Infer range for BIT_XOR.

runtime/vm/flow_graph_optimizer.cc

Index: runtime/vm/flow_graph_optimizer.cc
diff --git a/runtime/vm/flow_graph_optimizer.cc b/runtime/vm/flow_graph_optimizer.cc
index 9cedab65a54107586eec149848ec03778a56e011..f8d72e90888538e26cf4fa654217641693de0b2b 100644
--- a/runtime/vm/flow_graph_optimizer.cc
+++ b/runtime/vm/flow_graph_optimizer.cc
@@ -750,6 +750,27 @@ static void UnboxPhi(PhiInstr* phi) {
       break;
   }
 
+  if ((unboxed == kTagged) &&
+      phi->Type()->IsInt() &&
+      RangeUtils::Fits(phi->range(), RangeBoundary::kRangeBoundaryInt32)) {
+    bool should_unbox = false;
+    for (intptr_t i = 0; i < phi->InputCount(); i++) {
+      Definition* input = phi->InputAt(i)->definition();
+      if (input->IsBox() &&
+          RangeUtils::Fits(input->range(),
+                           RangeBoundary::kRangeBoundaryInt32)) {
+        should_unbox = true;
+      } else if (!input->IsConstant()) {
+        should_unbox = false;
+        break;
+      }
+    }
+
+    if (should_unbox) {
+      unboxed = kUnboxedInt32;
+    }
+  }
+
   phi->set_representation(unboxed);
 }