Re: [PATCH] RISC-V: Fix large memory usage of VSETVL PASS [PR113495]

[Robin Dapp <rdapp.gcc@gmail.com>]

> SPEC 2017 wrf benchmark expose unreasonble memory usage of VSETVL PASS
> that is, VSETVL PASS consume over 33 GB memory which make use impossible
> to compile SPEC 2017 wrf in a laptop.
> 
> The root cause is wasting-memory variables:

LGTM.	The new code matches compute_lcm_local_properties more
closely which makes sense to me.

One separate thing, nothing to do with this patch - I find
bitmap_union_of_preds_with_entry not wrong but weirdly written.
Probably because it was copied from somewhere and slightly
adjusted?  If you touch more code anyway, would you mind fixing it?

  for (ix = 0; ix < EDGE_COUNT (b->preds); ix++)
    {
      e = EDGE_PRED (b, ix);
      bitmap_copy (dst, src[e->src->index]);
      break;
    }
  if (ix == EDGE_COUNT (b->preds))
    bitmap_clear (dst);

The whole idea seems to _not_ skip the entry block.  So something
like if (EDGE_COUNT () == 0) {...} else { bitmap_copy (...)) should
be sufficient?  If the input is assumed to be empty we could even
skip the copy.

> -/* { dg-options "--param=riscv-autovec-preference=scalable -march=rv32gcv -mabi=ilp32 -fno-schedule-insns -fno-schedule-insns2 -fno-tree-vectorize" } */
> +/* { dg-options "--param=riscv-autovec-preference=scalable -march=rv32gcv -mabi=ilp32 -fno-tree-vectorize" } */

Why that change?  Was no-schedule necessary before and is not anymore?
Is it a result from the changes?  I'd hope not.

Regards
 Robin