Add a new attribute called 'jumptable' that creates jump-instruction tables for functions marked with this attribute.

It includes a pass that rewrites all indirect calls to jumptable functions to pass through these tables.

This also adds backend support for generating the jump-instruction tables on ARM and X86.
Note that since the jumptable attribute creates a second function pointer for a
function, any function marked with jumptable must also be marked with unnamed_addr.

llvm-svn: 210280

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -177,6 +177,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     return bitc::ATTR_KIND_INLINE_HINT;
   case Attribute::InReg:
     return bitc::ATTR_KIND_IN_REG;
+  case Attribute::JumpTable:
+    return bitc::ATTR_KIND_JUMP_TABLE;
   case Attribute::MinSize:
     return bitc::ATTR_KIND_MIN_SIZE;
   case Attribute::Naked: