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[InstCombine] Fix regression introduced at r227197.

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This patch fixes a problem I accidentally introduced in an instruction combine
on select instructions added at r227197. That revision taught the instruction
combiner how to fold a cttz/ctlz followed by a icmp plus select into a single
cttz/ctlz with flag 'is_zero_undef' cleared.

However, the new rule added at r227197 would have produced wrong results in the
case where a cttz/ctlz with flag 'is_zero_undef' cleared was follwed by a
zero-extend or truncate. In that case, the folded instruction would have
been inserted in a wrong location thus leaving the CFG in an inconsistent
state.

This patch fixes the problem and add two reproducible test cases to
existing test 'InstCombine/select-cmp-cttz-ctlz.ll'.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229124 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrea Di Biagio 2015-02-13 16:33:34 +00:00
parent 3229c883b9
commit d25126faae
2 changed files with 33 additions and 10 deletions
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16
lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -482,16 +482,12 @@ static Value *foldSelectCttzCtlz(ICmpInst *ICI, Value *TrueVal, Value *FalseVal,
match(Count, m_Intrinsic<Intrinsic::ctlz>(m_Specific(CmpLHS)))) {
IntrinsicInst *II = cast<IntrinsicInst>(Count);
IRBuilder<> Builder(II);
if (cast<ConstantInt>(II->getArgOperand(1))->isOne()) {
// Explicitly clear the 'undef_on_zero' flag.
IntrinsicInst *NewI = cast<IntrinsicInst>(II->clone());
Type *Ty = NewI->getArgOperand(1)->getType();
NewI->setArgOperand(1, Constant::getNullValue(Ty));
Builder.Insert(NewI);
Count = NewI;
}
return Builder.CreateZExtOrTrunc(Count, ValueOnZero->getType());
// Explicitly clear the 'undef_on_zero' flag.
IntrinsicInst *NewI = cast<IntrinsicInst>(II->clone());
Type *Ty = NewI->getArgOperand(1)->getType();
NewI->setArgOperand(1, Constant::getNullValue(Ty));
Builder.Insert(NewI);
return Builder.CreateZExtOrTrunc(NewI, ValueOnZero->getType());
}
return nullptr;

27
test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll
View File

@ -292,6 +292,33 @@ entry:
ret i16 %cond
}
define i64 @select_bug1(i32 %x) {
; CHECK-LABEL: @select_bug1(
; CHECK: [[VAR1:%[a-zA-Z0-9]+]] = tail call i32 @llvm.cttz.i32(i32 %x, i1 false)
; CHECK-NEXT: [[VAR2:%[a-zA-Z0-9]+]] = zext i32 [[VAR1]] to i64
; CHECK-NEXT: ret i64 [[VAR2]]
entry:
%0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 false)
%conv = zext i32 %0 to i64
%tobool = icmp ne i32 %x, 0
%cond = select i1 %tobool, i64 %conv, i64 32
ret i64 %cond
}
define i16 @select_bug2(i32 %x) {
; CHECK-LABEL: @select_bug2(
; CHECK: [[VAR1:%[a-zA-Z0-9]+]] = tail call i32 @llvm.cttz.i32(i32 %x, i1 false)
; CHECK-NEXT: [[VAR2:%[a-zA-Z0-9]+]] = trunc i32 [[VAR1]] to i16
; CHECK-NEXT: ret i16 [[VAR2]]
entry:
%0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 false)
%conv = trunc i32 %0 to i16
%tobool = icmp ne i32 %x, 0
%cond = select i1 %tobool, i16 %conv, i16 32
ret i16 %cond
}
declare i16 @llvm.ctlz.i16(i16, i1)
declare i32 @llvm.ctlz.i32(i32, i1)
declare i64 @llvm.ctlz.i64(i64, i1)