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[ConstantFolding] Don't treat negative GEP offsets as positive 

GEP offsets are signed, don't treat them as huge positive numbers.

llvm-svn: 275251
This commit is contained in:
David Majnemer 2016-07-13 05:16:16 +00:00
parent c2f791d8a7
commit 1b3db33e3d
2 changed files with 9 additions and 10 deletions
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11
llvm/lib/Analysis/ConstantFolding.cpp
View File

@ -845,15 +845,18 @@ Constant *SymbolicallyEvaluateGEP(const GEPOperator *GEP,
// Determine which element of the array the offset points into.
APInt ElemSize(BitWidth, DL.getTypeAllocSize(Ty));
if (ElemSize == 0)
if (ElemSize == 0) {
// The element size is 0. This may be [0 x Ty]*, so just use a zero
// index for this level and proceed to the next level to see if it can
// accommodate the offset.
NewIdxs.push_back(ConstantInt::get(IntPtrTy, 0));
else {
} else if (ElemSize.isAllOnesValue()) {
// Avoid signed overflow.
break;
} else {
// The element size is non-zero divide the offset by the element
// size (rounding down), to compute the index at this level.
APInt NewIdx = Offset.udiv(ElemSize);
APInt NewIdx = Offset.sdiv(ElemSize);
Offset -= NewIdx * ElemSize;
NewIdxs.push_back(ConstantInt::get(IntPtrTy, NewIdx));
}
@ -864,7 +867,7 @@ Constant *SymbolicallyEvaluateGEP(const GEPOperator *GEP,
// operand likely went through casts that are necessary to make the GEP
// sensible.
const StructLayout &SL = *DL.getStructLayout(STy);
if (Offset.uge(SL.getSizeInBytes()))
if (Offset.isNegative() || Offset.uge(SL.getSizeInBytes()))
break;
// Determine which field of the struct the offset points into. The

8
llvm/test/Transforms/InstCombine/getelementptr.ll
View File

@ -624,15 +624,11 @@ define i32 @test35() nounwind {
; CHECK: call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([17 x i8], [17 x i8]* @"\01LC8", i64 0, i64 0), i8* getelementptr inbounds (%t0, %t0* @s, i64 0, i32 1, i64 0)) [[NUW:#[0-9]+]]
}
; Instcombine should constant-fold the GEP so that indices that have
; static array extents are within bounds of those array extents.
; In the below, -1 is not in the range [0,11). After the transformation,
; the same address is computed, but 3 is in the range of [0,11).
; Don't treat signed offsets as unsigned.
define i8* @test36() nounwind {
ret i8* getelementptr ([11 x i8], [11 x i8]* @array, i32 0, i64 -1)
; CHECK-LABEL: @test36(
; CHECK: ret i8* getelementptr ([11 x i8], [11 x i8]* @array, i64 1676976733973595601, i64 4)
; CHECK: ret i8* getelementptr ([11 x i8], [11 x i8]* @array, i64 0, i64 -1)
}
; Instcombine shouldn't assume that gep(A,0,1) != gep(A,1,0).