New place to put compiler-specific functionality. This replaces Visibility.h,

and provides macros that can be used to make explicit instantiations of
template specializations, which is a gcc-specific feature.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@29908 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/Compiler.h

@@ -0,0 +1,40 @@
+//===-- llvm/Support/Compiler.h - Compiler abstraction support --*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by Chris Lattner and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines several macros, based on the current compiler.  This allows
+// use of compiler-specific features in a way that remains portable.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_COMPILER_H
+#define LLVM_SUPPORT_COMPILER_H
+
+// The VISIBILITY_HIDDEN macro, used for marking classes with the GCC-specific
+// visibility("hidden") attribute.
+#if __GNUC__ >= 4
+#define VISIBILITY_HIDDEN __attribute__ ((visibility("hidden")))
+#else
+#define VISIBILITY_HIDDEN
+#endif
+
+
+// C++ doesn't support 'extern template' of template specializations.  GCC does,
+// but requires __extension__ before it.  In the header, use this:
+//   EXTERN_TEMPLATE_INSTANTIATION(class foo<bar>);
+// in the .cpp file, use this:
+//   TEMPLATE_INSTANTIATION(class foo<bar>);
+#ifdef __GNUC__
+#define EXTERN_TEMPLATE_INSTANTIATION(X) __extension__ extern template X
+#define TEMPLATE_INSTANTIATION(X) template X
+#else
+#define EXTERN_TEMPLATE_INSTANTIATION(X)
+#define TEMPLATE_INSTANTIATION(X)
+#endif
+
+#endif