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[InstCombine] Preserve profile data with select instructions and binary operators #158375

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Merged
merged 12 commits into from
Sep 15, 2025
Merged

[InstCombine] Preserve profile data with select instructions and binary operators #158375

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5ac86b7
[InstCombine] Preserve profile data with select instructions and bina…
alanzhao1 Sep 12, 2025
cad50aa
fix missing trailing newline
alanzhao1 Sep 12, 2025
938a4d4
fix conditional
alanzhao1 Sep 12, 2025
5d7169e
test fixes
alanzhao1 Sep 12, 2025
701bf31
more test fixes
alanzhao1 Sep 12, 2025
fe929d4
code formatting fixes
alanzhao1 Sep 12, 2025
d2979b4
initialize ProfileData to nullptr
alanzhao1 Sep 12, 2025
52d9c46
assert that LHS and RHS profile are the same
alanzhao1 Sep 12, 2025
d8731d3
pass original select to MDFrom argument of CreateSelect
alanzhao1 Sep 12, 2025
dfbd3f3
use update_test_checks.py
alanzhao1 Sep 13, 2025
9acdfbd
remove profdata assert
alanzhao1 Sep 15, 2025
68356be
restore use of ProfcheckDisableMeatadataFixes
alanzhao1 Sep 15, 2025
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17 changes: 11 additions & 6 deletions llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -144,6 +144,8 @@ static cl::opt<unsigned>
MaxArraySize("instcombine-maxarray-size", cl::init(1024),
cl::desc("Maximum array size considered when doing a combine"));

extern cl::opt<bool> ProfcheckDisableMetadataFixes;

// FIXME: Remove this flag when it is no longer necessary to convert
// llvm.dbg.declare to avoid inaccurate debug info. Setting this to false
// increases variable availability at the cost of accuracy. Variables that
Expand Down Expand Up @@ -1361,6 +1363,10 @@ Value *InstCombinerImpl::SimplifySelectsFeedingBinaryOp(BinaryOperator &I,
if (!LHSIsSelect && !RHSIsSelect)
return nullptr;

SelectInst *SI = ProfcheckDisableMetadataFixes
? nullptr
: cast<SelectInst>(LHSIsSelect ? LHS : RHS);

FastMathFlags FMF;
BuilderTy::FastMathFlagGuard Guard(Builder);
if (isa<FPMathOperator>(&I)) {
Expand All @@ -1381,15 +1387,14 @@ Value *InstCombinerImpl::SimplifySelectsFeedingBinaryOp(BinaryOperator &I,
// We need an 'add' and exactly 1 arm of the select to have been simplified.
if (Opcode != Instruction::Add || (!True && !False) || (True && False))
return nullptr;

Value *N;
if (True && match(FVal, m_Neg(m_Value(N)))) {
Value *Sub = Builder.CreateSub(Z, N);
return Builder.CreateSelect(Cond, True, Sub, I.getName());
return Builder.CreateSelect(Cond, True, Sub, I.getName(), SI);
}
if (False && match(TVal, m_Neg(m_Value(N)))) {
Value *Sub = Builder.CreateSub(Z, N);
return Builder.CreateSelect(Cond, Sub, False, I.getName());
return Builder.CreateSelect(Cond, Sub, False, I.getName(), SI);
}
return nullptr;
};
Expand Down Expand Up @@ -1425,9 +1430,9 @@ Value *InstCombinerImpl::SimplifySelectsFeedingBinaryOp(BinaryOperator &I,
if (!True || !False)
return nullptr;

Value *SI = Builder.CreateSelect(Cond, True, False);
SI->takeName(&I);
return SI;
Value *NewSI = Builder.CreateSelect(Cond, True, False, I.getName(), SI);
NewSI->takeName(&I);
return NewSI;
}

/// Freely adapt every user of V as-if V was changed to !V.
Expand Down
54 changes: 54 additions & 0 deletions llvm/test/Transforms/InstCombine/preserve-profile.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,54 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals all --version 6
; RUN: opt < %s -passes=instcombine -S | FileCheck %s

define i32 @LHSBin(i1 %C) !prof !0 {
; CHECK-LABEL: define i32 @LHSBin(
; CHECK-SAME: i1 [[C:%.*]]) !prof [[PROF0:![0-9]+]] {
; CHECK-NEXT: [[V:%.*]] = select i1 [[C]], i32 1010, i32 20, !prof [[PROF1:![0-9]+]]
; CHECK-NEXT: ret i32 [[V]]
;
%A = select i1 %C, i32 1000, i32 10, !prof !1
%V = add i32 %A, 10
ret i32 %V
}

define i32 @RHSBin(i1 %C) !prof !0 {
; CHECK-LABEL: define i32 @RHSBin(
; CHECK-SAME: i1 [[C:%.*]]) !prof [[PROF0]] {
; CHECK-NEXT: [[V:%.*]] = select i1 [[C]], i32 1010, i32 20, !prof [[PROF1]]
; CHECK-NEXT: ret i32 [[V]]
;
%A = select i1 %C, i32 1000, i32 10, !prof !1
%V = add i32 10, %A
ret i32 %V;
}

define i32 @BothBin(i1 %C) !prof !0 {
; CHECK-LABEL: define i32 @BothBin(
; CHECK-SAME: i1 [[C:%.*]]) !prof [[PROF0]] {
; CHECK-NEXT: [[V:%.*]] = select i1 [[C]], i32 2000, i32 20, !prof [[PROF1]]
; CHECK-NEXT: ret i32 [[V]]
;
%A = select i1 %C, i32 1000, i32 10, !prof !1
%B = select i1 %C, i32 1000, i32 10, !prof !1
%V = add i32 %A, %B
ret i32 %V;
}

define i32 @NegBin(i1 %C) !prof !0 {
; CHECK-LABEL: define i32 @NegBin(
; CHECK-SAME: i1 [[C:%.*]]) !prof [[PROF0]] {
; CHECK-NEXT: [[V:%.*]] = select i1 [[C]], i32 1010, i32 0, !prof [[PROF1]]
; CHECK-NEXT: ret i32 [[V]]
;
%A = select i1 %C, i32 1000, i32 -10, !prof !1
%V = add i32 %A, 10
ret i32 %V
}

!0 = !{!"function_entry_count", i64 1000}
!1 = !{!"branch_weights", i32 2, i32 3}
;.
; CHECK: [[PROF0]] = !{!"function_entry_count", i64 1000}
; CHECK: [[PROF1]] = !{!"branch_weights", i32 2, i32 3}
;.