+ *
+ * Drivers for GPUs with no control flow support should simply call
+ *
+ * lower_if_to_cond_assign(instructions)
+ *
+ * to attempt to flatten all if-statements.
+ *
+ * Some GPUs (such as i965 prior to gen6) do support control flow, but have a
+ * maximum nesting depth N. Drivers for such hardware can call
+ *
+ * lower_if_to_cond_assign(instructions, N)
+ *
+ * to attempt to flatten any if-statements appearing at depth > N.