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Re: [RFC] Handle memset in DSE (take 2)
Jakub Jelinek wrote:
> On Wed, Jan 07, 2009 at 08:41:45AM +0100, Paolo Bonzini wrote:
>>> I'd much rather have an rtx object that explicitly gave the
>>> number of repetitions, and that could itself have BLKmode.
>>> Thinking about it, we don't need to make the object constant
>>> either, despite what I said before. How about:
>>>
>>> (repeat:BLK value count)
>>>
>>> where VALUE and COUNT are rtxes. If we want to support non-byte
>>> repeats, we could add a third length operand, to cope with the
>>> VOIDness of CONST_INT values.
>
> True, but I'm not sure we should introduce it now for 4.4, there
> are risks that we don't handle this new RTL code in all the routines
> where it has to be handled.
> No backend in the current trunk uses (set (mem:BLK [SNNN]) (const_int M))
> for M != 0, so ATM only the repeated zero is present in the RTL in between
> the passes, it currently is only present inside of DSE in DSE's structures for
> memset (&a, 2, sizeof a), never in the bb's.
>
> For 4.5 I agree that REPEAT or something similar makes a lot of sense.
Well, I interpreted Richard's suggestion as 4.5 material only, since
your patch was already committed 3 weeks ago anyway.
Paolo