[Frontend] Add a predefined macro that describes the Objective-C bool type

[arphaman]

Summary

This patch adds a new predefined macro named __OBJC_BOOL_IS_BOOL that describes the Objective-C boolean type: its value is zero if the Objective-C boolean uses the signed character type, otherwise its value is one as the Objective-C boolean uses the builtin boolean type.

[t.p.northover]

Looks reasonable to me.

Tim.

cfe/trunk/lib/Frontend/InitPreprocessor.cpp

#undef TOSTR2
   if (LangOpts.ObjC1) {
     if (LangOpts.ObjCRuntime.isNonFragile()) {
       Builder.defineMacro("__OBJC2__");
       
       if (LangOpts.ObjCExceptions)
         Builder.defineMacro("OBJC_ZEROCOST_EXCEPTIONS");
     }
 
+    Builder.defineMacro("__OBJC_BOOL_IS_BOOL",
+                        Twine(TI.useSignedCharForObjCBool() ? "0" : "1"));
+
     if (LangOpts.getGC() != LangOptions::NonGC)
       Builder.defineMacro("__OBJC_GC__");
 
     if (LangOpts.ObjCRuntime.isNeXTFamily())
       Builder.defineMacro("__NEXT_RUNTIME__");
 
     if (LangOpts.ObjCRuntime.getKind() == ObjCRuntime::ObjFW) {
       VersionTuple tuple = LangOpts.ObjCRuntime.getVersion();

cfe/trunk/test/Frontend/objc-bool-is-bool.m

+// RUN: %clang_cc1 -fsyntax-only -E -dM -triple=armv7k-apple-watchos %s | FileCheck --check-prefix=BOOL %s
+// RUN: %clang_cc1 -fsyntax-only -E -dM -triple=x86_64-apple-darwin16 %s | FileCheck --check-prefix=CHAR %s
+// RUN: %clang_cc1 -x c -fsyntax-only -E -dM -triple=x86_64-apple-darwin16 %s | FileCheck --check-prefix=NONE %s
+
+// rdar://21170440
+
+// BOOL: #define __OBJC_BOOL_IS_BOOL 1
+// BOOL-NOT: #define __OBJC_BOOL_IS_BOOL 0
+
+// CHAR: #define __OBJC_BOOL_IS_BOOL 0
+// CHAR-NOT: #define __OBJC_BOOL_IS_BOOL 1
+
+// NONE-NOT: __OBJC_BOOL_IS_BOOL