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Re: [PATCH ppc64,aarch64,alpha 00/15] Improve backend constant generation
- From: Richard Earnshaw <Richard dot Earnshaw at foss dot arm dot com>
- To: Richard Henderson <rth at redhat dot com>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
- Cc: David Edelsohn <dje dot gcc at gmail dot com>, Marcus Shawcroft <Marcus dot Shawcroft at arm dot com>
- Date: Wed, 12 Aug 2015 10:02:11 +0100
- Subject: Re: [PATCH ppc64,aarch64,alpha 00/15] Improve backend constant generation
- Authentication-results: sourceware.org; auth=none
- References: <1439341904-9345-1-git-send-email-rth at redhat dot com> <55CB0487 dot 1020505 at foss dot arm dot com> <55CB0731 dot 30905 at foss dot arm dot com>
On 12/08/15 09:43, Richard Earnshaw wrote:
> On 12/08/15 09:32, Richard Earnshaw wrote:
>> On 12/08/15 02:11, Richard Henderson wrote:
>>> I'm somewhat surprised that the operands to the logicals aren't
>>> visible at rtl generation time, given all the work done in gimple.
>>> And failing that, combine has enough REG_EQUAL notes that it ought
>>> to be able to put things back together and see the simpler pattern.
>>>
>>
>> We've tried it in the past. Exposing the individual steps prevents the
>> higher-level rtl-based optimizations since they can no-longer deal with
>> the complete sub-expression.
>
> Eg. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63724
>
> R.
>
And https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65768
R.