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[InstCombine][profcheck] Preserve profile with negated select conditionals #164342

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Oct 21, 2025
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[InstCombine][profcheck] Preserve profile with negated select conditionals #164342

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5a8f635
[InstCombine][profcheck] Preserve profile with negated select conditi…
alanzhao1 Oct 20, 2025
1640181
add the experiment flag
alanzhao1 Oct 21, 2025
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30 changes: 24 additions & 6 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3455,27 +3455,45 @@ Instruction *InstCombinerImpl::foldSelectOfBools(SelectInst &SI) {
// select a, false, b -> select !a, b, false
if (match(TrueVal, m_Specific(Zero))) {
Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
return SelectInst::Create(NotCond, FalseVal, Zero);
Instruction *MDFrom = ProfcheckDisableMetadataFixes ? nullptr : &SI;
SelectInst *NewSI =
SelectInst::Create(NotCond, FalseVal, Zero, "", nullptr, MDFrom);
NewSI->swapProfMetadata();
return NewSI;
}
// select a, b, true -> select !a, true, b
if (match(FalseVal, m_Specific(One))) {
Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
return SelectInst::Create(NotCond, One, TrueVal);
Instruction *MDFrom = ProfcheckDisableMetadataFixes ? nullptr : &SI;
SelectInst *NewSI =
SelectInst::Create(NotCond, One, TrueVal, "", nullptr, MDFrom);
NewSI->swapProfMetadata();
return NewSI;
}

// DeMorgan in select form: !a && !b --> !(a || b)
// select !a, !b, false --> not (select a, true, b)
if (match(&SI, m_LogicalAnd(m_Not(m_Value(A)), m_Not(m_Value(B)))) &&
(CondVal->hasOneUse() || TrueVal->hasOneUse()) &&
!match(A, m_ConstantExpr()) && !match(B, m_ConstantExpr()))
return BinaryOperator::CreateNot(Builder.CreateSelect(A, One, B));
!match(A, m_ConstantExpr()) && !match(B, m_ConstantExpr())) {
Instruction *MDFrom = ProfcheckDisableMetadataFixes ? nullptr : &SI;
SelectInst *NewSI =
cast<SelectInst>(Builder.CreateSelect(A, One, B, "", MDFrom));
NewSI->swapProfMetadata();
return BinaryOperator::CreateNot(NewSI);
}

// DeMorgan in select form: !a || !b --> !(a && b)
// select !a, true, !b --> not (select a, b, false)
if (match(&SI, m_LogicalOr(m_Not(m_Value(A)), m_Not(m_Value(B)))) &&
(CondVal->hasOneUse() || FalseVal->hasOneUse()) &&
!match(A, m_ConstantExpr()) && !match(B, m_ConstantExpr()))
return BinaryOperator::CreateNot(Builder.CreateSelect(A, B, Zero));
!match(A, m_ConstantExpr()) && !match(B, m_ConstantExpr())) {
Instruction *MDFrom = ProfcheckDisableMetadataFixes ? nullptr : &SI;
SelectInst *NewSI =
cast<SelectInst>(Builder.CreateSelect(A, B, Zero, "", MDFrom));
NewSI->swapProfMetadata();
return BinaryOperator::CreateNot(NewSI);
}

// select (select a, true, b), true, b -> select a, true, b
if (match(CondVal, m_Select(m_Value(A), m_One(), m_Value(B))) &&
Expand Down
27 changes: 20 additions & 7 deletions llvm/test/Transforms/InstCombine/select-and-or.ll
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@@ -1,11 +1,15 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals
; RUN: opt -S -passes=instcombine < %s | FileCheck %s

declare void @use(i1)
declare i1 @gen_i1()
declare <2 x i1> @gen_v2i1()

; Should not be converted to "and", which has different poison semantics.
;.
; CHECK: @g1 = external global i16
; CHECK: @g2 = external global i16
;.
define i1 @logical_and(i1 %a, i1 %b) {
; CHECK-LABEL: @logical_and(
; CHECK-NEXT: [[RES:%.*]] = select i1 [[A:%.*]], i1 [[B:%.*]], i1 false
Expand Down Expand Up @@ -225,29 +229,29 @@ define i1 @not_not_true(i1 %x, i1 %y) {

; (!x && !y) --> !(x || y)

define i1 @not_not_false(i1 %x, i1 %y) {
define i1 @not_not_false(i1 %x, i1 %y) !prof !0 {
; CHECK-LABEL: @not_not_false(
; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[X:%.*]], i1 true, i1 [[Y:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[X:%.*]], i1 true, i1 [[Y:%.*]], !prof [[PROF1:![0-9]+]]
; CHECK-NEXT: [[R:%.*]] = xor i1 [[TMP1]], true
; CHECK-NEXT: ret i1 [[R]]
;
%notx = xor i1 %x, true
%noty = xor i1 %y, true
%r = select i1 %notx, i1 %noty, i1 false
%r = select i1 %notx, i1 %noty, i1 false, !prof !1
ret i1 %r
}

; (!x || !y) --> !(x && y)

define i1 @not_true_not(i1 %x, i1 %y) {
define i1 @not_true_not(i1 %x, i1 %y) !prof !0 {
; CHECK-LABEL: @not_true_not(
; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[X:%.*]], i1 [[Y:%.*]], i1 false
; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[X:%.*]], i1 [[Y:%.*]], i1 false, !prof [[PROF1]]
; CHECK-NEXT: [[R:%.*]] = xor i1 [[TMP1]], true
; CHECK-NEXT: ret i1 [[R]]
;
%notx = xor i1 %x, true
%noty = xor i1 %y, true
%r = select i1 %notx, i1 true, i1 %noty
%r = select i1 %notx, i1 true, i1 %noty, !prof !1
ret i1 %r
}

Expand Down Expand Up @@ -1348,3 +1352,12 @@ define i8 @test_logical_commuted_and_ne_a_b(i1 %other_cond, i8 %a, i8 %b) {
%select = select i1 %or.cond, i8 %a, i8 %b
ret i8 %select
}

!0 = !{!"function_entry_count", i64 1000}
!1 = !{!"branch_weights", i32 2, i32 3}
;.
; CHECK: attributes #[[ATTR0:[0-9]+]] = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }
;.
; CHECK: [[META0:![0-9]+]] = !{!"function_entry_count", i64 1000}
; CHECK: [[PROF1]] = !{!"branch_weights", i32 3, i32 2}
;.
13 changes: 7 additions & 6 deletions llvm/test/Transforms/InstCombine/select-safe-transforms.ll
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Expand Up @@ -58,15 +58,15 @@ define i1 @cond_eq_or_const(i8 %X, i8 %Y) !prof !0 {
ret i1 %res
}

define i1 @xor_and(i1 %c, i32 %X, i32 %Y) {
define i1 @xor_and(i1 %c, i32 %X, i32 %Y) !prof !0 {
; CHECK-LABEL: @xor_and(
; CHECK-NEXT: [[COMP:%.*]] = icmp uge i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[NOT_C:%.*]] = xor i1 [[C:%.*]], true
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[NOT_C]], i1 true, i1 [[COMP]]
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[NOT_C]], i1 true, i1 [[COMP]], !prof [[PROF2:![0-9]+]]
; CHECK-NEXT: ret i1 [[SEL]]
;
%comp = icmp ult i32 %X, %Y
%sel = select i1 %c, i1 %comp, i1 false
%sel = select i1 %c, i1 %comp, i1 false, !prof !1
%res = xor i1 %sel, true
ret i1 %res
}
Expand Down Expand Up @@ -97,15 +97,15 @@ define <2 x i1> @xor_and3(<2 x i1> %c, <2 x i32> %X, <2 x i32> %Y) {
ret <2 x i1> %res
}

define i1 @xor_or(i1 %c, i32 %X, i32 %Y) {
define i1 @xor_or(i1 %c, i32 %X, i32 %Y) !prof !0 {
; CHECK-LABEL: @xor_or(
; CHECK-NEXT: [[COMP:%.*]] = icmp uge i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[NOT_C:%.*]] = xor i1 [[C:%.*]], true
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[NOT_C]], i1 [[COMP]], i1 false
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[NOT_C]], i1 [[COMP]], i1 false, !prof [[PROF2]]
; CHECK-NEXT: ret i1 [[SEL]]
;
%comp = icmp ult i32 %X, %Y
%sel = select i1 %c, i1 true, i1 %comp
%sel = select i1 %c, i1 true, i1 %comp, !prof !1
%res = xor i1 %sel, true
ret i1 %res
}
Expand Down Expand Up @@ -802,4 +802,5 @@ define <2 x i1> @not_logical_and2(i1 %b, <2 x i32> %a) {
;.
; CHECK: [[META0:![0-9]+]] = !{!"function_entry_count", i64 1000}
; CHECK: [[PROF1]] = !{!"branch_weights", i32 2, i32 3}
; CHECK: [[PROF2]] = !{!"branch_weights", i32 3, i32 2}
;.