So as Georg-Johann discusses in the BZ, reload_cse_move2add can generate 
incorrect code when optimizing code with clobbers.  Specifically in the 
case where we try to optimize a sequence of 4 operations down to 3 
operations we can reset INSN to the next instruction and continue the loop.

That skips the code to invalidate objects based on things like REG_INC 
nodes, stack pushes and most importantly clobbers attached to the 
current insn.

This patch factors all of the invalidation code used by 
reload_cse_move2add into a new function and calls it at the appropriate 
time.

Georg-Johann has confirmed this patch fixes his avr bug and I've had it 
in my tester over the weekend.  It's bootstrapped and regression tested 
on aarch64, m68k, sh4, alpha and hppa.  It's also regression tested 
successfully on a wide variety of other targets.


Pushing to the trunk momentarily.

Jeff