Re: [PATCH] if-to-switch: properly allow side effects only for first condition

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

On Thu, Jun 30, 2022 at 4:29 PM Martin Liška <mliska@suse.cz> wrote:
>
> Properly allow side effects only for a first BB in a condition chain.
>
> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
>
> Ready to be installed?

OK

> Thanks,
> Martin
>
>         PR tree-optimization/106126
>
> gcc/ChangeLog:
>
>         * gimple-if-to-switch.cc (struct condition_info): Save
>         has_side_effect.
>         (find_conditions): Parse all BBs.
>         (pass_if_to_switch::execute): Allow only side effects for first
>         BB.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.dg/tree-ssa/pr106126.c: New test.
> ---
>  gcc/gimple-if-to-switch.cc               | 20 +++++++++++---------
>  gcc/testsuite/gcc.dg/tree-ssa/pr106126.c | 12 ++++++++++++
>  2 files changed, 23 insertions(+), 9 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr106126.c
>
> diff --git a/gcc/gimple-if-to-switch.cc b/gcc/gimple-if-to-switch.cc
> index 70daae2003c..4441206c481 100644
> --- a/gcc/gimple-if-to-switch.cc
> +++ b/gcc/gimple-if-to-switch.cc
> @@ -61,9 +61,11 @@ struct condition_info
>  {
>    typedef auto_vec<std::pair<gphi *, tree>> mapping_vec;
>
> -  condition_info (gcond *cond): m_cond (cond), m_bb (gimple_bb (cond)),
> -    m_forwarder_bb (NULL), m_ranges (), m_true_edge (NULL), m_false_edge (NULL),
> -    m_true_edge_phi_mapping (), m_false_edge_phi_mapping ()
> +  condition_info (gcond *cond, bool has_side_effect): m_cond (cond),
> +    m_bb (gimple_bb (cond)), m_forwarder_bb (NULL), m_ranges (),
> +    m_true_edge (NULL), m_false_edge (NULL),
> +    m_true_edge_phi_mapping (), m_false_edge_phi_mapping (),
> +    m_has_side_effect (has_side_effect)
>    {
>      m_ranges.create (0);
>    }
> @@ -80,6 +82,7 @@ struct condition_info
>    edge m_false_edge;
>    mapping_vec m_true_edge_phi_mapping;
>    mapping_vec m_false_edge_phi_mapping;
> +  bool m_has_side_effect;
>  };
>
>  /* Recond PHI mapping for an original edge E and save these into vector VEC.  */
> @@ -389,16 +392,11 @@ find_conditions (basic_block bb,
>    if (cond == NULL)
>      return;
>
> -  /* An empty conditions_in_bbs indicates we are processing the first
> -     basic-block then no need check side effect.  */
> -  if (!conditions_in_bbs->is_empty () && !no_side_effect_bb (bb))
> -    return;
> -
>    tree lhs = gimple_cond_lhs (cond);
>    tree rhs = gimple_cond_rhs (cond);
>    tree_code code = gimple_cond_code (cond);
>
> -  condition_info *info = new condition_info (cond);
> +  condition_info *info = new condition_info (cond, !no_side_effect_bb (bb));
>
>    gassign *def;
>    if (code == NE_EXPR
> @@ -536,6 +534,10 @@ pass_if_to_switch::execute (function *fun)
>               if ((*info2)->m_false_edge != e)
>                 break;
>
> +             /* Only the first BB in a chain can have a side effect.  */
> +             if (info->m_has_side_effect)
> +               break;
> +
>               chain->m_entries.safe_push (*info2);
>               bitmap_set_bit (seen_bbs, e->src->index);
>               info = *info2;
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr106126.c b/gcc/testsuite/gcc.dg/tree-ssa/pr106126.c
> new file mode 100644
> index 00000000000..2f0fd44164b
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr106126.c
> @@ -0,0 +1,12 @@
> +/* PR tree-optimization/106126 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +char *var_1;
> +void pool_conda_matchspec() {
> +  for (; var_1 && *var_1 &&
> +         *var_1 != '<' && *var_1 != '>' &&
> +         *var_1 != '!' && *var_1 != '~';)
> +    if (*var_1 >= 'A' && *var_1 <= 'Z')
> +      *var_1 += 'A';
> +}
> --
> 2.36.1
>