On December 12, 2019 10:53:26 AM GMT+01:00, Jakub Jelinek <ja...@redhat.com> wrote: >On Thu, Dec 12, 2019 at 09:22:47AM +0000, Richard Sandiford wrote: >> > So there's no whole vector equality RTX but we have to pun to >integer >> > modes for that? The eq:SImode would suggest that. Guess we should >have >> > used a BImode vector representation... > >Probably something like >V2BImode/V4BImode/V8BImode/V16BImode/V32BImode/V64BImode, yes, but I'm >afraid changing it would be extremely hard, all the builtins that take >the >masks have int/long long arguments and we already generate terrible >code >for the mask registers with various PRs, using a different mode would >make >it even worse (but sure, more clear). >> > >> > Can you check whether we have any target with whole vector compare >patterns that would break here? > >All I can see is both x86 and rs6000 using eq:CC with vector operands >(the former in cbranchv*, the latter in various patterns that set both >vector mode comparison result and CCmode comparison result, and >aarch64 having cbranch even for vector modes, but only in define_expand >and >expanding that to ptest which uses UNSPECs. > >> I wonder how easy it would be to make the mask registers use >> MODE_VECTOR_BOOL instead of scalar integers... :-) > >I'm afraid hard. > >> For now I think the safest thing would be to punt, rather than assume >> one thing or the other. simplify_const_relational_operation doesn't >> handle many vector cases anyway, and most interesting optimisations >> like this should happen on gimple, where we know whether the >condition >> result is a vector or a scalar. > >If it starts being ambiguous somewhere, could we use some target macro >or >target hook to decide?
Ambiguous IL is bad :/ IL semantics dependent on a target hook, too. Just look at SHIFT_COUNT_TRUNCATED... Richard. We already use various target macros in this >code, >e.g. FLOAT_STORE_FLAG_VALUE, VECTOR_STORE_FLAG_VALUE, and if they >aren't >defined, we punt. >If we used some macro for this case too, we could punt by default if we >see >this case and only if the backend said how to handle vector cmp_mode >with >scalar int result we could fold it? > > Jakub
