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[CHR] Fix crash when marking merged condition unknown #173902

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Merged
peterwaller-arm merged 1 commit into from
Jan 2, 2026
Merged

[CHR] Fix crash when marking merged condition unknown #173902

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4 changes: 2 additions & 2 deletions llvm/lib/Transforms/Instrumentation/ControlHeightReduction.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1992,8 +1992,8 @@ void CHR::addToMergedCondition(bool IsTrueBiased, Value *Cond,

// Use logical and to avoid propagating poison from later conditions.
MergedCondition = IRB.CreateLogicalAnd(MergedCondition, Cond);
setExplicitlyUnknownBranchWeightsIfProfiled(
*cast<Instruction>(MergedCondition), DEBUG_TYPE);
if (auto *MergedInst = dyn_cast<Instruction>(MergedCondition))
setExplicitlyUnknownBranchWeightsIfProfiled(*MergedInst, DEBUG_TYPE, &F);
}

void CHR::transformScopes(SmallVectorImpl<CHRScope *> &CHRScopes) {
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33 changes: 33 additions & 0 deletions llvm/test/Transforms/PGOProfile/chr-unknown-profdata-crash.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,33 @@
; RUN: opt < %s -passes='require<profile-summary>,function(chr)' -force-chr -chr-merge-threshold=1 -disable-output

; Regression test for a crash in CHR when setting unknown profdata on the
; merged condition. IRBuilder::CreateLogicalAnd is implemented as a select and
; can constant-fold to a non-Instruction value (e.g. `i1 true`). The buggy code
; assumed it always produced an Instruction and did `cast<Instruction>(V)`,
; which can segfault in release builds.
define void @repro_crash() {
entry:
br i1 true, label %then, label %exit, !prof !15

then:
br label %exit

exit:
ret void
}

!llvm.module.flags = !{!0}
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@boomanaiden154 boomanaiden154 Dec 31, 2025

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A lot of this metadata looks unnecessary for the reproducer?

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@peterwaller-arm peterwaller-arm Jan 2, 2026

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I have tried to delete various unnecessary-looking pieces but did not quickly discover more I can remove and still preserve the crash on the bad version. llvm-reduce doesn't remove anything, either. If you have ideas of specific things to remove which preserve the crash, please let me know.

!0 = !{i32 1, !"ProfileSummary", !1}
!1 = !{!2, !3, !4, !5, !6, !7, !8, !9}
!2 = !{!"ProfileFormat", !"InstrProf"}
!3 = !{!"TotalCount", i64 10000}
!4 = !{!"MaxCount", i64 10}
!5 = !{!"MaxInternalCount", i64 1}
!6 = !{!"MaxFunctionCount", i64 1000}
!7 = !{!"NumCounts", i64 1}
!8 = !{!"NumFunctions", i64 1}
!9 = !{!"DetailedSummary", !10}
!10 = !{!11}
!11 = !{i32 999999, i64 1, i32 1}

!15 = !{!"branch_weights", i32 100, i32 1}