Define weak and __weak to mean ARC-style weak references, even in MRC.

Previously, __weak was silently accepted and ignored in MRC mode.
That makes this a potentially source-breaking change that we have to
roll out cautiously.  Accordingly, for the time being, actual support
for __weak references in MRC is experimental, and the compiler will
reject attempts to actually form such references.  The intent is to
eventually enable the feature by default in all non-GC modes.
(It is, of course, incompatible with ObjC GC's interpretation of
__weak.)

If you like, you can enable this feature with
  -Xclang -fobjc-weak
but like any -Xclang option, this option may be removed at any point,
e.g. if/when it is eventually enabled by default.

This patch also enables the use of the ARC __unsafe_unretained qualifier
in MRC.  Unlike __weak, this is being enabled immediately.  Since
variables are essentially __unsafe_unretained by default in MRC,
the only practical uses are (1) communication and (2) changing the
default behavior of by-value block capture.

As an implementation matter, this means that the ObjC ownership
qualifiers may appear in any ObjC language mode, and so this patch
removes a number of checks for getLangOpts().ObjCAutoRefCount
that were guarding the processing of these qualifiers.  I don't
expect this to be a significant drain on performance; it may even
be faster to just check for these qualifiers directly on a type
(since it's probably in a register anyway) than to do N dependent
loads to grab the LangOptions.

rdar://9674298

llvm-svn: 251041

1 files changed, 27 insertions, 21 deletions

diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index dc075793ac8..3d62d88917b 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -323,15 +323,17 @@ static void AddObjCXXARCLibstdcxxDefines(const LangOptions &LangOpts,
     
     Out << "template<typename _Tp> struct __is_scalar;\n"
         << "\n";
+
+    if (LangOpts.ObjCAutoRefCount) {
+      Out << "template<typename _Tp>\n"
+          << "struct __is_scalar<__attribute__((objc_ownership(strong))) _Tp> {\n"
+          << "  enum { __value = 0 };\n"
+          << "  typedef __false_type __type;\n"
+          << "};\n"
+          << "\n";
+    }
       
-    Out << "template<typename _Tp>\n"
-        << "struct __is_scalar<__attribute__((objc_ownership(strong))) _Tp> {\n"
-        << "  enum { __value = 0 };\n"
-        << "  typedef __false_type __type;\n"
-        << "};\n"
-        << "\n";
-      
-    if (LangOpts.ObjCARCWeak) {
+    if (LangOpts.ObjCWeak) {
       Out << "template<typename _Tp>\n"
           << "struct __is_scalar<__attribute__((objc_ownership(weak))) _Tp> {\n"
           << "  enum { __value = 0 };\n"
@@ -340,13 +342,15 @@ static void AddObjCXXARCLibstdcxxDefines(const LangOptions &LangOpts,
           << "\n";
     }
     
-    Out << "template<typename _Tp>\n"
-        << "struct __is_scalar<__attribute__((objc_ownership(autoreleasing)))"
-        << " _Tp> {\n"
-        << "  enum { __value = 0 };\n"
-        << "  typedef __false_type __type;\n"
-        << "};\n"
-        << "\n";
+    if (LangOpts.ObjCAutoRefCount) {
+      Out << "template<typename _Tp>\n"
+          << "struct __is_scalar<__attribute__((objc_ownership(autoreleasing)))"
+          << " _Tp> {\n"
+          << "  enum { __value = 0 };\n"
+          << "  typedef __false_type __type;\n"
+          << "};\n"
+          << "\n";
+    }
       
     Out << "}\n";
   }
@@ -851,9 +855,6 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
   else if (LangOpts.getStackProtector() == LangOptions::SSPReq)
     Builder.defineMacro("__SSP_ALL__", "3");
 
-  if (FEOpts.ProgramAction == frontend::RewriteObjC)
-    Builder.defineMacro("__weak", "__attribute__((objc_gc(weak)))");
-
   // Define a macro that exists only when using the static analyzer.
   if (FEOpts.ProgramAction == frontend::RunAnalysis)
     Builder.defineMacro("__clang_analyzer__");
@@ -861,7 +862,11 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
   if (LangOpts.FastRelaxedMath)
     Builder.defineMacro("__FAST_RELAXED_MATH__");
 
-  if (LangOpts.ObjCAutoRefCount) {
+  if (FEOpts.ProgramAction == frontend::RewriteObjC ||
+      LangOpts.getGC() != LangOptions::NonGC) {
+    Builder.defineMacro("__weak", "__attribute__((objc_gc(weak)))");
+    Builder.defineMacro("__strong", "__attribute__((objc_gc(strong)))");
+  } else if (LangOpts.ObjC1) {
     Builder.defineMacro("__weak", "__attribute__((objc_ownership(weak)))");
     Builder.defineMacro("__strong", "__attribute__((objc_ownership(strong)))");
     Builder.defineMacro("__autoreleasing",
@@ -928,10 +933,11 @@ void clang::InitializePreprocessor(
 
     // Install definitions to make Objective-C++ ARC work well with various
     // C++ Standard Library implementations.
-    if (LangOpts.ObjC1 && LangOpts.CPlusPlus && LangOpts.ObjCAutoRefCount) {
+    if (LangOpts.ObjC1 && LangOpts.CPlusPlus &&
+        (LangOpts.ObjCAutoRefCount || LangOpts.ObjCWeak)) {
       switch (InitOpts.ObjCXXARCStandardLibrary) {
       case ARCXX_nolib:
-        case ARCXX_libcxx:
+      case ARCXX_libcxx:
         break;
 
       case ARCXX_libstdcxx: