Re: [PATCH] MIPS: IEEE 754-2008 features support

[Richard Sandiford <rdsandiford at googlemail dot com>]

"Maciej W. Rozycki" <macro@codesourcery.com> writes:
>> The patch mostly looks good apart from that, but please use a single
>> enum for the 2008/legacy thing, both in mips.h and mips.opt.
>
>  Also mips.c and mips.md (and last but not least mips-opts.h).  Done.

I wasn't trying to list all the places that use the C enum.
I said mips.opt because I thought we should be able to use a single
mips.opt Enum too, a bit like we share mips_arch_opt_value for both
-march= and -mtune=.

>  Please also note that the writability of the individual new (HAS2008) 
> FCSR bits is optional e.g. a conforming processor may have NAN2008 
> hardwired to 1 and ABS2008 hardwired to 0 (or likewise with NAN2008 
> writable).

OK, I'd missed that this was allowed, sorry.  It just seems really
unfortunate...

>> > +# Return 1 if this is a MIPS target supporting -mnan=.
>> > +# Old versions of binutils may not support this option.
>> > +
>> > +proc check_effective_target_mips_nan { } {
>> > +    if { ![istarget mips*-*-*] } {
>> > +	return 0
>> > +    }
>> > +    return [check_no_compiler_messages mips_nan object {
>> > +	int dummy;
>> > +    } "-mnan=2008"]
>> > +}
>> 
>> The tests you added are dg-do compile tests, which stop after assembly
>> generation, so this guard shouldn't be needed.
>
>  It is needed in case the compiler was built without support for this 
> option i.e. configured against old binutils.  I verified that it indeed 
> triggered in this case:
>
> Executing on host: mips-linux-gnu-gcc  -fno-diagnostics-show-caret -fdiagnostics-color=never  -mnan=2008 -c  -o mips_nan21474.o mips_nan21474.c    (timeout = 300)
> mips-linux-gnu-gcc: error: unrecognized command line option '-mnan=2008'
> compiler exited with status 1
> output is:
> mips-linux-gnu-gcc: error: unrecognized command line option '-mnan=2008'

That seems like bad practice though.  In other cases we leave the
assembler to report options that it doesn't understand.  I think that's
better because it's then clearer that the assembler needs to be upgraded.

Within config/mips, the configure test should just control whether it's
safe to use .nan when no -mnan option has been given.  (This is what we
did for -mmicromips vs ".set nomicromips" FWIW.)

Richard