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[InstCombine] fold u <= (u <= (unsigned)b) into (u <= (unsigned)b). #136654

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[InstCombine] fold u <= (u <= (unsigned)b) into (u <= (unsigned)b). #136654

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8133b5a
[InstCombine] fold u <= (u <= (unsigned)b) into (u <= (unsigned)b).
YLChenZ Apr 22, 2025
5e5be45
[InstCombine] fold u <= (u <= (unsigned)b) into (u <= (unsigned)b).
YLChenZ Apr 22, 2025
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25 changes: 25 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 @@ -7435,6 +7435,31 @@ Instruction *InstCombinerImpl::visitICmpInst(ICmpInst &I) {
if (Value *V = simplifyICmpInst(I.getCmpPredicate(), Op0, Op1, Q))
return replaceInstUsesWith(I, V);

// Try to fold pattern: u <= (u <= b), b is boolean-like.
// This fold handles cases where Clang produces code like:
// %cmp1 = icmp ule i32 %u, zext i1 %b to i32
// %zext = zext i1 %cmp1 to i32
// %cmp2 = icmp ule i32 %u, %zext
// fold the comparison into: u <= b
if (I.getPredicate() == ICmpInst::ICMP_ULE) {
if (auto *Z = dyn_cast<ZExtInst>(Op1)) {
if (Z->getSrcTy()->isIntegerTy(1)) {
if (auto *Inner = dyn_cast<ICmpInst>(Z->getOperand(0))) {
if (Inner->getPredicate() == ICmpInst::ICMP_ULE &&
Inner->getOperand(0) == Op0 && Inner->hasOneUse()) {
Value *Bnd = Inner->getOperand(1);
bool IsBoolExt = isa<ZExtInst>(Bnd) &&
cast<ZExtInst>(Bnd)->getSrcTy()->isIntegerTy(1);
if (match(Bnd, m_ZeroInt()) || match(Bnd, m_One()) || IsBoolExt) {
Value *NewCmp = Builder.CreateICmpULE(Op0, Bnd, I.getName());
return replaceInstUsesWith(I, NewCmp);
}
}
}
}
}
}

// Comparing -val or val with non-zero is the same as just comparing val
// ie, abs(val) != 0 -> val != 0
if (I.getPredicate() == ICmpInst::ICMP_NE && match(Op1, m_Zero())) {
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35 changes: 35 additions & 0 deletions llvm/test/Transforms/InstCombine/icmp.ll
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Expand Up @@ -5400,3 +5400,38 @@ define i1 @icmp_samesign_logical_or(i32 %In) {
%V = select i1 %c1, i1 true, i1 %c2
ret i1 %V
}

;===----------------------------------------------------------------------===;
; Test folding of nested `icmp ule` when inner RHS is boolean-like
;===----------------------------------------------------------------------===;

define i32 @fold_nested_ule_bool(i32 %u, i1 %b) {
; CHECK-LABEL: @fold_nested_ule_bool(
; CHECK-NEXT: [[CONV:%.*]] = zext i1 [[B:%.*]] to i32
; CHECK-NEXT: [[CMP:%.*]] = icmp ule i32 [[U:%.*]], [[CONV]]
; CHECK-NEXT: [[CONV1:%.*]] = zext i1 [[CMP]] to i32
; CHECK-NEXT: ret i32 [[CONV1]]
;
%conv = zext i1 %b to i32
%cmp = icmp ule i32 %u, %conv
%conv1 = zext i1 %cmp to i32
%cmp2 = icmp ule i32 %u, %conv1
%conv3 = zext i1 %cmp2 to i32
ret i32 %conv3
}

define i32 @no_fold_nested_ule(i32 %u, i32 %b) {
; CHECK-LABEL: @no_fold_nested_ule(
; CHECK-NEXT: [[CMP1:%.*]] = icmp ule i32 [[U:%.*]], [[B:%.*]]
; CHECK-NEXT: [[Z1:%.*]] = zext i1 [[CMP1]] to i32
; CHECK-NEXT: [[CMP2:%.*]] = icmp ule i32 [[U]], [[Z1]]
; CHECK-NEXT: [[CONV:%.*]] = zext i1 [[CMP2]] to i32
; CHECK-NEXT: ret i32 [[CONV]]
;
%cmp1 = icmp ule i32 %u, %b
%z1 = zext i1 %cmp1 to i32
%cmp2 = icmp ule i32 %u, %z1
%conv = zext i1 %cmp2 to i32
ret i32 %conv
}

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