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Re: PATCH: PR target/50603: [x32] Unnecessary lea
On Tue, Oct 4, 2011 at 8:37 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>> OTOH, x86_64 and i686 targets can also benefit from this change. If
>>>> combine can't create more complex address (covered by lea), then it
>>>> will simply propagate memory operand back into the add insn. It looks
>>>> to me that we can't loose here, so:
>>>>
>>>> ?/* Improve address combine. ?*/
>>>> ?if (code == PLUS && MEM_P (src2))
>>>> ? ?src2 = force_reg (mode, src2);
>>>>
>>>> Any opinions?
>>>>
>>>
>>> It doesn't work with 64bit libstdc++:
>>
>> Yeah, yeah. ix86_output_mi_thunk has some ... ?issues.
>>
>> Please try attached patch that introduces ix86_emit_binop and uses it
>> in a bunch of places.
> I tried it on GCC. ?There are no regressions. ?The bugs are fixed for x32.
> Here are size comparison with GCC runtime libraries on ia32, x32 and
> x86-64:
> ?884093 ? 18600 ? 27064 ?929757 ? e2fdd old libstdc++.so
> ?884189 ? 18600 ? 27064 ?929853 ? e303d new libs/libstdc++.so
>
> The new code is
>
> mov ? ?0xc(%edi),%eax
> mov ? ?%eax,0x8(%esi)
> mov ? ?-0xc(%eax),%eax
> mov ? ?0x10(%edi),%edx
> lea ? ?0x8(%esi,%eax,1),%eax
>
> The old one is
>
> mov ? ?0xc(%edi),%edx
> lea ? ?0x8(%esi),%eax
> mov ? ?%edx,0x8(%esi)
> add ? ?-0xc(%edx),%eax
> mov ? ?0x10(%edi),%edx
The new code merged lea+add into one lea, so it looks quite OK to me.
Do you have some performance numbers?
Thanks,
Uros.