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.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210280 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/Attributes.h

@@ -75,6 +75,7 @@ public:
     Cold,                  ///< Marks function as being in a cold path.
     InlineHint,            ///< Source said inlining was desirable
     InReg,                 ///< Force argument to be passed in register
+    JumpTable,             ///< Build jump-instruction tables and replace refs.
     MinSize,               ///< Function must be optimized for size first
     Naked,                 ///< Naked function
     Nest,                  ///< Nested function static chain