From c4a209b96ff7ea75d3d74aa956223768a352d6d9 Mon Sep 17 00:00:00 2001
From: Andy Wingo <wingo@pobox.com>
Date: Tue, 8 Apr 2014 21:41:42 +0200
Subject: [PATCH] New pass to avoid free variable creation for self-recursion

* module/language/cps/self-references.scm: New pass, avoids the need for
  self-recursion to allocate free variables.

* module/Makefile.am:
* module/language/cps/compile-bytecode.scm: Wire up the new pass.
---
 module/Makefile.am                       |  1 +
 module/language/cps/compile-bytecode.scm |  2 +
 module/language/cps/self-references.scm  | 79 ++++++++++++++++++++++++
 3 files changed, 82 insertions(+)
 create mode 100644 module/language/cps/self-references.scm

diff --git a/module/Makefile.am b/module/Makefile.am
index 335e14c4b..a6b20aff9 100644
--- a/module/Makefile.am
+++ b/module/Makefile.am
@@ -133,6 +133,7 @@ CPS_LANG_SOURCES =						\
   language/cps/prune-top-level-scopes.scm			\
   language/cps/reify-primitives.scm				\
   language/cps/renumber.scm					\
+  language/cps/self-references.scm				\
   language/cps/slot-allocation.scm				\
   language/cps/simplify.scm					\
   language/cps/spec.scm						\
diff --git a/module/language/cps/compile-bytecode.scm b/module/language/cps/compile-bytecode.scm
index 77edf643b..3d95b8c4a 100644
--- a/module/language/cps/compile-bytecode.scm
+++ b/module/language/cps/compile-bytecode.scm
@@ -40,6 +40,7 @@
   #:use-module (language cps prune-top-level-scopes)
   #:use-module (language cps reify-primitives)
   #:use-module (language cps renumber)
+  #:use-module (language cps self-references)
   #:use-module (language cps simplify)
   #:use-module (language cps slot-allocation)
   #:use-module (language cps specialize-primcalls)
@@ -72,6 +73,7 @@
          (exp (run-pass exp elide-values #:elide-values? #t))
          (exp (run-pass exp prune-bailouts #:prune-bailouts? #t))
          (exp (run-pass exp eliminate-common-subexpressions #:cse? #t))
+         (exp (run-pass exp resolve-self-references #:resolve-self-references? #t))
          (exp (run-pass exp eliminate-dead-code #:eliminate-dead-code? #t))
          (exp (run-pass exp simplify #:simplify? #t)))
     ;; Passes that are needed:
diff --git a/module/language/cps/self-references.scm b/module/language/cps/self-references.scm
new file mode 100644
index 000000000..bde37a60e
--- /dev/null
+++ b/module/language/cps/self-references.scm
@@ -0,0 +1,79 @@
+;;; Continuation-passing style (CPS) intermediate language (IL)
+
+;; Copyright (C) 2013, 2014 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:
+;;;
+;;; A pass that prunes successors of expressions that bail out.
+;;;
+;;; Code:
+
+(define-module (language cps self-references)
+  #:use-module (ice-9 match)
+  #:use-module (language cps)
+  #:export (resolve-self-references))
+
+(define* (resolve-self-references fun #:optional (env '()))
+  (define (subst var)
+    (or (assq-ref env var) var))
+
+  (define (visit-cont cont)
+    (rewrite-cps-cont cont
+      (($ $cont label ($ $kargs names vars body))
+       (label ($kargs names vars ,(visit-term body))))
+      (($ $cont label ($ $kentry self tail clause))
+       (label ($kentry self ,tail
+                ,(and clause (visit-cont clause)))))
+      (($ $cont label ($ $kclause arity body alternate))
+       (label ($kclause ,arity ,(visit-cont body)
+                        ,(and alternate (visit-cont alternate)))))
+      (_ ,cont)))
+
+  (define (visit-term term)
+    (rewrite-cps-term term
+      (($ $letrec names vars funs body)
+       ($letrec names vars (map visit-recursive-fun funs vars)
+                ,(visit-term body)))
+      (($ $letk conts body)
+       ($letk ,(map visit-cont conts)
+         ,(visit-term body)))
+      (($ $continue k src exp)
+       ($continue k src ,(visit-exp exp)))))
+
+  (define (visit-exp exp)
+    (rewrite-cps-exp exp
+      ((or ($ $void) ($ $const) ($ $prim)) ,exp)
+      (($ $fun) ,(resolve-self-references exp env))
+      (($ $call proc args)
+       ($call (subst proc) ,(map subst args)))
+      (($ $callk k proc args)
+       ($callk k (subst proc) ,(map subst args)))
+      (($ $primcall name args)
+       ($primcall name ,(map subst args)))
+      (($ $values args)
+       ($values ,(map subst args)))
+      (($ $prompt escape? tag handler)
+       ($prompt escape? (subst tag) handler))))
+
+  (define (visit-recursive-fun fun var)
+    (match fun
+      (($ $fun src meta free (and cont ($ $cont _ ($ $kentry self))))
+       (resolve-self-references fun (acons var self env)))))
+
+  (rewrite-cps-exp fun
+    (($ $fun src meta free cont)
+     ($fun src meta (map subst free) ,(visit-cont cont)))))