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Canonicalize indices in a constantexpr GEP. If Indices exceed the

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static extents of the static array type, it causes GlobalOpt and
other passes to be more conservative. This canonicalization also
allows the constant folder to add "inbounds" to GEPs.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79440 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-08-19 18:18:36 +00:00
parent 6a402dc952
commit de0e587e63
2 changed files with 98 additions and 4 deletions
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52
lib/Analysis/ConstantFolding.cpp
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@ -131,6 +131,7 @@ static Constant *SymbolicallyEvaluateGEP(Constant* const* Ops, unsigned NumOps,
return 0;
uint64_t BasePtr = 0;
bool BaseIsInt = true;
if (!Ptr->isNullValue()) {
// If this is a inttoptr from a constant int, we can fold this as the base,
// otherwise we can't.
@ -140,19 +141,62 @@ static Constant *SymbolicallyEvaluateGEP(Constant* const* Ops, unsigned NumOps,
BasePtr = Base->getZExtValue();
if (BasePtr == 0)
return 0;
BaseIsInt = false;
}
// If this is a constant expr gep that is effectively computing an
// "offsetof", fold it into 'cast int Size to T*' instead of 'gep 0, 0, 12'
for (unsigned i = 1; i != NumOps; ++i)
if (!isa<ConstantInt>(Ops[i]))
return false;
return 0;
uint64_t Offset = TD->getIndexedOffset(Ptr->getType(),
(Value**)Ops+1, NumOps-1);
Constant *C = ConstantInt::get(TD->getIntPtrType(Context), Offset+BasePtr);
return ConstantExpr::getIntToPtr(C, ResultTy);
// If the base value for this address is a literal integer value, fold the
// getelementptr to the resulting integer value casted to the pointer type.
if (BaseIsInt) {
Constant *C = ConstantInt::get(TD->getIntPtrType(Context), Offset+BasePtr);
return ConstantExpr::getIntToPtr(C, ResultTy);
}
// Otherwise form a regular getelementptr. Recompute the indices so that
// we eliminate over-indexing of the notional static type array bounds.
// This makes it easy to determine if the getelementptr is "inbounds".
// Also, this helps GlobalOpt do SROA on GlobalVariables.
const Type *Ty = Ptr->getType();
SmallVector<Constant*, 32> NewIdxs;
for (unsigned Index = 1; Index != NumOps; ++Index) {
if (const SequentialType *ATy = dyn_cast<SequentialType>(Ty)) {
// Determine which element of the array the offset points into.
uint64_t ElemSize = TD->getTypeAllocSize(ATy->getElementType());
if (ElemSize == 0)
return 0;
uint64_t NewIdx = Offset / ElemSize;
Offset -= NewIdx * ElemSize;
NewIdxs.push_back(ConstantInt::get(TD->getIntPtrType(Context), NewIdx));
Ty = ATy->getElementType();
} else if (const StructType *STy = dyn_cast<StructType>(Ty)) {
// Determine which field of the struct the offset points into.
const StructLayout &SL = *TD->getStructLayout(STy);
unsigned ElIdx = SL.getElementContainingOffset(Offset);
NewIdxs.push_back(ConstantInt::get(Type::getInt32Ty(Context), ElIdx));
Offset -= SL.getElementOffset(ElIdx);
Ty = STy->getTypeAtIndex(ElIdx);
} else {
return 0;
}
}
// If the base is the start of a GlobalVariable and all the array indices
// remain in their static bounds, the GEP is inbounds. We can check that
// all indices are in bounds by just checking the first index only
// because we've just normalized all the indices.
if (isa<GlobalVariable>(Ptr) && NewIdxs[0]->isNullValue())
return ConstantExpr::getInBoundsGetElementPtr(Ptr,
&NewIdxs[0], NewIdxs.size());
// Otherwise it may not be inbounds.
return ConstantExpr::getGetElementPtr(Ptr, &NewIdxs[0], NewIdxs.size());
}
/// FoldBitCast - Constant fold bitcast, symbolically evaluating it with

50
test/Transforms/InstCombine/constant-fold-gep.ll Normal file
View File

@ -0,0 +1,50 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | FileCheck %s
; Constant folding should fix notionally out-of-bounds indices
; and add inbounds keywords.
%struct.X = type { [3 x i32], [3 x i32] }
@Y = internal global [3 x %struct.X] zeroinitializer
define void @frob() {
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 0), align 8
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 0), align 4
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 1), align 4
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 1), align 4
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 2), align 8
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 2), align 4
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 0, i32 1, i64 0), align 4
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 3), align 4
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 0, i32 1, i64 1), align 4
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 4), align 4
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 0, i32 1, i64 2), align 4
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 5), align 4
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 1, i32 0, i64 0), align 8
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 6), align 4
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 1, i32 0, i64 1), align 4
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 7), align 4
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 1, i32 0, i64 2), align 8
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 8), align 4
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 1, i32 1, i64 0), align 4
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 9), align 4
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 1, i32 1, i64 1), align 4
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 10), align 4
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 1, i32 1, i64 2), align 4
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 11), align 4
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 2, i32 0, i64 0), align 8
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 12), align 4
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 2, i32 0, i64 1), align 4
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 13), align 4
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 2, i32 0, i64 2), align 8
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 14), align 8
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 2, i32 1, i64 0), align 8
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 15), align 8
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 2, i32 1, i64 1), align 8
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 16), align 8
; CHECK: store i32 1, i32* getelementptr inbounds ([3 x %struct.X]* @Y, i64 0, i64 2, i32 1, i64 2), align 8
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 17), align 8
; CHECK: store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 1, i64 0, i32 0, i64 0), align 8
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 18), align 8
ret void
}