Add inlined implementation of Math.round.

src/compiler/js-builtin-reducer.cc

Index: src/compiler/js-builtin-reducer.cc
diff --git a/src/compiler/js-builtin-reducer.cc b/src/compiler/js-builtin-reducer.cc
index dbaa2930046b3039b3499841f7b3cbfb0c1480e8..adf6b84b4ee5e71bb308a191b1d6f95bc517785e 100644
--- a/src/compiler/js-builtin-reducer.cc
+++ b/src/compiler/js-builtin-reducer.cc
@@ -217,6 +217,69 @@ Reduction JSBuiltinReducer::ReduceMathCeil(Node* node) {
 }
 
 
+// ES6 draft 10-14-14, section 20.2.2.28.
+Reduction JSBuiltinReducer::ReduceMathRound(Node* node) {
+  if (machine()->HasFloat64Floor() && machine()->HasFloat64RoundTiesAway()) {
+    JSCallReduction r(node);
+    if (r.InputsMatchOne(Type::Number())) {
+      // This is based on the implementation from Crankshaft,
+      // see lithium-codegen-arm64.cc:LCodeGen::DoMathRoundD.
+      // Implementation will be selected for 32bit ARMv8, too.
+      // Math.round(a:number) ->
+      //   double res = Float64RoundTiesAway(a);
+      //   if (a >= 0.0 || a == res) {
+      //     return res;
+      //   } else {
+      //     return -abs(Float64Floor(a + 0.5))
+      //   }
+      Node* p = r.GetJSCallInput(0);
+      Node* control = graph()->start();
+      Node* rounded_away =
+          graph()->NewNode(machine()->Float64RoundTiesAway(), p);
+
+      Node* ge_zero = graph()->NewNode(simplified()->NumberLessThanOrEqual(),
+                                       jsgraph()->ZeroConstant(), p);
+      Node* eq_rounded =
+          graph()->NewNode(machine()->Float64Equal(), p, rounded_away);
+
+      Node* condition =
+          graph()->NewNode(machine()->WordOr(), eq_rounded, ge_zero);
+
+      Node* branch = graph()->NewNode(common()->Branch(), condition, control);
+      Node* if_true = graph()->NewNode(common()->IfTrue(), branch);
+      Node* if_false = graph()->NewNode(common()->IfFalse(), branch);
+      Node* merge = graph()->NewNode(common()->Merge(2), if_true, if_false);
+
+      Node* sum = graph()->NewNode(machine()->Float64Add(), p,
+                                   jsgraph()->Constant(0.5));
+      Node* floored = graph()->NewNode(machine()->Float64Floor(), sum);
+
+      // Now ensure negative sign.
+      // TODO(turbofan): use FNEG(FABS(x)) instructions here; they are
+      // available on ARM (which this implementation is targeted at).
+      Node* zero = jsgraph()->Constant(-0.0);
+      Node* tag = graph()->NewNode(machine()->Float64LessThan(), floored, zero);
+
+      Node* branch2 = graph()->NewNode(common()->Branch(), tag, control);
+      Node* if_true2 = graph()->NewNode(common()->IfTrue(), branch2);
+      Node* if_false2 = graph()->NewNode(common()->IfFalse(), branch2);
+      Node* merge2 = graph()->NewNode(common()->Merge(2), if_true2, if_false2);
+
+      Node* neg =
+          graph()->NewNode(simplified()->NumberSubtract(), zero, floored);
+      Node* value = graph()->NewNode(common()->Phi(kMachFloat64, 2), floored,
+                                     neg, merge2);
+
+      Node* res = graph()->NewNode(common()->Phi(kMachFloat64, 2), rounded_away,
+                                   value, merge);
+
+      return Replace(res);
+    }
+  }
+  return NoChange();
+}
+
+
 Reduction JSBuiltinReducer::Reduce(Node* node) {
   JSCallReduction r(node);
 
@@ -237,6 +300,8 @@ Reduction JSBuiltinReducer::Reduce(Node* node) {
       return ReplaceWithPureReduction(node, ReduceMathFloor(node));
     case kMathCeil:
       return ReplaceWithPureReduction(node, ReduceMathCeil(node));
+    case kMathRound:
+      return ReplaceWithPureReduction(node, ReduceMathRound(node));
     default:
       break;
   }