Andrew Pinski <pins...@gmail.com> writes:
> On Tue, Jul 28, 2015 at 1:36 PM, Richard Sandiford
> <richard.sandif...@arm.com> wrote:
>> Bootstrapped & regression-tested on x86_64-linux-gnu and aarch64-linux-gnu.
>> Also tested via config-list.mk. Committed as preapproved.
>>
>> Thanks,
>> Richard
>>
>>
>> gcc/
>> * target-insns.def (atomic_test_and_set): New targetm instruction
>> pattern.
>> * optabs.c (maybe_emit_atomic_test_and_set): Use it instead of
>> HAVE_*/gen_* interface.
>>
>> Index: gcc/target-insns.def
>> ===================================================================
>> --- gcc/target-insns.def 2015-07-28 21:00:09.815019853 +0100
>> +++ gcc/target-insns.def 2015-07-28 21:00:09.811019905 +0100
>> @@ -31,6 +31,7 @@
>>
>> Instructions should be documented in md.texi rather than here. */
>> DEF_TARGET_INSN (allocate_stack, (rtx x0, rtx x1))
>> +DEF_TARGET_INSN (atomic_test_and_set, (rtx x0, rtx x1, rtx x2))
>> DEF_TARGET_INSN (builtin_longjmp, (rtx x0))
>> DEF_TARGET_INSN (builtin_setjmp_receiver, (rtx x0))
>> DEF_TARGET_INSN (builtin_setjmp_setup, (rtx x0))
>> Index: gcc/optabs.c
>> ===================================================================
>> --- gcc/optabs.c 2015-07-28 21:00:09.815019853 +0100
>> +++ gcc/optabs.c 2015-07-28 21:00:09.811019905 +0100
>> @@ -7258,35 +7258,30 @@ maybe_emit_compare_and_swap_exchange_loo
>> using the atomic_test_and_set instruction pattern. A boolean value
>> is returned from the operation, using TARGET if possible. */
>>
>> -#ifndef HAVE_atomic_test_and_set
>> -#define HAVE_atomic_test_and_set 0
>> -#define CODE_FOR_atomic_test_and_set CODE_FOR_nothing
>> -#endif
>> -
>> static rtx
>> maybe_emit_atomic_test_and_set (rtx target, rtx mem, enum memmodel model)
>> {
>> machine_mode pat_bool_mode;
>> struct expand_operand ops[3];
>>
>> - if (!HAVE_atomic_test_and_set)
>> + if (!targetm.have_atomic_test_and_set ())
>> return NULL_RTX;
>
> I know this was not there before but this if should be marked as
> unlikely as most targets where someone is using __atomic_*/__sync_*
> will have those patterns.
I think that'd be premature optimisation. The path being guarded here
generates new rtl instructions, which is a much more expensive operation
than a mispredicated branch.
Thanks,
Richard
