[turbofan] Add support for Math.round to the JSBuiltinReducer.

src/compiler/js-builtin-reducer.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/js-builtin-reducer.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
 #include "src/compiler/simplified-operator.h"
 #include "src/objects-inl.h"
+#include "src/type-cache.h"
 #include "src/types.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 
 // Helper class to access JSCallFunction nodes that are potential candidates
 // for reduction when they have a BuiltinFunctionId associated with them.
 class JSCallReduction {
@@ skipping 57 matching lines @@
     DCHECK_EQ(IrOpcode::kJSCallFunction, node_->opcode());
     DCHECK_LT(index, GetJSCallArity());
     // Skip first (i.e. callee) and second (i.e. receiver) operand.
     return NodeProperties::GetValueInput(node_, index + 2);
   }
 
  private:
   Node* node_;
 };
 
-
 JSBuiltinReducer::JSBuiltinReducer(Editor* editor, JSGraph* jsgraph)
-    : AdvancedReducer(editor), jsgraph_(jsgraph) {}
-
+    : AdvancedReducer(editor),
+      jsgraph_(jsgraph),
+      type_cache_(TypeCache::Get()) {}
 
 // ECMA-262, section 15.8.2.11.
 Reduction JSBuiltinReducer::ReduceMathMax(Node* node) {
   JSCallReduction r(node);
   if (r.InputsMatchZero()) {
     // Math.max() -> -Infinity
     return Replace(jsgraph()->Constant(-V8_INFINITY));
   }
   if (r.InputsMatchOne(Type::Number())) {
     // Math.max(a:number) -> a
@@ skipping 32 matching lines @@
   JSCallReduction r(node);
   if (r.InputsMatchOne(Type::Number())) {
     // Math.fround(a:number) -> TruncateFloat64ToFloat32(a)
     Node* value =
         graph()->NewNode(machine()->TruncateFloat64ToFloat32(), r.left());
     return Replace(value);
   }
   return NoChange();
 }
 
+// ES6 section 20.2.2.28 Math.round ( x )
+Reduction JSBuiltinReducer::ReduceMathRound(Node* node) {
+  JSCallReduction r(node);
+  if (r.InputsMatchOne(type_cache_.kIntegerOrMinusZeroOrNaN)) {
+    // Math.round(a:integer \/ -0 \/ NaN) -> a
+    return Replace(r.left());
+  }
+  if (r.InputsMatchOne(Type::Number()) &&
+      machine()->Float64RoundUp().IsSupported()) {
+    // Math.round(a:number) -> Select(Float64LessThan(#0.5, Float64Sub(i, a)),
+    //                                Float64Sub(i, #1.0), i)
+    //   where i = Float64RoundUp(a)
+    Node* value = r.left();
+    Node* integer = graph()->NewNode(machine()->Float64RoundUp().op(), value);
+    Node* real = graph()->NewNode(machine()->Float64Sub(), integer, value);
+    return Replace(graph()->NewNode(
+        common()->Select(MachineRepresentation::kFloat64),
+        graph()->NewNode(machine()->Float64LessThan(),
+                         jsgraph()->Float64Constant(0.5), real),
+        graph()->NewNode(machine()->Float64Sub(), integer,
+                         jsgraph()->Float64Constant(1.0)),
+        integer));
+  }
+  return NoChange();
+}
 
 Reduction JSBuiltinReducer::Reduce(Node* node) {
   Reduction reduction = NoChange();
   JSCallReduction r(node);
 
   // Dispatch according to the BuiltinFunctionId if present.
   if (!r.HasBuiltinFunctionId()) return NoChange();
   switch (r.GetBuiltinFunctionId()) {
     case kMathMax:
       reduction = ReduceMathMax(node);
       break;
     case kMathImul:
       reduction = ReduceMathImul(node);
       break;
     case kMathFround:
       reduction = ReduceMathFround(node);
       break;
+    case kMathRound:
+      reduction = ReduceMathRound(node);
+      break;
     default:
       break;
   }
 
   // Replace builtin call assuming replacement nodes are pure values that don't
   // produce an effect. Replaces {node} with {reduction} and relaxes effects.
   if (reduction.Changed()) ReplaceWithValue(node, reduction.replacement());
 
   return reduction;
 }
@@ skipping 15 matching lines @@
 }
 
 
 SimplifiedOperatorBuilder* JSBuiltinReducer::simplified() const {
   return jsgraph()->simplified();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8