Concerns regarding the -ffp-contract=fast default

[Jakub Jelinek]

On Mon, Sep 18, 2023 at 01:26:54PM +0200, Martin Uecker wrote:
> > I think that changing the default to =standard without -ffast-math is
> > reasonable.
> > IIRC the standard allows such default if it's indicated, so it doesn't require
> > =off anywhere.
> 
> The C standard requires a pragma to turn control it on and off, 
> which GCC does not support.  The default is then implementation
> defined.

Perhaps we should add some initial hammer approach for the pragma, like
if you ever use the pragma to turn it somewhere off, it is turned off
globally, or ditto per function.  Might be far easier than trying to
make it precise that contraction is allowed in this expression and not in
this subexpression of that etc.  Of course, making it precise is the
ultimate goal.

	Jakub