[Bug fortran/110957] New: -ffpe-trap and -ffpe-summary options issues

[Bug fortran/110957] New: -ffpe-trap and -ffpe-summary options issues

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110957

            Bug ID: 110957
           Summary: -ffpe-trap and -ffpe-summary options issues
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ubizjak at gmail dot com
  Target Milestone: ---

A couple of issues with -ffpe-trap and -ffpe-summary options:

a) Invalid argument report should be switched:

$ gfortran -ffpe-summary=aaa ac.f90
f951: Fatal Error: Argument to ‘-ffpe-trap’ is not valid: aaa
compilation terminated.

$ gfortran -ffpe-trap=aaa ac.f90
f951: Fatal Error: Argument to ‘-ffpe-summary’ is not valid: aaa
compilation terminated.


b) Specifying also -fno-trapping-math should be detected and handled

$ gfortran -ffpe-trap=invalid -fno-trapping-math ac.f90
[no diagnostics]

The issue b) should either report incompatibility between options, or force
-ftrapping-math (probably with a warning). Ideally, -ffpe-* should always set
flag_trapping_math, in case the compiler switches to no trapping math by
default in future.

[Bug fortran/110957] -ffpe-trap and -ffpe-summary options issues

[anlauf at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110957

anlauf at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |anlauf at gcc dot gnu.org
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2023-08-13

--- Comment #1 from anlauf at gcc dot gnu.org ---
Confirmed (a).  Obvious fix:

diff --git a/gcc/fortran/options.cc b/gcc/fortran/options.cc
index 27311961325..2d4be853c66 100644
--- a/gcc/fortran/options.cc
+++ b/gcc/fortran/options.cc
@@ -586,7 +586,7 @@ gfc_handle_fpe_option (const char *arg, bool trap)
              break;
            }
          }
-      if (!result && !trap)
+      if (!result && trap)
        gfc_fatal_error ("Argument to %<-ffpe-trap%> is not valid: %s", arg);
       else if (!result)
        gfc_fatal_error ("Argument to %<-ffpe-summary%> is not valid: %s",
arg);


Regarding (b), the gfortran manual says:

-ffpe-summary=list

 list can be either ‘none’, ‘all’ or a comma-separated list ...


-ffpe-trap=list

 list is a (possibly empty) comma-separated list ...

Unfortunately, 'none' is not accepted for list here, but might be handy.

Need to check where the options conflict can be diagnosed.

[Bug fortran/110957] -ffpe-trap and -ffpe-summary options issues

[anlauf at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110957

--- Comment #2 from anlauf at gcc dot gnu.org ---
Created attachment 56071
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56071&action=edit
Patch to fix mixed up parsing of fpe options

The attached patch fixes the mixup and adds the possibility to specify
-ffpe-trap=none to clear previously enabled exceptions on the command line.
Will submit this to the list.

Regarding the treatment of -f(no-)trapping-math, I played around a little
bit, and I am unsure what to do.

In gfortran, the option -ffpe-trap only sets the FPU mask in the main and
does nothing else.  Which I think is the major (sole?) purpose.

On the other hand, -f(no-)trapping-math has implications that affect
e.g. reassociation.  Adding to gfc_post_options() something like

  if (gfc_option.fpe != 0 && !flag_trapping_math)
    {
      gfc_warning_now (0, "Option %<-ffpe-trap=%> enforces "
                       "%<-ftrapping-math%> for Fortran");
      flag_trapping_math = 1;
    }

will generate different warnings for -O3 -ffast-math, -Ofast, and might
create more confusion than help users.

I tend to think that this part should not be implemented (now), unless
we better understand the implications of what a change of the defaults
in gcc means to gfortran.

[Bug fortran/110957] -ffpe-trap and -ffpe-summary options issues

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110957

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Harald Anlauf <anlauf@gcc.gnu.org>:

https://gcc.gnu.org/g:458c253ccdae9df439b9a452d04e325101e5756e

commit r14-4631-g458c253ccdae9df439b9a452d04e325101e5756e
Author: Harald Anlauf <anlauf@gmx.de>
Date:   Fri Oct 6 22:21:56 2023 +0200

    fortran: fix handling of options -ffpe-trap and -ffpe-summary [PR110957]

    gcc/fortran/ChangeLog:

            PR fortran/110957
            * invoke.texi: Update documentation to reflect '-ffpe-trap=none'.
            * options.cc (gfc_handle_fpe_option): Fix mixup up of error
messages
            for options -ffpe-trap and -ffpe-summary.  Accept '-ffpe-trap=none'
            to clear FPU traps previously set on command line.