Concerns regarding the -ffp-contract=fast default

[Alexander Monakov]

On Mon, 18 Sep 2023, Jakub Jelinek wrote:

> 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.

When implementing -ffp-contract=standard I looked into implementing the
pragma (in a precise manner) and I didn't get the impression it would be
hard to implement for C. But I was somewhat discouraged by the lack of
front-end maintainers reaction to the patch implementing the =standard,
so I didn't pursue that.

The hardest part would be popping the pragma state when leaving a block,
which didn't seem difficult (at least for C).

Alexander