🚀 go-pugleaf

    I am currently writing (well, updating) a code which is
supposed to be (a) portable and (b) have one loop which will be
vectorized (on vector machines) and another, very similar, which will
not be.  (The scalar version is for the case when the loop will
only iterate a very few times.)

    My first attempt had the first loop be written in a typical
vectorizable form, the second I put enough scalars into to make
it scalar on one machine I used.  I later found that other
compilers were smarter, and *both* loops vectorized.  I suspect
that as compiler technology improves, any code which foils the
vectorizer now will either (a) soon be vectorizable or (b)
be so obfuscated that it will be slower than vector mode
with vector length one anyway.

    So, I am now going to try just putting in compiler directives,
enough so that most any vector machine should recognize one.  CONVEX
machines require "C$DIR SCALAR" just before the DO, while CRI machines
want "CDIR$ NOVECTOR" in the same place, so my scalar loop currently
starts out:

C$DIR SCALAR
CDIR$ NOVECTOR
      DO ....
 

Any other compiler directives that I should add to the list?

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(Boy, I wish someone would come up with a standard for such
compiler directives.)



Alan McKenney
E-mail: mckenney@cims.nyu.edu  <-- "accept no substitutes!"