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[InstrCombin] fold icmp with add/sub instructions having the same operands
Closes#143211
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‎llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

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Original file line numberDiff line numberDiff line change
@@ -7728,6 +7728,47 @@ Instruction *InstCombinerImpl::visitICmpInst(ICmpInst &I) {
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}
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}
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// In case of a comparison with add/sub instructions having the same operands,
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// check whether cmp operands have same signed no wrap. If so, just compare
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// the sub's second operand and zero.
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// For example:
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// %tmp1 = sub nsw i8 %x, %y
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// %tmp2 = add nsw i8 %x, %y
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// %cmp = icmp sgt i8 %tmp1, %tmp2
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// transform this into:
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// %cmp = icmp slt i32 %y, 0
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// This handles similar cases to transform.
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{
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Value *A, *B;
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auto *I0 = dyn_cast<OverflowingBinaryOperator>(Op0);
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auto *I1 = dyn_cast<OverflowingBinaryOperator>(Op1);
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bool UnsignedCmp = ICmpInst::isUnsigned(Pred);
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bool SignedCmp = ICmpInst::isSigned(Pred);
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bool EqualityCmp = ICmpInst::isEquality(Pred);
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if (I0 && I1) {
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bool I0NUW = I0->hasNoUnsignedWrap();
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bool I1NUW = I1->hasNoUnsignedWrap();
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bool I0NSW = I0->hasNoSignedWrap();
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bool I1NSW = I1->hasNoSignedWrap();
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bool Swaped = false;
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if ((UnsignedCmp && I0NUW && I1NUW) || (SignedCmp && I0NSW && I1NSW) ||
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(EqualityCmp && I0NUW && I0NSW && I1NUW && I1NSW)) {
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if (I0->getOpcode() == Instruction::Add &&
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I1->getOpcode() == Instruction::Sub) {
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std::swap(I0, I1);
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Swaped = true;
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}
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if (match(I0, m_Sub(m_Value(A), m_Value(B))) &&
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(match(I1, m_Add(m_Specific(A), m_Specific(B))) ||
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match(I1, m_Add(m_Specific(B), m_Specific(A))))) {
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return new ICmpInst(Swaped ? Pred : I.getSwappedPredicate(), B,
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ConstantInt::get(Op0->getType(), 0));
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}
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}
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}
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}
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// Try to optimize equality comparisons against alloca-based pointers.
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if (Op0->getType()->isPointerTy() && I.isEquality()) {
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assert(Op1->getType()->isPointerTy() &&

‎llvm/test/Transforms/InstCombine/icmp-subadd.ll

Lines changed: 114 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,114 @@
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
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; RUN: opt < %s -passes=instcombine -S | FileCheck %s
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define i1 @test-same-operands-sub-add-nsw-icmp-sgt(i8 %a, i8 %b) {
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; CHECK-LABEL: define i1 @test-same-operands-sub-add-nsw-icmp-sgt(
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; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
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; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[B]], 0
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; CHECK-NEXT: ret i1 [[CMP]]
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;
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%sub = sub nsw i8 %a, %b
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%add = add nsw i8 %a, %b
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%cmp = icmp sgt i8 %sub, %add
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ret i1 %cmp
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}
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define i1 @test-same-operands-sub-add-nsw-icmp-slt(i8 %a, i8 %b) {
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; CHECK-LABEL: define i1 @test-same-operands-sub-add-nsw-icmp-slt(
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; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
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; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[B]], 0
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; CHECK-NEXT: ret i1 [[CMP]]
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;
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%sub = sub nsw i8 %a, %b
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%add = add nsw i8 %a, %b
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%cmp = icmp slt i8 %sub, %add
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ret i1 %cmp
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}
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define i1 @test-same-operands-sub-add-nsw-icmp-sle(i8 %a, i8 %b) {
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; CHECK-LABEL: define i1 @test-same-operands-sub-add-nsw-icmp-sle(
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; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
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; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[B]], -1
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; CHECK-NEXT: ret i1 [[CMP]]
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;
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%sub = sub nsw i8 %a, %b
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%add = add nsw i8 %a, %b
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%cmp = icmp sle i8 %sub, %add
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ret i1 %cmp
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}
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define i1 @test-same-operands-sub-add-nsw-nuw-icmp-eq(i8 %a, i8 %b) {
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; CHECK-LABEL: define i1 @test-same-operands-sub-add-nsw-nuw-icmp-eq(
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; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
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; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[B]], 0
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; CHECK-NEXT: ret i1 [[CMP]]
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;
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%sub = sub nuw nsw i8 %a, %b
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%add = add nuw nsw i8 %a, %b
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%cmp = icmp eq i8 %sub, %add
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ret i1 %cmp
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}
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; Check not folded
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define i1 @test-same-operands-sub-add-nsw-icmp-eq(i8 %a, i8 %b) {
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; CHECK-LABEL: define i1 @test-same-operands-sub-add-nsw-icmp-eq(
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; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
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; CHECK-NEXT: [[SUB:%.*]] = sub nsw i8 [[A]], [[B]]
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; CHECK-NEXT: [[ADD:%.*]] = add nsw i8 [[A]], [[B]]
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; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[SUB]], [[ADD]]
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; CHECK-NEXT: ret i1 [[CMP]]
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;
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%sub = sub nsw i8 %a, %b
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%add = add nsw i8 %a, %b
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%cmp = icmp eq i8 %sub, %add
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ret i1 %cmp
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}
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define i1 @test-add-sub-nsw-icmp-sgt(i8 %a, i8 %b) {
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; CHECK-LABEL: define i1 @test-add-sub-nsw-icmp-sgt(
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; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
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; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[B]], 0
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; CHECK-NEXT: ret i1 [[CMP]]
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;
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%sub = sub nsw i8 %a, %b
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%add = add nsw i8 %a, %b
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%cmp = icmp sgt i8 %add, %sub
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ret i1 %cmp
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}
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define i1 @test-add-sub-nuw-icmp-uge(i8 %a, i8 %b) {
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; CHECK-LABEL: define i1 @test-add-sub-nuw-icmp-uge(
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; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
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; CHECK-NEXT: ret i1 true
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;
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%sub = sub nuw i8 %a, %b
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%add = add nuw i8 %a, %b
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%cmp = icmp uge i8 %add, %sub
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ret i1 %cmp
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}
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; Check not folded
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define i1 @test-add-sub-nuw-icmp-sge(i8 %a, i8 %b) {
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; CHECK-LABEL: define i1 @test-add-sub-nuw-icmp-sge(
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; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
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; CHECK-NEXT: [[SUB:%.*]] = sub nuw i8 [[A]], [[B]]
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; CHECK-NEXT: [[ADD:%.*]] = add nuw i8 [[A]], [[B]]
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; CHECK-NEXT: [[CMP:%.*]] = icmp sge i8 [[ADD]], [[SUB]]
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; CHECK-NEXT: ret i1 [[CMP]]
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;
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%sub = sub nuw i8 %a, %b
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%add = add nuw i8 %a, %b
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%cmp = icmp sge i8 %add, %sub
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ret i1 %cmp
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}
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define i1 @test-add-swap-sub-nuw-icmp-uge(i8 %a, i8 %b) {
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; CHECK-LABEL: define i1 @test-add-swap-sub-nuw-icmp-uge(
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; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
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; CHECK-NEXT: ret i1 true
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;
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%sub = sub nuw i8 %a, %b
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%add = add nuw i8 %b, %a
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%cmp = icmp uge i8 %add, %sub
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ret i1 %cmp
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}

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