r283063 - Alias must point to a definition

[Yaron Keren via cfe-commits]

The mangling is different when targeting MSVC ABI, see failure at

http://bb.pgr.jp/builders/ninja-x64-msvc-RA-centos6/builds/29889/steps/test_all/logs/Clang%20%3A%3A%20CodeGenCXX__alias-available-externally.cpp

maybe   -triple x86_64-pc-linux  ?

2016-10-02 6:06 GMT+03:00 Aditya Kumar via cfe-commits <
cfe-commits at lists.llvm.org>:

> Author: hiraditya
> Date: Sat Oct  1 22:06:36 2016
> New Revision: 283063
>
> URL: http://llvm.org/viewvc/llvm-project?rev=283063&view=rev
> Log:
> Alias must point to a definition
>
> Reapplying the patch after modifying the test case.
>
> Inlining the destructor caused the compiler to generate bad IR which
> failed the Verifier in the backend.
> https://llvm.org/bugs/show_bug.cgi?id=30341
>
> This patch disables alias to available_externally definitions.
>
> Reviewers: eugenis, rsmith
>
> Differential Revision: https://reviews.llvm.org/D24682
>
> Added:
>     cfe/trunk/test/CodeGenCXX/alias-available-externally.cpp
> Modified:
>     cfe/trunk/lib/CodeGen/CGCXX.cpp
>
> Modified: cfe/trunk/lib/CodeGen/CGCXX.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/
> CGCXX.cpp?rev=283063&r1=283062&r2=283063&view=diff
> ============================================================
> ==================
> --- cfe/trunk/lib/CodeGen/CGCXX.cpp (original)
> +++ cfe/trunk/lib/CodeGen/CGCXX.cpp Sat Oct  1 22:06:36 2016
> @@ -134,6 +134,11 @@ bool CodeGenModule::TryEmitDefinitionAsA
>    llvm::GlobalValue::LinkageTypes TargetLinkage =
>        getFunctionLinkage(TargetDecl);
>
> +  // available_externally definitions aren't real definitions, so we
> cannot
> +  // create an alias to one.
> +  if (TargetLinkage == llvm::GlobalValue::AvailableExternallyLinkage)
> +    return true;
> +
>    // Check if we have it already.
>    StringRef MangledName = getMangledName(AliasDecl);
>    llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
> @@ -156,14 +161,7 @@ bool CodeGenModule::TryEmitDefinitionAsA
>
>    // Instead of creating as alias to a linkonce_odr, replace all of the
> uses
>    // of the aliasee.
> -  if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) &&
> -     (TargetLinkage != llvm::GlobalValue::AvailableExternallyLinkage ||
> -      !TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) {
> -    // FIXME: An extern template instantiation will create functions with
> -    // linkage "AvailableExternally". In libc++, some classes also define
> -    // members with attribute "AlwaysInline" and expect no reference to
> -    // be generated. It is desirable to reenable this optimisation after
> -    // corresponding LLVM changes.
> +  if (llvm::GlobalValue::isDiscardableIfUnused(Linkage)) {
>      addReplacement(MangledName, Aliasee);
>      return false;
>    }
>
> Added: cfe/trunk/test/CodeGenCXX/alias-available-externally.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/
> CodeGenCXX/alias-available-externally.cpp?rev=283063&view=auto
> ============================================================
> ==================
> --- cfe/trunk/test/CodeGenCXX/alias-available-externally.cpp (added)
> +++ cfe/trunk/test/CodeGenCXX/alias-available-externally.cpp Sat Oct  1
> 22:06:36 2016
> @@ -0,0 +1,20 @@
> +// RUN: %clang_cc1 -O1 -std=c++11 -emit-llvm -disable-llvm-passes -o - %s
> | FileCheck %s
> +// Clang should not generate alias to available_externally definitions.
> +// Check that the destructor of Foo is defined.
> +// The destructors have different return type for different targets.
> +// CHECK: define linkonce_odr {{.*}} @_ZN3FooD2Ev
> +template <class CharT>
> +struct String {
> +  String() {}
> +  ~String();
> +};
> +
> +template <class CharT>
> +inline __attribute__((visibility("hidden"), always_inline))
> +String<CharT>::~String() {}
> +
> +extern template struct String<char>;
> +
> +struct Foo : public String<char> { Foo() { String<char> s; } };
> +
> +Foo f;
>
>
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