[gcc r13-6787] Terminate GORI calculations if a relation is not relevant.

[Andrew Macleod]

https://gcc.gnu.org/g:0963cb5fde158cce986523a90fa9edc51c881f31

commit r13-6787-g0963cb5fde158cce986523a90fa9edc51c881f31
Author: Andrew MacLeod <amacleod@redhat.com>
Date:   Mon Mar 20 16:11:12 2023 -0400

    Terminate GORI calculations if a relation is not relevant.
    
    We currently allow VARYING lhs GORI calculations to continue if there is
    a relation present in the hope it will eventually better refine a result.
    This adds a check that the relation is relevant to the outgoing range
    calculation first.  If it is not relevant, stop calculating.
    
            PR tree-optimization/109192
            * gimple-range-gori.cc (gori_compute::compute_operand_range):
            Terminate gori calculations if a relation is not relevant.
            * value-relation.h (value_relation::set_relation): Allow
            equality between op1 and op2 if they are the same.

Diff:
---
 gcc/gimple-range-gori.cc | 36 +++++++++++++++++++++++++++++++-----
 gcc/value-relation.h     |  2 +-
 2 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/gcc/gimple-range-gori.cc b/gcc/gimple-range-gori.cc
index beb1c0064b9..2f8d4704ea4 100644
--- a/gcc/gimple-range-gori.cc
+++ b/gcc/gimple-range-gori.cc
@@ -653,12 +653,38 @@ gori_compute::compute_operand_range (vrange &r, gimple *stmt,
   if (!op1_in_chain && !op2_in_chain)
     return false;
 
-  // If the lhs doesn't tell us anything and there are no relations, there
-  // is nothing to be learned.
-  if (lhs.varying_p () && !vrel_ptr)
-    return false;
+  bool res = false;
+  // If the lhs doesn't tell us anything only a relation can possibly enhance
+  // the result.
+  if (lhs.varying_p ())
+    {
+      if (!vrel_ptr)
+	return false;
+      // If there is a relation (ie: x != y) , it can only be relevant if
+      // a) both elements are in the defchain
+      //    c = x > y   // (x and y are in c's defchain)
+      if (op1_in_chain)
+	res = in_chain_p (vrel_ptr->op1 (), op1)
+	      && in_chain_p (vrel_ptr->op2 (), op1);
+      if (!res && op2_in_chain)
+	res = in_chain_p (vrel_ptr->op1 (), op2)
+	      || in_chain_p (vrel_ptr->op2 (), op2);
+      if (!res)
+	{
+	  // or b) one relation element is in the defchain of the other and the
+	  //       other is the LHS of this stmt.
+	  //  x = y + 2
+	  if (vrel_ptr->op1 () == handler.lhs ()
+	      && (vrel_ptr->op2 () == op1 || vrel_ptr->op2 () == op2))
+	    res = true;
+	  else if (vrel_ptr->op2 () == handler.lhs ()
+		   && (vrel_ptr->op1 () == op1 || vrel_ptr->op1 () == op2))
+	    res = true;
+	}
+      if (!res)
+	return false;
+    }
 
-  bool res;
   // Process logicals as they have special handling.
   if (is_gimple_logical_p (stmt))
     {
diff --git a/gcc/value-relation.h b/gcc/value-relation.h
index 340f9c42554..897cf467dd3 100644
--- a/gcc/value-relation.h
+++ b/gcc/value-relation.h
@@ -445,7 +445,7 @@ value_relation::set_relation (relation_kind r, tree n1, tree n2)
 {
   gcc_checking_assert (TREE_CODE (n1) == SSA_NAME
 		       && TREE_CODE (n2) == SSA_NAME);
-  if (n1 == n2)
+  if (n1 == n2 && r != VREL_EQ)
     {
       related = VREL_VARYING;
       name1 = NULL_TREE;