[UBSan] Add !nosanitize metadata to the code generated by UBSan.

This is used to mark the instructions emitted by Clang to implement
variety of UBSan checks. Generally, we don't want to instrument these
instructions with another sanitizers (like ASan).

Reviewed in http://reviews.llvm.org/D4544

llvm-svn: 213291

clang/lib/CodeGen/CodeGenFunction.h

@@ -247,6 +247,17 @@ public:
   /// \brief Sanitizer options to use for this function.
   const SanitizerOptions *SanOpts;
 
+  /// \brief True if CodeGen currently emits code implementing sanitizer checks.
+  bool IsSanitizerScope;
+
+  /// \brief RAII object to set/unset CodeGenFunction::IsSanitizerScope.
+  class SanitizerScope {
+    CodeGenFunction *CGF;
+  public:
+    SanitizerScope(CodeGenFunction *CGF);
+    ~SanitizerScope();
+  };
+
   /// In ARC, whether we should autorelease the return value.
   bool AutoreleaseResult;