Re: [PATCH, GCC/ARM, ping] Optional -mthumb for Thumb only targets

[Christophe Lyon <christophe dot lyon at linaro dot org>]

Hi Thomas,


On 18 November 2016 at 17:51, Thomas Preudhomme
<thomas.preudhomme@foss.arm.com> wrote:
> On 11/11/16 14:35, Kyrill Tkachov wrote:
>>
>>
>> On 08/11/16 13:36, Thomas Preudhomme wrote:
>>>
>>> Ping?
>>>
>>> Best regards,
>>>
>>> Thomas
>>>
>>> On 25/10/16 18:07, Thomas Preudhomme wrote:
>>>>
>>>> Hi,
>>>>
>>>> Currently when a user compiles for a thumb-only target (such as Cortex-M
>>>> processors) without specifying the -mthumb option GCC throws the error
>>>> "target
>>>> CPU does not support ARM mode". This is suboptimal from a usability
>>>> point of
>>>> view: the -mthumb could be deduced from the -march or -mcpu option when
>>>> there is
>>>> no ambiguity.
>>>>
>>>> This patch implements this behavior by extending the DRIVER_SELF_SPECS
>>>> to
>>>> automatically append -mthumb to the command line for thumb-only targets.
>>>> It does
>>>> so by checking the last -march option if any is given or the last -mcpu
>>>> option
>>>> otherwise. There is no ordering issue because conflicting -mcpu and
>>>> -march is
>>>> already handled.
>>>>
>>>> Note that the logic cannot be implemented in function
>>>> arm_option_override
>>>> because we need to provide the modified command line to the GCC driver
>>>> for
>>>> finding the right multilib path and the function arm_option_override is
>>>> executed
>>>> too late for that effect.
>>>>
>>>> ChangeLog entries are as follow:
>>>>
>>>> *** gcc/ChangeLog ***
>>>>
>>>> 2016-10-18  Terry Guo  <terry.guo@arm.com>
>>>>             Thomas Preud'homme <thomas.preudhomme@arm.com>
>>>>
>>>>         PR target/64802
>>>>         * common/config/arm/arm-common.c (arm_target_thumb_only): New
>>>> function.
>>>>         * config/arm/arm-opts.h: Include arm-flags.h.
>>>>         (struct arm_arch_core_flag): Define.
>>>>         (arm_arch_core_flags): Define.
>>>>         * config/arm/arm-protos.h: Include arm-flags.h.
>>>>         (FL_NONE, FL_ANY, FL_CO_PROC, FL_ARCH3M, FL_MODE26, FL_MODE32,
>>>>         FL_ARCH4, FL_ARCH5, FL_THUMB, FL_LDSCHED, FL_STRONG, FL_ARCH5E,
>>>>         FL_XSCALE, FL_ARCH6, FL_VFPV2, FL_WBUF, FL_ARCH6K, FL_THUMB2,
>>>> FL_NOTM,
>>>>         FL_THUMB_DIV, FL_VFPV3, FL_NEON, FL_ARCH7EM, FL_ARCH7,
>>>> FL_ARM_DIV,
>>>>         FL_ARCH8, FL_CRC32, FL_SMALLMUL, FL_NO_VOLATILE_CE, FL_IWMMXT,
>>>>         FL_IWMMXT2, FL_ARCH6KZ, FL2_ARCH8_1, FL2_ARCH8_2, FL2_FP16INST,
>>>>         FL_TUNE, FL_FOR_ARCH2, FL_FOR_ARCH3, FL_FOR_ARCH3M,
>>>> FL_FOR_ARCH4,
>>>>         FL_FOR_ARCH4T, FL_FOR_ARCH5, FL_FOR_ARCH5T, FL_FOR_ARCH5E,
>>>>         FL_FOR_ARCH5TE, FL_FOR_ARCH5TEJ, FL_FOR_ARCH6, FL_FOR_ARCH6J,
>>>>         FL_FOR_ARCH6K, FL_FOR_ARCH6Z, FL_FOR_ARCH6ZK, FL_FOR_ARCH6KZ,
>>>>         FL_FOR_ARCH6T2, FL_FOR_ARCH6M, FL_FOR_ARCH7, FL_FOR_ARCH7A,
>>>>         FL_FOR_ARCH7VE, FL_FOR_ARCH7R, FL_FOR_ARCH7M, FL_FOR_ARCH7EM,
>>>>         FL_FOR_ARCH8A, FL2_FOR_ARCH8_1A, FL2_FOR_ARCH8_2A,
>>>> FL_FOR_ARCH8M_BASE,
>>>>         FL_FOR_ARCH8M_MAIN, arm_feature_set, ARM_FSET_MAKE,
>>>>         ARM_FSET_MAKE_CPU1, ARM_FSET_MAKE_CPU2, ARM_FSET_CPU1,
>>>> ARM_FSET_CPU2,
>>>>         ARM_FSET_EMPTY, ARM_FSET_ANY, ARM_FSET_HAS_CPU1,
>>>> ARM_FSET_HAS_CPU2,
>>>>         ARM_FSET_HAS_CPU, ARM_FSET_ADD_CPU1, ARM_FSET_ADD_CPU2,
>>>>         ARM_FSET_DEL_CPU1, ARM_FSET_DEL_CPU2, ARM_FSET_UNION,
>>>> ARM_FSET_INTER,
>>>>         ARM_FSET_XOR, ARM_FSET_EXCLUDE, ARM_FSET_IS_EMPTY,
>>>>         ARM_FSET_CPU_SUBSET): Move to ...
>>>>         * config/arm/arm-flags.h: This new file.
>>>>         * config/arm/arm.h (TARGET_MODE_SPEC_FUNCTIONS): Define.
>>>>         (EXTRA_SPEC_FUNCTIONS): Add TARGET_MODE_SPEC_FUNCTIONS to its
>>>> value.
>>>>         (TARGET_MODE_SPECS): Define.
>>>>         (DRIVER_SELF_SPECS): Add TARGET_MODE_SPECS to its value.
>>>>
>>>>
>>>> *** gcc/testsuite/ChangeLog ***
>>>>
>>>> 2016-10-11  Thomas Preud'homme <thomas.preudhomme@arm.com>
>>>>
>>>>         PR target/64802
>>>>         * gcc.target/arm/optional_thumb-1.c: New test.
>>>>         * gcc.target/arm/optional_thumb-2.c: New test.
>>>>         * gcc.target/arm/optional_thumb-3.c: New test.
>>>>
>>>>
>>>> No regression when running the testsuite for -mcpu=cortex-m0 -mthumb,
>>>> -mcpu=cortex-m0 -marm and -mcpu=cortex-a8 -marm
>>>>
>>>> Is this ok for trunk?
>>>>
>>
>> This looks like a useful usability improvement.
>> This is ok after a bootstrap on an arm-none-linux-gnueabihf target.
>>
>> Sorry for the delay,
>> Kyrill
>
>
> I've rebased the patch on top of the arm_feature_set type consistency fix
> [1] and committed it. The committed patch is in attachment for reference.
>
> [1] https://gcc.gnu.org/ml/gcc-patches/2016-11/msg01680.html
>

Since this commit (242597), I've noticed that:
- the 2 new tests optional_thumb-1.c and optional_thumb-2.c fail
if GCC was configured --with-mode=arm. The error message is:
cc1: error: target CPU does not support ARM mode

- on armeb --with-mode=arm, gcc.dg/vect/pr64252.c fails at execution

See: http://people.linaro.org/~christophe.lyon/cross-validation/gcc/trunk/242597/report-build-info.html

Christophe


> Best regards,
>
> Thomas