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[InstCombine] Add a >= b - a<=b to scmp and ucmp folds #164009

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[InstCombine] Add a >= b - a<=b to scmp and ucmp folds #164009

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46142b5
Pre-commit test (NFC)
AZero13 Oct 17, 2025
c73157e
[InstCombine] Add a >= b - a<=b to scmp and ucmp folds
AZero13 Oct 17, 2025
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24 changes: 17 additions & 7 deletions llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1660,6 +1660,7 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
return replaceInstUsesWith(I, Constant::getNullValue(I.getType()));

// sext(A < B) + zext(A > B) => ucmp/scmp(A, B)
// sext(A <= B) + zext(A >= B) => ucmp/scmp(A, B)
CmpPredicate LTPred, GTPred;
if (match(&I,
m_c_Add(m_SExt(m_c_ICmp(LTPred, m_Value(A), m_Value(B))),
Expand All @@ -1670,13 +1671,22 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
std::swap(A, B);
}

if (ICmpInst::isLT(LTPred) && ICmpInst::isGT(GTPred) &&
ICmpInst::isSigned(LTPred) == ICmpInst::isSigned(GTPred))
return replaceInstUsesWith(
I, Builder.CreateIntrinsic(
Ty,
ICmpInst::isSigned(LTPred) ? Intrinsic::scmp : Intrinsic::ucmp,
{A, B}));
if (ICmpInst::isSigned(LTPred) == ICmpInst::isSigned(GTPred)) {
Intrinsic::ID IID =
ICmpInst::isSigned(LTPred) ? Intrinsic::scmp : Intrinsic::ucmp;

// Handle strict inequalities: sext(A < B) + zext(A > B) => scmp/ucmp(A,
// B)
if (ICmpInst::isLT(LTPred) && ICmpInst::isGT(GTPred)) {
return replaceInstUsesWith(I, Builder.CreateIntrinsic(Ty, IID, {A, B}));
}

// Handle non-strict inequalities: sext(A <= B) + zext(A >= B) =>
// scmp/ucmp(A, B)
if (ICmpInst::isLE(LTPred) && ICmpInst::isGE(GTPred)) {
return replaceInstUsesWith(I, Builder.CreateIntrinsic(Ty, IID, {A, B}));
}
}
}

// A+B --> A|B iff A and B have no bits set in common.
Expand Down
174 changes: 174 additions & 0 deletions llvm/test/Transforms/InstCombine/sext-a-lt-b-plus-zext-a-gt-b-to-uscmp.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -182,3 +182,177 @@ define i8 @signed_add_neg5(i32 %a, i32 %b) {
%r = add i8 %lt8, %gt8
ret i8 %r
}

; sext(A s<= B) + zext(A s>= B) => scmp(A, B)
define i8 @signed_add_ge_le(i32 %a, i32 %b) {
; CHECK-LABEL: define i8 @signed_add_ge_le(
; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
; CHECK-NEXT: [[R:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[A]], i32 [[B]])
; CHECK-NEXT: ret i8 [[R]]
;
%le = icmp sle i32 %a, %b
%le8 = sext i1 %le to i8
%ge = icmp sge i32 %a, %b
%ge8 = zext i1 %ge to i8
%r = add i8 %le8, %ge8
ret i8 %r
}

; Unsigned version of >= and <=
define i8 @unsigned_add_ge_le(i32 %a, i32 %b) {
; CHECK-LABEL: define i8 @unsigned_add_ge_le(
; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
; CHECK-NEXT: [[R:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[A]], i32 [[B]])
; CHECK-NEXT: ret i8 [[R]]
;
%le = icmp ule i32 %a, %b
%le8 = sext i1 %le to i8
%ge = icmp uge i32 %a, %b
%ge8 = zext i1 %ge to i8
%r = add i8 %le8, %ge8
ret i8 %r
}

; zext(A s>= B) - zext(A s<= B) => scmp(A, B)
define i8 @signed_sub_ge_le(i32 %a, i32 %b) {
; CHECK-LABEL: define i8 @signed_sub_ge_le(
; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
; CHECK-NEXT: [[R:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[A]], i32 [[B]])
; CHECK-NEXT: ret i8 [[R]]
;
%le = icmp sle i32 %a, %b
%le8 = zext i1 %le to i8
%ge = icmp sge i32 %a, %b
%ge8 = zext i1 %ge to i8
%r = sub i8 %ge8, %le8
ret i8 %r
}

; Unsigned version of >= and <= subtraction
define i8 @unsigned_sub_ge_le(i32 %a, i32 %b) {
; CHECK-LABEL: define i8 @unsigned_sub_ge_le(
; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
; CHECK-NEXT: [[R:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[A]], i32 [[B]])
; CHECK-NEXT: ret i8 [[R]]
;
%le = icmp ule i32 %a, %b
%le8 = zext i1 %le to i8
%ge = icmp uge i32 %a, %b
%ge8 = zext i1 %ge to i8
%r = sub i8 %ge8, %le8
ret i8 %r
}

; Constant canonicalization: (a > 4) - (a < 6) => scmp(a, 5)
define i8 @signed_sub_const_canonicalization(i32 %a) {
; CHECK-LABEL: define i8 @signed_sub_const_canonicalization(
; CHECK-SAME: i32 [[A:%.*]]) {
; CHECK-NEXT: [[LT:%.*]] = icmp slt i32 [[A]], 6
; CHECK-NEXT: [[LT8_NEG:%.*]] = sext i1 [[LT]] to i8
; CHECK-NEXT: [[GT:%.*]] = icmp sgt i32 [[A]], 4
; CHECK-NEXT: [[GT8:%.*]] = zext i1 [[GT]] to i8
; CHECK-NEXT: [[R:%.*]] = add nsw i8 [[LT8_NEG]], [[GT8]]
; CHECK-NEXT: ret i8 [[R]]
;
%lt = icmp slt i32 %a, 6
%lt8 = zext i1 %lt to i8
%gt = icmp sgt i32 %a, 4
%gt8 = zext i1 %gt to i8
%r = sub i8 %gt8, %lt8
ret i8 %r
}

; Constant canonicalization: (a >= 5) - (a <= 5) => scmp(a, 5)
define i8 @signed_sub_const_canonicalization2(i32 %a) {
; CHECK-LABEL: define i8 @signed_sub_const_canonicalization2(
; CHECK-SAME: i32 [[A:%.*]]) {
; CHECK-NEXT: [[LE:%.*]] = icmp slt i32 [[A]], 6
; CHECK-NEXT: [[LE8_NEG:%.*]] = sext i1 [[LE]] to i8
; CHECK-NEXT: [[GE:%.*]] = icmp sgt i32 [[A]], 4
; CHECK-NEXT: [[GE8:%.*]] = zext i1 [[GE]] to i8
; CHECK-NEXT: [[R:%.*]] = add nsw i8 [[LE8_NEG]], [[GE8]]
; CHECK-NEXT: ret i8 [[R]]
;
%le = icmp sle i32 %a, 5
%le8 = zext i1 %le to i8
%ge = icmp sge i32 %a, 5
%ge8 = zext i1 %ge to i8
%r = sub i8 %ge8, %le8
ret i8 %r
}

; Unsigned constant canonicalization: (a > 4) - (a < 6) => ucmp(a, 5)
define i8 @unsigned_sub_const_canonicalization(i32 %a) {
; CHECK-LABEL: define i8 @unsigned_sub_const_canonicalization(
; CHECK-SAME: i32 [[A:%.*]]) {
; CHECK-NEXT: [[LT:%.*]] = icmp ult i32 [[A]], 6
; CHECK-NEXT: [[LT8_NEG:%.*]] = sext i1 [[LT]] to i8
; CHECK-NEXT: [[GT:%.*]] = icmp ugt i32 [[A]], 4
; CHECK-NEXT: [[GT8:%.*]] = zext i1 [[GT]] to i8
; CHECK-NEXT: [[R:%.*]] = add nsw i8 [[LT8_NEG]], [[GT8]]
; CHECK-NEXT: ret i8 [[R]]
;
%lt = icmp ult i32 %a, 6
%lt8 = zext i1 %lt to i8
%gt = icmp ugt i32 %a, 4
%gt8 = zext i1 %gt to i8
%r = sub i8 %gt8, %lt8
ret i8 %r
}

; Constant canonicalization with >= and <=: (a >= 5) - (a <= 5) => scmp(a, 5)
define i8 @signed_sub_const_canonicalization_ge_le(i32 %a) {
; CHECK-LABEL: define i8 @signed_sub_const_canonicalization_ge_le(
; CHECK-SAME: i32 [[A:%.*]]) {
; CHECK-NEXT: [[LE:%.*]] = icmp slt i32 [[A]], 6
; CHECK-NEXT: [[LE8_NEG:%.*]] = sext i1 [[LE]] to i8
; CHECK-NEXT: [[GE:%.*]] = icmp sgt i32 [[A]], 4
; CHECK-NEXT: [[GE8:%.*]] = zext i1 [[GE]] to i8
; CHECK-NEXT: [[R:%.*]] = add nsw i8 [[LE8_NEG]], [[GE8]]
; CHECK-NEXT: ret i8 [[R]]
;
%le = icmp sle i32 %a, 5
%le8 = zext i1 %le to i8
%ge = icmp sge i32 %a, 5
%ge8 = zext i1 %ge to i8
%r = sub i8 %ge8, %le8
ret i8 %r
}

; More constant canonicalization: (a > 2) - (a < 4) => scmp(a, 3)
define i8 @signed_sub_const_canonicalization3(i32 %a) {
; CHECK-LABEL: define i8 @signed_sub_const_canonicalization3(
; CHECK-SAME: i32 [[A:%.*]]) {
; CHECK-NEXT: [[LT:%.*]] = icmp slt i32 [[A]], 4
; CHECK-NEXT: [[LT8_NEG:%.*]] = sext i1 [[LT]] to i8
; CHECK-NEXT: [[GT:%.*]] = icmp sgt i32 [[A]], 2
; CHECK-NEXT: [[GT8:%.*]] = zext i1 [[GT]] to i8
; CHECK-NEXT: [[R:%.*]] = add nsw i8 [[LT8_NEG]], [[GT8]]
; CHECK-NEXT: ret i8 [[R]]
;
%lt = icmp slt i32 %a, 4
%lt8 = zext i1 %lt to i8
%gt = icmp sgt i32 %a, 2
%gt8 = zext i1 %gt to i8
%r = sub i8 %gt8, %lt8
ret i8 %r
}

; Negative test: constants that are more than one apart - should NOT canonicalize
define i8 @signed_sub_const_no_canonicalization(i32 %a) {
; CHECK-LABEL: define i8 @signed_sub_const_no_canonicalization(
; CHECK-SAME: i32 [[A:%.*]]) {
; CHECK-NEXT: [[LT:%.*]] = icmp slt i32 [[A]], 10
; CHECK-NEXT: [[LT8_NEG:%.*]] = sext i1 [[LT]] to i8
; CHECK-NEXT: [[GT:%.*]] = icmp sgt i32 [[A]], 4
; CHECK-NEXT: [[GT8:%.*]] = zext i1 [[GT]] to i8
; CHECK-NEXT: [[R:%.*]] = add nsw i8 [[LT8_NEG]], [[GT8]]
; CHECK-NEXT: ret i8 [[R]]
;
%lt = icmp slt i32 %a, 10
%lt8 = zext i1 %lt to i8
%gt = icmp sgt i32 %a, 4
%gt8 = zext i1 %gt to i8
%r = sub i8 %gt8, %lt8
ret i8 %r
}