--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/stack-ptr-mod.c	Fri Jul 17 14:47:48 2009 +0900
@@ -0,0 +1,111 @@
+/* Discover if the stack pointer is modified in a function. 
+   Copyright (C) 2007, 2008
+   Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "tree.h"
+#include "rtl.h"
+#include "regs.h"
+#include "expr.h"
+#include "tree-pass.h"
+#include "basic-block.h"
+#include "flags.h"
+#include "output.h"
+#include "df.h"
+
+/* Determine if the stack pointer is constant over the life of the function.
+   Only useful before prologues have been emitted.  */
+
+static void
+notice_stack_pointer_modification_1 (rtx x, const_rtx pat ATTRIBUTE_UNUSED,
+				     void *data ATTRIBUTE_UNUSED)
+{
+  if (x == stack_pointer_rtx
+      /* The stack pointer is only modified indirectly as the result
+	 of a push until later.  See the comments in rtl.texi
+	 regarding Embedded Side-Effects on Addresses.  */
+      || (MEM_P (x)
+	  && GET_RTX_CLASS (GET_CODE (XEXP (x, 0))) == RTX_AUTOINC
+	  && XEXP (XEXP (x, 0), 0) == stack_pointer_rtx))
+    current_function_sp_is_unchanging = 0;
+}
+
+static void
+notice_stack_pointer_modification (void)
+{
+  basic_block bb;
+  rtx insn;
+
+  /* Assume that the stack pointer is unchanging if alloca hasn't
+     been used.  */
+  current_function_sp_is_unchanging = !cfun->calls_alloca;
+  if (current_function_sp_is_unchanging)
+    FOR_EACH_BB (bb)
+      FOR_BB_INSNS (bb, insn)
+        {
+	  if (INSN_P (insn))
+	    {
+	      /* Check if insn modifies the stack pointer.  */
+	      note_stores (PATTERN (insn),
+			   notice_stack_pointer_modification_1,
+			   NULL);
+	      if (! current_function_sp_is_unchanging)
+		return;
+	    }
+	}
+
+  /* The value coming into this pass was 0, and the exit block uses
+     are based on this.  If the value is now 1, we need to redo the
+     exit block uses.  */
+  if (df && current_function_sp_is_unchanging)
+    df_update_exit_block_uses ();
+}
+
+  /* Some targets can emit simpler epilogues if they know that sp was
+     not ever modified during the function.  After reload, of course,
+     we've already emitted the epilogue so there's no sense searching.  */
+
+static unsigned int
+rest_of_handle_stack_ptr_mod (void)
+{
+  notice_stack_pointer_modification ();
+  return 0;
+}
+
+struct rtl_opt_pass pass_stack_ptr_mod =
+{
+ {
+  RTL_PASS,
+  NULL,		                        /* name */
+  NULL,                                 /* gate */
+  rest_of_handle_stack_ptr_mod,         /* execute */
+  NULL,                                 /* sub */
+  NULL,                                 /* next */
+  0,                                    /* static_pass_number */
+  0,                                    /* tv_id */
+  0,                                    /* properties_required */
+  0,                                    /* properties_provided */
+  0,                                    /* properties_destroyed */
+  0,                                    /* todo_flags_start */
+  0                                     /* todo_flags_finish */
+ }
+};