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

lib/LTO/LTOCodeGenerator.cpp

@@ -96,6 +96,7 @@ void LTOCodeGenerator::initializeLTOPasses() {
   initializeConstantMergePass(R);
   initializeDAHPass(R);
   initializeInstCombinerPass(R);
+  initializeJumpInstrTablesPass(R);
   initializeSimpleInlinerPass(R);
   initializePruneEHPass(R);
   initializeGlobalDCEPass(R);