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

> 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@...>
>
>        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@...>
>
>        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@...>
>
>        PR fortran/52428
>        * gfortran.dg/int_range_io_1.f90: New test.
>
>
> --
> Janne Blomqvist