https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119016
--- Comment #10 from Tamar Christina <tnfchris at gcc dot gnu.org> --- (In reply to rguent...@suse.de from comment #9) > On Wed, 26 Feb 2025, tnfchris at gcc dot gnu.org wrote: > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119016 > > > > --- Comment #8 from Tamar Christina <tnfchris at gcc dot gnu.org> --- > > (In reply to rguent...@suse.de from comment #7) > > > On Wed, 26 Feb 2025, tnfchris at gcc dot gnu.org wrote: > > > > > > > Because of the scalar code doing DI mode loads, and the misalignment > > > > being > > > > HImode, I don't think the alignment can be reached by peeling. > > > > > > > > i.e. I don't think you can reach target alignment, and unless I'm > > > > missing > > > > something, get_misalign_in_elems does not have a failure mode for when > > > > target > > > > alignment can't be reached? > > > > > > get_misalign_in_elems of course returns garbage when the access isn't > > > element aligned - we're not supposed to compute it in this case. > > > > Indeed, so it looks like we need an additional check in the pre-header that > > checks if the address's misalignment can be corrected to target alignment. > > No, we should not attempt to peel such DR instead - IIRC > we check alignment_reachable for this, so I'm not sure why it doens't > work. > But you can't. the misalignment is dynamic, not static. You statically can't know. i.e. char p[] = { 0x2f, 0x2a, 0xa, 0x20, 0x20, 0x20, 0x62, 0x75, 0x67, 0x33, 0x33, 0x37, 0x39, 0x37, 0x32, 0x33, 0x2e, 0x63, 0xa, 0x2a, 0x2f, 0xa, 0xa, 0x23, 0x69, 0x6e, 0x63, }; if (foo (&p[2], sizeof(p)-2)) return 0; return 1; foo doesn't know that you misaligned p. when vectorizing p all you know if an unknown alignment.
