[turbofan] Add constant-folding for CheckedFloat64ToInt32.

BUG=v8:5267
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2612763002
Cr-Commit-Position: refs/heads/master@{#42060}

src/compiler/simplified-operator-reducer.cc

@@ -129,6 +129,15 @@ Reduction SimplifiedOperatorReducer::Reduce(Node* node) {
       }
       break;
     }
+    case IrOpcode::kCheckedFloat64ToInt32: {
+      Float64Matcher m(node->InputAt(0));
+      if (m.HasValue() && IsInt32Double(m.Value())) {
+        Node* value = jsgraph()->Int32Constant(static_cast<int32_t>(m.Value()));
+        ReplaceWithValue(node, value);
+        return Replace(value);
+      }
+      break;
+    }
     case IrOpcode::kCheckedTaggedToInt32:
     case IrOpcode::kCheckedTaggedSignedToInt32: {
       NodeMatcher m(node->InputAt(0));

test/unittests/compiler/simplified-operator-reducer-unittest.cc

@@ -335,6 +335,22 @@ TEST_F(SimplifiedOperatorReducerTest, TruncateTaggedToWord32WithConstant) {
   }
 }
 
+// -----------------------------------------------------------------------------
+// CheckedFloat64ToInt32
+
+TEST_F(SimplifiedOperatorReducerTest, CheckedFloat64ToInt32WithConstant) {
+  Node* effect = graph()->start();
+  Node* control = graph()->start();
+  TRACED_FOREACH(int32_t, n, kInt32Values) {
+    Reduction r = Reduce(
+        graph()->NewNode(simplified()->CheckedFloat64ToInt32(
+                             CheckForMinusZeroMode::kDontCheckForMinusZero),
+                         Float64Constant(n), effect, control));
+    ASSERT_TRUE(r.Changed());
+    EXPECT_THAT(r.replacement(), IsInt32Constant(n));
+  }
+}
+
 // -----------------------------------------------------------------------------
 // CheckHeapObject