Re: [PATCH] range-op: add VREL_LT relation effect for div [PR126748]

On 8/14/2026 8:19 PM, Andrea Pinski wrote:
> On Wed, Aug 12, 2026 at 2:24 AM Daniel Barboza
> <[email protected]> wrote:
>>
>> Given A div B, if we know for certain that A and B are positive
>> and A < B, we can infer that A div B is zero.
>>
>> Bootstrapped and regression tested in x86_64, aarch64 and riscv64.
> 
> Ok.
> 
> You want to handle PR 126745 also? It is EQ for both division and mod.
> It was this week's easy issue but nobody has picked it up yet. Plus
> that is a step forward in the ability to remove dom since dom is the
> only pass that handles it so far :).

Sure, I'll take a look.

Daniel

> 
> 
>>
>>          PR tree-optimization/126748
>>
>> gcc/ChangeLog:
>>
>>          * range-op.cc (class operator_div): declarations.
>>          (operator_div::op1_op2_relation_effect): add op1/op2 relation
>>          range equal zero for op1/op2 if op1 < op2 and both op1 and op2
>>          are positives.
>>
>> gcc/testsuite/ChangeLog:
>>
>>          * gcc.dg/tree-ssa/pr126748.c: New test.
>> ---
>>   gcc/range-op.cc                          | 35 ++++++++++++++++++++++++
>>   gcc/testsuite/gcc.dg/tree-ssa/pr126748.c | 26 ++++++++++++++++++
>>   2 files changed, 61 insertions(+)
>>   create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr126748.c
>>
>> diff --git a/gcc/range-op.cc b/gcc/range-op.cc
>> index b878a6052c6..85755ef679e 100644
>> --- a/gcc/range-op.cc
>> +++ b/gcc/range-op.cc
>> @@ -2497,6 +2497,7 @@ class operator_div : public cross_product_operator
>>   {
>>     using range_operator::update_bitmask;
>>     using range_operator::op2_range;
>> +  using range_operator::op1_op2_relation_effect;
>>   public:
>>     operator_div (tree_code div_kind) { m_code = div_kind; }
>>     bool op2_range (irange &r, tree type, const irange &lhs, const irange &,
>> @@ -2509,6 +2510,11 @@ public:
>>     virtual bool wi_op_overflows (wide_int &res, tree type,
>>                                  const wide_int &, const wide_int &)
>>       const final override;
>> +  bool op1_op2_relation_effect (irange &lhs_range,
>> +                               tree type,
>> +                               const irange &op1_range,
>> +                               const irange &op2_range,
>> +                               relation_kind rel) const final override;
>>     void update_bitmask (irange &r, const irange &lh, const irange &rh)
>>       const final override
>>       { update_known_bitmask (r, m_code, lh, rh); }
>> @@ -2622,6 +2628,35 @@ operator_div::wi_fold (irange &r, tree type,
>>     gcc_checking_assert (!r.undefined_p ());
>>   }
>>
>> +bool
>> +operator_div::op1_op2_relation_effect (irange &lhs_range,
>> +                                      tree type,
>> +                                      const irange &op1_range,
>> +                                      const irange &op2_range,
>> +                                      relation_kind rel) const
>> +{
>> +  if (rel == VREL_VARYING)
>> +    return false;
>> +
>> +  int_range<2> rel_range;
>> +
>> +  switch (rel)
>> +    {
>> +    /* op1/op2 = 0 if op1 < op2 and both op1 and op2
>> +       are known positives.  */
>> +    case VREL_LT:
>> +      if (TYPE_UNSIGNED (type)
>> +         || (wi::ge_p (op1_range.lower_bound (), 0, SIGNED)
>> +             && wi::ge_p (op2_range.lower_bound (), 0, SIGNED)))
>> +       rel_range.set_zero (type);
>> +      break;
>> +    default:
>> +      return false;
>> +    }
>> +
>> +  lhs_range.intersect (rel_range);
>> +  return true;
>> +}
>>
>>   class operator_exact_divide : public operator_div
>>   {
>> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr126748.c b/gcc/testsuite/gcc.dg/tree-ssa/pr126748.c
>> new file mode 100644
>> index 00000000000..063187a904c
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr126748.c
>> @@ -0,0 +1,26 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2 -fdump-tree-evrp" } */
>> +
>> +unsigned f(unsigned a, unsigned b)
>> +{
>> +    if (b >= a) __builtin_unreachable();
>> +    return b / a;
>> +}
>> +
>> +int fs(int a, int b)
>> +{
>> +  a = __builtin_abs(a);
>> +  b = __builtin_abs(b);
>> +  if (b >= a) __builtin_unreachable();
>> +  return b / a;
>> +}
>> +
>> +/* This can't be simplified.  */
>> +int fs2(int a, int b)
>> +{
>> +  if (b >= a) __builtin_unreachable();
>> +  return b / a;
>> +}
>> +
>> +/* { dg-final { scan-tree-dump-times "return 0;" 2 "evrp" } } */
>> +/* { dg-final { scan-tree-dump-times " / " 1 "evrp" } } */
>> --
>> 2.43.0
>>