https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80198
--- Comment #21 from rguenther at suse dot de <rguenther at suse dot de> --- On Wed, 27 Jan 2021, rsandifo at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80198 > > --- Comment #20 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot > gnu.org> --- > (In reply to Richard Biener from comment #19) > > So I think when you consider > > > > void __attribute__((noinline)) fun(int * a, int * b, int c) > > { > > int i; > > for (i=0; i < 256; i++) { > > a[i] = b[i] | c; > > } > > } > > > > we can improve the versioning condition to allow a dependence distance > > of zero. > This one was fixed by r10-4803. E.g. for aarch64 we now have: > > add x3, x1, 4 > sub x3, x0, x3 > cmp x3, 8 > bls .L5 Ah, yeah - I failed to decipher the generated check: _7 = b_12 + 4; _22 = a_10 - _7; _23 = (sizetype) _22; if (_23 > 8) the difference is -4U and thus > 8 when a == b. > > Likewise with > > > > void __attribute__((noipa)) generic(int * a, int * b, int c) > > { > > int i; > > a = __builtin_assume_aligned (a, 16); > > b = __builtin_assume_aligned (b, 16); > > for (i=0; i < 256; i++) { > > a[i] = b[i] | c; > > } > > } > > > > we fail to realize no versioning check is required - the distance is > > either zero or a multiple of 16. > > > > Richard - ISTR you added some alignment considerations to the alias > > versioning code, but it doesn't seem to help? > I don't remember adding anything for that, but yeah, I agree it looks > like we need it.
