Extend -fstack-protector-strong to cover calls with return slot

[Jakub Jelinek]

On Tue, Jan 07, 2014 at 01:51:00PM +0100, Florian Weimer wrote:
> +static bool
> +stack_protect_return_slot_p ()
> +{
> +  basic_block bb;
> +  
> +  FOR_ALL_BB_FN (bb, cfun)
> +    for (gimple_stmt_iterator gsi = gsi_start_bb (bb);
> +	 !gsi_end_p (gsi); gsi_next (&gsi))
> +      {
> +	gimple stmt = gsi_stmt (gsi);
> +	if (is_gimple_call (stmt) && gimple_call_return_slot_opt_p (stmt))

I have to repeat, this is not the right test, it really is just an
optimization hint, nothing else.  Just look where it is set (unless it is
C++ where some NRV is performed in the FE as mandated by the languages)
- in pass_return_slot, which is an optimization pass, not run with -O0 or
-Og at all.  So, you'd stack protect something only if not -O0 or -Og, that
is just wrong, and only if it was suitable for NRV.  You really want to
protect all functions that call something that is returned by hidden
reference.

	Jakub