From 053734c4c8c3e00d3faa47ad153f61c5bb18cdab Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Fri, 19 Aug 2011 03:34:56 -0600
Subject: [PATCH] fix compiler handling of top-/module-level constants

The JIT and bytecode compiler disagreed on the definition of
"constant". Now there are two levels: "constant" means constant across
all instantiations, and "fixed" means constant for a given instantation.
The JIT uses this distinction to generate direct-primitive calls
or not. (Without the distinction, a direct jump to `reverse' could
be wrong, because `racket/base' might get instantiated with the
JIT disabled or not.)

Also, fixed a bug in the JIT's `vector-set!' code in the case that
the target vector is a top-/module-level reference that is ready,
fixed, or constant.

original commit: 7eb2042bd9296235ae425fcc56a05931a65d47d4
---
 collects/compiler/decompile.rkt  | 14 +++++++++-----
 collects/compiler/zo-marshal.rkt |  4 ++--
 collects/compiler/zo-parse.rkt   |  7 +++++--
 3 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/collects/compiler/decompile.rkt b/collects/compiler/decompile.rkt
index ca9b60c7a5..903e6843ef 100644
--- a/collects/compiler/decompile.rkt
+++ b/collects/compiler/decompile.rkt
@@ -186,7 +186,7 @@
     [(struct def-values (ids rhs))
      `(define-values ,(map (lambda (tl)
                              (match tl
-                               [(struct toplevel (depth pos const? mutated?))
+                               [(struct toplevel (depth pos const? set-const?))
                                 (list-ref/protect (glob-desc-vars globs) pos 'def-vals)]))
                            ids)
         ,(decompile-expr rhs globs stack closed))]
@@ -250,10 +250,14 @@
   (match expr
     [(struct toplevel (depth pos const? ready?))
      (let ([id (list-ref/protect (glob-desc-vars globs) pos 'toplevel)])
-       (if (or no-check? const? ready?)
-           id
-           `(#%checked ,id)))]))
-             
+       (cond
+        [no-check? id]
+        [(and (not const?) (not ready?))
+         `(#%checked ,id)]
+        #;[(and const? ready?) `(#%const ,id)]
+        #;[const? `(#%iconst ,id)]
+        [else id]))]))
+
 (define (decompile-expr expr globs stack closed)
   (match expr
     [(struct toplevel (depth pos const? ready?))
diff --git a/collects/compiler/zo-marshal.rkt b/collects/compiler/zo-marshal.rkt
index 124b01c48c..e435a97080 100644
--- a/collects/compiler/zo-marshal.rkt
+++ b/collects/compiler/zo-marshal.rkt
@@ -554,8 +554,8 @@
                         (if (or const? ready?)
                             (cons pos
                                   (bitwise-ior 
-                                   (if const? #x1 0)
-                                   (if ready? #x2 0)))
+                                   (if const? #x2 0)
+                                   (if ready? #x1 0)))
                             pos))
                        out)]
        [(struct topsyntax (depth pos midpt))
diff --git a/collects/compiler/zo-parse.rkt b/collects/compiler/zo-parse.rkt
index d1aaf68478..3c559ec62b 100644
--- a/collects/compiler/zo-parse.rkt
+++ b/collects/compiler/zo-parse.rkt
@@ -33,10 +33,13 @@
 ;; Bytecode unmarshalers for various forms
 
 (define (read-toplevel v)
-  (define SCHEME_TOPLEVEL_CONST #x01)
-  (define SCHEME_TOPLEVEL_READY #x02)
+  (define SCHEME_TOPLEVEL_CONST #x02)
+  (define SCHEME_TOPLEVEL_READY #x01)
   (match v
     [(cons depth (cons pos flags))
+     ;; In the VM, the two flag bits are actually interpreted
+     ;; as a number when the toplevel is a reference, but we
+     ;; interpret the bits as flags here for backward compatibility.
      (make-toplevel depth pos 
                     (positive? (bitwise-and flags SCHEME_TOPLEVEL_CONST))
                     (positive? (bitwise-and flags SCHEME_TOPLEVEL_READY)))]