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From: "amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/106280] dom_oracle::register_transitives is
 expensive for deep dominator trees
Date: Thu, 14 Jul 2022 17:03:12 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106280

--- Comment #1 from Andrew Macleod <amacleod at redhat dot com> ---
Created attachment 53300
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D53300&action=3Dedit
proposed patch

See if this helps.=20=20

All of the lookup routines check to see first is there is an existing relat=
ion
for an SSA_NAME before deciding what to do.  I forgot to do that with the
transitive code.

So, this patch does 2 things.=20
1) If a relation is being registered which already exist, the set routine n=
ow
returns NULL for the record as there will be no new work to do
2) IF this is a new relation, before calling register_transitives checks if
either operand was in a relation before (its just a quick bitmap check). If
neither was, there is no possibility of a transitive relation, so no need to
look.

This eliminates a lot of unnecessary work, and based on the pass times spits
out at the end, appears to save a lot of time in the various VRP passes (ov=
er
50% time reduction) in your test case.  It also makes some marginal
improvements in GCC source files compilation.=