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InstCombine: Don't combine constants on unsigned icmps

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Fixes a miscompile introduced in r204912.  It would miscompile code like
(unsigned)(a + -49) <= 5U.  The transform would turn this into
(unsigned)a < 55U, which would return true for values in [0, 49], when
it should not.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204948 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Kleckner 2014-03-27 17:49:27 +00:00
parent 0c6d96cf16
commit 63b11ef6d4
2 changed files with 12 additions and 1 deletions
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3
lib/Transforms/InstCombine/InstCombineCompares.cpp
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@ -3010,7 +3010,8 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
return FoldICmpAddOpCst(I, X, Cst, I.getSwappedPredicate());
ConstantInt *Cst2;
if (match(Op1, m_ConstantInt(Cst)) &&
if (I.isSigned() &&
match(Op1, m_ConstantInt(Cst)) &&
match(Op0, m_Add(m_Value(X), m_ConstantInt(Cst2))) &&
cast<BinaryOperator>(Op0)->hasNoSignedWrap()) {
// icmp X+Cst2, Cst --> icmp X, Cst-Cst2

10
test/Transforms/InstCombine/icmp.ll
View File

@ -1409,3 +1409,13 @@ entry:
%conv = zext i1 %cmp to i32
ret i32 %conv
}
; CHECK-LABEL: icmp_add_const_ult
; CHECK: %cmp = icmp ult i32 %add, 6
define i32 @icmp_add_const_ult(i32 %a) #0 {
entry:
%add = add nsw i32 %a, -49
%cmp = icmp ult i32 %add, 6
%conv = zext i1 %cmp to i32
ret i32 %conv
}