Re: [PATCH] Ranger : Do not process abnormal ssa-names.

[Jeff Law <jeffreyalaw@gmail.com>]

On 10/15/2021 7:50 AM, Andrew MacLeod via Gcc-patches wrote:
> I've been looking at the pathological time issue ranger has with the 
> testcase from, uuuuuh..  PR 97623 I think.  I've lost the details, but 
> kept the file since it was showing unpleasant behaviour.
>
> Most of the time is spent in callbacks from substitute_and_fold to 
> value_on_edge()  dealing with PHI results and arguments.  Turns out, 
> its virtually all wasted time dealing with SSA_NAMES with the 
> OCCURS_IN_ABNORMAL_PHI flag set..
>
> This patch tells ranger not to consider any SSA_NAMEs which occur in 
> abnormal PHIs.  This reduces the memory footprint of all the caches, 
> and also has a ripple effect with the new threader code which uses the 
> GORI exports and imports tables, making it faster as well as no 
> ssa-name with the abnormal flag set will be entered into the tables.
>
> That alone was not quite enough, as all the sheer volume of call backs 
> still took time,  so I added checks in the value_of_* class of 
> routines used by substitute_and_fold to indicate there is no constant 
> value available for any SSA_NAME with that flag set.
>
> On my x86_64 box, before this change, that test case looked like:
>
> tree VRP                           :   7.76 (  4%)   0.23 ( 5%) 8.02 
> (  4%)   537k (  0%)
> tree VRP threader                  :   7.20 (  4%)   0.08 (  2%) 7.28 
> (  4%)   392k (  0%)
> tree Early VRP                     :  39.22 ( 22%)   0.07 (  2%) 39.44 
> ( 22%)  1142k (  0%)
>
> And with this patch , the results are:
>
>  tree VRP                           :   7.57 (  6%)   0.26 ( 5%) 7.85 
> (  6%)   537k (  0%)
>  tree VRP threader                  :   0.62 (  0%)   0.02 ( 0%) 0.65 
> (  0%)   392k (  0%)
>  tree Early VRP                     :   4.00 (  3%)   0.01 ( 0%) 4.03 
> (  3%)  1142k (  0%)
>
> Which is a significant improvement, both for EVRP and the threader..
>
> The patch adjusts the ranger folder, as well as the hybrid folder.
>
> bootstrapped on x86_64-pc-linux-gnu with no regressions and no missed 
> cases that I have been able to find.
>
> I don't want to push it quite yet as I wanted feedback to make sure we 
> don't actually do anything I'm not aware of with SSA_NAMES which have 
> the ABNORMAL_PHI flag set.  Most of the code i can find in VRP and 
> vr-values appears to punt, so I presume not even considering those 
> names is fine?
>
> This also seems like something that might be worth back-porting, 
> especially the hybrid pass parts...
Punting on the abnormals seems perfectly fine to me.  They rarely, if 
ever, provide information that improves optimization.

Jeff