Add speculatable function attribute

This attribute tells the optimizer that the function may be speculated.

Patch by Tom Stellard

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301680 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -688,6 +688,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     return bitc::ATTR_KIND_RETURNS_TWICE;
   case Attribute::SExt:
     return bitc::ATTR_KIND_S_EXT;
+  case Attribute::Speculatable:
+    return bitc::ATTR_KIND_SPECULATABLE;
   case Attribute::StackAlignment:
     return bitc::ATTR_KIND_STACK_ALIGNMENT;
   case Attribute::StackProtect: