[Bug fortran/59604] New: Constant comparisons with -fno-range-check and int(z'...')

[Bug fortran/59604] New: Constant comparisons with -fno-range-check and int(z'...')

[tkoenig at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59604

            Bug ID: 59604
           Summary: Constant comparisons with -fno-range-check and
                    int(z'...')
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tkoenig at gcc dot gnu.org

Trying out a fix for PR 58003, I found that the following program was of the
opinion that -1 does not equal -1:

ig25@linux-fd1f:~/Krempel/NoRange> cat bar.f90
program test
  use iso_fortran_env
  implicit none

  integer, parameter :: wt = int32

  print *, int(z'FFFFFFFF',wt)
  print *, int(z'FFFFFFFF',wt) /= -1

end program test
ig25@linux-fd1f:~/Krempel/NoRange> gfortran -fno-range-check bar.f90 
ig25@linux-fd1f:~/Krempel/NoRange> ./a.out
          -1
 T

[Bug fortran/59604] Constant comparisons with -fno-range-check and int(z'...')

[tkoenig at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59604

--- Comment #1 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
TRANSFER gets this right.

[Bug fortran/59604] Constant comparisons with -fno-range-check and int(z'...')

[kargl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59604

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kargl at gcc dot gnu.org

--- Comment #2 from kargl at gcc dot gnu.org ---
(In reply to Thomas Koenig from comment #1)
> TRANSFER gets this right.

It is unclear what you mean here.

A simplified program that removes the complication of the IO
and ISO C binding is

program test
  if (int(z'FFFFFFFF') /= -1) call abort
end program test

% gfc4x -o z -fno-range-check -fdump-tree-original a.f90
% ./z

Program aborted. Backtrace:
#0  0x4807A01C
#1  0x4807B8CF
#2  0x48134C17
#3  0x8048792 in MAIN__ at a.f90:0
Abort (core dumped)

%cat a.f90.003t.orginal
test ()
{
  _gfortran_abort ();
  L.1:;
}


main (integer(kind=4) argc, character(kind=1) * * argv)
{
  static integer(kind=4) options.0[9] = {68, 1023, 0, 0, 1, 1, 0, 0, 31};

  _gfortran_set_args (argc, argv);
  _gfortran_set_options (9, &options.0[0]);
  test ();
  return 0;
}


I believe the problem lies in gfc_simplify_int.  From what I can
tell, there is never a conversion of a boz to an integer, until we
reach code generation.  The call chain is 

gfc_simplify_int -> simplify->intconv -> gfc_convert_constant ->
gfc_int2int.

By the time we reach gfc_int2int, the boz should have been converted
to the integer, but isn't.  Now, if we compare gfc_simplify_int to
gfc_simplify_real, we see in gfc_simplify_real,

  if (convert_boz (e, kind) == &gfc_bad_expr)
    return &gfc_bad_expr;

where convert_boz will do an explicit conversion of a boz to a 
real type.  There isn't a similar functionality for integer.

[Bug fortran/59604] Constant comparisons with -fno-range-check and int(z'...')

[sgk at troutmask dot apl.washington.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59604

--- Comment #3 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
On Fri, Dec 27, 2013 at 06:10:23PM +0000, kargl at gcc dot gnu.org wrote:
> 
> By the time we reach gfc_int2int, the boz should have been converted
> to the integer, but isn't.  Now, if we compare gfc_simplify_int to
> gfc_simplify_real, we see in gfc_simplify_real,
> 
>   if (convert_boz (e, kind) == &gfc_bad_expr)
>     return &gfc_bad_expr;
> 
> where convert_boz will do an explicit conversion of a boz to a 
> real type.  There isn't a similar functionality for integer.
> 

I forgot to mention that gfortran may be delaying the conversion
under the translation to the middle-end, so tit can rely on
the middle-end for wrap-around semantics of twos-complement
signed integer arithmetic.

[Bug fortran/59604] Constant comparisons with -fno-range-check and int(z'...')

[tkoenig at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59604

Thomas Koenig <tkoenig at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |58003

--- Comment #4 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
(In reply to kargl from comment #2)
> (In reply to Thomas Koenig from comment #1)
> > TRANSFER gets this right.
> 
> It is unclear what you mean here.

What I mean is that

program test
  if (transfer(z'FFFFFFFF',1) /= -1) call abort
end program test

does not call abort.

Also setting this as blocking 58003, because an obvious
fix to that bug would replace an ICE with a wrong-code
bug for some corner cases (not preferable :-)

[Bug fortran/59604] Constant comparisons with -fno-range-check and int(z'...')

[tkoenig at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59604

Thomas Koenig <tkoenig at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |UNCONFIRMED
     Ever confirmed|1                           |0

--- Comment #7 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
(In reply to Steve Kargl from comment #5)
> On Fri, Dec 27, 2013 at 07:53:00PM +0000, tkoenig at gcc dot gnu.org wrote:
> > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59604
> > 
> > Thomas Koenig <tkoenig at gcc dot gnu.org> changed:
> > 
> >            What    |Removed                     |Added
> > ----------------------------------------------------------------------------
> >              Blocks|                            |58003
> > 
> > --- Comment #4 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
> > (In reply to kargl from comment #2)
> > > (In reply to Thomas Koenig from comment #1)
> > > > TRANSFER gets this right.
> > > 
> > > It is unclear what you mean here.
> > 
> > What I mean is that
> > 
> > program test
> >   if (transfer(z'FFFFFFFF',1) /= -1) call abort
> > end program test
> > 
> > does not call abort.
> 
> I suspect that the above is not portable as transfer() simply copies
> bits.  z'FFFFFFF' is an integer(8) (or integer(16)) entity.  Transfer()
> is copying 32-bits from that entity.  It is clear from the 
> -fdump-tree-original that middle-end is "converting" the resulting
> 32-bit thing into -1.  So, you're relying on twos-complement wrap
> around semantics.

As gcc supports only twos complement arithmetic, I think this is OK.

[Bug fortran/59604] Constant comparisons with -fno-range-check and int(z'...')

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59604

Dominique d'Humieres <dominiq at lps dot ens.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|2013-12-28 00:00:00         |2013-12-29
     Ever confirmed|0                           |1

[Bug fortran/59604] Constant comparisons with -fno-range-check and int(z'...')

[tkoenig at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59604

--- Comment #8 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
Author: tkoenig
Date: Sun Apr 27 10:48:56 2014
New Revision: 209836

URL: http://gcc.gnu.org/viewcvs?rev=209836&root=gcc&view=rev
Log:
2014-03-27  Thomas Koenig  <tkoenig@gcc.gnu.org>

    PR fortran/59604
    PR fortran/58003
    * gfortran.h (gfc_convert_mpz_to_signed):  Add prototype.
    * arith.c (gfc_int2int):  Convert number to signed if
    arithmetic overflow is not checked.
    * simplify.c (convert_mpz_to_unsigned): Only trigger assert for
    size if range checking is in force.
    (convert_mpz_to_signed):  Make non-static, rename to
    (gfc_convert_mpz_to_signed).
    (simplify_dshift): Use gfc_convert_mpz_to_signed.
    (gfc_simplify_ibclr):  Likewise.
    (gfc_simplify_ibits):  Likewise.
    (gfc_simplify_ibset):  Likewise.
    (simplify_shift):  Likewise.
    (gfc_simplify_ishiftc):  Likewise.
    (gfc_simplify_maskr):  Likewise.
    (gfc_simplify_maskl):  Likewise.

2014-03-27  Thomas Koenig  <tkoenig@gcc.gnu.org>

    PR fortran/59604
    PR fortran/58003
    * gfortran.dg/no_range_check_3.f90:  New test.


Added:
    trunk/gcc/testsuite/gfortran.dg/no_range_check_3.f90
Modified:
    trunk/gcc/fortran/ChangeLog
    trunk/gcc/fortran/arith.c
    trunk/gcc/fortran/gfortran.h
    trunk/gcc/fortran/simplify.c
    trunk/gcc/testsuite/ChangeLog

[Bug fortran/59604] Constant comparisons with -fno-range-check and int(z'...')

[tkoenig at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59604

Thomas Koenig <tkoenig at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #9 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
Fixed on trunk, closing.  I don't think this
is bad enough for a backport.