Fix linking for some users who already have tsan enabled code and are trying to

link it against llvm code, by making our definitions weak. "Some users."

llvm-svn: 144596

llvm/include/llvm/Support/Compiler.h

@@ -61,12 +61,19 @@
 #define LLVM_ATTRIBUTE_READONLY
 #endif
 
+#if (__GNUC__ >= 4)
+#define LLVM_ATTRIBUTE_WEAK __attribute__((__weak__))
+#else
+#define LLVM_ATTRIBUTE_WEAK
+#endif
+
 #if (__GNUC__ >= 4)
 #define BUILTIN_EXPECT(EXPR, VALUE) __builtin_expect((EXPR), (VALUE))
 #else
 #define BUILTIN_EXPECT(EXPR, VALUE) (EXPR)
 #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>);

llvm/lib/Support/Valgrind.cpp

@@ -56,10 +56,10 @@ void llvm::sys::ValgrindDiscardTranslations(const void *Addr, size_t Len) {
 // These functions require no implementation, tsan just looks at the arguments
 // they're called with.
 extern "C" {
-void AnnotateHappensBefore(const char *file, int line,
+LLVM_ATTRIBUTE_WEAK void AnnotateHappensBefore(const char *file, int line,
                                                const volatile void *cv) {}
-void AnnotateHappensAfter(const char *file, int line,
+LLVM_ATTRIBUTE_WEAK void AnnotateHappensAfter(const char *file, int line,
                                               const volatile void *cv) {}
-void AnnotateIgnoreWritesBegin(const char *file, int line) {}
-void AnnotateIgnoreWritesEnd(const char *file, int line) {}
+LLVM_ATTRIBUTE_WEAK void AnnotateIgnoreWritesBegin(const char *file, int line){}
+LLVM_ATTRIBUTE_WEAK void AnnotateIgnoreWritesEnd(const char *file, int line) {}
 }