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[InstSimplify] Teach simplifyICmpWithConstant about samesign #125899

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[InstSimplify] Teach simplifyICmpWithConstant about samesign #125899

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d6dc555
ValueTracking: pre-commit constrange-samesign tests
artagnon Feb 5, 2025
e86e626
InstSimplify: teach simplifyICmpWithConstant about samesign
artagnon Feb 14, 2025
bb06f65
InstSimplify: check UseInstrInfo; address review
artagnon Feb 17, 2025
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37 changes: 24 additions & 13 deletions llvm/lib/Analysis/InstructionSimplify.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2999,21 +2999,32 @@ static Value *simplifyICmpWithConstant(CmpPredicate Pred, Value *LHS,
return ConstantInt::getBool(ITy, !TrueIfSigned);
}

// Rule out tautological comparisons (eg., ult 0 or uge 0).
ConstantRange RHS_CR = ConstantRange::makeExactICmpRegion(Pred, *C);
if (RHS_CR.isEmptySet())
return ConstantInt::getFalse(ITy);
if (RHS_CR.isFullSet())
return ConstantInt::getTrue(ITy);

ConstantRange LHS_CR =
ConstantRange LCR =
computeConstantRange(LHS, CmpInst::isSigned(Pred), IIQ.UseInstrInfo);
if (!LHS_CR.isFullSet()) {
if (RHS_CR.contains(LHS_CR))
return ConstantInt::getTrue(ITy);
if (RHS_CR.inverse().contains(LHS_CR))

auto CheckCR = [&](const ConstantRange &CR) -> Constant * {
// Rule out tautological comparisons (eg., ult 0 or uge 0).
if (CR.isEmptySet())
return ConstantInt::getFalse(ITy);
}
if (CR.isFullSet())
return ConstantInt::getTrue(ITy);

if (!LCR.isFullSet()) {
if (CR.contains(LCR))
return ConstantInt::getTrue(ITy);
if (CR.inverse().contains(LCR))
return ConstantInt::getFalse(ITy);
}
return nullptr;
};

// Check unsigned and signed versions of relational predicates with samesign.
if (auto *K = CheckCR(ConstantRange::makeExactICmpRegion(Pred, *C)))
return K;
if (IIQ.UseInstrInfo && Pred.hasSameSign() && ICmpInst::isRelational(Pred))
if (auto *K = CheckCR(ConstantRange::makeExactICmpRegion(
ICmpInst::getSignedPredicate(Pred), *C)))
return K;

// (mul nuw/nsw X, MulC) != C --> true (if C is not a multiple of MulC)
// (mul nuw/nsw X, MulC) == C --> false (if C is not a multiple of MulC)
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36 changes: 36 additions & 0 deletions llvm/test/Analysis/ValueTracking/constant-ranges.ll
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Expand Up @@ -160,6 +160,15 @@ define i1 @srem_posC_okay0(i8 %x) {
ret i1 %r
}

define i1 @srem_posC_okay0_samesign(i8 %x) {
; CHECK-LABEL: @srem_posC_okay0_samesign(
; CHECK-NEXT: ret i1 true
;
%val = srem i8 34, %x
%r = icmp samesign ule i8 %val, 34
ret i1 %r
}

define i1 @srem_posC_okay1(i8 %x) {
; CHECK-LABEL: @srem_posC_okay1(
; CHECK-NEXT: ret i1 true
Expand All @@ -169,6 +178,15 @@ define i1 @srem_posC_okay1(i8 %x) {
ret i1 %r
}

define i1 @srem_posC_okay1_samesign(i8 %x) {
; CHECK-LABEL: @srem_posC_okay1_samesign(
; CHECK-NEXT: ret i1 false
;
%val = srem i8 34, %x
%r = icmp samesign uge i8 %val, -3
ret i1 %r
}

define i1 @srem_negC_okay0(i8 %x) {
; CHECK-LABEL: @srem_negC_okay0(
; CHECK-NEXT: ret i1 true
Expand All @@ -178,6 +196,15 @@ define i1 @srem_negC_okay0(i8 %x) {
ret i1 %r
}

define i1 @srem_negC_okay0_samesign(i8 %x) {
; CHECK-LABEL: @srem_negC_okay0_samesign(
; CHECK-NEXT: ret i1 true
;
%val = srem i8 -34, %x
%r = icmp samesign ule i8 %val, 0
ret i1 %r
}

define i1 @srem_negC_okay1(i8 %x) {
; CHECK-LABEL: @srem_negC_okay1(
; CHECK-NEXT: ret i1 true
Expand All @@ -187,6 +214,15 @@ define i1 @srem_negC_okay1(i8 %x) {
ret i1 %r
}

define i1 @srem_negC_okay1_samesign(i8 %x) {
; CHECK-LABEL: @srem_negC_okay1_samesign(
; CHECK-NEXT: ret i1 true
;
%val = srem i8 -34, %x
%r = icmp samesign uge i8 %val, -34
ret i1 %r
}

define i1 @srem_posC_fail0(i8 %x) {
; CHECK-LABEL: @srem_posC_fail0(
; CHECK-NEXT: [[VAL:%.*]] = srem i8 34, [[X:%.*]]
Expand Down