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llvm-6502/lib/Transforms/Scalar/ScalarReplAggregates.cpp
Mehdi Amini 529919ff31 DataLayout is mandatory, update the API to reflect it with references. 
Summary:
Now that the DataLayout is a mandatory part of the module, let's start
cleaning the codebase. This patch is a first attempt at doing that.

This patch is not exactly NFC as for instance some places were passing
a nullptr instead of the DataLayout, possibly just because there was a
default value on the DataLayout argument to many functions in the API.
Even though it is not purely NFC, there is no change in the
validation.

I turned as many pointer to DataLayout to references, this helped
figuring out all the places where a nullptr could come up.

I had initially a local version of this patch broken into over 30
independant, commits but some later commit were cleaning the API and
touching part of the code modified in the previous commits, so it
seemed cleaner without the intermediate state.

Test Plan:

Reviewers: echristo

Subscribers: llvm-commits

From: Mehdi Amini <mehdi.amini@apple.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231740 91177308-0d34-0410-b5e6-96231b3b80d8
2015-03-10 02:37:25 +00:00

2631 lines
102 KiB
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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 they
// often interact, especially for C++ programs. As such, iterating between
// SRoA, then Mem2Reg until we run out of things to promote works well.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Operator.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
using namespace llvm;
#define DEBUG_TYPE "scalarrepl"
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");
namespace {
struct SROA : public FunctionPass {
SROA(int T, bool hasDT, char &ID, int ST, int AT, int SLT)
: FunctionPass(ID), HasDomTree(hasDT) {
if (T == -1)
SRThreshold = 128;
else
SRThreshold = T;
if (ST == -1)
StructMemberThreshold = 32;
else
StructMemberThreshold = ST;
if (AT == -1)
ArrayElementThreshold = 8;
else
ArrayElementThreshold = AT;
if (SLT == -1)
// Do not limit the scalar integer load size if no threshold is given.
ScalarLoadThreshold = -1;
else
ScalarLoadThreshold = SLT;
}
bool runOnFunction(Function &F) override;
bool performScalarRepl(Function &F);
bool performPromotion(Function &F);
private:
bool HasDomTree;
/// 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) {}
};
/// SRThreshold - The maximum alloca size to considered for SROA.
unsigned SRThreshold;
/// StructMemberThreshold - The maximum number of members a struct can
/// contain to be considered for SROA.
unsigned StructMemberThreshold;
/// ArrayElementThreshold - The maximum number of elements an array can
/// have to be considered for SROA.
unsigned ArrayElementThreshold;
/// ScalarLoadThreshold - The maximum size in bits of scalars to load when
/// converting to scalar
unsigned ScalarLoadThreshold;
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,
Type *MemOpType, bool isStore, AllocaInfo &Info,
Instruction *TheAccess, bool AllowWholeAccess);
bool TypeHasComponent(Type *T, uint64_t Offset, uint64_t Size,
const DataLayout &DL);
uint64_t FindElementAndOffset(Type *&T, uint64_t &Offset, Type *&IdxTy,
const DataLayout &DL);
void DoScalarReplacement(AllocaInst *AI,
std::vector<AllocaInst*> &WorkList);
void DeleteDeadInstructions();
void RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
SmallVectorImpl<AllocaInst *> &NewElts);
void RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset,
SmallVectorImpl<AllocaInst *> &NewElts);
void RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset,
SmallVectorImpl<AllocaInst *> &NewElts);
void RewriteLifetimeIntrinsic(IntrinsicInst *II, AllocaInst *AI,
uint64_t Offset,
SmallVectorImpl<AllocaInst *> &NewElts);
void RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst,
AllocaInst *AI,
SmallVectorImpl<AllocaInst *> &NewElts);
void RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI,
SmallVectorImpl<AllocaInst *> &NewElts);
void RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI,
SmallVectorImpl<AllocaInst *> &NewElts);
bool ShouldAttemptScalarRepl(AllocaInst *AI);
};
// SROA_DT - SROA that uses DominatorTree.
struct SROA_DT : public SROA {
static char ID;
public:
SROA_DT(int T = -1, int ST = -1, int AT = -1, int SLT = -1) :
SROA(T, true, ID, ST, AT, SLT) {
initializeSROA_DTPass(*PassRegistry::getPassRegistry());
}
// getAnalysisUsage - This pass does not require any passes, but we know it
// will not alter the CFG, so say so.
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.setPreservesCFG();
}
};
// SROA_SSAUp - SROA that uses SSAUpdater.
struct SROA_SSAUp : public SROA {
static char ID;
public:
SROA_SSAUp(int T = -1, int ST = -1, int AT = -1, int SLT = -1) :
SROA(T, false, ID, ST, AT, SLT) {
initializeSROA_SSAUpPass(*PassRegistry::getPassRegistry());
}
// getAnalysisUsage - This pass does not require any passes, but we know it
// will not alter the CFG, so say so.
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AssumptionCacheTracker>();
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(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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_DEPENDENCY(AssumptionCacheTracker)
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,
int StructMemberThreshold,
int ArrayElementThreshold,
int ScalarLoadThreshold) {
if (UseDomTree)
return new SROA_DT(Threshold, StructMemberThreshold, ArrayElementThreshold,
ScalarLoadThreshold);
return new SROA_SSAUp(Threshold, StructMemberThreshold,
ArrayElementThreshold, ScalarLoadThreshold);
}
//===----------------------------------------------------------------------===//
// 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 DataLayout &DL;
unsigned ScalarLoadThreshold;
/// 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.
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;
/// HadDynamicAccess - True if some element of this alloca was dynamic.
/// We don't yet have support for turning a dynamic access into a large
/// integer.
bool HadDynamicAccess;
public:
explicit ConvertToScalarInfo(unsigned Size, const DataLayout &DL,
unsigned SLT)
: AllocaSize(Size), DL(DL), ScalarLoadThreshold(SLT), IsNotTrivial(false),
ScalarKind(Unknown), VectorTy(nullptr), HadNonMemTransferAccess(false),
HadDynamicAccess(false) { }
AllocaInst *TryConvert(AllocaInst *AI);
private:
bool CanConvertToScalar(Value *V, uint64_t Offset, Value* NonConstantIdx);
void MergeInTypeForLoadOrStore(Type *In, uint64_t Offset);
bool MergeInVectorType(VectorType *VInTy, uint64_t Offset);
void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset,
Value *NonConstantIdx);
Value *ConvertScalar_ExtractValue(Value *NV, Type *ToType,
uint64_t Offset, Value* NonConstantIdx,
IRBuilder<> &Builder);
Value *ConvertScalar_InsertValue(Value *StoredVal, Value *ExistingVal,
uint64_t Offset, Value* NonConstantIdx,
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, nullptr) || !IsNotTrivial)
return nullptr;
// 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;
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.
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;
// Do not convert to scalar integer if the alloca size exceeds the
// scalar load threshold.
if (BitWidth > ScalarLoadThreshold)
return nullptr;
if ((ScalarKind == ImplicitVector || ScalarKind == Integer) &&
!HadNonMemTransferAccess && !DL.fitsInLegalInteger(BitWidth))
return nullptr;
// Dynamic accesses on integers aren't yet supported. They need us to shift
// by a dynamic amount which could be difficult to work out as we might not
// know whether to use a left or right shift.
if (ScalarKind == Integer && HadDynamicAccess)
return nullptr;
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, nullptr, "",
AI->getParent()->begin());
ConvertUsesToScalar(AI, NewAI, 0, nullptr);
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 two cases we handle here:
/// 1) A union of vector types of the same size and potentially its elements.
/// Here we turn element accesses into insert/extract element operations.
/// This promotes a <4 x float> with a store of float to the third element
/// into a <4 x float> that uses insert element.
/// 2) A fully general blob of memory, which we turn into some (potentially
/// large) integer type with extract and insert operations where the loads
/// and stores would mutate the memory. We mark this by setting VectorTy
/// to VoidTy.
void ConvertToScalarInfo::MergeInTypeForLoadOrStore(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 (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 || EltSize == VectorTy->getElementType()
->getPrimitiveSizeInBits()/8)) {
if (!VectorTy) {
ScalarKind = ImplicitVector;
VectorTy = VectorType::get(In, AllocaSize/EltSize);
}
return;
}
}
// Otherwise, we have a case that we can't handle with an optimized vector
// form. We can still turn this into a large integer.
ScalarKind = Integer;
}
/// MergeInVectorType - Handles the vector case of MergeInTypeForLoadOrStore,
/// returning true if the type was successfully merged and false otherwise.
bool ConvertToScalarInfo::MergeInVectorType(VectorType *VInTy,
uint64_t Offset) {
if (VInTy->getBitWidth()/8 == AllocaSize && Offset == 0) {
// If we're storing/loading a vector of the right size, allow it as a
// vector. If this the first vector we see, remember the type so that
// we know the element size. If this is a subsequent access, ignore it
// even if it is a differing type but the same size. Worst case we can
// bitcast the resultant vectors.
if (!VectorTy)
VectorTy = VInTy;
ScalarKind = Vector;
return true;
}
return false;
}
/// 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,
Value* NonConstantIdx) {
for (User *U : V->users()) {
Instruction *UI = cast<Instruction>(U);
if (LoadInst *LI = dyn_cast<LoadInst>(UI)) {
// Don't break volatile loads.
if (!LI->isSimple())
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>(UI)) {
// Storing the pointer, not into the value?
if (SI->getOperand(0) == V || !SI->isSimple()) 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>(UI)) {
if (!onlyUsedByLifetimeMarkers(BCI))
IsNotTrivial = true; // Can't be mem2reg'd.
if (!CanConvertToScalar(BCI, Offset, NonConstantIdx))
return false;
continue;
}
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(UI)) {
// If this is a GEP with a variable indices, we can't handle it.
PointerType* PtrTy = dyn_cast<PointerType>(GEP->getPointerOperandType());
if (!PtrTy)
return false;
// Compute the offset that this GEP adds to the pointer.
SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end());
Value *GEPNonConstantIdx = nullptr;
if (!GEP->hasAllConstantIndices()) {
if (!isa<VectorType>(PtrTy->getElementType()))
return false;
if (NonConstantIdx)
return false;
GEPNonConstantIdx = Indices.pop_back_val();
if (!GEPNonConstantIdx->getType()->isIntegerTy(32))
return false;
HadDynamicAccess = true;
} else
GEPNonConstantIdx = NonConstantIdx;
uint64_t GEPOffset = DL.getIndexedOffset(PtrTy,
Indices);
// See if all uses can be converted.
if (!CanConvertToScalar(GEP, Offset+GEPOffset, GEPNonConstantIdx))
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>(UI)) {
// Store to dynamic index.
if (NonConstantIdx)
return false;
// 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>(UI)) {
// Store to dynamic index.
if (NonConstantIdx)
return false;
ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength());
if (!Len || Len->getZExtValue() != AllocaSize || Offset != 0)
return false;
IsNotTrivial = true; // Can't be mem2reg'd.
continue;
}
// If this is a lifetime intrinsic, we can handle it.
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(UI)) {
if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
II->getIntrinsicID() == Intrinsic::lifetime_end) {
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,
Value* NonConstantIdx) {
while (!Ptr->use_empty()) {
Instruction *User = cast<Instruction>(Ptr->user_back());
if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) {
ConvertUsesToScalar(CI, NewAI, Offset, NonConstantIdx);
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());
Value* GEPNonConstantIdx = nullptr;
if (!GEP->hasAllConstantIndices()) {
assert(!NonConstantIdx &&
"Dynamic GEP reading from dynamic GEP unsupported");
GEPNonConstantIdx = Indices.pop_back_val();
} else
GEPNonConstantIdx = NonConstantIdx;
uint64_t GEPOffset = DL.getIndexedOffset(GEP->getPointerOperandType(),
Indices);
ConvertUsesToScalar(GEP, NewAI, Offset+GEPOffset*8, GEPNonConstantIdx);
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);
Value *NewLoadVal
= ConvertScalar_ExtractValue(LoadedVal, LI->getType(), Offset,
NonConstantIdx, 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,
NonConstantIdx, 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!");
assert(!NonConstantIdx && "Cannot replace dynamic memset with insert");
int64_t SNumBytes = cast<ConstantInt>(MSI->getLength())->getSExtValue();
if (SNumBytes > 0 && (SNumBytes >> 32) == 0) {
unsigned NumBytes = static_cast<unsigned>(SNumBytes);
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, nullptr, 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");
assert(!NonConstantIdx && "Cannot replace dynamic transfer with insert");
// 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, DL, 0));
if (GetUnderlyingObject(MTI->getSource(), DL, 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();
PointerType* SPTy = cast<PointerType>(SrcPtr->getType());
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(), DL, 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");
PointerType* DPTy = cast<PointerType>(MTI->getDest()->getType());
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;
}
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(User)) {
if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
II->getIntrinsicID() == Intrinsic::lifetime_end) {
// There's no need to preserve these, as the resulting alloca will be
// converted to a register anyways.
II->eraseFromParent();
continue;
}
}
llvm_unreachable("Unsupported operation!");
}
}
/// ConvertScalar_ExtractValue - Extract a value of type ToType from an integer
/// or vector value FromVal, extracting the bits from the offset specified by
/// Offset. This returns the value, which is of type ToType.
///
/// This happens when we are converting an "integer union" to a single
/// integer scalar, or when we are converting a "vector union" to a vector with
/// insert/extractelement instructions.
///
/// Offset is an offset from the original alloca, in bits that need to be
/// shifted to the right.
Value *ConvertToScalarInfo::
ConvertScalar_ExtractValue(Value *FromVal, Type *ToType,
uint64_t Offset, Value* NonConstantIdx,
IRBuilder<> &Builder) {
// If the load is of the whole new alloca, no conversion is needed.
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 (VectorType *VTy = dyn_cast<VectorType>(FromType)) {
unsigned FromTypeSize = DL.getTypeAllocSize(FromType);
unsigned ToTypeSize = DL.getTypeAllocSize(ToType);
if (FromTypeSize == ToTypeSize)
return Builder.CreateBitCast(FromVal, ToType);
// Otherwise it must be an element access.
unsigned Elt = 0;
if (Offset) {
unsigned EltSize = DL.getTypeAllocSizeInBits(VTy->getElementType());
Elt = Offset/EltSize;
assert(EltSize*Elt == Offset && "Invalid modulus in validity checking");
}
// Return the element extracted out of it.
Value *Idx;
if (NonConstantIdx) {
if (Elt)
Idx = Builder.CreateAdd(NonConstantIdx,
Builder.getInt32(Elt),
"dyn.offset");
else
Idx = NonConstantIdx;
} else
Idx = Builder.getInt32(Elt);
Value *V = Builder.CreateExtractElement(FromVal, Idx);
if (V->getType() != ToType)
V = Builder.CreateBitCast(V, ToType);
return V;
}
// If ToType is a first class aggregate, extract out each of the pieces and
// use insertvalue's to form the FCA.
if (StructType *ST = dyn_cast<StructType>(ToType)) {
assert(!NonConstantIdx &&
"Dynamic indexing into struct types not supported");
const StructLayout &Layout = *DL.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),
nullptr, Builder);
Res = Builder.CreateInsertValue(Res, Elt, i);
}
return Res;
}
if (ArrayType *AT = dyn_cast<ArrayType>(ToType)) {
assert(!NonConstantIdx &&
"Dynamic indexing into array types not supported");
uint64_t EltSize = DL.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, nullptr,
Builder);
Res = Builder.CreateInsertValue(Res, Elt, i);
}
return Res;
}
// Otherwise, this must be a union that was converted to an integer value.
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 (DL.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 = DL.getTypeStoreSizeInBits(NTy) -
DL.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));
else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth())
FromVal = Builder.CreateShl(FromVal,
ConstantInt::get(FromVal->getType(), -ShAmt));
// Finally, unconditionally truncate the integer to the right width.
unsigned LIBitWidth = DL.getTypeSizeInBits(ToType);
if (LIBitWidth < NTy->getBitWidth())
FromVal =
Builder.CreateTrunc(FromVal, IntegerType::get(FromVal->getContext(),
LIBitWidth));
else if (LIBitWidth > NTy->getBitWidth())
FromVal =
Builder.CreateZExt(FromVal, IntegerType::get(FromVal->getContext(),
LIBitWidth));
// 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);
} else {
// Otherwise must be a pointer.
FromVal = Builder.CreateIntToPtr(FromVal, ToType);
}
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.
///
/// NonConstantIdx is an index value if there was a GEP with a non-constant
/// index value. If this is 0 then all GEPs used to find this insert address
/// are constant.
Value *ConvertToScalarInfo::
ConvertScalar_InsertValue(Value *SV, Value *Old,
uint64_t Offset, Value* NonConstantIdx,
IRBuilder<> &Builder) {
// Convert the stored type to the actual type, shift it left to insert
// then 'or' into place.
Type *AllocaType = Old->getType();
LLVMContext &Context = Old->getContext();
if (VectorType *VTy = dyn_cast<VectorType>(AllocaType)) {
uint64_t VecSize = DL.getTypeAllocSizeInBits(VTy);
uint64_t ValSize = DL.getTypeAllocSizeInBits(SV->getType());
// Changing the whole vector with memset or with an access of a different
// vector type?
if (ValSize == VecSize)
return Builder.CreateBitCast(SV, AllocaType);
// Must be an element insertion.
Type *EltTy = VTy->getElementType();
if (SV->getType() != EltTy)
SV = Builder.CreateBitCast(SV, EltTy);
uint64_t EltSize = DL.getTypeAllocSizeInBits(EltTy);
unsigned Elt = Offset/EltSize;
Value *Idx;
if (NonConstantIdx) {
if (Elt)
Idx = Builder.CreateAdd(NonConstantIdx,
Builder.getInt32(Elt),
"dyn.offset");
else
Idx = NonConstantIdx;
} else
Idx = Builder.getInt32(Elt);
return Builder.CreateInsertElement(Old, SV, Idx);
}
// If SV is a first-class aggregate value, insert each value recursively.
if (StructType *ST = dyn_cast<StructType>(SV->getType())) {
assert(!NonConstantIdx &&
"Dynamic indexing into struct types not supported");
const StructLayout &Layout = *DL.getStructLayout(ST);
for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
Value *Elt = Builder.CreateExtractValue(SV, i);
Old = ConvertScalar_InsertValue(Elt, Old,
Offset+Layout.getElementOffsetInBits(i),
nullptr, Builder);
}
return Old;
}
if (ArrayType *AT = dyn_cast<ArrayType>(SV->getType())) {
assert(!NonConstantIdx &&
"Dynamic indexing into array types not supported");
uint64_t EltSize = DL.getTypeAllocSizeInBits(AT->getElementType());
for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
Value *Elt = Builder.CreateExtractValue(SV, i);
Old = ConvertScalar_InsertValue(Elt, Old, Offset+i*EltSize, nullptr,
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 = DL.getTypeSizeInBits(SV->getType());
unsigned DestWidth = DL.getTypeSizeInBits(AllocaType);
unsigned SrcStoreWidth = DL.getTypeStoreSizeInBits(SV->getType());
unsigned DestStoreWidth = DL.getTypeStoreSizeInBits(AllocaType);
if (SV->getType()->isFloatingPointTy() || SV->getType()->isVectorTy())
SV = Builder.CreateBitCast(SV, IntegerType::get(SV->getContext(),SrcWidth));
else if (SV->getType()->isPointerTy())
SV = Builder.CreatePtrToInt(SV, DL.getIntPtrType(SV->getType()));
// Zero extend or truncate the value if needed.
if (SV->getType() != AllocaType) {
if (SV->getType()->getPrimitiveSizeInBits() <
AllocaType->getPrimitiveSizeInBits())
SV = Builder.CreateZExt(SV, AllocaType);
else {
// Truncation may be needed if storing more than the alloca can hold
// (undefined behavior).
SV = Builder.CreateTrunc(SV, AllocaType);
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 (DL.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));
Mask <<= ShAmt;
} else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) {
SV = Builder.CreateLShr(SV, ConstantInt::get(SV->getType(), -ShAmt));
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) {
if (skipOptnoneFunction(F))
return false;
bool Changed = performPromotion(F);
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;
DIBuilder *DIB;
SmallVector<DbgDeclareInst *, 4> DDIs;
SmallVector<DbgValueInst *, 4> DVIs;
public:
AllocaPromoter(const SmallVectorImpl<Instruction*> &Insts, SSAUpdater &S,
DIBuilder *DB)
: LoadAndStorePromoter(Insts, S), AI(nullptr), DIB(DB) {}
void run(AllocaInst *AI, const SmallVectorImpl<Instruction*> &Insts) {
// Remember which alloca we're promoting (for isInstInList).
this->AI = AI;
if (auto *L = LocalAsMetadata::getIfExists(AI)) {
if (auto *DebugNode = MetadataAsValue::getIfExists(AI->getContext(), L)) {
for (User *U : DebugNode->users())
if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U))
DDIs.push_back(DDI);
else if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(U))
DVIs.push_back(DVI);
}
}
LoadAndStorePromoter::run(Insts);
AI->eraseFromParent();
for (SmallVectorImpl<DbgDeclareInst *>::iterator I = DDIs.begin(),
E = DDIs.end(); I != E; ++I) {
DbgDeclareInst *DDI = *I;
DDI->eraseFromParent();
}
for (SmallVectorImpl<DbgValueInst *>::iterator I = DVIs.begin(),
E = DVIs.end(); I != E; ++I) {
DbgValueInst *DVI = *I;
DVI->eraseFromParent();
}
}
bool isInstInList(Instruction *I,
const SmallVectorImpl<Instruction*> &Insts) const override {
if (LoadInst *LI = dyn_cast<LoadInst>(I))
return LI->getOperand(0) == AI;
return cast<StoreInst>(I)->getPointerOperand() == AI;
}
void updateDebugInfo(Instruction *Inst) const override {
for (SmallVectorImpl<DbgDeclareInst *>::const_iterator I = DDIs.begin(),
E = DDIs.end(); I != E; ++I) {
DbgDeclareInst *DDI = *I;
if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
ConvertDebugDeclareToDebugValue(DDI, SI, *DIB);
else if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
ConvertDebugDeclareToDebugValue(DDI, LI, *DIB);
}
for (SmallVectorImpl<DbgValueInst *>::const_iterator I = DVIs.begin(),
E = DVIs.end(); I != E; ++I) {
DbgValueInst *DVI = *I;
Value *Arg = nullptr;
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
// If an argument is zero extended then use argument directly. The ZExt
// may be zapped by an optimization pass in future.
if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
Arg = dyn_cast<Argument>(ZExt->getOperand(0));
if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
Arg = dyn_cast<Argument>(SExt->getOperand(0));
if (!Arg)
Arg = SI->getOperand(0);
} else if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
Arg = LI->getOperand(0);
} else {
continue;
}
Instruction *DbgVal = DIB->insertDbgValueIntrinsic(
Arg, 0, DIVariable(DVI->getVariable()),
DIExpression(DVI->getExpression()), Inst);
DbgVal->setDebugLoc(DVI->getDebugLoc());
}
}
};
} // 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 DataLayout &DL = SI->getModule()->getDataLayout();
bool TDerefable = SI->getTrueValue()->isDereferenceablePointer(DL);
bool FDerefable = SI->getFalseValue()->isDereferenceablePointer(DL);
for (User *U : SI->users()) {
LoadInst *LI = dyn_cast<LoadInst>(U);
if (!LI || !LI->isSimple()) 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()))
return false;
if (!FDerefable &&
!isSafeToLoadUnconditionally(SI->getFalseValue(), LI,
LI->getAlignment()))
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) {
// 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 (User *U : PN->users()) {
LoadInst *LI = dyn_cast<LoadInst>(U);
if (!LI || !LI->isSimple()) 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());
}
const DataLayout &DL = PN->getModule()->getDataLayout();
// 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);
Value *InVal = PN->getIncomingValue(i);
// If the terminator of the predecessor has side-effects (an invoke),
// there is no safe place to put a load in the predecessor.
if (Pred->getTerminator()->mayHaveSideEffects())
return false;
// If the value is produced by the terminator of the predecessor
// (an invoke), there is no valid place to put a load in the predecessor.
if (Pred->getTerminator() == InVal)
return false;
// If the predecessor has a single successor, then the edge isn't critical.
if (Pred->getTerminator()->getNumSuccessors() == 1)
continue;
// 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(DL) ||
isSafeToLoadUnconditionally(InVal, Pred->getTerminator(), MaxAlign))
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 DataLayout &DL) {
SetVector<Instruction*, SmallVector<Instruction*, 4>,
SmallPtrSet<Instruction*, 4> > InstsToRewrite;
for (User *U : AI->users()) {
if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
if (!LI->isSimple())
return false;
continue;
}
if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
if (SI->getOperand(0) == AI || !SI->isSimple())
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, DL);
}
// 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))
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))
return false;
InstsToRewrite.insert(PN);
continue;
}
if (BitCastInst *BCI = dyn_cast<BitCastInst>(U)) {
if (onlyUsedByLifetimeMarkers(BCI)) {
InstsToRewrite.insert(BCI);
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 (BitCastInst *BCI = dyn_cast<BitCastInst>(InstsToRewrite[i])) {
// This could only be a bitcast used by nothing but lifetime intrinsics.
for (BitCastInst::user_iterator I = BCI->user_begin(), E = BCI->user_end();
I != E;)
cast<Instruction>(*I++)->eraseFromParent();
BCI->eraseFromParent();
continue;
}
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->user_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 AA info if present.
TrueLoad->setAlignment(LI->getAlignment());
FalseLoad->setAlignment(LI->getAlignment());
AAMDNodes Tags;
LI->getAAMetadata(Tags);
if (Tags) {
TrueLoad->setAAMetadata(Tags);
FalseLoad->setAAMetadata(Tags);
}
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;
}
Type *LoadTy = cast<PointerType>(PN->getType())->getElementType();
PHINode *NewPN = PHINode::Create(LoadTy, PN->getNumIncomingValues(),
PN->getName()+".ld", PN);
// Get the AA tags 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->user_back());
AAMDNodes AATags;
SomeLoad->getAAMetadata(AATags);
unsigned Align = SomeLoad->getAlignment();
// Rewrite all loads of the PN to use the new PHI.
while (!PN->use_empty()) {
LoadInst *LI = cast<LoadInst>(PN->user_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) {
Load = new LoadInst(PN->getIncomingValue(i),
PN->getName() + "." + Pred->getName(),
Pred->getTerminator());
Load->setAlignment(Align);
if (AATags) Load->setAAMetadata(AATags);
}
NewPN->addIncoming(Load, Pred);
}
PN->eraseFromParent();
}
++NumAdjusted;
return true;
}
bool SROA::performPromotion(Function &F) {
std::vector<AllocaInst*> Allocas;
const DataLayout &DL = F.getParent()->getDataLayout();
DominatorTree *DT = nullptr;
if (HasDomTree)
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
AssumptionCache &AC =
getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function
DIBuilder DIB(*F.getParent(), /*AllowUnresolved*/ false);
bool Changed = false;
SmallVector<Instruction*, 64> Insts;
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, DL))
Allocas.push_back(AI);
if (Allocas.empty()) break;
if (HasDomTree)
PromoteMemToReg(Allocas, *DT, nullptr, &AC);
else {
SSAUpdater SSA;
for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
AllocaInst *AI = Allocas[i];
// Build list of instructions to promote.
for (User *U : AI->users())
Insts.push_back(cast<Instruction>(U));
AllocaPromoter(Insts, SSA, &DIB).run(AI, Insts);
Insts.clear();
}
}
NumPromoted += Allocas.size();
Changed = true;
}
return Changed;
}
/// ShouldAttemptScalarRepl - Decide if an alloca is a good candidate for
/// SROA. It must be a struct or array type with a small number of elements.
bool SROA::ShouldAttemptScalarRepl(AllocaInst *AI) {
Type *T = AI->getAllocatedType();
// Do not promote any struct that has too many members.
if (StructType *ST = dyn_cast<StructType>(T))
return ST->getNumElements() <= StructMemberThreshold;
// Do not promote any array that has too many elements.
if (ArrayType *AT = dyn_cast<ArrayType>(T))
return AT->getNumElements() <= ArrayElementThreshold;
return false;
}
// performScalarRepl - This algorithm is a simple worklist driven algorithm,
// which runs on all of the alloca instructions in the entry block, removing
// them if they are only used by getelementptr instructions.
//
bool SROA::performScalarRepl(Function &F) {
std::vector<AllocaInst*> WorkList;
const DataLayout &DL = F.getParent()->getDataLayout();
// 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 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 = DL.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, DL, ScalarLoadThreshold)
.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 (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), nullptr,
AI->getAlignment(),
AI->getName() + "." + Twine(i), AI);
ElementAllocas.push_back(NA);
WorkList.push_back(NA); // Add to worklist for recursive processing
}
} else {
ArrayType *AT = cast<ArrayType>(AI->getAllocatedType());
ElementAllocas.reserve(AT->getNumElements());
Type *ElTy = AT->getElementType();
for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
AllocaInst *NA = new AllocaInst(ElTy, nullptr, 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 = nullptr;
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) {
const DataLayout &DL = I->getModule()->getDataLayout();
for (Use &U : I->uses()) {
Instruction *User = cast<Instruction>(U.getUser());
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 || Length->isNegative())
return MarkUnsafe(Info, User);
isSafeMemAccess(Offset, Length->getZExtValue(), nullptr,
U.getOperandNo() == 0, Info, MI,
true /*AllowWholeAccess*/);
} else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
if (!LI->isSimple())
return MarkUnsafe(Info, User);
Type *LIType = LI->getType();
isSafeMemAccess(Offset, DL.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->isSimple() || SI->getOperand(0) == I)
return MarkUnsafe(Info, User);
Type *SIType = SI->getOperand(0)->getType();
isSafeMemAccess(Offset, DL.getTypeAllocSize(SIType), SIType, true, Info,
SI, true /*AllowWholeAccess*/);
Info.hasALoadOrStore = true;
} else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(User)) {
if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
II->getIntrinsicID() != Intrinsic::lifetime_end)
return MarkUnsafe(Info, User);
} 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).second)
return;
const DataLayout &DL = I->getModule()->getDataLayout();
for (User *U : I->users()) {
Instruction *UI = cast<Instruction>(U);
if (BitCastInst *BC = dyn_cast<BitCastInst>(UI)) {
isSafePHISelectUseForScalarRepl(BC, Offset, Info);
} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(UI)) {
// 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, UI);
isSafePHISelectUseForScalarRepl(GEPI, Offset, Info);
} else if (LoadInst *LI = dyn_cast<LoadInst>(UI)) {
if (!LI->isSimple())
return MarkUnsafe(Info, UI);
Type *LIType = LI->getType();
isSafeMemAccess(Offset, DL.getTypeAllocSize(LIType), LIType, false, Info,
LI, false /*AllowWholeAccess*/);
Info.hasALoadOrStore = true;
} else if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
// Store is ok if storing INTO the pointer, not storing the pointer
if (!SI->isSimple() || SI->getOperand(0) == I)
return MarkUnsafe(Info, UI);
Type *SIType = SI->getOperand(0)->getType();
isSafeMemAccess(Offset, DL.getTypeAllocSize(SIType), SIType, true, Info,
SI, false /*AllowWholeAccess*/);
Info.hasALoadOrStore = true;
} else if (isa<PHINode>(UI) || isa<SelectInst>(UI)) {
isSafePHISelectUseForScalarRepl(UI, Offset, Info);
} else {
return MarkUnsafe(Info, UI);
}
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;
bool NonConstant = false;
unsigned NonConstantIdxSize = 0;
// 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());
// If this GEP is non-constant then the last operand must have been a
// dynamic index into a vector. Pop this now as it has no impact on the
// constant part of the offset.
if (NonConstant)
Indices.pop_back();
const DataLayout &DL = GEPI->getModule()->getDataLayout();
Offset += DL.getIndexedOffset(GEPI->getPointerOperandType(), Indices);
if (!TypeHasComponent(Info.AI->getAllocatedType(), Offset, NonConstantIdxSize,
DL))
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(Type *T, unsigned &NumElts,
Type *&EltTy) {
if (ArrayType *AT = dyn_cast<ArrayType>(T)) {
NumElts = AT->getNumElements();
EltTy = (NumElts == 0 ? nullptr : AT->getElementType());
return true;
}
if (StructType *ST = dyn_cast<StructType>(T)) {
NumElts = ST->getNumContainedTypes();
EltTy = (NumElts == 0 ? nullptr : 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(Type *T1, Type *T2) {
if (T1 == T2)
return true;
unsigned NumElts1, NumElts2;
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,
Type *MemOpType, bool isStore,
AllocaInfo &Info, Instruction *TheAccess,
bool AllowWholeAccess) {
const DataLayout &DL = TheAccess->getModule()->getDataLayout();
// Check if this is a load/store of the entire alloca.
if (Offset == 0 && AllowWholeAccess &&
MemSize == DL.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.
Type *T = Info.AI->getAllocatedType();
if (TypeHasComponent(T, Offset, MemSize, DL)) {
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(Type *T, uint64_t Offset, uint64_t Size,
const DataLayout &DL) {
Type *EltTy;
uint64_t EltSize;
if (StructType *ST = dyn_cast<StructType>(T)) {
const StructLayout *Layout = DL.getStructLayout(ST);
unsigned EltIdx = Layout->getElementContainingOffset(Offset);
EltTy = ST->getContainedType(EltIdx);
EltSize = DL.getTypeAllocSize(EltTy);
Offset -= Layout->getElementOffset(EltIdx);
} else if (ArrayType *AT = dyn_cast<ArrayType>(T)) {
EltTy = AT->getElementType();
EltSize = DL.getTypeAllocSize(EltTy);
if (Offset >= AT->getNumElements() * EltSize)
return false;
Offset %= EltSize;
} else if (VectorType *VT = dyn_cast<VectorType>(T)) {
EltTy = VT->getElementType();
EltSize = DL.getTypeAllocSize(EltTy);
if (Offset >= VT->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, DL);
}
/// 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,
SmallVectorImpl<AllocaInst *> &NewElts) {
const DataLayout &DL = I->getModule()->getDataLayout();
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E;) {
Use &TheUse = *UI++;
Instruction *User = cast<Instruction>(TheUse.getUser());
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 == DL.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 (IntrinsicInst *II = dyn_cast<IntrinsicInst>(User)) {
if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
II->getIntrinsicID() == Intrinsic::lifetime_end) {
RewriteLifetimeIntrinsic(II, AI, Offset, NewElts);
}
continue;
}
if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
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() &&
DL.getTypeAllocSize(LIType) ==
DL.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);
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() &&
DL.getTypeAllocSize(SIType) ==
DL.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,
SmallVectorImpl<AllocaInst *> &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 alloca containing offset zero (which is normally at
// index zero, but might not be in cases involving structs with elements
// of size zero).
Type *T = AI->getAllocatedType();
uint64_t EltOffset = 0;
Type *IdxTy;
uint64_t Idx = FindElementAndOffset(T, EltOffset, IdxTy,
BC->getModule()->getDataLayout());
Instruction *Val = NewElts[Idx];
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(Type *&T, uint64_t &Offset, Type *&IdxTy,
const DataLayout &DL) {
uint64_t Idx = 0;
if (StructType *ST = dyn_cast<StructType>(T)) {
const StructLayout *Layout = DL.getStructLayout(ST);
Idx = Layout->getElementContainingOffset(Offset);
T = ST->getContainedType(Idx);
Offset -= Layout->getElementOffset(Idx);
IdxTy = Type::getInt32Ty(T->getContext());
return Idx;
} else if (ArrayType *AT = dyn_cast<ArrayType>(T)) {
T = AT->getElementType();
uint64_t EltSize = DL.getTypeAllocSize(T);
Idx = Offset / EltSize;
Offset -= Idx * EltSize;
IdxTy = Type::getInt64Ty(T->getContext());
return Idx;
}
VectorType *VT = cast<VectorType>(T);
T = VT->getElementType();
uint64_t EltSize = DL.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,
SmallVectorImpl<AllocaInst *> &NewElts) {
uint64_t OldOffset = Offset;
const DataLayout &DL = GEPI->getModule()->getDataLayout();
SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end());
// If the GEP was dynamic then it must have been a dynamic vector lookup.
// In this case, it must be the last GEP operand which is dynamic so keep that
// aside until we've found the constant GEP offset then add it back in at the
// end.
Value* NonConstantIdx = nullptr;
if (!GEPI->hasAllConstantIndices())
NonConstantIdx = Indices.pop_back_val();
Offset += DL.getIndexedOffset(GEPI->getPointerOperandType(), Indices);
RewriteForScalarRepl(GEPI, AI, Offset, NewElts);
Type *T = AI->getAllocatedType();
Type *IdxTy;
uint64_t OldIdx = FindElementAndOffset(T, OldOffset, IdxTy, DL);
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, DL);
// 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;
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, DL);
NewArgs.push_back(ConstantInt::get(IdxTy, EltIdx));
}
if (NonConstantIdx) {
Type* GepTy = T;
// This GEP has a dynamic index. We need to add "i32 0" to index through
// any structs or arrays in the original type until we get to the vector
// to index.
while (!isa<VectorType>(GepTy)) {
NewArgs.push_back(Constant::getNullValue(i32Ty));
GepTy = cast<CompositeType>(GepTy)->getTypeAtIndex(0U);
}
NewArgs.push_back(NonConstantIdx);
}
Instruction *Val = NewElts[Idx];
if (NewArgs.size() > 1) {
Val = GetElementPtrInst::CreateInBounds(Val, NewArgs, "", 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);
}
/// RewriteLifetimeIntrinsic - II is a lifetime.start/lifetime.end. Rewrite it
/// to mark the lifetime of the scalarized memory.
void SROA::RewriteLifetimeIntrinsic(IntrinsicInst *II, AllocaInst *AI,
uint64_t Offset,
SmallVectorImpl<AllocaInst *> &NewElts) {
ConstantInt *OldSize = cast<ConstantInt>(II->getArgOperand(0));
// Put matching lifetime markers on everything from Offset up to
// Offset+OldSize.
Type *AIType = AI->getAllocatedType();
const DataLayout &DL = II->getModule()->getDataLayout();
uint64_t NewOffset = Offset;
Type *IdxTy;
uint64_t Idx = FindElementAndOffset(AIType, NewOffset, IdxTy, DL);
IRBuilder<> Builder(II);
uint64_t Size = OldSize->getLimitedValue();
if (NewOffset) {
// Splice the first element and index 'NewOffset' bytes in. SROA will
// split the alloca again later.
unsigned AS = AI->getType()->getAddressSpace();
Value *V = Builder.CreateBitCast(NewElts[Idx], Builder.getInt8PtrTy(AS));
V = Builder.CreateGEP(V, Builder.getInt64(NewOffset));
IdxTy = NewElts[Idx]->getAllocatedType();
uint64_t EltSize = DL.getTypeAllocSize(IdxTy) - NewOffset;
if (EltSize > Size) {
EltSize = Size;
Size = 0;
} else {
Size -= EltSize;
}
if (II->getIntrinsicID() == Intrinsic::lifetime_start)
Builder.CreateLifetimeStart(V, Builder.getInt64(EltSize));
else
Builder.CreateLifetimeEnd(V, Builder.getInt64(EltSize));
++Idx;
}
for (; Idx != NewElts.size() && Size; ++Idx) {
IdxTy = NewElts[Idx]->getAllocatedType();
uint64_t EltSize = DL.getTypeAllocSize(IdxTy);
if (EltSize > Size) {
EltSize = Size;
Size = 0;
} else {
Size -= EltSize;
}
if (II->getIntrinsicID() == Intrinsic::lifetime_start)
Builder.CreateLifetimeStart(NewElts[Idx],
Builder.getInt64(EltSize));
else
Builder.CreateLifetimeEnd(NewElts[Idx],
Builder.getInt64(EltSize));
}
DeadInsts.push_back(II);
}
/// 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,
SmallVectorImpl<AllocaInst *> &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 = nullptr;
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 (SmallVectorImpl<Value *>::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.
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()));
const DataLayout &DL = MI->getModule()->getDataLayout();
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 = nullptr;
unsigned OtherEltAlign = MemAlignment;
if (OtherPtr) {
Value *Idx[2] = { Zero,
ConstantInt::get(Type::getInt32Ty(MI->getContext()), i) };
OtherElt = GetElementPtrInst::CreateInBounds(OtherPtr, Idx,
OtherPtr->getName()+"."+Twine(i),
MI);
uint64_t EltOffset;
PointerType *OtherPtrTy = cast<PointerType>(OtherPtr->getType());
Type *OtherTy = OtherPtrTy->getElementType();
if (StructType *ST = dyn_cast<StructType>(OtherTy)) {
EltOffset = DL.getStructLayout(ST)->getElementOffset(i);
} else {
Type *EltTy = cast<SequentialType>(OtherTy)->getElementType();
EltOffset = DL.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];
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.
Type *ValTy = EltTy->getScalarType();
// Construct an integer with the right value.
unsigned EltSize = DL.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->isVectorTy()) {
unsigned NumElts = cast<VectorType>(EltTy)->getNumElements();
StoreVal = ConstantVector::getSplat(NumElts, StoreVal);
}
}
new StoreInst(StoreVal, EltPtr, MI);
continue;
}
// Otherwise, if we're storing a byte variable, use a memset call for
// this element.
}
unsigned EltSize = DL.getTypeAllocSize(EltTy);
if (!EltSize)
continue;
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,
SmallVectorImpl<AllocaInst *> &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);
Type *AllocaEltTy = AI->getAllocatedType();
const DataLayout &DL = SI->getModule()->getDataLayout();
uint64_t AllocaSizeBits = DL.getTypeAllocSizeInBits(AllocaEltTy);
IRBuilder<> Builder(SI);
// Handle tail padding by extending the operand
if (DL.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 (StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) {
const StructLayout *Layout = DL.getStructLayout(EltSTy);
for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
// Get the number of bits to shift SrcVal to get the value.
Type *FieldTy = EltSTy->getElementType(i);
uint64_t Shift = Layout->getElementOffsetInBits(i);
if (DL.isBigEndian())
Shift = AllocaSizeBits - Shift - DL.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 = DL.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 {
ArrayType *ATy = cast<ArrayType>(AllocaEltTy);
Type *ArrayEltTy = ATy->getElementType();
uint64_t ElementOffset = DL.getTypeAllocSizeInBits(ArrayEltTy);
uint64_t ElementSizeBits = DL.getTypeSizeInBits(ArrayEltTy);
uint64_t Shift;
if (DL.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 (DL.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,
SmallVectorImpl<AllocaInst *> &NewElts) {
// Extract each element out of the NewElts according to its structure offset
// and form the result value.
Type *AllocaEltTy = AI->getAllocatedType();
const DataLayout &DL = LI->getModule()->getDataLayout();
uint64_t AllocaSizeBits = DL.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 = nullptr;
uint64_t ArrayEltBitOffset = 0;
if (StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) {
Layout = DL.getStructLayout(EltSTy);
} else {
Type *ArrayEltTy = cast<ArrayType>(AllocaEltTy)->getElementType();
ArrayEltBitOffset = DL.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];
Type *FieldTy =
cast<PointerType>(SrcField->getType())->getElementType();
uint64_t FieldSizeBits = DL.getTypeSizeInBits(FieldTy);
// Ignore zero sized fields like {}, they obviously contain no data.
if (FieldSizeBits == 0) continue;
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 (DL.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 (DL.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(Type *Ty, const DataLayout &DL) {
if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
Ty = ATy->getElementType();
return DL.getTypeSizeInBits(Ty) != DL.getTypeAllocSizeInBits(Ty);
}
// SROA currently handles only Arrays and Structs.
StructType *STy = cast<StructType>(Ty);
const StructLayout *SL = DL.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+DL.getTypeSizeInBits(STy->getElementType(i-1));
if (PrevFieldEnd < FieldBitOffset)
return true;
}
PrevFieldBitOffset = FieldBitOffset;
}
// Check for tail padding.
if (unsigned EltCount = STy->getNumElements()) {
unsigned PrevFieldEnd = PrevFieldBitOffset +
DL.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;
}
const DataLayout &DL = AI->getModule()->getDataLayout();
// 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(), DL))
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 (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;
}
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