[gcc r13-6584] Speedup PTA solving for call constraint sets

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:413ec1d12c50f8e2e6adb4de30482780bdfdeeb4

commit r13-6584-g413ec1d12c50f8e2e6adb4de30482780bdfdeeb4
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Mar 10 14:15:14 2023 +0100

    Speedup PTA solving for call constraint sets
    
    With calls we now often get contraints like
    
      callarg = *callarg + UNKNOWN
    
    or similar cases.  The important thing to note is that this
    complex constraint changes the node solution itself, so when
    solving the node is marked as changed immediately again.  When
    that happens it's profitable to iterate that self-cycle immediately
    so we maximize cache reuse and build up the successor graph quickly
    to get better topological ordering and reduce the number of
    iterations of the solving.
    
    For a testcase derived from ceph this reduces the time spent in
    PTA solving from 453s to 92s which is quite significant.
    
            * tree-ssa-structalias.cc (solve_graph): Immediately
            iterate self-cycles.

Diff:
---
 gcc/tree-ssa-structalias.cc | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/gcc/tree-ssa-structalias.cc b/gcc/tree-ssa-structalias.cc
index 07e0fd6827a..c3c5bce42df 100644
--- a/gcc/tree-ssa-structalias.cc
+++ b/gcc/tree-ssa-structalias.cc
@@ -2775,8 +2775,15 @@ solve_graph (constraint_graph_t graph)
 	    continue;
 
 	  /* If the node has changed, we need to process the
-	     complex constraints and outgoing edges again.  */
-	  if (bitmap_clear_bit (changed, i))
+	     complex constraints and outgoing edges again.  For complex
+	     constraints that modify i itself, like the common group of
+	       callarg = callarg + UNKNOWN;
+	       callarg = *callarg + UNKNOWN;
+	       *callarg = callescape;
+	     make sure to iterate immediately because that maximizes
+	     cache reuse and expands the graph quickest, leading to
+	     better visitation order in the next iteration.  */
+	  while (bitmap_clear_bit (changed, i))
 	    {
 	      unsigned int j;
 	      constraint_t c;
@@ -2794,7 +2801,7 @@ solve_graph (constraint_graph_t graph)
 		     ???  But we shouldn't ended up with "changed" set ...  */
 		  if (vi->oldsolution
 		      && bitmap_bit_p (vi->oldsolution, anything_id))
-		    continue;
+		    break;
 		  bitmap_copy (pts, get_varinfo (find (anything_id))->solution);
 		}
 	      else if (vi->oldsolution)
@@ -2803,7 +2810,7 @@ solve_graph (constraint_graph_t graph)
 		bitmap_copy (pts, vi->solution);
 
 	      if (bitmap_empty_p (pts))
-		continue;
+		break;
 
 	      if (vi->oldsolution)
 		bitmap_ior_into (vi->oldsolution, pts);