[Bug tree-optimization/108696] New: querying relations is slow

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108696

            Bug ID: 108696
           Summary: querying relations is slow
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

With the compiler.i testcase from PR26854 I notice we do quite a lot of bitmap
intersections via dom_oracle::query_relation for the case (which hits 99% of
the time) when a SSA name doesn't have any relation but equiv_set () returns a
newly allocated bitmap with just the self-equivalence recorded.

The self-equivalence case isn't used to prune the work done by query_relation
it seems.  Maybe find_relation_dom does that via

  // IF either name does not occur in a relation anywhere, there isnt one.
  if (!bitmap_bit_p (m_relation_set, v1) || !bitmap_bit_p (m_relation_set, v2))
    return VREL_VARYING;

but we still get all the way to the query_relation overload which eventually
does the intersection with m_relation_set which is a lot more expensive than
this.

A naiive

diff --git a/gcc/value-relation.cc b/gcc/value-relation.cc
index f5b1e67e420..f58d5050bdb 100644
--- a/gcc/value-relation.cc
+++ b/gcc/value-relation.cc
@@ -1373,6 +1373,10 @@ dom_oracle::query_relation (basic_block bb, tree ssa1,
tree ssa2)
   unsigned v2 = SSA_NAME_VERSION (ssa2);
   if (v1 == v2)
     return VREL_EQ;
+ 
+  // IF either name does not occur in a relation anywhere, there isnt one.
+  if (!bitmap_bit_p (m_relation_set, v1) || !bitmap_bit_p (m_relation_set,
v2))
+    return VREL_VARYING;

   // Check for equivalence first.  They must be in each equivalency set.
   const_bitmap equiv1 = equiv_set (ssa1, bb);

cuts

 dominator optimization             :  17.35 ( 15%) 

down to

 dominator optimization             :  16.17 ( 14%)

note almost all of the DOM time is spent in ranger for this testcase.