Should we have a "don't simplify floating point at all" flag?

[David Tweed]

Hi,

> What would the community feel about the addition of a flag which led to
the
> behaviour of not applying any simplification to
> floating point instructions (but only affecting those simplifications)? I
> should stress that we're not committing to implementing this,
> more getting a feel for if it's worth investigating feasibility some more.

| I think it would be better to add more information to the IR so that the
| optimizers can make correct decisions.  For example, LLVM has been lacking
| proper support for rounding modes forever, maybe now is a good time to fix
that?

That may be the better long-term solution. One of the issues is that it's
often
a combination of the "set rounding mode" with fixed features of the hardware
(eg, the hardware only offers flush-denormals-to-zero behaviour) that
affects
things. I haven't (at least yet) really looked in any detail at just how
complex
all this gets.

Cheers,
Dave