Mark CheckMaps that can cause migration with ChangesNewSpacePromotion.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index b4fc65635f47b6db2396208e73b0b3b9e124f996..7bac08c117be5c6b69d97c4f5ff2a4ec24eb0f0c 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -2553,10 +2553,12 @@ class HCheckMaps: public HTemplateInstruction<2> {
                          HValue* value, SmallMapList* maps,
                          HValue *typecheck = NULL) {
     HCheckMaps* check_map = new(zone) HCheckMaps(value, zone, typecheck);
+    bool has_migration_target = false;
     for (int i = 0; i < maps->length(); i++) {
       check_map->map_set_.Add(maps->at(i), zone);

[danno, 2013/08/13 09:17:41]

Why not choke-point the Add method, looking for maps with the migration target
flag set, that way the "has_migration_target" logic be handled in the
constructor, I think it's a little cleaner than in the New method

-      check_map->has_migration_target_ |= maps->at(i)->is_migration_target();
+      has_migration_target |= maps->at(i)->is_migration_target();
     }
+    if (has_migration_target) check_map->MarkMigrationTarget();
     check_map->map_set_.Sort();
     return check_map;
   }
@@ -2599,6 +2601,11 @@ class HCheckMaps: public HTemplateInstruction<2> {
   }
 
  private:
+  void MarkMigrationTarget() {
+    has_migration_target_ = true;
+    SetGVNFlag(kChangesNewSpacePromotion);
+  }
+
   // Clients should use one of the static New* methods above.
   HCheckMaps(HValue* value, Zone *zone, HValue* typecheck)
       : HTemplateInstruction<2>(value->type()),