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Re: Improving Asan code on ARM targets


Andrew Pinski wrote:
> Yury Gribov wrote:
>> Andrew Pinski wrote:
>>> Yury Gribov wrote:
>>>> I've recently noticed that GCC generates suboptimal code
>>>> for Asan on ARM targets. E.g. for a 4-byte memory access check
>>>
>>> Does the patch series at located at:
>>> http://gcc.gnu.org/ml/gcc-patches/2014-02/msg01407.html
>>> http://gcc.gnu.org/ml/gcc-patches/2014-02/msg01405.html
>>> Fix this code generation issue?  I suspect it does and improves more
>>> than just the above code.
>>
>> No, they don't help as is.
>
> I think it would good to figure out how to improve this code gen
> with the above patches rather than changing asan.
> I suspect it might easy to expand them to handle this case too.

I was indeed able to reuse Zhenqiang's work. After updating select_ccmp_cmp_order hook to also return suggestions on how to change comparisons to allow better code generation (so it sounds more like select_ccmp_cmp_layout now) I was able to use this information in expand_ccmp_expr to generate optimal code.

The patch is still a draft (only supports Asan's case) and I think I'll wait until Zhenqiang's conditional compare patches get into trunk before going deeper (not sure when this is going to happen though...).

-Y


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