[llvm] [DebugInfo][GVNSink] Merging debug locations of sinked instructions (PR #92859)

[Shan Huang via llvm-commits]

https://github.com/Apochens created https://github.com/llvm/llvm-project/pull/92859

Fix #85069 .

>From 6c995f0d83bab755025e64e6dd1ee2a6895136c0 Mon Sep 17 00:00:00 2001
From: Apochens <52285902006 at stu.ecnu.edu.cn>
Date: Tue, 21 May 2024 05:18:43 +0000
Subject: [PATCH] merging instruction locations

---
 llvm/lib/Transforms/Scalar/GVNSink.cpp                     | 4 +++-
 llvm/test/Transforms/GVNSink/sink-ignore-dbg-intrinsics.ll | 7 +++++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Transforms/Scalar/GVNSink.cpp b/llvm/lib/Transforms/Scalar/GVNSink.cpp
index b0f716cb17598..3dfa2dd9df27f 100644
--- a/llvm/lib/Transforms/Scalar/GVNSink.cpp
+++ b/llvm/lib/Transforms/Scalar/GVNSink.cpp
@@ -921,8 +921,10 @@ void GVNSink::sinkLastInstruction(ArrayRef<BasicBlock *> Blocks,
     }
 
   for (auto *I : Insts)
-    if (I != I0)
+    if (I != I0) {
       I->replaceAllUsesWith(I0);
+      I0->applyMergedLocation(I0->getDebugLoc(), I->getDebugLoc());
+    }
   foldPointlessPHINodes(BBEnd);
 
   // Finally nuke all instructions apart from the common instruction.
diff --git a/llvm/test/Transforms/GVNSink/sink-ignore-dbg-intrinsics.ll b/llvm/test/Transforms/GVNSink/sink-ignore-dbg-intrinsics.ll
index 8aafd689e781d..e54a17a155b8c 100644
--- a/llvm/test/Transforms/GVNSink/sink-ignore-dbg-intrinsics.ll
+++ b/llvm/test/Transforms/GVNSink/sink-ignore-dbg-intrinsics.ll
@@ -1,6 +1,8 @@
 ; RUN: opt < %s -passes=gvn-sink -S | FileCheck %s
 
 ; Test that GVNSink correctly performs the sink optimization in the presence of debug information
+; Test that GVNSink correctly merges the debug locations of sinked instruction, eg, propagating
+; the merged debug location of `%add` and `%add1` to the sinked add instruction.
 
 ; Function Attrs: noinline nounwind uwtable
 define dso_local i32 @fun(i32 noundef %a, i32 noundef %b) #0 !dbg !10 {
@@ -8,8 +10,9 @@ define dso_local i32 @fun(i32 noundef %a, i32 noundef %b) #0 !dbg !10 {
 ; CHECK-SAME:    i32 noundef [[A:%.*]], i32 noundef [[B:%.*]])
 ; CHECK:       if.end:
 ; CHECK:         [[B_SINK:%.*]] = phi i32 [ [[B]], %if.else ], [ [[A]], %if.then ]
-; CHECK:         [[ADD1:%.*]] = add nsw i32 [[B_SINK]], 1
-; CHECK:         [[XOR2:%.*]] = xor i32 [[ADD1]], 1
+; CHECK:         [[ADD1:%.*]] = add nsw i32 [[B_SINK]], 1, !dbg [[DBG:![0-9]+]]
+; CHECK:         [[XOR2:%.*]] = xor i32 [[ADD1]], 1, !dbg [[DBG:![0-9]+]]
+; CHECK:       [[DBG]] = !DILocation(line: 0,
 ;
 entry:
   tail call void @llvm.dbg.value(metadata i32 %a, metadata !15, metadata !DIExpression()), !dbg !16