On Tue, Aug 15, 2017 at 4:11 PM, Wilco Dijkstra <wilco.dijks...@arm.com> wrote: > Richard Biener wrote: >> > We also change the association of >> > >> > x / (y * C) -> (x / C) / y >> > >> > If C is a constant. >> >> Why's that profitable? > > It enables (x * C1) / (y * C2) -> (x * C1/C2) / y for example. > Also 1/y is now available to the reciprocal optimization, see > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71026 for details.
Sure, but on its own it's going to be slower. So this isn't the correct way to enable those followup transforms. >> > x / (- y) -> (-x) / y >> >> Why? (it's only one of the possible canonicalizations) > > Same here, y is now available for reciprocal optimization. The > negate may now be optimized, for example (a * b) / -y -> (-a*b) / y > will use a negated multiple on various targets. Fair enough. Though if it were x / -(a*b) you'd regress that case. Richard. > > Wilco
