From eae7c5d5d7f0413b59b35f1e31e8f019336cfcd1 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Wed, 16 Nov 2011 20:23:25 -0700
Subject: [PATCH] fix place-GC problem with empty_self_modidx's shift cache

---
 src/racket/gc2/newgc.c  | 18 ++++++++++++++++++
 src/racket/src/module.c |  3 ++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/src/racket/gc2/newgc.c b/src/racket/gc2/newgc.c
index 8d6b3792a4..77d704a43c 100644
--- a/src/racket/gc2/newgc.c
+++ b/src/racket/gc2/newgc.c
@@ -2987,6 +2987,24 @@ void GC_mark2(const void *const_p, struct NewGC *gc)
       }
   }
 
+#if 0
+  if (page->size_class < 2) {
+    if (page->page_type == PAGE_TAGGED) {
+      void *q;
+      if (page->size_class)
+        q = MED_OBJHEAD(p, page->size) + 1;
+      else
+        q = p;
+      if (((objhead *)q)[-1].type == PAGE_TAGGED) {
+        if (!((objhead *)q)[-1].moved) {
+          if ((*(short *)q < 0) || (*(short *)q > 1000))
+            abort();
+        }
+      }
+    }
+  }
+#endif
+
 #ifdef NEWGC_BTC_ACCOUNT
   /* toss this over to the BTC mark routine if we're doing accounting */
   if(gc->doing_memory_accounting) { 
diff --git a/src/racket/src/module.c b/src/racket/src/module.c
index a8884b112d..53f203dd55 100644
--- a/src/racket/src/module.c
+++ b/src/racket/src/module.c
@@ -3435,7 +3435,8 @@ static Scheme_Object *do_modidx_shift(Scheme_Object *modidx,
         i = 0;
       } else {
         /* May have GCed: */
-        if (cvec && !sbm->shift_cache)
+        if (cvec && !sbm->shift_cache
+            && !SAME_OBJ((Scheme_Object *)sbm, empty_self_modidx))
           sbm->shift_cache = cvec;
 
         if (i >= c) {