[Debuginfo][GVNHoist] Fix #86227: update the debug location of the hoisted GEP

[Apochens]

This PR fixes #86227.

[llvmbot]

@llvm/pr-subscribers-debuginfo

@llvm/pr-subscribers-llvm-transforms

Author: Shan Huang (Apochens)

Changes

This PR fixes #86227.

---

Full diff: https://github.com/llvm/llvm-project/pull/86236.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/Scalar/GVNHoist.cpp (+8)
• (added) llvm/test/Transforms/GVNHoist/hoist-merge-geps.ll (+66)

diff --git a/llvm/lib/Transforms/Scalar/GVNHoist.cpp b/llvm/lib/Transforms/Scalar/GVNHoist.cpp
index b564f00eb9d166..b95421d2035b58 100644
--- a/llvm/lib/Transforms/Scalar/GVNHoist.cpp
+++ b/llvm/lib/Transforms/Scalar/GVNHoist.cpp
@@ -951,6 +951,14 @@ void GVNHoist::makeGepsAvailable(Instruction *Repl, BasicBlock *HoistPt,
       OtherGep = cast<GetElementPtrInst>(
           cast<StoreInst>(OtherInst)->getPointerOperand());
     ClonedGep->andIRFlags(OtherGep);
+    
+    // Merge debug locations of GEPs, because the hoisted GEP replaces those
+    // in branches. When cloning, ClonedGep preserves the debug location of 
+    // Gepd, so Gep is skipped to avoid merging it twice.
+    if (OtherGep != Gep) {
+      ClonedGep->applyMergedLocation(
+        ClonedGep->getDebugLoc(), OtherGep->getDebugLoc());
+    }
   }
 
   // Replace uses of Gep with ClonedGep in Repl.
diff --git a/llvm/test/Transforms/GVNHoist/hoist-merge-geps.ll b/llvm/test/Transforms/GVNHoist/hoist-merge-geps.ll
new file mode 100644
index 00000000000000..045b3c2c78280d
--- /dev/null
+++ b/llvm/test/Transforms/GVNHoist/hoist-merge-geps.ll
@@ -0,0 +1,66 @@
+; RUN: opt -S -passes=gvn-hoist < %s | FileCheck %s 
+
+; Function Attrs: noinline nounwind uwtable
+define dso_local void @func(i32 noundef %a, ptr noundef %b) #0 !dbg !10 {
+; Check the merged debug location of hoisted GEP
+; CHECK: entry
+; CHECK: %{{[a-zA-Z0-9_]*}} = getelementptr {{.*}} !dbg [[MERGED_DL:![0-9]+]]
+; CHECK: [[MERGED_DL]] = !DILocation(line: 0, scope: !{{[0-9]+}})
+entry:
+  tail call void @llvm.dbg.value(metadata i32 %a, metadata !16, metadata !DIExpression()), !dbg !17
+  tail call void @llvm.dbg.value(metadata ptr %b, metadata !18, metadata !DIExpression()), !dbg !17
+  %tobool = icmp ne i32 %a, 0, !dbg !19
+  br i1 %tobool, label %if.then, label %if.else, !dbg !21
+
+if.then:                                          ; preds = %entry
+  %arrayidx = getelementptr inbounds i32, ptr %b, i64 1, !dbg !22
+  store i32 1, ptr %arrayidx, align 4, !dbg !24
+  br label %if.end, !dbg !25
+
+if.else:                                          ; preds = %entry
+  %arrayidx1 = getelementptr inbounds i32, ptr %b, i64 1, !dbg !26
+  store i32 1, ptr %arrayidx1, align 4, !dbg !28
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  ret void, !dbg !29
+}
+
+; Function Attrs: nocallback nofree nosync nounwind speculatable willreturn memory(none)
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+; Function Attrs: nocallback nofree nosync nounwind speculatable willreturn memory(none)
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5, !6, !7, !8}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 19.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "main.c", directory: "/root/llvm-test/GVNHoist")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 8, !"PIC Level", i32 2}
+!6 = !{i32 7, !"PIE Level", i32 2}
+!7 = !{i32 7, !"uwtable", i32 2}
+!8 = !{i32 7, !"frame-pointer", i32 2}
+!10 = distinct !DISubprogram(name: "func", scope: !1, file: !1, line: 1, type: !11, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !15)
+!11 = !DISubroutineType(types: !12)
+!12 = !{null, !13, !14}
+!13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!14 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !13, size: 64)
+!15 = !{}
+!16 = !DILocalVariable(name: "a", arg: 1, scope: !10, file: !1, line: 1, type: !13)
+!17 = !DILocation(line: 0, scope: !10)
+!18 = !DILocalVariable(name: "b", arg: 2, scope: !10, file: !1, line: 1, type: !14)
+!19 = !DILocation(line: 2, column: 9, scope: !20)
+!20 = distinct !DILexicalBlock(scope: !10, file: !1, line: 2, column: 9)
+!21 = !DILocation(line: 2, column: 9, scope: !10)
+!22 = !DILocation(line: 3, column: 9, scope: !23)
+!23 = distinct !DILexicalBlock(scope: !20, file: !1, line: 2, column: 12)
+!24 = !DILocation(line: 3, column: 14, scope: !23)
+!25 = !DILocation(line: 4, column: 5, scope: !23)
+!26 = !DILocation(line: 5, column: 9, scope: !27)
+!27 = distinct !DILexicalBlock(scope: !20, file: !1, line: 4, column: 12)
+!28 = !DILocation(line: 5, column: 14, scope: !27)
+!29 = !DILocation(line: 7, column: 1, scope: !10)

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[Apochens]

@jmorse @SLTozer @dwblaikie Please review this.

[SLTozer]

Change and test LGTM, with some minor nits for the test, and also clang-format is needed (you can see the suggested changes from the PR checks here).

[SLTozer]

Minor nits, we can delete the ; Function Attrs lines and the attribute references (#0 and #1).

[Apochens]

Thanks for your comments. I fixed these minor issues, and now the test would be better.

[SLTozer]

Changes look good!

[github-actions]

✅ With the latest revision this PR passed the Python code formatter.

[Apochens]

Ping!