Re: Target control of Fortran options

[Paul Koning <paulkoning@comcast.net>]

> On Oct 4, 2018, at 4:06 AM, Richard Biener <richard.guenther@gmail.com> wrote:
> 
> On Wed, Oct 3, 2018 at 11:04 PM Paul Koning <paulkoning@comcast.net> wrote:
>> 
>> In the C and C++ parts of GCC, the target has some ways to adjust the compiler options depending on target settings.  I'm looking for a way to do that with gfortran.
>> 
>> The specific issue is in pdp11, which has an option to specify that "float" is 8 bytes (same as "double") rather than 4 bytes.  And the 8 byte choice is the default.
>> 
>> As a result, if I invoke gfortran for that target, I get an ICE because real*4 can't be found.  If I say -fdefault-real-8 it works.
>> 
>> So what I'm hoping to do is to have the target switch processing code (for the TARGET_HANDLE_OPTION hook) react to the -mfloat32 and -mfloat64 switches by passing appropriate -fdefault-real-* switches to Fortran.  Is that possible?
> 
> I think Fortran has to do it the same way the C family does.
> float/double get assigned
> by looking at FLOAT_TYPE_SIZE / [LONG_]DOUBLE_TYPE_SIZE.  Iff that's not good
> for the Fortran FE we'd have to define additional target hooks the FE can use.

It appears that Fortran has a different approach.  Fortran has syntax like "REAL*8" to request a float of a specific size.  And what gfortran does is assume that "REAL" without  a size specifier means "REAL*n" for a well known fixed n.  Without switches, n is 4, which is indeed the common answer.  But in my case, there isn't any 4-byte float type unless you say -mfloat32.

Maybe the answer is "that's a wrong thing to do".  If so, I suppose I could change it -- it was done before I got involved and I don't know for what reason.

	paul