From e36787bdebb7403ea180a140d88cf695d5eaea4c Mon Sep 17 00:00:00 2001
From: Vincent St-Amour <stamourv@racket-lang.org>
Date: Thu, 4 Nov 2010 11:21:40 -0400
Subject: [PATCH] Fixed potential danger with fixnum optimizations. (cherry
 picked from commit c0a6137c67228933ad94d88409ffd86e30e922ae)

---
 .../typed-scheme/typecheck/tc-expr-unit.rkt     | 17 ++++++++++++++---
 collects/typed-scheme/types/abbrev.rkt          |  3 +++
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/collects/typed-scheme/typecheck/tc-expr-unit.rkt b/collects/typed-scheme/typecheck/tc-expr-unit.rkt
index d0788b9a7c..0fd0402a41 100644
--- a/collects/typed-scheme/typecheck/tc-expr-unit.rkt
+++ b/collects/typed-scheme/typecheck/tc-expr-unit.rkt
@@ -21,6 +21,17 @@
 (import tc-if^ tc-lambda^ tc-app^ tc-let^ check-subforms^)
 (export tc-expr^)
 
+;; Is the number a fixnum on all the platforms Racket supports?
+;; This check is done at compile time to typecheck literals.
+;; Since a zo file compiled on a 64-bit system can be used on 32-bit
+;; systems, we can't use the host fixnum? predicate, or large 64-bit
+;; fixnums will typecheck as fixnums but not be actual fixnums on the
+;; target system. In combination with fixnum typed optimizations, bad
+;; things could happen.
+(define (portable-fixnum? n)
+  (and (exact-integer? n)
+       (< n (expt 2 31))))
+
 ;; return the type of a literal value
 ;; scheme-value -> type
 (define (tc-literal v-stx [expected #f])
@@ -34,9 +45,9 @@
     [i:boolean (-val (syntax-e #'i))]
     [i:identifier (-val (syntax-e #'i))]
     [0 -Zero]
-    [(~var i (3d (conjoin number? fixnum? positive?))) -PositiveFixnum]
-    [(~var i (3d (conjoin number? fixnum? negative?))) -NegativeFixnum]
-    [(~var i (3d (conjoin number? fixnum?))) -Fixnum]
+    [(~var i (3d (conjoin number? portable-fixnum? positive?))) -PositiveFixnum]
+    [(~var i (3d (conjoin number? portable-fixnum? negative?))) -NegativeFixnum]
+    [(~var i (3d (conjoin number? portable-fixnum?))) -Fixnum]
     [(~var i (3d exact-positive-integer?)) -ExactPositiveInteger]
     [(~var i (3d exact-nonnegative-integer?)) -ExactNonnegativeInteger]
     [(~var i (3d exact-integer?)) -Integer]
diff --git a/collects/typed-scheme/types/abbrev.rkt b/collects/typed-scheme/types/abbrev.rkt
index e69967b355..68bbdbfc4d 100644
--- a/collects/typed-scheme/types/abbrev.rkt
+++ b/collects/typed-scheme/types/abbrev.rkt
@@ -174,6 +174,9 @@
 (define -ExactPositiveInteger
   (make-Base 'Exact-Positive-Integer #'exact-positive-integer?))
 
+;; We can safely use the fixnum? prediate here, unlike in tc-expr-unit.
+;; The fixnum? here will be part of the generated contracts, which run
+;; on the target system, so we're safe.
 (define -PositiveFixnum
   (make-Base 'Positive-Fixnum #'(and/c number? fixnum? positive?)))
 (define -NegativeFixnum