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This just in, it is a *bad idea* to use 'udiv' on an offset of

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a pointer. A very bad idea. Let's not do that. Fixes PR14105.

Note that this wasn't *that* glaring of an oversight. Originally, these
routines were only called on offsets within an alloca, which are
intrinsically positive. But over the evolution of the pass, they ended
up being called for arbitrary offsets, and things went downhill...

llvm-svn: 166095
This commit is contained in:
Chandler Carruth 2012-10-17 09:23:48 +00:00
parent 4314405e52
commit 7d68167eb0
2 changed files with 23 additions and 3 deletions
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6
lib/Transforms/Scalar/SROA.cpp
View File

@ -1828,7 +1828,7 @@ static Value *getNaturalGEPRecursively(IRBuilder<> &IRB, const DataLayout &TD,
if (ElementSizeInBits % 8)
return 0; // GEPs over non-multiple of 8 size vector elements are invalid.
APInt ElementSize(Offset.getBitWidth(), ElementSizeInBits / 8);
APInt NumSkippedElements = Offset.udiv(ElementSize);
APInt NumSkippedElements = Offset.sdiv(ElementSize);
if (NumSkippedElements.ugt(VecTy->getNumElements()))
return 0;
Offset -= NumSkippedElements * ElementSize;
@ -1840,7 +1840,7 @@ static Value *getNaturalGEPRecursively(IRBuilder<> &IRB, const DataLayout &TD,
if (ArrayType *ArrTy = dyn_cast<ArrayType>(Ty)) {
Type *ElementTy = ArrTy->getElementType();
APInt ElementSize(Offset.getBitWidth(), TD.getTypeAllocSize(ElementTy));
APInt NumSkippedElements = Offset.udiv(ElementSize);
APInt NumSkippedElements = Offset.sdiv(ElementSize);
if (NumSkippedElements.ugt(ArrTy->getNumElements()))
return 0;
@ -1896,7 +1896,7 @@ static Value *getNaturalGEPWithOffset(IRBuilder<> &IRB, const DataLayout &TD,
APInt ElementSize(Offset.getBitWidth(), TD.getTypeAllocSize(ElementTy));
if (ElementSize == 0)
return 0; // Zero-length arrays can't help us build a natural GEP.
APInt NumSkippedElements = Offset.udiv(ElementSize);
APInt NumSkippedElements = Offset.sdiv(ElementSize);
Offset -= NumSkippedElements * ElementSize;
Indices.push_back(IRB.getInt(NumSkippedElements));

20
test/Transforms/SROA/basictest.ll
View File

@ -1063,3 +1063,23 @@ entry:
call void @llvm.lifetime.end(i64 -1, i8* %0)
ret void
}
define void @PR14105({ [16 x i8] }* %ptr) {
; Ensure that when rewriting the GEP index '-1' for this alloca we preserve is
; sign as negative. We use a volatile memcpy to ensure promotion never actually
; occurs.
; CHECK: @PR14105
entry:
%a = alloca { [16 x i8] }, align 8
; CHECK: alloca [16 x i8], align 8
%gep = getelementptr inbounds { [16 x i8] }* %ptr, i64 -1
; CHECK-NEXT: getelementptr inbounds { [16 x i8] }* %ptr, i64 -1, i32 0, i64 0
%cast1 = bitcast { [16 x i8 ] }* %gep to i8*
%cast2 = bitcast { [16 x i8 ] }* %a to i8*
call void @llvm.memcpy.p0i8.p0i8.i32(i8* %cast1, i8* %cast2, i32 16, i32 8, i1 true)
ret void
; CHECK: ret
}