Re: [PATCH] gcc/ira.c: Check !HAVE_FP_INSTEAD_INSNS when frame pointer is needed and as global register

[Chen Gang <xili_gchen_5257@hotmail.com>]

On 10/13/15 07:02, Mike Stump wrote:
> On Oct 12, 2015, at 3:32 PM, Chen Gang <xili_gchen_5257@hotmail.com> wrote:
>>
>> OK, thanks. If we really need to fix it, which target hook should I use?
>> (or do we need a new target hook?)
> 
> So, the first discussion would be if it is, or is not a bug.  If it isn’t, then there is no fix.  No fix, no target hook.  So far, Bernd said not a bug.
> 

OK, under the bugzilla, the maintainer treated it as expected behavior
(not a bug). For me, we need more explanation for it (why we treat it
as expected behavior).


> So, I’ll note that one _can_ do this with the stack pointer, as a fixed register.
> When the frame pointer is fixed, one cannot do this.
> 

Excuse me, I do not quite understand, could you please provide more
details?

> The code that does this is:
> 
>   /* Diagnose uses of the hard frame pointer when it is used as a global                                                                                                                                                   
>      register.  Often we can get away with letting the user appropriate                                                                                                                                                     
>      the frame pointer, but we should let them know when code generation                                                                                                                                                    
>      makes that impossible.  */
>   if (global_regs[HARD_FRAME_POINTER_REGNUM] && frame_pointer_needed)
>     {
>       tree decl = global_regs_decl[HARD_FRAME_POINTER_REGNUM];
>       error_at (DECL_SOURCE_LOCATION (current_function_decl),
>                 "frame pointer required, but reserved");
>       inform (DECL_SOURCE_LOCATION (decl), "for %qD", decl);
>     }
> 
> to `fix it’, one would simple remove this chunk as misguided and fix up any code gen issues exposed.
> 

If there were not only one issues related with it, for me, what you said
sounds reasonable to me.


Thanks.
-- 
Chen Gang (陈刚)

Open, share, and attitude like air, water, and life which God blessed