[clang] [DebugInfo] Correct the line attribution for IF branches (PR #108300)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-codegen

Author: Paul T Robinson (pogo59)

<details>
<summary>Changes</summary>

An 'if' statement introduces a scope, but in some cases the conditional branch to the then/else blocks had a debug-info attribution that did not include the scope. This led to some inefficiency in the DWARF line table.

---
Full diff: https://github.com/llvm/llvm-project/pull/108300.diff


2 Files Affected:

- (modified) clang/lib/CodeGen/CGStmt.cpp (+1) 
- (added) clang/test/CodeGenCXX/debug-info-line-if-2.cpp (+45) 


``````````diff
diff --git a/clang/lib/CodeGen/CGStmt.cpp b/clang/lib/CodeGen/CGStmt.cpp
index b138c87a853495..2fae4cf666c6b9 100644
--- a/clang/lib/CodeGen/CGStmt.cpp
+++ b/clang/lib/CodeGen/CGStmt.cpp
@@ -815,6 +815,7 @@ void CodeGenFunction::EmitIfStmt(const IfStmt &S) {
   // C99 6.8.4.1: The first substatement is executed if the expression compares
   // unequal to 0.  The condition must be a scalar type.
   LexicalScope ConditionScope(*this, S.getCond()->getSourceRange());
+  ApplyDebugLocation DL(*this, S.getCond());
 
   if (S.getInit())
     EmitStmt(S.getInit());
diff --git a/clang/test/CodeGenCXX/debug-info-line-if-2.cpp b/clang/test/CodeGenCXX/debug-info-line-if-2.cpp
new file mode 100644
index 00000000000000..8ab96a7daf4c47
--- /dev/null
+++ b/clang/test/CodeGenCXX/debug-info-line-if-2.cpp
@@ -0,0 +1,45 @@
+// RUN: %clang_cc1 -debug-info-kind=limited -gno-column-info -triple=x86_64-pc-linux -emit-llvm %s -o - | FileCheck  %s
+
+// The important thing is that the compare and the conditional branch have
+// locs with the same scope (the lexical block for the 'if'). By turning off
+// column info, they end up with the same !dbg record, which halves the number
+// of checks to verify the scope.
+
+int c = 2;
+
+int f() {
+#line 100
+  if (int a = 5; a > c)
+    return 1;
+  return 0;
+}
+// CHECK-LABEL: define {{.*}} @_Z1fv()
+// CHECK:       = icmp {{.*}} !dbg [[F_CMP:![0-9]+]]
+// CHECK-NEXT:  br i1 {{.*}} !dbg [[F_CMP]]
+
+int g() {
+#line 200
+  if (int a = f())
+    return 2;
+  return 3;
+}
+// CHECK-LABEL: define {{.*}} @_Z1gv()
+// CHECK:       = icmp {{.*}} !dbg [[G_CMP:![0-9]+]]
+// CHECK-NEXT:  br i1 {{.*}} !dbg [[G_CMP]]
+
+int h() {
+#line 300
+  if (c > 3)
+    return 4;
+  return 5;
+}
+// CHECK-LABEL: define {{.*}} @_Z1hv()
+// CHECK:       = icmp {{.*}} !dbg [[H_CMP:![0-9]+]]
+// CHECK-NEXT:  br i1 {{.*}} !dbg [[H_CMP]]
+
+// CHECK-DAG: [[F_CMP]] = !DILocation(line: 100, scope: [[F_SCOPE:![0-9]+]]
+// CHECK-DAG: [[F_SCOPE]] = distinct !DILexicalBlock({{.*}} line: 100)
+// CHECK-DAG: [[G_CMP]] = !DILocation(line: 200, scope: [[G_SCOPE:![0-9]+]]
+// CHECK-DAG: [[G_SCOPE]] = distinct !DILexicalBlock({{.*}} line: 200)
+// CHECK-DAG: [[H_CMP]] = !DILocation(line: 300, scope: [[H_SCOPE:![0-9]+]]
+// CHECK-DAG: [[H_SCOPE]] = distinct !DILexicalBlock({{.*}} line: 300)

``````````

</details>


https://github.com/llvm/llvm-project/pull/108300