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79b3bd395d
llvm-6502/lib/Transforms/Scalar/ScalarReplAggregates.cpp
Chris Lattner 79b3bd395d If an alloca only has two types of uses: 1) reads 2) a memcpy/memmove that 
copies from a constant global, then we can change the reads to read from the
global instead of from the alloca.  This eliminates the alloca and the memcpy,
and promotes secondary optimizations (because the loads are now loads from
a constant global).

This is important for a common C idiom:

void foo() {
   int A[] = {1,2,3,4,5,6,7,8,9...};
   ... only reads of A ...
}

For some reason, people forget to mark the array static or const.

This triggers on these multisource benchmarks:
JM/ldecode: block_pos, [3 x [4 x [4 x i32]]]
FreeBench/mason: m, [18 x i32], inlined 4 times
MiBench/office-stringsearch: search_strings, [1332 x i8*]
MiBench/office-stringsearch: find_strings, [1333 x i8*]
Prolangs-C++/city: dirs, [9 x i8*], inlined 4 places

and these spec benchmarks:
177.mesa: message, [8 x [32 x i8]]
186.crafty: bias_rl45, [64 x i32]
186.crafty: diag_sq, [64 x i32]
186.crafty: empty, [9 x i8]
186.crafty: xlate, [15 x i8]
186.crafty: status, [13 x i8]
186.crafty: bdinfo, [25 x i8]
445.gobmk: routines, [16 x i8*]
458.sjeng: piece_rep, [14 x i8*]
458.sjeng: t, [13 x i32], inlined 4 places.
464.h264ref: block8x8_idx, [3 x [4 x [4 x i32]]]
464.h264ref: block_pos, [3 x [4 x [4 x i32]]]
464.h264ref: j_off_tab, [12 x i32]

This implements Transforms/ScalarRepl/memcpy-from-global.ll


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36429 91177308-0d34-0410-b5e6-96231b3b80d8
2007-04-25 06:40:51 +00:00

1220 lines
49 KiB
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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 {
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<ETForest>();
AU.addRequired<DominanceFrontier>();
AU.addRequired<TargetData>();
AU.setPreservesCFG();
}
private:
int isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI);
int isSafeUseOfAllocation(Instruction *User, AllocationInst *AI);
bool isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI);
bool isSafeUseOfBitCastedAllocation(BitCastInst *User, AllocationInst *AI);
int isSafeAllocaToScalarRepl(AllocationInst *AI);
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);
};
RegisterPass<SROA> X("scalarrepl", "Scalar Replacement of Aggregates");
}
// Public interface to the ScalarReplAggregates pass
FunctionPass *llvm::createScalarReplAggregatesPass() { return new SROA(); }
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;
const TargetData &TD = getAnalysis<TargetData>();
ETForest &ET = getAnalysis<ETForest>();
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, TD))
Allocas.push_back(AI);
if (Allocas.empty()) break;
PromoteMemToReg(Allocas, ET, DF, TD);
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);
// 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()))) {
// 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.
///
int SROA::isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI) {
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 0;
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())
return 0; // Using pointer arithmetic to navigate the array.
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;
}
}
}
}
if (!isSafeElementUse(GEP, AreAllZeroIndices, AI)) return 0;
break;
}
case Instruction::BitCast:
if (isFirstElt &&
isSafeUseOfBitCastedAllocation(cast<BitCastInst>(User), AI))
break;
DOUT << " Transformation preventing inst: " << *User;
return 0;
case Instruction::Call:
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
if (isFirstElt && isSafeMemIntrinsicOnAllocation(MI, AI))
break;
}
DOUT << " Transformation preventing inst: " << *User;
return 0;
default:
DOUT << " Transformation preventing inst: " << *User;
return 0;
}
}
return 3; // 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.
///
int SROA::isSafeUseOfAllocation(Instruction *User, AllocationInst *AI) {
if (BitCastInst *C = dyn_cast<BitCastInst>(User))
return isSafeUseOfBitCastedAllocation(C, AI) ? 3 : 0;
if (!isa<GetElementPtrInst>(User)) return 0;
GetElementPtrInst *GEPI = cast<GetElementPtrInst>(User);
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 0;
++I;
if (I == E) return 0; // 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 0;
// 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 0;
if (IdxVal->getZExtValue() >= NumElements)
return 0;
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))
return 1; // Canonicalization required!
return 0;
}
}
// If there are any non-simple uses of this getelementptr, make sure to reject
// them.
return isSafeElementUse(GEPI, IsAllZeroIndices, AI);
}
/// 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.
bool SROA::isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI){
// If not constant length, give up.
ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength());
if (!Length) return false;
// If not the whole aggregate, give up.
const TargetData &TD = getAnalysis<TargetData>();
if (Length->getZExtValue() != TD.getTypeSize(AI->getType()->getElementType()))
return false;
// We only know about memcpy/memset/memmove.
if (!isa<MemCpyInst>(MI) && !isa<MemSetInst>(MI) && !isa<MemMoveInst>(MI))
return false;
// Otherwise, we can transform it.
return true;
}
/// isSafeUseOfBitCastedAllocation - Return true if all users of this bitcast
/// are
bool SROA::isSafeUseOfBitCastedAllocation(BitCastInst *BC, AllocationInst *AI) {
for (Value::use_iterator UI = BC->use_begin(), E = BC->use_end();
UI != E; ++UI) {
if (BitCastInst *BCU = dyn_cast<BitCastInst>(UI)) {
if (!isSafeUseOfBitCastedAllocation(BCU, AI))
return false;
} else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(UI)) {
if (!isSafeMemIntrinsicOnAllocation(MI, AI))
return false;
} else {
return false;
}
}
return true;
}
/// 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 packed 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, 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, 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();
}
}
/// 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.
//
int isSafe = 3;
for (Value::use_iterator I = AI->use_begin(), E = AI->use_end();
I != E; ++I) {
isSafe &= isSafeUseOfAllocation(cast<Instruction>(*I), AI);
if (isSafe == 0) {
DOUT << "Cannot transform: " << *AI << " due to user: " << **I;
return 0;
}
}
// If we require cleanup, isSafe is now 1, otherwise it is 3.
return isSafe;
}
/// 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 packed 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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