Replace return primcalls with $values

* module/language/cps/compile-bytecode.scm:
* module/language/cps/contification.scm:
* module/language/cps/slot-allocation.scm:
* module/language/cps/type-fold.scm:
* module/language/cps/verify.scm:
* module/language/tree-il/compile-cps.scm: Never generate a return
  primcall.  Instead use $values.

module/language/cps/compile-bytecode.scm

@@ -136,9 +136,7 @@
          (for-each (match-lambda
                     ((src . dst) (emit-mov asm (from-sp dst) (from-sp src))))
                    (lookup-parallel-moves label allocation))
-         (emit-return-values asm (1+ (length args))))
+         (emit-return-values asm (1+ (length args))))))
-        (($ $primcall 'return (arg))
-         (emit-return asm (from-sp (slot arg))))))
 
     (define (compile-value label exp dst)
       (match exp

module/language/cps/contification.scm

@@ -415,12 +415,9 @@ function set."
               ,(match (intmap-ref conts k*)
                  (($ $kreceive)
                   (match exp
-                    (($ $primcall 'return (val))
-                     (build-exp ($primcall 'values (val))))
                     (($ $call) exp)
-                    ;; Except for 'return, a primcall that can continue
+                    ;; A primcall that can continue to $ktail can also
-                    ;; to $ktail can also continue to $kreceive.  TODO:
+                    ;; continue to $kreceive.
-                    ;; replace 'return with 'values, for consistency.
                     (($ $primcall) exp)
                     (($ $values vals)
                      (build-exp ($primcall 'values vals)))))

module/language/cps/slot-allocation.scm

@@ -660,9 +660,6 @@ are comparable with eqv?.  A tmp slot may be used."
                     (call-size label (1+ (length args)) size))
                    (($ $values args)
                     (shuffle-size (get-shuffles label) size))
-                   (($ $primcall 'return (arg))
-                    ;; Return will shuffle arg into fp-relative slot 1.
-                    (max size 2))
                    (_ size)))))
       (($ $kreceive)
        (values frame-sizes clause

module/language/cps/type-fold.scm

@@ -276,7 +276,7 @@
            (with-cps cps
              (letv bool)
              (letk kbool ($kargs (#f) (bool)
-                           ($continue k src ($primcall 'return (bool)))))
+                           ($continue k src ($values (bool)))))
              ($ (convert-to-logtest kbool)))))
         (with-cps cps #f))))
 

module/language/cps/verify.scm

@@ -258,9 +258,7 @@ definitions that are available at LABEL."
           (when (false-if-exception (prim-arity name))
             (error "primitive should continue to $kargs, not $kreceive" name)))
          (($ $ktail)
-          (unless (eq? name 'return)
+          (error "primitive should continue to $kargs, not $ktail" name))))
-            (when (false-if-exception (prim-arity name))
-              (error "primitive should continue to $kargs, not $ktail" name))))))
       (($ $prompt escape? tag handler)
        (assert-nullary)
        (match (intmap-ref conts handler)

module/language/tree-il/compile-cps.scm

@@ -249,7 +249,7 @@
         (with-cps cps
           (let$ body (with-cps-constants ((unspecified *unspecified*))
                        (build-term
-                         ($continue k src ($primcall 'return (unspecified))))))
+                         ($continue k src ($values (unspecified))))))
           (letk kvoid ($kargs () () ,body))
           kvoid))
        (($ $kreceive arity kargs)
@@ -287,7 +287,7 @@
         (with-cps cps
           (letv val)
           (letk kval ($kargs ('val) (val)
-                       ($continue k src ($primcall 'return (val)))))
+                       ($continue k src ($values (val)))))
           kval))
        (($ $kreceive arity kargs)
         (match arity