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Re: [PATCH] Fix overzealous DSE on sparc
Richard Guenther <richard.guenther@gmail.com> writes:
> On Thu, May 3, 2012 at 10:31 AM, Richard Sandiford
> <rdsandiford@googlemail.com> wrote:
>> David Miller <davem@davemloft.net> writes:
>>> From: Richard Sandiford <rdsandiford@googlemail.com>
>>> Date: Wed, 02 May 2012 20:37:58 +0100
>>>
>>>> I think the DSE assuption is fair though. ÂIf you reuse MEMs like
>>>> this, then they're no longer just serving the purpose described by
>>>> MEM_EXPR.
>>>
>>> The following seems to work, and matches what calls.c does when it
>>> passes a value by reference. ÂIs this what you had in mind?
>>
>> Yeah, looks good to me.
>
> I don't think that will work reliably (well, maybe now by luck, so better than
> nothing). You'd at least need to adjust the ESCAPED points-to set of the
> function, too (yes, DSE does very very conservative use analysis right now).
Ah.
> Why not simply clear MEM_EXPR for the MEM?
The problem is that MEM rtxes aren't shared. AIUI, the store will already
have been emitted by this point, using a distinct (but equivalent) MEM rtx.
Richard