> I am sorry for misleading description. By "propagate register 172 in > insn79 and delete insn78" > I was meaning that gcc replaces reg 172 in insn79 with another > register contains ZERO and > that register(saying reg X) is defined in other basic blocks.
OK, in this case I think you need to find out why no local pass before the problematic global pass does the obvious constant propagation into insn 79. -- Eric Botcazou
