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Simplify (a % b) lt/ge (b-1) into (a % b) eq/ne (b-1) #72504

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Jan 16, 2024
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Simplify (a % b) lt/ge (b-1) into (a % b) eq/ne (b-1) #72504

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d7dcc05
[InstCombine] Add test coverage for (a % b) lt/le/ge/gt (b(-/+)1) (NFC).
elhewaty Nov 17, 2023
ab83673
[InstCombine] Fold (a (s/u)% b) (s/u)(le/ge/lt/gt) (b (-/+) 1)
elhewaty Jan 15, 2024
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45 changes: 45 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2519,6 +2519,30 @@ Instruction *InstCombinerImpl::foldICmpShrConstant(ICmpInst &Cmp,
Instruction *InstCombinerImpl::foldICmpSRemConstant(ICmpInst &Cmp,
BinaryOperator *SRem,
const APInt &C) {
{
const APInt *C1;
ICmpInst::Predicate Pred = Cmp.getPredicate();
if ((match(SRem->getOperand(1), m_NonNegative(C1))) &&
((Pred == ICmpInst::ICMP_SLT && C == *C1 - 1) ||
(Pred == ICmpInst::ICMP_SGT && C == *C1 - 2) ||
(Pred == ICmpInst::ICMP_SGT && C == -*C1 + 1) ||
(Pred == ICmpInst::ICMP_SLT && C == -*C1 + 2))) {
// icmp slt (X s% C), (C - 1) --> icmp ne (X s% C), (C - 1), if C >= 0
// icmp sgt (X s% C), (C - 2) --> icmp eq (X s% C), (C - 1), if C >= 0
// icmp sgt (X s% C), (-C + 1) --> icmp ne (X s% C), (-C + 1), if C >= 0
// icmp slt (X s% C), (-C + 2) --> icmp eq (X s% C), (-C + 1), if C >= 0
return new ICmpInst(
((Pred == ICmpInst::ICMP_SLT && C == *C1 - 1) ||
(Pred == ICmpInst::ICMP_SGT && C == -*C1 + 1))
? ICmpInst::ICMP_NE
: ICmpInst::ICMP_EQ,
SRem,
ConstantInt::get(SRem->getType(), C == -*C1 + 1 || C == -*C1 + 2
? -*C1 + 1
: *C1 - 1));
}
}

// Match an 'is positive' or 'is negative' comparison of remainder by a
// constant power-of-2 value:
// (X % pow2C) sgt/slt 0
Expand Down Expand Up @@ -2566,6 +2590,23 @@ Instruction *InstCombinerImpl::foldICmpSRemConstant(ICmpInst &Cmp,
return new ICmpInst(ICmpInst::ICMP_UGT, And, ConstantInt::get(Ty, SignMask));
}

Instruction *InstCombinerImpl::foldICmpURemConstant(ICmpInst &Cmp,
BinaryOperator *URem,
const APInt &C) {
const APInt *C1;
ICmpInst::Predicate Pred = Cmp.getPredicate();
if (match(URem->getOperand(1), m_APInt(C1)) &&
((Pred == ICmpInst::ICMP_ULT && C == *C1 - 1) ||
(Pred == ICmpInst::ICMP_UGT && C == *C1 - 2 && C.ugt(1)))) {
// icmp ult (X u% C), (C - 1) --> icmp ne (X u% C), (C - 1)
// icmp ugt (X u% C), (C - 2) --> icmp eq (X u% C), (C - 1), if C >u 1
return new ICmpInst(Pred == ICmpInst::ICMP_UGT ? ICmpInst::ICMP_EQ
: ICmpInst::ICMP_NE,
URem, ConstantInt::get(URem->getType(), *C1 - 1));
}
return nullptr;
}

/// Fold icmp (udiv X, Y), C.
Instruction *InstCombinerImpl::foldICmpUDivConstant(ICmpInst &Cmp,
BinaryOperator *UDiv,
Expand Down Expand Up @@ -3703,6 +3744,10 @@ Instruction *InstCombinerImpl::foldICmpBinOpWithConstant(ICmpInst &Cmp,
if (Instruction *I = foldICmpSRemConstant(Cmp, BO, C))
return I;
break;
case Instruction::URem:
if (Instruction *I = foldICmpURemConstant(Cmp, BO, C))
return I;
break;
case Instruction::UDiv:
if (Instruction *I = foldICmpUDivConstant(Cmp, BO, C))
return I;
Expand Down
2 changes: 2 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineInternal.h
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Expand Up @@ -663,6 +663,8 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
const APInt &C);
Instruction *foldICmpSRemConstant(ICmpInst &Cmp, BinaryOperator *UDiv,
const APInt &C);
Instruction *foldICmpURemConstant(ICmpInst &Cmp, BinaryOperator *UDiv,
const APInt &C);
Instruction *foldICmpUDivConstant(ICmpInst &Cmp, BinaryOperator *UDiv,
const APInt &C);
Instruction *foldICmpDivConstant(ICmpInst &Cmp, BinaryOperator *Div,
Expand Down
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