> Am 20.08.2019 um 13:54 schrieb Richard Sandiford <richard.sandif...@arm.com>:
>
> Ilya Leoshkevich <i...@linux.ibm.com> writes:
>>> Am 20.08.2019 um 12:13 schrieb Richard Sandiford
>>> <richard.sandif...@arm.com>:
>>>
>>> Ilya Leoshkevich <i...@linux.ibm.com> writes:
>>>> z13 supports only non-signaling vector comparisons. This means we
>>>> cannot vectorize LT, LE, GT, GE and LTGT when compiling for z13.
>>>> However, we cannot express this restriction today: the code only checks
>>>> whether vcond$a$b optab, which does not contain information about the
>>>> operation.
>>>>
>>>> Introduce a hook that tells whether target supports certain vector
>>>> comparison operations with certain modes.
>>>>
>>>> gcc/ChangeLog:
>>>>
>>>> 2019-08-09 Ilya Leoshkevich <i...@linux.ibm.com>
>>>>
>>>> * doc/tm.texi (TARGET_VCOND_SUPPORTED_P): Document.
>>>> * doc/tm.texi.in (TARGET_VCOND_SUPPORTED_P): Document.
>>>> * optabs-tree.c (expand_vec_cond_expr_p): Use vcond_supported_p
>>>> in addition to get_vcond_icode.
>>>> * target.def (vcond_supported_p): New hook.
>>>> * targhooks.c (default_vcond_supported_p): Likewise.
>>>> * targhooks.h (default_vcond_supported_p): Likewise.
>>>
>>> IMO it'd be cleaner to have a new optabs-query.[hc] helper that uses
>>> the predicate for operand 3 to test whether a particular comparison
>>> is supported. I guess this would require a cached rtx to avoid
>>> generating too much garbage rtl though (via GTY((cache))).
>>
>> How can I implement such a predicate? Would calling maybe_gen_insn with
>> a fake rtx be reasonable? In this case, what would be the best way to
>> generate fake input operands? The existing code that calls
>> maybe_gen_insn gets the corresponding rtxes from upper layers.
>
> I was thinking of something like optabs.c:can_compare_p, but with
> some caching to reduce the overhead, and comparing registers rather
> than constants. E.g.:
>
> static rtx cached_binop GTY ((cached));
>
> rtx
> get_cached_binop (machine_mode mode, rtx_code code, machine_mode op_mode)
> {
> ...create or modify cached_binop, with register operands...;
> return cached_binop;
> }
Thanks, I got it working! Still need to run the regtest, but the result
looks promising.
I have a question about caching. If I define just `static rtx
cached_binop`, like you suggest, I would expect to see constant cache
misses. Shouldn't it be something like `hash_map<tuple<enum rtx_code,
machine_mode, machine_mode>, rtx>`?
