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...

Andrew