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llvm-6502/lib/Transforms/Scalar/ScalarReplAggregates.cpp
Chris Lattner 8976e5950f fix PR5436 by making the 'simple' case of SRoA not promote out of range 
array indexes.  The "complex" case of SRoA still handles them, and correctly.

This fixes a weirdness where we'd correctly avoid transforming A[0][42] if
the 42 was too large, but we'd only do it if it was one gep, not two separate
ones.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90007 91177308-0d34-0410-b5e6-96231b3b80d8
2009-11-27 16:37:41 +00:00

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//===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This transformation implements the well known scalar replacement of
// aggregates transformation. This xform breaks up alloca instructions of
// aggregate type (structure or array) into individual alloca instructions for
// each member (if possible). Then, if possible, it transforms the individual
// alloca instructions into nice clean scalar SSA form.
//
// This combines a simple SRoA algorithm with the Mem2Reg algorithm because
// often interact, especially for C++ programs. As such, iterating between
// SRoA, then Mem2Reg until we run out of things to promote works well.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "scalarrepl"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/LLVMContext.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/IRBuilder.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumReplaced, "Number of allocas broken up");
STATISTIC(NumPromoted, "Number of allocas promoted");
STATISTIC(NumConverted, "Number of aggregates converted to scalar");
STATISTIC(NumGlobals, "Number of allocas copied from constant global");
namespace {
struct SROA : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
explicit SROA(signed T = -1) : FunctionPass(&ID) {
if (T == -1)
SRThreshold = 128;
else
SRThreshold = T;
}
bool runOnFunction(Function &F);
bool performScalarRepl(Function &F);
bool performPromotion(Function &F);
// getAnalysisUsage - This pass does not require any passes, but we know it
// will not alter the CFG, so say so.
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<DominatorTree>();
AU.addRequired<DominanceFrontier>();
AU.setPreservesCFG();
}
private:
TargetData *TD;
/// AllocaInfo - When analyzing uses of an alloca instruction, this captures
/// information about the uses. All these fields are initialized to false
/// and set to true when something is learned.
struct AllocaInfo {
/// isUnsafe - This is set to true if the alloca cannot be SROA'd.
bool isUnsafe : 1;
/// needsCleanup - This is set to true if there is some use of the alloca
/// that requires cleanup.
bool needsCleanup : 1;
/// isMemCpySrc - This is true if this aggregate is memcpy'd from.
bool isMemCpySrc : 1;
/// isMemCpyDst - This is true if this aggregate is memcpy'd into.
bool isMemCpyDst : 1;
AllocaInfo()
: isUnsafe(false), needsCleanup(false),
isMemCpySrc(false), isMemCpyDst(false) {}
};
unsigned SRThreshold;
void MarkUnsafe(AllocaInfo &I) { I.isUnsafe = true; }
int isSafeAllocaToScalarRepl(AllocaInst *AI);
void isSafeUseOfAllocation(Instruction *User, AllocaInst *AI,
AllocaInfo &Info);
void isSafeElementUse(Value *Ptr, bool isFirstElt, AllocaInst *AI,
AllocaInfo &Info);
void isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocaInst *AI,
unsigned OpNo, AllocaInfo &Info);
void isSafeUseOfBitCastedAllocation(BitCastInst *User, AllocaInst *AI,
AllocaInfo &Info);
void DoScalarReplacement(AllocaInst *AI,
std::vector<AllocaInst*> &WorkList);
void CleanupGEP(GetElementPtrInst *GEP);
void CleanupAllocaUsers(AllocaInst *AI);
AllocaInst *AddNewAlloca(Function &F, const Type *Ty, AllocaInst *Base);
void RewriteBitCastUserOfAlloca(Instruction *BCInst, AllocaInst *AI,
SmallVector<AllocaInst*, 32> &NewElts);
void RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *BCInst,
AllocaInst *AI,
SmallVector<AllocaInst*, 32> &NewElts);
void RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI,
SmallVector<AllocaInst*, 32> &NewElts);
void RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI,
SmallVector<AllocaInst*, 32> &NewElts);
bool CanConvertToScalar(Value *V, bool &IsNotTrivial, const Type *&VecTy,
bool &SawVec, uint64_t Offset, unsigned AllocaSize);
void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset);
Value *ConvertScalar_ExtractValue(Value *NV, const Type *ToType,
uint64_t Offset, IRBuilder<> &Builder);
Value *ConvertScalar_InsertValue(Value *StoredVal, Value *ExistingVal,
uint64_t Offset, IRBuilder<> &Builder);
static Instruction *isOnlyCopiedFromConstantGlobal(AllocaInst *AI);
};
}
char SROA::ID = 0;
static RegisterPass<SROA> X("scalarrepl", "Scalar Replacement of Aggregates");
// Public interface to the ScalarReplAggregates pass
FunctionPass *llvm::createScalarReplAggregatesPass(signed int Threshold) {
return new SROA(Threshold);
}
bool SROA::runOnFunction(Function &F) {
TD = getAnalysisIfAvailable<TargetData>();
bool Changed = performPromotion(F);
// FIXME: ScalarRepl currently depends on TargetData more than it
// theoretically needs to. It should be refactored in order to support
// target-independent IR. Until this is done, just skip the actual
// scalar-replacement portion of this pass.
if (!TD) return Changed;
while (1) {
bool LocalChange = performScalarRepl(F);
if (!LocalChange) break; // No need to repromote if no scalarrepl
Changed = true;
LocalChange = performPromotion(F);
if (!LocalChange) break; // No need to re-scalarrepl if no promotion
}
return Changed;
}
bool SROA::performPromotion(Function &F) {
std::vector<AllocaInst*> Allocas;
DominatorTree &DT = getAnalysis<DominatorTree>();
DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function
bool Changed = false;
while (1) {
Allocas.clear();
// Find allocas that are safe to promote, by looking at all instructions in
// the entry node
for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca?
if (isAllocaPromotable(AI))
Allocas.push_back(AI);
if (Allocas.empty()) break;
PromoteMemToReg(Allocas, DT, DF);
NumPromoted += Allocas.size();
Changed = true;
}
return Changed;
}
/// getNumSAElements - Return the number of elements in the specific struct or
/// array.
static uint64_t getNumSAElements(const Type *T) {
if (const StructType *ST = dyn_cast<StructType>(T))
return ST->getNumElements();
return cast<ArrayType>(T)->getNumElements();
}
// performScalarRepl - This algorithm is a simple worklist driven algorithm,
// which runs on all of the malloc/alloca instructions in the function, removing
// them if they are only used by getelementptr instructions.
//
bool SROA::performScalarRepl(Function &F) {
std::vector<AllocaInst*> WorkList;
// Scan the entry basic block, adding any alloca's and mallocs 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();
continue;
}
// If this alloca is impossible for us to promote, reject it early.
if (AI->isArrayAllocation() || !AI->getAllocatedType()->isSized())
continue;
// Check to see if this allocation is only modified by a memcpy/memmove from
// a constant global. If this is the case, we can change all users to use
// the constant global instead. This is commonly produced by the CFE by
// constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A'
// is only subsequently read.
if (Instruction *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) {
DEBUG(errs() << "Found alloca equal to global: " << *AI << '\n');
DEBUG(errs() << " memcpy = " << *TheCopy << '\n');
Constant *TheSrc = cast<Constant>(TheCopy->getOperand(2));
AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType()));
TheCopy->eraseFromParent(); // Don't mutate the global.
AI->eraseFromParent();
++NumGlobals;
Changed = true;
continue;
}
// Check to see if we can perform the core SROA transformation. We cannot
// transform the allocation instruction if it is an array allocation
// (allocations OF arrays are ok though), and an allocation of a scalar
// value cannot be decomposed at all.
uint64_t AllocaSize = TD->getTypeAllocSize(AI->getAllocatedType());
// Do not promote [0 x %struct].
if (AllocaSize == 0) continue;
// Do not promote any struct whose size is too big.
if (AllocaSize > SRThreshold) continue;
if ((isa<StructType>(AI->getAllocatedType()) ||
isa<ArrayType>(AI->getAllocatedType())) &&
// Do not promote any struct into more than "32" separate vars.
getNumSAElements(AI->getAllocatedType()) <= SRThreshold/4) {
// Check that all of the users of the allocation are capable of being
// transformed.
switch (isSafeAllocaToScalarRepl(AI)) {
default: llvm_unreachable("Unexpected value!");
case 0: // Not safe to scalar replace.
break;
case 1: // Safe, but requires cleanup/canonicalizations first
CleanupAllocaUsers(AI);
// FALL THROUGH.
case 3: // Safe to scalar replace.
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.
bool IsNotTrivial = false;
const Type *VectorTy = 0;
bool HadAVector = false;
if (CanConvertToScalar(AI, IsNotTrivial, VectorTy, HadAVector,
0, unsigned(AllocaSize)) && IsNotTrivial) {
AllocaInst *NewAI;
// 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.
if (VectorTy && isa<VectorType>(VectorTy) && HadAVector) {
DEBUG(errs() << "CONVERT TO VECTOR: " << *AI << "\n TYPE = "
<< *VectorTy << '\n');
// Create and insert the vector alloca.
NewAI = new AllocaInst(VectorTy, 0, "", AI->getParent()->begin());
ConvertUsesToScalar(AI, NewAI, 0);
} else {
DEBUG(errs() << "CONVERT TO SCALAR INTEGER: " << *AI << "\n");
// Create and insert the integer alloca.
const Type *NewTy = IntegerType::get(AI->getContext(), AllocaSize*8);
NewAI = new AllocaInst(NewTy, 0, "", AI->getParent()->begin());
ConvertUsesToScalar(AI, NewAI, 0);
}
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(errs() << "Found inst to SROA: " << *AI << '\n');
SmallVector<AllocaInst*, 32> ElementAllocas;
if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) {
ElementAllocas.reserve(ST->getNumContainedTypes());
for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) {
AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0,
AI->getAlignment(),
AI->getName() + "." + Twine(i), AI);
ElementAllocas.push_back(NA);
WorkList.push_back(NA); // Add to worklist for recursive processing
}
} else {
const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType());
ElementAllocas.reserve(AT->getNumElements());
const Type *ElTy = AT->getElementType();
for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(),
AI->getName() + "." + Twine(i), AI);
ElementAllocas.push_back(NA);
WorkList.push_back(NA); // Add to worklist for recursive processing
}
}
// Now that we have created the alloca instructions that we want to use,
// expand the getelementptr instructions to use them.
//
while (!AI->use_empty()) {
Instruction *User = cast<Instruction>(AI->use_back());
if (BitCastInst *BCInst = dyn_cast<BitCastInst>(User)) {
RewriteBitCastUserOfAlloca(BCInst, AI, ElementAllocas);
BCInst->eraseFromParent();
continue;
}
// 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)
if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
Value *Insert = UndefValue::get(LI->getType());
for (unsigned i = 0, e = ElementAllocas.size(); i != e; ++i) {
Value *Load = new LoadInst(ElementAllocas[i], "load", LI);
Insert = InsertValueInst::Create(Insert, Load, i, "insert", LI);
}
LI->replaceAllUsesWith(Insert);
LI->eraseFromParent();
continue;
}
// 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)
if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
Value *Val = SI->getOperand(0);
for (unsigned i = 0, e = ElementAllocas.size(); i != e; ++i) {
Value *Extract = ExtractValueInst::Create(Val, i, Val->getName(), SI);
new StoreInst(Extract, ElementAllocas[i], SI);
}
SI->eraseFromParent();
continue;
}
GetElementPtrInst *GEPI = cast<GetElementPtrInst>(User);
// We now know that the GEP is of the form: GEP <ptr>, 0, <cst>
unsigned Idx =
(unsigned)cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue();
assert(Idx < ElementAllocas.size() && "Index out of range?");
AllocaInst *AllocaToUse = ElementAllocas[Idx];
Value *RepValue;
if (GEPI->getNumOperands() == 3) {
// Do not insert a new getelementptr instruction with zero indices, only
// to have it optimized out later.
RepValue = AllocaToUse;
} else {
// We are indexing deeply into the structure, so we still need a
// getelement ptr instruction to finish the indexing. This may be
// expanded itself once the worklist is rerun.
//
SmallVector<Value*, 8> NewArgs;
NewArgs.push_back(Constant::getNullValue(
Type::getInt32Ty(AI->getContext())));
NewArgs.append(GEPI->op_begin()+3, GEPI->op_end());
RepValue = GetElementPtrInst::Create(AllocaToUse, NewArgs.begin(),
NewArgs.end(), "", GEPI);
RepValue->takeName(GEPI);
}
// If this GEP is to the start of the aggregate, check for memcpys.
if (Idx == 0 && GEPI->hasAllZeroIndices())
RewriteBitCastUserOfAlloca(GEPI, AI, ElementAllocas);
// Move all of the users over to the new GEP.
GEPI->replaceAllUsesWith(RepValue);
// Delete the old GEP
GEPI->eraseFromParent();
}
// Finally, delete the Alloca instruction
AI->eraseFromParent();
NumReplaced++;
}
/// isSafeElementUse - Check to see if this use is an allowed use for a
/// getelementptr instruction of an array aggregate allocation. isFirstElt
/// indicates whether Ptr is known to the start of the aggregate.
///
void SROA::isSafeElementUse(Value *Ptr, bool isFirstElt, AllocaInst *AI,
AllocaInfo &Info) {
for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end();
I != E; ++I) {
Instruction *User = cast<Instruction>(*I);
switch (User->getOpcode()) {
case Instruction::Load: break;
case Instruction::Store:
// Store is ok if storing INTO the pointer, not storing the pointer
if (User->getOperand(0) == Ptr) return MarkUnsafe(Info);
break;
case Instruction::GetElementPtr: {
GetElementPtrInst *GEP = cast<GetElementPtrInst>(User);
bool AreAllZeroIndices = isFirstElt;
if (GEP->getNumOperands() > 1 &&
(!isa<ConstantInt>(GEP->getOperand(1)) ||
!cast<ConstantInt>(GEP->getOperand(1))->isZero()))
// Using pointer arithmetic to navigate the array.
return MarkUnsafe(Info);
// Verify that any array subscripts are in range.
for (gep_type_iterator GEPIt = gep_type_begin(GEP),
E = gep_type_end(GEP); GEPIt != E; ++GEPIt) {
// Ignore struct elements, no extra checking needed for these.
if (isa<StructType>(*GEPIt))
continue;
// This GEP indexes an array. Verify that this is an in-range
// constant integer. Specifically, consider A[0][i]. We cannot know that
// the user isn't doing invalid things like allowing i to index an
// out-of-range subscript that accesses A[1]. Because of this, we have
// to reject SROA of any accesses into structs where any of the
// components are variables.
ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPIt.getOperand());
if (!IdxVal) return MarkUnsafe(Info);
// Are all indices still zero?
AreAllZeroIndices &= IdxVal->isZero();
if (const ArrayType *AT = dyn_cast<ArrayType>(*GEPIt)) {
if (IdxVal->getZExtValue() >= AT->getNumElements())
return MarkUnsafe(Info);
} else if (const VectorType *VT = dyn_cast<VectorType>(*GEPIt)) {
if (IdxVal->getZExtValue() >= VT->getNumElements())
return MarkUnsafe(Info);
}
}
isSafeElementUse(GEP, AreAllZeroIndices, AI, Info);
if (Info.isUnsafe) return;
break;
}
case Instruction::BitCast:
if (isFirstElt) {
isSafeUseOfBitCastedAllocation(cast<BitCastInst>(User), AI, Info);
if (Info.isUnsafe) return;
break;
}
DEBUG(errs() << " Transformation preventing inst: " << *User << '\n');
return MarkUnsafe(Info);
case Instruction::Call:
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
if (isFirstElt) {
isSafeMemIntrinsicOnAllocation(MI, AI, I.getOperandNo(), Info);
if (Info.isUnsafe) return;
break;
}
}
DEBUG(errs() << " Transformation preventing inst: " << *User << '\n');
return MarkUnsafe(Info);
default:
DEBUG(errs() << " Transformation preventing inst: " << *User << '\n');
return MarkUnsafe(Info);
}
}
return; // All users look ok :)
}
/// AllUsersAreLoads - Return true if all users of this value are loads.
static bool AllUsersAreLoads(Value *Ptr) {
for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end();
I != E; ++I)
if (cast<Instruction>(*I)->getOpcode() != Instruction::Load)
return false;
return true;
}
/// isSafeUseOfAllocation - Check to see if this user is an allowed use for an
/// aggregate allocation.
///
void SROA::isSafeUseOfAllocation(Instruction *User, AllocaInst *AI,
AllocaInfo &Info) {
if (BitCastInst *C = dyn_cast<BitCastInst>(User))
return isSafeUseOfBitCastedAllocation(C, AI, Info);
if (LoadInst *LI = dyn_cast<LoadInst>(User))
if (!LI->isVolatile())
return;// Loads (returning a first class aggregrate) are always rewritable
if (StoreInst *SI = dyn_cast<StoreInst>(User))
if (!SI->isVolatile() && SI->getOperand(0) != AI)
return;// Store is ok if storing INTO the pointer, not storing the pointer
GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User);
if (GEPI == 0)
return MarkUnsafe(Info);
gep_type_iterator I = gep_type_begin(GEPI), E = gep_type_end(GEPI);
// The GEP is not safe to transform if not of the form "GEP <ptr>, 0, <cst>".
if (I == E ||
I.getOperand() != Constant::getNullValue(I.getOperand()->getType())) {
return MarkUnsafe(Info);
}
++I;
if (I == E) return MarkUnsafe(Info); // ran out of GEP indices??
bool IsAllZeroIndices = true;
// If the first index is a non-constant index into an array, see if we can
// handle it as a special case.
if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) {
if (!isa<ConstantInt>(I.getOperand())) {
IsAllZeroIndices = 0;
uint64_t NumElements = AT->getNumElements();
// If this is an array index and the index is not constant, we cannot
// promote... that is unless the array has exactly one or two elements in
// it, in which case we CAN promote it, but we have to canonicalize this
// out if this is the only problem.
if ((NumElements == 1 || NumElements == 2) &&
AllUsersAreLoads(GEPI)) {
Info.needsCleanup = true;
return; // Canonicalization required!
}
return MarkUnsafe(Info);
}
}
// Walk through the GEP type indices, checking the types that this indexes
// into.
for (; I != E; ++I) {
// Ignore struct elements, no extra checking needed for these.
if (isa<StructType>(*I))
continue;
ConstantInt *IdxVal = dyn_cast<ConstantInt>(I.getOperand());
if (!IdxVal) return MarkUnsafe(Info);
// Are all indices still zero?
IsAllZeroIndices &= IdxVal->isZero();
if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) {
// This GEP indexes an array. Verify that this is an in-range constant
// integer. Specifically, consider A[0][i]. We cannot know that the user
// isn't doing invalid things like allowing i to index an out-of-range
// subscript that accesses A[1]. Because of this, we have to reject SROA
// of any accesses into structs where any of the components are variables.
if (IdxVal->getZExtValue() >= AT->getNumElements())
return MarkUnsafe(Info);
} else if (const VectorType *VT = dyn_cast<VectorType>(*I)) {
if (IdxVal->getZExtValue() >= VT->getNumElements())
return MarkUnsafe(Info);
}
}
// If there are any non-simple uses of this getelementptr, make sure to reject
// them.
return isSafeElementUse(GEPI, IsAllZeroIndices, AI, Info);
}
/// isSafeMemIntrinsicOnAllocation - Return true if the specified memory
/// intrinsic can be promoted by SROA. At this point, we know that the operand
/// of the memintrinsic is a pointer to the beginning of the allocation.
void SROA::isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocaInst *AI,
unsigned OpNo, AllocaInfo &Info) {
// If not constant length, give up.
ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength());
if (!Length) return MarkUnsafe(Info);
// If not the whole aggregate, give up.
if (Length->getZExtValue() !=
TD->getTypeAllocSize(AI->getType()->getElementType()))
return MarkUnsafe(Info);
// We only know about memcpy/memset/memmove.
if (!isa<MemIntrinsic>(MI))
return MarkUnsafe(Info);
// Otherwise, we can transform it. Determine whether this is a memcpy/set
// into or out of the aggregate.
if (OpNo == 1)
Info.isMemCpyDst = true;
else {
assert(OpNo == 2);
Info.isMemCpySrc = true;
}
}
/// isSafeUseOfBitCastedAllocation - Return true if all users of this bitcast
/// are
void SROA::isSafeUseOfBitCastedAllocation(BitCastInst *BC, AllocaInst *AI,
AllocaInfo &Info) {
for (Value::use_iterator UI = BC->use_begin(), E = BC->use_end();
UI != E; ++UI) {
if (BitCastInst *BCU = dyn_cast<BitCastInst>(UI)) {
isSafeUseOfBitCastedAllocation(BCU, AI, Info);
} else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(UI)) {
isSafeMemIntrinsicOnAllocation(MI, AI, UI.getOperandNo(), Info);
} else if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
if (SI->isVolatile())
return MarkUnsafe(Info);
// If storing the entire alloca in one chunk through a bitcasted pointer
// to integer, we can transform it. This happens (for example) when you
// cast a {i32,i32}* to i64* and store through it. This is similar to the
// memcpy case and occurs in various "byval" cases and emulated memcpys.
if (isa<IntegerType>(SI->getOperand(0)->getType()) &&
TD->getTypeAllocSize(SI->getOperand(0)->getType()) ==
TD->getTypeAllocSize(AI->getType()->getElementType())) {
Info.isMemCpyDst = true;
continue;
}
return MarkUnsafe(Info);
} else if (LoadInst *LI = dyn_cast<LoadInst>(UI)) {
if (LI->isVolatile())
return MarkUnsafe(Info);
// If loading the entire alloca in one chunk through a bitcasted pointer
// to integer, we can transform it. This happens (for example) when you
// cast a {i32,i32}* to i64* and load through it. This is similar to the
// memcpy case and occurs in various "byval" cases and emulated memcpys.
if (isa<IntegerType>(LI->getType()) &&
TD->getTypeAllocSize(LI->getType()) ==
TD->getTypeAllocSize(AI->getType()->getElementType())) {
Info.isMemCpySrc = true;
continue;
}
return MarkUnsafe(Info);
} else if (isa<DbgInfoIntrinsic>(UI)) {
// If one user is DbgInfoIntrinsic then check if all users are
// DbgInfoIntrinsics.
if (OnlyUsedByDbgInfoIntrinsics(BC)) {
Info.needsCleanup = true;
return;
}
else
MarkUnsafe(Info);
}
else {
return MarkUnsafe(Info);
}
if (Info.isUnsafe) return;
}
}
/// RewriteBitCastUserOfAlloca - BCInst (transitively) bitcasts AI, or indexes
/// to its first element. Transform users of the cast to use the new values
/// instead.
void SROA::RewriteBitCastUserOfAlloca(Instruction *BCInst, AllocaInst *AI,
SmallVector<AllocaInst*, 32> &NewElts) {
Value::use_iterator UI = BCInst->use_begin(), UE = BCInst->use_end();
while (UI != UE) {
Instruction *User = cast<Instruction>(*UI++);
if (BitCastInst *BCU = dyn_cast<BitCastInst>(User)) {
RewriteBitCastUserOfAlloca(BCU, AI, NewElts);
if (BCU->use_empty()) BCU->eraseFromParent();
continue;
}
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
// This must be memcpy/memmove/memset of the entire aggregate.
// Split into one per element.
RewriteMemIntrinUserOfAlloca(MI, BCInst, AI, NewElts);
continue;
}
if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
// If this is a store of the entire alloca from an integer, rewrite it.
RewriteStoreUserOfWholeAlloca(SI, AI, NewElts);
continue;
}
if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
// If this is a load of the entire alloca to an integer, rewrite it.
RewriteLoadUserOfWholeAlloca(LI, AI, NewElts);
continue;
}
// Otherwise it must be some other user of a gep of the first pointer. Just
// leave these alone.
continue;
}
}
/// 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 *BCInst,
AllocaInst *AI,
SmallVector<AllocaInst*, 32> &NewElts) {
// If this is a memcpy/memmove, construct the other pointer as the
// appropriate type. The "Other" pointer is the pointer that goes to memory
// that doesn't have anything to do with the alloca that we are promoting. For
// memset, this Value* stays null.
Value *OtherPtr = 0;
LLVMContext &Context = MI->getContext();
unsigned MemAlignment = MI->getAlignment();
if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) { // memmove/memcopy
if (BCInst == MTI->getRawDest())
OtherPtr = MTI->getRawSource();
else {
assert(BCInst == 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) {
// It is likely that OtherPtr is a bitcast, if so, remove it.
if (BitCastInst *BC = dyn_cast<BitCastInst>(OtherPtr))
OtherPtr = BC->getOperand(0);
// All zero GEPs are effectively bitcasts.
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(OtherPtr))
if (GEP->hasAllZeroIndices())
OtherPtr = GEP->getOperand(0);
if (ConstantExpr *BCE = dyn_cast<ConstantExpr>(OtherPtr))
if (BCE->getOpcode() == Instruction::BitCast)
OtherPtr = BCE->getOperand(0);
// If the pointer is not the right type, insert a bitcast to the right
// type.
if (OtherPtr->getType() != AI->getType())
OtherPtr = new BitCastInst(OtherPtr, AI->getType(), OtherPtr->getName(),
MI);
}
// Process each element of the aggregate.
Value *TheFn = MI->getOperand(0);
const Type *BytePtrTy = MI->getRawDest()->getType();
bool SROADest = MI->getRawDest() == BCInst;
Constant *Zero = Constant::getNullValue(Type::getInt32Ty(MI->getContext()));
for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
// If this is a memcpy/memmove, emit a GEP of the other element address.
Value *OtherElt = 0;
unsigned OtherEltAlign = MemAlignment;
if (OtherPtr) {
Value *Idx[2] = { Zero,
ConstantInt::get(Type::getInt32Ty(MI->getContext()), i) };
OtherElt = GetElementPtrInst::Create(OtherPtr, Idx, Idx + 2,
OtherPtr->getNameStr()+"."+Twine(i),
MI);
uint64_t EltOffset;
const PointerType *OtherPtrTy = cast<PointerType>(OtherPtr->getType());
if (const StructType *ST =
dyn_cast<StructType>(OtherPtrTy->getElementType())) {
EltOffset = TD->getStructLayout(ST)->getElementOffset(i);
} else {
const Type *EltTy =
cast<SequentialType>(OtherPtr->getType())->getElementType();
EltOffset = TD->getTypeAllocSize(EltTy)*i;
}
// The alignment of the other pointer is the guaranteed alignment of the
// element, which is affected by both the known alignment of the whole
// mem intrinsic and the alignment of the element. If the alignment of
// the memcpy (f.e.) is 32 but the element is at a 4-byte offset, then the
// known alignment is just 4 bytes.
OtherEltAlign = (unsigned)MinAlign(OtherEltAlign, EltOffset);
}
Value *EltPtr = NewElts[i];
const Type *EltTy = cast<PointerType>(EltPtr->getType())->getElementType();
// If we got down to a scalar, insert a load or store as appropriate.
if (EltTy->isSingleValueType()) {
if (isa<MemTransferInst>(MI)) {
if (SROADest) {
// From Other to Alloca.
Value *Elt = new LoadInst(OtherElt, "tmp", false, OtherEltAlign, MI);
new StoreInst(Elt, EltPtr, MI);
} else {
// From Alloca to Other.
Value *Elt = new LoadInst(EltPtr, "tmp", MI);
new StoreInst(Elt, OtherElt, false, OtherEltAlign, MI);
}
continue;
}
assert(isa<MemSetInst>(MI));
// If the stored element is zero (common case), just store a null
// constant.
Constant *StoreVal;
if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getOperand(2))) {
if (CI->isZero()) {
StoreVal = Constant::getNullValue(EltTy); // 0.0, null, 0, <0,0>
} else {
// If EltTy is a vector type, get the element type.
const Type *ValTy = EltTy->getScalarType();
// Construct an integer with the right value.
unsigned EltSize = TD->getTypeSizeInBits(ValTy);
APInt OneVal(EltSize, CI->getZExtValue());
APInt TotalVal(OneVal);
// Set each byte.
for (unsigned i = 0; 8*i < EltSize; ++i) {
TotalVal = TotalVal.shl(8);
TotalVal |= OneVal;
}
// Convert the integer value to the appropriate type.
StoreVal = ConstantInt::get(Context, TotalVal);
if (isa<PointerType>(ValTy))
StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy);
else if (ValTy->isFloatingPoint())
StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy);
assert(StoreVal->getType() == ValTy && "Type mismatch!");
// If the requested value was a vector constant, create it.
if (EltTy != ValTy) {
unsigned NumElts = cast<VectorType>(ValTy)->getNumElements();
SmallVector<Constant*, 16> Elts(NumElts, StoreVal);
StoreVal = ConstantVector::get(&Elts[0], NumElts);
}
}
new StoreInst(StoreVal, EltPtr, MI);
continue;
}
// Otherwise, if we're storing a byte variable, use a memset call for
// this element.
}
// Cast the element pointer to BytePtrTy.
if (EltPtr->getType() != BytePtrTy)
EltPtr = new BitCastInst(EltPtr, BytePtrTy, EltPtr->getNameStr(), MI);
// Cast the other pointer (if we have one) to BytePtrTy.
if (OtherElt && OtherElt->getType() != BytePtrTy)
OtherElt = new BitCastInst(OtherElt, BytePtrTy,OtherElt->getNameStr(),
MI);
unsigned EltSize = TD->getTypeAllocSize(EltTy);
// Finally, insert the meminst for this element.
if (isa<MemTransferInst>(MI)) {
Value *Ops[] = {
SROADest ? EltPtr : OtherElt, // Dest ptr
SROADest ? OtherElt : EltPtr, // Src ptr
ConstantInt::get(MI->getOperand(3)->getType(), EltSize), // Size
// Align
ConstantInt::get(Type::getInt32Ty(MI->getContext()), OtherEltAlign)
};
CallInst::Create(TheFn, Ops, Ops + 4, "", MI);
} else {
assert(isa<MemSetInst>(MI));
Value *Ops[] = {
EltPtr, MI->getOperand(2), // Dest, Value,
ConstantInt::get(MI->getOperand(3)->getType(), EltSize), // Size
Zero // Align
};
CallInst::Create(TheFn, Ops, Ops + 4, "", MI);
}
}
MI->eraseFromParent();
}
/// RewriteStoreUserOfWholeAlloca - We found an store of an integer that
/// overwrites the entire allocation. Extract out the pieces of the stored
/// integer and store them individually.
void SROA::RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI,
SmallVector<AllocaInst*, 32> &NewElts){
// Extract each element out of the integer according to its structure offset
// and store the element value to the individual alloca.
Value *SrcVal = SI->getOperand(0);
const Type *AllocaEltTy = AI->getType()->getElementType();
uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy);
// If this isn't a store of an integer to the whole alloca, it may be a store
// to the first element. Just ignore the store in this case and normal SROA
// will handle it.
if (!isa<IntegerType>(SrcVal->getType()) ||
TD->getTypeAllocSizeInBits(SrcVal->getType()) != AllocaSizeBits)
return;
// Handle tail padding by extending the operand
if (TD->getTypeSizeInBits(SrcVal->getType()) != AllocaSizeBits)
SrcVal = new ZExtInst(SrcVal,
IntegerType::get(SI->getContext(), AllocaSizeBits),
"", SI);
DEBUG(errs() << "PROMOTING STORE TO WHOLE ALLOCA: " << *AI << '\n' << *SI
<< '\n');
// There are two forms here: AI could be an array or struct. Both cases
// have different ways to compute the element offset.
if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) {
const StructLayout *Layout = TD->getStructLayout(EltSTy);
for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
// Get the number of bits to shift SrcVal to get the value.
const Type *FieldTy = EltSTy->getElementType(i);
uint64_t Shift = Layout->getElementOffsetInBits(i);
if (TD->isBigEndian())
Shift = AllocaSizeBits-Shift-TD->getTypeAllocSizeInBits(FieldTy);
Value *EltVal = SrcVal;
if (Shift) {
Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift);
EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal,
"sroa.store.elt", SI);
}
// Truncate down to an integer of the right size.
uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy);
// Ignore zero sized fields like {}, they obviously contain no data.
if (FieldSizeBits == 0) continue;
if (FieldSizeBits != AllocaSizeBits)
EltVal = new TruncInst(EltVal,
IntegerType::get(SI->getContext(), FieldSizeBits),
"", SI);
Value *DestField = NewElts[i];
if (EltVal->getType() == FieldTy) {
// Storing to an integer field of this size, just do it.
} else if (FieldTy->isFloatingPoint() || isa<VectorType>(FieldTy)) {
// Bitcast to the right element type (for fp/vector values).
EltVal = new BitCastInst(EltVal, FieldTy, "", SI);
} else {
// Otherwise, bitcast the dest pointer (for aggregates).
DestField = new BitCastInst(DestField,
PointerType::getUnqual(EltVal->getType()),
"", SI);
}
new StoreInst(EltVal, DestField, SI);
}
} else {
const ArrayType *ATy = cast<ArrayType>(AllocaEltTy);
const Type *ArrayEltTy = ATy->getElementType();
uint64_t ElementOffset = TD->getTypeAllocSizeInBits(ArrayEltTy);
uint64_t ElementSizeBits = TD->getTypeSizeInBits(ArrayEltTy);
uint64_t Shift;
if (TD->isBigEndian())
Shift = AllocaSizeBits-ElementOffset;
else
Shift = 0;
for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
// Ignore zero sized fields like {}, they obviously contain no data.
if (ElementSizeBits == 0) continue;
Value *EltVal = SrcVal;
if (Shift) {
Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift);
EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal,
"sroa.store.elt", SI);
}
// Truncate down to an integer of the right size.
if (ElementSizeBits != AllocaSizeBits)
EltVal = new TruncInst(EltVal,
IntegerType::get(SI->getContext(),
ElementSizeBits),"",SI);
Value *DestField = NewElts[i];
if (EltVal->getType() == ArrayEltTy) {
// Storing to an integer field of this size, just do it.
} else if (ArrayEltTy->isFloatingPoint() || isa<VectorType>(ArrayEltTy)) {
// Bitcast to the right element type (for fp/vector values).
EltVal = new BitCastInst(EltVal, ArrayEltTy, "", SI);
} else {
// Otherwise, bitcast the dest pointer (for aggregates).
DestField = new BitCastInst(DestField,
PointerType::getUnqual(EltVal->getType()),
"", SI);
}
new StoreInst(EltVal, DestField, SI);
if (TD->isBigEndian())
Shift -= ElementOffset;
else
Shift += ElementOffset;
}
}
SI->eraseFromParent();
}
/// RewriteLoadUserOfWholeAlloca - We found an load of the entire allocation to
/// an integer. Load the individual pieces to form the aggregate value.
void SROA::RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI,
SmallVector<AllocaInst*, 32> &NewElts) {
// Extract each element out of the NewElts according to its structure offset
// and form the result value.
const Type *AllocaEltTy = AI->getType()->getElementType();
uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy);
// If this isn't a load of the whole alloca to an integer, it may be a load
// of the first element. Just ignore the load in this case and normal SROA
// will handle it.
if (!isa<IntegerType>(LI->getType()) ||
TD->getTypeAllocSizeInBits(LI->getType()) != AllocaSizeBits)
return;
DEBUG(errs() << "PROMOTING LOAD OF WHOLE ALLOCA: " << *AI << '\n' << *LI
<< '\n');
// There are two forms here: AI could be an array or struct. Both cases
// have different ways to compute the element offset.
const StructLayout *Layout = 0;
uint64_t ArrayEltBitOffset = 0;
if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) {
Layout = TD->getStructLayout(EltSTy);
} else {
const Type *ArrayEltTy = cast<ArrayType>(AllocaEltTy)->getElementType();
ArrayEltBitOffset = TD->getTypeAllocSizeInBits(ArrayEltTy);
}
Value *ResultVal =
Constant::getNullValue(IntegerType::get(LI->getContext(), AllocaSizeBits));
for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
// Load the value from the alloca. If the NewElt is an aggregate, cast
// the pointer to an integer of the same size before doing the load.
Value *SrcField = NewElts[i];
const Type *FieldTy =
cast<PointerType>(SrcField->getType())->getElementType();
uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy);
// Ignore zero sized fields like {}, they obviously contain no data.
if (FieldSizeBits == 0) continue;
const IntegerType *FieldIntTy = IntegerType::get(LI->getContext(),
FieldSizeBits);
if (!isa<IntegerType>(FieldTy) && !FieldTy->isFloatingPoint() &&
!isa<VectorType>(FieldTy))
SrcField = new BitCastInst(SrcField,
PointerType::getUnqual(FieldIntTy),
"", LI);
SrcField = new LoadInst(SrcField, "sroa.load.elt", LI);
// If SrcField is a fp or vector of the right size but that isn't an
// integer type, bitcast to an integer so we can shift it.
if (SrcField->getType() != FieldIntTy)
SrcField = new BitCastInst(SrcField, FieldIntTy, "", LI);
// Zero extend the field to be the same size as the final alloca so that
// we can shift and insert it.
if (SrcField->getType() != ResultVal->getType())
SrcField = new ZExtInst(SrcField, ResultVal->getType(), "", LI);
// Determine the number of bits to shift SrcField.
uint64_t Shift;
if (Layout) // Struct case.
Shift = Layout->getElementOffsetInBits(i);
else // Array case.
Shift = i*ArrayEltBitOffset;
if (TD->isBigEndian())
Shift = AllocaSizeBits-Shift-FieldIntTy->getBitWidth();
if (Shift) {
Value *ShiftVal = ConstantInt::get(SrcField->getType(), Shift);
SrcField = BinaryOperator::CreateShl(SrcField, ShiftVal, "", LI);
}
ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI);
}
// Handle tail padding by truncating the result
if (TD->getTypeSizeInBits(LI->getType()) != AllocaSizeBits)
ResultVal = new TruncInst(ResultVal, LI->getType(), "", LI);
LI->replaceAllUsesWith(ResultVal);
LI->eraseFromParent();
}
/// HasPadding - Return true if the specified type has any structure or
/// alignment padding, false otherwise.
static bool HasPadding(const Type *Ty, const TargetData &TD) {
if (const StructType *STy = dyn_cast<StructType>(Ty)) {
const StructLayout *SL = TD.getStructLayout(STy);
unsigned PrevFieldBitOffset = 0;
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
unsigned FieldBitOffset = SL->getElementOffsetInBits(i);
// Padding in sub-elements?
if (HasPadding(STy->getElementType(i), TD))
return true;
// Check to see if there is any padding between this element and the
// previous one.
if (i) {
unsigned PrevFieldEnd =
PrevFieldBitOffset+TD.getTypeSizeInBits(STy->getElementType(i-1));
if (PrevFieldEnd < FieldBitOffset)
return true;
}
PrevFieldBitOffset = FieldBitOffset;
}
// Check for tail padding.
if (unsigned EltCount = STy->getNumElements()) {
unsigned PrevFieldEnd = PrevFieldBitOffset +
TD.getTypeSizeInBits(STy->getElementType(EltCount-1));
if (PrevFieldEnd < SL->getSizeInBits())
return true;
}
} else if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
return HasPadding(ATy->getElementType(), TD);
} else if (const VectorType *VTy = dyn_cast<VectorType>(Ty)) {
return HasPadding(VTy->getElementType(), TD);
}
return TD.getTypeSizeInBits(Ty) != TD.getTypeAllocSizeInBits(Ty);
}
/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of
/// an aggregate can be broken down into elements. Return 0 if not, 3 if safe,
/// or 1 if safe after canonicalization has been performed.
///
int 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;
for (Value::use_iterator I = AI->use_begin(), E = AI->use_end();
I != E; ++I) {
isSafeUseOfAllocation(cast<Instruction>(*I), AI, Info);
if (Info.isUnsafe) {
DEBUG(errs() << "Cannot transform: " << *AI << "\n due to user: "
<< **I << '\n');
return 0;
}
}
// 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->getType()->getElementType(), *TD))
return 0;
// If we require cleanup, return 1, otherwise return 3.
return Info.needsCleanup ? 1 : 3;
}
/// CleanupGEP - GEP is used by an Alloca, which can be prompted after the GEP
/// is canonicalized here.
void SROA::CleanupGEP(GetElementPtrInst *GEPI) {
gep_type_iterator I = gep_type_begin(GEPI);
++I;
const ArrayType *AT = dyn_cast<ArrayType>(*I);
if (!AT)
return;
uint64_t NumElements = AT->getNumElements();
if (isa<ConstantInt>(I.getOperand()))
return;
if (NumElements == 1) {
GEPI->setOperand(2,
Constant::getNullValue(Type::getInt32Ty(GEPI->getContext())));
return;
}
assert(NumElements == 2 && "Unhandled case!");
// All users of the GEP must be loads. At each use of the GEP, insert
// two loads of the appropriate indexed GEP and select between them.
Value *IsOne = new ICmpInst(GEPI, ICmpInst::ICMP_NE, I.getOperand(),
Constant::getNullValue(I.getOperand()->getType()),
"isone");
// Insert the new GEP instructions, which are properly indexed.
SmallVector<Value*, 8> Indices(GEPI->op_begin()+1, GEPI->op_end());
Indices[1] = Constant::getNullValue(Type::getInt32Ty(GEPI->getContext()));
Value *ZeroIdx = GetElementPtrInst::Create(GEPI->getOperand(0),
Indices.begin(),
Indices.end(),
GEPI->getName()+".0", GEPI);
Indices[1] = ConstantInt::get(Type::getInt32Ty(GEPI->getContext()), 1);
Value *OneIdx = GetElementPtrInst::Create(GEPI->getOperand(0),
Indices.begin(),
Indices.end(),
GEPI->getName()+".1", GEPI);
// Replace all loads of the variable index GEP with loads from both
// indexes and a select.
while (!GEPI->use_empty()) {
LoadInst *LI = cast<LoadInst>(GEPI->use_back());
Value *Zero = new LoadInst(ZeroIdx, LI->getName()+".0", LI);
Value *One = new LoadInst(OneIdx , LI->getName()+".1", LI);
Value *R = SelectInst::Create(IsOne, One, Zero, LI->getName(), LI);
LI->replaceAllUsesWith(R);
LI->eraseFromParent();
}
GEPI->eraseFromParent();
}
/// CleanupAllocaUsers - If SROA reported that it can promote the specified
/// allocation, but only if cleaned up, perform the cleanups required.
void SROA::CleanupAllocaUsers(AllocaInst *AI) {
// At this point, we know that the end result will be SROA'd and promoted, so
// we can insert ugly code if required so long as sroa+mem2reg will clean it
// up.
for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
UI != E; ) {
User *U = *UI++;
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U))
CleanupGEP(GEPI);
else {
Instruction *I = cast<Instruction>(U);
SmallVector<DbgInfoIntrinsic *, 2> DbgInUses;
if (!isa<StoreInst>(I) && OnlyUsedByDbgInfoIntrinsics(I, &DbgInUses)) {
// Safe to remove debug info uses.
while (!DbgInUses.empty()) {
DbgInfoIntrinsic *DI = DbgInUses.back(); DbgInUses.pop_back();
DI->eraseFromParent();
}
I->eraseFromParent();
}
}
}
}
/// MergeInType - Add the 'In' type to the accumulated type (Accum) 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.
static void MergeInType(const Type *In, uint64_t Offset, const Type *&VecTy,
unsigned AllocaSize, const TargetData &TD,
LLVMContext &Context) {
// If this could be contributing to a vector, analyze it.
if (VecTy != Type::getVoidTy(Context)) { // either null or a vector type.
// If the In type is a vector that is the same size as the alloca, see if it
// matches the existing VecTy.
if (const VectorType *VInTy = dyn_cast<VectorType>(In)) {
if (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 (VecTy == 0)
VecTy = VInTy;
return;
}
} else if (In->isFloatTy() || In->isDoubleTy() ||
(isa<IntegerType>(In) && In->getPrimitiveSizeInBits() >= 8 &&
isPowerOf2_32(In->getPrimitiveSizeInBits()))) {
// If we're accessing something that could be an element of a vector, see
// if the implied vector agrees with what we already have and if Offset is
// compatible with it.
unsigned EltSize = In->getPrimitiveSizeInBits()/8;
if (Offset % EltSize == 0 &&
AllocaSize % EltSize == 0 &&
(VecTy == 0 ||
cast<VectorType>(VecTy)->getElementType()
->getPrimitiveSizeInBits()/8 == EltSize)) {
if (VecTy == 0)
VecTy = 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.
VecTy = Type::getVoidTy(Context);
}
/// CanConvertToScalar - V is a pointer. If we can convert the pointee and all
/// its accesses to use a to 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 SROA::CanConvertToScalar(Value *V, bool &IsNotTrivial, const Type *&VecTy,
bool &SawVec, uint64_t Offset,
unsigned AllocaSize) {
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) {
Instruction *User = cast<Instruction>(*UI);
if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
// Don't break volatile loads.
if (LI->isVolatile())
return false;
MergeInType(LI->getType(), Offset, VecTy,
AllocaSize, *TD, V->getContext());
SawVec |= isa<VectorType>(LI->getType());
continue;
}
if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
// Storing the pointer, not into the value?
if (SI->getOperand(0) == V || SI->isVolatile()) return 0;
MergeInType(SI->getOperand(0)->getType(), Offset,
VecTy, AllocaSize, *TD, V->getContext());
SawVec |= isa<VectorType>(SI->getOperand(0)->getType());
continue;
}
if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
if (!CanConvertToScalar(BCI, IsNotTrivial, VecTy, SawVec, Offset,
AllocaSize))
return false;
IsNotTrivial = true;
continue;
}
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) {
// If this is a GEP with a variable indices, we can't handle it.
if (!GEP->hasAllConstantIndices())
return false;
// Compute the offset that this GEP adds to the pointer.
SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end());
uint64_t GEPOffset = TD->getIndexedOffset(GEP->getOperand(0)->getType(),
&Indices[0], Indices.size());
// See if all uses can be converted.
if (!CanConvertToScalar(GEP, IsNotTrivial, VecTy, SawVec,Offset+GEPOffset,
AllocaSize))
return false;
IsNotTrivial = true;
continue;
}
// If this is a constant sized memset of a constant value (e.g. 0) we can
// handle it.
if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) {
// Store of constant value and constant size.
if (isa<ConstantInt>(MSI->getValue()) &&
isa<ConstantInt>(MSI->getLength())) {
IsNotTrivial = true;
continue;
}
}
// If this is a memcpy or memmove into or out of the whole allocation, we
// can handle it like a load or store of the scalar type.
if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) {
if (ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength()))
if (Len->getZExtValue() == AllocaSize && Offset == 0) {
IsNotTrivial = true;
continue;
}
}
// Ignore dbg intrinsic.
if (isa<DbgInfoIntrinsic>(User))
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 SROA::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset) {
while (!Ptr->use_empty()) {
Instruction *User = cast<Instruction>(Ptr->use_back());
if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) {
ConvertUsesToScalar(CI, NewAI, Offset);
CI->eraseFromParent();
continue;
}
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) {
// Compute the offset that this GEP adds to the pointer.
SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end());
uint64_t GEPOffset = TD->getIndexedOffset(GEP->getOperand(0)->getType(),
&Indices[0], Indices.size());
ConvertUsesToScalar(GEP, NewAI, Offset+GEPOffset*8);
GEP->eraseFromParent();
continue;
}
IRBuilder<> Builder(User->getParent(), User);
if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
// The load is a bit extract from NewAI shifted right by Offset bits.
Value *LoadedVal = Builder.CreateLoad(NewAI, "tmp");
Value *NewLoadVal
= ConvertScalar_ExtractValue(LoadedVal, LI->getType(), Offset, Builder);
LI->replaceAllUsesWith(NewLoadVal);
LI->eraseFromParent();
continue;
}
if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
assert(SI->getOperand(0) != Ptr && "Consistency error!");
// FIXME: Remove once builder has Twine API.
Value *Old = Builder.CreateLoad(NewAI, (NewAI->getName()+".in").str().c_str());
Value *New = ConvertScalar_InsertValue(SI->getOperand(0), Old, Offset,
Builder);
Builder.CreateStore(New, NewAI);
SI->eraseFromParent();
continue;
}
// If this is a constant sized memset of a constant value (e.g. 0) we can
// transform it into a store of the expanded constant value.
if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) {
assert(MSI->getRawDest() == Ptr && "Consistency error!");
unsigned NumBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
if (NumBytes != 0) {
unsigned Val = cast<ConstantInt>(MSI->getValue())->getZExtValue();
// Compute the value replicated the right number of times.
APInt APVal(NumBytes*8, Val);
// Splat the value if non-zero.
if (Val)
for (unsigned i = 1; i != NumBytes; ++i)
APVal |= APVal << 8;
// FIXME: Remove once builder has Twine API.
Value *Old = Builder.CreateLoad(NewAI, (NewAI->getName()+".in").str().c_str());
Value *New = ConvertScalar_InsertValue(
ConstantInt::get(User->getContext(), APVal),
Old, Offset, Builder);
Builder.CreateStore(New, NewAI);
}
MSI->eraseFromParent();
continue;
}
// If this is a memcpy or memmove into or out of the whole allocation, we
// can handle it like a load or store of the scalar type.
if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) {
assert(Offset == 0 && "must be store to start of alloca");
// If the source and destination are both to the same alloca, then this is
// a noop copy-to-self, just delete it. Otherwise, emit a load and store
// as appropriate.
AllocaInst *OrigAI = cast<AllocaInst>(Ptr->getUnderlyingObject());
if (MTI->getSource()->getUnderlyingObject() != 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();
SrcPtr = Builder.CreateBitCast(SrcPtr, NewAI->getType());
LoadInst *SrcVal = Builder.CreateLoad(SrcPtr, "srcval");
SrcVal->setAlignment(MTI->getAlignment());
Builder.CreateStore(SrcVal, NewAI);
} else if (MTI->getDest()->getUnderlyingObject() != 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");
Value *DstPtr = Builder.CreateBitCast(MTI->getDest(), NewAI->getType());
StoreInst *NewStore = Builder.CreateStore(SrcVal, DstPtr);
NewStore->setAlignment(MTI->getAlignment());
} else {
// Noop transfer. Src == Dst
}
MTI->eraseFromParent();
continue;
}
// If user is a dbg info intrinsic then it is safe to remove it.
if (isa<DbgInfoIntrinsic>(User)) {
User->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 *SROA::ConvertScalar_ExtractValue(Value *FromVal, const Type *ToType,
uint64_t Offset, IRBuilder<> &Builder) {
// If the load is of the whole new alloca, no conversion is needed.
if (FromVal->getType() == ToType && Offset == 0)
return FromVal;
// If the result alloca is a vector type, this is either an element
// access or a bitcast to another vector type of the same size.
if (const VectorType *VTy = dyn_cast<VectorType>(FromVal->getType())) {
if (isa<VectorType>(ToType))
return Builder.CreateBitCast(FromVal, ToType, "tmp");
// Otherwise it must be an element access.
unsigned Elt = 0;
if (Offset) {
unsigned EltSize = TD->getTypeAllocSizeInBits(VTy->getElementType());
Elt = Offset/EltSize;
assert(EltSize*Elt == Offset && "Invalid modulus in validity checking");
}
// Return the element extracted out of it.
Value *V = Builder.CreateExtractElement(FromVal, ConstantInt::get(
Type::getInt32Ty(FromVal->getContext()), Elt), "tmp");
if (V->getType() != ToType)
V = Builder.CreateBitCast(V, ToType, "tmp");
return V;
}
// If ToType is a first class aggregate, extract out each of the pieces and
// use insertvalue's to form the FCA.
if (const StructType *ST = dyn_cast<StructType>(ToType)) {
const StructLayout &Layout = *TD->getStructLayout(ST);
Value *Res = UndefValue::get(ST);
for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
Value *Elt = ConvertScalar_ExtractValue(FromVal, ST->getElementType(i),
Offset+Layout.getElementOffsetInBits(i),
Builder);
Res = Builder.CreateInsertValue(Res, Elt, i, "tmp");
}
return Res;
}
if (const ArrayType *AT = dyn_cast<ArrayType>(ToType)) {
uint64_t EltSize = TD->getTypeAllocSizeInBits(AT->getElementType());
Value *Res = UndefValue::get(AT);
for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
Value *Elt = ConvertScalar_ExtractValue(FromVal, AT->getElementType(),
Offset+i*EltSize, Builder);
Res = Builder.CreateInsertValue(Res, Elt, i, "tmp");
}
return Res;
}
// Otherwise, this must be a union that was converted to an integer value.
const IntegerType *NTy = cast<IntegerType>(FromVal->getType());
// If this is a big-endian system and the load is narrower than the
// full alloca type, we need to do a shift to get the right bits.
int ShAmt = 0;
if (TD->isBigEndian()) {
// On big-endian machines, the lowest bit is stored at the bit offset
// from the pointer given by getTypeStoreSizeInBits. This matters for
// integers with a bitwidth that is not a multiple of 8.
ShAmt = TD->getTypeStoreSizeInBits(NTy) -
TD->getTypeStoreSizeInBits(ToType) - Offset;
} else {
ShAmt = Offset;
}
// Note: we support negative bitwidths (with shl) which are not defined.
// We do this to support (f.e.) loads off the end of a structure where
// only some bits are used.
if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth())
FromVal = Builder.CreateLShr(FromVal,
ConstantInt::get(FromVal->getType(),
ShAmt), "tmp");
else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth())
FromVal = Builder.CreateShl(FromVal,
ConstantInt::get(FromVal->getType(),
-ShAmt), "tmp");
// Finally, unconditionally truncate the integer to the right width.
unsigned LIBitWidth = TD->getTypeSizeInBits(ToType);
if (LIBitWidth < NTy->getBitWidth())
FromVal =
Builder.CreateTrunc(FromVal, IntegerType::get(FromVal->getContext(),
LIBitWidth), "tmp");
else if (LIBitWidth > NTy->getBitWidth())
FromVal =
Builder.CreateZExt(FromVal, IntegerType::get(FromVal->getContext(),
LIBitWidth), "tmp");
// If the result is an integer, this is a trunc or bitcast.
if (isa<IntegerType>(ToType)) {
// Should be done.
} else if (ToType->isFloatingPoint() || isa<VectorType>(ToType)) {
// Just do a bitcast, we know the sizes match up.
FromVal = Builder.CreateBitCast(FromVal, ToType, "tmp");
} else {
// Otherwise must be a pointer.
FromVal = Builder.CreateIntToPtr(FromVal, ToType, "tmp");
}
assert(FromVal->getType() == ToType && "Didn't convert right?");
return FromVal;
}
/// ConvertScalar_InsertValue - Insert the value "SV" into the existing integer
/// or vector value "Old" at the offset specified by Offset.
///
/// This happens when we are converting an "integer union" to a
/// single integer scalar, or when we are converting a "vector union" to a
/// vector with insert/extractelement instructions.
///
/// Offset is an offset from the original alloca, in bits that need to be
/// shifted to the right.
Value *SROA::ConvertScalar_InsertValue(Value *SV, Value *Old,
uint64_t Offset, IRBuilder<> &Builder) {
// Convert the stored type to the actual type, shift it left to insert
// then 'or' into place.
const Type *AllocaType = Old->getType();
LLVMContext &Context = Old->getContext();
if (const VectorType *VTy = dyn_cast<VectorType>(AllocaType)) {
uint64_t VecSize = TD->getTypeAllocSizeInBits(VTy);
uint64_t ValSize = TD->getTypeAllocSizeInBits(SV->getType());
// Changing the whole vector with memset or with an access of a different
// vector type?
if (ValSize == VecSize)
return Builder.CreateBitCast(SV, AllocaType, "tmp");
uint64_t EltSize = TD->getTypeAllocSizeInBits(VTy->getElementType());
// Must be an element insertion.
unsigned Elt = Offset/EltSize;
if (SV->getType() != VTy->getElementType())
SV = Builder.CreateBitCast(SV, VTy->getElementType(), "tmp");
SV = Builder.CreateInsertElement(Old, SV,
ConstantInt::get(Type::getInt32Ty(SV->getContext()), Elt),
"tmp");
return SV;
}
// If SV is a first-class aggregate value, insert each value recursively.
if (const StructType *ST = dyn_cast<StructType>(SV->getType())) {
const StructLayout &Layout = *TD->getStructLayout(ST);
for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
Value *Elt = Builder.CreateExtractValue(SV, i, "tmp");
Old = ConvertScalar_InsertValue(Elt, Old,
Offset+Layout.getElementOffsetInBits(i),
Builder);
}
return Old;
}
if (const ArrayType *AT = dyn_cast<ArrayType>(SV->getType())) {
uint64_t EltSize = TD->getTypeAllocSizeInBits(AT->getElementType());
for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
Value *Elt = Builder.CreateExtractValue(SV, i, "tmp");
Old = ConvertScalar_InsertValue(Elt, Old, Offset+i*EltSize, Builder);
}
return Old;
}
// If SV is a float, convert it to the appropriate integer type.
// If it is a pointer, do the same.
unsigned SrcWidth = TD->getTypeSizeInBits(SV->getType());
unsigned DestWidth = TD->getTypeSizeInBits(AllocaType);
unsigned SrcStoreWidth = TD->getTypeStoreSizeInBits(SV->getType());
unsigned DestStoreWidth = TD->getTypeStoreSizeInBits(AllocaType);
if (SV->getType()->isFloatingPoint() || isa<VectorType>(SV->getType()))
SV = Builder.CreateBitCast(SV,
IntegerType::get(SV->getContext(),SrcWidth), "tmp");
else if (isa<PointerType>(SV->getType()))
SV = Builder.CreatePtrToInt(SV, TD->getIntPtrType(SV->getContext()), "tmp");
// Zero extend or truncate the value if needed.
if (SV->getType() != AllocaType) {
if (SV->getType()->getPrimitiveSizeInBits() <
AllocaType->getPrimitiveSizeInBits())
SV = Builder.CreateZExt(SV, AllocaType, "tmp");
else {
// Truncation may be needed if storing more than the alloca can hold
// (undefined behavior).
SV = Builder.CreateTrunc(SV, AllocaType, "tmp");
SrcWidth = DestWidth;
SrcStoreWidth = DestStoreWidth;
}
}
// If this is a big-endian system and the store is narrower than the
// full alloca type, we need to do a shift to get the right bits.
int ShAmt = 0;
if (TD->isBigEndian()) {
// On big-endian machines, the lowest bit is stored at the bit offset
// from the pointer given by getTypeStoreSizeInBits. This matters for
// integers with a bitwidth that is not a multiple of 8.
ShAmt = DestStoreWidth - SrcStoreWidth - Offset;
} else {
ShAmt = Offset;
}
// Note: we support negative bitwidths (with shr) which are not defined.
// We do this to support (f.e.) stores off the end of a structure where
// only some bits in the structure are set.
APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth));
if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) {
SV = Builder.CreateShl(SV, ConstantInt::get(SV->getType(),
ShAmt), "tmp");
Mask <<= ShAmt;
} else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) {
SV = Builder.CreateLShr(SV, ConstantInt::get(SV->getType(),
-ShAmt), "tmp");
Mask = Mask.lshr(-ShAmt);
}
// Mask out the bits we are about to insert from the old value, and or
// in the new bits.
if (SrcWidth != DestWidth) {
assert(DestWidth > SrcWidth);
Old = Builder.CreateAnd(Old, ConstantInt::get(Context, ~Mask), "mask");
SV = Builder.CreateOr(Old, SV, "ins");
}
return SV;
}
/// PointsToConstantGlobal - Return true if V (possibly indirectly) points to
/// some part of a constant global variable. This intentionally only accepts
/// constant expressions because we don't can't rewrite arbitrary instructions.
static bool PointsToConstantGlobal(Value *V) {
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
return GV->isConstant();
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
if (CE->getOpcode() == Instruction::BitCast ||
CE->getOpcode() == Instruction::GetElementPtr)
return PointsToConstantGlobal(CE->getOperand(0));
return false;
}
/// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived)
/// pointer to an alloca. Ignore any reads of the pointer, return false if we
/// see any stores or other unknown uses. If we see pointer arithmetic, keep
/// track of whether it moves the pointer (with isOffset) but otherwise traverse
/// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to
/// the alloca, and if the source pointer is a pointer to a constant global, we
/// can optimize this.
static bool isOnlyCopiedFromConstantGlobal(Value *V, Instruction *&TheCopy,
bool isOffset) {
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) {
if (LoadInst *LI = dyn_cast<LoadInst>(*UI))
// Ignore non-volatile loads, they are always ok.
if (!LI->isVolatile())
continue;
if (BitCastInst *BCI = dyn_cast<BitCastInst>(*UI)) {
// If uses of the bitcast are ok, we are ok.
if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset))
return false;
continue;
}
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) {
// If the GEP has all zero indices, it doesn't offset the pointer. If it
// doesn't, it does.
if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy,
isOffset || !GEP->hasAllZeroIndices()))
return false;
continue;
}
// If this is isn't our memcpy/memmove, reject it as something we can't
// handle.
if (!isa<MemTransferInst>(*UI))
return false;
// If we already have seen a copy, reject the second one.
if (TheCopy) return false;
// If the pointer has been offset from the start of the alloca, we can't
// safely handle this.
if (isOffset) return false;
// If the memintrinsic isn't using the alloca as the dest, reject it.
if (UI.getOperandNo() != 1) return false;
MemIntrinsic *MI = cast<MemIntrinsic>(*UI);
// If the source of the memcpy/move is not a constant global, reject it.
if (!PointsToConstantGlobal(MI->getOperand(2)))
return false;
// Otherwise, the transform is safe. Remember the copy instruction.
TheCopy = MI;
}
return true;
}
/// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only
/// modified by a copy from a constant global. If we can prove this, we can
/// replace any uses of the alloca with uses of the global directly.
Instruction *SROA::isOnlyCopiedFromConstantGlobal(AllocaInst *AI) {
Instruction *TheCopy = 0;
if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false))
return TheCopy;
return 0;
}
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