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Re: PATCH: PR target/40470: unable to find a registe r to spill in class ‘SSE_FIRST_REG’


On Thu, Jun 18, 2009 at 7:33 AM, Jeff Law<law@redhat.com> wrote:
> H.J. Lu wrote:
>>
>> On Thu, Jun 18, 2009 at 4:52 AM, Steven Bosscher<stevenb.gcc@gmail.com>
>> wrote:
>>
>>>
>>> On 6/18/09, Richard Guenther <richard.guenther@gmail.com> wrote:
>>>
>>>>>
>>>>> So my proposed solution would be: Do not allow combine to propagate
>>>>> SETany _SRC that contains hard regs.
>>>>>
>>>>
>>>> At least not if that increases the number of uses of the hard reg.
>>>> If we can distinguish that case properly.
>>>>
>>>
>>> In HJ's example, the number of uses remains the same...
>>>
>>>
>>
>> Fixing combiner affects all targets with unknown performance impact.
>> Is this a good idea for 4.3 and 4.4? My patch is very much limited to
>> SSE4 intrinsics and also there are many cases which show early hard
>> register assignment improves code quality. Should we consider my
>> patch for 4.3 and 4.4?
>>
>
> It's a correctness issue HJ! ?This is something the combiner has always been
> expected to deal with. ?The fact that it's not doing so now is a bug, plain
> and simple.
> Given my experience exposing hard regs early, the performance impact of
> fixing the compiler should be far smaller than exposing the hard reg. ? ?As
> I've stated previously, I will object to installing your patch until such
> time as someone has investigated the combiner bug and we can evaluate the
> impact of fixing the combiner bug.
>

Who will look into this combiner bug? Any estimate when it will be
investigated?

Thanks.

-- 
H.J.


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