From: Reid Kleckner <rnk@google.com>
Date: Thu, 12 Sep 2019 17:55:48 +0000 (+0000)
Subject: Don't warn about selectany on implicitly inline variables
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=becdd39246301ef33e9a368f3ecaea97c8ee17cb;p=clang

Don't warn about selectany on implicitly inline variables

Summary:
This avoids a -Wignored-attribute warning on the code pattern Microsoft
recommends for integral const static data members defined in headers
here:
https://docs.microsoft.com/en-us/cpp/build/reference/microsoft-extensions-to-c-and-cpp?view=vs-2019

The attribute is redundant, but it is necessary when compiling in C++14
modes with /Za, which disables MSVC's extension that treats such
variables as implicitly inline.

Fixes PR43270

Reviewers: epastor, thakis, hans

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D67426

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@371749 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 663674dd74..91311cc948 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -2652,6 +2652,15 @@ static void checkNewAttributesAfterDef(Sema &S, Decl *New, const Decl *Old) {
         --E;
         continue;
       }
+    } else if (isa<SelectAnyAttr>(NewAttribute) &&
+               cast<VarDecl>(New)->isInline() &&
+               !cast<VarDecl>(New)->isInlineSpecified()) {
+      // Don't warn about applying selectany to implicitly inline variables.
+      // Older compilers and language modes would require the use of selectany
+      // to make such variables inline, and it would have no effect if we
+      // honored it.
+      ++I;
+      continue;
     }
 
     S.Diag(NewAttribute->getLocation(),
diff --git a/test/SemaCXX/declspec-selectany.cpp b/test/SemaCXX/declspec-selectany.cpp
new file mode 100644
index 0000000000..7e64a2924c
--- /dev/null
+++ b/test/SemaCXX/declspec-selectany.cpp
@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -std=c++14 %s -triple x86_64-windows-msvc -fdeclspec -verify
+// RUN: %clang_cc1 -std=c++17 %s -triple x86_64-windows-msvc -fdeclspec -verify
+// RUN: %clang_cc1 -std=c++14 %s -triple x86_64-scei-ps4 -fdeclspec -verify
+
+// MSVC emits this error too.
+const int __declspec(selectany) test1 = 0; // expected-error {{'selectany' can only be applied to data items with external linkage}}
+
+extern const int test2;
+const int test2 = 42; // expected-note {{previous definition is here}}
+extern __declspec(selectany) const int test2; // expected-warning {{attribute declaration must precede definition}}
+
+extern const int test3;
+const int __declspec(selectany) test3 = 42; // Standard usage.
+
+struct Test4 {
+  static constexpr int sdm = 0;
+};
+__declspec(selectany) constexpr int Test4::sdm; // no warning