From 90a4a81274bcc12f9d6ca8c7259d2f0247d5b80c Mon Sep 17 00:00:00 2001
From: simonmar <unknown>
Date: Fri, 18 Nov 2005 14:24:47 +0000
Subject: [PATCH] [project @ 2005-11-18 14:24:47 by simonmar] Omit the
 __DISCARD__() call in FB_ if __GNUC__ >= 3.  It doesn't
 appear to be necessary now, and it prevents some gcc
 optimisations.

---
 ghc/includes/TailCalls.h |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/ghc/includes/TailCalls.h b/ghc/includes/TailCalls.h
index 750b398..f62b10e 100644
--- a/ghc/includes/TailCalls.h
+++ b/ghc/includes/TailCalls.h
@@ -251,6 +251,8 @@ but uses $$dyncall if necessary to cope, just in case you aren't.
   function and these markers is shredded by the mangler.
   -------------------------------------------------------------------------- */
 
+#ifndef FB_
+#if __GNUC__ < 3
 /*  The following __DISCARD__() has become necessary with gcc 2.96 on x86.
  *  It prevents gcc from moving stack manipulation code from the function
  *  body (aka the Real Code) into the function prologue, ie, from moving it
@@ -260,9 +262,17 @@ but uses $$dyncall if necessary to cope, just in case you aren't.
  *  it just doesn't choose to do it at the moment.
  *  -= chak
  */
- 
-#ifndef FB_
 #define FB_    __asm__ volatile ("--- BEGIN ---"); __DISCARD__ ();
+#else
+/* The __DISCARD__() doesn't appear to be necessary with gcc >= 3.2 at
+ * least, and it does cause some difficulty, preventing gcc from
+ * optimising around the beginning of the function.  In particular,
+ * gcc leaves some stack assignments in the prologue when the call is
+ * present. --SDM
+
+ */
+#define FB_    __asm__ volatile ("--- BEGIN ---");
+#endif
 #endif
 
 #ifndef FE_
-- 
1.7.10.4