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

We can reduce Math.round(v) to a sequence of

  let i = Float64RoundUp(v);
  let r = i - v;
  return r > 0.5 ? 1.0 + i : i;

if the target supports the Float64RoundUp machine operator (i.e.
roundsd with RoundUp rounding on Intel processors with SSE4.1).

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/1640393002

Cr-Commit-Position: refs/heads/master@{#33572}

src/compiler/js-builtin-reducer.cc

@@ -8,6 +8,7 @@
 #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 {
@@ -85,10 +86,10 @@ class JSCallReduction {
   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) {
@@ -141,6 +142,31 @@ Reduction JSBuiltinReducer::ReduceMathFround(Node* node) {
   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();
@@ -158,6 +184,9 @@ Reduction JSBuiltinReducer::Reduce(Node* node) {
     case kMathFround:
       reduction = ReduceMathFround(node);
       break;
+    case kMathRound:
+      reduction = ReduceMathRound(node);
+      break;
     default:
       break;
   }

src/compiler/js-builtin-reducer.h

@@ -9,6 +9,10 @@
 
 namespace v8 {
 namespace internal {
+
+// Forward declarations.
+class TypeCache;
+
 namespace compiler {
 
 // Forward declarations.
@@ -30,6 +34,7 @@ class JSBuiltinReducer final : public AdvancedReducer {
   Reduction ReduceMathMax(Node* node);
   Reduction ReduceMathImul(Node* node);
   Reduction ReduceMathFround(Node* node);
+  Reduction ReduceMathRound(Node* node);
 
   Graph* graph() const;
   JSGraph* jsgraph() const { return jsgraph_; }
@@ -38,7 +43,8 @@ class JSBuiltinReducer final : public AdvancedReducer {
   MachineOperatorBuilder* machine() const;
   SimplifiedOperatorBuilder* simplified() const;
 
-  JSGraph* jsgraph_;
+  JSGraph* const jsgraph_;
+  TypeCache const& type_cache_;
 };
 
 }  // namespace compiler

src/compiler/simplified-lowering.cc

@@ -1388,6 +1388,7 @@ class RepresentationSelector {
       case IrOpcode::kFloat64RoundDown:
       case IrOpcode::kFloat64RoundTruncate:
       case IrOpcode::kFloat64RoundTiesAway:
+      case IrOpcode::kFloat64RoundUp:
         return VisitUnop(node, UseInfo::Float64(), NodeOutputInfo::Float64());
       case IrOpcode::kFloat64Equal:
       case IrOpcode::kFloat64LessThan: