[machine-operator-reducer] fix float truncation

src/compiler/machine-operator-reducer.cc

Index: src/compiler/machine-operator-reducer.cc
diff --git a/src/compiler/machine-operator-reducer.cc b/src/compiler/machine-operator-reducer.cc
index 5951fb612a9f75feb3f456f840a8c2d364cb80a2..b4134d2c901b277e67e38f2ca49ef522ed998884 100644
--- a/src/compiler/machine-operator-reducer.cc
+++ b/src/compiler/machine-operator-reducer.cc
@@ -648,7 +648,18 @@ Reduction MachineOperatorReducer::ReduceTruncateFloat64ToInt32(Node* node) {
   Float64Matcher m(node->InputAt(0));
   if (m.HasValue()) return ReplaceInt32(DoubleToInt32(m.Value()));
   if (m.IsChangeInt32ToFloat64()) return Replace(m.node()->InputAt(0));
-  if (m.IsRoundInt64ToFloat64()) return Replace(m.node()->InputAt(0));
+  if (m.IsRoundInt64ToFloat64()) {
+    Node* value = m.node()->InputAt(0);
+    Type* type = NodeProperties::GetType(value);
+    Type::RangeType* range = type->GetRange();
+
+    // Rounding int64 to float64 should not loose precision

[titzer, 2015/11/24 19:30:35]

s/loose/lose/

[fedor.indutny, 2015/11/24 19:33:37]

Acknowledged.

+    if (range != nullptr && range->Min() >= 0 &&
+        range->Max() <= 0xFFFFFFFFFFFFFULL) {
+      return Replace(
+          graph()->NewNode(machine()->TruncateInt64ToInt32(), value));
+    }
+  }
   if (m.IsPhi()) {
     Node* const phi = m.node();
     DCHECK_EQ(kRepFloat64, RepresentationOf(OpParameter<MachineType>(phi)));