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Re: REG_EH_REGION notes and substitutions into insn


On Wed, Nov 07, 2001 at 09:48:56AM -0500, Richard Kenner wrote:
> Suppose we have a SET insn from MEM that has a REG_EH_REGION note since
> the address is variable and then suppose CSE or combine makes it a
> constant.

You mean e.g. something of the form

  (insn (set (reg)
	     (mem/u (lo_sum (reg) (symbol_ref ".LC0"))))
     (REG_EH_REGION (const_int)
       (REG_EQUAL (const_double))))

?

Ideally cse or combine or whatever would have noticed that the
memory doesn't trap -- possibly by the fact that it added a
REG_EQUAL note, as if it doesn't change the form of the mem,
may_trap_p may still return true.

Once the REG_EH_REGION note is removed, the edge removal would
be taken care of by purge_dead_edges.


r~


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