Re: Repost [PATCH 1/6] Add -mcpu=future

[Michael Meissner <meissner@linux.ibm.com>]

On Tue, Feb 20, 2024 at 06:35:34PM +0800, Kewen.Lin wrote:
> Hi Mike,
> 
> Sorry for late reply (just back from vacation).
> 
> on 2024/2/8 03:58, Michael Meissner wrote:
> > On Wed, Feb 07, 2024 at 05:21:10PM +0800, Kewen.Lin wrote:
> >> on 2024/2/6 14:01, Michael Meissner wrote:
> >> Sorry for the possible confusion here, the "tune_proc" that I referred to is
> >> the variable in the above else branch:
> >>
> >>    enum processor_type tune_proc = (TARGET_POWERPC64 ? PROCESSOR_DEFAULT64 : PROCESSOR_DEFAULT);
> >>
> >> It's either PROCESSOR_DEFAULT64 or PROCESSOR_DEFAULT, so it doesn't have a
> >> chance to be PROCESSOR_FUTURE, so the checking "tune_proc == PROCESSOR_FUTURE"
> >> is useless.
> > 
> > PROCESSOR_DEFAULT can be PROCESSOR_FUTURE if somebody configures GCC with
> > --with-cpu=future.  While in general it shouldn't occur, it is helpful to
> > consider all of the corner cases.
> 
> But it sounds not true, I think you meant TARGET_CPU_DEFAULT instead?
> 
> On one local ppc64le machine I tried to configure with --with-cpu=power10,
> I got {,OPTION_}TARGET_CPU_DEFAULT "power10" but PROCESSOR_DEFAULT is still
> PROCESSOR_POWER7 (PROCESSOR_DEFAULT64 is PROCESSOR_POWER8).  I think these
> PROCESSOR_DEFAULT{,64} are defined by various headers:

Yes, I was mistaken.  You are correct TARGET_CPU_DEFAULT is set.  I will change
the comments.

> gcc/config/rs6000/aix71.h:#define PROCESSOR_DEFAULT PROCESSOR_POWER7
> gcc/config/rs6000/aix71.h:#define PROCESSOR_DEFAULT64 PROCESSOR_POWER7
> gcc/config/rs6000/aix72.h:#define PROCESSOR_DEFAULT PROCESSOR_POWER7
> gcc/config/rs6000/aix72.h:#define PROCESSOR_DEFAULT64 PROCESSOR_POWER7
> gcc/config/rs6000/aix73.h:#define PROCESSOR_DEFAULT PROCESSOR_POWER8
> gcc/config/rs6000/aix73.h:#define PROCESSOR_DEFAULT64 PROCESSOR_POWER8
> gcc/config/rs6000/darwin.h:#define PROCESSOR_DEFAULT  PROCESSOR_PPC7400
> gcc/config/rs6000/darwin.h:#define PROCESSOR_DEFAULT64  PROCESSOR_POWER4
> gcc/config/rs6000/freebsd64.h:#define PROCESSOR_DEFAULT PROCESSOR_PPC7450
> gcc/config/rs6000/freebsd64.h:#define PROCESSOR_DEFAULT64 PROCESSOR_POWER8
> gcc/config/rs6000/linux64.h:#define PROCESSOR_DEFAULT PROCESSOR_POWER7
> gcc/config/rs6000/linux64.h:#define PROCESSOR_DEFAULT64 PROCESSOR_POWER8
> gcc/config/rs6000/rs6000.h:#define PROCESSOR_DEFAULT   PROCESSOR_PPC603
> gcc/config/rs6000/rs6000.h:#define PROCESSOR_DEFAULT64 PROCESSOR_RS64A
> gcc/config/rs6000/vxworks.h:#define PROCESSOR_DEFAULT PROCESSOR_PPC604
> 
> , and they are unlikely to be updated later, no?
> 
> btw, the given --with-cpu=future will make cpu_index never negative so
> 
>   ...
>   else if (cpu_index >= 0)
>     rs6000_tune_index = tune_index = cpu_index;
>   else
>     ... 
> 
> so there is no chance to enter "else" arm, that is, that arm only takes
> effect when no cpu/tune is given (neither -m{cpu,tune} nor --with-cpu=).

Note, this is existing code.  I didn't modify it.  If we want to change it, we
should do it as another patch.

-- 
Michael Meissner, IBM
PO Box 98, Ayer, Massachusetts, USA, 01432
email: meissner@linux.ibm.com