Re: [AArch64] Rework ARMv8.1 command line options.

[James Greenhalgh <james dot greenhalgh at arm dot com>]

On Mon, Nov 16, 2015 at 04:31:32PM +0000, Matthew Wahab wrote:
> Hello,
> 
> The command line options for target selection allow ARMv8.1 extensions
> to be individually enabled/disabled. They also allow the extensions to
> be enabled with -march=armv8-a. This doesn't reflect the ARMv8.1
> architecture which requires all extensions to be enabled and doesn't make
> them available for ARMv8.
> 
> This patch removes the options for the individual ARMv8.1 extensions
> except for +lse. This means that setting -march=armv8.1-a will enable
> all extensions required by ARMv8.1 and that the ARMv8.1 extensions can't
> be used with -march=armv8.
> 
> The exception to this is +lse since there may be existing code expecting
> to be built with -march=armv8-a+lse. Note that +crc, which is enabled by
> -march=armv8.1-a, is still an option for -march=armv8-a.
> 
> This patch depends on the patch series
> https://gcc.gnu.org/ml/gcc-patches/2015-10/msg02429.html.
> 
> Tested aarch64-none-elf with cross-compiled check-gcc and
> aarch64-none-linux-gnu with native bootstrap and make check.
> 
> Ok for trunk?
> Matthew
> 
> gcc/
> 2015-11-16  Matthew Wahab  <matthew.wahab@arm.com>
> 
> 	* config/aarch64/aarch64-options-extensions.def: Remove
> 	AARCH64_FL_RDMA from "fp" and "simd".  Remove "pan", "lor",
> 	"rdma".
> 	* config/aarch64/aarch64.h (AARCH64_FL_PAN): Remove.
> 	(AARCH64_FL_LOR): Remove.
> 	(AARCH64_FL_RDMA): Remove.
> 	(AARCH64_FL_V8_1): New.
> 	(AARCH64_FL_FOR_AARCH8_1): Replace AARCH64_FL_PAN, AARCH64_FL_LOR
> 	and AARCH64_FL_RDMA with AARCH64_FL_V8_1.
> 	(AARCH64_ISA_RDMA): Replace AARCH64_FL_RDMA with AARCH64_FL_V8_1.
> 	* doc/invoke.texi (AArch64 - Feature Modifiers): Remove "pan",
> 	"lor" and "rdma".

I think I mentioned it in another review, but this patch seems a good place
to solve the problem. Could you please update the documentation to explain
what you've written above. As it stands I find myself confused by which
features GCC will make available at -march=armv8-a and -march=armv8.1-a.

Thanks,
James

> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 8057ac9..710198a 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -12674,13 +12674,6 @@ instructions.  This is on by default for all possible values for options
>  @option{-march} and @option{-mcpu}.
>  @item lse
>  Enable Large System Extension instructions.
> -@item pan
> -Enable Privileged Access Never support.
> -@item lor
> -Enable Limited Ordering Regions support.
> -@item rdma
> -Enable ARMv8.1 Advanced SIMD instructions.  This implies Advanced SIMD
> -is enabled.
>  
>  @end table
>  
> -- 
> 2.1.4
>