[AArch64] PR target/105157 Increase number of cores TARGET_CPU_DEFAULT can encode

Hi,

This addresses the compile-time increase seen in the PR target/105157. 
This was being caused by selecting the wrong core tuning, as when we 
added the latest AArch64 the TARGET_CPU_generic tuning was pushed beyond 
the 0x3f mask we used to encode both target cpu and attributes into 
TARGET_CPU_DEFAULT.

This is a quick fix to increase the number of allowed cores for now late 
in stage 4, but for next GCC we plan to fix this in a more suitable and 
maintainable manner.

gcc/ChangeLog:

         PR target/105157
         * config.gcc: Shift ext_mask by TARGET_CPU_NBITS.
         * config/aarch64/aarch64.h (TARGET_CPU_NBITS): New macro.
         (TARGET_CPU_MASK): Likewise.
         (TARGET_CPU_DEFAULT): Use TARGET_CPU_NBITS.
         * config/aarch64/aarch64.cc (aarch64_get_tune_cpu): Use 
TARGET_CPU_MASK.
         (aarch64_get_arch): Likewise.
         (aarch64_override_options): Use TARGET_CPU_NBITS.
         (aarch64_run_selftests): Add test to guarantee TARGET_CPU_NBITS 
is big enough.

"Andre Vieira (lists)" <andre.simoesdiasvieira@arm.com> writes:
> Hi,
>
> This addresses the compile-time increase seen in the PR target/105157. 
> This was being caused by selecting the wrong core tuning, as when we 
> added the latest AArch64 the TARGET_CPU_generic tuning was pushed beyond 
> the 0x3f mask we used to encode both target cpu and attributes into 
> TARGET_CPU_DEFAULT.
>
> This is a quick fix to increase the number of allowed cores for now late 
> in stage 4, but for next GCC we plan to fix this in a more suitable and 
> maintainable manner.
>
> gcc/ChangeLog:
>
>          PR target/105157
>          * config.gcc: Shift ext_mask by TARGET_CPU_NBITS.
>          * config/aarch64/aarch64.h (TARGET_CPU_NBITS): New macro.
>          (TARGET_CPU_MASK): Likewise.
>          (TARGET_CPU_DEFAULT): Use TARGET_CPU_NBITS.
>          * config/aarch64/aarch64.cc (aarch64_get_tune_cpu): Use 
> TARGET_CPU_MASK.
>          (aarch64_get_arch): Likewise.
>          (aarch64_override_options): Use TARGET_CPU_NBITS.
>          (aarch64_run_selftests): Add test to guarantee TARGET_CPU_NBITS 
> is big enough.

Looks good, just a minor nit:

>
> diff --git a/gcc/config.gcc b/gcc/config.gcc
> index 2cc5aeec9e46aacc46e4e509d01f57f9f6585169..8946984f5e93cd6fe5364b44e74c64e714ba1d6a 100644
> --- a/gcc/config.gcc
> +++ b/gcc/config.gcc
> @@ -4239,7 +4239,7 @@ case "${target}" in
>  				ext_val=`echo $ext_val | sed -e 's/[a-z0-9]\+//'`
>  			  done
>  
> -			  ext_mask="(("$ext_mask") << 6)"
> +			  ext_mask="(("$ext_mask") << TARGET_CPU_NBITS)"
>  			  if [ x"$base_id" != x ]; then
>  				target_cpu_cname="TARGET_CPU_$base_id | $ext_mask"
>  			  fi
> diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
> index efa46ac0b8799b5849b609d591186e26e5cb37ff..97b2d38dac9f13717e90f4f6996ab94814922950 100644
> --- a/gcc/config/aarch64/aarch64.h
> +++ b/gcc/config/aarch64/aarch64.h
> @@ -813,10 +813,17 @@ enum target_cpus
>    TARGET_CPU_generic
>  };
>  
> +

Nit: excess extra line.

> +/* Define how many bits are used to represent the CPU in TARGET_CPU_DEFAULT.
> +   This needs to be big enough to fit the value of TARGET_CPU_generic.
> +   All bits after this are used to represent the AARCH64_CPU_DEFAULT_FLAGS.  */
> +#define TARGET_CPU_NBITS 8
> +#define TARGET_CPU_MASK ((1 << TARGET_CPU_NBITS) - 1)
> +
>  /* If there is no CPU defined at configure, use generic as default.  */
>  #ifndef TARGET_CPU_DEFAULT
>  #define TARGET_CPU_DEFAULT \
> -  (TARGET_CPU_generic | (AARCH64_CPU_DEFAULT_FLAGS << 6))
> +  (TARGET_CPU_generic | (AARCH64_CPU_DEFAULT_FLAGS << TARGET_CPU_NBITS))
>  #endif
>  
>  /* If inserting NOP before a mult-accumulate insn remember to adjust the
> diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
> index d66626748e5edc46e46edf10e243114a9f74be97..9d83e007d7a31455c167bf21124cf9fbc0d31788 100644
> --- a/gcc/config/aarch64/aarch64.cc
> +++ b/gcc/config/aarch64/aarch64.cc
> @@ -18062,12 +18062,12 @@ aarch64_get_tune_cpu (enum aarch64_processor cpu)
>    if (cpu != aarch64_none)
>      return &all_cores[cpu];
>  
> -  /* The & 0x3f is to extract the bottom 6 bits that encode the
> -     default cpu as selected by the --with-cpu GCC configure option
> +  /* The & TARGET_CPU_MASK is to extract the bottom TARGET_CPU_NBITS bits that
> +     encode the default cpu as selected by the --with-cpu GCC configure option
>       in config.gcc.
>       ???: The whole TARGET_CPU_DEFAULT and AARCH64_CPU_DEFAULT_FLAGS
>       flags mechanism should be reworked to make it more sane.  */
> -  return &all_cores[TARGET_CPU_DEFAULT & 0x3f];
> +  return &all_cores[TARGET_CPU_DEFAULT & TARGET_CPU_MASK];
>  }
>  
>  /* Return the architecture corresponding to the enum ARCH.
> @@ -18079,7 +18079,8 @@ aarch64_get_arch (enum aarch64_arch arch)
>    if (arch != aarch64_no_arch)
>      return &all_architectures[arch];
>  
> -  const struct processor *cpu = &all_cores[TARGET_CPU_DEFAULT & 0x3f];
> +  const struct processor *cpu
> +    = &all_cores[TARGET_CPU_DEFAULT & TARGET_CPU_MASK];
>  
>    return &all_architectures[cpu->arch];
>  }
> @@ -18166,7 +18167,7 @@ aarch64_override_options (void)
>  	{
>  	  /* Get default configure-time CPU.  */
>  	  selected_cpu = aarch64_get_tune_cpu (aarch64_none);
> -	  aarch64_isa_flags = TARGET_CPU_DEFAULT >> 6;
> +	  aarch64_isa_flags = TARGET_CPU_DEFAULT >> TARGET_CPU_NBITS;
>  	}
>  
>        if (selected_tune)
> @@ -27260,6 +27261,9 @@ aarch64_run_selftests (void)
>  {
>    aarch64_test_loading_full_dump ();
>    aarch64_test_fractional_cost ();
> +  /* Check whether the TARGET_CPU_MASK is big enough to fit all of the definded
> +     CPUs.  */
> +  ASSERT_TRUE (TARGET_CPU_generic < TARGET_CPU_MASK);

I think this would be better as a static assert at the top level:

  static_assert (TARGET_CPU_generic < TARGET_CPU_MASK,
		 "TARGET_CPU_NBITS is big enough");

OK with that change, thanks.

Richard

>  }
>  
>  } // namespace selftest

On 08/04/2022 08:04, Richard Sandiford wrote:
> I think this would be better as a static assert at the top level:
>
>    static_assert (TARGET_CPU_generic < TARGET_CPU_MASK,
> 		 "TARGET_CPU_NBITS is big enough");
The motivation being that you want this to be checked regardless of 
whether we are using CHECKING_P?

"Andre Vieira (lists)" <andre.simoesdiasvieira@arm.com> writes:
> On 08/04/2022 08:04, Richard Sandiford wrote:
>> I think this would be better as a static assert at the top level:
>>
>>    static_assert (TARGET_CPU_generic < TARGET_CPU_MASK,
>> 		 "TARGET_CPU_NBITS is big enough");
> The motivation being that you want this to be checked regardless of 
> whether we are using CHECKING_P?

Yeah, that's one reason.  Others are that static_asserts are caught at
the earliest possible moment (as a build failure) and that they don't
require any object code.

Thanks,
Richard