[Bug target/99312] New: __ARM_ARCH is not implemented correctly when compiled with -march=armv8.1-a

[Bug target/99312] New: __ARM_ARCH is not implemented correctly when compiled with -march=armv8.1-a

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99312

            Bug ID: 99312
           Summary: __ARM_ARCH is not implemented correctly when compiled
                    with -march=armv8.1-a
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

The latest ACLE dated Q3 2020 has the following for how __ARM_ARCH should be
defined for ARMv8.1-a and above:
For an Arm architecture ArmvX.Y, __ARM_ARCH = X * 100 + Y. E.g.
for Armv8.1 __ARM_ARCH = 801.
----- CUT ----
Currently GCC just does 8.

[Bug target/99312] __ARM_ARCH is not implemented correctly when compiled with -march=armv8.1-a

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99312

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
https://developer.arm.com/documentation/101028/latest

[Bug target/99312] __ARM_ARCH is not implemented correctly when compiled with -march=armv8.1-a

[ktkachov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99312

ktkachov at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ktkachov at gcc dot gnu.org

--- Comment #2 from ktkachov at gcc dot gnu.org ---
We intend to deprecate that macro going forward as it's not a useful way for
testing architecture features in aarch64. It made sense in the pre-Armv7-a
days, but now the recommended way to test for features is the __ARM_FEATURE*
macros.

The scheme is also not very well-suited for things like the recent AArch64
Armv8-R.

Is there a particular use case that you have in mind?

[Bug target/99312] __ARM_ARCH is not implemented correctly when compiled with -march=armv8.1-a

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99312

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to ktkachov from comment #2)
> We intend to deprecate that macro going forward as it's not a useful way for
> testing architecture features in aarch64. It made sense in the pre-Armv7-a
> days, but now the recommended way to test for features is the __ARM_FEATURE*
> macros.

Which is interesting because x86 is going in the opposite direction and having
ISA "levels".

> 
> The scheme is also not very well-suited for things like the recent AArch64
> Armv8-R.
> 
> Is there a particular use case that you have in mind?

A customer was asking for how to detect the ISA Level at compile time and
runtime.

[Bug target/99312] __ARM_ARCH is not implemented correctly when compiled with -march=armv8.1-a

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99312

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
ODP is one place where this is used:
https://opendataplane.github.io/odp/structodp__system__info__t.html

[Bug target/99312] __ARM_ARCH is not implemented correctly when compiled with -march=armv8.1-a

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99312

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                URL|                            |https://gcc.gnu.org/piperma
                   |                            |il/gcc-patches/2021-March/5
                   |                            |66322.html
           Keywords|                            |patch

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Also Naveen posted a patch earlier today:
https://gcc.gnu.org/pipermail/gcc-patches/2021-March/566322.html

[Bug target/99312] __ARM_ARCH is not implemented correctly when compiled with -march=armv8.1-a

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99312

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2021-03-07
     Ever confirmed|0                           |1

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed, Naveen posted the patch already.

[Bug target/99312] __ARM_ARCH is not implemented correctly when compiled with -march=armv8.1-a

[rearnsha at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99312

Richard Earnshaw <rearnsha at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |Vedant.VijayYevale@infineon
                   |                            |.com

--- Comment #7 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
*** Bug 109415 has been marked as a duplicate of this bug. ***

[Bug target/99312] __ARM_ARCH is not implemented correctly when compiled with -march=armv8.1-a

[rearnsha at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99312

--- Comment #8 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
Applies to both AArch64 and Arm back-ends.