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Move folding of icmp with zero after checking for min/max idioms.

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Summary:
The following transformation for cmp instruction:

  icmp smin(x, PositiveValue), 0 -> icmp x, 0

should only be done after checking for min/max to prevent infinite
looping caused by a reverse canonicalization. That is why this
transformation was moved to place after the mentioned check.

Reviewers: spatel, efriedma

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D38934

Patch by: Artur Gainullin <artur.gainullin@intel.com>

llvm-svn: 315895
This commit is contained in:
Nikolai Bozhenov 2017-10-16 09:19:21 +00:00
parent 4543affa98
commit 0e7ebbccc7
3 changed files with 24 additions and 12 deletions
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33
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -1318,6 +1318,24 @@ static Instruction *processUGT_ADDCST_ADD(ICmpInst &I, Value *A, Value *B,
return ExtractValueInst::Create(Call, 1, "sadd.overflow");
}
// Handle (icmp sgt smin(PosA, B) 0) -> (icmp sgt B 0)
Instruction *InstCombiner::foldICmpWithZero(ICmpInst &Cmp) {
CmpInst::Predicate Pred = Cmp.getPredicate();
Value *X = Cmp.getOperand(0);
if (match(Cmp.getOperand(1), m_Zero()) && Pred == ICmpInst::ICMP_SGT) {
Value *A, *B;
SelectPatternResult SPR = matchSelectPattern(X, A, B);
if (SPR.Flavor == SPF_SMIN) {
if (isKnownPositive(A, DL, 0, &AC, &Cmp, &DT))
return new ICmpInst(Pred, B, Cmp.getOperand(1));
if (isKnownPositive(B, DL, 0, &AC, &Cmp, &DT))
return new ICmpInst(Pred, A, Cmp.getOperand(1));
}
}
return nullptr;
}
// Fold icmp Pred X, C.
Instruction *InstCombiner::foldICmpWithConstant(ICmpInst &Cmp) {
CmpInst::Predicate Pred = Cmp.getPredicate();
@ -1349,17 +1367,6 @@ Instruction *InstCombiner::foldICmpWithConstant(ICmpInst &Cmp) {
return Res;
}
// (icmp sgt smin(PosA, B) 0) -> (icmp sgt B 0)
if (C->isNullValue() && Pred == ICmpInst::ICMP_SGT) {
SelectPatternResult SPR = matchSelectPattern(X, A, B);
if (SPR.Flavor == SPF_SMIN) {
if (isKnownPositive(A, DL, 0, &AC, &Cmp, &DT))
return new ICmpInst(Pred, B, Cmp.getOperand(1));
if (isKnownPositive(B, DL, 0, &AC, &Cmp, &DT))
return new ICmpInst(Pred, A, Cmp.getOperand(1));
}
}
// FIXME: Use m_APInt to allow folds for splat constants.
ConstantInt *CI = dyn_cast<ConstantInt>(Cmp.getOperand(1));
if (!CI)
@ -4462,6 +4469,10 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
(SI->getOperand(2) == Op0 && SI->getOperand(1) == Op1))
return nullptr;
// Do this after checking for min/max to prevent infinite looping.
if (Instruction *Res = foldICmpWithZero(I))
return Res;
// FIXME: We only do this after checking for min/max to prevent infinite
// looping caused by a reverse canonicalization of these patterns for min/max.
// FIXME: The organization of folds is a mess. These would naturally go into

1
llvm/lib/Transforms/InstCombine/InstCombineInternal.h
View File

@ -700,6 +700,7 @@ private:
Instruction *foldICmpInstWithConstantNotInt(ICmpInst &Cmp);
Instruction *foldICmpBinOp(ICmpInst &Cmp);
Instruction *foldICmpEquality(ICmpInst &Cmp);
Instruction *foldICmpWithZero(ICmpInst &Cmp);
Instruction *foldICmpSelectConstant(ICmpInst &Cmp, SelectInst *Select,
ConstantInt *C);

2
llvm/test/Transforms/InstCombine/minmax-fold.ll
View File

@ -507,7 +507,7 @@ define i32 @clamp_check_for_no_infinite_loop1(i32 %i) {
; CHECK-LABEL: @clamp_check_for_no_infinite_loop1(
; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i32 [[I:%.*]], 255
; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[CMP1]], i32 [[I]], i32 255
; CHECK-NEXT: [[TMP1:%.*]] = icmp sgt i32 [[I]], 0
; CHECK-NEXT: [[TMP1:%.*]] = icmp sgt i32 [[SEL1]], 0
; CHECK-NEXT: [[RES:%.*]] = select i1 [[TMP1]], i32 [[SEL1]], i32 0
; CHECK-NEXT: ret i32 [[RES]]
;