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

[Aldy Hernandez <aldyh@redhat.com>]

On 10/15/21 3:50 PM, Andrew MacLeod 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?

The backward threader skips both edges with EDGE_ABNORMAL set as well as 
phi results to have SSA_NAME_OCCURS_IN_ABNORMAL_PHI.

The forward threader skips out on all abnormal edges as well.  It seems 
to even avoid threading through blocks where one of the 2 outgoing edges 
is abnormal.  Dunno if this was an oversight, or just being extra careful.

Anywhoooo, at least from the threaders you're safe.

Aldy