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[InstSimplify] Simplify uadd.sat(X, Y) u>= X + Y and usub.sat(X, Y) u<= X, Y (#104698)
These patterns are found in harfbuzz/typst. Alive2: https://alive2.llvm.org/ce/z/cxyjYV
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‎llvm/lib/Analysis/InstructionSimplify.cpp

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Original file line numberDiff line numberDiff line change
@@ -3718,6 +3718,14 @@ static Value *simplifyICmpWithIntrinsicOnLHS(CmpInst::Predicate Pred,
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if (Pred == ICmpInst::ICMP_ULT)
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return ConstantInt::getFalse(getCompareTy(II));
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}
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// uadd.sat(X, Y) uge X + Y
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if (match(RHS, m_c_Add(m_Specific(II->getArgOperand(0)),
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m_Specific(II->getArgOperand(1))))) {
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if (Pred == ICmpInst::ICMP_UGE)
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return ConstantInt::getTrue(getCompareTy(II));
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if (Pred == ICmpInst::ICMP_ULT)
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return ConstantInt::getFalse(getCompareTy(II));
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}
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return nullptr;
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case Intrinsic::usub_sat:
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// usub.sat(X, Y) ule X
@@ -3727,6 +3735,14 @@ static Value *simplifyICmpWithIntrinsicOnLHS(CmpInst::Predicate Pred,
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if (Pred == ICmpInst::ICMP_UGT)
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return ConstantInt::getFalse(getCompareTy(II));
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}
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// usub.sat(X, Y) ule X - Y
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if (match(RHS, m_Sub(m_Specific(II->getArgOperand(0)),
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m_Specific(II->getArgOperand(1))))) {
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if (Pred == ICmpInst::ICMP_ULE)
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return ConstantInt::getTrue(getCompareTy(II));
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if (Pred == ICmpInst::ICMP_UGT)
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return ConstantInt::getFalse(getCompareTy(II));
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}
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return nullptr;
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default:
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return nullptr;

‎llvm/test/Transforms/InstSimplify/saturating-add-sub.ll

Lines changed: 116 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -932,3 +932,119 @@ define i1 @usub_uge_fail(i8 %x, i8 %y) {
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%cmp = icmp uge i8 %sat, %x
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ret i1 %cmp
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}
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define i1 @icmp_ult_uaddsat_add(i32 %x, i32 %y) {
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; CHECK-LABEL: @icmp_ult_uaddsat_add(
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; CHECK-NEXT: ret i1 false
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;
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%uaddsat = call i32 @llvm.uadd.sat.i32(i32 %x, i32 %y)
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%add = add i32 %x, %y
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%cmp = icmp ult i32 %uaddsat, %add
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ret i1 %cmp
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}
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define i1 @icmp_uge_uaddsat_add(i32 %x, i32 %y) {
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; CHECK-LABEL: @icmp_uge_uaddsat_add(
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; CHECK-NEXT: ret i1 true
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;
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%uaddsat = call i32 @llvm.uadd.sat.i32(i32 %x, i32 %y)
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%add = add i32 %x, %y
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%cmp = icmp uge i32 %uaddsat, %add
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ret i1 %cmp
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}
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define i1 @icmp_ugt_uaddsat_add_commuted1(i32 %x, i32 %y) {
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; CHECK-LABEL: @icmp_ugt_uaddsat_add_commuted1(
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; CHECK-NEXT: ret i1 false
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;
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%uaddsat = call i32 @llvm.uadd.sat.i32(i32 %x, i32 %y)
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%add = add i32 %x, %y
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%cmp = icmp ugt i32 %add, %uaddsat
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ret i1 %cmp
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}
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define i1 @icmp_ult_uaddsat_add_commuted2(i32 %x, i32 %y) {
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; CHECK-LABEL: @icmp_ult_uaddsat_add_commuted2(
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; CHECK-NEXT: ret i1 false
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;
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%xx = mul i32 %x, 998244353
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%yy = mul i32 %y, 998244353
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%uaddsat = call i32 @llvm.uadd.sat.i32(i32 %xx, i32 %yy)
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%add = add i32 %yy, %xx ; thwart complexity-based canonicalization
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%cmp = icmp ult i32 %uaddsat, %add
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ret i1 %cmp
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}
977+
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define i1 @icmp_ule_usubsat_sub(i32 %x, i32 %y) {
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; CHECK-LABEL: @icmp_ule_usubsat_sub(
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; CHECK-NEXT: ret i1 true
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;
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%usubsat = call i32 @llvm.usub.sat.i32(i32 %x, i32 %y)
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%add = sub i32 %x, %y
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%cmp = icmp ule i32 %usubsat, %add
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ret i1 %cmp
986+
}
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define i1 @icmp_ugt_usubsat_sub(i32 %x, i32 %y) {
989+
; CHECK-LABEL: @icmp_ugt_usubsat_sub(
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; CHECK-NEXT: ret i1 false
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;
992+
%usubsat = call i32 @llvm.usub.sat.i32(i32 %x, i32 %y)
993+
%add = sub i32 %x, %y
994+
%cmp = icmp ugt i32 %usubsat, %add
995+
ret i1 %cmp
996+
}
997+
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; Negative tests
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define i1 @icmp_ult_uaddsat_add_mismatch(i32 %x, i32 %y, i32 %z) {
1001+
; CHECK-LABEL: @icmp_ult_uaddsat_add_mismatch(
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; CHECK-NEXT: [[UADDSAT:%.*]] = call i32 @llvm.uadd.sat.i32(i32 [[X:%.*]], i32 [[Z:%.*]])
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; CHECK-NEXT: [[ADD:%.*]] = add i32 [[X]], [[Y:%.*]]
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; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[UADDSAT]], [[ADD]]
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; CHECK-NEXT: ret i1 [[CMP]]
1006+
;
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%uaddsat = call i32 @llvm.uadd.sat.i32(i32 %x, i32 %z)
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%add = add i32 %x, %y
1009+
%cmp = icmp ult i32 %uaddsat, %add
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ret i1 %cmp
1011+
}
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1013+
define i1 @icmp_ult_uaddsat_add_wrong_pred(i32 %x, i32 %y) {
1014+
; CHECK-LABEL: @icmp_ult_uaddsat_add_wrong_pred(
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; CHECK-NEXT: [[UADDSAT:%.*]] = call i32 @llvm.uadd.sat.i32(i32 [[X:%.*]], i32 [[Y:%.*]])
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; CHECK-NEXT: [[ADD:%.*]] = add i32 [[X]], [[Y]]
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; CHECK-NEXT: [[CMP:%.*]] = icmp ule i32 [[UADDSAT]], [[ADD]]
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; CHECK-NEXT: ret i1 [[CMP]]
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;
1020+
%uaddsat = call i32 @llvm.uadd.sat.i32(i32 %x, i32 %y)
1021+
%add = add i32 %x, %y
1022+
%cmp = icmp ule i32 %uaddsat, %add
1023+
ret i1 %cmp
1024+
}
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1026+
define i1 @icmp_ult_uaddsat_add_wrong_op(i32 %x, i32 %y) {
1027+
; CHECK-LABEL: @icmp_ult_uaddsat_add_wrong_op(
1028+
; CHECK-NEXT: [[UADDSAT:%.*]] = call i32 @llvm.uadd.sat.i32(i32 [[X:%.*]], i32 [[Y:%.*]])
1029+
; CHECK-NEXT: [[SUB:%.*]] = sub i32 [[X]], [[Y]]
1030+
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[UADDSAT]], [[SUB]]
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; CHECK-NEXT: ret i1 [[CMP]]
1032+
;
1033+
%uaddsat = call i32 @llvm.uadd.sat.i32(i32 %x, i32 %y)
1034+
%sub = sub i32 %x, %y
1035+
%cmp = icmp ult i32 %uaddsat, %sub
1036+
ret i1 %cmp
1037+
}
1038+
1039+
define i1 @icmp_ule_usubsat_sub_commuted(i32 %x, i32 %y) {
1040+
; CHECK-LABEL: @icmp_ule_usubsat_sub_commuted(
1041+
; CHECK-NEXT: [[USUBSAT:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[X:%.*]], i32 [[Y:%.*]])
1042+
; CHECK-NEXT: [[ADD:%.*]] = sub i32 [[Y]], [[X]]
1043+
; CHECK-NEXT: [[CMP:%.*]] = icmp ule i32 [[USUBSAT]], [[ADD]]
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; CHECK-NEXT: ret i1 [[CMP]]
1045+
;
1046+
%usubsat = call i32 @llvm.usub.sat.i32(i32 %x, i32 %y)
1047+
%add = sub i32 %y, %x
1048+
%cmp = icmp ule i32 %usubsat, %add
1049+
ret i1 %cmp
1050+
}

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