On Sat, Mar 25, 2017 at 12:24 AM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Fri, Mar 24, 2017 at 4:14 PM, Luc Van Oostenryck > <luc.vanoostenryck@xxxxxxxxx> wrote: >> More precisely, use a table to get the opcdoe corresponding >> to the negated compare and use a more explicit name for the >> function. > > Side note: this code should verify that it doesn't operate on a > floating point compare. > > You can't negate a FP compare, because the negation doesn't > necessarily have the opposite value. > > For example, "a < b" is *not* the same as "!(a >= b)" for floating > point values when one of them is a NaN. Both < and >= will compare as > false, so "negating" the op won't actually negate the resulting > logical operation. > > Linus Yes, indeed. I've some plan to add better handling of floating-point and the compare is part of it. It'll need a new set of instructions to do it correctly (precisely because for fp numbers once you care about NaNs/unordered "a < b" is *not* the same as "!(a >= b)"). But there is also a number of bugs I want to solve, especially one related to the misplacement of phi-node and another about missing reloads. For the moment I think we can pretend that all the fp values we deal with are ordered ones. -- Luc -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
