FTR, testing and reporting only, not to be installed.

Index: gcc/cfgexpand.c
===================================================================
--- gcc/cfgexpand.c.orig	2011-02-10 09:27:16.004373533 -0200
+++ gcc/cfgexpand.c	2011-02-10 09:29:49.418374663 -0200
@@ -1311,18 +1311,41 @@ create_stack_guard (void)
   crtl->stack_protect_guard = guard;
 }
 
+/* A subroutine of expand_used_vars.  Walk down through the BLOCK tree
+   expanding variables.  Those variables that can be put into registers
+   are allocated pseudos; those that can't are put on the stack.
+
+   TOPLEVEL is true if this is the outermost BLOCK.  */
+
+static HOST_WIDE_INT
+account_used_vars_for_block (tree block, bool toplevel)
+{
+  tree t;
+  HOST_WIDE_INT size = 0;
+
+  /* Expand all variables at this level.  */
+  for (t = BLOCK_VARS (block); t ; t = DECL_CHAIN (t))
+    size += expand_one_var (t, toplevel, false);
+
+  /* Expand all variables at containing levels.  */
+  for (t = BLOCK_SUBBLOCKS (block); t ; t = BLOCK_CHAIN (t))
+    size += account_used_vars_for_block (t, false);
+
+  return size;
+}
+
 /* Prepare for expanding variables.  */
 static void
-init_vars_expansion (void)
+init_vars_expansion (tree decl)
 {
   tree t;
   unsigned ix;
   /* Set TREE_USED on all variables in the local_decls.  */
-  FOR_EACH_LOCAL_DECL (cfun, ix, t)
+  FOR_EACH_LOCAL_DECL (DECL_STRUCT_FUNCTION (decl), ix, t)
     TREE_USED (t) = 1;
 
   /* Clear TREE_USED on all variables associated with a block scope.  */
-  clear_tree_used (DECL_INITIAL (current_function_decl));
+  clear_tree_used (DECL_INITIAL (decl));
 
   /* Initialize local stack smashing state.  */
   has_protected_decls = false;
@@ -1354,6 +1377,8 @@ HOST_WIDE_INT
 estimated_stack_frame_size (struct cgraph_node *node)
 {
   HOST_WIDE_INT size = 0;
+  HOST_WIDE_INT delta;
+  unsigned ix;
   size_t i;
   tree var;
   referenced_var_iterator rvi;
@@ -1377,6 +1402,34 @@ estimated_stack_frame_size (struct cgrap
       fini_vars_expansion ();
     }
 
+  delta = size;
+
+  init_vars_expansion (node->decl);
+
+  FOR_EACH_LOCAL_DECL (fn, ix, var)
+    {
+      /* TREE_USED marks local variables that do not appear in lexical
+	 blocks.  We don't want to expand those that do twice.  */
+      if (TREE_USED (var))
+        delta -= expand_one_var (var, true, false);
+    }
+  delta -= account_used_vars_for_block (DECL_INITIAL (node->decl), true);
+
+  if (stack_vars_num > 0)
+    {
+      /* Fake sorting the stack vars for account_stack_vars ().  */
+      stack_vars_sorted = XNEWVEC (size_t, stack_vars_num);
+      for (i = 0; i < stack_vars_num; ++i)
+	stack_vars_sorted[i] = i;
+      delta -= account_stack_vars ();
+      fini_vars_expansion ();
+    }
+
+  if (delta)
+    inform (input_location,
+	    "guestimated stack size for %q+D changed by %li to %li",
+	    node->decl, (long)delta, (long)size);
+
   current_function_decl = save;
   pop_cfun ();
 
@@ -1400,7 +1453,7 @@ expand_used_vars (void)
     frame_phase = off ? align - off : 0;
   }
 
-  init_vars_expansion ();
+  init_vars_expansion (current_function_decl);
 
   for (i = 0; i < SA.map->num_partitions; i++)
     {