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

> PING
>
> On Thu, Apr 26, 2012 at 12:08 AM, Janne Blomqvist
> <blomqvist.janne@...> wrote:
>> 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
>
>
>
> --
> Janne Blomqvist