Re: [PATCH] vect: Check that vector factor is a compile-time constant

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Feb 22, 2023 at 5:42 PM Michael Collison <collison@rivosinc.com> wrote:
>
> Richard how would I check for a full masked main vector loop?

It's LOOP_VINFO_FULLY_MASKED_P I think.  For the odd prologue peeling
you see you might want to check why vect_use_loop_mask_for_alignment_p
isn't true (possibly because exactly LOOP_VINFO_FULLY_MASKED_P is not true ...)

> On 2/22/23 03:20, Richard Biener wrote:
> > On Wed, Feb 22, 2023 at 12:03 AM Michael Collison <collison@rivosinc.com> wrote:
> >> While working on autovectorizing for the RISCV port I encountered an
> >> issue where vect_do_peeling assumes that the vectorization factor is a
> >> compile-time constant. The vectorization is not a compile-time constant
> >> on RISCV.
> >>
> >> Tested on RISCV and x86_64-linux-gnu. Okay?
> > I wonder how you arrive at prologue peeling with a non-constant VF?
> > In any case it would probably be better to use constant_lower_bound (vf)
> > here?  Also it looks wrong to apply this limit in case we are using
> > a fully masked main vector loop.  But as said, the specific case of
> > non-constant VF and prologue peeling probably wasn't supposed to happen,
> > instead the prologue usually is applied via an offset to a fully masked loop?
> >
> > Richard?
> >
> > Thanks,
> > Richard.
> >
> >> Michael
> >>
> >> gcc/
> >>
> >>       * tree-vect-loop-manip.cc (vect_do_peeling): Verify
> >>       that vectorization factor is a compile-time constant.
> >>
> >> ---
> >>    gcc/tree-vect-loop-manip.cc | 2 +-
> >>    1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
> >> index 6aa3d2ed0bf..1ad1961c788 100644
> >> --- a/gcc/tree-vect-loop-manip.cc
> >> +++ b/gcc/tree-vect-loop-manip.cc
> >> @@ -2930,7 +2930,7 @@ vect_do_peeling (loop_vec_info loop_vinfo, tree
> >> niters, tree nitersm1,
> >>          niters = vect_build_loop_niters (loop_vinfo, &new_var_p);
> >>          /* It's guaranteed that vector loop bound before vectorization is at
> >>         least VF, so set range information for newly generated var. */
> >> -      if (new_var_p)
> >> +      if (new_var_p && vf.is_constant ())
> >>        {
> >>          value_range vr (type,
> >>                  wi::to_wide (build_int_cst (type, vf)),
> >> --
> >> 2.34.1
> >>