Stop adding <imp-def> operands when expanding REG_SEQUENCE.

These extra operands are not needed by register allocators using
VirtRegRewriter, and RAFast don't need them any longer.

By omitting the <imp-def> operands, it becomes possible for the new
register coalescer to track which lanes are valid and which are undef.

llvm-svn: 164073

llvm/lib/CodeGen/TwoAddressInstructionPass.cpp

@@ -1758,10 +1758,6 @@ bool TwoAddressInstructionPass::EliminateRegSequences() {
         if (MO.isReg() && MO.isDef() && MO.getReg() == DstReg)
           MO.setIsUndef();
       }
-      // Make sure there is a full non-subreg imp-def operand on the
-      // instruction.  This shouldn't be necessary, but it seems that at least
-      // RAFast requires it.
-      Def->addRegisterDefined(DstReg, TRI);
       DEBUG(dbgs() << "First def: " << *Def);
     }