Bug 1237564 - Fix minor bug with a lexical declaration shadowing a non-configurable global. r=shu

--HG--
extra : rebase_source : d8c67ef94022fb06870f18e605c841f3447105f2

js/src/jit-test/tests/basic/bug1237564.js

@@ -0,0 +1,8 @@
+// |jit-test| error:ReferenceError: can't access lexical
+try {
+    evaluate("let x = (() => { throw 3 })();");
+} catch(e) {
+    assertEq(e, 3);
+}
+Object.defineProperty(this, "x", {});
+(function() { x = 3; })();

js/src/jit/BaselineCompiler.cpp

@@ -2242,11 +2242,11 @@ BaselineCompiler::emit_JSOP_BINDGNAME()
                 frame.push(ObjectValue(*globalLexical));
                 return true;
             }
-        }
-
-        // We can bind name to the global object if the property exists on the
-        // global and is non-configurable, as then it cannot be shadowed.
-        if (Shape* shape = script->global().lookup(cx, name)) {
+        } else if (Shape* shape = script->global().lookup(cx, name)) {
+            // If the property does not currently exist on the global lexical
+            // scope, we can bind name to the global object if the property
+            // exists on the global and is non-configurable, as then it cannot
+            // be shadowed.
             if (!shape->configurable()) {
                 frame.push(ObjectValue(script->global()));
                 return true;