[committed,nvptx] Add march-map

Hi,

Say we have an sm_50 board, and we want to run a benchmark using the highest
possible march setting.

Currently there's march=sm_30, march=sm_35, march=sm_53, but no march=sm_50.

So, we'd need to pick march=sm_35.

Likewise, for a test script that handles multiple boards, we'd need a mapping
from native board sm_xx to march, which might have to be updated with newer
gcc releases.

Add an option march-map, such that we can just specify march-map=sm_50, and
let the compiler map this to the appropriate march.

The option is implemented as a list of aliases, such that we have a somewhat
lengthy (17 lines in total):
...
$ gcc --help=target
  ...
  -march-map=sm_30            Same as -misa=sm_30.
  -march-map=sm_32            Same as -misa=sm_30.
  ...
  -march-map=sm_87            Same as -misa=sm_80.
  -march-map=sm_90            Same as -misa=sm_80.
...

This implementation was chosen in the hope that it'll be easier if
we end up with some misa multilib.

It would be nice to have the mapping list generated from an updated
nvptx-sm.def, but for now it's spelled out in nvptx.opt.

Tested on nvptx.

Committed to trunk.

Thanks,
- Tom

[nvptx] Add march-map

gcc/ChangeLog:

2022-03-29  Tom de Vries  <tdevries@suse.de>

	PR target/104714
	* config/nvptx/nvptx.opt (march-map=*): Add aliases.

gcc/testsuite/ChangeLog:

2022-03-29  Tom de Vries  <tdevries@suse.de>

	PR target/104714
	* gcc.target/nvptx/march-map.c: New test.

---
 gcc/config/nvptx/nvptx.opt                 | 51 ++++++++++++++++++++++++++++++
 gcc/testsuite/gcc.target/nvptx/march-map.c |  5 +++
 2 files changed, 56 insertions(+)

Hi Tom!

On 2022-03-29T14:03:22+0200, Tom de Vries via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> Say we have an sm_50 board, and we want to run a benchmark using the highest
> possible march setting.
>
> Currently there's march=sm_30, march=sm_35, march=sm_53, but no march=sm_50.
>
> So, we'd need to pick march=sm_35.
>
> Likewise, for a test script that handles multiple boards, we'd need a mapping
> from native board sm_xx to march, which might have to be updated with newer
> gcc releases.

ACK.

> Add an option march-map, such that we can just specify march-map=sm_50, and
> let the compiler map this to the appropriate march.

So, I understand that the idea is, that users should use
'-march-map=[...]' instead of '-misa=[...]' or alias '-march=[...]',
because the former ('-march-map=[...]') will always Do The Right Thing:
pick the best available SM level for GCC/nvptx code generation (like
you've said: may change with GCC releases, and users then don't have to
change their receipes), and it'll never error out, in contrast to
'-misa=[...]' or alias '-march=[...]' do when the requested architecture
isn't directly supported:

    xgcc: error: unrecognized argument in option ‘-misa=sm_50’
    xgcc: note: valid arguments to ‘-misa=’ are: sm_30 sm_35 sm_53 sm_70 sm_75 sm_80; did you mean ‘sm_30’?

My question, though, is: why did you add a new option name '-march-map'
instead of directly using '-march' for that (instead of "[nvptx] Add
march alias for misa", added on the same day)?  Would you accept a patch
that: (a) un-aliases '-march' -> '-misa', and (b) renames '-march-map' to
'-march', and (c) sets up a '-march-map' -> '-march' alias for backwards
compatibility (if so desired)?  Regarding (a), (b), in my opinion,
there's no backwards compatibility issue there: the "new '-march'" will
simply accept more options than the "old '-march'" did.  Regarding (c),
I'd even drop the user-visible '-march-map' option completely; I suppose
nobody's really used that by now?


Grüße
 Thomas


> The option is implemented as a list of aliases, such that we have a somewhat
> lengthy (17 lines in total):
> ...
> $ gcc --help=target
>   ...
>   -march-map=sm_30            Same as -misa=sm_30.
>   -march-map=sm_32            Same as -misa=sm_30.
>   ...
>   -march-map=sm_87            Same as -misa=sm_80.
>   -march-map=sm_90            Same as -misa=sm_80.
> ...
>
> This implementation was chosen in the hope that it'll be easier if
> we end up with some misa multilib.
>
> It would be nice to have the mapping list generated from an updated
> nvptx-sm.def, but for now it's spelled out in nvptx.opt.
>
> Tested on nvptx.
>
> Committed to trunk.
>
> Thanks,
> - Tom
>
> [nvptx] Add march-map
>
> gcc/ChangeLog:
>
> 2022-03-29  Tom de Vries  <tdevries@suse.de>
>
>       PR target/104714
>       * config/nvptx/nvptx.opt (march-map=*): Add aliases.
>
> gcc/testsuite/ChangeLog:
>
> 2022-03-29  Tom de Vries  <tdevries@suse.de>
>
>       PR target/104714
>       * gcc.target/nvptx/march-map.c: New test.
>
> ---
>  gcc/config/nvptx/nvptx.opt                 | 51 ++++++++++++++++++++++++++++++
>  gcc/testsuite/gcc.target/nvptx/march-map.c |  5 +++
>  2 files changed, 56 insertions(+)
>
> diff --git a/gcc/config/nvptx/nvptx.opt b/gcc/config/nvptx/nvptx.opt
> index b5d0170e9e9..58eddeeabf4 100644
> --- a/gcc/config/nvptx/nvptx.opt
> +++ b/gcc/config/nvptx/nvptx.opt
> @@ -60,6 +60,57 @@ march=
>  Target RejectNegative Joined Alias(misa=)
>  Alias:
>
> +march-map=sm_30
> +Target RejectNegative Alias(misa=,sm_30)
> +
> +march-map=sm_32
> +Target RejectNegative Alias(misa=,sm_30)
> +
> +march-map=sm_35
> +Target RejectNegative Alias(misa=,sm_35)
> +
> +march-map=sm_37
> +Target RejectNegative Alias(misa=,sm_35)
> +
> +march-map=sm_50
> +Target RejectNegative Alias(misa=,sm_35)
> +
> +march-map=sm_52
> +Target RejectNegative Alias(misa=,sm_35)
> +
> +march-map=sm_53
> +Target RejectNegative Alias(misa=,sm_53)
> +
> +march-map=sm_60
> +Target RejectNegative Alias(misa=,sm_53)
> +
> +march-map=sm_61
> +Target RejectNegative Alias(misa=,sm_53)
> +
> +march-map=sm_62
> +Target RejectNegative Alias(misa=,sm_53)
> +
> +march-map=sm_70
> +Target RejectNegative Alias(misa=,sm_70)
> +
> +march-map=sm_72
> +Target RejectNegative Alias(misa=,sm_70)
> +
> +march-map=sm_75
> +Target RejectNegative Alias(misa=,sm_75)
> +
> +march-map=sm_80
> +Target RejectNegative Alias(misa=,sm_80)
> +
> +march-map=sm_86
> +Target RejectNegative Alias(misa=,sm_80)
> +
> +march-map=sm_87
> +Target RejectNegative Alias(misa=,sm_80)
> +
> +march-map=sm_90
> +Target RejectNegative Alias(misa=,sm_80)
> +
>  Enum
>  Name(ptx_version) Type(int)
>  Known PTX ISA versions (for use with the -mptx= option):
> diff --git a/gcc/testsuite/gcc.target/nvptx/march-map.c b/gcc/testsuite/gcc.target/nvptx/march-map.c
> new file mode 100644
> index 00000000000..00838e55fc0
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/nvptx/march-map.c
> @@ -0,0 +1,5 @@
> +/* { dg-options "-march-map=sm_50" } */
> +
> +#include "main.c"
> +
> +/* { dg-final { scan-assembler-times "\\.target\tsm_35" 1 } } */
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