[DebugInfo][LowerConstantIntrinsics] Fix the missing debug location of new branch instruction (#97145)

Fix #97142 .

Author: Apochens

llvm/lib/Transforms/Scalar/LowerConstantIntrinsics.cpp

@@ -85,8 +85,11 @@ static bool replaceConditionalBranchesOnConstant(Instruction *II,
     if (Target && Target != Other) {
       BasicBlock *Source = BI->getParent();
       Other->removePredecessor(Source);
+
+      Instruction *NewBI = BranchInst::Create(Target, Source);
+      NewBI->setDebugLoc(BI->getDebugLoc());
       BI->eraseFromParent();
-      BranchInst::Create(Target, Source);
+
       if (DTU)
         DTU->applyUpdates({{DominatorTree::Delete, Source, Other}});
       if (pred_empty(Other))

llvm/test/Transforms/LowerConstantIntrinsics/preserving-debugloc-br.ll

@@ -0,0 +1,48 @@
+; RUN: opt -S -passes=lower-constant-intrinsics < %s | FileCheck %s
+
+; Check that LowerConstantIntrinsics's replaceConditionalBranchesOnConstant() correctly
+; propagates the debug location from the old br instruction to the new one.
+
+; Function Attrs: nounwind
+define i32 @test_branch(i32 %in) !dbg !5 {
+; CHECK-LABEL: define i32 @test_branch(
+; CHECK:           br label %[[FALSE:.*]], !dbg [[DBG8:![0-9]+]]
+; CHECK:       [[FALSE]]:
+;
+  %v = call i1 @llvm.is.constant.i32(i32 %in), !dbg !8
+  br i1 %v, label %True, label %False, !dbg !9
+
+True:                                             ; preds = %0
+  %call1 = tail call i32 @subfun_1(), !dbg !10
+  ret i32 %call1, !dbg !11
+
+False:                                            ; preds = %0
+  %call2 = tail call i32 @subfun_2(), !dbg !12
+  ret i32 %call2, !dbg !13
+}
+
+declare i32 @subfun_1()
+declare i32 @subfun_2()
+
+declare i1 @llvm.is.constant.i32(i32)
+
+!llvm.dbg.cu = !{!0}
+!llvm.debugify = !{!2, !3}
+!llvm.module.flags = !{!4}
+
+; CHECK: [[DBG8]] = !DILocation(line: 2,
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+!1 = !DIFile(filename: "main.ll", directory: "/")
+!2 = !{i32 6}
+!3 = !{i32 0}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "test_branch", linkageName: "test_branch", 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)