[DebugInfo][Reassociate] Fix missing debug location drop

llvm/lib/Transforms/Scalar/Reassociate.cpp

@@ -844,7 +844,13 @@ static Value *NegateValue(Value *V, Instruction *BI,
                      ->getIterator();
     }
 
+    // Check that if TheNeg is moved out of its parent block, we drop its
+    // debug location to avoid extra coverage.
+    // See test dropping_debugloc_the_neg.ll for a detailed example.
+    if (TheNeg->getParent() != InsertPt->getParent())
+      TheNeg->dropLocation();
     TheNeg->moveBefore(*InsertPt->getParent(), InsertPt);
+
     if (TheNeg->getOpcode() == Instruction::Sub) {
       TheNeg->setHasNoUnsignedWrap(false);
       TheNeg->setHasNoSignedWrap(false);

llvm/test/Transforms/Reassociate/dropping_debugloc_the_neg.ll

@@ -0,0 +1,54 @@
+; RUN: opt < %s -passes=reassociate -S | FileCheck %s
+
+; Check that Reassociate's NegateValue() drops the debug location of `%sub2` 
+; when moving it out of the loop's body (`%for.body`) to `%for.cond`.
+
+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)