On Sat, Feb 16, 2019 at 12:10:22PM +0100, Richard Biener wrote:
> On February 16, 2019 8:12:34 AM GMT+01:00, Jakub Jelinek <ja...@redhat.com>
> wrote:
> >Both the C and C++ standard guarantee that the argc argument to main is
> >non-negative, the following patch sets (or adjusts) the corresponding
> >SSA_NAME_RANGE_INFO. While main is just one, with IPA VRP it can also
> >propagate etc. I had to change one testcase because it started
> >optimizing
> >it better (the test has been folded away), so no sinking was done.
>
> Can we handle this in _nonnegative_p? Also make it work independent of
We could. But I was wondering if that wouldn't be too costly to check it
there for each SSA_NAME tested (at least something like is this a default
definition SSA_NAME of a PARM_DECL in MAIN_DECL_P (DECL_NAME
(current_function_decl))). Furthermore, I think VRP doesn't use the
*_nonnegative_*p APIs except for gimple_stmt_nonnegative_warnv_p
and so it would need to be repeated in VRP anyway. I vaguely remember we
didn't want to use value ranges in *nonnegative_*_p and *nonnegative_*_p
in VRP because that would cause weird behavior.
> langhooks by looking up the translation unit decl from cfun via walking
> contexts?
It is very well possible that MAIN_DECL_P is true only for actual main
that _start calls even for other languages, I know for sure that
it is the case of Fortran, just haven't analyzed what exactly is Ada doing
(it has some main_identifier_node code in there), or Go, D etc.
> Is this a regression?
The patch fixes the regression on #c0 in that PR, though admittedly only
if it is in main and not in some other random function with random int
argument. So, if you want to defer this for GCC 10, I can surely wait with
that.
Jakub
