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[IR] Add MD_prof to the Keep list of dropUBImplyingAttrsAndMetadata #154635

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Merged
merged 2 commits into from
Sep 12, 2025
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[IR] Add MD_prof to the Keep list of dropUBImplyingAttrsAndMetadata #154635

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f040170
[Local] preserve `MD_prof` in `hoistAllInstructionsInto`
mtrofin Aug 20, 2025
edc8794
Merge branch 'main' into users/mtrofin/08-20-_local_preserve_md_prof_…
mtrofin Sep 12, 2025
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7 changes: 4 additions & 3 deletions llvm/lib/IR/Instruction.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -553,16 +553,17 @@ void Instruction::dropUBImplyingAttrsAndUnknownMetadata(
}

void Instruction::dropUBImplyingAttrsAndMetadata(ArrayRef<unsigned> Keep) {
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I think the Keep is no longer needed now, but I guess it doesn't hurt to keep it...

// !annotation metadata does not impact semantics.
// !annotation and !prof metadata does not impact semantics.
// !range, !nonnull and !align produce poison, so they are safe to speculate.
// !noundef and various AA metadata must be dropped, as it generally produces
// immediate undefined behavior.
static const unsigned KnownIDs[] = {
LLVMContext::MD_annotation, LLVMContext::MD_range,
LLVMContext::MD_nonnull, LLVMContext::MD_align};
LLVMContext::MD_nonnull, LLVMContext::MD_align, LLVMContext::MD_prof};
SmallVector<unsigned> KeepIDs;
KeepIDs.reserve(Keep.size() + std::size(KnownIDs));
append_range(KeepIDs, KnownIDs);
append_range(KeepIDs, (!ProfcheckDisableMetadataFixes ? KnownIDs
: drop_end(KnownIDs)));
append_range(KeepIDs, Keep);
dropUBImplyingAttrsAndUnknownMetadata(KeepIDs);
}
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5 changes: 1 addition & 4 deletions llvm/lib/Transforms/Scalar/LICM.cpp
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Expand Up @@ -1705,10 +1705,7 @@ static void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
// time in isGuaranteedToExecute if we don't actually have anything to
// drop. It is a compile time optimization, not required for correctness.
!SafetyInfo->isGuaranteedToExecute(I, DT, CurLoop)) {
if (ProfcheckDisableMetadataFixes)
I.dropUBImplyingAttrsAndMetadata();
else
I.dropUBImplyingAttrsAndMetadata({LLVMContext::MD_prof});
I.dropUBImplyingAttrsAndMetadata();
}

if (isa<PHINode>(I))
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21 changes: 14 additions & 7 deletions llvm/test/Transforms/SimplifyCFG/PhiBlockMerge.ll
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@@ -1,20 +1,21 @@
; NOTE: Assertions have been autogenerated by update_test_checks.py
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals all --version 5
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I think you don't need the --check-globals, just the new version is enough.

; Test merging of blocks that only have PHI nodes in them
;
; RUN: opt < %s -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S | FileCheck %s
;

define i32 @test(i1 %a, i1 %b) {
; CHECK-LABEL: @test(
; CHECK: M:
; CHECK-NEXT: [[DOT:%.*]] = select i1 %b, i32 0, i32 1
; CHECK-NEXT: [[W:%.*]] = select i1 %a, i32 2, i32 [[DOT]]
; CHECK-LABEL: define i32 @test(
; CHECK-SAME: i1 [[A:%.*]], i1 [[B:%.*]]) {
; CHECK-NEXT: [[M:.*:]]
; CHECK-NEXT: [[SPEC_SELECT:%.*]] = select i1 [[B]], i32 0, i32 1, !prof [[PROF0:![0-9]+]]
; CHECK-NEXT: [[W:%.*]] = select i1 [[A]], i32 2, i32 [[SPEC_SELECT]], !prof [[PROF1:![0-9]+]]
; CHECK-NEXT: [[R:%.*]] = add i32 [[W]], 1
; CHECK-NEXT: ret i32 [[R]]
;
br i1 %a, label %M, label %O
br i1 %a, label %M, label %O, !prof !0
O: ; preds = %0
br i1 %b, label %N, label %Q
br i1 %b, label %N, label %Q, !prof !1
Q: ; preds = %O
br label %N
N: ; preds = %Q, %O
Expand All @@ -27,3 +28,9 @@ M: ; preds = %N, %0
ret i32 %R
}

!0 = !{!"branch_weights", i32 11, i32 7}
!1 = !{!"branch_weights", i32 3, i32 5}
;.
; CHECK: [[PROF0]] = !{!"branch_weights", i32 3, i32 5}
; CHECK: [[PROF1]] = !{!"branch_weights", i32 11, i32 7}
;.
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