[PATCH] simplify-rtx: Generalize (and X (ior (not X) Y) -> (and X Y)

[Segher Boessenkool]

On Mon, Dec 29, 2014 at 12:14:31PM +0000, Alan Lawrence wrote:
> Just a quick thought: will this catch e.g. (and (not X) (ior X Y))?

It doesn't (and nothing else does, either; I checked).

> That's
> equivalent to (and (not X) (ior (not (not X)) Y)), i.e. (and X' (ior (not
> X') Y)) with X'=(not X), under the assumption that (not (not X)) is
> equivalent to X. However I suspect for cases of this form, GET_CODE (XEXP
> (op1, <n>)) != NOT...?

Right.  We'd have to check that in  (and A (ior B C))  A is equal to the
NOT of B or C.  Or, we could transform it to  (ior (and A B) (and A C))
and see if that simplifies to something simpler.  Also for IOR and AND
swapped.  Dunno what other cases we miss.  I'm a bit worried about the
cost of a more general test, and how do you determine "what is simpler"
anyway, in not-so-simple cases.

Either way, my patch fixes a testsuite fail ;-)


Segher