Re: [PATCH] PR57518, RA generated redundent code

[Xinliang David Li <davidxl at google dot com>]

Should the patch be ported to in 48 branch?

thanks,

David

On Wed, Jun 19, 2013 at 11:46 AM, Vladimir Makarov <vmakarov@redhat.com> wrote:
> On 13-06-19 1:23 AM, Wei Mi wrote:
>>
>> Ping.
>>
>> On Wed, Jun 12, 2013 at 2:44 PM, Wei Mi <wmi@google.com> wrote:
>>>
>>> Hi,
>>>
>>> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57518
>>>
>>> pr57518 happened because update_equiv_regs in IRA marked a reg
>>> equivalent with a mem, lowered its mem_cost in scan_one_insn, set
>>> NO_REGS to its rclass, but didn't consider the reg was used in
>>> paradoxical subreg which prevented the reg from being replaced by mem
>>> in LRA phase.
>>>
>>> This patch is to check whether a reg is used in a paradoxical subreg
>>> in update_equiv_regs before reg is set as equivalent to a mem.
>>>
>>> bootstrap and regression test on x86_64-linux-gnu ok. Is it ok for
>>> trunk and gcc-4.8 branch?
>>>
>>>
> Thanks for working on this PR, Wei, and sorry for the delay with the answer
> (I was on vacation).
>
> In general, the PR analysis and the proposed solution looks ok.  I only
> worry that you are adding additional full scan of all RTL code.  It might
> add 0.5% to GCC compilation time if data cache is rewritten (which will
> happen for moderate size or big functions). It would be nice to do it on
> some other existing RTL traversing. Unfortunately, this info is calculated
> later (reg_max_width in reload or biggest_mode in LRA).  I am in doubt that
> other solutions I see now are better:
>
>   o calculate this info in regstat_...  function and store it in reg_info_p
>   o calculate it with update_equiv_regs and use it for invalidation the
> equiv info later
>
> The first one increases reg_info_p footprint and calculation is done many
> times although it is used once.
> The second one results in complicated code.
>
> So I think the current patch is ok to commit.
>
> Thanks, again.
>
>
>