On Mon, Aug 3, 2015 at 7:20 PM, Kyrill Tkachov <kyrylo.tkac...@arm.com> wrote:
>>>>> Looking at the x86 movcc expansion code (ix86_expand_int_movcc) I >>>>> don't think this is a good idea. In the expander, there is already >>>>> quite some target-dependent code that goes great length to utilize sbb >>>>> insn as much as possible, before cmove is used. >>>>> >>>>> IMO, as far as x86 is concerned, the best solution would be to revert >>>>> the change. ix86_expand_int_movcc already does some tricks from your >>>>> patch in a target-efficient way. Generic change that was introduced by >>>>> your patch now interferes with this expansion. >>>> >>>> Well, technically the transformation was already there, it was just >>>> never >>>> reached for an x86 compilation because noce_try_cmove was tried in front >>>> of >>>> it >>>> and used a target-specific expansion. >>>> In any case, how's this proposal? >>>> The transformation noce_try_store_flag_constants >>>> /* if (test) x = a; else x = b; >>>> => x = (-(test != 0) & (b - a)) + a; */ >>>> >>>> Is a catch-all-immediates transformation in >>>> noce_try_store_flag_constants. >>>> What if we moved it to noce_try_cmove and performed it only if the >>>> target-specific >>>> conditional move expansion there failed? >>>> >>>> That way we can try the x86_64-specific sequence first and still give >>>> the >>>> opportunity >>>> to noce_try_store_flag_constants to perform the transformations that can >>>> benefit targets >>>> that don't have highly specific conditional move expanders. >>> >>> Yes, let's try this approach. As was found out, some targets (e.g. >>> x86) hide lots of different target-dependent expansion strategies into >>> movcc expander. Perhaps this fact should be documented in the comment >>> in the generic code? >> >> Ok, I'll work on that approach and add a comment. > > > I'm testing a patch that fix the testcases on x86_64 and does not > harm codegen on aarch64. Feel free to file a PR and assign it to me. PR67103 [1] [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67103 Thanks, Uros.
