[gcc/devel/c++-modules] Optimize alias subset recording

[Nathan Sidwell]

https://gcc.gnu.org/g:6c5776676108e36e82b3c4a42156a3937f3dc7f7

commit 6c5776676108e36e82b3c4a42156a3937f3dc7f7
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Jan 14 08:48:20 2020 +0100

    Optimize alias subset recording
    
    When an alias-set is an already existing subset there is no need
    to re-record its children as childs of the parent.
    
    2020-01-15  Richard Biener  <rguenther@suse.de>
    
    	* alias.c (record_alias_subset): Avoid redundant work when
    	subset is already recorded.

Diff:
---
 gcc/ChangeLog |  5 +++++
 gcc/alias.c   | 11 +++++++----
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 4da4d04..8ef8577 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2020-01-15  Richard Biener  <rguenther@suse.de>
+
+	* alias.c (record_alias_subset): Avoid redundant work when
+	subset is already recorded.
+
 2020-01-14  David Malcolm  <dmalcolm@redhat.com>
 
 	* doc/invoke.texi (-fdiagnostics-show-cwe): Add note that some of
diff --git a/gcc/alias.c b/gcc/alias.c
index 9629b5a..3794f9b 100644
--- a/gcc/alias.c
+++ b/gcc/alias.c
@@ -1164,10 +1164,16 @@ record_alias_subset (alias_set_type superset, alias_set_type subset)
     superset_entry->has_zero_child = 1;
   else
     {
-      subset_entry = get_alias_set_entry (subset);
       if (!superset_entry->children)
 	superset_entry->children
 	  = hash_map<alias_set_hash, int>::create_ggc (64);
+
+      /* Enter the SUBSET itself as a child of the SUPERSET.  If it was
+	 already there we're done.  */
+      if (superset_entry->children->put (subset, 0))
+	return;
+
+      subset_entry = get_alias_set_entry (subset);
       /* If there is an entry for the subset, enter all of its children
 	 (if they are not already present) as children of the SUPERSET.  */
       if (subset_entry)
@@ -1185,9 +1191,6 @@ record_alias_subset (alias_set_type superset, alias_set_type subset)
 		superset_entry->children->put ((*iter).first, (*iter).second);
 	    }
 	}
-
-      /* Enter the SUBSET itself as a child of the SUPERSET.  */
-      superset_entry->children->put (subset, 0);
     }
 }