[clang] [Clang][DebugInfo] Clang generates an extra spurious unnamed 'dbg.declare' (PR #69681)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Carlos Alberto Enciso (CarlosAlbertoEnciso)

<details>
<summary>Changes</summary>

Do not emit call to llvm.dbg.declare when the variable declaration
is a DecompositionDecl as its instance class is always unnamed.

The emitted debug declare looks like:
```
call void @<!-- -->llvm.dbg.declare(metadata ..., metadata !xx, metadata ...)
!xx = !DILocalVariable(scope: !..., file: !..., line: ..., type: !...)
```


---
Full diff: https://github.com/llvm/llvm-project/pull/69681.diff


4 Files Affected:

- (modified) clang/lib/CodeGen/CGDebugInfo.cpp (+5-1) 
- (modified) clang/test/CodeGenCXX/debug-info-structured-binding-bitfield.cpp (-3) 
- (added) clang/test/CodeGenCXX/debug-info-structured-binding-field.cpp (+20) 
- (modified) clang/test/CodeGenCXX/debug-info-structured-binding.cpp (-2) 


``````````diff
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index c430713b0d77d79..b2646cd1d2a0f53 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -4879,11 +4879,15 @@ CGDebugInfo::EmitDeclareOfAutoVariable(const VarDecl *VD, llvm::Value *Storage,
                                        const bool UsePointerValue) {
   assert(CGM.getCodeGenOpts().hasReducedDebugInfo());
 
-  if (auto *DD = dyn_cast<DecompositionDecl>(VD))
+  if (auto *DD = dyn_cast<DecompositionDecl>(VD)) {
     for (auto *B : DD->bindings()) {
       EmitDeclare(B, Storage, std::nullopt, Builder,
                   VD->getType()->isReferenceType());
     }
+    // Don't emit an llvm.dbg.declare for the composite storage as it doesn't
+    // correspond to a user variable.
+    return nullptr;
+  }
 
   return EmitDeclare(VD, Storage, std::nullopt, Builder, UsePointerValue);
 }
diff --git a/clang/test/CodeGenCXX/debug-info-structured-binding-bitfield.cpp b/clang/test/CodeGenCXX/debug-info-structured-binding-bitfield.cpp
index b5ee96224565d3a..0234e41009f6225 100644
--- a/clang/test/CodeGenCXX/debug-info-structured-binding-bitfield.cpp
+++ b/clang/test/CodeGenCXX/debug-info-structured-binding-bitfield.cpp
@@ -189,7 +189,6 @@ struct S11 {
 // CHECK-LABEL: define dso_local void @_Z4fS11v
 // CHECK:                        alloca %struct.S11, align 4
 // CHECK-NEXT:    [[TMP0:%.*]] = alloca %struct.S11, align 4
-// CHECK:         call void @llvm.dbg.declare(metadata ptr [[TMP0]]
 // CHECK-NOT:     call void @llvm.dbg.declare(metadata ptr [[TMP0]]
 //
 void fS11() {
@@ -206,7 +205,6 @@ struct S12 {
 // CHECK:                        alloca %struct.S12, align 4
 // CHECK-NEXT:    [[TMP0:%.*]] = alloca %struct.S12, align 4
 // CHECK:         call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata [[S12_A:![0-9]+]], metadata !DIExpression())
-// CHECK:         call void @llvm.dbg.declare(metadata ptr [[TMP0]]
 // CHECK-NOT:     call void @llvm.dbg.declare(metadata ptr [[TMP0]]
 //
 void fS12() {
@@ -222,7 +220,6 @@ struct __attribute__((packed)) S13 {
 // CHECK-LABEL: define dso_local void @_Z4fS13v
 // CHECK:                        alloca %struct.S13, align 1
 // CHECK-NEXT:    [[TMP0:%.*]] = alloca %struct.S13, align 1
-// CHECK:         call void @llvm.dbg.declare(metadata ptr [[TMP0]], metadata {{.*}}, metadata !DIExpression())
 // CHECK-NOT:     call void @llvm.dbg.declare(metadata ptr [[TMP0]]
 //
 void fS13() {
diff --git a/clang/test/CodeGenCXX/debug-info-structured-binding-field.cpp b/clang/test/CodeGenCXX/debug-info-structured-binding-field.cpp
new file mode 100644
index 000000000000000..928d22776d21093
--- /dev/null
+++ b/clang/test/CodeGenCXX/debug-info-structured-binding-field.cpp
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -emit-llvm -debug-info-kind=standalone %s -o - | FileCheck %s
+
+struct Tuple {
+  int Fld_1;
+  int Fld_2;
+};
+__attribute__((optnone)) Tuple get() { return {10, 20}; }
+
+// CHECK-LABEL: define dso_local noundef i32 @main
+// CHECK:      %retval = alloca i32, align 4
+// CHECK-NEXT: [[T0:%.*]] = alloca %struct.Tuple, align 4
+// CHECK:      call void @llvm.dbg.declare(metadata ptr [[T0]], metadata {{.*}}, metadata !DIExpression())
+// CHECK:      call void @llvm.dbg.declare(metadata ptr [[T0]], metadata {{.*}}, metadata !DIExpression(DW_OP_plus_uconst, {{[0-9]+}}))
+// CHECK-NOT:  call void @llvm.dbg.declare(metadata ptr [[T0]], metadata {{.*}}, metadata !DIExpression())
+//
+int main() {
+  auto [Var_1, Var_2] = get();
+
+  return Var_1 + Var_2;
+}
diff --git a/clang/test/CodeGenCXX/debug-info-structured-binding.cpp b/clang/test/CodeGenCXX/debug-info-structured-binding.cpp
index 8d4ae0aaf32636b..163c152efa19d0b 100644
--- a/clang/test/CodeGenCXX/debug-info-structured-binding.cpp
+++ b/clang/test/CodeGenCXX/debug-info-structured-binding.cpp
@@ -2,10 +2,8 @@
 
 // CHECK: call void @llvm.dbg.declare(metadata ptr %{{[0-9]+}}, metadata !{{[0-9]+}}, metadata !DIExpression())
 // CHECK: call void @llvm.dbg.declare(metadata ptr %{{[0-9]+}}, metadata !{{[0-9]+}}, metadata !DIExpression(DW_OP_plus_uconst, {{[0-9]+}}))
-// CHECK: call void @llvm.dbg.declare(metadata ptr %{{[0-9]+}}, metadata !{{[0-9]+}}, metadata !DIExpression())
 // CHECK: call void @llvm.dbg.declare(metadata ptr %{{[0-9]+}}, metadata !{{[0-9]+}}, metadata !DIExpression(DW_OP_deref))
 // CHECK: call void @llvm.dbg.declare(metadata ptr %{{[0-9]+}}, metadata !{{[0-9]+}}, metadata !DIExpression(DW_OP_deref, DW_OP_plus_uconst, {{[0-9]+}}))
-// CHECK: call void @llvm.dbg.declare(metadata ptr %{{[0-9]+}}, metadata !{{[0-9]+}}, metadata !DIExpression())
 struct A {
   int x;
   int y;

``````````

</details>


https://github.com/llvm/llvm-project/pull/69681