Work around more MSC optimzer bugs

mrbgems/mruby-random/src/random.c

@@ -220,12 +220,30 @@ mrb_ary_shuffle_bang(mrb_state *mrb, mrb_value ary)
 
  /*
  * MSC compiler bug generating invalid instructions with optimization
- * enabled
+ * enabled. MSC errantly uses a hardcoded value with optimizations on
+ * when using a fixed value from a union.
+ * Creating a temp volatile variable and reassigning back to the original
+ * value tricks the compiler to not perform this optimization;
  */
 #if defined _MSC_VER && _MSC_VER >= 1923
-  volatile mrb_value rr;
-  rr = r;
-  r = rr;
+  /* C++ will not cast away volatile easily, so we cannot do something like
+   * volatile mrb_value rr = r; r = (mrb_value)rr; with C++.
+   * That cast does work with C.
+   * We also have to trick the compiler to not optimize away the const_cast entirely
+   * by creating and manipulating an intermediate volatile pointer.
+   */
+  volatile mrb_value *v_r;
+  volatile mrb_int ii;
+  mrb_value *p_r;
+  v_r = &r;
+  ii = 2;
+  v_r = v_r + 2;
+#if defined __cplusplus
+  p_r = const_cast<mrb_value*>(v_r - ii);
+#else
+  p_r = (mrb_value*)v_r - ii;
+#endif
+  r = *p_r;
 #endif
 
   if (RARRAY_LEN(ary) > 1) {