Fix handling of constant global variable assignments.

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 6bc7f6982fb798f442eb5a55da8b380ac7868d0c..bb0ceada840fdbde9bdd0ae2f8adb37ffbbf90e0 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -5909,18 +5909,27 @@ void HOptimizedGraphBuilder::HandleGlobalVariableAssignment(
     Handle<GlobalObject> global(current_info()->global_object());
     Handle<PropertyCell> cell(global->GetPropertyCell(&lookup));
     if (cell->type()->IsConstant()) {
-      IfBuilder builder(this);
-      HValue* constant = Add<HConstant>(cell->type()->AsConstant());
-      if (cell->type()->AsConstant()->IsNumber()) {
-        builder.If<HCompareNumericAndBranch>(value, constant, Token::EQ);
+      Handle<Object> constant = cell->type()->AsConstant();
+      if (value->IsConstant()) {
+        HConstant* c_value = HConstant::cast(value);
+        if (!constant.is_identical_to(c_value->handle(isolate()))) {
+          Add<HDeoptimize>("Constant global variable assignment",
+                           Deoptimizer::EAGER);
+        }
       } else {
-        builder.If<HCompareObjectEqAndBranch>(value, constant);
+        HValue* c_constant = Add<HConstant>(constant);
+        IfBuilder builder(this);
+        if (constant->IsNumber()) {
+          builder.If<HCompareNumericAndBranch>(value, c_constant, Token::EQ);
+        } else {
+          builder.If<HCompareObjectEqAndBranch>(value, c_constant);
+        }
+        builder.Then();
+        builder.Else();
+        Add<HDeoptimize>("Constant global variable assignment",
+                         Deoptimizer::EAGER);
+        builder.End();
       }
-      builder.Then();
-      builder.Else();
-      Add<HDeoptimize>("Constant global variable assignment",
-                       Deoptimizer::EAGER);
-      builder.End();
     }
     HInstruction* instr =
         Add<HStoreGlobalCell>(value, cell, lookup.GetPropertyDetails());