x86-64: optimizations (nil is r14)

[iskamag]

No description provided.

[froggey]

Does this update the (defmethod emit-lap (backend-function (instruction ir:constant-instruction) uses defs) path? There's a special case in there for loading nil

If you wanted to be super thorough you could map over every compiled function on the system, disassemble them, then look for loads of literal nil in the output.
Something like (map nil #'disassemble (get-all-objects (lambda (obj) (%object-of-type-p obj +object-tag-function+)))) then grep the output or sth

[iskamag]

It did but I removed that in the "un-break" commit (don't remember why). You can re-add that in a seperate PR and see if the CI completes.

((eql value nil)
 (emit `(lap:mov32 ,(lap::convert-width dest 32) :r14)))
((eql value t)
 (emit `(lap:mov32 ,(lap::convert-width dest 32) ,value)))

Still a lot of the gains are in the stack clearing epilogue.

[iskamag]

Actually, why did I convert width for r14 there?