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...)
