Fwd: [PATCH, doc/ARM] Remove false affirmation that Thumb cannot use an FPU

[Richard Earnshaw (lists)]

On 18/08/16 07:00, Sandra Loosemore wrote:
> On 08/11/2016 04:31 AM, Thomas Preudhomme wrote:
> 
>> diff --git a/gcc/doc/fragments.texi b/gcc/doc/fragments.texi
>> index
>> b6d8541c8ca820fa732363a05221e2cd4d1251c2..abf4e128671bb4751d21f24bb69625593d3c839e
>> 100644
>> --- a/gcc/doc/fragments.texi
>> +++ b/gcc/doc/fragments.texi
>> @@ -117,12 +117,15 @@ specified, there are combinations that should
>> not be built.  In that
>>  case, set @code{MULTILIB_EXCEPTIONS} to be all of the switch exceptions
>>  in shell case syntax that should not be built.
>>
>> -For example the ARM processor cannot execute both hardware floating
>> -point instructions and the reduced size THUMB instructions at the same
>> -time, so there is no need to build libraries with both of these
>> -options enabled.  Therefore @code{MULTILIB_EXCEPTIONS} is set to:
>> +For example on ARM targets @option{-mfloat-abi=soft} requests to use a
>> +softfloat implementation for floating-point operations.  Therefore, it
>> +does not make sense to find both @option{-mfloat-abi=soft} and an
>> +@option{mfpu} option on the command line so @code{MULTILIB_EXCEPTIONS}
>> +could contain the following exception (assuming that
>> +@option{-mfloat-abi} comes after in @code{MULTILIB_OPTIONS} and given
>> +that @option{-mfloat-abi=soft} is the default value):
>>  @smallexample
>> -*mthumb/*mhard-float*
>> +*mfpu=*
>>  @end smallexample
>>
>>  @findex MULTILIB_REQUIRED
> 
> This version still has a lot of copy-editing issues.  I suggest
> rewriting as:
> 
>   For example, on ARM targets @option{-mfloat-abi=soft} requests use of
>   software floating-point operations, so it
>   does not make sense to build libraries with both
>   @option{-mfloat-abi=soft} and an @option{-mfpu} option.
>   @code{MULTILIB_EXCEPTIONS} could contain the following exception
> 
> but here I get stuck in suggesting a rewrite, because I can't parse this
> part at all to figure out what you're trying to say:
> 
>   (assuming that
>   @option{-mfloat-abi} comes after in @code{MULTILIB_OPTIONS} and given
>   that @option{-mfloat-abi=soft} is the default value):
> 
> "comes after in"?  Comes after what?  If the order is important here,
> the documentation should explain why instead of just "assuming" things
> about it.
> 
> -Sandra the confused
> 

I think it's probably best to just drop the entire parenthetical
subcluase.  This is documentation of how to use MULTILIB_EXCEPTIONS not
precise documentation on what needs to be done on ARM.

In fact, it might be better to just rewrite the whole section based on a
theoretical machine that has two ISAs, one which can support
floating-point and one which can't.  You then get back to essentially
the same text as we had originally but anonymised and future proofed.

R.