Add new pass to optimize branch chains to table dispatch

* module/language/cps/switch.scm: New pass.

* module/Makefile.am (SOURCES):
* am/bootstrap.am (SOURCES): Add switch.scm.

* module/system/base/optimize.scm (available-optimizations):
* module/language/cps/optimize.scm (optimize-first-order-cps): Run
  switch optimization at level 2.

* libguile/hash.c (JENKINS_LOOKUP3_HASHWORD2): Add note regarding
  cross-compilation.

* module/language/cps/graphs.scm (intmap-select): New definition.
* module/language/cps/utils.scm (compute-singly-referenced-labels): Move
  here, from various places.  Doesn't take a body intset argument.

* module/language/cps/contification.scm:
* module/language/cps/closure-conversion.scm:
* module/language/cps/simplify.scm: Use compute-singly-referenced-labels
  from utils.

* module/language/cps/effects-analysis.scm (annotation->memory-kind*):
  (annotation->memory-kind): Add symbol annotation cases.

module/language/cps/contification.scm

@@ -40,37 +40,6 @@
   #:use-module (language cps with-cps)
   #:export (contify))
 
-(define (compute-singly-referenced-labels conts)
-  "Compute the set of labels in CONTS that have exactly one
-predecessor."
-  (define (add-ref label cont single multiple)
-    (define (ref k single multiple)
-      (if (intset-ref single k)
-          (values single (intset-add! multiple k))
-          (values (intset-add! single k) multiple)))
-    (define (ref0) (values single multiple))
-    (define (ref1 k) (ref k single multiple))
-    (define (ref2 k k*)
-      (if k*
-          (let-values (((single multiple) (ref k single multiple)))
-            (ref k* single multiple))
-          (ref1 k)))
-    (match cont
-      (($ $kreceive arity k) (ref1 k))
-      (($ $kfun src meta self ktail kclause) (ref2 ktail kclause))
-      (($ $ktail) (ref0))
-      (($ $kclause arity kbody kalt) (ref2 kbody kalt))
-      (($ $kargs names syms ($ $continue k)) (ref1 k))
-      (($ $kargs names syms ($ $branch kf kt)) (ref2 kf kt))
-      (($ $kargs names syms ($ $switch kf kt*))
-       (fold2 ref (cons kf kt*) single multiple))
-      (($ $kargs names syms ($ $prompt k kh)) (ref2 k kh))
-      (($ $kargs names syms ($ $throw)) (ref0))))
-  (let*-values (((single multiple) (values empty-intset empty-intset))
-                ((single multiple) (intmap-fold add-ref conts single multiple)))
-    (intset-subtract (persistent-intset single)
-                     (persistent-intset multiple))))
-
 (define (compute-functions conts)
   "Compute a map from $kfun label to bound variable names for all
 functions in CONTS.  Functions have two bound variable names: their self