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

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: !...)

Author: CarlosAlbertoEnciso

clang/lib/CodeGen/CGDebugInfo.cpp

@@ -4881,11 +4881,15 @@ 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);
 }

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() {

clang/test/CodeGenCXX/debug-info-structured-binding.cpp

@@ -1,11 +1,16 @@
-// RUN: %clang_cc1 -emit-llvm -debug-info-kind=standalone -triple %itanium_abi_triple %s -o - | FileCheck %s
+// RUN: %clang_cc1 -emit-llvm -debug-info-kind=standalone -triple %itanium_abi_triple %s -o - | FileCheck %s --implicit-check-not="call void @llvm.dbg.declare"
+
+// CHECK: call void @llvm.dbg.declare(metadata ptr %{{[a-z]+}}, metadata ![[VAR_0:[0-9]+]], metadata !DIExpression())
+// CHECK: call void @llvm.dbg.declare(metadata ptr %{{[0-9]+}}, metadata ![[VAR_1:[0-9]+]], metadata !DIExpression())
+// CHECK: call void @llvm.dbg.declare(metadata ptr %{{[0-9]+}}, metadata ![[VAR_2:[0-9]+]], metadata !DIExpression(DW_OP_plus_uconst, 4))
+// CHECK: call void @llvm.dbg.declare(metadata ptr %{{[0-9]+}}, metadata ![[VAR_3:[0-9]+]], metadata !DIExpression(DW_OP_deref))
+// CHECK: call void @llvm.dbg.declare(metadata ptr %{{[0-9]+}}, metadata ![[VAR_4:[0-9]+]], metadata !DIExpression(DW_OP_deref, DW_OP_plus_uconst, 4))
+// CHECK: ![[VAR_0]] = !DILocalVariable(name: "a"
+// CHECK: ![[VAR_1]] = !DILocalVariable(name: "x1"
+// CHECK: ![[VAR_2]] = !DILocalVariable(name: "y1"
+// CHECK: ![[VAR_3]] = !DILocalVariable(name: "x2"
+// CHECK: ![[VAR_4]] = !DILocalVariable(name: "y2"
 
-// 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;