This looks fine to me.  Go ahead and uncomment the memcpy() line (I
presume you commented it out in order to demonstrate the basic
transformation without the dead code elimination).  Be sure to add a
testcase.

Antoine, the issue with JUMP_IF variants is that they interfere with
other existing byte code optimizations, resulting in a net loss.

BTW, don't expect much of a real-world speed-up from this patch.  The
JUMP_ABSOLUTE opcode is very fast.