On Wed, 17 Oct 2018, H.J. Lu wrote:
We may simplify
(subreg (vec_merge (vec_duplicate X) (vector) (const_int 1)) 0)
to X when mode of X is the same as of mode of subreg.
Hello,
we already have code to simplify vec_select(vec_merge):
/* If we select elements in a vec_merge that all come from the same
operand, select from that operand directly. */
It would make sense to me to make the subreg transform as similar to it as
possible, in particular you don't need to special case vec_duplicate, the
transformation would see that everything comes from the first vector,
produce (subreg (vec_duplicate X) 0), and let another transformation
optimize that.
(I had tried at some point to canonicalize subreg to vec_select to avoid
repeating such transformations, but it was rejected as a very bad idea)
--
Marc Glisse
