Re: redundant bitmap_bit_p followed by bitmap_clear_bit [was: Re: [COMMITTED] Kill second order relations in the path solver.]

[Aldy Hernandez <aldyh@redhat.com>]

I'm not convinced this makes the code clearer to read, especially if
it's not on a critical path.  But if you feel strongly, please submit
a patch ;-).

Aldy

On Mon, Nov 1, 2021 at 3:10 PM Bernhard Reutner-Fischer
<rep.dot.nop@gmail.com> wrote:
>
> On Thu, 28 Oct 2021 01:55:30 +0200
> Bernhard Reutner-Fischer <rep.dot.nop@gmail.com> wrote:
>
> > On Wed, 27 Oct 2021 20:13:21 +0200
> > Aldy Hernandez via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
>
> > > @@ -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.
>
> > > +  relation_chain **prev = &(m_relations.m_head);
> >
> > s/[()]//
> > thanks,
>
> There seems to be two other spots where a redundant bitmap_bit_p checks
> if we want to bitmap_clear_bit. In dse and ira.
> Like:
> $ cat ~/coccinelle/gcc_bitmap_bit_p-0.cocci ; echo EOF
> // replace redundant bitmap_bit_p() bitmap_clear_bit with the latter
> @ rule1 @
> identifier fn;
> expression bitmap, bit;
> @@
>
> fn(...) {
> <...
> (
> -if (bitmap_bit_p (bitmap, bit))
> +if (bitmap_clear_bit (bitmap, bit))
> {
>   ...
> -  bitmap_clear_bit (bitmap, bit);
>   ...
> }
> |
> -if (bitmap_bit_p (bitmap, bit))
> +if (bitmap_clear_bit (bitmap, bit))
> {
>   ...
> }
> ...
> -bitmap_clear_bit (bitmap, bit);
> )
> ...>
> }
> EOF
> $ find gcc/ -type f -a \( -name "*.c" -o -name "*.cc" \) -a \( ! -path "gcc/testsuite/*" -a ! -path "gcc/contrib/*" \) -exec spatch -sp_file ~/coccinelle/gcc_bitmap_bit_p-0.cocci --show-diff {} \;
> diff =
> --- gcc/dse.c
> +++ /tmp/cocci-output-1104419-443759-dse.c
> @@ -3238,9 +3238,8 @@ mark_reachable_blocks (sbitmap unreachab
>    edge e;
>    edge_iterator ei;
>
> -  if (bitmap_bit_p (unreachable_blocks, bb->index))
> +  if (bitmap_clear_bit(unreachable_blocks, bb->index))
>      {
> -      bitmap_clear_bit (unreachable_blocks, bb->index);
>        FOR_EACH_EDGE (e, ei, bb->preds)
>         {
>           mark_reachable_blocks (unreachable_blocks, e->src);
> diff =
> --- gcc/ira.c
> +++ /tmp/cocci-output-1104678-d8679a-ira.c
> @@ -2944,17 +2944,15 @@ mark_elimination (int from, int to)
>    FOR_EACH_BB_FN (bb, cfun)
>      {
>        r = DF_LR_IN (bb);
> -      if (bitmap_bit_p (r, from))
> +      if (bitmap_clear_bit(r, from))
>         {
> -         bitmap_clear_bit (r, from);
>           bitmap_set_bit (r, to);
>         }
>        if (! df_live)
>          continue;
>        r = DF_LIVE_IN (bb);
> -      if (bitmap_bit_p (r, from))
> +      if (bitmap_clear_bit(r, from))
>         {
> -         bitmap_clear_bit (r, from);
>           bitmap_set_bit (r, to);
>         }
>      }
> # in ira.c one would have to fixup the curly braces manually
> PS: coccinelle seems to ruin the spaces before braces in the '+' even
> though i have written them correctly according to GNU style..
>