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Sep 14, 2025
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[InstCombine] Fold select pattern with sub and negation to abs intrinsic #156246

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AZero13 Aug 31, 2025
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[InstCombine] Fold select pattern with sub and negation to abs intrinsic
AZero13 Aug 31, 2025
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Fix issues
AZero13 Sep 10, 2025
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39 changes: 39 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1153,6 +1153,45 @@ static Value *foldAbsDiff(ICmpInst *Cmp, Value *TVal, Value *FVal,
return Builder.CreateBinaryIntrinsic(Intrinsic::abs, TI, Builder.getTrue());
}

// Match: (A > B) ? (A - B) : (0 - (A - B)) --> abs(A - B)
// Also handles commuted cases like (B < A), (A >= B), (B <= A) after
// normalization
if (Pred == CmpInst::ICMP_SGT &&
match(TI, m_NSWSub(m_Specific(A), m_Specific(B))) &&
match(FI, m_Neg(m_Specific(TI)))) {
return Builder.CreateBinaryIntrinsic(Intrinsic::abs, TI,
Builder.getFalse());
}

// Match: (A < B) ? (0 - (A - B)) : (A - B) --> abs(A - B)
// This handles cases like (A <= B) after normalization
if (Pred == CmpInst::ICMP_SLT &&
match(TI, m_Neg(m_NSWSub(m_Specific(A), m_Specific(B)))) &&
match(FI, m_NSWSub(m_Specific(A), m_Specific(B)))) {
return Builder.CreateBinaryIntrinsic(Intrinsic::abs, FI,
Builder.getFalse());
}

// Match: (A > B) ? (0 - (B - A)) : (B - A) --> abs(B - A)
// This handles cases like (B <= A) after normalization where the subtraction
// operands are swapped
if (Pred == CmpInst::ICMP_SGT &&
match(TI, m_Neg(m_NSWSub(m_Specific(B), m_Specific(A)))) &&
match(FI, m_NSWSub(m_Specific(B), m_Specific(A)))) {
return Builder.CreateBinaryIntrinsic(Intrinsic::abs, FI,
Builder.getFalse());
}

// Match: (A < B) ? (B - A) : (0 - (B - A)) --> abs(B - A)
// This handles cases where comparison operands are swapped relative to
// subtraction
if (Pred == CmpInst::ICMP_SLT &&
match(TI, m_NSWSub(m_Specific(B), m_Specific(A))) &&
match(FI, m_Neg(m_Specific(TI)))) {
return Builder.CreateBinaryIntrinsic(Intrinsic::abs, TI,
Builder.getFalse());
}

return nullptr;
}

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137 changes: 137 additions & 0 deletions llvm/test/Transforms/InstCombine/abs-intrinsic.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -859,4 +859,141 @@ define i32 @abs_range_metadata(i32 %x) {
%b = and i32 %a, 15
ret i32 %b
}

!1 = !{i32 0, i32 16}

define i32 @abs_diff(i32 %x, i32 %y) {
; CHECK-LABEL: @abs_diff(
; CHECK-NEXT: [[SUB:%.*]] = sub nsw i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.abs.i32(i32 [[SUB]], i1 false)
; CHECK-NEXT: ret i32 [[COND]]
;
%sub = sub nsw i32 %x, %y
%cmp = icmp sgt i32 %x, %y
%sub1 = sub i32 0, %sub
%cond = select i1 %cmp, i32 %sub, i32 %sub1
ret i32 %cond
}

define i32 @abs_diff_neg_no_nsw_neg(i32 %x, i32 %y) {
; CHECK-LABEL: @abs_diff_neg_no_nsw_neg(
; CHECK-NEXT: [[SUB:%.*]] = sub i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i32 [[X]], [[Y]]
; CHECK-NEXT: [[SUB1:%.*]] = sub i32 0, [[SUB]]
; CHECK-NEXT: [[COND:%.*]] = select i1 [[CMP]], i32 [[SUB]], i32 [[SUB1]]
; CHECK-NEXT: ret i32 [[COND]]
;
%sub = sub i32 %x, %y
%cmp = icmp sgt i32 %x, %y
%sub1 = sub i32 0, %sub
%cond = select i1 %cmp, i32 %sub, i32 %sub1
ret i32 %cond
}

define i32 @abs_diff_neg(i32 %x, i32 %y) {
; CHECK-LABEL: @abs_diff_neg(
; CHECK-NEXT: [[SUB:%.*]] = sub nsw i32 [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i32 [[X]], [[Y]]
; CHECK-NEXT: [[SUB1:%.*]] = sub i32 0, [[SUB]]
; CHECK-NEXT: [[COND:%.*]] = select i1 [[CMP]], i32 [[SUB]], i32 [[SUB1]]
; CHECK-NEXT: ret i32 [[COND]]
;
%sub = sub nsw i32 %y, %x
%cmp = icmp sgt i32 %x, %y
%sub1 = sub i32 0, %sub
%cond = select i1 %cmp, i32 %sub, i32 %sub1
ret i32 %cond
}

define i32 @abs_diff_neg_no_nsw(i32 %x, i32 %y) {
; CHECK-LABEL: @abs_diff_neg_no_nsw(
; CHECK-NEXT: [[SUB:%.*]] = sub i32 [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i32 [[X]], [[Y]]
; CHECK-NEXT: [[SUB1:%.*]] = sub i32 0, [[SUB]]
; CHECK-NEXT: [[COND:%.*]] = select i1 [[CMP]], i32 [[SUB]], i32 [[SUB1]]
; CHECK-NEXT: ret i32 [[COND]]
;
%sub = sub i32 %y, %x
%cmp = icmp sgt i32 %x, %y
%sub1 = sub i32 0, %sub
%cond = select i1 %cmp, i32 %sub, i32 %sub1
ret i32 %cond
}

define i32 @abs_diff_ge(i32 %x, i32 %y) {
; CHECK-LABEL: @abs_diff_ge(
; CHECK-NEXT: [[SUB:%.*]] = sub nsw i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.abs.i32(i32 [[SUB]], i1 false)
; CHECK-NEXT: ret i32 [[COND]]
;
%sub = sub nsw i32 %x, %y
%cmp = icmp sge i32 %x, %y
%sub1 = sub i32 0, %sub
%cond = select i1 %cmp, i32 %sub, i32 %sub1
ret i32 %cond
}

define i32 @abs_diff_slt_commute(i32 %x, i32 %y) {
; CHECK-LABEL: @abs_diff_slt_commute(
; CHECK-NEXT: [[SUB:%.*]] = sub nsw i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.abs.i32(i32 [[SUB]], i1 false)
; CHECK-NEXT: ret i32 [[COND]]
;
%sub = sub nsw i32 %x, %y
%cmp = icmp slt i32 %y, %x
%sub1 = sub i32 0, %sub
%cond = select i1 %cmp, i32 %sub, i32 %sub1
ret i32 %cond
}

define i32 @abs_diff_sge_same(i32 %x, i32 %y) {
; CHECK-LABEL: @abs_diff_sge_same(
; CHECK-NEXT: [[SUB:%.*]] = sub nsw i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.abs.i32(i32 [[SUB]], i1 false)
; CHECK-NEXT: ret i32 [[COND]]
;
%sub = sub nsw i32 %x, %y
%cmp = icmp sge i32 %x, %y
%sub1 = sub i32 0, %sub
%cond = select i1 %cmp, i32 %sub, i32 %sub1
ret i32 %cond
}

define i32 @abs_diff_sle_inverted(i32 %x, i32 %y) {
; CHECK-LABEL: @abs_diff_sle_inverted(
; CHECK-NEXT: [[SUB:%.*]] = sub nsw i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.abs.i32(i32 [[SUB]], i1 false)
; CHECK-NEXT: ret i32 [[COND]]
;
%sub = sub nsw i32 %x, %y
%cmp = icmp sle i32 %x, %y
%sub1 = sub i32 0, %sub
%cond = select i1 %cmp, i32 %sub1, i32 %sub
ret i32 %cond
}

define i32 @abs_diff_sle_commute(i32 %x, i32 %y) {
; CHECK-LABEL: @abs_diff_sle_commute(
; CHECK-NEXT: [[SUB:%.*]] = sub nsw i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.abs.i32(i32 [[SUB]], i1 false)
; CHECK-NEXT: ret i32 [[COND]]
;
%sub = sub nsw i32 %x, %y
%cmp = icmp sle i32 %y, %x
%sub1 = sub i32 0, %sub
%cond = select i1 %cmp, i32 %sub, i32 %sub1
ret i32 %cond
}

define i8 @abs_diff_sle_y_x(i8 %x, i8 %y) {
; CHECK-LABEL: @abs_diff_sle_y_x(
; CHECK-NEXT: [[SUB:%.*]] = sub nsw i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[COND:%.*]] = call i8 @llvm.abs.i8(i8 [[SUB]], i1 false)
; CHECK-NEXT: ret i8 [[COND]]
;
%sub = sub nsw i8 %x, %y
%cmp = icmp sle i8 %y, %x
%sub1 = sub i8 0, %sub
%cond = select i1 %cmp, i8 %sub, i8 %sub1
ret i8 %cond
}