[gcc r13-1608] Avoid calling range_from_dom when dominator is already resolved.

[Andrew Macleod <amacleod@gcc.gnu.org>]

https://gcc.gnu.org/g:12a9b98ac574bc8092a75849b5c462135d35c31d

commit r13-1608-g12a9b98ac574bc8092a75849b5c462135d35c31d
Author: Andrew MacLeod <amacleod@redhat.com>
Date:   Fri Jul 8 13:30:49 2022 -0400

    Avoid calling range_from_dom when dominator is already resolved.
    
    range_from_dom makes a recursive call to resolve the immediate dominator
    when there are multiple incoming edges to a block.  This is not necessary
    when the dominator already has an on-entry cache value.
    
            PR tree-optimization/106234
            * gimple-range-cache.cc (ranger_cache::range_from_dom): Check dominator
            cache value before recursively resolving it.

Diff:
---
 gcc/gimple-range-cache.cc | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/gcc/gimple-range-cache.cc b/gcc/gimple-range-cache.cc
index 9be8bc6123b..da7b8055d42 100644
--- a/gcc/gimple-range-cache.cc
+++ b/gcc/gimple-range-cache.cc
@@ -1359,10 +1359,11 @@ ranger_cache::range_from_dom (vrange &r, tree name, basic_block start_bb,
 	    m_workback.quick_push (prev_bb);
 	  else if (mode == RFD_FILL)
 	    {
-	      // Multiple incoming edges, so recursively satisfy this block,
-	      // store the range, then calculate the incoming range for PREV_BB.
-	      if (def_bb != bb)
+	      // Multiple incoming edges, so recursively satisfy this block
+	      // if it doesn't already have a value, and store the range.
+	      if (!m_on_entry.bb_range_p (name, bb) && def_bb != bb)
 		{
+		  // If the dominator has not been set, look it up.
 		  range_from_dom (r, name, bb, RFD_FILL);
 		  // If the range can't be store, don't try to accumulate
 		  // the range in PREV_BB due to excessive recalculations.