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Added instcombine pattern to spot comparing -val or val against 0. 

(val != 0) == (-val != 0) so "abs(val) != 0" becomes "val != 0"

Fixes <rdar://problem/10482509>

llvm-svn: 145563
This commit is contained in:
Pete Cooper 2011-12-01 03:58:40 +00:00
parent b1a0292240
commit bc5c524b71
2 changed files with 24 additions and 0 deletions
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14
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -1795,6 +1795,20 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
if (Value *V = SimplifyICmpInst(I.getPredicate(), Op0, Op1, TD))
return ReplaceInstUsesWith(I, V);
// comparing -val or val with non-zero is the same as just comparing val
// ie, (val != 0) == (-val != 0)
if (I.getPredicate() == ICmpInst::ICMP_NE && match(Op1, m_Zero()))
{
Value *Cond, *SubSrc, *SelectFalse;
if (match(Op0, m_Select(m_Value(Cond), m_Sub(m_Zero(), m_Value(SubSrc)),
m_Value(SelectFalse)))) {
if (SubSrc == SelectFalse) {
return CmpInst::Create(Instruction::ICmp, I.getPredicate(),
SubSrc, Op1);
}
}
}
Type *Ty = Op0->getType();
// icmp's with boolean values can always be turned into bitwise operations

10
llvm/test/Transforms/InstCombine/compare-abs-nonzero.ll Normal file
View File

@ -0,0 +1,10 @@
; RUN: opt < %s -instcombine -S | grep -v {select}
define zeroext i1 @cmpabs(i64 %val) nounwind uwtable readnone ssp {
entry:
%sub = sub nsw i64 0, %val
%cmp = icmp slt i64 %val, 0
%sub.val = select i1 %cmp, i64 %sub, i64 %val
%tobool = icmp ne i64 %sub.val, 0
ret i1 %tobool
}