Re: [PATCH] Replace VRP threader with a hybrid forward threader.

[Richard Biener <richard.guenther@gmail.com>]

On September 27, 2021 6:07:40 PM GMT+02:00, Aldy Hernandez via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
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>On 9/27/21 5:27 PM, Aldy Hernandez wrote:
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>> On 9/27/21 5:01 PM, Jeff Law wrote:
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>>> On 9/24/2021 9:46 AM, Aldy Hernandez wrote:
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>>> And the big question, is the pass running after VRP2 doing anything 
>>> particularly useful?  Do we want to try and kill it now, or later?
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>> Interesting question.  Perhaps if we convert DOM threading to a hybrid 
>> model, it will render the post-VRP threader completely useless.  Huhh... 
>> That could kill 2 birds with one stone... we get rid of a threading 
>> pass, and we don't need to worry about as much about the super-fast ranger.
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>These are just a few of the threading passes at -O2:
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>a.c.192t.thread3   <-- bck threader
>a.c.193t.dom3      <-- fwd threader
>a.c.194t.strlen1
>a.c.195t.thread4   <-- bck threader
>a.c.196t.vrp2
>a.c.197t.vrp-thread2 <-- fwd threader
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>That's almost 4 back to back threaders!
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>*pause for effect*

We've always known we have too many of these once Jeff triplicated all the backwards threading ones. I do hope we manage to reduce the number for GCC 12. Esp. If the new ones are slower because they no longer use simple lattices. 

Richard. 

>Aldy
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