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Re: PATCH: PR target/40470: unable to find a registe r to spill in class ‘SSE_FIRST_REG’
On Wed, Jun 17, 2009 at 8:36 AM, H.J. Lu<hjl.tools@gmail.com> wrote:
> On Wed, Jun 17, 2009 at 8:22 AM, Jeff Law<law@redhat.com> wrote:
>> Steven Bosscher wrote:
>>>
>>> On 6/17/09, Jeff Law <law@redhat.com> wrote:
>>>
>>>>
>>>> Richard Guenther wrote:
>>>>
>>>>>
>>>>> On Wed, Jun 17, 2009 at 4:01 PM, H.J. Lu<hongjiu.lu@intel.com> wrote:
>>>>>
>>>>>
>>>>>
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> Some SSE4 instructions have implicit XMM0 operand. This patch helps RA
>>>>>> deal with them by forcing operand into XMM0 during expand. OK for trunk
>>>>>> and 4.4?
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>> I don't think it's a particularly good idea to put things in hardregs
>>>>> that early.
>>>>>
>>>>>
>>>>>
>>>>
>>>> Agreed. ?In fact, it can have horrific performance impacts.
>>>>
>>>
>>> Why? Most optimizazions that can be done for this insn can only be
>>> done on GIMPLE, right? ?And the insn must have that specific register.
>>> So unless I am missing something, I don't see why this patch would do
>>> any harm.
>>>
>>
>> It'll completely disable the RTL loop optimizers. ?Granted this is less
>> important today than before, but it's still bad. ?And more importantly, the
>> register allocators and reload should be fixed to DTRT rather than hacking
>> around them.
>
> I am all for it. Vladimir, how hard to fix RA for this?
>
This fails in gcc 4.3/4.4/4.5. Fixing RA/reload sounds good for
4.5. Is that a good idea for 4.4, especially for 4.3? Can I apply
my patch to 4.3 first?
Thanks.
--
H.J.