[clang] [clang] Add CodeGen tests for CWG 5xx issues (PR #84303)

[Vlad Serebrennikov via cfe-commits]

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@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -std=c++98 %s -triple x86_64-linux-gnu -emit-llvm -o - -fexceptions -fcxx-exceptions -pedantic-errors | llvm-cxxfilt -n | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++11 %s -triple x86_64-linux-gnu -emit-llvm -o - -fexceptions -fcxx-exceptions -pedantic-errors | llvm-cxxfilt -n | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++14 %s -triple x86_64-linux-gnu -emit-llvm -o - -fexceptions -fcxx-exceptions -pedantic-errors | llvm-cxxfilt -n | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++17 %s -triple x86_64-linux-gnu -emit-llvm -o - -fexceptions -fcxx-exceptions -pedantic-errors | llvm-cxxfilt -n | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++20 %s -triple x86_64-linux-gnu -emit-llvm -o - -fexceptions -fcxx-exceptions -pedantic-errors | llvm-cxxfilt -n | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++23 %s -triple x86_64-linux-gnu -emit-llvm -o - -fexceptions -fcxx-exceptions -pedantic-errors | llvm-cxxfilt -n | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++2c %s -triple x86_64-linux-gnu -emit-llvm -o - -fexceptions -fcxx-exceptions -pedantic-errors | llvm-cxxfilt -n | FileCheck %s --check-prefixes CHECK
+
+namespace dr571 { // dr571: 2.7
+  typedef int &ir;
+  int n;
+  const ir r = n;
+  // expected-warning at -1 {{'const' qualifier on reference type 'ir' (aka 'int &') has no effect}}
+  ir r2 = n;
+}
+
+// Entities have external linkage by default.
+
+// CHECK: @dr571::r = constant ptr @dr571::n
+// CHECK: @dr571::r2 = constant ptr @dr571::n
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Endilll wrote:

According to https://llvm.org/docs/LangRef.html#linkage-types, entities with no linkage specified are external, and that's what matters in this test, as it has direct correspondence to linkage the Standard speaks of.

I'm not sure what do we need to pass to `-cc1` to make `dso_local` appear as CE does, but my understanding that if you load your dynamic library multiple times into the same process, each would maintain its own set of `dso_local` entities. So it's like internal linkage, but on dynamic linker level.

https://github.com/llvm/llvm-project/pull/84303