On Sep 29, 2020, Richard Biener <richard.guent...@gmail.com> wrote: > On Tue, Sep 29, 2020 at 9:23 AM Alexandre Oliva <ol...@adacore.com> wrote:
>> On Sep 28, 2020, Richard Biener <richard.guent...@gmail.com> wrote: > ifcombine should stop using fold*, yeah Wow, that's quite a lot of work for no expected improvement in codegen. I don't expect to be able to justify such an undertaking :-( > I also think it will not end up using the simplifications using loads. Yeah, ifcombine's bb_no_side_effects_p gives up on any gimple_vuse in the inner block. that won't do when the whole point is to merge loads from memory. That seems excessive. Since we rule out any memory-changing side effects, I suppose we could get away with checking for volatile operands there. Then, adding just a little SSA_DEF chasing, I believe I could bring all of the fold_truth_andor_1 logic I've worked on into ifcombine without much difficulty, and then we could do away with at least that part of fold_truth_andor. > Specifically your patch seems to introduce splitting of loads > at alignment boundaries ... when there's another compare involving a load from either side of the crossed alignment boundary. Even on arches that can do unaligned loads, the result is no worse, and if there are multiple fields crossing consecutive alignment boundaries, the codegen and performance difference can be pretty significant. >> I *think* ifcombine could even be extended so as to reuse the >> separate-test logic I put in, by looking for non-immediate dominating >> outer conditions for the inner condition. A further modified version of >> fold_truth_andor_1 could then be used to combine the separate tests. > I think the structure of ifcombine doesn't exactly match what > fold_truth_andor does How so? AFAICT ifcombine_ifandif deals exactly with the (gimplified version of the) structure I described in the patch that started the thread: (a.x1 EQNE b.x1) ANDOR (a.y1 EQNE b.y1) -- Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/ Free Software Activist GNU Toolchain Engineer
