Re: [PATCH][AArch64] Allow const0_rtx operand for atomic compare-exchange patterns

[Kyrill Tkachov <kyrylo.tkachov@foss.arm.com>]

Ping.

Thanks,
Kyrill

On 24/04/17 10:37, Kyrill Tkachov wrote:
> Pinging this back into context so that I don't forget about it...
>
> https://gcc.gnu.org/ml/gcc-patches/2017-02/msg01648.html
>
> Thanks,
> Kyrill
>
> On 28/02/17 12:29, Kyrill Tkachov wrote:
>> Hi all,
>>
>> For the testcase in this patch we currently generate:
>> foo:
>>         mov     w1, 0
>>         ldaxr   w2, [x0]
>>         cmp     w2, 3
>>         bne     .L2
>>         stxr    w3, w1, [x0]
>>         cmp     w3, 0
>> .L2:
>>         cset    w0, eq
>>         ret
>>
>> Note that the STXR could have been storing the WZR register instead of moving zero into w1.
>> This is due to overly strict predicates and constraints in the store exclusive pattern and the
>> atomic compare exchange expanders and splitters.
>> This simple patch fixes that in the patterns concerned and with it we can generate:
>> foo:
>>         ldaxr   w1, [x0]
>>         cmp     w1, 3
>>         bne     .L2
>>         stxr    w2, wzr, [x0]
>>         cmp     w2, 0
>> .L2:
>>         cset    w0, eq
>>         ret
>>
>>
>> Bootstrapped and tested on aarch64-none-linux-gnu.
>> Ok for GCC 8?
>>
>> Thanks,
>> Kyrill
>>
>> 2017-02-28  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>>
>>     * config/aarch64/atomics.md (atomic_compare_and_swap<mode> expander):
>>     Use aarch64_reg_or_zero predicate for operand 4.
>>     (aarch64_compare_and_swap<mode> define_insn_and_split):
>>     Use aarch64_reg_or_zero predicate for operand 3.  Add 'Z' constraint.
>>     (aarch64_store_exclusive<mode>): Likewise for operand 2.
>>
>> 2017-02-28  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>>
>>     * gcc.target/aarch64/atomic_cmp_exchange_zero_reg_1.c: New test.
>