[Patch, fortran] PR 52428 Reading of large negative values and range checking

[Janne Blomqvist <blomqvist dot janne at gmail dot com>]

Hi,

currently when -frange-check is enabled, we check for overflow when
doing a formatted read of an integer value. This check, however, is
against the Fortran numerical model (see 13.4 in F2008), which defines
a symmetric interval [-huge(), huge()], whereas all targets gfortran
supports use a two's complement representation with a range of
[-huge()-1, huge()].

However, there is no checking against the numerical model when doing
arithmetic, and thus we can generate and write the value -huge()-1,
but we cannot read it back in! With the -fno-range-check option, this
overflow checking can be disabled, but at the cost of disabling all
overflow checking, which leads to reading nonsense values if the
hardware supported range overflows.

The attached patch changes this logic such that overflow checking
against the hardware supported range [-huge()-1, huge()] is always
done when reading, regardless of the -frange-check flag setting. This
also seems to be what ifort 12.0 does, I haven't checked other
compilers.

For some more arguments back and forth, see the PR.

Regtested on x86_64-unknown-linux-gnu, Ok for trunk?

gcc/fortran ChangeLog:

2012-04-25  Janne Blomqvist  <jb@gcc.gnu.org>

        PR fortran/52428
        * gfortran.texi: Update _gfortran_set_options documentation.
        * invoke.texi: Remove runtime behavior description of
        -fno-range-check.
        * trans-decl.c (create_main_function): Don't pass the range-check
        setting to the library.


libgfortran ChangeLog:

2012-04-25  Janne Blomqvist  <jb@gcc.gnu.org>

        PR fortran/52428
        * io/io.h (max_value): Rename to si_max, remove second argument.
        * io/list_read.c (convert_integer): Use unsigned types when
        parsing the digits, set max value depending on the sign.
        * io/read.c (max_value): Rename to si_max, remove second argument,
        simplify.
        (read_decimal): Set max value depending on sign, always check
        overflow.
        (read_radix): Calculate max unsigned value directly.
        * libgfortran.h (struct compile_options_t): Remove range_check
        field.
        * runtime/compile_options.c (set_options): Skip handling
        options[7].
        (init_compile_options): Don't set removed field.


gcc/testsuite ChangeLog:

2012-04-25  Janne Blomqvist  <jb@gcc.gnu.org>

        PR fortran/52428
        * gfortran.dg/int_range_io_1.f90: New test.


-- 
Janne Blomqvist

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