Hi! On Thu, Sep 17, 2020 at 01:12:19PM +0930, Alan Modra wrote: > On Wed, Sep 16, 2020 at 07:02:06PM -0500, Segher Boessenkool wrote: > > > + /* Test both regs even though the one in the mask is > > > + constrained to be equal to the output. Increasing > > > + cost may well result in rejecting an invalid insn > > > + earlier. */ > > > > Is that ever actually useful? > > Possibly not in this particular case, but I did see cases where > invalid insns were rejected early by costing non-reg sub-expressions.
But does that ever change generated code? This makes the compiler a lot harder to read and understand. To the point that such micro-optimisations makes worthwhile optimisations hard or impossible to do. Segher
