[clang] [CIR] Add empty handlers for Using and UsingShadow decls (PR #143032)

[Andy Kaylor via cfe-commits]

https://github.com/andykaylor created https://github.com/llvm/llvm-project/pull/143032

This adds emitTopLevelDecl "handlers" for Using and UsingShadow. These don't actually need any handling, but they need to be present in the switch to avoid hitting the default handler, which issues a diagnostic about the decl kind not being implemented.

There are several other decl kinds that don't need any handling. Those will be added when I have test cases for them.

>From 409e45f7c5bcb3d8549b373cfeac9f4c4cc0e8a4 Mon Sep 17 00:00:00 2001
From: Andy Kaylor <akaylor at nvidia.com>
Date: Thu, 5 Jun 2025 10:07:50 -0700
Subject: [PATCH] [CIR] Add empty handlers for Using and UsingShadow decls

This adds emitTopLevelDecl "handlers" for Using and UsingShadow. These
don't actually need any handling, but they need to be present in the
switch to avoid hitting the default handler, which issues a diagnostic
about the decl kind not being implemented.

There are several other decl kinds that don't need any handling. Those
will be added when I have test cases for them.
---
 clang/lib/CIR/CodeGen/CIRGenModule.cpp |  5 +++
 clang/test/CIR/CodeGen/namespace.cpp   | 43 ++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/clang/lib/CIR/CodeGen/CIRGenModule.cpp b/clang/lib/CIR/CodeGen/CIRGenModule.cpp
index 87e364197ce7e..1c8945206d448 100644
--- a/clang/lib/CIR/CodeGen/CIRGenModule.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenModule.cpp
@@ -1135,6 +1135,7 @@ void CIRGenModule::emitTopLevelDecl(Decl *decl) {
     emitGlobalOpenACCDecl(cast<OpenACCDeclareDecl>(decl));
     break;
   case Decl::Enum:
+  case Decl::Using:          // using X; [C++]
   case Decl::UsingDirective: // using namespace X; [C++]
   case Decl::Typedef:
   case Decl::TypeAlias: // using foo = bar; [C++11]
@@ -1143,6 +1144,10 @@ void CIRGenModule::emitTopLevelDecl(Decl *decl) {
     assert(!cir::MissingFeatures::generateDebugInfo());
     break;
 
+  // No code generation needed.
+  case Decl::UsingShadow:
+    break;
+
   // C++ Decls
   case Decl::LinkageSpec:
   case Decl::Namespace:
diff --git a/clang/test/CIR/CodeGen/namespace.cpp b/clang/test/CIR/CodeGen/namespace.cpp
index caa43f960c6c2..14490d505140c 100644
--- a/clang/test/CIR/CodeGen/namespace.cpp
+++ b/clang/test/CIR/CodeGen/namespace.cpp
@@ -50,3 +50,46 @@ int f4(void) {
 // CHECK:   %[[G3_ADDR:.*]] = cir.get_global @_ZN4test5test22g3E : !cir.ptr<!s32i>
 // CHECK:   %[[G3_VAL:.*]] = cir.load{{.*}} %[[G3_ADDR]] : !cir.ptr<!s32i>, !s32i
 // CHECK:   %[[SUM2:.*]] = cir.binop(add, %[[SUM]], %[[G3_VAL]]) nsw : !s32i
+
+using test2::f3;
+using test2::g3;
+
+int f5() {
+  f3();
+  return g3;
+}
+
+// CHECK: cir.func @_Z2f5v()
+// CHECK:   cir.call @_ZN4test5test22f3Ev()
+// CHECK:   %[[G3_ADDR:.*]] = cir.get_global @_ZN4test5test22g3E : !cir.ptr<!s32i>
+// CHECK:   %[[G3_VAL:.*]] = cir.load{{.*}} %[[G3_ADDR]] : !cir.ptr<!s32i>, !s32i
+
+namespace test3 {
+  struct S {
+    int a;
+  } s;
+}
+
+using test3::s;
+
+int f6() {
+  return s.a;
+}
+
+// CHECK: cir.func @_Z2f6v()
+// CHECK:   cir.get_global @_ZN5test31sE : !cir.ptr<!rec_test33A3AS>
+// CHECK:   cir.get_member %{{.*}}[0] {name = "a"}
+
+int shadowedFunc() {
+  return 3;
+}
+
+namespace shadow {
+  using ::shadowedFunc;
+}
+
+void f7() {
+  shadow::shadowedFunc();
+}
+
+// CHECK: cir.func @_Z2f7v()