From 42f74b5982c6d9d435c303ba59a1f847be65cb12 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Sat, 17 Nov 2012 10:01:22 -0700
Subject: [PATCH] JIT tweak: stack-clearing operations do not disturb registers

---
 src/racket/src/jitstate.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/racket/src/jitstate.c b/src/racket/src/jitstate.c
index a67bc4530d..3d6f272af9 100644
--- a/src/racket/src/jitstate.c
+++ b/src/racket/src/jitstate.c
@@ -762,11 +762,17 @@ int scheme_stack_safety(mz_jit_state *jitter, int cnt, int offset)
      that we make, so that whatever happens to be there isn't
      traversed in case of a GC. the value of JIT_RUNSTACK is
      handy to use as a "clear" value. */
-  int i;
+  int i, valid;
+
+  valid = mz_CURRENT_REG_STATUS_VALID();
+
   for (i = 0; i < cnt; i++) {
     mz_rs_stxi(i+offset, JIT_RUNSTACK);
     CHECK_LIMIT();
   }
+
+  if (valid) mz_SET_REG_STATUS_VALID(1);
+
   return 1;
 }