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llvm-mirror/lib/Transforms/Scalar/ScalarReplAggregates.cpp
Nick Lewycky 465651fe6e Fix likely typo, reduce number of instruction name collisions. 
llvm-svn: 134235
2011-07-01 06:27:03 +00:00

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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/DIBuilder.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/Loads.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/Transforms/Utils/SSAUpdater.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/SetVector.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(NumAdjusted, "Number of scalar allocas adjusted to allow promotion");
STATISTIC(NumConverted, "Number of aggregates converted to scalar");
STATISTIC(NumGlobals, "Number of allocas copied from constant global");
namespace {
struct SROA : public FunctionPass {
SROA(int T, bool hasDT, char &ID)
: FunctionPass(ID), HasDomTree(hasDT) {
if (T == -1)
SRThreshold = 128;
else
SRThreshold = T;
}
bool runOnFunction(Function &F);
bool performScalarRepl(Function &F);
bool performPromotion(Function &F);
private:
bool HasDomTree;
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 {
/// The alloca to promote.
AllocaInst *AI;
/// CheckedPHIs - This is a set of verified PHI nodes, to prevent infinite
/// looping and avoid redundant work.
SmallPtrSet<PHINode*, 8> CheckedPHIs;
/// 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;
/// hasSubelementAccess - This is true if a subelement of the alloca is
/// ever accessed, or false if the alloca is only accessed with mem
/// intrinsics or load/store that only access the entire alloca at once.
bool hasSubelementAccess : 1;
/// hasALoadOrStore - This is true if there are any loads or stores to it.
/// The alloca may just be accessed with memcpy, for example, which would
/// not set this.
bool hasALoadOrStore : 1;
explicit AllocaInfo(AllocaInst *ai)
: AI(ai), isUnsafe(false), isMemCpySrc(false), isMemCpyDst(false),
hasSubelementAccess(false), hasALoadOrStore(false) {}
};
unsigned SRThreshold;
void MarkUnsafe(AllocaInfo &I, Instruction *User) {
I.isUnsafe = true;
DEBUG(dbgs() << " Transformation preventing inst: " << *User << '\n');
}
bool isSafeAllocaToScalarRepl(AllocaInst *AI);
void isSafeForScalarRepl(Instruction *I, uint64_t Offset, AllocaInfo &Info);
void isSafePHISelectUseForScalarRepl(Instruction *User, uint64_t Offset,
AllocaInfo &Info);
void isSafeGEP(GetElementPtrInst *GEPI, uint64_t &Offset, AllocaInfo &Info);
void isSafeMemAccess(uint64_t Offset, uint64_t MemSize,
const Type *MemOpType, bool isStore, AllocaInfo &Info,
Instruction *TheAccess, bool AllowWholeAccess);
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, SmallVector<Instruction*, 4> &ToDelete);
};
// SROA_DT - SROA that uses DominatorTree.
struct SROA_DT : public SROA {
static char ID;
public:
SROA_DT(int T = -1) : SROA(T, true, ID) {
initializeSROA_DTPass(*PassRegistry::getPassRegistry());
}
// 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.setPreservesCFG();
}
};
// SROA_SSAUp - SROA that uses SSAUpdater.
struct SROA_SSAUp : public SROA {
static char ID;
public:
SROA_SSAUp(int T = -1) : SROA(T, false, ID) {
initializeSROA_SSAUpPass(*PassRegistry::getPassRegistry());
}
// 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.setPreservesCFG();
}
};
}
char SROA_DT::ID = 0;
char SROA_SSAUp::ID = 0;
INITIALIZE_PASS_BEGIN(SROA_DT, "scalarrepl",
"Scalar Replacement of Aggregates (DT)", false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTree)
INITIALIZE_PASS_END(SROA_DT, "scalarrepl",
"Scalar Replacement of Aggregates (DT)", false, false)
INITIALIZE_PASS_BEGIN(SROA_SSAUp, "scalarrepl-ssa",
"Scalar Replacement of Aggregates (SSAUp)", false, false)
INITIALIZE_PASS_END(SROA_SSAUp, "scalarrepl-ssa",
"Scalar Replacement of Aggregates (SSAUp)", false, false)
// Public interface to the ScalarReplAggregates pass
FunctionPass *llvm::createScalarReplAggregatesPass(int Threshold,
bool UseDomTree) {
if (UseDomTree)
return new SROA_DT(Threshold);
return new SROA_SSAUp(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 in bytes.
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;
/// ScalarKind - Tracks the kind of alloca being considered for promotion,
/// computed based on the uses of the alloca rather than the LLVM type system.
enum {
Unknown,
// Accesses via GEPs that are consistent with element access of a vector
// type. This will not be converted into a vector unless there is a later
// access using an actual vector type.
ImplicitVector,
// Accesses via vector operations and GEPs that are consistent with the
// layout of a vector type.
Vector,
// An integer bag-of-bits with bitwise operations for insertion and
// extraction. Any combination of types can be converted into this kind
// of scalar.
Integer
} ScalarKind;
/// 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 VectorType *VectorTy;
/// HadNonMemTransferAccess - True if there is at least one access to the
/// alloca that is not a MemTransferInst. We don't want to turn structs into
/// large integers unless there is some potential for optimization.
bool HadNonMemTransferAccess;
public:
explicit ConvertToScalarInfo(unsigned Size, const TargetData &td)
: AllocaSize(Size), TD(td), IsNotTrivial(false), ScalarKind(Unknown),
VectorTy(0), HadNonMemTransferAccess(false) { }
AllocaInst *TryConvert(AllocaInst *AI);
private:
bool CanConvertToScalar(Value *V, uint64_t Offset);
void MergeInTypeForLoadOrStore(const Type *In, uint64_t Offset);
bool MergeInVectorType(const VectorType *VInTy, 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.
/// 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 an alloca has only memset / memcpy uses, it may still have an Unknown
// ScalarKind. Treat it as an Integer below.
if (ScalarKind == Unknown)
ScalarKind = Integer;
// FIXME: It should be possible to promote the vector type up to the alloca's
// size.
if (ScalarKind == Vector && VectorTy->getBitWidth() != AllocaSize * 8)
ScalarKind = Integer;
// 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 (ScalarKind == Vector) {
assert(VectorTy && "Missing type for vector scalar.");
DEBUG(dbgs() << "CONVERT TO VECTOR: " << *AI << "\n TYPE = "
<< *VectorTy << '\n');
NewTy = VectorTy; // Use the vector type.
} else {
unsigned BitWidth = AllocaSize * 8;
if ((ScalarKind == ImplicitVector || ScalarKind == Integer) &&
!HadNonMemTransferAccess && !TD.fitsInLegalInteger(BitWidth))
return 0;
DEBUG(dbgs() << "CONVERT TO SCALAR INTEGER: " << *AI << "\n");
// Create and insert the integer alloca.
NewTy = IntegerType::get(AI->getContext(), BitWidth);
}
AllocaInst *NewAI = new AllocaInst(NewTy, 0, "", AI->getParent()->begin());
ConvertUsesToScalar(AI, NewAI, 0);
return NewAI;
}
/// MergeInTypeForLoadOrStore - 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 three 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 union of vector types with power-of-2 size differences, e.g. a float,
/// <2 x float> and <4 x float>. Here we turn element accesses into insert
/// and extract element operations, and <2 x float> accesses into a cast to
/// <2 x double>, an extract, and a cast back to <2 x float>.
/// 3) 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::MergeInTypeForLoadOrStore(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 (ScalarKind == Integer)
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)) {
if (MergeInVectorType(VInTy, Offset))
return;
} else if (In->isFloatTy() || In->isDoubleTy() ||
(In->isIntegerTy() && In->getPrimitiveSizeInBits() >= 8 &&
isPowerOf2_32(In->getPrimitiveSizeInBits()))) {
// Full width accesses can be ignored, because they can always be turned
// into bitcasts.
unsigned EltSize = In->getPrimitiveSizeInBits()/8;
if (EltSize == AllocaSize)
return;
// 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.
if (Offset % EltSize == 0 && AllocaSize % EltSize == 0 &&
(!VectorTy || Offset * 8 < VectorTy->getPrimitiveSizeInBits())) {
if (!VectorTy) {
ScalarKind = ImplicitVector;
VectorTy = VectorType::get(In, AllocaSize/EltSize);
return;
}
unsigned CurrentEltSize = VectorTy->getElementType()
->getPrimitiveSizeInBits()/8;
if (EltSize == CurrentEltSize)
return;
if (In->isIntegerTy() && isPowerOf2_32(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.
ScalarKind = Integer;
}
/// MergeInVectorType - Handles the vector case of MergeInTypeForLoadOrStore,
/// returning true if the type was successfully merged and false otherwise.
bool ConvertToScalarInfo::MergeInVectorType(const VectorType *VInTy,
uint64_t Offset) {
// TODO: Support nonzero offsets?
if (Offset != 0)
return false;
// Only allow vectors that are a power-of-2 away from the size of the alloca.
if (!isPowerOf2_64(AllocaSize / (VInTy->getBitWidth() / 8)))
return false;
// If this the first vector we see, remember the type so that we know the
// element size.
if (!VectorTy) {
ScalarKind = Vector;
VectorTy = VInTy;
return true;
}
unsigned BitWidth = VectorTy->getBitWidth();
unsigned InBitWidth = VInTy->getBitWidth();
// Vectors of the same size can be converted using a simple bitcast.
if (InBitWidth == BitWidth && AllocaSize == (InBitWidth / 8)) {
ScalarKind = Vector;
return true;
}
const Type *ElementTy = VectorTy->getElementType();
const Type *InElementTy = VInTy->getElementType();
// Do not allow mixed integer and floating-point accesses from vectors of
// different sizes.
if (ElementTy->isFloatingPointTy() != InElementTy->isFloatingPointTy())
return false;
if (ElementTy->isFloatingPointTy()) {
// Only allow floating-point vectors of different sizes if they have the
// same element type.
// TODO: This could be loosened a bit, but would anything benefit?
if (ElementTy != InElementTy)
return false;
// There are no arbitrary-precision floating-point types, which limits the
// number of legal vector types with larger element types that we can form
// to bitcast and extract a subvector.
// TODO: We could support some more cases with mixed fp128 and double here.
if (!(BitWidth == 64 || BitWidth == 128) ||
!(InBitWidth == 64 || InBitWidth == 128))
return false;
} else {
assert(ElementTy->isIntegerTy() && "Vector elements must be either integer "
"or floating-point.");
unsigned BitWidth = ElementTy->getPrimitiveSizeInBits();
unsigned InBitWidth = InElementTy->getPrimitiveSizeInBits();
// Do not allow integer types smaller than a byte or types whose widths are
// not a multiple of a byte.
if (BitWidth < 8 || InBitWidth < 8 ||
BitWidth % 8 != 0 || InBitWidth % 8 != 0)
return false;
}
// Pick the largest of the two vector types.
ScalarKind = Vector;
if (InBitWidth > BitWidth)
VectorTy = VInTy;
return true;
}
/// 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;
HadNonMemTransferAccess = true;
MergeInTypeForLoadOrStore(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;
HadNonMemTransferAccess = true;
MergeInTypeForLoadOrStore(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.
HadNonMemTransferAccess = true;
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.
if (!isa<ConstantInt>(MSI->getValue()))
return false;
// Store of constant size.
ConstantInt *Len = dyn_cast<ConstantInt>(MSI->getLength());
if (!Len)
return false;
// If the size differs from the alloca, we can only convert the alloca to
// an integer bag-of-bits.
// FIXME: This should handle all of the cases that are currently accepted
// as vector element insertions.
if (Len->getZExtValue() != AllocaSize || Offset != 0)
ScalarKind = Integer;
IsNotTrivial = true; // Can't be mem2reg'd.
HadNonMemTransferAccess = true;
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);
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, &TD, 0));
if (GetUnderlyingObject(MTI->getSource(), &TD, 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(), &TD, 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!");
}
}
/// getScaledElementType - Gets a scaled element type for a partial vector
/// access of an alloca. The input types must be integer or floating-point
/// scalar or vector types, and the resulting type is an integer, float or
/// double.
static const Type *getScaledElementType(const Type *Ty1, const Type *Ty2,
unsigned NewBitWidth) {
bool IsFP1 = Ty1->isFloatingPointTy() ||
(Ty1->isVectorTy() &&
cast<VectorType>(Ty1)->getElementType()->isFloatingPointTy());
bool IsFP2 = Ty2->isFloatingPointTy() ||
(Ty2->isVectorTy() &&
cast<VectorType>(Ty2)->getElementType()->isFloatingPointTy());
LLVMContext &Context = Ty1->getContext();
// Prefer floating-point types over integer types, as integer types may have
// been created by earlier scalar replacement.
if (IsFP1 || IsFP2) {
if (NewBitWidth == 32)
return Type::getFloatTy(Context);
if (NewBitWidth == 64)
return Type::getDoubleTy(Context);
}
return Type::getIntNTy(Context, NewBitWidth);
}
/// CreateShuffleVectorCast - Creates a shuffle vector to convert one vector
/// to another vector of the same element type which has the same allocation
/// size but different primitive sizes (e.g. <3 x i32> and <4 x i32>).
static Value *CreateShuffleVectorCast(Value *FromVal, const Type *ToType,
IRBuilder<> &Builder) {
const Type *FromType = FromVal->getType();
const VectorType *FromVTy = cast<VectorType>(FromType);
const VectorType *ToVTy = cast<VectorType>(ToType);
assert((ToVTy->getElementType() == FromVTy->getElementType()) &&
"Vectors must have the same element type");
Value *UnV = UndefValue::get(FromType);
unsigned numEltsFrom = FromVTy->getNumElements();
unsigned numEltsTo = ToVTy->getNumElements();
SmallVector<Constant*, 3> Args;
const Type* Int32Ty = Builder.getInt32Ty();
unsigned minNumElts = std::min(numEltsFrom, numEltsTo);
unsigned i;
for (i=0; i != minNumElts; ++i)
Args.push_back(ConstantInt::get(Int32Ty, i));
if (i < numEltsTo) {
Constant* UnC = UndefValue::get(Int32Ty);
for (; i != numEltsTo; ++i)
Args.push_back(UnC);
}
Constant *Mask = ConstantVector::get(Args);
return Builder.CreateShuffleVector(FromVal, UnV, Mask, "tmpV");
}
/// 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.
const Type *FromType = FromVal->getType();
if (FromType == 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>(FromType)) {
unsigned FromTypeSize = TD.getTypeAllocSize(FromType);
unsigned ToTypeSize = TD.getTypeAllocSize(ToType);
if (FromTypeSize == ToTypeSize) {
// If the two types have the same primitive size, use a bit cast.
// Otherwise, it is two vectors with the same element type that has
// the same allocation size but different number of elements so use
// a shuffle vector.
if (FromType->getPrimitiveSizeInBits() ==
ToType->getPrimitiveSizeInBits())
return Builder.CreateBitCast(FromVal, ToType, "tmp");
else
return CreateShuffleVectorCast(FromVal, ToType, Builder);
}
if (isPowerOf2_64(FromTypeSize / ToTypeSize)) {
assert(!(ToType->isVectorTy() && Offset != 0) && "Can't extract a value "
"of a smaller vector type at a nonzero offset.");
const Type *CastElementTy = getScaledElementType(FromType, ToType,
ToTypeSize * 8);
unsigned NumCastVectorElements = FromTypeSize / ToTypeSize;
LLVMContext &Context = FromVal->getContext();
const Type *CastTy = VectorType::get(CastElementTy,
NumCastVectorElements);
Value *Cast = Builder.CreateBitCast(FromVal, CastTy, "tmp");
unsigned EltSize = TD.getTypeAllocSizeInBits(CastElementTy);
unsigned Elt = Offset/EltSize;
assert(EltSize*Elt == Offset && "Invalid modulus in validity checking");
Value *Extract = Builder.CreateExtractElement(Cast, ConstantInt::get(
Type::getInt32Ty(Context), Elt), "tmp");
return Builder.CreateBitCast(Extract, 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) {
// If the two types have the same primitive size, use a bit cast.
// Otherwise, it is two vectors with the same element type that has
// the same allocation size but different number of elements so use
// a shuffle vector.
if (VTy->getPrimitiveSizeInBits() ==
SV->getType()->getPrimitiveSizeInBits())
return Builder.CreateBitCast(SV, AllocaType, "tmp");
else
return CreateShuffleVectorCast(SV, VTy, Builder);
}
if (isPowerOf2_64(VecSize / ValSize)) {
assert(!(SV->getType()->isVectorTy() && Offset != 0) && "Can't insert a "
"value of a smaller vector type at a nonzero offset.");
const Type *CastElementTy = getScaledElementType(VTy, SV->getType(),
ValSize);
unsigned NumCastVectorElements = VecSize / ValSize;
LLVMContext &Context = SV->getContext();
const Type *OldCastTy = VectorType::get(CastElementTy,
NumCastVectorElements);
Value *OldCast = Builder.CreateBitCast(Old, OldCastTy, "tmp");
Value *SVCast = Builder.CreateBitCast(SV, CastElementTy, "tmp");
unsigned EltSize = TD.getTypeAllocSizeInBits(CastElementTy);
unsigned Elt = Offset/EltSize;
assert(EltSize*Elt == Offset && "Invalid modulus in validity checking");
Value *Insert =
Builder.CreateInsertElement(OldCast, SVCast, ConstantInt::get(
Type::getInt32Ty(Context), Elt), "tmp");
return Builder.CreateBitCast(Insert, AllocaType, "tmp");
}
// Must be an element insertion.
assert(SV->getType() == VTy->getElementType());
uint64_t EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType());
unsigned Elt = Offset/EltSize;
return Builder.CreateInsertElement(Old, SV,
ConstantInt::get(Type::getInt32Ty(SV->getContext()), Elt),
"tmp");
}
// 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;
}
namespace {
class AllocaPromoter : public LoadAndStorePromoter {
AllocaInst *AI;
public:
AllocaPromoter(const SmallVectorImpl<Instruction*> &Insts, SSAUpdater &S,
DbgDeclareInst *DD, DIBuilder *&DB)
: LoadAndStorePromoter(Insts, S, DD, DB), AI(0) {}
void run(AllocaInst *AI, const SmallVectorImpl<Instruction*> &Insts) {
// Remember which alloca we're promoting (for isInstInList).
this->AI = AI;
LoadAndStorePromoter::run(Insts);
AI->eraseFromParent();
}
virtual bool isInstInList(Instruction *I,
const SmallVectorImpl<Instruction*> &Insts) const {
if (LoadInst *LI = dyn_cast<LoadInst>(I))
return LI->getOperand(0) == AI;
return cast<StoreInst>(I)->getPointerOperand() == AI;
}
};
} // end anon namespace
/// isSafeSelectToSpeculate - Select instructions that use an alloca and are
/// subsequently loaded can be rewritten to load both input pointers and then
/// select between the result, allowing the load of the alloca to be promoted.
/// From this:
/// %P2 = select i1 %cond, i32* %Alloca, i32* %Other
/// %V = load i32* %P2
/// to:
/// %V1 = load i32* %Alloca -> will be mem2reg'd
/// %V2 = load i32* %Other
/// %V = select i1 %cond, i32 %V1, i32 %V2
///
/// We can do this to a select if its only uses are loads and if the operand to
/// the select can be loaded unconditionally.
static bool isSafeSelectToSpeculate(SelectInst *SI, const TargetData *TD) {
bool TDerefable = SI->getTrueValue()->isDereferenceablePointer();
bool FDerefable = SI->getFalseValue()->isDereferenceablePointer();
for (Value::use_iterator UI = SI->use_begin(), UE = SI->use_end();
UI != UE; ++UI) {
LoadInst *LI = dyn_cast<LoadInst>(*UI);
if (LI == 0 || LI->isVolatile()) return false;
// Both operands to the select need to be dereferencable, either absolutely
// (e.g. allocas) or at this point because we can see other accesses to it.
if (!TDerefable && !isSafeToLoadUnconditionally(SI->getTrueValue(), LI,
LI->getAlignment(), TD))
return false;
if (!FDerefable && !isSafeToLoadUnconditionally(SI->getFalseValue(), LI,
LI->getAlignment(), TD))
return false;
}
return true;
}
/// isSafePHIToSpeculate - PHI instructions that use an alloca and are
/// subsequently loaded can be rewritten to load both input pointers in the pred
/// blocks and then PHI the results, allowing the load of the alloca to be
/// promoted.
/// From this:
/// %P2 = phi [i32* %Alloca, i32* %Other]
/// %V = load i32* %P2
/// to:
/// %V1 = load i32* %Alloca -> will be mem2reg'd
/// ...
/// %V2 = load i32* %Other
/// ...
/// %V = phi [i32 %V1, i32 %V2]
///
/// We can do this to a select if its only uses are loads and if the operand to
/// the select can be loaded unconditionally.
static bool isSafePHIToSpeculate(PHINode *PN, const TargetData *TD) {
// For now, we can only do this promotion if the load is in the same block as
// the PHI, and if there are no stores between the phi and load.
// TODO: Allow recursive phi users.
// TODO: Allow stores.
BasicBlock *BB = PN->getParent();
unsigned MaxAlign = 0;
for (Value::use_iterator UI = PN->use_begin(), UE = PN->use_end();
UI != UE; ++UI) {
LoadInst *LI = dyn_cast<LoadInst>(*UI);
if (LI == 0 || LI->isVolatile()) return false;
// For now we only allow loads in the same block as the PHI. This is a
// common case that happens when instcombine merges two loads through a PHI.
if (LI->getParent() != BB) return false;
// Ensure that there are no instructions between the PHI and the load that
// could store.
for (BasicBlock::iterator BBI = PN; &*BBI != LI; ++BBI)
if (BBI->mayWriteToMemory())
return false;
MaxAlign = std::max(MaxAlign, LI->getAlignment());
}
// Okay, we know that we have one or more loads in the same block as the PHI.
// We can transform this if it is safe to push the loads into the predecessor
// blocks. The only thing to watch out for is that we can't put a possibly
// trapping load in the predecessor if it is a critical edge.
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *Pred = PN->getIncomingBlock(i);
// If the predecessor has a single successor, then the edge isn't critical.
if (Pred->getTerminator()->getNumSuccessors() == 1)
continue;
Value *InVal = PN->getIncomingValue(i);
// If the InVal is an invoke in the pred, we can't put a load on the edge.
if (InvokeInst *II = dyn_cast<InvokeInst>(InVal))
if (II->getParent() == Pred)
return false;
// If this pointer is always safe to load, or if we can prove that there is
// already a load in the block, then we can move the load to the pred block.
if (InVal->isDereferenceablePointer() ||
isSafeToLoadUnconditionally(InVal, Pred->getTerminator(), MaxAlign, TD))
continue;
return false;
}
return true;
}
/// tryToMakeAllocaBePromotable - This returns true if the alloca only has
/// direct (non-volatile) loads and stores to it. If the alloca is close but
/// not quite there, this will transform the code to allow promotion. As such,
/// it is a non-pure predicate.
static bool tryToMakeAllocaBePromotable(AllocaInst *AI, const TargetData *TD) {
SetVector<Instruction*, SmallVector<Instruction*, 4>,
SmallPtrSet<Instruction*, 4> > InstsToRewrite;
for (Value::use_iterator UI = AI->use_begin(), UE = AI->use_end();
UI != UE; ++UI) {
User *U = *UI;
if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
if (LI->isVolatile())
return false;
continue;
}
if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
if (SI->getOperand(0) == AI || SI->isVolatile())
return false; // Don't allow a store OF the AI, only INTO the AI.
continue;
}
if (SelectInst *SI = dyn_cast<SelectInst>(U)) {
// If the condition being selected on is a constant, fold the select, yes
// this does (rarely) happen early on.
if (ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition())) {
Value *Result = SI->getOperand(1+CI->isZero());
SI->replaceAllUsesWith(Result);
SI->eraseFromParent();
// This is very rare and we just scrambled the use list of AI, start
// over completely.
return tryToMakeAllocaBePromotable(AI, TD);
}
// If it is safe to turn "load (select c, AI, ptr)" into a select of two
// loads, then we can transform this by rewriting the select.
if (!isSafeSelectToSpeculate(SI, TD))
return false;
InstsToRewrite.insert(SI);
continue;
}
if (PHINode *PN = dyn_cast<PHINode>(U)) {
if (PN->use_empty()) { // Dead PHIs can be stripped.
InstsToRewrite.insert(PN);
continue;
}
// If it is safe to turn "load (phi [AI, ptr, ...])" into a PHI of loads
// in the pred blocks, then we can transform this by rewriting the PHI.
if (!isSafePHIToSpeculate(PN, TD))
return false;
InstsToRewrite.insert(PN);
continue;
}
return false;
}
// If there are no instructions to rewrite, then all uses are load/stores and
// we're done!
if (InstsToRewrite.empty())
return true;
// If we have instructions that need to be rewritten for this to be promotable
// take care of it now.
for (unsigned i = 0, e = InstsToRewrite.size(); i != e; ++i) {
if (SelectInst *SI = dyn_cast<SelectInst>(InstsToRewrite[i])) {
// Selects in InstsToRewrite only have load uses. Rewrite each as two
// loads with a new select.
while (!SI->use_empty()) {
LoadInst *LI = cast<LoadInst>(SI->use_back());
IRBuilder<> Builder(LI);
LoadInst *TrueLoad =
Builder.CreateLoad(SI->getTrueValue(), LI->getName()+".t");
LoadInst *FalseLoad =
Builder.CreateLoad(SI->getFalseValue(), LI->getName()+".f");
// Transfer alignment and TBAA info if present.
TrueLoad->setAlignment(LI->getAlignment());
FalseLoad->setAlignment(LI->getAlignment());
if (MDNode *Tag = LI->getMetadata(LLVMContext::MD_tbaa)) {
TrueLoad->setMetadata(LLVMContext::MD_tbaa, Tag);
FalseLoad->setMetadata(LLVMContext::MD_tbaa, Tag);
}
Value *V = Builder.CreateSelect(SI->getCondition(), TrueLoad, FalseLoad);
V->takeName(LI);
LI->replaceAllUsesWith(V);
LI->eraseFromParent();
}
// Now that all the loads are gone, the select is gone too.
SI->eraseFromParent();
continue;
}
// Otherwise, we have a PHI node which allows us to push the loads into the
// predecessors.
PHINode *PN = cast<PHINode>(InstsToRewrite[i]);
if (PN->use_empty()) {
PN->eraseFromParent();
continue;
}
const Type *LoadTy = cast<PointerType>(PN->getType())->getElementType();
PHINode *NewPN = PHINode::Create(LoadTy, PN->getNumIncomingValues(),
PN->getName()+".ld", PN);
// Get the TBAA tag and alignment to use from one of the loads. It doesn't
// matter which one we get and if any differ, it doesn't matter.
LoadInst *SomeLoad = cast<LoadInst>(PN->use_back());
MDNode *TBAATag = SomeLoad->getMetadata(LLVMContext::MD_tbaa);
unsigned Align = SomeLoad->getAlignment();
// Rewrite all loads of the PN to use the new PHI.
while (!PN->use_empty()) {
LoadInst *LI = cast<LoadInst>(PN->use_back());
LI->replaceAllUsesWith(NewPN);
LI->eraseFromParent();
}
// Inject loads into all of the pred blocks. Keep track of which blocks we
// insert them into in case we have multiple edges from the same block.
DenseMap<BasicBlock*, LoadInst*> InsertedLoads;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *Pred = PN->getIncomingBlock(i);
LoadInst *&Load = InsertedLoads[Pred];
if (Load == 0) {
Load = new LoadInst(PN->getIncomingValue(i),
PN->getName() + "." + Pred->getName(),
Pred->getTerminator());
Load->setAlignment(Align);
if (TBAATag) Load->setMetadata(LLVMContext::MD_tbaa, TBAATag);
}
NewPN->addIncoming(Load, Pred);
}
PN->eraseFromParent();
}
++NumAdjusted;
return true;
}
bool SROA::performPromotion(Function &F) {
std::vector<AllocaInst*> Allocas;
DominatorTree *DT = 0;
if (HasDomTree)
DT = &getAnalysis<DominatorTree>();
BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function
bool Changed = false;
SmallVector<Instruction*, 64> Insts;
DIBuilder *DIB = 0;
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 (tryToMakeAllocaBePromotable(AI, TD))
Allocas.push_back(AI);
if (Allocas.empty()) break;
if (HasDomTree)
PromoteMemToReg(Allocas, *DT);
else {
SSAUpdater SSA;
for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
AllocaInst *AI = Allocas[i];
// Build list of instructions to promote.
for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
UI != E; ++UI)
Insts.push_back(cast<Instruction>(*UI));
DbgDeclareInst *DDI = FindAllocaDbgDeclare(AI);
if (DDI && !DIB)
DIB = new DIBuilder(*AI->getParent()->getParent()->getParent());
AllocaPromoter(Insts, SSA, DDI, DIB).run(AI, Insts);
Insts.clear();
}
}
NumPromoted += Allocas.size();
Changed = true;
}
// FIXME: Is there a better way to handle the lazy initialization of DIB
// so that there doesn't need to be an explicit delete?
delete DIB;
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 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.
SmallVector<Instruction *, 4> ToDelete;
if (MemTransferInst *Copy = isOnlyCopiedFromConstantGlobal(AI, ToDelete)) {
DEBUG(dbgs() << "Found alloca equal to global: " << *AI << '\n');
DEBUG(dbgs() << " memcpy = " << *Copy << '\n');
for (unsigned i = 0, e = ToDelete.size(); i != e; ++i)
ToDelete[i]->eraseFromParent();
Constant *TheSrc = cast<Constant>(Copy->getSource());
AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType()));
Copy->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, 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, Offset, Info);
} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
uint64_t GEPOffset = Offset;
isSafeGEP(GEPI, GEPOffset, Info);
if (!Info.isUnsafe)
isSafeForScalarRepl(GEPI, GEPOffset, Info);
} else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength());
if (Length == 0)
return MarkUnsafe(Info, User);
isSafeMemAccess(Offset, Length->getZExtValue(), 0,
UI.getOperandNo() == 0, Info, MI,
true /*AllowWholeAccess*/);
} else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
if (LI->isVolatile())
return MarkUnsafe(Info, User);
const Type *LIType = LI->getType();
isSafeMemAccess(Offset, TD->getTypeAllocSize(LIType),
LIType, false, Info, LI, true /*AllowWholeAccess*/);
Info.hasALoadOrStore = true;
} 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)
return MarkUnsafe(Info, User);
const Type *SIType = SI->getOperand(0)->getType();
isSafeMemAccess(Offset, TD->getTypeAllocSize(SIType),
SIType, true, Info, SI, true /*AllowWholeAccess*/);
Info.hasALoadOrStore = true;
} else if (isa<PHINode>(User) || isa<SelectInst>(User)) {
isSafePHISelectUseForScalarRepl(User, Offset, Info);
} else {
return MarkUnsafe(Info, User);
}
if (Info.isUnsafe) return;
}
}
/// isSafePHIUseForScalarRepl - If we see a PHI node or select using a pointer
/// derived from the alloca, we can often still split the alloca into elements.
/// This is useful if we have a large alloca where one element is phi'd
/// together somewhere: we can SRoA and promote all the other elements even if
/// we end up not being able to promote this one.
///
/// All we require is that the uses of the PHI do not index into other parts of
/// the alloca. The most important use case for this is single load and stores
/// that are PHI'd together, which can happen due to code sinking.
void SROA::isSafePHISelectUseForScalarRepl(Instruction *I, uint64_t Offset,
AllocaInfo &Info) {
// If we've already checked this PHI, don't do it again.
if (PHINode *PN = dyn_cast<PHINode>(I))
if (!Info.CheckedPHIs.insert(PN))
return;
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)) {
isSafePHISelectUseForScalarRepl(BC, Offset, Info);
} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
// Only allow "bitcast" GEPs for simplicity. We could generalize this,
// but would have to prove that we're staying inside of an element being
// promoted.
if (!GEPI->hasAllZeroIndices())
return MarkUnsafe(Info, User);
isSafePHISelectUseForScalarRepl(GEPI, Offset, Info);
} else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
if (LI->isVolatile())
return MarkUnsafe(Info, User);
const Type *LIType = LI->getType();
isSafeMemAccess(Offset, TD->getTypeAllocSize(LIType),
LIType, false, Info, LI, false /*AllowWholeAccess*/);
Info.hasALoadOrStore = true;
} 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)
return MarkUnsafe(Info, User);
const Type *SIType = SI->getOperand(0)->getType();
isSafeMemAccess(Offset, TD->getTypeAllocSize(SIType),
SIType, true, Info, SI, false /*AllowWholeAccess*/);
Info.hasALoadOrStore = true;
} else if (isa<PHINode>(User) || isa<SelectInst>(User)) {
isSafePHISelectUseForScalarRepl(User, Offset, Info);
} else {
return MarkUnsafe(Info, User);
}
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,
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, GEPI);
}
// 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(Info.AI->getAllocatedType(), Offset, 0))
MarkUnsafe(Info, GEPI);
}
/// isHomogeneousAggregate - Check if type T is a struct or array containing
/// elements of the same type (which is always true for arrays). If so,
/// return true with NumElts and EltTy set to the number of elements and the
/// element type, respectively.
static bool isHomogeneousAggregate(const Type *T, unsigned &NumElts,
const Type *&EltTy) {
if (const ArrayType *AT = dyn_cast<ArrayType>(T)) {
NumElts = AT->getNumElements();
EltTy = (NumElts == 0 ? 0 : AT->getElementType());
return true;
}
if (const StructType *ST = dyn_cast<StructType>(T)) {
NumElts = ST->getNumContainedTypes();
EltTy = (NumElts == 0 ? 0 : ST->getContainedType(0));
for (unsigned n = 1; n < NumElts; ++n) {
if (ST->getContainedType(n) != EltTy)
return false;
}
return true;
}
return false;
}
/// isCompatibleAggregate - Check if T1 and T2 are either the same type or are
/// "homogeneous" aggregates with the same element type and number of elements.
static bool isCompatibleAggregate(const Type *T1, const Type *T2) {
if (T1 == T2)
return true;
unsigned NumElts1, NumElts2;
const Type *EltTy1, *EltTy2;
if (isHomogeneousAggregate(T1, NumElts1, EltTy1) &&
isHomogeneousAggregate(T2, NumElts2, EltTy2) &&
NumElts1 == NumElts2 &&
EltTy1 == EltTy2)
return true;
return false;
}
/// 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.
///
/// If AllowWholeAccess is true, then this allows uses of the entire alloca as a
/// unit. If false, it only allows accesses known to be in a single element.
void SROA::isSafeMemAccess(uint64_t Offset, uint64_t MemSize,
const Type *MemOpType, bool isStore,
AllocaInfo &Info, Instruction *TheAccess,
bool AllowWholeAccess) {
// Check if this is a load/store of the entire alloca.
if (Offset == 0 && AllowWholeAccess &&
MemSize == TD->getTypeAllocSize(Info.AI->getAllocatedType())) {
// This can be safe for MemIntrinsics (where MemOpType is 0) and integer
// loads/stores (which are essentially the same as the MemIntrinsics with
// regard to copying padding between elements). But, if an alloca is
// flagged as both a source and destination of such operations, we'll need
// to check later for padding between elements.
if (!MemOpType || MemOpType->isIntegerTy()) {
if (isStore)
Info.isMemCpyDst = true;
else
Info.isMemCpySrc = true;
return;
}
// This is also safe for references using a type that is compatible with
// the type of the alloca, so that loads/stores can be rewritten using
// insertvalue/extractvalue.
if (isCompatibleAggregate(MemOpType, Info.AI->getAllocatedType())) {
Info.hasSubelementAccess = true;
return;
}
}
// Check if the offset/size correspond to a component within the alloca type.
const Type *T = Info.AI->getAllocatedType();
if (TypeHasComponent(T, Offset, MemSize)) {
Info.hasSubelementAccess = true;
return;
}
return MarkUnsafe(Info, TheAccess);
}
/// 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;) {
Use &TheUse = UI.getUse();
Instruction *User = cast<Instruction>(*UI++);
if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) {
RewriteBitCast(BC, AI, Offset, NewElts);
continue;
}
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
RewriteGEP(GEPI, AI, Offset, NewElts);
continue;
}
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.
continue;
}
if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
const Type *LIType = LI->getType();
if (isCompatibleAggregate(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);
IRBuilder<> Builder(LI);
for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
Value *Load = Builder.CreateLoad(NewElts[i], "load");
Insert = Builder.CreateInsertValue(Insert, Load, i, "insert");
}
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);
}
continue;
}
if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
Value *Val = SI->getOperand(0);
const Type *SIType = Val->getType();
if (isCompatibleAggregate(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)
IRBuilder<> Builder(SI);
for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
Value *Extract = Builder.CreateExtractValue(Val, i, Val->getName());
Builder.CreateStore(Extract, NewElts[i]);
}
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);
}
continue;
}
if (isa<SelectInst>(User) || isa<PHINode>(User)) {
// If we have a PHI user of the alloca itself (as opposed to a GEP or
// bitcast) we have to rewrite it. GEP and bitcast uses will be RAUW'd to
// the new pointer.
if (!isa<AllocaInst>(I)) continue;
assert(Offset == 0 && NewElts[0] &&
"Direct alloca use should have a zero offset");
// If we have a use of the alloca, we know the derived uses will be
// utilizing just the first element of the scalarized result. Insert a
// bitcast of the first alloca before the user as required.
AllocaInst *NewAI = NewElts[0];
BitCastInst *BCI = new BitCastInst(NewAI, AI->getType(), "", NewAI);
NewAI->moveBefore(BCI);
TheUse = BCI;
continue;
}
}
}
/// 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.
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);
}
}
new StoreInst(StoreVal, EltPtr, MI);
continue;
}
// Otherwise, if we're storing a byte variable, use a memset call for
// this element.
}
unsigned EltSize = TD->getTypeAllocSize(EltTy);
IRBuilder<> Builder(MI);
// Finally, insert the meminst for this element.
if (isa<MemSetInst>(MI)) {
Builder.CreateMemSet(EltPtr, MI->getArgOperand(1), EltSize,
MI->isVolatile());
} else {
assert(isa<MemTransferInst>(MI));
Value *Dst = SROADest ? EltPtr : OtherElt; // Dest ptr
Value *Src = SROADest ? OtherElt : EltPtr; // Src ptr
if (isa<MemCpyInst>(MI))
Builder.CreateMemCpy(Dst, Src, EltSize, OtherEltAlign,MI->isVolatile());
else
Builder.CreateMemMove(Dst, Src, EltSize,OtherEltAlign,MI->isVolatile());
}
}
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);
IRBuilder<> Builder(SI);
// Handle tail padding by extending the operand
if (TD->getTypeSizeInBits(SrcVal->getType()) != AllocaSizeBits)
SrcVal = Builder.CreateZExt(SrcVal,
IntegerType::get(SI->getContext(), AllocaSizeBits));
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 = Builder.CreateLShr(EltVal, ShiftVal, "sroa.store.elt");
}
// 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 = Builder.CreateTrunc(EltVal,
IntegerType::get(SI->getContext(), FieldSizeBits));
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 = Builder.CreateBitCast(EltVal, FieldTy);
} else {
// Otherwise, bitcast the dest pointer (for aggregates).
DestField = Builder.CreateBitCast(DestField,
PointerType::getUnqual(EltVal->getType()));
}
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 = Builder.CreateLShr(EltVal, ShiftVal, "sroa.store.elt");
}
// Truncate down to an integer of the right size.
if (ElementSizeBits != AllocaSizeBits)
EltVal = Builder.CreateTrunc(EltVal,
IntegerType::get(SI->getContext(),
ElementSizeBits));
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 = Builder.CreateBitCast(EltVal, ArrayEltTy);
} else {
// Otherwise, bitcast the dest pointer (for aggregates).
DestField = Builder.CreateBitCast(DestField,
PointerType::getUnqual(EltVal->getType()));
}
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 in between the elements that would be split apart
/// by SROA; return false otherwise.
static bool HasPadding(const Type *Ty, const TargetData &TD) {
if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
Ty = ATy->getElementType();
return TD.getTypeSizeInBits(Ty) != TD.getTypeAllocSizeInBits(Ty);
}
// SROA currently handles only Arrays and Structs.
const StructType *STy = 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);
// 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 false;
}
/// 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(AI);
isSafeForScalarRepl(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;
// If the alloca never has an access to just *part* of it, but is accessed
// via loads and stores, then we should use ConvertToScalarInfo to promote
// the alloca instead of promoting each piece at a time and inserting fission
// and fusion code.
if (!Info.hasSubelementAccess && Info.hasALoadOrStore) {
// If the struct/array just has one element, use basic SRoA.
if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) {
if (ST->getNumElements() > 1) return false;
} else {
if (cast<ArrayType>(AI->getAllocatedType())->getNumElements() > 1)
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,
SmallVector<Instruction *, 4> &LifetimeMarkers) {
// We track lifetime intrinsics as we encounter them. If we decide to go
// ahead and replace the value with the global, this lets the caller quickly
// eliminate the markers.
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,
LifetimeMarkers))
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(),
LifetimeMarkers))
return false;
continue;
}
if (CallSite CS = U) {
// 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 a readonly/readnone call site, then we know it is just a
// load (but one that potentially returns the value itself), so we can
// ignore it if we know that the value isn't captured.
unsigned ArgNo = CS.getArgumentNo(UI);
if (CS.onlyReadsMemory() &&
(CS.getInstruction()->use_empty() ||
CS.paramHasAttr(ArgNo+1, Attribute::NoCapture)))
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.
if (CS.paramHasAttr(ArgNo+1, Attribute::ByVal))
continue;
}
// Lifetime intrinsics can be handled by the caller.
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(U)) {
if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
II->getIntrinsicID() == Intrinsic::lifetime_end) {
assert(II->use_empty() && "Lifetime markers have no result to use!");
LifetimeMarkers.push_back(II);
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,
SmallVector<Instruction*, 4> &ToDelete) {
MemTransferInst *TheCopy = 0;
if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false, ToDelete))
return TheCopy;
return 0;
}
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