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

[Thomas Preudhomme]

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

Best regards,

Thomas
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