Check elimination: Learn from if(CompareMap(x)) on true branch.

BUG=
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/99043002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18210 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-check-elimination.cc

@@ -127,6 +127,23 @@ class HCheckTable : public ZoneObject {
       new_entry->check_ = NULL;
       new_entry->maps_ = old_entry->maps_->Copy(phase_->zone());
     }
+    if (succ->predecessors()->length() == 1) {
+      HControlInstruction* end = succ->predecessors()->at(0)->end();
+      if (end->IsCompareMap() && end->SuccessorAt(0) == succ) {
+        // Learn on the true branch of if(CompareMap(x)).
+        HCompareMap* cmp = HCompareMap::cast(end);
+        HValue* object = cmp->value()->ActualValue();
+        HCheckTableEntry* entry = copy->Find(object);
+        if (entry == NULL) {
+          copy->Insert(object, cmp->map());
+        } else {
+          MapSet list = new(phase_->zone()) UniqueSet<Map>();
+          list->Add(cmp->map(), phase_->zone());
+          entry->maps_ = list;
+        }
+      }
+      // TODO(titzer): is it worthwhile to learn on false branch too?
+    }
     return copy;
   }
 

test/mjsunit/compiler/compare_map_elim.js

+// Copyright 2010 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Flags: --allow-natives-syntax --check-elimination
+
+a = {
+  f: function() { this.y = 3; }
+};
+b = {
+  f: function() { this.y = 4; }
+};
+
+function x(z) {
+  return z.f();
+}
+
+x(a);
+x(b);
+x(a);
+x(b);
+x(a);
+x(b);
+
+%OptimizeFunctionOnNextCall(x)
+
+x(a);
+x(b);