &Info);
void isSafeMemAccess(AllocaInst *AI, uint64_t Offset, uint64_t MemSize,
const Type *MemOpType, bool isStore, AllocaInfo &Info);
bool TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size);
uint64_t FindElementAndOffset(const Type *&T, uint64_t &Offset,
const Type *&IdxTy);
void DoScalarReplacement(AllocaInst *AI,
std::vector<AllocaInst*> &WorkList);
void DeleteDeadInstructions();
void RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
SmallVector<AllocaInst*, 32> &NewElts);
void RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset,
SmallVector<AllocaInst*, 32> &NewElts);
void RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset,
SmallVector<AllocaInst*, 32> &NewElts);
void RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst,
AllocaInst *AI,
SmallVector<AllocaInst*, 32> &NewElts);
void RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI,
SmallVector<AllocaInst*, 32> &NewElts);
void RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI,
SmallVector<AllocaInst*, 32> &NewElts);
static MemTransferInst *isOnlyCopiedFromConstantGlobal(AllocaInst *AI);
};
}
char SROA::ID = 0;
INITIALIZE_PASS_BEGIN(SROA, "scalarrepl",
"Scalar Replacement of Aggregates", false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTree)
INITIALIZE_PASS_DEPENDENCY(DominanceFrontier)
INITIALIZE_PASS_END(SROA, "scalarrepl",
"Scalar Replacement of Aggregates", false, false)
// Public interface to the ScalarReplAggregates pass
FunctionPass *llvm::createScalarReplAggregatesPass(signed int Threshold) {
return new SROA(Threshold);
}
//===----------------------------------------------------------------------===//
// Convert To Scalar Optimization.
//===----------------------------------------------------------------------===//
namespace {
/// ConvertToScalarInfo - This class implements the "Convert To Scalar"
/// optimization, which scans the uses of an alloca and determines if it can
/// rewrite it in terms of a single new alloca that can be mem2reg'd.
class ConvertToScalarInfo {
/// AllocaSize - The size of the alloca being considered.
unsigned AllocaSize;
const TargetData &TD;
/// IsNotTrivial - This is set to true if there is some access to the object
/// which means that mem2reg can't promote it.
bool IsNotTrivial;
/// VectorTy - This tracks the type that we should promote the vector to if
/// it is possible to turn it into a vector. This starts out null, and if it
/// isn't possible to turn into a vector type, it gets set to VoidTy.
const Type *VectorTy;
/// HadAVector - True if there is at least one vector access to the alloca.
/// We don't want to turn random arrays into vectors and use vector element
/// insert/extract, but if there are element accesses to something that is
/// also declared as a vector, we do want to promote to a vector.
bool HadAVector;
public:
explicit ConvertToScalarInfo(unsigned Size, const TargetData &td)
: AllocaSize(Size), TD(td) {
IsNotTrivial = false;
VectorTy = 0;
HadAVector = false;
}
AllocaInst *TryConvert(AllocaInst *AI);
private:
bool CanConvertToScalar(Value *V, uint64_t Offset);
void MergeInType(const Type *In, uint64_t Offset);
void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset);
Value *ConvertScalar_ExtractValue(Value *NV, const Type *ToType,
uint64_t Offset, IRBuilder<> &Builder);
Value *ConvertScalar_InsertValue(Value *StoredVal, Value *ExistingVal,
uint64_t Offset, IRBuilder<> &Builder);
};
} // end anonymous namespace.
/// IsVerbotenVectorType - Return true if this is a vector type ScalarRepl isn't
/// allowed to form. We do this to avoid MMX types, which is a complete hack,
/// but is required until the backend is fixed.
static bool IsVerbotenVectorType(const VectorType *VTy, const Instruction *I) {
StringRef Triple(I->getParent()->getParent()->getParent()->getTargetTriple());
if (!Triple.startswith("i386") &&
!Triple.startswith("x86_64"))
return false;
// Reject all the MMX vector types.
switch (VTy->getNumElements()) {
default: return false;
case 1: return VTy->getElementType()->isIntegerTy(64);
case 2: return VTy->getElementType()->isIntegerTy(32);
case 4: return VTy->getElementType()->isIntegerTy(16);
case 8: return VTy->getElementType()->isIntegerTy(8);
}
}
/// TryConvert - Analyze the specified alloca, and if it is safe to do so,
/// rewrite it to be a new alloca which is mem2reg'able. This returns the new
/// alloca if possible or null if not.
AllocaInst *ConvertToScalarInfo::TryConvert(AllocaInst *AI) {
// If we can't convert this scalar, or if mem2reg can trivially do it, bail
// out.
if (!CanConvertToScalar(AI, 0) || !IsNotTrivial)
return 0;
// If we were able to find a vector type that can handle this with
// insert/extract elements, and if there was at least one use that had
// a vector type, promote this to a vector. We don't want to promote
// random stuff that doesn't use vectors (e.g. <9 x double>) because then
// we just get a lot of insert/extracts. If at least one vector is
// involved, then we probably really do have a union of vector/array.
const Type *NewTy;
if (VectorTy && VectorTy->isVectorTy() && HadAVector &&
!IsVerbotenVectorType(cast<VectorType>(VectorTy), AI)) {
DEBUG(dbgs() << "CONVERT TO VECTOR: " << *AI << "\n TYPE = "
<< *VectorTy << '\n');
NewTy = VectorTy; // Use the vector type.
} else {
DEBUG(dbgs() << "CONVERT TO SCALAR INTEGER: " << *AI << "\n");
// Create and insert the integer alloca.
NewTy = IntegerType::get(AI->getContext(), AllocaSize*8);
}
AllocaInst *NewAI = new AllocaInst(NewTy, 0, "", AI->getParent()->begin());
ConvertUsesToScalar(AI, NewAI, 0);
return NewAI;
}
/// MergeInType - Add the 'In' type to the accumulated vector type (VectorTy)
/// so far at the offset specified by Offset (which is specified in bytes).
///
/// There are two cases we handle here:
/// 1) A union of vector types of the same size and potentially its elements.
/// Here we turn element accesses into insert/extract element operations.
/// This promotes a <4 x float> with a store of float to the third element
/// into a <4 x float> that uses insert element.
/// 2) A fully general blob of memory, which we turn into some (potentially
/// large) integer type with extract and insert operations where the loads
/// and stores would mutate the memory. We mark this by setting VectorTy
/// to VoidTy.
void ConvertToScalarInfo::MergeInType(const Type *In, uint64_t Offset) {
// If we already decided to turn this into a blob of integer memory, there is
// nothing to be done.
if (VectorTy && VectorTy->isVoidTy())
return;
// If this could be contributing to a vector, analyze it.
// If the In type is a vector that is the same size as the alloca, see if it
// matches the existing VecTy.
if (const VectorType *VInTy = dyn_cast<VectorType>(In)) {
// Remember if we saw a vector type.
HadAVector = true;
if (VInTy->getBitWidth()/8 == AllocaSize && Offset == 0) {
// If we're storing/loading a vector of the right size, allow it as a
// vector. If this the first vector we see, remember the type so that
// we know the element size. If this is a subsequent access, ignore it
// even if it is a differing type but the same size. Worst case we can
// bitcast the resultant vectors.
if (VectorTy == 0)
VectorTy = VInTy;
return;
}
} else if (In->isFloatTy() || In->isDoubleTy() ||
(In->isIntegerTy() && In->getPrimitiveSizeInBits() >= 8 &&
isPowerOf2_32(In->getPrimitiveSizeInBits()))) {
// If we're accessing something that could be an element of a vector, see
// if the implied vector agrees with what we already have and if Offset is
// compatible with it.
unsigned EltSize = In->getPrimitiveSizeInBits()/8;
if (Offset % EltSize == 0 && AllocaSize % EltSize == 0 &&
(VectorTy == 0 ||
cast<VectorType>(VectorTy)->getElementType()
->getPrimitiveSizeInBits()/8 == EltSize)) {
if (VectorTy == 0)
VectorTy = VectorType::get(In, AllocaSize/EltSize);
return;
}
}
// Otherwise, we have a case that we can't handle with an optimized vector
// form. We can still turn this into a large integer.
VectorTy = Type::getVoidTy(In->getContext());
}
/// CanConvertToScalar - V is a pointer. If we can convert the pointee and all
/// its accesses to a single vector type, return true and set VecTy to
/// the new type. If we could convert the alloca into a single promotable
/// integer, return true but set VecTy to VoidTy. Further, if the use is not a
/// completely trivial use that mem2reg could promote, set IsNotTrivial. Offset
/// is the current offset from the base of the alloca being analyzed.
///
/// If we see at least one access to the value that is as a vector type, set the
/// SawVec flag.
bool ConvertToScalarInfo::CanConvertToScalar(Value *V, uint64_t Offset) {
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) {
Instruction *User = cast<Instruction>(*UI);
if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
// Don't break volatile loads.
if (LI->isVolatile())
return false;
// Don't touch MMX operations.
if (LI->getType()->isX86_MMXTy())
return false;
MergeInType(LI->getType(), Offset);
continue;
}
if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
// Storing the pointer, not into the value?
if (SI->getOperand(0) == V || SI->isVolatile()) return false;
// Don't touch MMX operations.
if (SI->getOperand(0)->getType()->isX86_MMXTy())
return false;
MergeInType(SI->getOperand(0)->getType(), Offset);
continue;
}
if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
IsNotTrivial = true; // Can't be mem2reg'd.
if (!CanConvertToScalar(BCI, Offset))
return false;
continue;
}
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) {
// If this is a GEP with a variable indices, we can't handle it.
if (!GEP->hasAllConstantIndices())
return false;
// Compute the offset that this GEP adds to the pointer.
SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end());
uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(),
&Indices[0], Indices.size());
// See if all uses can be converted.
if (!CanConvertToScalar(GEP, Offset+GEPOffset))
return false;
IsNotTrivial = true; // Can't be mem2reg'd.
continue;
}
// If this is a constant sized memset of a constant value (e.g. 0) we can
// handle it.
if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) {
// Store of constant value and constant size.
if (!isa<ConstantInt>(MSI->getValue()) ||
!isa<ConstantInt>(MSI->getLength()))
return false;
IsNotTrivial = true; // Can't be mem2reg'd.
continue;
}
// If this is a memcpy or memmove into or out of the whole allocation, we
// can handle it like a load or store of the scalar type.
if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) {
ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength());
if (Len == 0 || Len->getZExtValue() != AllocaSize || Offset != 0)
return false;
IsNotTrivial = true; // Can't be mem2reg'd.
continue;
}
// Otherwise, we cannot handle this!
return false;
}
return true;
}
/// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca
/// directly. This happens when we are converting an "integer union" to a
/// single integer scalar, or when we are converting a "vector union" to a
/// vector with insert/extractelement instructions.
///
/// Offset is an offset from the original alloca, in bits that need to be
/// shifted to the right. By the end of this, there should be no uses of Ptr.
void ConvertToScalarInfo::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI,
uint64_t Offset) {
while (!Ptr->use_empty()) {
Instruction *User = cast<Instruction>(Ptr->use_back());
if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) {
ConvertUsesToScalar(CI, NewAI, Offset);
CI->eraseFromParent();
continue;
}
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) {
// Compute the offset that this GEP adds to the pointer.
SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end());
uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(),
&Indices[0], Indices.size());
ConvertUsesToScalar(GEP, NewAI, Offset+GEPOffset*8);
GEP->eraseFromParent();
continue;
}
IRBuilder<> Builder(User->getParent(), User);
if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
// The load is a bit extract from NewAI shifted right by Offset bits.
Value *LoadedVal = Builder.CreateLoad(NewAI, "tmp");
Value *NewLoadVal
= ConvertScalar_ExtractValue(LoadedVal, LI->getType(), Offset, Builder);
LI->replaceAllUsesWith(NewLoadVal);
LI->eraseFromParent();
continue;
}
if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
assert(SI->getOperand(0) != Ptr && "Consistency error!");
Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in");
Value *New = ConvertScalar_InsertValue(SI->getOperand(0), Old, Offset,
Builder);
Builder.CreateStore(New, NewAI);
SI->eraseFromParent();
// If the load we just inserted is now dead, then the inserted store
// overwrote the entire thing.
if (Old->use_empty())
Old->eraseFromParent();
continue;
}
// If this is a constant sized memset of a constant value (e.g. 0) we can
// transform it into a store of the expanded constant value.
if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) {
assert(MSI->getRawDest() == Ptr && "Consistency error!");
unsigned NumBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
if (NumBytes != 0) {
unsigned Val = cast<ConstantInt>(MSI->getValue())->getZExtValue();
// Compute the value replicated the right number of times.
APInt APVal(NumBytes*8, Val);
// Splat the value if non-zero.
if (Val)
for (unsigned i = 1; i != NumBytes; ++i)
APVal |= APVal << 8;
Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in");
Value *New = ConvertScalar_InsertValue(
ConstantInt::get(User->getContext(), APVal),
Old, Offset, Builder);
Builder.CreateStore(New, NewAI);
// If the load we just inserted is now dead, then the memset overwrote
// the entire thing.
if (Old->use_empty())
Old->eraseFromParent();
}
MSI->eraseFromParent();
continue;
}
// If this is a memcpy or memmove into or out of the whole allocation, we
// can handle it like a load or store of the scalar type.
if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) {
assert(Offset == 0 && "must be store to start of alloca");
// If the source and destination are both to the same alloca, then this is
// a noop copy-to-self, just delete it. Otherwise, emit a load and store
// as appropriate.
AllocaInst *OrigAI = cast<AllocaInst>(GetUnderlyingObject(Ptr, 0));
if (GetUnderlyingObject(MTI->getSource(), 0) != OrigAI) {
// Dest must be OrigAI, change this to be a load from the original
// pointer (bitcasted), then a store to our new alloca.
assert(MTI->getRawDest() == Ptr && "Neither use is of pointer?");
Value *SrcPtr = MTI->getSource();
const PointerType* SPTy = cast<PointerType>(SrcPtr->getType());
const PointerType* AIPTy = cast<PointerType>(NewAI->getType());
if (SPTy->getAddressSpace() != AIPTy->getAddressSpace()) {
AIPTy = PointerType::get(AIPTy->getElementType(),
SPTy->getAddressSpace());
}
SrcPtr = Builder.CreateBitCast(SrcPtr, AIPTy);
LoadInst *SrcVal = Builder.CreateLoad(SrcPtr, "srcval");
SrcVal->setAlignment(MTI->getAlignment());
Builder.CreateStore(SrcVal, NewAI);
} else if (GetUnderlyingObject(MTI->getDest(), 0) != OrigAI) {
// Src must be OrigAI, change this to be a load from NewAI then a store
// through the original dest pointer (bitcasted).
assert(MTI->getRawSource() == Ptr && "Neither use is of pointer?");
LoadInst *SrcVal = Builder.CreateLoad(NewAI, "srcval");
const PointerType* DPTy = cast<PointerType>(MTI->getDest()->getType());
const PointerType* AIPTy = cast<PointerType>(NewAI->getType());
if (DPTy->getAddressSpace() != AIPTy->getAddressSpace()) {
AIPTy = PointerType::get(AIPTy->getElementType(),
DPTy->getAddressSpace());
}
Value *DstPtr = Builder.CreateBitCast(MTI->getDest(), AIPTy);
StoreInst *NewStore = Builder.CreateStore(SrcVal, DstPtr);
NewStore->setAlignment(MTI->getAlignment());
} else {
// Noop transfer. Src == Dst
}
MTI->eraseFromParent();
continue;
}
llvm_unreachable("Unsupported operation!");
}
}
/// ConvertScalar_ExtractValue - Extract a value of type ToType from an integer
/// or vector value FromVal, extracting the bits from the offset specified by
/// Offset. This returns the value, which is of type ToType.
///
/// This happens when we are converting an "integer union" to a single
/// integer scalar, or when we are converting a "vector union" to a vector with
/// insert/extractelement instructions.
///
/// Offset is an offset from the original alloca, in bits that need to be
/// shifted to the right.
Value *ConvertToScalarInfo::
ConvertScalar_ExtractValue(Value *FromVal, const Type *ToType,
uint64_t Offset, IRBuilder<> &Builder) {
// If the load is of the whole new alloca, no conversion is needed.
if (FromVal->getType() == ToType && Offset == 0)
return FromVal;
// If the result alloca is a vector type, this is either an element
// access or a bitcast to another vector type of the same size.
if (const VectorType *VTy = dyn_cast<VectorType>(FromVal->getType())) {
if (ToType->isVectorTy())
return Builder.CreateBitCast(FromVal, ToType, "tmp");
// Otherwise it must be an element access.
unsigned Elt = 0;
if (Offset) {
unsigned EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType());
Elt = Offset/EltSize;
assert(EltSize*Elt == Offset && "Invalid modulus in validity checking");
}
// Return the element extracted out of it.
Value *V = Builder.CreateExtractElement(FromVal, ConstantInt::get(
Type::getInt32Ty(FromVal->getContext()), Elt), "tmp");
if (V->getType() != ToType)
V = Builder.CreateBitCast(V, ToType, "tmp");
return V;
}
// If ToType is a first class aggregate, extract out each of the pieces and
// use insertvalue's to form the FCA.
if (const StructType *ST = dyn_cast<StructType>(ToType)) {
const StructLayout &Layout = *TD.getStructLayout(ST);
Value *Res = UndefValue::get(ST);
for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
Value *Elt = ConvertScalar_ExtractValue(FromVal, ST->getElementType(i),
Offset+Layout.getElementOffsetInBits(i),
Builder);
Res = Builder.CreateInsertValue(Res, Elt, i, "tmp");
}
return Res;
}
if (const ArrayType *AT = dyn_cast<ArrayType>(ToType)) {
uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType());
Value *Res = UndefValue::get(AT);
for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
Value *Elt = ConvertScalar_ExtractValue(FromVal, AT->getElementType(),
Offset+i*EltSize, Builder);
Res = Builder.CreateInsertValue(Res, Elt, i, "tmp");
}
return Res;
}
// Otherwise, this must be a union that was converted to an integer value.
const IntegerType *NTy = cast<IntegerType>(FromVal->getType());
// If this is a big-endian system and the load is narrower than the
// full alloca type, we need to do a shift to get the right bits.
int ShAmt = 0;
if (TD.isBigEndian()) {
// On big-endian machines, the lowest bit is stored at the bit offset
// from the pointer given by getTypeStoreSizeInBits. This matters for
// integers with a bitwidth that is not a multiple of 8.
ShAmt = TD.getTypeStoreSizeInBits(NTy) -
TD.getTypeStoreSizeInBits(ToType) - Offset;
} else {
ShAmt = Offset;
}
// Note: we support negative bitwidths (with shl) which are not defined.
// We do this to support (f.e.) loads off the end of a structure where
// only some bits are used.
if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth())
FromVal = Builder.CreateLShr(FromVal,
ConstantInt::get(FromVal->getType(),
ShAmt), "tmp");
else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth())
FromVal = Builder.CreateShl(FromVal,
ConstantInt::get(FromVal->getType(),
-ShAmt), "tmp");
// Finally, unconditionally truncate the integer to the right width.
unsigned LIBitWidth = TD.getTypeSizeInBits(ToType);
if (LIBitWidth < NTy->getBitWidth())
FromVal =
Builder.CreateTrunc(FromVal, IntegerType::get(FromVal->getContext(),
LIBitWidth), "tmp");
else if (LIBitWidth > NTy->getBitWidth())
FromVal =
Builder.CreateZExt(FromVal, IntegerType::get(FromVal->getContext(),
LIBitWidth), "tmp");
// If the result is an integer, this is a trunc or bitcast.
if (ToType->isIntegerTy()) {
// Should be done.
} else if (ToType->isFloatingPointTy() || ToType->isVectorTy()) {
// Just do a bitcast, we know the sizes match up.
FromVal = Builder.CreateBitCast(FromVal, ToType, "tmp");
} else {
// Otherwise must be a pointer.
FromVal = Builder.CreateIntToPtr(FromVal, ToType, "tmp");
}
assert(FromVal->getType() == ToType && "Didn't convert right?");
return FromVal;
}
/// ConvertScalar_InsertValue - Insert the value "SV" into the existing integer
/// or vector value "Old" at the offset specified by Offset.
///
/// This happens when we are converting an "integer union" to a
/// single integer scalar, or when we are converting a "vector union" to a
/// vector with insert/extractelement instructions.
///
/// Offset is an offset from the original alloca, in bits that need to be
/// shifted to the right.
Value *ConvertToScalarInfo::
ConvertScalar_InsertValue(Value *SV, Value *Old,
uint64_t Offset, IRBuilder<> &Builder) {
// Convert the stored type to the actual type, shift it left to insert
// then 'or' into place.
const Type *AllocaType = Old->getType();
LLVMContext &Context = Old->getContext();
if (const VectorType *VTy = dyn_cast<VectorType>(AllocaType)) {
uint64_t VecSize = TD.getTypeAllocSizeInBits(VTy);
uint64_t ValSize = TD.getTypeAllocSizeInBits(SV->getType());
// Changing the whole vector with memset or with an access of a different
// vector type?
if (ValSize == VecSize)
return Builder.CreateBitCast(SV, AllocaType, "tmp");
uint64_t EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType());
// Must be an element insertion.
unsigned Elt = Offset/EltSize;
if (SV->getType() != VTy->getElementType())
SV = Builder.CreateBitCast(SV, VTy->getElementType(), "tmp");
SV = Builder.CreateInsertElement(Old, SV,
ConstantInt::get(Type::getInt32Ty(SV->getContext()), Elt),
"tmp");
return SV;
}
// If SV is a first-class aggregate value, insert each value recursively.
if (const StructType *ST = dyn_cast<StructType>(SV->getType())) {
const StructLayout &Layout = *TD.getStructLayout(ST);
for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
Value *Elt = Builder.CreateExtractValue(SV, i, "tmp");
Old = ConvertScalar_InsertValue(Elt, Old,
Offset+Layout.getElementOffsetInBits(i),
Builder);
}
return Old;
}
if (const ArrayType *AT = dyn_cast<ArrayType>(SV->getType())) {
uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType());
for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
Value *Elt = Builder.CreateExtractValue(SV, i, "tmp");
Old = ConvertScalar_InsertValue(Elt, Old, Offset+i*EltSize, Builder);
}
return Old;
}
// If SV is a float, convert it to the appropriate integer type.
// If it is a pointer, do the same.
unsigned SrcWidth = TD.getTypeSizeInBits(SV->getType());
unsigned DestWidth = TD.getTypeSizeInBits(AllocaType);
unsigned SrcStoreWidth = TD.getTypeStoreSizeInBits(SV->getType());
unsigned DestStoreWidth = TD.getTypeStoreSizeInBits(AllocaType);
if (SV->getType()->isFloatingPointTy() || SV->getType()->isVectorTy())
SV = Builder.CreateBitCast(SV,
IntegerType::get(SV->getContext(),SrcWidth), "tmp");
else if (SV->getType()->isPointerTy())
SV = Builder.CreatePtrToInt(SV, TD.getIntPtrType(SV->getContext()), "tmp");
// Zero extend or truncate the value if needed.
if (SV->getType() != AllocaType) {
if (SV->getType()->getPrimitiveSizeInBits() <
AllocaType->getPrimitiveSizeInBits())
SV = Builder.CreateZExt(SV, AllocaType, "tmp");
else {
// Truncation may be needed if storing more than the alloca can hold
// (undefined behavior).
SV = Builder.CreateTrunc(SV, AllocaType, "tmp");
SrcWidth = DestWidth;
SrcStoreWidth = DestStoreWidth;
}
}
// If this is a big-endian system and the store is narrower than the
// full alloca type, we need to do a shift to get the right bits.
int ShAmt = 0;
if (TD.isBigEndian()) {
// On big-endian machines, the lowest bit is stored at the bit offset
// from the pointer given by getTypeStoreSizeInBits. This matters for
// integers with a bitwidth that is not a multiple of 8.
ShAmt = DestStoreWidth - SrcStoreWidth - Offset;
} else {
ShAmt = Offset;
}
// Note: we support negative bitwidths (with shr) which are not defined.
// We do this to support (f.e.) stores off the end of a structure where
// only some bits in the structure are set.
APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth));
if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) {
SV = Builder.CreateShl(SV, ConstantInt::get(SV->getType(),
ShAmt), "tmp");
Mask <<= ShAmt;
} else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) {
SV = Builder.CreateLShr(SV, ConstantInt::get(SV->getType(),
-ShAmt), "tmp");
Mask = Mask.lshr(-ShAmt);
}
// Mask out the bits we are about to insert from the old value, and or
// in the new bits.
if (SrcWidth != DestWidth) {
assert(DestWidth > SrcWidth);
Old = Builder.CreateAnd(Old, ConstantInt::get(Context, ~Mask), "mask");
SV = Builder.CreateOr(Old, SV, "ins");
}
return SV;
}
//===----------------------------------------------------------------------===//
// SRoA Driver
//===----------------------------------------------------------------------===//
bool SROA::runOnFunction(Function &F) {
TD = getAnalysisIfAvailable<TargetData>();
bool Changed = performPromotion(F);
// FIXME: ScalarRepl currently depends on TargetData more than it
// theoretically needs to. It should be refactored in order to support
// target-independent IR. Until this is done, just skip the actual
// scalar-replacement portion of this pass.
if (!TD) return Changed;
while (1) {
bool LocalChange = performScalarRepl(F);
if (!LocalChange) break; // No need to repromote if no scalarrepl
Changed = true;
LocalChange = performPromotion(F);
if (!LocalChange) break; // No need to re-scalarrepl if no promotion
}
return Changed;
}
bool SROA::performPromotion(Function &F) {
std::vector<AllocaInst*> Allocas;
DominatorTree &DT = getAnalysis<DominatorTree>();
DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function
bool Changed = false;
while (1) {
Allocas.clear();
// Find allocas that are safe to promote, by looking at all instructions in
// the entry node
for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca?
if (isAllocaPromotable(AI))
Allocas.push_back(AI);
if (Allocas.empty()) break;
PromoteMemToReg(Allocas, DT, DF);
NumPromoted += Allocas.size();
Changed = true;
}
return Changed;
}
/// ShouldAttemptScalarRepl - Decide if an alloca is a good candidate for
/// SROA. It must be a struct or array type with a small number of elements.
static bool ShouldAttemptScalarRepl(AllocaInst *AI) {
const Type *T = AI->getAllocatedType();
// Do not promote any struct into more than 32 separate vars.
if (const StructType *ST = dyn_cast<StructType>(T))
return ST->getNumElements() <= 32;
// Arrays are much less likely to be safe for SROA; only consider
// them if they are very small.
if (const ArrayType *AT = dyn_cast<ArrayType>(T))
return AT->getNumElements() <= 8;
return false;
}
// performScalarRepl - This algorithm is a simple worklist driven algorithm,
// which runs on all of the malloc/alloca instructions in the function, removing
// them if they are only used by getelementptr instructions.
//
bool SROA::performScalarRepl(Function &F) {
std::vector<AllocaInst*> WorkList;
// Scan the entry basic block, adding allocas to the worklist.
BasicBlock &BB = F.getEntryBlock();
for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I)
if (AllocaInst *A = dyn_cast<AllocaInst>(I))
WorkList.push_back(A);
// Process the worklist
bool Changed = false;
while (!WorkList.empty()) {
AllocaInst *AI = WorkList.back();
WorkList.pop_back();
// Handle dead allocas trivially. These can be formed by SROA'ing arrays
// with unused elements.
if (AI->use_empty()) {
AI->eraseFromParent();
Changed = true;
continue;
}
// If this alloca is impossible for us to promote, reject it early.
if (AI->isArrayAllocation() || !AI->getAllocatedType()->isSized())
continue;
// Check to see if this allocation is only modified by a memcpy/memmove from
// a constant global. If this is the case, we can change all users to use
// the constant global instead. This is commonly produced by the CFE by
// constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A'
// is only subsequently read.
if (MemTransferInst *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) {
DEBUG(dbgs() << "Found alloca equal to global: " << *AI << '\n');
DEBUG(dbgs() << " memcpy = " << *TheCopy << '\n');
Constant *TheSrc = cast<Constant>(TheCopy->getSource());
AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType()));
TheCopy->eraseFromParent(); // Don't mutate the global.
AI->eraseFromParent();
++NumGlobals;
Changed = true;
continue;
}
// Check to see if we can perform the core SROA transformation. We cannot
// transform the allocation instruction if it is an array allocation
// (allocations OF arrays are ok though), and an allocation of a scalar
// value cannot be decomposed at all.
uint64_t AllocaSize = TD->getTypeAllocSize(AI->getAllocatedType());
// Do not promote [0 x %struct].
if (AllocaSize == 0) continue;
// Do not promote any struct whose size is too big.
if (AllocaSize > SRThreshold) continue;
// If the alloca looks like a good candidate for scalar replacement, and if
// all its users can be transformed, then split up the aggregate into its
// separate elements.
if (ShouldAttemptScalarRepl(AI) && isSafeAllocaToScalarRepl(AI)) {
DoScalarReplacement(AI, WorkList);
Changed = true;
continue;
}
// If we can turn this aggregate value (potentially with casts) into a
// simple scalar value that can be mem2reg'd into a register value.
// IsNotTrivial tracks whether this is something that mem2reg could have
// promoted itself. If so, we don't want to transform it needlessly. Note
// that we can't just check based on the type: the alloca may be of an i32
// but that has pointer arithmetic to set byte 3 of it or something.
if (AllocaInst *NewAI =
ConvertToScalarInfo((unsigned)AllocaSize, *TD).TryConvert(AI)) {
NewAI->takeName(AI);
AI->eraseFromParent();
++NumConverted;
Changed = true;
continue;
}
// Otherwise, couldn't process this alloca.
}
return Changed;
}
/// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl
/// predicate, do SROA now.
void SROA::DoScalarReplacement(AllocaInst *AI,
std::vector<AllocaInst*> &WorkList) {
DEBUG(dbgs() << "Found inst to SROA: " << *AI << '\n');
SmallVector<AllocaInst*, 32> ElementAllocas;
if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) {
ElementAllocas.reserve(ST->getNumContainedTypes());
for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) {
AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0,
AI->getAlignment(),
AI->getName() + "." + Twine(i), AI);
ElementAllocas.push_back(NA);
WorkList.push_back(NA); // Add to worklist for recursive processing
}
} else {
const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType());
ElementAllocas.reserve(AT->getNumElements());
const Type *ElTy = AT->getElementType();
for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(),
AI->getName() + "." + Twine(i), AI);
ElementAllocas.push_back(NA);
WorkList.push_back(NA); // Add to worklist for recursive processing
}
}
// Now that we have created the new alloca instructions, rewrite all the
// uses of the old alloca.
RewriteForScalarRepl(AI, AI, 0, ElementAllocas);
// Now erase any instructions that were made dead while rewriting the alloca.
DeleteDeadInstructions();
AI->eraseFromParent();
++NumReplaced;
}
/// DeleteDeadInstructions - Erase instructions on the DeadInstrs list,
/// recursively including all their operands that become trivially dead.
void SROA::DeleteDeadInstructions() {
while (!DeadInsts.empty()) {
Instruction *I = cast<Instruction>(DeadInsts.pop_back_val());
for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI)
if (Instruction *U = dyn_cast<Instruction>(*OI)) {
// Zero out the operand and see if it becomes trivially dead.
// (But, don't add allocas to the dead instruction list -- they are
// already on the worklist and will be deleted separately.)
*OI = 0;
if (isInstructionTriviallyDead(U) && !isa<AllocaInst>(U))
DeadInsts.push_back(U);
}
I->eraseFromParent();
}
}
/// isSafeForScalarRepl - Check if instruction I is a safe use with regard to
/// performing scalar replacement of alloca AI. The results are flagged in
/// the Info parameter. Offset indicates the position within AI that is
/// referenced by this instruction.
void SROA::isSafeForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
AllocaInfo &Info) {
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) {
Instruction *User = cast<Instruction>(*UI);
if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) {
isSafeForScalarRepl(BC, AI, Offset, Info);
} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
uint64_t GEPOffset = Offset;
isSafeGEP(GEPI, AI, GEPOffset, Info);
if (!Info.isUnsafe)
isSafeForScalarRepl(GEPI, AI, GEPOffset, Info);
} else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength());
if (Length)
isSafeMemAccess(AI, Offset, Length->getZExtValue(), 0,
UI.getOperandNo() == 0, Info);
else
MarkUnsafe(Info);
} else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
if (!LI->isVolatile()) {
const Type *LIType = LI->getType();
isSafeMemAccess(AI, Offset, TD->getTypeAllocSize(LIType),
LIType, false, Info);
} else
MarkUnsafe(Info);
} else if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
// Store is ok if storing INTO the pointer, not storing the pointer
if (!SI->isVolatile() && SI->getOperand(0) != I) {
const Type *SIType = SI->getOperand(0)->getType();
isSafeMemAccess(AI, Offset, TD->getTypeAllocSize(SIType),
SIType, true, Info);
} else
MarkUnsafe(Info);
} else {
DEBUG(errs() << " Transformation preventing inst: " << *User << '\n');
MarkUnsafe(Info);
}
if (Info.isUnsafe) return;
}
}
/// isSafeGEP - Check if a GEP instruction can be handled for scalar
/// replacement. It is safe when all the indices are constant, in-bounds
/// references, and when the resulting offset corresponds to an element within
/// the alloca type. The results are flagged in the Info parameter. Upon
/// return, Offset is adjusted as specified by the GEP indices.
void SROA::isSafeGEP(GetElementPtrInst *GEPI, AllocaInst *AI,
uint64_t &Offset, AllocaInfo &Info) {
gep_type_iterator GEPIt = gep_type_begin(GEPI), E = gep_type_end(GEPI);
if (GEPIt == E)
return;
// Walk through the GEP type indices, checking the types that this indexes
// into.
for (; GEPIt != E; ++GEPIt) {
// Ignore struct elements, no extra checking needed for these.
if ((*GEPIt)->isStructTy())
continue;
ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPIt.getOperand());
if (!IdxVal)
return MarkUnsafe(Info);
}
// Compute the offset due to this GEP and check if the alloca has a
// component element at that offset.
SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end());
Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(),
&Indices[0], Indices.size());
if (!TypeHasComponent(AI->getAllocatedType(), Offset, 0))
MarkUnsafe(Info);
}
/// isSafeMemAccess - Check if a load/store/memcpy operates on the entire AI
/// alloca or has an offset and size that corresponds to a component element
/// within it. The offset checked here may have been formed from a GEP with a
/// pointer bitcasted to a different type.
void SROA::isSafeMemAccess(AllocaInst *AI, uint64_t Offset, uint64_t MemSize,
const Type *MemOpType, bool isStore,
AllocaInfo &Info) {
// Check if this is a load/store of the entire alloca.
if (Offset == 0 && MemSize == TD->getTypeAllocSize(AI->getAllocatedType())) {
bool UsesAggregateType = (MemOpType == AI->getAllocatedType());
// This is safe for MemIntrinsics (where MemOpType is 0), integer types
// (which are essentially the same as the MemIntrinsics, especially with
// regard to copying padding between elements), or references using the
// aggregate type of the alloca.
if (!MemOpType || MemOpType->isIntegerTy() || UsesAggregateType) {
if (!UsesAggregateType) {
if (isStore)
Info.isMemCpyDst = true;
else
Info.isMemCpySrc = true;
}
return;
}
}
// Check if the offset/size correspond to a component within the alloca type.
const Type *T = AI->getAllocatedType();
if (TypeHasComponent(T, Offset, MemSize))
return;
return MarkUnsafe(Info);
}
/// TypeHasComponent - Return true if T has a component type with the
/// specified offset and size. If Size is zero, do not check the size.
bool SROA::TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size) {
const Type *EltTy;
uint64_t EltSize;
if (const StructType *ST = dyn_cast<StructType>(T)) {
const StructLayout *Layout = TD->getStructLayout(ST);
unsigned EltIdx = Layout->getElementContainingOffset(Offset);
EltTy = ST->getContainedType(EltIdx);
EltSize = TD->getTypeAllocSize(EltTy);
Offset -= Layout->getElementOffset(EltIdx);
} else if (const ArrayType *AT = dyn_cast<ArrayType>(T)) {
EltTy = AT->getElementType();
EltSize = TD->getTypeAllocSize(EltTy);
if (Offset >= AT->getNumElements() * EltSize)
return false;
Offset %= EltSize;
} else {
return false;
}
if (Offset == 0 && (Size == 0 || EltSize == Size))
return true;
// Check if the component spans multiple elements.
if (Offset + Size > EltSize)
return false;
return TypeHasComponent(EltTy, Offset, Size);
}
/// RewriteForScalarRepl - Alloca AI is being split into NewElts, so rewrite
/// the instruction I, which references it, to use the separate elements.
/// Offset indicates the position within AI that is referenced by this
/// instruction.
void SROA::RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
SmallVector<AllocaInst*, 32> &NewElts) {
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) {
Instruction *User = cast<Instruction>(*UI);
if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) {
RewriteBitCast(BC, AI, Offset, NewElts);
} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
RewriteGEP(GEPI, AI, Offset, NewElts);
} else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength());
uint64_t MemSize = Length->getZExtValue();
if (Offset == 0 &&
MemSize == TD->getTypeAllocSize(AI->getAllocatedType()))
RewriteMemIntrinUserOfAlloca(MI, I, AI, NewElts);
// Otherwise the intrinsic can only touch a single element and the
// address operand will be updated, so nothing else needs to be done.
} else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
const Type *LIType = LI->getType();
if (LIType == AI->getAllocatedType()) {
// Replace:
// %res = load { i32, i32 }* %alloc
// with:
// %load.0 = load i32* %alloc.0
// %insert.0 insertvalue { i32, i32 } zeroinitializer, i32 %load.0, 0
// %load.1 = load i32* %alloc.1
// %insert = insertvalue { i32, i32 } %insert.0, i32 %load.1, 1
// (Also works for arrays instead of structs)
Value *Insert = UndefValue::get(LIType);
for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
Value *Load = new LoadInst(NewElts[i], "load", LI);
Insert = InsertValueInst::Create(Insert, Load, i, "insert", LI);
}
LI->replaceAllUsesWith(Insert);
DeadInsts.push_back(LI);
} else if (LIType->isIntegerTy() &&
TD->getTypeAllocSize(LIType) ==
TD->getTypeAllocSize(AI->getAllocatedType())) {
// If this is a load of the entire alloca to an integer, rewrite it.
RewriteLoadUserOfWholeAlloca(LI, AI, NewElts);
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
Value *Val = SI->getOperand(0);
const Type *SIType = Val->getType();
if (SIType == AI->getAllocatedType()) {
// Replace:
// store { i32, i32 } %val, { i32, i32 }* %alloc
// with:
// %val.0 = extractvalue { i32, i32 } %val, 0
// store i32 %val.0, i32* %alloc.0
// %val.1 = extractvalue { i32, i32 } %val, 1
// store i32 %val.1, i32* %alloc.1
// (Also works for arrays instead of structs)
for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
Value *Extract = ExtractValueInst::Create(Val, i, Val->getName(), SI);
new StoreInst(Extract, NewElts[i], SI);
}
DeadInsts.push_back(SI);
} else if (SIType->isIntegerTy() &&
TD->getTypeAllocSize(SIType) ==
TD->getTypeAllocSize(AI->getAllocatedType())) {
// If this is a store of the entire alloca from an integer, rewrite it.
RewriteStoreUserOfWholeAlloca(SI, AI, NewElts);
}
}
}
}
/// RewriteBitCast - Update a bitcast reference to the alloca being replaced
/// and recursively continue updating all of its uses.
void SROA::RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset,
SmallVector<AllocaInst*, 32> &NewElts) {
RewriteForScalarRepl(BC, AI, Offset, NewElts);
if (BC->getOperand(0) != AI)
return;
// The bitcast references the original alloca. Replace its uses with
// references to the first new element alloca.
Instruction *Val = NewElts[0];
if (Val->getType() != BC->getDestTy()) {
Val = new BitCastInst(Val, BC->getDestTy(), "", BC);
Val->takeName(BC);
}
BC->replaceAllUsesWith(Val);
DeadInsts.push_back(BC);
}
/// FindElementAndOffset - Return the index of the element containing Offset
/// within the specified type, which must be either a struct or an array.
/// Sets T to the type of the element and Offset to the offset within that
/// element. IdxTy is set to the type of the index result to be used in a
/// GEP instruction.
uint64_t SROA::FindElementAndOffset(const Type *&T, uint64_t &Offset,
const Type *&IdxTy) {
uint64_t Idx = 0;
if (const StructType *ST = dyn_cast<StructType>(T)) {
const StructLayout *Layout = TD->getStructLayout(ST);
Idx = Layout->getElementContainingOffset(Offset);
T = ST->getContainedType(Idx);
Offset -= Layout->getElementOffset(Idx);
IdxTy = Type::getInt32Ty(T->getContext());
return Idx;
}
const ArrayType *AT = cast<ArrayType>(T);
T = AT->getElementType();
uint64_t EltSize = TD->getTypeAllocSize(T);
Idx = Offset / EltSize;
Offset -= Idx * EltSize;
IdxTy = Type::getInt64Ty(T->getContext());
return Idx;
}
/// RewriteGEP - Check if this GEP instruction moves the pointer across
/// elements of the alloca that are being split apart, and if so, rewrite
/// the GEP to be relative to the new element.
void SROA::RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset,
SmallVector<AllocaInst*, 32> &NewElts) {
uint64_t OldOffset = Offset;
SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end());
Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(),
&Indices[0], Indices.size());
RewriteForScalarRepl(GEPI, AI, Offset, NewElts);
const Type *T = AI->getAllocatedType();
const Type *IdxTy;
uint64_t OldIdx = FindElementAndOffset(T, OldOffset, IdxTy);
if (GEPI->getOperand(0) == AI)
OldIdx = ~0ULL; // Force the GEP to be rewritten.
T = AI->getAllocatedType();
uint64_t EltOffset = Offset;
uint64_t Idx = FindElementAndOffset(T, EltOffset, IdxTy);
// If this GEP does not move the pointer across elements of the alloca
// being split, then it does not needs to be rewritten.
if (Idx == OldIdx)
return;
const Type *i32Ty = Type::getInt32Ty(AI->getContext());
SmallVector<Value*, 8> NewArgs;
NewArgs.push_back(Constant::getNullValue(i32Ty));
while (EltOffset != 0) {
uint64_t EltIdx = FindElementAndOffset(T, EltOffset, IdxTy);
NewArgs.push_back(ConstantInt::get(IdxTy, EltIdx));
}
Instruction *Val = NewElts[Idx];
if (NewArgs.size() > 1) {
Val = GetElementPtrInst::CreateInBounds(Val, NewArgs.begin(),
NewArgs.end(), "", GEPI);
Val->takeName(GEPI);
}
if (Val->getType() != GEPI->getType())
Val = new BitCastInst(Val, GEPI->getType(), Val->getName(), GEPI);
GEPI->replaceAllUsesWith(Val);
DeadInsts.push_back(GEPI);
}
/// RewriteMemIntrinUserOfAlloca - MI is a memcpy/memset/memmove from or to AI.
/// Rewrite it to copy or set the elements of the scalarized memory.
void SROA::RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst,
AllocaInst *AI,
SmallVector<AllocaInst*, 32> &NewElts) {
// If this is a memcpy/memmove, construct the other pointer as the
// appropriate type. The "Other" pointer is the pointer that goes to memory
// that doesn't have anything to do with the alloca that we are promoting. For
// memset, this Value* stays null.
Value *OtherPtr = 0;
unsigned MemAlignment = MI->getAlignment();
if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) { // memmove/memcopy
if (Inst == MTI->getRawDest())
OtherPtr = MTI->getRawSource();
else {
assert(Inst == MTI->getRawSource());
OtherPtr = MTI->getRawDest();
}
}
// If there is an other pointer, we want to convert it to the same pointer
// type as AI has, so we can GEP through it safely.
if (OtherPtr) {
unsigned AddrSpace =
cast<PointerType>(OtherPtr->getType())->getAddressSpace();
// Remove bitcasts and all-zero GEPs from OtherPtr. This is an
// optimization, but it's also required to detect the corner case where
// both pointer operands are referencing the same memory, and where
// OtherPtr may be a bitcast or GEP that currently being rewritten. (This
// function is only called for mem intrinsics that access the whole
// aggregate, so non-zero GEPs are not an issue here.)
OtherPtr = OtherPtr->stripPointerCasts();
// Copying the alloca to itself is a no-op: just delete it.
if (OtherPtr == AI || OtherPtr == NewElts[0]) {
// This code will run twice for a no-op memcpy -- once for each operand.
// Put only one reference to MI on the DeadInsts list.
for (SmallVector<Value*, 32>::const_iterator I = DeadInsts.begin(),
E = DeadInsts.end(); I != E; ++I)
if (*I == MI) return;
DeadInsts.push_back(MI);
return;
}
// If the pointer is not the right type, insert a bitcast to the right
// type.
const Type *NewTy =
PointerType::get(AI->getType()->getElementType(), AddrSpace);
if (OtherPtr->getType() != NewTy)
OtherPtr = new BitCastInst(OtherPtr, NewTy, OtherPtr->getName(), MI);
}
// Process each element of the aggregate.
Value *TheFn = MI->getCalledValue();
const Type *BytePtrTy = MI->getRawDest()->getType();
bool SROADest = MI->getRawDest() == Inst;
Constant *Zero = Constant::getNullValue(Type::getInt32Ty(MI->getContext()));
for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
// If this is a memcpy/memmove, emit a GEP of the other element address.
Value *OtherElt = 0;
unsigned OtherEltAlign = MemAlignment;
if (OtherPtr) {
Value *Idx[2] = { Zero,
ConstantInt::get(Type::getInt32Ty(MI->getContext()), i) };
OtherElt = GetElementPtrInst::CreateInBounds(OtherPtr, Idx, Idx + 2,
OtherPtr->getName()+"."+Twine(i),
MI);
uint64_t EltOffset;
const PointerType *OtherPtrTy = cast<PointerType>(OtherPtr->getType());
const Type *OtherTy = OtherPtrTy->getElementType();
if (const StructType *ST = dyn_cast<StructType>(OtherTy)) {
EltOffset = TD->getStructLayout(ST)->getElementOffset(i);
} else {
const Type *EltTy = cast<SequentialType>(OtherTy)->getElementType();
EltOffset = TD->getTypeAllocSize(EltTy)*i;
}
// The alignment of the other pointer is the guaranteed alignment of the
// element, which is affected by both the known alignment of the whole
// mem intrinsic and the alignment of the element. If the alignment of
// the memcpy (f.e.) is 32 but the element is at a 4-byte offset, then the
// known alignment is just 4 bytes.
OtherEltAlign = (unsigned)MinAlign(OtherEltAlign, EltOffset);
}
Value *EltPtr = NewElts[i];
const Type *EltTy = cast<PointerType>(EltPtr->getType())->getElementType();
// If we got down to a scalar, insert a load or store as appropriate.
if (EltTy->isSingleValueType()) {
if (isa<MemTransferInst>(MI)) {
if (SROADest) {
// From Other to Alloca.
Value *Elt = new LoadInst(OtherElt, "tmp", false, OtherEltAlign, MI);
new StoreInst(Elt, EltPtr, MI);
} else {
// From Alloca to Other.
Value *Elt = new LoadInst(EltPtr, "tmp", MI);
new StoreInst(Elt, OtherElt, false, OtherEltAlign, MI);
}
continue;
}
assert(isa<MemSetInst>(MI));
// If the stored element is zero (common case), just store a null
// constant.
Constant *StoreVal;
if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getArgOperand(1))) {
if (CI->isZero()) {
StoreVal = Constant::getNullValue(EltTy); // 0.0, null, 0, <0,0>
} else {
// If EltTy is a vector type, get the element type.
const Type *ValTy = EltTy->getScalarType();
// Construct an integer with the right value.
unsigned EltSize = TD->getTypeSizeInBits(ValTy);
APInt OneVal(EltSize, CI->getZExtValue());
APInt TotalVal(OneVal);
// Set each byte.
for (unsigned i = 0; 8*i < EltSize; ++i) {
TotalVal = TotalVal.shl(8);
TotalVal |= OneVal;
}
// Convert the integer value to the appropriate type.
StoreVal = ConstantInt::get(CI->getContext(), TotalVal);
if (ValTy->isPointerTy())
StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy);
else if (ValTy->isFloatingPointTy())
StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy);
assert(StoreVal->getType() == ValTy && "Type mismatch!");
// If the requested value was a vector constant, create it.
if (EltTy != ValTy) {
unsigned NumElts = cast<VectorType>(ValTy)->getNumElements();
SmallVector<Constant*, 16> Elts(NumElts, StoreVal);
StoreVal = ConstantVector::get(&Elts[0], NumElts);
}
}
new StoreInst(StoreVal, EltPtr, MI);
continue;
}
// Otherwise, if we're storing a byte variable, use a memset call for
// this element.
}
// Cast the element pointer to BytePtrTy.
if (EltPtr->getType() != BytePtrTy)
EltPtr = new BitCastInst(EltPtr, BytePtrTy, EltPtr->getName(), MI);
// Cast the other pointer (if we have one) to BytePtrTy.
if (OtherElt && OtherElt->getType() != BytePtrTy) {
// Preserve address space of OtherElt
const PointerType* OtherPTy = cast<PointerType>(OtherElt->getType());
const PointerType* PTy = cast<PointerType>(BytePtrTy);
if (OtherPTy->getElementType() != PTy->getElementType()) {
Type *NewOtherPTy = PointerType::get(PTy->getElementType(),
OtherPTy->getAddressSpace());
OtherElt = new BitCastInst(OtherElt, NewOtherPTy,
OtherElt->getName(), MI);
}
}
unsigned EltSize = TD->getTypeAllocSize(EltTy);
// Finally, insert the meminst for this element.
if (isa<MemTransferInst>(MI)) {
Value *Ops[] = {
SROADest ? EltPtr : OtherElt, // Dest ptr
SROADest ? OtherElt : EltPtr, // Src ptr
ConstantInt::get(MI->getArgOperand(2)->getType(), EltSize), // Size
// Align
ConstantInt::get(Type::getInt32Ty(MI->getContext()), OtherEltAlign),
MI->getVolatileCst()
};
// In case we fold the address space overloaded memcpy of A to B
// with memcpy of B to C, change the function to be a memcpy of A to C.
const Type *Tys[] = { Ops[0]->getType(), Ops[1]->getType(),
Ops[2]->getType() };
Module *M = MI->getParent()->getParent()->getParent();
TheFn = Intrinsic::getDeclaration(M, MI->getIntrinsicID(), Tys, 3);
CallInst::Create(TheFn, Ops, Ops + 5, "", MI);
} else {
assert(isa<MemSetInst>(MI));
Value *Ops[] = {
EltPtr, MI->getArgOperand(1), // Dest, Value,
ConstantInt::get(MI->getArgOperand(2)->getType(), EltSize), // Size
Zero, // Align
ConstantInt::getFalse(MI->getContext()) // isVolatile
};
const Type *Tys[] = { Ops[0]->getType(), Ops[2]->getType() };
Module *M = MI->getParent()->getParent()->getParent();
TheFn = Intrinsic::getDeclaration(M, Intrinsic::memset, Tys, 2);
CallInst::Create(TheFn, Ops, Ops + 5, "", MI);
}
}
DeadInsts.push_back(MI);
}
/// RewriteStoreUserOfWholeAlloca - We found a store of an integer that
/// overwrites the entire allocation. Extract out the pieces of the stored
/// integer and store them individually.
void SROA::RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI,
SmallVector<AllocaInst*, 32> &NewElts){
// Extract each element out of the integer according to its structure offset
// and store the element value to the individual alloca.
Value *SrcVal = SI->getOperand(0);
const Type *AllocaEltTy = AI->getAllocatedType();
uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy);
// Handle tail padding by extending the operand
if (TD->getTypeSizeInBits(SrcVal->getType()) != AllocaSizeBits)
SrcVal = new ZExtInst(SrcVal,
IntegerType::get(SI->getContext(), AllocaSizeBits),
"", SI);
DEBUG(dbgs() << "PROMOTING STORE TO WHOLE ALLOCA: " << *AI << '\n' << *SI
<< '\n');
// There are two forms here: AI could be an array or struct. Both cases
// have different ways to compute the element offset.
if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) {
const StructLayout *Layout = TD->getStructLayout(EltSTy);
for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
// Get the number of bits to shift SrcVal to get the value.
const Type *FieldTy = EltSTy->getElementType(i);
uint64_t Shift = Layout->getElementOffsetInBits(i);
if (TD->isBigEndian())
Shift = AllocaSizeBits-Shift-TD->getTypeAllocSizeInBits(FieldTy);
Value *EltVal = SrcVal;
if (Shift) {
Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift);
EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal,
"sroa.store.elt", SI);
}
// Truncate down to an integer of the right size.
uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy);
// Ignore zero sized fields like {}, they obviously contain no data.
if (FieldSizeBits == 0) continue;
if (FieldSizeBits != AllocaSizeBits)
EltVal = new TruncInst(EltVal,
IntegerType::get(SI->getContext(), FieldSizeBits),
"", SI);
Value *DestField = NewElts[i];
if (EltVal->getType() == FieldTy) {
// Storing to an integer field of this size, just do it.
} else if (FieldTy->isFloatingPointTy() || FieldTy->isVectorTy()) {
// Bitcast to the right element type (for fp/vector values).
EltVal = new BitCastInst(EltVal, FieldTy, "", SI);
} else {
// Otherwise, bitcast the dest pointer (for aggregates).
DestField = new BitCastInst(DestField,
PointerType::getUnqual(EltVal->getType()),
"", SI);
}
new StoreInst(EltVal, DestField, SI);
}
} else {
const ArrayType *ATy = cast<ArrayType>(AllocaEltTy);
const Type *ArrayEltTy = ATy->getElementType();
uint64_t ElementOffset = TD->getTypeAllocSizeInBits(ArrayEltTy);
uint64_t ElementSizeBits = TD->getTypeSizeInBits(ArrayEltTy);
uint64_t Shift;
if (TD->isBigEndian())
Shift = AllocaSizeBits-ElementOffset;
else
Shift = 0;
for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
// Ignore zero sized fields like {}, they obviously contain no data.
if (ElementSizeBits == 0) continue;
Value *EltVal = SrcVal;
if (Shift) {
Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift);
EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal,
"sroa.store.elt", SI);
}
// Truncate down to an integer of the right size.
if (ElementSizeBits != AllocaSizeBits)
EltVal = new TruncInst(EltVal,
IntegerType::get(SI->getContext(),
ElementSizeBits),"",SI);
Value *DestField = NewElts[i];
if (EltVal->getType() == ArrayEltTy) {
// Storing to an integer field of this size, just do it.
} else if (ArrayEltTy->isFloatingPointTy() ||
ArrayEltTy->isVectorTy()) {
// Bitcast to the right element type (for fp/vector values).
EltVal = new BitCastInst(EltVal, ArrayEltTy, "", SI);
} else {
// Otherwise, bitcast the dest pointer (for aggregates).
DestField = new BitCastInst(DestField,
PointerType::getUnqual(EltVal->getType()),
"", SI);
}
new StoreInst(EltVal, DestField, SI);
if (TD->isBigEndian())
Shift -= ElementOffset;
else
Shift += ElementOffset;
}
}
DeadInsts.push_back(SI);
}
/// RewriteLoadUserOfWholeAlloca - We found a load of the entire allocation to
/// an integer. Load the individual pieces to form the aggregate value.
void SROA::RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI,
SmallVector<AllocaInst*, 32> &NewElts) {
// Extract each element out of the NewElts according to its structure offset
// and form the result value.
const Type *AllocaEltTy = AI->getAllocatedType();
uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy);
DEBUG(dbgs() << "PROMOTING LOAD OF WHOLE ALLOCA: " << *AI << '\n' << *LI
<< '\n');
// There are two forms here: AI could be an array or struct. Both cases
// have different ways to compute the element offset.
const StructLayout *Layout = 0;
uint64_t ArrayEltBitOffset = 0;
if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) {
Layout = TD->getStructLayout(EltSTy);
} else {
const Type *ArrayEltTy = cast<ArrayType>(AllocaEltTy)->getElementType();
ArrayEltBitOffset = TD->getTypeAllocSizeInBits(ArrayEltTy);
}
Value *ResultVal =
Constant::getNullValue(IntegerType::get(LI->getContext(), AllocaSizeBits));
for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
// Load the value from the alloca. If the NewElt is an aggregate, cast
// the pointer to an integer of the same size before doing the load.
Value *SrcField = NewElts[i];
const Type *FieldTy =
cast<PointerType>(SrcField->getType())->getElementType();
uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy);
// Ignore zero sized fields like {}, they obviously contain no data.
if (FieldSizeBits == 0) continue;
const IntegerType *FieldIntTy = IntegerType::get(LI->getContext(),
FieldSizeBits);
if (!FieldTy->isIntegerTy() && !FieldTy->isFloatingPointTy() &&
!FieldTy->isVectorTy())
SrcField = new BitCastInst(SrcField,
PointerType::getUnqual(FieldIntTy),
"", LI);
SrcField = new LoadInst(SrcField, "sroa.load.elt", LI);
// If SrcField is a fp or vector of the right size but that isn't an
// integer type, bitcast to an integer so we can shift it.
if (SrcField->getType() != FieldIntTy)
SrcField = new BitCastInst(SrcField, FieldIntTy, "", LI);
// Zero extend the field to be the same size as the final alloca so that
// we can shift and insert it.
if (SrcField->getType() != ResultVal->getType())
SrcField = new ZExtInst(SrcField, ResultVal->getType(), "", LI);
// Determine the number of bits to shift SrcField.
uint64_t Shift;
if (Layout) // Struct case.
Shift = Layout->getElementOffsetInBits(i);
else // Array case.
Shift = i*ArrayEltBitOffset;
if (TD->isBigEndian())
Shift = AllocaSizeBits-Shift-FieldIntTy->getBitWidth();
if (Shift) {
Value *ShiftVal = ConstantInt::get(SrcField->getType(), Shift);
SrcField = BinaryOperator::CreateShl(SrcField, ShiftVal, "", LI);
}
// Don't create an 'or x, 0' on the first iteration.
if (!isa<Constant>(ResultVal) ||
!cast<Constant>(ResultVal)->isNullValue())
ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI);
else
ResultVal = SrcField;
}
// Handle tail padding by truncating the result
if (TD->getTypeSizeInBits(LI->getType()) != AllocaSizeBits)
ResultVal = new TruncInst(ResultVal, LI->getType(), "", LI);
LI->replaceAllUsesWith(ResultVal);
DeadInsts.push_back(LI);
}
/// HasPadding - Return true if the specified type has any structure or
/// alignment padding, false otherwise.
static bool HasPadding(const Type *Ty, const TargetData &TD) {
if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty))
return HasPadding(ATy->getElementType(), TD);
if (const VectorType *VTy = dyn_cast<VectorType>(Ty))
return HasPadding(VTy->getElementType(), TD);
if (const StructType *STy = dyn_cast<StructType>(Ty)) {
const StructLayout *SL = TD.getStructLayout(STy);
unsigned PrevFieldBitOffset = 0;
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
unsigned FieldBitOffset = SL->getElementOffsetInBits(i);
// Padding in sub-elements?
if (HasPadding(STy->getElementType(i), TD))
return true;
// Check to see if there is any padding between this element and the
// previous one.
if (i) {
unsigned PrevFieldEnd =
PrevFieldBitOffset+TD.getTypeSizeInBits(STy->getElementType(i-1));
if (PrevFieldEnd < FieldBitOffset)
return true;
}
PrevFieldBitOffset = FieldBitOffset;
}
// Check for tail padding.
if (unsigned EltCount = STy->getNumElements()) {
unsigned PrevFieldEnd = PrevFieldBitOffset +
TD.getTypeSizeInBits(STy->getElementType(EltCount-1));
if (PrevFieldEnd < SL->getSizeInBits())
return true;
}
}
return TD.getTypeSizeInBits(Ty) != TD.getTypeAllocSizeInBits(Ty);
}
/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of
/// an aggregate can be broken down into elements. Return 0 if not, 3 if safe,
/// or 1 if safe after canonicalization has been performed.
bool SROA::isSafeAllocaToScalarRepl(AllocaInst *AI) {
// Loop over the use list of the alloca. We can only transform it if all of
// the users are safe to transform.
AllocaInfo Info;
isSafeForScalarRepl(AI, AI, 0, Info);
if (Info.isUnsafe) {
DEBUG(dbgs() << "Cannot transform: " << *AI << '\n');
return false;
}
// Okay, we know all the users are promotable. If the aggregate is a memcpy
// source and destination, we have to be careful. In particular, the memcpy
// could be moving around elements that live in structure padding of the LLVM
// types, but may actually be used. In these cases, we refuse to promote the
// struct.
if (Info.isMemCpySrc && Info.isMemCpyDst &&
HasPadding(AI->getAllocatedType(), *TD))
return false;
return true;
}
/// PointsToConstantGlobal - Return true if V (possibly indirectly) points to
/// some part of a constant global variable. This intentionally only accepts
/// constant expressions because we don't can't rewrite arbitrary instructions.
static bool PointsToConstantGlobal(Value *V) {
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
return GV->isConstant();
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
if (CE->getOpcode() == Instruction::BitCast ||
CE->getOpcode() == Instruction::GetElementPtr)
return PointsToConstantGlobal(CE->getOperand(0));
return false;
}
/// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived)
/// pointer to an alloca. Ignore any reads of the pointer, return false if we
/// see any stores or other unknown uses. If we see pointer arithmetic, keep
/// track of whether it moves the pointer (with isOffset) but otherwise traverse
/// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to
/// the alloca, and if the source pointer is a pointer to a constant global, we
/// can optimize this.
static bool isOnlyCopiedFromConstantGlobal(Value *V, MemTransferInst *&TheCopy,
bool isOffset) {
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) {
User *U = cast<Instruction>(*UI);
if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
// Ignore non-volatile loads, they are always ok.
if (LI->isVolatile()) return false;
continue;
}
if (BitCastInst *BCI = dyn_cast<BitCastInst>(U)) {
// If uses of the bitcast are ok, we are ok.
if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset))
return false;
continue;
}
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
// If the GEP has all zero indices, it doesn't offset the pointer. If it
// doesn't, it does.
if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy,
isOffset || !GEP->hasAllZeroIndices()))
return false;
continue;
}
if (CallSite CS = U) {
// If this is a readonly/readnone call site, then we know it is just a
// load and we can ignore it.
if (CS.onlyReadsMemory())
continue;
// If this is the function being called then we treat it like a load and
// ignore it.
if (CS.isCallee(UI))
continue;
// If this is being passed as a byval argument, the caller is making a
// copy, so it is only a read of the alloca.
unsigned ArgNo = CS.getArgumentNo(UI);
if (CS.paramHasAttr(ArgNo+1, Attribute::ByVal))
continue;
}
// If this is isn't our memcpy/memmove, reject it as something we can't
// handle.
MemTransferInst *MI = dyn_cast<MemTransferInst>(U);
if (MI == 0)
return false;
// If the transfer is using the alloca as a source of the transfer, then
// ignore it since it is a load (unless the transfer is volatile).
if (UI.getOperandNo() == 1) {
if (MI->isVolatile()) return false;
continue;
}
// If we already have seen a copy, reject the second one.
if (TheCopy) return false;
// If the pointer has been offset from the start of the alloca, we can't
// safely handle this.
if (isOffset) return false;
// If the memintrinsic isn't using the alloca as the dest, reject it.
if (UI.getOperandNo() != 0) return false;
// If the source of the memcpy/move is not a constant global, reject it.
if (!PointsToConstantGlobal(MI->getSource()))
return false;
// Otherwise, the transform is safe. Remember the copy instruction.
TheCopy = MI;
}
return true;
}
/// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only
/// modified by a copy from a constant global. If we can prove this, we can
/// replace any uses of the alloca with uses of the global directly.
MemTransferInst *SROA::isOnlyCopiedFromConstantGlobal(AllocaInst *AI) {
MemTransferInst *TheCopy = 0;
if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false))
return TheCopy;
return 0;
}
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