[Bug tree-optimization/62217] [4.9/5 Regression] DOM confuses complete unrolling which in turn causes VRP to warn

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62217

--- Comment #12 from Richard Biener <rguenth at gcc dot gnu.org> ---
Index: gcc/tree-ssa-dom.c
===================================================================
--- gcc/tree-ssa-dom.c  (revision 220755)
+++ gcc/tree-ssa-dom.c  (working copy)
@@ -2291,11 +2291,16 @@ cprop_operand (gimple stmt, use_operand_
       if (!may_propagate_copy (op, val))
        return;

-      /* Do not propagate copies into simple IV increment statements.
-         See PR23821 for how this can disturb IV analysis.  */
-      if (TREE_CODE (val) != INTEGER_CST
-         && simple_iv_increment_p (stmt))
-       return;
+      /* Do not propagate copies into BIVs.
+         See PR23821 and PR62217 for how this can disturb IV and
+        number of iteration analysis.  */
+      if (TREE_CODE (val) != INTEGER_CST)
+       {
+         gimple def = SSA_NAME_DEF_STMT (op);
+         if (gimple_code (def) == GIMPLE_PHI
+             && gimple_bb (def)->loop_father->header == gimple_bb (def))
+           return;
+       }

       /* Dump details.  */
       if (dump_file && (dump_flags & TDF_DETAILS))


fixes the warning on the branch, not sure yet if the missed-optimization on
the trunk.  It extends an existing heuristic to not replace a BIV use
in an increment to not replace any BIV use (???  Best if we'd know if the
equivalence were temporary only...)