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Re: [PATCH 00/30] [ARM] Reworking the -mcpu, -march and -mfpu options


On 12/06/17 12:49, Christophe Lyon wrote:
> On 10 June 2017 at 01:27, Richard Earnshaw (lists)
> <Richard.Earnshaw@arm.com> wrote:
>> On 09/06/17 23:45, Christophe Lyon wrote:
>>> Hi Richard,
>>>
>>>
>>> On 9 June 2017 at 14:53, Richard Earnshaw <Richard.Earnshaw@arm.com> wrote:
>>>>
>>>> During the ARM BoF at the Cauldron last year I mentioned that I wanted
>>>> to rework the way GCC on ARM handles the command line options.  The
>>>> problem was that most users, and even many experts, can't remember
>>>> which FPU/SIMD unit comes with which CPU and that consequently many
>>>> users were inadvertenly generating sub-optimal code for their system.
>>>>
>>>> This patch series implements the proposed change and provides support
>>>> for a generic way of adding optional features to architectures and CPU
>>>> names.  The documentation patches at the end of the series explain the
>>>> new syntax, so I won't repeat all that here.  Suffice to say here that
>>>> the result is that the -mfpu option now defaults to 'auto', which
>>>> allows the compiler to infer the floating-point and simd options from
>>>> the CPU/architecture options and that these options can normally be
>>>> expressed in a context-specific manner like +simd or +fp without
>>>> having to know precisely which variant is implemented.  Long term I'd
>>>> like to deprecate -mfpu and entirely move over to the new syntax; but
>>>> it's too early to start that process now.
>>>>
>>>> All the patches in the series should build a working basic compiler,
>>>> but the multilib selection will not work correctly until the relevant
>>>> patches towards the end are applied.  It is not really feasible to
>>>> retain that functionality without collapsing too many of the patches
>>>> together into one hunk.  It's also possible that some tests in the
>>>> testsuite may exhibit transient misbehaviour, but there should be no
>>>> regressions by the end of the sequence (some tests no-longer run in
>>>> the default configurations because the default CPU does not have
>>>> floating-point support).
>>>>
>>>> Just two patches are to the generic code, but both are fairly trivial.
>>>> One permits the sbitmap code to be used in the driver programs and the
>>>> other provides a way of escaping the meta-character in some multilib
>>>> reuse strings.
>>>>
>>>> I won't apply any of this series until those two patches have been
>>>> approved, and I won't commit anything before the middle of next week
>>>> even then.  This is a fairly complex change and it deserves some time
>>>> for people to comment before committing.
>>>>
>>>> R.
>>>>
>>>> Richard Earnshaw (30):
>>>>   [arm] Use strings for -march, -mcpu and -mtune options
>>>>   [arm] Rewrite -march and -mcpu options for passing to the assembler
>>>>   [arm] Don't pass -mfpu=auto through to the assembler.
>>>>   [arm] Allow +opt on arbitrary cpu and architecture specifications
>>>>   [arm] Add architectural options
>>>>   [arm] Add default FPUs for CPUs.
>>>>   [build] Make sbitmap code available to the driver programs
>>>>   [arm] Split CPU, architecture and tuning data tables.
>>>>   [ARM] Move cpu and architecture option name parsing code to
>>>>     arm-common.c
>>>>   [arm] Use standard option parsing code for detecting thumb-only
>>>>     targets
>>>>   [arm] Allow CPU and architecture extensions to be defined as aliases
>>>>   [arm] Allow new extended syntax CPU and architecture names during
>>>>     configure
>>>>   [arm] Force a CPU default in the config args defaults list.
>>>>   [arm] Generate a canonical form for -march
>>>>   [arm] Make -mfloat-abi=softfp work when there are no FPU instructions
>>>>   [arm] Update basic multilib configuration
>>>>   [arm] Make 'auto' the default FPU selection option.
>>>>   [arm] Rewrite t-aprofile using new selector methodology
>>>>   [arm] Explicitly set .fpu in cmse_nonsecure_call.S
>>>>   [genmultilib] Allow explicit periods to be escaped in MULTILIB_REUSE
>>>>   [arm][testsuite] Use -march=armv7-a+fp when testing hard-float ABI.
>>>>   [arm] Rewrite t-rmprofile multilib specification
>>>>   [arm][rtems] Update t-rtems for new option framework
>>>>   [arm][linux-eabi] Ensure all multilib variables are reset
>>>>   [arm][phoenix] reset all multilib variables
>>>>   [arm] Rework multlib builds for symbianelf
>>>>   [arm][fuchsia] Rework multilib support
>>>>   [arm] Add a few missing architecture extension options.
>>>>   [arm][doc] Document new -march= syntax.
>>>>   [arm][doc] Document changes to -mcpu, -mtune and -mfpu.
>>>>
>>>>  gcc/Makefile.in                           |    2 +-
>>>>  gcc/common/config/arm/arm-common.c        |  651 +++++++-
>>>>  gcc/config.gcc                            |   17 +-
>>>>  gcc/config/arm/arm-builtins.c             |    4 +-
>>>>  gcc/config/arm/arm-cpu-cdata.h            | 2444 +++++++++++++++++++++++------
>>>>  gcc/config/arm/arm-cpu-data.h             | 1410 ++---------------
>>>>  gcc/config/arm/arm-cpu.h                  |   38 +
>>>>  gcc/config/arm/arm-cpus.in                |  237 ++-
>>>>  gcc/config/arm/arm-isa.h                  |   20 +-
>>>>  gcc/config/arm/arm-protos.h               |   56 +-
>>>>  gcc/config/arm/arm-tables.opt             |   21 +-
>>>>  gcc/config/arm/arm.c                      |  337 ++--
>>>>  gcc/config/arm/arm.h                      |   75 +-
>>>>  gcc/config/arm/arm.opt                    |   15 +-
>>>>  gcc/config/arm/bpabi.h                    |    4 -
>>>>  gcc/config/arm/elf.h                      |    6 +-
>>>>  gcc/config/arm/linux-elf.h                |    3 -
>>>>  gcc/config/arm/netbsd-elf.h               |    4 -
>>>>  gcc/config/arm/parsecpu.awk               |  295 +++-
>>>>  gcc/config/arm/t-aprofile                 |  200 +--
>>>>  gcc/config/arm/t-arm-elf                  |  173 +-
>>>>  gcc/config/arm/t-fuchsia                  |   33 +
>>>>  gcc/config/arm/t-linux-eabi               |    4 +
>>>>  gcc/config/arm/t-multilib                 |  126 +-
>>>>  gcc/config/arm/t-phoenix                  |   20 +-
>>>>  gcc/config/arm/t-rmprofile                |  147 +-
>>>>  gcc/config/arm/t-rtems                    |   49 +-
>>>>  gcc/config/arm/t-symbian                  |   34 +-
>>>>  gcc/config/arm/vxworks.h                  |    2 -
>>>>  gcc/doc/fragments.texi                    |   10 +-
>>>>  gcc/doc/invoke.texi                       |  371 ++++-
>>>>  gcc/genmultilib                           |    4 +-
>>>>  gcc/testsuite/gcc.dg/pr59418.c            |    2 +-
>>>>  gcc/testsuite/gcc.target/arm/multilib.exp |  685 ++++++++
>>>>  gcc/testsuite/gcc.target/arm/pr51915.c    |    2 +-
>>>>  gcc/testsuite/gcc.target/arm/pr52006.c    |    2 +-
>>>>  gcc/testsuite/gcc.target/arm/pr53187.c    |    2 +-
>>>>  libgcc/config/arm/cmse_nonsecure_call.S   |    8 +
>>>>  38 files changed, 5073 insertions(+), 2440 deletions(-)
>>>>  create mode 100644 gcc/config/arm/t-fuchsia
>>>>  create mode 100644 gcc/testsuite/gcc.target/arm/multilib.exp
>>>>
>>>> ----------------2.7.4--
>>>>
>>>
>>> I wanted to run a validation with the full series applied as one patch
>>> over r249050,
>>> so I just downloaded all the patches, concatenated them in order, but the result
>>> fails to apply. (conflicts with arm-cpu-cdata.h, arm-cpus.in,
>>> t-aprofile, t-rmprofile)
>>>
>>> Am I missing something?
>>>
>>> Thanks,
>>>
>>> Christophe
>>>
>>
>> I really appreciate you trying to do this...
>>
>> I rebased the patch series sometime on Tuesday/Wednesday just before Jim
>> Wilson committed his falkor change; you'll need to back out to just
>> before r248944.  I can't think of anything else that might have just
>> gone in that might conflict.  For arm-cpu-cdata.h (and the other
>> auto-generated files, like arm-cpu-data.h) you can just delete the file
>> and it will be rebuilt automatically, the others really do need the
>> conflict to be resolved.
>>
>> Obviously I'll rebase again just before the commit, but propagating such
>> changes through the patch series is quite tedious and I don't want to do
>> it any more than necessary :-).
>>
>> It would be easier if the generated files weren't checked in to the
>> repository...
>>
>> R.
> 
> Hi Richard,
> 
> Starting a validation of the whole patch against r248942 did work, thanks.
> 
> The results are here:
> http://people.linaro.org/~christophe.lyon/cross-validation/gcc-test-patches/248942-rework-cpu-arch-fpu.patch/report-build-info.html
> 
> Regressions are detected in many configurations, unfortunately.
> Some may be caused by the fact that I've upgraded to dejagnu-1.6+ for
> my testing,
> and thus "multilib flags" are now prepended rather than appended, but
> I don't think that's the majority.
> 
> To help you understand/group all the reports:
> - all "arm-none-linux-gnueabi" with REGRESSED now have:
> FAIL: gcc.target/arm/neon-thumb2-move.c (test for excess errors)

See later.

> FAIL: gcc.target/arm/no-volatile-in-it.c scan-assembler-not ldrgt
> - same for the 2 configs arm-none-eabi --with-cpu=cortex-a9

I'm checking a fix for this, I think I understand what's going on here.

> 
> - all "arm-none-linux-gnueabihf" and "armeb-none-linux-gnueabihf" with
> REGRESSED now have:
> FAIL: gcc.target/arm/no-volatile-in-it.c scan-assembler-not ldrgt
> 
> - arm-none-eabi --with-cpu=cortex-m3 now has:
> FAIL:
>     gcc.target/arm/no-volatile-in-it.c scan-assembler-not ldrgt
>     gcc.target/arm/thumb2-slow-flash-data-2.c (test for excess errors)
>     gcc.target/arm/thumb2-slow-flash-data-3.c (test for excess errors)
>     gcc.target/arm/thumb2-slow-flash-data-4.c (test for excess errors)
>     gcc.target/arm/thumb2-slow-flash-data-5.c (test for excess errors)
> UNRESOLVED:
>     gcc.target/arm/thumb2-slow-flash-data-4.c scan-assembler-times #1\\.0e\\+0 3
>     gcc.target/arm/thumb2-slow-flash-data-5.c scan-assembler-not #1\\.0e\\+0
> 
> - The 2 cells with "BIG-REG" mean regressions where detected, but the report
> is >100kb so it was attached as a .xz file, click on 'BIG-REG" to download it.
> 
> - the cells with "BETTER" can be questionable: it means no new failure
> appeared, but PASS -> UNSUPPORTED is considered as "better". Here
> we have cases with several thousands (!) of tests becoming unsupported,
> which looks a bit suspicious.
> 
> Among other things, I've noticed that when passing -march=armv5t,
> arm_neon_ok fails:
> xgcc -march=armv5t -fno-diagnostics-show-caret
> -fdiagnostics-color=never -mfpu=neon -mfloat-abi=softfp -march=
> armv7-a -c -o arm_neon_ok15574.o arm_neon_ok15574.c
> arm_neon_ok15574.c:9:4: error: #error Architecture does not support NEON.
> compiler exited with status 1
> 
> I'd expect -march=armv7-a to allow to use -mfpu=neon?
> 

It does.  The problem seems to be a generic one in the driver in that
the rewrite rules are always passed the first instance of -march and not
the last.  Indeed, with the aarch64 compiler, if I write

gcc -mcpu=native -mcpu=cortex-a53

then the driver will rewrite this as

./cc1 -mcpu=cortex-a53 -mcpu=<expansion of native cpu name>

which doesn't seem to be the right thing at all.

So we either have a generic problem with all option rewriting, or there
are some subtle details of it that we've not figured out yet.

Joseph, is there a way to get the rewrite rules to receive the *last*
instance of a flag rather than the first?  Or is the current behaviour
simply wrong?

R.

> Regarding the new multilib.exp tests introduced by the patch, my testing
> did not run it because I have no configuration setting aprofile or rmprofile.
> Maybe it's time I add one, or update the existing ones.
> I didn't see any message "skipping multilib tests due to
> multilib_flags setting",
> but I guess that's because my runs are not verbose enough. That being said,
> I'm not sure how the multilib_flags are set in board_info? Is that derived from
> RUNTESTFLAGS?
> 
> From this report page, you can also click on "sum" and "log" (when
> present) to download the gcc.sum or gcc.log files.
> 
> Feel free to ask more details if I haven't been clear enough.
> 
> Thanks,
> 
> Christophe
> 


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