[llvm] [DebugInfo][Reassociate] Fix missing debug location drop (PR #95355)

[Shan Huang via llvm-commits]

https://github.com/Apochens created https://github.com/llvm/llvm-project/pull/95355

Fix #95343 .

>From bf740834fc24443aaae71492980fa72b45ee52bd Mon Sep 17 00:00:00 2001
From: Apochens <52285902006 at stu.ecnu.edu.cn>
Date: Thu, 13 Jun 2024 04:57:02 +0000
Subject: [PATCH] fix missing debug location drop

---
 llvm/lib/Transforms/Scalar/Reassociate.cpp    |  1 +
 .../Reassociate/dropping_debugloc_the_neg.ll  | 51 +++++++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100644 llvm/test/Transforms/Reassociate/dropping_debugloc_the_neg.ll

diff --git a/llvm/lib/Transforms/Scalar/Reassociate.cpp b/llvm/lib/Transforms/Scalar/Reassociate.cpp
index f36e21b296bd1..73196e60470e0 100644
--- a/llvm/lib/Transforms/Scalar/Reassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/Reassociate.cpp
@@ -845,6 +845,7 @@ static Value *NegateValue(Value *V, Instruction *BI,
     }
 
     TheNeg->moveBefore(*InsertPt->getParent(), InsertPt);
+    TheNeg->dropLocation();
     if (TheNeg->getOpcode() == Instruction::Sub) {
       TheNeg->setHasNoUnsignedWrap(false);
       TheNeg->setHasNoSignedWrap(false);
diff --git a/llvm/test/Transforms/Reassociate/dropping_debugloc_the_neg.ll b/llvm/test/Transforms/Reassociate/dropping_debugloc_the_neg.ll
new file mode 100644
index 0000000000000..e3a25627a40e0
--- /dev/null
+++ b/llvm/test/Transforms/Reassociate/dropping_debugloc_the_neg.ll
@@ -0,0 +1,51 @@
+; RUN: opt < %s -passes=reassociate -S | FileCheck %s
+
+define void @fn1(i32 %a, i1 %c, ptr %ptr) !dbg !5 {
+; CHECK-LABEL: define void @fn1(
+; CHECK:       for.cond:
+; CHECK:        [[SUB2:%.*]] = sub i32 0, %d.0{{$}}
+; CHECK:       for.body:
+;
+entry:
+  br label %for.cond, !dbg !8
+
+for.cond:                                         ; preds = %for.body, %entry
+  %d.0 = phi i32 [ 1, %entry ], [ 2, %for.body ], !dbg !9
+  br i1 %c, label %for.end, label %for.body, !dbg !10
+
+for.body:                                         ; preds = %for.cond
+  %sub1 = sub i32 %a, %d.0, !dbg !11
+  %dead1 = add i32 %sub1, 1, !dbg !12
+  %dead2 = mul i32 %dead1, 3, !dbg !13
+  %dead3 = mul i32 %dead2, %sub1, !dbg !14
+  %sub2 = sub nsw i32 0, %d.0, !dbg !15
+  store i32 %sub2, ptr %ptr, align 4, !dbg !16
+  br label %for.cond, !dbg !17
+
+for.end:                                          ; preds = %for.cond
+  ret void, !dbg !18
+}
+
+!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: "debugloc.ll", directory: "/")
+!2 = !{i32 11}
+!3 = !{i32 0}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "fn1", linkageName: "fn1", 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)
+!9 = !DILocation(line: 2, column: 1, scope: !5)
+!10 = !DILocation(line: 3, column: 1, scope: !5)
+!11 = !DILocation(line: 4, column: 1, scope: !5)
+!12 = !DILocation(line: 5, column: 1, scope: !5)
+!13 = !DILocation(line: 6, column: 1, scope: !5)
+!14 = !DILocation(line: 7, column: 1, scope: !5)
+!15 = !DILocation(line: 8, column: 1, scope: !5)
+!16 = !DILocation(line: 9, column: 1, scope: !5)
+!17 = !DILocation(line: 10, column: 1, scope: !5)
+!18 = !DILocation(line: 11, column: 1, scope: !5)