On 6/24/2026 1:38 AM, Andrea Pinski wrote:
On Mon, Jun 22, 2026 at 2:01 AM Richard Biener
<[email protected]> wrote:
On Mon, Jun 22, 2026 at 7:29 AM Eikansh Gupta
<[email protected]> wrote:
Add a pattern for `(trunc)copysign ((extend)x, CST)`. Only the sign of
CST matters, not its value, so it can be simplified to
`copysign (x, +-0.0)` depending on the sign of CST. When signed zeros
are not honored their sign may be lost, so `copysign (x, +-1.0)` is used
instead.
Is it worth that trouble? Why not always use +-1.0?
Jeff asked him to change it to be that way but I think it is not so
useful. So yes using +-1.0 should be used. Though +1 will turn into
ABS_EXPR anyways.
I was thinking more about the -1.0. That needs two bits set while -0.0
is a single bit twiddle from +0.0 and is trivially synthesizable without
having to pull the value out of the constant pool. Of course if
HONOR_SIGNED_ZEROs is off, then +-1.0 is a better selectdion.
It's not likely a big deal, so if y'all want to go with +-1.0 I'm not
going to worry much about it. I expect every design I care about to
support Zfa where those are all predefined constants.
jeff
