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
