Re: [PATCH] range-op.cc: add VREL_EQ relation effect for div and mod [PR126745]

On Tue, Aug 18, 2026 at 2:28 PM Daniel Barboza
<[email protected]> wrote:
>
> For res = a / b and a == b, set 'res' to one.
>
> For res = a % b and a == b, set 'res' to zero.
>
> Both are done by dom2/dom3 already.  With this change we're now
> doing it earlier (with -O2) in evrp.
>
> Bootstrapped and regtested in x86_64.
>
>         PR tree-optimization/126745
>
> gcc/ChangeLog:
>
>         * range-op.cc (operator_div::op1_op2_relation_effect): add
>         VREL_EQ range equal one for op1/op2 and op1%op2 if op1 == op2.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.dg/tree-ssa/pr126745.c: New test.
> ---
>  gcc/range-op.cc                          | 36 ++++++++++++++++++++++++
>  gcc/testsuite/gcc.dg/tree-ssa/pr126745.c | 16 +++++++++++
>  2 files changed, 52 insertions(+)
>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr126745.c
>
> diff --git a/gcc/range-op.cc b/gcc/range-op.cc
> index bb055623872..0311cef7d47 100644
> --- a/gcc/range-op.cc
> +++ b/gcc/range-op.cc
> @@ -2641,6 +2641,7 @@ operator_div::op1_op2_relation_effect (irange &lhs_range,
>      return false;
>
>    int_range<2> rel_range;
> +  wide_int one;
>
>    switch (rel)
>      {
> @@ -2652,6 +2653,10 @@ operator_div::op1_op2_relation_effect (irange &lhs_range,
>               && wi::ge_p (op2_range.lower_bound (), 0, SIGNED)))
>         rel_range.set_zero (type);
>        break;
> +    case VREL_EQ:
> +      one = wi::one (TYPE_PRECISION (type));
> +      rel_range.set (type, one, one);
> +      break;

Move the declaration of one into here. That is do this:

    case VREL_EQ:
      {
        wide_int one = wi::one (TYPE_PRECISION (type));
        rel_range.set (type, one, one);
        break;
      }

Otherwise ok.


>      default:
>        return false;
>      }
> @@ -4380,6 +4385,7 @@ class operator_trunc_mod : public range_operator
>    using range_operator::op1_range;
>    using range_operator::op2_range;
>    using range_operator::update_bitmask;
> +  using range_operator::op1_op2_relation_effect;
>  public:
>    virtual void wi_fold (irange &r, tree type,
>                         const wide_int &lh_lb,
> @@ -4396,6 +4402,11 @@ public:
>                           relation_trio) const;
>    void update_bitmask (irange &r, const irange &lh, const irange &rh) const
>      { update_known_bitmask (r, TRUNC_MOD_EXPR, lh, rh); }
> +  bool op1_op2_relation_effect (irange &lhs_range,
> +                               tree type,
> +                               const irange &op1_range,
> +                               const irange &op2_range,
> +                               relation_kind rel) const final override;
>  } op_trunc_mod;
>
>  void
> @@ -4536,6 +4547,31 @@ operator_trunc_mod::op2_range (irange &r, tree type,
>    return false;
>  }
>
> +bool
> +operator_trunc_mod::op1_op2_relation_effect (irange &lhs_range,
> +                                            tree type,
> +                                            const irange &,
> +                                            const irange &,
> +                                            relation_kind rel) const
> +{
> +  if (rel == VREL_VARYING)
> +    return false;
> +
> +  int_range<2> rel_range;
> +
> +  switch (rel)
> +    {
> +    case VREL_EQ:
> +      rel_range.set_zero (type);
> +      break;
> +    default:
> +      return false;
> +    }
> +
> +  lhs_range.intersect (rel_range);
> +  return true;
> +}
> +
>
>  class operator_logical_not : public range_operator
>  {
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr126745.c b/gcc/testsuite/gcc.dg/tree-ssa/pr126745.c
> new file mode 100644
> index 00000000000..77405653ba2
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr126745.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-evrp" } */
> +
> +int f (int a, int b)
> +{
> +    if (a != b) __builtin_unreachable ();
> +    return a / b;
> +}
> +/* { dg-final { scan-tree-dump-times "return 1;" 1 "evrp" } } */
> +
> +int f2 (int a, int b)
> +{
> +    if (a != b) __builtin_unreachable ();
> +    return a % b;
> +}
> +/* { dg-final { scan-tree-dump-times "return 0;" 1 "evrp" } } */
> --
> 2.43.0
>