Bug 1018621 - Fix strict mode arguments observability in Ion. (r=nbp)

js/src/jit-test/tests/ion/bug1018621.js

@@ -0,0 +1,7 @@
+function strictSome(k) {
+  "use strict";
+  for (var i = 0; i < args.length; i++)
+    assertEq(arguments[i], args[i], "wrong argument " + i);
+}
+args = [8, 6, 7, NaN, undefined, 0.3];
+strictSome.call(NaN, 8, 6, 7, NaN, undefined, 0.3);

js/src/jit/CompileInfo.h

@@ -425,8 +425,11 @@ class CompileInfo
 
         // Function.arguments can be used to access all arguments in non-strict
         // scripts, so we can't optimize out any arguments.
-        if (!script()->strict() && firstArgSlot() <= slot && slot - firstArgSlot() < nargs())
+        if ((hasArguments() || !script()->strict()) &&
+            firstArgSlot() <= slot && slot - firstArgSlot() < nargs())
+        {
             return true;
+        }
 
         return false;
     }