On 1/7/19 10:23 AM, Jakub Jelinek wrote:
> On Sun, Dec 16, 2018 at 06:13:57PM +0200, Dimitar Dimitrov wrote:
>> -  /* Clobbering the STACK POINTER register is an error.  */
>> +  /* Clobbered STACK POINTER register is not saved/restored by GCC,
>> +     which is often unexpected by users.  See PR52813.  */
>>    if (overlaps_hard_reg_set_p (regset, Pmode, STACK_POINTER_REGNUM))
>>      {
>> -      error ("Stack Pointer register clobbered by %qs in %<asm%>", regname);
>> +      warning (0, "Stack Pointer register clobbered by %qs in %<asm%>",
>> +	       regname);
>> +      warning (0, "GCC has always ignored Stack Pointer %<asm%> clobbers");
> 
> Why do we write Stack Pointer rather than stack pointer?  That is really
> weird.  The second warning would be a note based on the first one, i.e.
> if (warning ()) note ();
> and better have some -W* option to silence the warning.
> 

Yes, thanks for this suggestion.

Meanwhile I found out, that the stack clobber has only been ignored up to
gcc-5 (at least with lra targets, not really sure about reload targets).
From gcc-6 on, with the exception of PR arm/77904 which was a regression due
to the underlying lra change, but fixed later, and back-ported to gcc-6.3.0,
this works for all targets I tried so far.

To me, it starts to look like a rather unique and useful feature, that I would
like to keep working.


Attached is an updated version if my patch, using the suggested warning option,
and a note with the details.


Bootstrapped on x86_64-pc-linux-gnu.
Is it OK for trunk?


Thanks
Bernd.