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[SeparateConstOffsetFromGEP] Fixed a bug related to unsigned modulo 

The dividend in "signed % unsigned" is treated as unsigned instead of signed,
causing unexpected behavior such as -64 % (uint64_t)24 == 0.

Added a regression test in split-gep.ll

Patched by Hao Liu.

llvm-svn: 220618
This commit is contained in:
Jingyue Wu 2014-10-25 18:34:03 +00:00
parent aa139573f6
commit fe72fcebf6
2 changed files with 30 additions and 6 deletions
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12
llvm/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
View File

@ -720,16 +720,16 @@ bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) {
Instruction *NewGEP = GEP->clone();
NewGEP->insertBefore(GEP);
uint64_t ElementTypeSizeOfGEP =
DL->getTypeAllocSize(GEP->getType()->getElementType());
// Per ANSI C standard, signed / unsigned = unsigned and signed % unsigned =
// unsigned.. Therefore, we cast ElementTypeSizeOfGEP to signed because it is
// used with unsigned integers later.
int64_t ElementTypeSizeOfGEP = static_cast<int64_t>(
DL->getTypeAllocSize(GEP->getType()->getElementType()));
Type *IntPtrTy = DL->getIntPtrType(GEP->getType());
if (AccumulativeByteOffset % ElementTypeSizeOfGEP == 0) {
// Very likely. As long as %gep is natually aligned, the byte offset we
// extracted should be a multiple of sizeof(*%gep).
// Per ANSI C standard, signed / unsigned = unsigned. Therefore, we
// cast ElementTypeSizeOfGEP to signed.
int64_t Index =
AccumulativeByteOffset / static_cast<int64_t>(ElementTypeSizeOfGEP);
int64_t Index = AccumulativeByteOffset / ElementTypeSizeOfGEP;
NewGEP = GetElementPtrInst::Create(
NewGEP, ConstantInt::get(IntPtrTy, Index, true), GEP->getName(), GEP);
} else {

24
llvm/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll
View File

@ -253,3 +253,27 @@ entry:
ret float* %p
; CHECK-NEXT: ret
}
; The source code used to be buggy in checking
; (AccumulativeByteOffset % ElementTypeSizeOfGEP == 0)
; where AccumulativeByteOffset is signed but ElementTypeSizeOfGEP is unsigned.
; The compiler would promote AccumulativeByteOffset to unsigned, causing
; unexpected results. For example, while -64 % (int64_t)24 != 0,
; -64 % (uint64_t)24 == 0.
%struct3 = type { i64, i32 }
%struct2 = type { %struct3, i32 }
%struct1 = type { i64, %struct2 }
%struct0 = type { i32, i32, i64*, [100 x %struct1] }
define %struct2* @sign_mod_unsign(%struct0* %ptr, i64 %idx) {
; CHECK-LABEL: @sign_mod_unsign(
entry:
%arrayidx = add nsw i64 %idx, -2
; CHECK-NOT: add
%ptr2 = getelementptr inbounds %struct0* %ptr, i64 0, i32 3, i64 %arrayidx, i32 1
; CHECK: [[PTR:%[a-zA-Z0-9]+]] = getelementptr %struct0* %ptr, i64 0, i32 3, i64 %idx, i32 1
; CHECK: [[PTR1:%[a-zA-Z0-9]+]] = bitcast %struct2* [[PTR]] to i8*
; CHECK: getelementptr i8* [[PTR1]], i64 -64
; CHECK: bitcast
ret %struct2* %ptr2
; CHECK-NEXT: ret
}