https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95141
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot
gnu.org
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
So there's already (OVF) at
((long unsigned int) IA1 & 158(OVF)) & 1
but we only check
375 if (TREE_OVERFLOW_P (ret)
376 && !TREE_OVERFLOW_P (op0)
377 && !TREE_OVERFLOW_P (op1))
378 overflow_warning (EXPR_LOC_OR_LOC (expr, input_location), ret,
expr);
which doesn't catch the pre-existing overflow on op0 which then propagates.
The original overflow is introduced folding short 158 to signed char -98(OVF)
via convert.c:do_narrow:
437 /* We should do away with all this once we have a proper
438 type promotion/demotion pass, see PR45397. */
439 expr = maybe_fold_build2_loc (dofold, loc, ex_form, typex,
440 convert (typex, arg0),
441 convert (typex, arg1));
specifically the convert (typex, arg1).
Now TREE_OVERFLOW in general is quite a fragile thing, but it's tempting to
adjust the overflow_warning guard for this case ...
The do_narrow code also specifically looks for overflow cases that matter
and does not perform narrowing then so clearing TREE_OVERFLOW there would
also look reasonable.
Thus like the following? Should be cheaper than adding walk_tree to the
diagnostic guard.
diff --git a/gcc/convert.c b/gcc/convert.c
index 42509c518a9..ed00ded1a89 100644
--- a/gcc/convert.c
+++ b/gcc/convert.c
@@ -436,9 +436,16 @@ do_narrow (location_t loc,
}
/* We should do away with all this once we have a proper
type promotion/demotion pass, see PR45397. */
+ /* Above we checked for all cases where overflow matters, avoid
+ geneating overflowed constants here which otherwise propagate
+ and cause spurious warnings, see PR95141. */
+ tree converted_arg1 = convert (typex, arg1);
+ if (TREE_OVERFLOW_P (converted_arg1)
+ && !TREE_OVERFLOW_P (arg1))
+ converted_arg1 = drop_tree_overflow (converted_arg1);
expr = maybe_fold_build2_loc (dofold, loc, ex_form, typex,
convert (typex, arg0),
- convert (typex, arg1));
+ converted_arg1);
return convert (type, expr);
}
