Add $switch CPS term kind

* module/language/cps.scm ($switch): New term.
* doc/ref/compiler.texi (CPS in Guile): Add documentation.

* module/language/cps.scm (build-term, parse-cps, unparse-cps)
* module/language/cps/closure-conversion.scm (compute-non-operator-uses)
  (compute-singly-referenced-labels, rewrite-shared-closure-calls)
  (compute-free-vars, convert-one)
* module/language/cps/compile-bytecode.scm (compile-function)
* module/language/cps/contification.scm (compute-singly-referenced-labels)
  (compute-contification-candidates, apply-contification)
* module/language/cps/cse.scm (compute-truthy-expressions)
  (forward-cont, term-successors, eliminate-common-subexpressions-in-fun)
* module/language/cps/dce.scm (compute-known-allocations)
  (compute-live-code, process-eliminations)
* module/language/cps/devirtualize-integers.scm (compute-use-counts)
  (peel-trace)
* module/language/cps/effects-analysis.scm (compute-effects)
* module/language/cps/licm.scm (hoist-one, hoist-in-loop)
* module/language/cps/loop-instrumentation.scm (compute-loop-headers)
* module/language/cps/peel-loops.scm (rename-cont)
* module/language/cps/renumber.scm (sort-labels-locally, renumber)
* module/language/cps/rotate-loops.scm (rotate-loop)
  (rotate-loops-in-function)
* module/language/cps/self-references.scm (resolve-self-references)
* module/language/cps/simplify.scm (compute-singly-referenced-vars)
  (eta-reduce, compute-singly-referenced-labels, beta-reduce)
* module/language/cps/slot-allocation.scm (compute-defs-and-uses)
  (add-prompt-control-flow-edges, compute-var-representations)
* module/language/cps/specialize-numbers.scm (compute-significant-bits)
* module/language/cps/split-rec.scm (compute-free-vars)
* module/language/cps/type-fold.scm (local-type-fold)
* module/language/cps/types.scm (successor-count, infer-types)
* module/language/cps/utils.scm (compute-function-body)
  (compute-successors, compute-predecessors)
* module/language/cps/verify.scm (compute-available-definitions)
  (check-valid-var-uses, check-arities): Add support for new term.

module/language/cps.scm

@@ -1,6 +1,6 @@
 ;;; Continuation-passing style (CPS) intermediate language (IL)
 
-;; Copyright (C) 2013, 2014, 2015, 2017, 2018 Free Software Foundation, Inc.
+;; Copyright (C) 2013-2015,2017-2018,2020 Free Software Foundation, Inc.
 
 ;;;; This library is free software; you can redistribute it and/or
 ;;;; modify it under the terms of the GNU Lesser General Public
@@ -127,7 +127,7 @@
             $kreceive $kargs $kfun $ktail $kclause
 
             ;; Terms.
-            $continue $branch $prompt $throw
+            $continue $branch $switch $prompt $throw
 
             ;; Expressions.
             $const $prim $fun $rec $const-fun $code
@@ -180,6 +180,7 @@
 ;; Terms.
 (define-cps-type $continue k src exp)
 (define-cps-type $branch kf kt src op param args)
+(define-cps-type $switch kf kt* src arg)
 (define-cps-type $prompt k kh src escape? tag)
 (define-cps-type $throw src op param args)
 
@@ -221,7 +222,7 @@
      (make-$kclause (build-arity arity) kbody kalternate))))
 
 (define-syntax build-term
-  (syntax-rules (unquote $continue $branch $prompt $throw)
+  (syntax-rules (unquote $continue $branch $switch $prompt $throw)
     ((_ (unquote exp))
      exp)
     ((_ ($continue k src exp))
@@ -232,6 +233,8 @@
      (make-$branch kf kt src op param (list arg ...)))
     ((_ ($branch kf kt src op param args))
      (make-$branch kf kt src op param args))
+    ((_ ($switch kf kt* src arg))
+     (make-$switch kf kt* src arg))
     ((_ ($prompt k kh src escape? tag))
      (make-$prompt k kh src escape? tag))
     ((_ ($throw src op param (unquote args)))
@@ -299,6 +302,8 @@
      (build-term ($continue k (src exp) ,(parse-cps exp))))
     (('branch kf kt op param arg ...)
      (build-term ($branch kf kt (src exp) op param arg)))
+    (('switch kf (kt* ...) arg)
+     (build-term ($switch kf kt* (src exp) arg)))
     (('prompt k kh escape? tag)
      (build-term ($prompt k kh (src exp) escape? tag)))
     (('throw op param arg ...)
@@ -350,6 +355,8 @@
      `(continue ,k ,(unparse-cps exp)))
     (($ $branch kf kt src op param args)
      `(branch ,kf ,kt ,op ,param ,@args))
+    (($ $switch kf kt* src arg)
+     `(switch ,kf ,kt* ,arg))
     (($ $prompt k kh src escape? tag)
      `(prompt ,k ,kh ,escape? ,tag))
     (($ $throw src op param args)