[COMMITTED] Kill second order relations in the path solver.

[Bernhard Reutner-Fischer]

On Wed, 27 Oct 2021 20:13:21 +0200
Aldy Hernandez via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:

[would have to think about this some more but it's late here. Nits:]

> diff --git a/gcc/value-relation.cc b/gcc/value-relation.cc
> index 2acf375ca9a..0ad4f7a9495 100644
> --- a/gcc/value-relation.cc
> +++ b/gcc/value-relation.cc
> @@ -1297,8 +1297,9 @@ path_oracle::killing_def (tree ssa)
>        fprintf (dump_file, "\n");
>      }
>  
> +  unsigned v = SSA_NAME_VERSION (ssa);
>    bitmap b = BITMAP_ALLOC (&m_bitmaps);
> -  bitmap_set_bit (b, SSA_NAME_VERSION (ssa));
> +  bitmap_set_bit (b, v);
>    equiv_chain *ptr = (equiv_chain *) obstack_alloc (&m_chain_obstack,
>  						    sizeof (equiv_chain));
>    ptr->m_names = b;
> @@ -1306,6 +1307,24 @@ path_oracle::killing_def (tree ssa)
>    ptr->m_next = m_equiv.m_next;
>    m_equiv.m_next = ptr;
>    bitmap_ior_into (m_equiv.m_names, b);
> +
> +  // Walk the relation list an remove SSA from any relations.

s/an /and /

> +  if (!bitmap_bit_p (m_relations.m_names, v))
> +    return;
> +
> +  bitmap_clear_bit (m_relations.m_names, v);

IIRC bitmap_clear_bit returns true if the bit was set, false otherwise,
so should be used as if(!bitmap_clear_bit) above.
I would not be surprised if this generates better code as we probably
do not grok to optimize the !bit_p else clear_bit combo. Shame (?).

> +  relation_chain **prev = &(m_relations.m_head);

s/[()]//
thanks,

> +  relation_chain *next = NULL;
> +  for (relation_chain *ptr = m_relations.m_head; ptr; ptr = next)
> +    {
> +      gcc_checking_assert (*prev == ptr);
> +      next = ptr->m_next;
> +      if (SSA_NAME_VERSION (ptr->op1 ()) == v
> +	  || SSA_NAME_VERSION (ptr->op2 ()) == v)
> +	*prev = ptr->m_next;
> +      else
> +	prev = &(ptr->m_next);
> +    }
>  }
>  
>  // Register relation K between SSA1 and SSA2, resolving unknowns by