Reduce the number of copies emitted as machine instructions by

generating results in vregs that will need them.  In the case of something
like this:  CopyToReg((add X, Y), reg1024), we no longer emit code like
this:

   reg1025 = add X, Y
   reg1024 = reg 1025

Instead, we emit:

   reg1024 = add X, Y

Whoa! :)

llvm-svn: 24111