[llvm-branch-commits] [llvm] [KeyInstr][JumpThreading] Remap atoms duping bb with cond br on phi into pred (PR #133488)

[Orlando Cazalet-Hyams via llvm-branch-commits]

https://github.com/OCHyams created https://github.com/llvm/llvm-project/pull/133488

See test for details.

>From 6488f4bca69bc26d1d58ea36b9dff4532d4858a9 Mon Sep 17 00:00:00 2001
From: Orlando Cazalet-Hyams <orlando.hyams at sony.com>
Date: Tue, 25 Mar 2025 15:24:05 +0000
Subject: [PATCH] [KeyInstr][JumpThreading] Remap atoms duping bb with cond br
 on phi into pred

See test for details.
---
 llvm/lib/Transforms/Scalar/JumpThreading.cpp  |  9 ++
 ...-threading-dup-cond-br-on-phi-into-pred.ll | 87 +++++++++++++++++++
 2 files changed, 96 insertions(+)
 create mode 100644 llvm/test/DebugInfo/KeyInstructions/Generic/jump-threading-dup-cond-br-on-phi-into-pred.ll

diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index d320f7dce11db..67f59b9864b1e 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -2683,6 +2683,9 @@ bool JumpThreadingPass::duplicateCondBranchOnPHIIntoPred(
   // PredBB block.  Evaluate PHI nodes in BB.
   ValueToValueMapTy ValueMapping;
 
+  // Remember the position before the inserted instructions.
+  auto RItBeforeInsertPt = std::next(OldPredBranch->getReverseIterator());
+
   BasicBlock::iterator BI = BB->begin();
   for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
     ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
@@ -2702,6 +2705,8 @@ bool JumpThreadingPass::duplicateCondBranchOnPHIIntoPred(
 
     // Remap debug variable operands.
     remapDebugVariable(ValueMapping, New);
+    if (const DebugLoc &DL = New->getDebugLoc())
+      mapAtomInstance(DL, ValueMapping);
 
     // If this instruction can be simplified after the operands are updated,
     // just use the simplified value instead.  This frequently happens due to
@@ -2740,6 +2745,10 @@ bool JumpThreadingPass::duplicateCondBranchOnPHIIntoPred(
   addPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB,
                                   ValueMapping);
 
+  // KeyInstructions: Remap the cloned instructions' atoms only.
+  remapSourceAtoms(ValueMapping, std::prev(RItBeforeInsertPt)->getIterator(),
+                   OldPredBranch->getIterator());
+
   updateSSA(BB, PredBB, ValueMapping);
 
   // PredBB no longer jumps to BB, remove entries in the PHI node for the edge
diff --git a/llvm/test/DebugInfo/KeyInstructions/Generic/jump-threading-dup-cond-br-on-phi-into-pred.ll b/llvm/test/DebugInfo/KeyInstructions/Generic/jump-threading-dup-cond-br-on-phi-into-pred.ll
new file mode 100644
index 0000000000000..ca1c748cc787a
--- /dev/null
+++ b/llvm/test/DebugInfo/KeyInstructions/Generic/jump-threading-dup-cond-br-on-phi-into-pred.ll
@@ -0,0 +1,87 @@
+; RUN: opt %s --passes=jump-threading -S -o - -S | FileCheck %s
+
+;;        +-> T1 -+
+;;        |       v      +-> T2
+;; Entry -+       Merge -+
+;;        |       ^      +-> F2
+;;        +-> F1 -+
+;;
+;; Duplicate Merge into T1 then fold Merge into its only pred F1 (taking its name).
+;;
+;;        +-> T1 -----> T2
+;;        |     \       ^
+;;        |      \     /
+;;        |       \   /
+;; Entry -+        +----+
+;;        |         /   v 
+;;        +--> Merge -> F2
+;;
+;; Check the duplicated  (into T1) instructions' atoms are remapped.
+
+; CHECK: T1:
+; CHECK-NEXT: %v1 = call i32 @f1()
+; CHECK-NEXT: %cond3 = icmp eq i32 %v1, 412
+; CHECK-NEXT: %C1 = add i32 %v1, 1, !dbg [[G3R2:!.*]]
+; CHECK-NEXT: store i32 %C1, ptr %p, align 4, !dbg [[G3R1:!.*]]
+
+; CHECK: Merge:
+; CHECK-NEXT: %v2 = call i32 @f2()
+; CHECK-NEXT: store i32 1, ptr %p, align 4, !dbg [[G1R1:!.*]]
+; CHECK-NEXT: %C = add i32 %v2, 1, !dbg [[G2R2:!.*]]
+; CHECK-NEXT: store i32 %C, ptr %p, align 4, !dbg [[G2R1:!.*]]
+
+; CHECK: [[G3R2]] = !DILocation({{.*}}, atomGroup: 3, atomRank: 2)
+; CHECK: [[G3R1]] = !DILocation({{.*}}, atomGroup: 3, atomRank: 1)
+; CHECK: [[G1R1]] = !DILocation({{.*}}, atomGroup: 1, atomRank: 1)
+; CHECK: [[G2R2]] = !DILocation({{.*}}, atomGroup: 2, atomRank: 2)
+; CHECK: [[G2R1]] = !DILocation({{.*}}, atomGroup: 2, atomRank: 1)
+
+define i32 @test5(i1 %cond, i1 %cond2, ptr %p) !dbg !5 {
+  br i1 %cond, label %T1, label %F1
+
+T1:                                               ; preds = %0
+  %v1 = call i32 @f1()
+  %cond3 = icmp eq i32 %v1, 412
+  br label %Merge
+
+F1:                                               ; preds = %0
+  %v2 = call i32 @f2()
+  store i32 1, ptr %p, align 4, !dbg !8
+  br label %Merge
+
+Merge:                                            ; preds = %F1, %T1
+  %A = phi i1 [ %cond3, %T1 ], [ %cond2, %F1 ]
+  %B = phi i32 [ %v1, %T1 ], [ %v2, %F1 ]
+  %C = add i32 %B, 1, !dbg !9
+  store i32 %C, ptr %p, align 4, !dbg !10
+  br i1 %A, label %T2, label %F2
+
+T2:                                               ; preds = %Merge
+  call void @f3()
+  ret i32 %B
+
+F2:                                               ; preds = %Merge
+  ret i32 %B
+}
+
+declare i32 @f1()
+
+declare i32 @f2()
+
+declare void @f3()
+
+!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: "test.ll", directory: "/")
+!2 = !{i32 12}
+!3 = !{i32 0}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "test5", linkageName: "test5", scope: null, file: !1, line: 1, type: !6, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+!6 = !DISubroutineType(types: !7)
+!7 = !{}
+!8 = !DILocation(line: 1, column: 1, scope: !5, atomGroup: 1, atomRank: 1)
+!9 = !DILocation(line: 2, column: 1, scope: !5, atomGroup: 2, atomRank: 2)
+!10 = !DILocation(line: 2, column: 1, scope: !5, atomGroup: 2, atomRank: 1)