[PATCH][ARM] PR 65489: Accept VSTRUCT constants in arm_legitimate_constant_p

[Kyrill Tkachov]

On 04/04/15 17:11, Ramana Radhakrishnan wrote:
> On Mon, Mar 23, 2015 at 4:15 PM, Kyrill Tkachov <kyrylo.tkachov@arm.com> wrote:
>> Hi all,
>>
>> The ICE in the PR happens on arm during the hoist pass when the code
>> generates a SET rtx of the form:
>> (set (reg:OI) (const_int 0)). It checks whether const_int 0 is a
>> general_operand for OImode which involves asking the backend whether it's a
>> legitimate constant.
>>
>> arm_legitimate_constant_p_1 explicitly rejects OImode constants as a result
>> of the fix for PR 46329
>> https://gcc.gnu.org/ml/gcc-patches/2011-04/msg00200.html
>>
>> This results in gcse using an emit_insn of the SET rtx rather than trying to
>> do an emit_move_insn
>> which would have worked in this case.
>>
>>  From reading the thread I get the impression that the ICE there was caused
>> by reload and coproc_secondary_reload_class behaving weirdly. We're now
>> using LRA and
>> SECONDARY_INPUT_RELOAD_CLASS and SECONDARY_OUTPUT_RELOAD_CLASS which are the
>> only users of coproc_secondary_reload_class are no longer used.
>>
>> I removed the restriction on constants for these large modes in
>> arm_legitimate_constant_p_1 and the testcases in PR 46329 all work fine.
>> Bootstrap, testing and building various vector workloads also didn't show
>> any problems.
>>
>> Is this the right way to go for this?
>> If so, ok for trunk?
>>
>> The ICE in this PR happens on a recently added testcase to
>> gcc.c-torture/execute/ and this patch fixes that, so no new testcase is
>> added. Jakub mentioned that maybe the testcase can be modified to manually
>> perform the lowering done in his patch to potentially trigger this on older
>> gcc versions, but I'm not sure how that would be done.
>> The problem is that something is generating OImode moves that I think can
>> only be done in the vector form of the testcase, so I'm not entirely
>> convinced that it's reproducible on 4.9 and 4.8.
>
> This is OK for trunk now that we are in wide-int mode on trunk for the ARM port.

Thanks,
committed with r221892.

Kyrill

>
> Thanks,
> Ramana
>
>> Thanks,
>> Kyrill
>>
>> Thanks,
>> Kyrill
>>
>> 2015-03-23  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>>
>>      PR target/65489
>>      * config/arm/arm.c (arm_legitimate_constant_p_1): Remove restriction
>>      on constants for NEON VSTRUCT modes.