Add writeonly IR attribute

Summary:
This complements the earlier addition of IntrWriteMem and IntrWriteArgMem
LLVM intrinsic properties, see D18291.

Also start using the attribute for memset, memcpy, and memmove intrinsics,
and remove their special-casing in BasicAliasAnalysis.

Reviewers: reames, joker.eph

Subscribers: joker.eph, llvm-commits

Differential Revision: http://reviews.llvm.org/D18714

llvm-svn: 274485

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -667,6 +667,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     return bitc::ATTR_KIND_SWIFT_SELF;
   case Attribute::UWTable:
     return bitc::ATTR_KIND_UW_TABLE;
+  case Attribute::WriteOnly:
+    return bitc::ATTR_KIND_WRITEONLY;
   case Attribute::ZExt:
     return bitc::ATTR_KIND_Z_EXT;
   case Attribute::EndAttrKinds: