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Re: [RFD] Using the 'memory constraint' trick to avoid memory clobber doesn't work
- From: Hans-Peter Nilsson <hp at bitrange dot com>
- To: David Wohlferd <dw at LimeGreenSocks dot com>
- Cc: Richard Biener <richard dot guenther at gmail dot com>, y dot gribov at samsung dot com, "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>, Gerald Pfeifer <gerald at pfeifer dot com>
- Date: Thu, 13 Nov 2014 08:53:09 -0500 (EST)
- Subject: Re: [RFD] Using the 'memory constraint' trick to avoid memory clobber doesn't work
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On Thu, 13 Nov 2014, David Wohlferd wrote:
> Sorry for the (very) delayed response. I'm still looking for feedback here so
> I can fix the docs.
Thank you for your diligence.
> As I said before, triggering a full memory clobber for anything over 16 bytes
> (and most sizes under 16 bytes) makes this feature all but useless. So if
> that's really what's happening, we need to decide what to do next:
> 1) Can this be "fixed?"
> 2) Do we want to doc the current behavior?
> 3) Or do we just remove this section?
> I think it could be a nice performance win for inline asm if it could be made
> to work right, but I have no idea what might be involved in that. Failing
> that, I guess if it doesn't work and isn't going to work, I'd recommend
> removing the text for this feature.
> Since all 3 suggestions require a doc change, I'll just say that I'm prepared
> to start work on the doc patch as soon as someone lets me know what the plan
> Richard? Hans-Peter? Your thoughts?
I've forgot if someone mentioned whether we have a test-case in
our test-suite for this feature. If we don't, then 3; removal.
If we do, I guess it's flawed or at least not agreeing with the
documentation? Then it *might* be worth the effort fixing that
and additional test-coverage (depending on the person stepping
up...) but 3 is IMHO still an arguably sane option.