[Bug tree-optimization/106280] dom_oracle::register_transitives is expensive for deep dominator trees

["amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106280

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

See if this helps.  

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

So, this patch does 2 things. 
1) If a relation is being registered which already exist, the set routine now
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 (over
50% time reduction) in your test case.  It also makes some marginal
improvements in GCC source files compilation.