RE: [PATCH v3 1/3] config/arm: avoid mcpu and march conflicts

[Wathsala Wathawana Vithanage <wathsala.vithanage@arm.com>]

Hi Pavan,

> The compiler options march and mtune are a subset of mcpu and will lead to
> conflicts if improper march is chosen for a given mcpu.
> To avoid conflicts, force part number march when mcpu is available and is
> supported by the compiler.

Why would one force the march specified in the part number when mcpu for
that part number is also available and supported by the compiler?

> 
> Example:
> 	march = armv9-a
> 	mcpu = neoverse-n2
> 
> 	mcpu supported, march supported
> 	machine_args = ['-mcpu=neoverse-n2', '-march=armv9-a']

-march restricts the compiler to baseline architecture of the -mcpu.
For instance, Neoverse-n1's baseline architecture is armv8.2-a, 
but it has some extensions from armv8.3-a, armv8.4-a, and armv8.5-a. 
By setting -march to armv8.2-a the compiler will strictly omit extensions
from 8.3, 8.4 and 8.5 resulting in a suboptimal outcome.

> 
> 	mcpu supported, march not supported
> 	machine_args = ['-mcpu=neoverse-n2']

This will result in the best outcome.

> 
> 	mcpu not supported, march supported
> 	machine_args = ['-march=armv9-a']

This too may result in a suboptimal outcome as optimization space
is limited to the given march (not using extensions from later 
architectures when available).

> 
> 	mcpu not supported, march not supported
> 	machine_args = ['-march=armv8.6-a']

Compiler knows nothing about the target CPU or the architecture.
I think it's better to exit the build process with an error. 

> 
> Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
> ---
> v2 Changes:
> - Cleanup march inconsistencies. (Juraj Linkes)
> - Unify fallback march selection. (Juraj Linkes)
> - Tag along ARM WFE patch.
> v3 Changes:
> - Fix missing 'fallback_march' key check.
> 
>  config/arm/meson.build | 108 +++++++++++++++++++++++++---------------
> -
>  1 file changed, 66 insertions(+), 42 deletions(-)
> 
> diff --git a/config/arm/meson.build b/config/arm/meson.build index
> 36f21d22599a..ba859bd060b5 100644
> --- a/config/arm/meson.build
> +++ b/config/arm/meson.build
> @@ -58,18 +58,18 @@ implementer_generic = {  }
> 
>  part_number_config_arm = {
> -    '0xd03': {'compiler_options':  ['-mcpu=cortex-a53']},
> -    '0xd04': {'compiler_options':  ['-mcpu=cortex-a35']},
> -    '0xd05': {'compiler_options':  ['-mcpu=cortex-a55']},
> -    '0xd07': {'compiler_options':  ['-mcpu=cortex-a57']},
> -    '0xd08': {'compiler_options':  ['-mcpu=cortex-a72']},
> -    '0xd09': {'compiler_options':  ['-mcpu=cortex-a73']},
> -    '0xd0a': {'compiler_options':  ['-mcpu=cortex-a75']},
> -    '0xd0b': {'compiler_options':  ['-mcpu=cortex-a76']},
> +    '0xd03': {'mcpu': 'cortex-a53'},
> +    '0xd04': {'mcpu': 'cortex-a35'},
> +    '0xd05': {'mcpu': 'cortex-a55'},
> +    '0xd07': {'mcpu': 'cortex-a57'},
> +    '0xd08': {'mcpu': 'cortex-a72'},
> +    '0xd09': {'mcpu': 'cortex-a73'},
> +    '0xd0a': {'mcpu': 'cortex-a75'},
> +    '0xd0b': {'mcpu': 'cortex-a76'},
>      '0xd0c': {
>          'march': 'armv8.2-a',
>          'march_features': ['crypto', 'rcpc'],
> -        'compiler_options':  ['-mcpu=neoverse-n1'],
> +        'mcpu': 'neoverse-n1',
>          'flags': [
>              ['RTE_MACHINE', '"neoverse-n1"'],
>              ['RTE_ARM_FEATURE_ATOMICS', true], @@ -81,7 +81,7 @@
> part_number_config_arm = {
>      '0xd40': {
>          'march': 'armv8.4-a',
>          'march_features': ['sve'],
> -        'compiler_options':  ['-mcpu=neoverse-v1'],
> +        'mcpu': 'neoverse-v1',
>          'flags': [
>              ['RTE_MACHINE', '"neoverse-v1"'],
>              ['RTE_ARM_FEATURE_ATOMICS', true], @@ -92,8 +92,9 @@
> part_number_config_arm = {
>          'march': 'armv8.4-a',
>      },
>      '0xd49': {
> +        'march': 'armv9-a',
>          'march_features': ['sve2'],
> -        'compiler_options': ['-mcpu=neoverse-n2'],
> +        'mcpu': 'neoverse-n2',
>          'flags': [
>              ['RTE_MACHINE', '"neoverse-n2"'],
>              ['RTE_ARM_FEATURE_ATOMICS', true], @@ -127,21 +128,23 @@
> implementer_cavium = {
>      ],
>      'part_number_config': {
>          '0xa1': {
> -            'compiler_options': ['-mcpu=thunderxt88'],
> +            'mcpu': 'thunderxt88',
>              'flags': flags_part_number_thunderx
>          },
>          '0xa2': {
> -            'compiler_options': ['-mcpu=thunderxt81'],
> +            'mcpu': 'thunderxt81',
>              'flags': flags_part_number_thunderx
>          },
>          '0xa3': {
> -            'compiler_options': ['-march=armv8-a+crc', '-mcpu=thunderxt83'],
> +            'march': 'armv8-a',
> +            'march_features': ['crc'],
> +            'mcpu': 'thunderxt83',
>              'flags': flags_part_number_thunderx
>          },
>          '0xaf': {
>              'march': 'armv8.1-a',
>              'march_features': ['crc', 'crypto'],
> -            'compiler_options': ['-mcpu=thunderx2t99'],
> +            'mcpu': 'thunderx2t99',
>              'flags': [
>                  ['RTE_MACHINE', '"thunderx2"'],
>                  ['RTE_ARM_FEATURE_ATOMICS', true], @@ -153,7 +156,7 @@
> implementer_cavium = {
>          '0xb2': {
>              'march': 'armv8.2-a',
>              'march_features': ['crc', 'crypto', 'lse'],
> -            'compiler_options': ['-mcpu=octeontx2'],
> +            'mcpu': 'octeontx2',
>              'flags': [
>                  ['RTE_MACHINE', '"cn9k"'],
>                  ['RTE_ARM_FEATURE_ATOMICS', true], @@ -176,7 +179,7 @@
> implementer_ampere = {
>          '0x0': {
>              'march': 'armv8-a',
>              'march_features': ['crc', 'crypto'],
> -            'compiler_options':  ['-mtune=emag'],
> +            'mcpu': 'emag',
>              'flags': [
>                  ['RTE_MACHINE', '"eMAG"'],
>                  ['RTE_MAX_LCORE', 32],
> @@ -186,7 +189,7 @@ implementer_ampere = {
>          '0xac3': {
>              'march': 'armv8.6-a',
>              'march_features': ['crc', 'crypto'],
> -            'compiler_options':  ['-mcpu=ampere1'],
> +            'mcpu': 'ampere1',
>              'flags': [
>                  ['RTE_MACHINE', '"AmpereOne"'],
>                  ['RTE_MAX_LCORE', 320], @@ -206,7 +209,7 @@
> implementer_hisilicon = {
>          '0xd01': {
>              'march': 'armv8.2-a',
>              'march_features': ['crypto'],
> -            'compiler_options': ['-mtune=tsv110'],
> +            'mcpu': 'tsv110',
>              'flags': [
>                  ['RTE_MACHINE', '"Kunpeng 920"'],
>                  ['RTE_ARM_FEATURE_ATOMICS', true], @@ -695,11 +698,21 @@ if
> update_flags
> 
>      machine_args = [] # Clear previous machine args
> 
> +    candidate_mcpu = ''
> +    if part_number_config.has_key('mcpu')
> +        mcpu = part_number_config['mcpu']
> +        if (cc.has_argument('-mcpu=' + mcpu))
> +            candidate_mcpu = mcpu
> +        endif
> +    endif
> +
>      # probe supported archs and their features
>      candidate_march = ''
>      if part_number_config.has_key('march')
> -        if part_number_config.get('force_march', false)
> -            candidate_march = part_number_config['march']
> +        if part_number_config.get('force_march', false) or candidate_mcpu != ''
> +            if cc.has_argument('-march=' +  part_number_config['march'])
> +                candidate_march = part_number_config['march']
> +            endif
>          else
>              supported_marchs = ['armv8.6-a', 'armv8.5-a', 'armv8.4-a', 'armv8.3-
> a',
>                                  'armv8.2-a', 'armv8.1-a', 'armv8-a'] @@ -717,32 +730,43
> @@ if update_flags
>                  endif
>              endforeach
>          endif
> -        if candidate_march == ''
> -            error('No suitable armv8 march version found.')
> -        endif
> +
>          if candidate_march != part_number_config['march']
> -            warning('Configuration march version is ' +
> -                    '@0@, but the compiler supports only @1@.'
> -                    .format(part_number_config['march'], candidate_march))
> +            warning('Configuration march version is @0@, not supported.'
> +                    .format(part_number_config['march']))
> +            if candidate_march != ''
> +                warning('Using march version @0@.'.format(candidate_march))
> +            endif
>          endif
> -        candidate_march = '-march=' + candidate_march
> 
> -        march_features = []
> -        if part_number_config.has_key('march_features')
> -            march_features += part_number_config['march_features']
> -        endif
> -        if soc_config.has_key('extra_march_features')
> -            march_features += soc_config['extra_march_features']
> +        if candidate_march == '' and candidate_mcpu == ''
> +            error('No suitable ARM march/mcpu version found.')
>          endif
> -        foreach feature: march_features
> -            if cc.has_argument('+'.join([candidate_march, feature]))
> -                candidate_march = '+'.join([candidate_march, feature])
> -            else
> -                warning('The compiler does not support feature @0@'
> -                    .format(feature))
> +
> +        if candidate_march != ''
> +            candidate_march = '-march=' + candidate_march
> +            march_features = []
> +            if part_number_config.has_key('march_features')
> +                march_features += part_number_config['march_features']
>              endif
> -        endforeach
> -        machine_args += candidate_march
> +            if soc_config.has_key('extra_march_features')
> +                march_features += soc_config['extra_march_features']
> +            endif
> +            foreach feature: march_features
> +                if cc.has_argument('+'.join([candidate_march, feature]))
> +                    candidate_march = '+'.join([candidate_march, feature])
> +                else
> +                    warning('The compiler does not support feature @0@'
> +                        .format(feature))
> +                endif
> +            endforeach
> +            machine_args += candidate_march
> +        endif
> +    endif
> +
> +    if candidate_mcpu != ''
> +        candidate_mcpu = '-mcpu=' + candidate_mcpu
> +        machine_args += candidate_mcpu
>      endif
> 
>      # apply supported compiler options
> --
> 2.43.0