Some improvements to the handling of C11 atomic types:

- Add atomic-to/from-nonatomic cast types
- Emit atomic operations for arithmetic on atomic types
- Emit non-atomic stores for initialisation of atomic types, but atomic stores and loads for every other store / load
- Add a __atomic_init() intrinsic which does a non-atomic store to an _Atomic() type.  This is needed for the corresponding C11 stdatomic.h function.
- Enables the relevant __has_feature() checks.  The feature isn't 100% complete yet, but it's done enough that we want people testing it.

Still to do:

- Make the arithmetic operations on atomic types (e.g. Atomic(int) foo = 1; foo++;) use the correct LLVM intrinsic if one exists, not a loop with a cmpxchg.
- Add a signal fence builtin
- Properly set the fenv state in atomic operations on floating point values
- Correctly handle things like _Atomic(_Complex double) which are too large for an atomic cmpxchg on some platforms (this requires working out what 'correctly' means in this context)
- Fix the many remaining corner cases

llvm-svn: 148242

clang/lib/Frontend/InitPreprocessor.cpp

@@ -325,6 +325,14 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
   Builder.defineMacro("__GNUC__", "4");
   Builder.defineMacro("__GXX_ABI_VERSION", "1002");
 
+  // Define macros for the C11 / C++11 memory orderings
+  Builder.defineMacro("__ATOMIC_RELAXED", "0");
+  Builder.defineMacro("__ATOMIC_CONSUME", "1");
+  Builder.defineMacro("__ATOMIC_ACQUIRE", "2");
+  Builder.defineMacro("__ATOMIC_RELEASE", "3");
+  Builder.defineMacro("__ATOMIC_ACQ_REL", "4");
+  Builder.defineMacro("__ATOMIC_SEQ_CST", "5");
+
   // As sad as it is, enough software depends on the __VERSION__ for version
   // checks that it is necessary to report 4.2.1 (the base GCC version we claim
   // compatibility with) first.