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Re: [PATCH, ARM] Misaligned access support for ARM Neon
- From: Mark Mitchell <mark at codesourcery dot com>
- To: Julian Brown <julian at codesourcery dot com>
- Cc: Richard Earnshaw <rearnsha at arm dot com>, gcc-patches at gcc dot gnu dot org, Paul Brook <paul at codesourcery dot com>
- Date: Tue, 08 Jun 2010 08:25:38 -0700
- Subject: Re: [PATCH, ARM] Misaligned access support for ARM Neon
- References: <20091117171931.053faec2@rex.config> <1259593368.6000.40.camel@e200601-lin.cambridge.arm.com> <20091218172204.3c0eab5b@rex.config> <200912211220.12265.paul@codesourcery.com> <20100518013108.5514d986@rex.config> <20100604135031.3d77a087@rex.config> <1275668777.6827.83.camel@e102346-lin.cambridge.arm.com> <20100607200848.0fe3ab59@rex.config>
Julian Brown wrote:
> This patch actually doesn't try to do anything to address the mapping
> between the memory representation of vectors and element numberings --
> it just allows misaligned accesses to be used (using element
> load/store instructions), albeit only in little-endian mode. I believe
> this makes the autovectoriser much more useful for real-world code (i.e.
> able to trigger in many more cases, and/or able to produce better
> output).
This seems to me to be a monotonic improvement in the capabilities of
the ARM back-end, and an accurate model of the little-endian ARM NEON
ISA. So, while solving the general problem (which may require
significant work on the generic parts of the compiler) is certainly
desirable, it seems to me that this is a definite win, with no major
downside.
Richard, you wrote:
> I've no particular objection to this patch
Is that an approval, or would you like to discuss further?
I'm not trying to apply pressure, and, for avoidance of doubt, my
opinion above is my opinion as a (lapsed) GCC engineer, not anything
RM/SC-ish. Just want to understand where we stand, and trying to flush
our changes...
Thanks,
--
Mark Mitchell
CodeSourcery
mark@codesourcery.com
(650) 331-3385 x713