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

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;
     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