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Re: [PATCH 4.8, i386]: Enable post-reload compare optimization pass (PR28685)
On Tue, Feb 7, 2012 at 11:00 AM, Uros Bizjak <ubizjak@gmail.com> wrote:
>>> Hmm. ?Well, the only thing that's going to work for x86 is the double-compare
>>> elimination portion.
>>>
>>> If we want to use this pass for x86, then for 4.8 we should also fix the
>>> discrepancy between the compare-elim canonical
>>>
>>> ?[(operate)
>>> ? (set-cc)]
>>>
>>> and the combine canonical
>>>
>>> ?[(set-cc)
>>> ? (operate)]
>>>
>>> (Because of the simplicity of the substitution in compare-elim, I prefer
>>> the former as the canonical canonical.)
>>
>> You are probably referring to following testcase:
>>
>> --cut here--
>> int test (int a, int b)
>> {
>> ?int lt = a + b < 0;
>> ?int eq = a + b == 0;
>> ?if (lt)
>> ? ?return 1;
>> ?return eq;
>> }
>> --cut here--
>>
>> where combine creates:
>>
>> Trying 8 -> 9:
>> Successfully matched this instruction:
>> (parallel [
>> ? ? ? ?(set (reg:CCZ 17 flags)
>> ? ? ? ? ? ?(compare:CCZ (plus:SI (reg/v:SI 63 [ a ])
>> ? ? ? ? ? ? ? ? ? ?(reg/v:SI 64 [ b ]))
>> ? ? ? ? ? ? ? ?(const_int 0 [0])))
>> ? ? ? ?(set (reg:SI 60 [ D.1710 ])
>> ? ? ? ? ? ?(plus:SI (reg/v:SI 63 [ a ])
>> ? ? ? ? ? ? ? ?(reg/v:SI 64 [ b ])))
>> ? ?])
>
> Attached patch teaches combine to swap operands of a double set
> pattern and retries recognition. Also added are minimum
> target-dependant changes to handle the testcase above.
Please ignore this idea. I am preparing target-only patchset that
moves x86 entirely to post-reload flags handling (similar to rx and
mn10300 targets). Not a 4.7 material in any way.
Uros.