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Date: Thu, 16 Jul 2015 15:20:00 -0000
From: Richard Earnshaw <Richard.Earnshaw@foss.arm.com>
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To: Michael Matz <matz@suse.de>
CC: Jim Wilson <jim.wilson@linaro.org>,  Richard Biener <richard.guenther@gmail.com>, Jeff Law <law@redhat.com>,  "gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH, ARM] stop changing signedness in PROMOTE_MODE
References: <CABXYE2VXjy7=5Y=c1TCxLE8KuwLtwBYBhTB24xrWDvWAeiBwbQ@mail.gmail.com> <559BEB2D.7040800@redhat.com> <CABXYE2UbBP24fBEgDJp5+S1fhFpNHPJgjM=SypsWbc4hV1xbbw@mail.gmail.com> <DDEC7CC8-74EE-4ACF-97C8-EE5A7D53CDB6@gmail.com> <CABXYE2X4OhMvyK-z+yQvDkcT0TgKUc2Nv+YdhXWZnJDNDMeJqg@mail.gmail.com> <CAFiYyc1M4OqAs9tEhNObnXyC6xsBtFE8XeMrGPV1WoCc-VKY-g@mail.gmail.com> <alpine.LSU.2.20.1507131651560.23227@wotan.suse.de> <55A53519.6040305@foss.arm.com> <CABXYE2VKvB70mvYTrV5fgH4z+h4+G0cFM8Q+X-UL=aCb+-ZPFA@mail.gmail.com> <alpine.LSU.2.20.1507151457570.23227@wotan.suse.de> <CABXYE2Us3rBaVr02+cxGKm8KrUU8MbX=dGKauim=zhMOL3L5OQ@mail.gmail.com> <55A775B9.8040701@foss.arm.com> <alpine.LSU.2.20.1507161658110.23227@wotan.suse.de>
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On 16/07/15 16:00, Michael Matz wrote:
> Hi,
> 
> On Thu, 16 Jul 2015, Richard Earnshaw wrote:
> 
>>>>> Now that we do have the problem, we can't fix it without an ARM port 
>>>>> ABI change, which is undesirable, so we may have to fix it with a MI 
>>>>> change.
>>>>
>>>> What's the ABI implication of fixing the inconsistency?
>>>
>>
>> I think that's the wrong question.  We wouldn't change the ABI to fix an 
>> internal problem in GCC.  So the real question is what's the performance 
>> impact of changing PROMOTE_MODE to be the same as the ABI requirements?
> 
> Perhaps, I really only wanted to get a feeling what type of changes 
> in code generation would result with the flip.  I wonder why this ABI 
> implication was no problem back when PROMOTE_MODE and 
> target.promote_function_mode were seperated and the inconsistency 
> introduced.
> 
> 
> Ciao,
> Michael.
> 

Promote_function_mode requirements were new with the EABI.  However, I
think it's probably only recent changes in the mid-end that have exposed
the problem.

R.