Re: [PATCH] Adjust range type of calls into fold_range for IPA passes [PR114985]

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

On Fri, May 10, 2024 at 11:24 AM Aldy Hernandez <aldyh@redhat.com> wrote:
>
> There are various calls into fold_range() that have the wrong type
> associated with the range temporary used to hold the result.  This
> used to work, because we could store either integers or pointers in a
> Value_Range, but is no longer the case with prange's.  Now you must
> explicitly state which type of range the temporary will hold before
> storing into it.  You can change this at a later time with set_type(),
> but you must always have a type before using the temporary, and it
> must match what fold_range() returns.
>
> This patch adjusts the IPA code to restore the previous functionality,
> so I can re-enable the prange code, but I do question whether the
> previous code was correct.  I have added appropriate comments to help
> the maintainers, but someone with more knowledge should revamp this
> going forward.
>
> The basic problem is that pointer comparisons return a boolean, but
> the IPA code is initializing the resulting range as a pointer.  This
> wasn't a problem, because fold_range() would previously happily force
> the range into an integer one, and everything would work.  But now we
> must initialize the range to an integer before calling into
> fold_range.  The thing is, that the failing case sets the result back
> into a pointer, which is just weird but existing behavior.  I have
> documented this in the code.
>
>           if (!handler
>               || !op_res.supports_type_p (vr_type)
>               || !handler.fold_range (op_res, vr_type, srcvr, op_vr))
>             /* For comparison operators, the type here may be
>                different than the range type used in fold_range above.
>                For example, vr_type may be a pointer, whereas the type
>                returned by fold_range will always be a boolean.
>
>                This shouldn't cause any problems, as the set_varying
>                below will happily change the type of the range in
>                op_res, and then the cast operation in
>                ipa_vr_operation_and_type_effects will ultimately leave
>                things in the desired type, but it is confusing.
>
>                Perhaps the original intent was to use the type of
>                op_res here?  */
>             op_res.set_varying (vr_type);
>
> BTW, this is not to say that the original gimple IR was wrong, but that
> IPA is setting the range type of the result of fold_range() to the type of
> the operands, which does not necessarily match in the case of a
> comparison.
>
> I am just restoring previous behavior here, but I do question whether it
> was right to begin with.
>
> Testing currently in progress on x86-64 and ppc64le with prange enabled.
>
> OK pending tests?

I think this "intermediate" patch is unnecessary and instead the code should
be fixed correctly, avoiding missed-optimization regressions.

Richard.

> gcc/ChangeLog:
>
>         PR tree-optimization/114985
>         * ipa-cp.cc (ipa_value_range_from_jfunc): Adjust type of op_res.
>         (propagate_vr_across_jump_function): Same.
>         * ipa-fnsummary.cc (evaluate_conditions_for_known_args): Adjust
>         type for res.
>         * ipa-prop.h (ipa_type_for_fold_range): New.
> ---
>  gcc/ipa-cp.cc        | 18 ++++++++++++++++--
>  gcc/ipa-fnsummary.cc |  6 +++++-
>  gcc/ipa-prop.h       | 13 +++++++++++++
>  3 files changed, 34 insertions(+), 3 deletions(-)
>
> diff --git a/gcc/ipa-cp.cc b/gcc/ipa-cp.cc
> index 5781f50c854..3c395632364 100644
> --- a/gcc/ipa-cp.cc
> +++ b/gcc/ipa-cp.cc
> @@ -1730,7 +1730,7 @@ ipa_value_range_from_jfunc (vrange &vr,
>         }
>        else
>         {
> -         Value_Range op_res (vr_type);
> +         Value_Range op_res (ipa_type_for_fold_range (operation, vr_type));
>           Value_Range res (vr_type);
>           tree op = ipa_get_jf_pass_through_operand (jfunc);
>           Value_Range op_vr (TREE_TYPE (op));
> @@ -1741,6 +1741,19 @@ ipa_value_range_from_jfunc (vrange &vr,
>           if (!handler
>               || !op_res.supports_type_p (vr_type)
>               || !handler.fold_range (op_res, vr_type, srcvr, op_vr))
> +           /* For comparison operators, the type here may be
> +              different than the range type used in fold_range above.
> +              For example, vr_type may be a pointer, whereas the type
> +              returned by fold_range will always be a boolean.
> +
> +              This shouldn't cause any problems, as the set_varying
> +              below will happily change the type of the range in
> +              op_res, and then the cast operation in
> +              ipa_vr_operation_and_type_effects will ultimately leave
> +              things in the desired type, but it is confusing.
> +
> +              Perhaps the original intent was to use the type of
> +              op_res here?  */
>             op_res.set_varying (vr_type);
>
>           if (ipa_vr_operation_and_type_effects (res,
> @@ -2540,7 +2553,7 @@ propagate_vr_across_jump_function (cgraph_edge *cs, ipa_jump_func *jfunc,
>         {
>           tree op = ipa_get_jf_pass_through_operand (jfunc);
>           Value_Range op_vr (TREE_TYPE (op));
> -         Value_Range op_res (param_type);
> +         Value_Range op_res (ipa_type_for_fold_range (operation, param_type));
>           range_op_handler handler (operation);
>
>           ipa_range_set_and_normalize (op_vr, op);
> @@ -2549,6 +2562,7 @@ propagate_vr_across_jump_function (cgraph_edge *cs, ipa_jump_func *jfunc,
>               || !ipa_supports_p (operand_type)
>               || !handler.fold_range (op_res, operand_type,
>                                       src_lats->m_value_range.m_vr, op_vr))
> +           /* See note in ipa_value_range_from_jfunc.  */
>             op_res.set_varying (param_type);
>
>           ipa_vr_operation_and_type_effects (vr,
> diff --git a/gcc/ipa-fnsummary.cc b/gcc/ipa-fnsummary.cc
> index 07a853f78e3..4deba2394f5 100644
> --- a/gcc/ipa-fnsummary.cc
> +++ b/gcc/ipa-fnsummary.cc
> @@ -502,7 +502,8 @@ evaluate_conditions_for_known_args (struct cgraph_node *node,
>                   if (vr.varying_p () || vr.undefined_p ())
>                     break;
>
> -                 Value_Range res (op->type);
> +                 Value_Range res (ipa_type_for_fold_range (op->code,
> +                                                           op->type));
>                   if (!op->val[0])
>                     {
>                       Value_Range varying (op->type);
> @@ -511,6 +512,7 @@ evaluate_conditions_for_known_args (struct cgraph_node *node,
>                       if (!handler
>                           || !res.supports_type_p (op->type)
>                           || !handler.fold_range (res, op->type, vr, varying))
> +                       /* See note in ipa_value_from_jfunc.  */
>                         res.set_varying (op->type);
>                     }
>                   else if (!op->val[1])
> @@ -525,9 +527,11 @@ evaluate_conditions_for_known_args (struct cgraph_node *node,
>                           || !handler.fold_range (res, op->type,
>                                                   op->index ? op0 : vr,
>                                                   op->index ? vr : op0))
> +                       /* See note in ipa_value_from_jfunc.  */
>                         res.set_varying (op->type);
>                     }
>                   else
> +                   /* See note in ipa_value_from_jfunc.  */
>                     res.set_varying (op->type);
>                   vr = res;
>                 }
> diff --git a/gcc/ipa-prop.h b/gcc/ipa-prop.h
> index 93d1b87b1f7..8493dd19b92 100644
> --- a/gcc/ipa-prop.h
> +++ b/gcc/ipa-prop.h
> @@ -1277,6 +1277,19 @@ ipa_range_set_and_normalize (vrange &r, tree val)
>      r.set (val, val);
>  }
>
> +/* Return the resulting type for a fold_range() operation for OP and
> +   TYPE.  */
> +
> +inline tree
> +ipa_type_for_fold_range (tree_code op, tree type)
> +{
> +  /* Comparisons return boolean regardless of their input operands.  */
> +  if (TREE_CODE_CLASS (op) == tcc_comparison)
> +    return boolean_type_node;
> +
> +  return type;
> +}
> +
>  bool ipa_return_value_range (Value_Range &range, tree decl);
>  void ipa_record_return_value_range (Value_Range val);
>  bool ipa_jump_functions_equivalent_p (ipa_jump_func *jf1, ipa_jump_func *jf2);
> --
> 2.45.0
>