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llvm-mirror/lib/Transforms/Scalar/ScalarReplAggregates.cpp
Chris Lattner cf6dd53ad8 Fix an accidental commit. 
llvm-svn: 40758
2007-08-02 21:33:36 +00:00

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//===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and 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/Pass.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/Compiler.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.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 VISIBILITY_HIDDEN SROA : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
explicit SROA(signed T = -1) : FunctionPass((intptr_t)&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.addRequired<TargetData>();
AU.setPreservesCFG();
}
private:
/// 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;
/// needsCanon - This is set to true if there is some use of the alloca
/// that requires canonicalization.
bool needsCanon : 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), needsCanon(false),
isMemCpySrc(false), isMemCpyDst(false) {}
};
unsigned SRThreshold;
void MarkUnsafe(AllocaInfo &I) { I.isUnsafe = true; }
int isSafeAllocaToScalarRepl(AllocationInst *AI);
void isSafeUseOfAllocation(Instruction *User, AllocationInst *AI,
AllocaInfo &Info);
void isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI,
AllocaInfo &Info);
void isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI,
unsigned OpNo, AllocaInfo &Info);
void isSafeUseOfBitCastedAllocation(BitCastInst *User, AllocationInst *AI,
AllocaInfo &Info);
void DoScalarReplacement(AllocationInst *AI,
std::vector<AllocationInst*> &WorkList);
void CanonicalizeAllocaUsers(AllocationInst *AI);
AllocaInst *AddNewAlloca(Function &F, const Type *Ty, AllocationInst *Base);
void RewriteBitCastUserOfAlloca(Instruction *BCInst, AllocationInst *AI,
SmallVector<AllocaInst*, 32> &NewElts);
const Type *CanConvertToScalar(Value *V, bool &IsNotTrivial);
void ConvertToScalar(AllocationInst *AI, const Type *Ty);
void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, unsigned Offset);
static Instruction *isOnlyCopiedFromConstantGlobal(AllocationInst *AI);
};
char SROA::ID = 0;
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) {
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;
}
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;
}
// 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<AllocationInst*> 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 (AllocationInst *A = dyn_cast<AllocationInst>(I))
WorkList.push_back(A);
const TargetData &TD = getAnalysis<TargetData>();
// Process the worklist
bool Changed = false;
while (!WorkList.empty()) {
AllocationInst *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 we can turn this aggregate value (potentially with casts) into a
// simple scalar value that can be mem2reg'd into a register value.
bool IsNotTrivial = false;
if (const Type *ActualType = CanConvertToScalar(AI, IsNotTrivial))
if (IsNotTrivial && ActualType != Type::VoidTy) {
ConvertToScalar(AI, ActualType);
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.
if (!AI->isArrayAllocation() &&
(isa<StructType>(AI->getAllocatedType()) ||
isa<ArrayType>(AI->getAllocatedType())) &&
AI->getAllocatedType()->isSized() &&
TD.getTypeSize(AI->getAllocatedType()) < SRThreshold) {
// Check that all of the users of the allocation are capable of being
// transformed.
switch (isSafeAllocaToScalarRepl(AI)) {
default: assert(0 && "Unexpected value!");
case 0: // Not safe to scalar replace.
break;
case 1: // Safe, but requires cleanup/canonicalizations first
CanonicalizeAllocaUsers(AI);
// FALL THROUGH.
case 3: // Safe to scalar replace.
DoScalarReplacement(AI, WorkList);
Changed = true;
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)) {
DOUT << "Found alloca equal to global: " << *AI;
DOUT << " memcpy = " << *TheCopy;
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;
}
// Otherwise, couldn't process this.
}
return Changed;
}
/// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl
/// predicate, do SROA now.
void SROA::DoScalarReplacement(AllocationInst *AI,
std::vector<AllocationInst*> &WorkList) {
DOUT << "Found inst to SROA: " << *AI;
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() + "." + utostr(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() + "." + utostr(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;
}
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::Int32Ty));
NewArgs.append(GEPI->op_begin()+3, GEPI->op_end());
RepValue = new GetElementPtrInst(AllocaToUse, &NewArgs[0],
NewArgs.size(), "", GEPI);
RepValue->takeName(GEPI);
}
// If this GEP is to the start of the aggregate, check for memcpys.
if (Idx == 0) {
bool IsStartOfAggregateGEP = true;
for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i) {
if (!isa<ConstantInt>(GEPI->getOperand(i))) {
IsStartOfAggregateGEP = false;
break;
}
if (!cast<ConstantInt>(GEPI->getOperand(i))->isZero()) {
IsStartOfAggregateGEP = false;
break;
}
}
if (IsStartOfAggregateGEP)
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, AllocationInst *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) {
if (!isa<ConstantInt>(GEP->getOperand(1)) ||
!cast<ConstantInt>(GEP->getOperand(1))->isZero())
// Using pointer arithmetic to navigate the array.
return MarkUnsafe(Info);
if (AreAllZeroIndices) {
for (unsigned i = 2, e = GEP->getNumOperands(); i != e; ++i) {
if (!isa<ConstantInt>(GEP->getOperand(i)) ||
!cast<ConstantInt>(GEP->getOperand(i))->isZero()) {
AreAllZeroIndices = false;
break;
}
}
}
}
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;
}
DOUT << " Transformation preventing inst: " << *User;
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;
}
}
DOUT << " Transformation preventing inst: " << *User;
return MarkUnsafe(Info);
default:
DOUT << " Transformation preventing inst: " << *User;
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, AllocationInst *AI,
AllocaInfo &Info) {
if (BitCastInst *C = dyn_cast<BitCastInst>(User))
return isSafeUseOfBitCastedAllocation(C, AI, Info);
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 this is a use of an array allocation, do a bit more checking for sanity.
if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) {
uint64_t NumElements = AT->getNumElements();
if (ConstantInt *Idx = dyn_cast<ConstantInt>(I.getOperand())) {
IsAllZeroIndices &= Idx->isZero();
// Check to make sure that index falls within the array. If not,
// something funny is going on, so we won't do the optimization.
//
if (Idx->getZExtValue() >= NumElements)
return MarkUnsafe(Info);
// We cannot scalar repl this level of the array unless any array
// sub-indices are in-range constants. In particular, 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].
//
// Scalar replacing *just* the outer index of the array is probably not
// going to be a win anyway, so just give up.
for (++I; I != E && (isa<ArrayType>(*I) || isa<VectorType>(*I)); ++I) {
uint64_t NumElements;
if (const ArrayType *SubArrayTy = dyn_cast<ArrayType>(*I))
NumElements = SubArrayTy->getNumElements();
else
NumElements = cast<VectorType>(*I)->getNumElements();
ConstantInt *IdxVal = dyn_cast<ConstantInt>(I.getOperand());
if (!IdxVal) return MarkUnsafe(Info);
if (IdxVal->getZExtValue() >= NumElements)
return MarkUnsafe(Info);
IsAllZeroIndices &= IdxVal->isZero();
}
} else {
IsAllZeroIndices = 0;
// 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.needsCanon = true;
return; // Canonicalization required!
}
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, AllocationInst *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.
const TargetData &TD = getAnalysis<TargetData>();
if (Length->getZExtValue() != TD.getTypeSize(AI->getType()->getElementType()))
return MarkUnsafe(Info);
// We only know about memcpy/memset/memmove.
if (!isa<MemCpyInst>(MI) && !isa<MemSetInst>(MI) && !isa<MemMoveInst>(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, AllocationInst *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 {
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, AllocationInst *AI,
SmallVector<AllocaInst*, 32> &NewElts) {
Constant *Zero = Constant::getNullValue(Type::Int32Ty);
const TargetData &TD = getAnalysis<TargetData>();
Value::use_iterator UI = BCInst->use_begin(), UE = BCInst->use_end();
while (UI != UE) {
if (BitCastInst *BCU = dyn_cast<BitCastInst>(*UI)) {
RewriteBitCastUserOfAlloca(BCU, AI, NewElts);
++UI;
BCU->eraseFromParent();
continue;
}
// Otherwise, must be memcpy/memmove/memset of the entire aggregate. Split
// into one per element.
MemIntrinsic *MI = dyn_cast<MemIntrinsic>(*UI);
// If it's not a mem intrinsic, it must be some other user of a gep of the
// first pointer. Just leave these alone.
if (!MI) {
++UI;
continue;
}
// If this is a memcpy/memmove, construct the other pointer as the
// appropriate type.
Value *OtherPtr = 0;
if (MemCpyInst *MCI = dyn_cast<MemCpyInst>(MI)) {
if (BCInst == MCI->getRawDest())
OtherPtr = MCI->getRawSource();
else {
assert(BCInst == MCI->getRawSource());
OtherPtr = MCI->getRawDest();
}
} else if (MemMoveInst *MMI = dyn_cast<MemMoveInst>(MI)) {
if (BCInst == MMI->getRawDest())
OtherPtr = MMI->getRawSource();
else {
assert(BCInst == MMI->getRawSource());
OtherPtr = MMI->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.
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);
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;
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;
if (OtherPtr) {
OtherElt = new GetElementPtrInst(OtherPtr, Zero,
ConstantInt::get(Type::Int32Ty, i),
OtherPtr->getNameStr()+"."+utostr(i),
MI);
}
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->isFirstClassType()) {
if (isa<MemCpyInst>(MI) || isa<MemMoveInst>(MI)) {
Value *Elt = new LoadInst(SROADest ? OtherElt : EltPtr, "tmp",
MI);
new StoreInst(Elt, SROADest ? EltPtr : OtherElt, MI);
continue;
} else {
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;
if (const VectorType *VTy = dyn_cast<VectorType>(ValTy))
ValTy = VTy->getElementType();
// Construct an integer with the right value.
unsigned EltSize = TD.getTypeSize(ValTy);
APInt OneVal(EltSize*8, CI->getZExtValue());
APInt TotalVal(OneVal);
// Set each byte.
for (unsigned i = 0; i != EltSize-1; ++i) {
TotalVal = TotalVal.shl(8);
TotalVal |= OneVal;
}
// Convert the integer value to the appropriate type.
StoreVal = ConstantInt::get(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.getTypeSize(EltTy);
// Finally, insert the meminst for this element.
if (isa<MemCpyInst>(MI) || isa<MemMoveInst>(MI)) {
Value *Ops[] = {
SROADest ? EltPtr : OtherElt, // Dest ptr
SROADest ? OtherElt : EltPtr, // Src ptr
ConstantInt::get(MI->getOperand(3)->getType(), EltSize), // Size
Zero // Align
};
new CallInst(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
};
new CallInst(TheFn, Ops, Ops + 4, "", MI);
}
}
// Finally, MI is now dead, as we've modified its actions to occur on all of
// the elements of the aggregate.
++UI;
MI->eraseFromParent();
}
}
/// HasStructPadding - Return true if the specified type has any structure
/// padding, false otherwise.
static bool HasStructPadding(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->getElementOffset(i)*8;
// Padding in sub-elements?
if (HasStructPadding(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->getSizeInBytes()*8)
return true;
}
} else if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
return HasStructPadding(ATy->getElementType(), TD);
}
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.
///
int SROA::isSafeAllocaToScalarRepl(AllocationInst *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) {
DOUT << "Cannot transform: " << *AI << " due to user: " << **I;
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 &&
HasStructPadding(AI->getType()->getElementType(),
getAnalysis<TargetData>()))
return 0;
// If we require cleanup, return 1, otherwise return 3.
return Info.needsCanon ? 1 : 3;
}
/// CanonicalizeAllocaUsers - If SROA reported that it can promote the specified
/// allocation, but only if cleaned up, perform the cleanups required.
void SROA::CanonicalizeAllocaUsers(AllocationInst *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; ) {
GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI++);
if (!GEPI) continue;
gep_type_iterator I = gep_type_begin(GEPI);
++I;
if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) {
uint64_t NumElements = AT->getNumElements();
if (!isa<ConstantInt>(I.getOperand())) {
if (NumElements == 1) {
GEPI->setOperand(2, Constant::getNullValue(Type::Int32Ty));
} else {
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(ICmpInst::ICMP_NE, I.getOperand(),
Constant::getNullValue(I.getOperand()->getType()),
"isone", GEPI);
// 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::Int32Ty);
Value *ZeroIdx = new GetElementPtrInst(GEPI->getOperand(0),
&Indices[0], Indices.size(),
GEPI->getName()+".0", GEPI);
Indices[1] = ConstantInt::get(Type::Int32Ty, 1);
Value *OneIdx = new GetElementPtrInst(GEPI->getOperand(0),
&Indices[0], Indices.size(),
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 = new SelectInst(IsOne, One, Zero, LI->getName(), LI);
LI->replaceAllUsesWith(R);
LI->eraseFromParent();
}
GEPI->eraseFromParent();
}
}
}
}
}
/// MergeInType - Add the 'In' type to the accumulated type so far. If the
/// types are incompatible, return true, otherwise update Accum and return
/// false.
///
/// There are three cases we handle here:
/// 1) An effectively-integer union, where the pieces are stored into as
/// smaller integers (common with byte swap and other idioms).
/// 2) A union of vector types of the same size and potentially its elements.
/// Here we turn element accesses into insert/extract element operations.
/// 3) A union of scalar types, such as int/float or int/pointer. Here we
/// merge together into integers, allowing the xform to work with #1 as
/// well.
static bool MergeInType(const Type *In, const Type *&Accum,
const TargetData &TD) {
// If this is our first type, just use it.
const VectorType *PTy;
if (Accum == Type::VoidTy || In == Accum) {
Accum = In;
} else if (In == Type::VoidTy) {
// Noop.
} else if (In->isInteger() && Accum->isInteger()) { // integer union.
// Otherwise pick whichever type is larger.
if (cast<IntegerType>(In)->getBitWidth() >
cast<IntegerType>(Accum)->getBitWidth())
Accum = In;
} else if (isa<PointerType>(In) && isa<PointerType>(Accum)) {
// Pointer unions just stay as one of the pointers.
} else if (isa<VectorType>(In) || isa<VectorType>(Accum)) {
if ((PTy = dyn_cast<VectorType>(Accum)) &&
PTy->getElementType() == In) {
// Accum is a vector, and we are accessing an element: ok.
} else if ((PTy = dyn_cast<VectorType>(In)) &&
PTy->getElementType() == Accum) {
// In is a vector, and accum is an element: ok, remember In.
Accum = In;
} else if ((PTy = dyn_cast<VectorType>(In)) && isa<VectorType>(Accum) &&
PTy->getBitWidth() == cast<VectorType>(Accum)->getBitWidth()) {
// Two vectors of the same size: keep Accum.
} else {
// Cannot insert an short into a <4 x int> or handle
// <2 x int> -> <4 x int>
return true;
}
} else {
// Pointer/FP/Integer unions merge together as integers.
switch (Accum->getTypeID()) {
case Type::PointerTyID: Accum = TD.getIntPtrType(); break;
case Type::FloatTyID: Accum = Type::Int32Ty; break;
case Type::DoubleTyID: Accum = Type::Int64Ty; break;
default:
assert(Accum->isInteger() && "Unknown FP type!");
break;
}
switch (In->getTypeID()) {
case Type::PointerTyID: In = TD.getIntPtrType(); break;
case Type::FloatTyID: In = Type::Int32Ty; break;
case Type::DoubleTyID: In = Type::Int64Ty; break;
default:
assert(In->isInteger() && "Unknown FP type!");
break;
}
return MergeInType(In, Accum, TD);
}
return false;
}
/// getUIntAtLeastAsBitAs - Return an unsigned integer type that is at least
/// as big as the specified type. If there is no suitable type, this returns
/// null.
const Type *getUIntAtLeastAsBitAs(unsigned NumBits) {
if (NumBits > 64) return 0;
if (NumBits > 32) return Type::Int64Ty;
if (NumBits > 16) return Type::Int32Ty;
if (NumBits > 8) return Type::Int16Ty;
return Type::Int8Ty;
}
/// CanConvertToScalar - V is a pointer. If we can convert the pointee to a
/// single scalar integer type, return that type. Further, if the use is not
/// a completely trivial use that mem2reg could promote, set IsNotTrivial. If
/// there are no uses of this pointer, return Type::VoidTy to differentiate from
/// failure.
///
const Type *SROA::CanConvertToScalar(Value *V, bool &IsNotTrivial) {
const Type *UsedType = Type::VoidTy; // No uses, no forced type.
const TargetData &TD = getAnalysis<TargetData>();
const PointerType *PTy = cast<PointerType>(V->getType());
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)) {
if (MergeInType(LI->getType(), UsedType, TD))
return 0;
} else if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
// Storing the pointer, not into the value?
if (SI->getOperand(0) == V) return 0;
// NOTE: We could handle storing of FP imms into integers here!
if (MergeInType(SI->getOperand(0)->getType(), UsedType, TD))
return 0;
} else if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) {
IsNotTrivial = true;
const Type *SubTy = CanConvertToScalar(CI, IsNotTrivial);
if (!SubTy || MergeInType(SubTy, UsedType, TD)) return 0;
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) {
// Check to see if this is stepping over an element: GEP Ptr, int C
if (GEP->getNumOperands() == 2 && isa<ConstantInt>(GEP->getOperand(1))) {
unsigned Idx = cast<ConstantInt>(GEP->getOperand(1))->getZExtValue();
unsigned ElSize = TD.getTypeSize(PTy->getElementType());
unsigned BitOffset = Idx*ElSize*8;
if (BitOffset > 64 || !isPowerOf2_32(ElSize)) return 0;
IsNotTrivial = true;
const Type *SubElt = CanConvertToScalar(GEP, IsNotTrivial);
if (SubElt == 0) return 0;
if (SubElt != Type::VoidTy && SubElt->isInteger()) {
const Type *NewTy =
getUIntAtLeastAsBitAs(TD.getTypeSize(SubElt)*8+BitOffset);
if (NewTy == 0 || MergeInType(NewTy, UsedType, TD)) return 0;
continue;
}
} else if (GEP->getNumOperands() == 3 &&
isa<ConstantInt>(GEP->getOperand(1)) &&
isa<ConstantInt>(GEP->getOperand(2)) &&
cast<ConstantInt>(GEP->getOperand(1))->isZero()) {
// We are stepping into an element, e.g. a structure or an array:
// GEP Ptr, int 0, uint C
const Type *AggTy = PTy->getElementType();
unsigned Idx = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue();
if (const ArrayType *ATy = dyn_cast<ArrayType>(AggTy)) {
if (Idx >= ATy->getNumElements()) return 0; // Out of range.
} else if (const VectorType *VectorTy = dyn_cast<VectorType>(AggTy)) {
// Getting an element of the vector.
if (Idx >= VectorTy->getNumElements()) return 0; // Out of range.
// Merge in the vector type.
if (MergeInType(VectorTy, UsedType, TD)) return 0;
const Type *SubTy = CanConvertToScalar(GEP, IsNotTrivial);
if (SubTy == 0) return 0;
if (SubTy != Type::VoidTy && MergeInType(SubTy, UsedType, TD))
return 0;
// We'll need to change this to an insert/extract element operation.
IsNotTrivial = true;
continue; // Everything looks ok
} else if (isa<StructType>(AggTy)) {
// Structs are always ok.
} else {
return 0;
}
const Type *NTy = getUIntAtLeastAsBitAs(TD.getTypeSize(AggTy)*8);
if (NTy == 0 || MergeInType(NTy, UsedType, TD)) return 0;
const Type *SubTy = CanConvertToScalar(GEP, IsNotTrivial);
if (SubTy == 0) return 0;
if (SubTy != Type::VoidTy && MergeInType(SubTy, UsedType, TD))
return 0;
continue; // Everything looks ok
}
return 0;
} else {
// Cannot handle this!
return 0;
}
}
return UsedType;
}
/// ConvertToScalar - The specified alloca passes the CanConvertToScalar
/// predicate and is non-trivial. Convert it to something that can be trivially
/// promoted into a register by mem2reg.
void SROA::ConvertToScalar(AllocationInst *AI, const Type *ActualTy) {
DOUT << "CONVERT TO SCALAR: " << *AI << " TYPE = "
<< *ActualTy << "\n";
++NumConverted;
BasicBlock *EntryBlock = AI->getParent();
assert(EntryBlock == &EntryBlock->getParent()->getEntryBlock() &&
"Not in the entry block!");
EntryBlock->getInstList().remove(AI); // Take the alloca out of the program.
// Create and insert the alloca.
AllocaInst *NewAI = new AllocaInst(ActualTy, 0, AI->getName(),
EntryBlock->begin());
ConvertUsesToScalar(AI, NewAI, 0);
delete AI;
}
/// 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, unsigned Offset) {
const TargetData &TD = getAnalysis<TargetData>();
while (!Ptr->use_empty()) {
Instruction *User = cast<Instruction>(Ptr->use_back());
if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
// The load is a bit extract from NewAI shifted right by Offset bits.
Value *NV = new LoadInst(NewAI, LI->getName(), LI);
if (NV->getType() == LI->getType()) {
// We win, no conversion needed.
} else if (const VectorType *PTy = dyn_cast<VectorType>(NV->getType())) {
// If the result alloca is a vector type, this is either an element
// access or a bitcast to another vector type.
if (isa<VectorType>(LI->getType())) {
NV = new BitCastInst(NV, LI->getType(), LI->getName(), LI);
} else {
// Must be an element access.
unsigned Elt = Offset/(TD.getTypeSize(PTy->getElementType())*8);
NV = new ExtractElementInst(
NV, ConstantInt::get(Type::Int32Ty, Elt), "tmp", LI);
}
} else if (isa<PointerType>(NV->getType())) {
assert(isa<PointerType>(LI->getType()));
// Must be ptr->ptr cast. Anything else would result in NV being
// an integer.
NV = new BitCastInst(NV, LI->getType(), LI->getName(), LI);
} else {
const IntegerType *NTy = cast<IntegerType>(NV->getType());
unsigned LIBitWidth = TD.getTypeSizeInBits(LI->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()) {
ShAmt = NTy->getBitWidth()-LIBitWidth-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())
NV = BinaryOperator::createLShr(NV,
ConstantInt::get(NV->getType(),ShAmt),
LI->getName(), LI);
else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth())
NV = BinaryOperator::createShl(NV,
ConstantInt::get(NV->getType(),-ShAmt),
LI->getName(), LI);
// Finally, unconditionally truncate the integer to the right width.
if (LIBitWidth < NTy->getBitWidth())
NV = new TruncInst(NV, IntegerType::get(LIBitWidth),
LI->getName(), LI);
// If the result is an integer, this is a trunc or bitcast.
if (isa<IntegerType>(LI->getType())) {
assert(NV->getType() == LI->getType() && "Truncate wasn't enough?");
} else if (LI->getType()->isFloatingPoint()) {
// Just do a bitcast, we know the sizes match up.
NV = new BitCastInst(NV, LI->getType(), LI->getName(), LI);
} else {
// Otherwise must be a pointer.
NV = new IntToPtrInst(NV, LI->getType(), LI->getName(), LI);
}
}
LI->replaceAllUsesWith(NV);
LI->eraseFromParent();
} else if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
assert(SI->getOperand(0) != Ptr && "Consistency error!");
// Convert the stored type to the actual type, shift it left to insert
// then 'or' into place.
Value *SV = SI->getOperand(0);
const Type *AllocaType = NewAI->getType()->getElementType();
if (SV->getType() == AllocaType) {
// All is well.
} else if (const VectorType *PTy = dyn_cast<VectorType>(AllocaType)) {
Value *Old = new LoadInst(NewAI, NewAI->getName()+".in", SI);
// If the result alloca is a vector type, this is either an element
// access or a bitcast to another vector type.
if (isa<VectorType>(SV->getType())) {
SV = new BitCastInst(SV, AllocaType, SV->getName(), SI);
} else {
// Must be an element insertion.
unsigned Elt = Offset/(TD.getTypeSize(PTy->getElementType())*8);
SV = new InsertElementInst(Old, SV,
ConstantInt::get(Type::Int32Ty, Elt),
"tmp", SI);
}
} else if (isa<PointerType>(AllocaType)) {
// If the alloca type is a pointer, then all the elements must be
// pointers.
if (SV->getType() != AllocaType)
SV = new BitCastInst(SV, AllocaType, SV->getName(), SI);
} else {
Value *Old = new LoadInst(NewAI, NewAI->getName()+".in", SI);
// If SV is a float, convert it to the appropriate integer type.
// If it is a pointer, do the same, and also handle ptr->ptr casts
// here.
unsigned SrcWidth = TD.getTypeSizeInBits(SV->getType());
unsigned DestWidth = AllocaType->getPrimitiveSizeInBits();
if (SV->getType()->isFloatingPoint())
SV = new BitCastInst(SV, IntegerType::get(SrcWidth),
SV->getName(), SI);
else if (isa<PointerType>(SV->getType()))
SV = new PtrToIntInst(SV, TD.getIntPtrType(), SV->getName(), SI);
// Always zero extend the value if needed.
if (SV->getType() != AllocaType)
SV = new ZExtInst(SV, AllocaType, SV->getName(), SI);
// 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()) {
ShAmt = DestWidth-SrcWidth-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 = BinaryOperator::createShl(SV,
ConstantInt::get(SV->getType(), ShAmt),
SV->getName(), SI);
Mask <<= ShAmt;
} else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) {
SV = BinaryOperator::createLShr(SV,
ConstantInt::get(SV->getType(),-ShAmt),
SV->getName(), SI);
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 = BinaryOperator::createAnd(Old, ConstantInt::get(~Mask),
Old->getName()+".mask", SI);
SV = BinaryOperator::createOr(Old, SV, SV->getName()+".ins", SI);
}
}
new StoreInst(SV, NewAI, SI);
SI->eraseFromParent();
} else if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) {
ConvertUsesToScalar(CI, NewAI, Offset);
CI->eraseFromParent();
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) {
const PointerType *AggPtrTy =
cast<PointerType>(GEP->getOperand(0)->getType());
const TargetData &TD = getAnalysis<TargetData>();
unsigned AggSizeInBits = TD.getTypeSize(AggPtrTy->getElementType())*8;
// Check to see if this is stepping over an element: GEP Ptr, int C
unsigned NewOffset = Offset;
if (GEP->getNumOperands() == 2) {
unsigned Idx = cast<ConstantInt>(GEP->getOperand(1))->getZExtValue();
unsigned BitOffset = Idx*AggSizeInBits;
NewOffset += BitOffset;
} else if (GEP->getNumOperands() == 3) {
// We know that operand #2 is zero.
unsigned Idx = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue();
const Type *AggTy = AggPtrTy->getElementType();
if (const SequentialType *SeqTy = dyn_cast<SequentialType>(AggTy)) {
unsigned ElSizeBits = TD.getTypeSize(SeqTy->getElementType())*8;
NewOffset += ElSizeBits*Idx;
} else if (const StructType *STy = dyn_cast<StructType>(AggTy)) {
unsigned EltBitOffset =
TD.getStructLayout(STy)->getElementOffset(Idx)*8;
NewOffset += EltBitOffset;
} else {
assert(0 && "Unsupported operation!");
abort();
}
} else {
assert(0 && "Unsupported operation!");
abort();
}
ConvertUsesToScalar(GEP, NewAI, NewOffset);
GEP->eraseFromParent();
} else {
assert(0 && "Unsupported operation!");
abort();
}
}
}
/// 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 (isa<LoadInst>(*UI)) {
// Ignore loads, they are always ok.
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<MemCpyInst>(*UI) && !isa<MemMoveInst>(*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(AllocationInst *AI) {
Instruction *TheCopy = 0;
if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false))
return TheCopy;
return 0;
}
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