I have finally seen the light. The code to change the opcode must live higher in

the loop, and in both cases. In the first case, it is a VReg that is a constant
so it may be actually converted to a constant. In the second case, it is already
a constant, but then if it doesn't change its type (e.g. to become a register
and have the value loaded from memory if it is too large to live in its
instruction field), we must change the opcode BEFORE the 'continue', otherwise
we miss the opportunity.

llvm-svn: 6602