Basic array capacity feedback via allocation sites.

test/mjsunit/array-constructor-feedback.js

Index: test/mjsunit/array-constructor-feedback.js
diff --git a/test/mjsunit/array-constructor-feedback.js b/test/mjsunit/array-constructor-feedback.js
index c2c1a1842f7d580800bbed37b62527f45f1454b1..6878e80bf2f281bcc5e4768c31c1c714d50271a3 100644
--- a/test/mjsunit/array-constructor-feedback.js
+++ b/test/mjsunit/array-constructor-feedback.js
@@ -62,6 +62,7 @@ function assertKind(expected, obj, name_opt) {
   assertEquals(expected, getKind(obj), name_opt);
 }
 
+
 // Test: If a call site goes megamorphic, it retains the ability to
 // use allocation site feedback (if FLAG_allocation_site_pretenuring
 // is on).
@@ -217,3 +218,52 @@ function assertKind(expected, obj, name_opt) {
     assertFalse(isHoley(a));
   }
 })();
+
+
+// Test: verify that elements capacity feedback works
+(function() {
+  // It works for optimized functions with a no-argument array call.
+  function foo() { return new Array(); }
+  a = foo();
+  a.push(1, 2, 3, 4, 5, 6);
+  assertEquals(25, %GetElementsCapacity(a));
+  %OptimizeFunctionOnNextCall(foo);
+  b = foo();
+  assertEquals(25, %GetElementsCapacity(b));
+
+  // It works for optimized functions with a constant argument array call.
+  function bar() { return new Array(1); }
+  a = bar();
+  a.push(1, 2, 3, 4, 5, 6);
+  assertEquals(26, %GetElementsCapacity(a));
+  %OptimizeFunctionOnNextCall(bar);
+  b = bar();
+  assertEquals(26, %GetElementsCapacity(b));
+
+  // It doesn't work for functions with a non-constant length for array.
+  function nonconst(l) { return new Array(l); }
+  a = nonconst(1);
+  a.push(1, 2, 3, 4, 5, 6);
+  assertEquals(26, %GetElementsCapacity(a));
+  %OptimizeFunctionOnNextCall(nonconst);
+  b = nonconst(3);
+  assertEquals(3, %GetElementsCapacity(b));
+
+  // It doesn't work for multiple arguments to the array constructor.
+  function some_args() { return new Array(1, 2, 3); }
+  a = some_args();
+  a.push(1, 2, 3, 4, 5, 6);
+  assertEquals(29, %GetElementsCapacity(a));
+  %OptimizeFunctionOnNextCall(some_args);
+  b = some_args();
+  assertEquals(3, %GetElementsCapacity(b));
+
+  // It doesn't work for literals.
+  function with_literal() { var a = [1,2]; return a; }
+  a = with_literal();
+  a.push(1, 2, 3, 4, 5, 6);
+  assertEquals(28, %GetElementsCapacity(a));
+  %OptimizeFunctionOnNextCall(with_literal);
+  b = with_literal();
+  assertEquals(0, %GetElementsCapacity(b));
+})();