Add a new target independent COPY instruction and code to lower it.

The COPY instruction is intended to replace the target specific copy
instructions for virtual registers as well as the EXTRACT_SUBREG and
INSERT_SUBREG instructions in MachineFunctions. It won't we used in a selection
DAG.

COPY is lowered to native register copies by LowerSubregs.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@107529 91177308-0d34-0410-b5e6-96231b3b80d8

utils/TableGen/CodeGenTarget.cpp

@@ -344,6 +344,7 @@ void CodeGenTarget::ComputeInstrsByEnum() const {
     "COPY_TO_REGCLASS",
     "DBG_VALUE",
     "REG_SEQUENCE",
+    "COPY",
     0
   };
   const DenseMap<const Record*, CodeGenInstruction*> &Insts = getInstructions();