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[KeyInstr][JumpThreading] Remap atoms in blocks duplicated for threading #133486

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May 7, 2025
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[KeyInstr][JumpThreading] Remap atoms in blocks duplicated for threading #133486

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[KeyInstr][JumpThreading] Remap atoms in blocks duplicated for threading
OCHyams Mar 25, 2025
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OCHyams May 7, 2025
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OCHyams May 7, 2025
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15 changes: 15 additions & 0 deletions llvm/lib/Transforms/Scalar/JumpThreading.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2011,6 +2011,14 @@ void JumpThreadingPass::updateSSA(BasicBlock *BB, BasicBlock *NewBB,
}
}

static void remapSourceAtoms(ValueToValueMapTy &VM, BasicBlock::iterator Begin,
BasicBlock::iterator End) {
if (VM.AtomMap.empty())
return;
for (auto It = Begin; It != End; ++It)
RemapSourceAtom(&*It, VM);
}

/// Clone instructions in range [BI, BE) to NewBB. For PHI nodes, we only clone
/// arguments that come from PredBB. Return the map from the variables in the
/// source basic block to the variables in the newly created basic block.
Expand Down Expand Up @@ -2075,6 +2083,8 @@ void JumpThreadingPass::cloneInstructions(ValueToValueMapTy &ValueMapping,
PHINode *NewPN = PHINode::Create(PN->getType(), 1, PN->getName(), NewBB);
NewPN->addIncoming(PN->getIncomingValueForBlock(PredBB), PredBB);
ValueMapping[PN] = NewPN;
if (const DebugLoc &DL = PN->getDebugLoc())
mapAtomInstance(DL, ValueMapping);
}

// Clone noalias scope declarations in the threaded block. When threading a
Expand Down Expand Up @@ -2103,6 +2113,8 @@ void JumpThreadingPass::cloneInstructions(ValueToValueMapTy &ValueMapping,
adaptNoAliasScopes(New, ClonedScopes, Context);

CloneAndRemapDbgInfo(New, &*BI);
if (const DebugLoc &DL = New->getDebugLoc())
mapAtomInstance(DL, ValueMapping);

if (RetargetDbgValueIfPossible(New))
continue;
Expand Down Expand Up @@ -2330,6 +2342,9 @@ void JumpThreadingPass::threadThroughTwoBasicBlocks(BasicBlock *PredPredBB,
{DominatorTree::Insert, PredPredBB, NewBB},
{DominatorTree::Delete, PredPredBB, PredBB}});

// Remap source location atoms beacuse we're duplicating control flow.
remapSourceAtoms(ValueMapping, NewBB->begin(), NewBB->end());
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I'd say "comment pls", but I suppose the fact there's "source" in the name gives a hint as to what's going on.


updateSSA(PredBB, NewBB, ValueMapping);

// Clean up things like PHI nodes with single operands, dead instructions,
Expand Down
68 changes: 68 additions & 0 deletions llvm/test/DebugInfo/KeyInstructions/Generic/jump-threading-2-bbs.ll
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@@ -0,0 +1,68 @@
; RUN: opt -S -passes=jump-threading,verify %s | FileCheck %s

;; Modified from llvm/test/Transforms/JumpThreading/thread-two-bbs.ll
;;
;; JumpThreading duplicates bb.cond2 to thread through bb.file to bb.f2 or exit.
;;
;; Check the duplicated instructions get remapped atom groups.

; CHECK: bb.cond2:
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CHECK-LABEL?

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@pogo59 pogo59 Apr 11, 2025 •
edited
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I wouldn't. The point of CHECK-LABEL is to subdivide the checked text; here, CHECK is followed by a series of CHECK-NEXT, so the grouping effect of -LABEL isn't needed.

; CHECK-NEXT: call void @f1()
; CHECK-NEXT: %tobool1 = icmp eq i32 %cond2, 0, !dbg [[G1R2:!.*]]
; CHECK-NEXT: br i1 %tobool1, label %exit, label %exit, !dbg [[G1R1:!.*]]

; CHECK: bb.cond2.thread:
; CHECK-NEXT: %tobool12 = icmp eq i32 %cond2, 0, !dbg [[G2R2:!.*]]
; CHECK-NEXT: br i1 %tobool12, label %bb.f2, label %exit, !dbg [[G2R1:!.*]]

; CHECK: [[G1R2]] = !DILocation(line: 1, column: 1, scope: ![[#]], atomGroup: 1, atomRank: 2)
; CHECK: [[G1R1]] = !DILocation(line: 1, column: 1, scope: ![[#]], atomGroup: 1, atomRank: 1)
; CHECK: [[G2R2]] = !DILocation(line: 1, column: 1, scope: ![[#]], atomGroup: 2, atomRank: 2)
; CHECK: [[G2R1]] = !DILocation(line: 1, column: 1, scope: ![[#]], atomGroup: 2, atomRank: 1)

@a = global i32 0, align 4

define void @foo(i32 %cond1, i32 %cond2) !dbg !5 {
entry:
%tobool = icmp eq i32 %cond1, 0
br i1 %tobool, label %bb.cond2, label %bb.f1

bb.f1: ; preds = %entry
call void @f1()
br label %bb.cond2

bb.cond2: ; preds = %bb.f1, %entry
%ptr = phi ptr [ null, %bb.f1 ], [ @a, %entry ]
%tobool1 = icmp eq i32 %cond2, 0, !dbg !9
br i1 %tobool1, label %bb.file, label %exit, !dbg !10

bb.file: ; preds = %bb.cond2
%cmp = icmp eq ptr %ptr, null
br i1 %cmp, label %exit, label %bb.f2

bb.f2: ; preds = %bb.file
call void @f2()
br label %exit

exit: ; preds = %bb.f2, %bb.file, %bb.cond2
ret void
}

declare void @f1()

declare void @f2()

!llvm.dbg.cu = !{!0}
!llvm.debugify = !{!2, !3}
!llvm.module.flags = !{!4}

!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
!1 = !DIFile(filename: "<stdin>", directory: "/")
!2 = !{i32 16}
!3 = !{i32 0}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = distinct !DISubprogram(name: "foo", linkageName: "foo", scope: null, file: !1, line: 1, type: !6, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
!6 = !DISubroutineType(types: !7)
!7 = !{}
!9 = !DILocation(line: 1, column: 1, scope: !5, atomGroup: 1, atomRank: 2)
!10 = !DILocation(line: 1, column: 1, scope: !5, atomGroup: 1, atomRank: 1)
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