Port elide-values pass to CPS2

* module/language/cps2/elide-values.scm: New file.
* module/language/cps2/optimize.scm (optimize): Wire up elide-values.
* module/Makefile.am: Add new file.

module/Makefile.am

@@ -153,6 +153,7 @@ CPS2_LANG_SOURCES =						\
   language/cps2/contification.scm				\
   language/cps2/dce.scm						\
   language/cps2/effects-analysis.scm				\
+  language/cps2/elide-values.scm				\
   language/cps2/prune-top-level-scopes.scm			\
   language/cps2/renumber.scm					\
   language/cps2/optimize.scm					\

module/language/cps2/elide-values.scm

@@ -0,0 +1,88 @@
+;;; Continuation-passing style (CPS) intermediate language (IL)
+
+;; Copyright (C) 2013, 2014, 2015 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
+;;;; License as published by the Free Software Foundation; either
+;;;; version 3 of the License, or (at your option) any later version.
+;;;;
+;;;; This library is distributed in the hope that it will be useful,
+;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;;; Lesser General Public License for more details.
+;;;;
+;;;; You should have received a copy of the GNU Lesser General Public
+;;;; License along with this library; if not, write to the Free Software
+;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+;;; Commentary:
+;;;
+;;; Primcalls that don't correspond to VM instructions are treated as if
+;;; they are calls, and indeed the later reify-primitives pass turns
+;;; them into calls.  Because no return arity checking is done for these
+;;; primitives, if a later optimization pass simplifies the primcall to
+;;; a VM operation, the tail of the simplification has to be a
+;;; primcall to 'values.  Most of these primcalls can be elided, and
+;;; that is the job of this pass.
+;;;
+;;; Code:
+
+(define-module (language cps2 elide-values)
+  #:use-module (ice-9 match)
+  #:use-module (language cps2)
+  #:use-module (language cps2 utils)
+  #:use-module (language cps2 with-cps)
+  #:use-module (language cps intmap)
+  #:export (elide-values))
+
+(define (inline-values cps k src args)
+  (match (intmap-ref cps k)
+    (($ $ktail)
+     (with-cps cps
+       (build-term
+         ($continue k src ($values args)))))
+    (($ $kreceive ($ $arity req () rest () #f) kargs)
+     (cond
+      ((and (not rest) (= (length args) (length req)))
+       (with-cps cps
+         (build-term
+           ($continue kargs src ($values args)))))
+      ((and rest (>= (length args) (length req)))
+       (let ()
+         (define (build-rest cps k tail)
+           (match tail
+             (()
+              (with-cps cps
+                (build-term ($continue k src ($const '())))))
+             ((v . tail)
+              (with-cps cps
+                (letv rest)
+                (letk krest ($kargs ('rest) (rest)
+                              ($continue k src ($primcall 'cons (v rest)))))
+                ($ (build-rest krest tail))))))
+         (with-cps cps
+           (letv rest)
+           (letk krest ($kargs ('rest) (rest)
+                         ($continue kargs src
+                           ($values ,(append (list-head args (length req))
+                                             (list rest))))))
+           ($ (build-rest krest (list-tail args (length req)))))))
+      (else (with-cps cps #f))))))
+
+(define (elide-values conts)
+  (with-fresh-name-state conts
+    (persistent-intmap
+     (intmap-fold
+      (lambda (label cont out)
+        (match cont
+          (($ $kargs names vars ($ $continue k src ($ $primcall 'values args)))
+           (call-with-values (lambda () (inline-values out k src args))
+             (lambda (out term)
+               (if term
+                   (let ((cont (build-cont ($kargs names vars ,term))))
+                     (intmap-replace! out label cont))
+                   out))))
+          (_ out)))
+      conts
+      conts))))

module/language/cps2/optimize.scm

@@ -27,6 +27,7 @@
   #:use-module (language cps2 constructors)
   #:use-module (language cps2 contification)
   #:use-module (language cps2 dce)
+  #:use-module (language cps2 elide-values)
   #:use-module (language cps2 prune-top-level-scopes)
   #:use-module (language cps2 simplify)
   #:use-module (language cps2 specialize-primcalls)
@@ -62,7 +63,7 @@
   (run-pass! contify #:contify? #t)
   (run-pass! inline-constructors #:inline-constructors? #t)
   (run-pass! specialize-primcalls #:specialize-primcalls? #t)
-  ;; (run-pass! elide-values #:elide-values? #t)
+  (run-pass! elide-values #:elide-values? #t)
   ;; (run-pass! prune-bailouts #:prune-bailouts? #t)
   ;; (run-pass! eliminate-common-subexpressions #:cse? #t)
   ;; (run-pass! type-fold #:type-fold? #t)