the dynamic stack is really a stack now, instead of a list

* libguile/dynstack.h:
* libguile/dynstack.c: New files, implementing the dynamic stack as a
  true stack instead of a linked list.  This lowers the cost of
  dynwinds: frames, winders, prompts, with-fluids, and dynamic-wind.
  For the most part, we allocate these items directly on the stack.

* libguile/dynwinds.h:
* libguile/dynwinds.c: Adapt all manipulators of the wind stack to use
  interfaces from dynstack.c.  Remove heap-allocated winder and frame
  object types.
  (scm_dowinds, scm_i_dowinds): Remove these.  The first was exported,
  but it was not a public interface.

* libguile/continuations.c:
* libguile/continuations.h (scm_t_contregs): Continuation objects
  reference scm_t_dynstack* values now.  Adapt to the new interfaces.

* libguile/control.c:
* libguile/control.h: There is no longer a scm_tc7_prompt kind of object
  that can be allocated on the heap.  Instead, the prompt flags, key,
  and registers are pushed on the dynwind stack.  (The registers are
  still on the heap.)  Also, since the vm_cont will reference the
  dynwinds, make the partial continuation stub take just one extra arg,
  instead of storing the intwinds separately in the object table.

* libguile/fluids.c:
* libguile/fluids.h: No more with-fluids objects; instead, the fluids go
  on the dynstack.  The values still have to be on the heap, though.
  (scm_prepare_fluids, scm_swap_fluids): New internal functions,
  replacing scm_i_make_with_fluids and scm_i_swap_with_fluids.

* libguile/print.c: Remove prompt and with-fluids printers.

* libguile/tags.h: Revert prompt and with-fluids tc7 values to what they
  were before they were allocated.

* libguile/vm-i-system.c (partial_cont_call): Just pop the vmcont, the
  intwinds will not be passed as a second arg.  Rewind the dynamic stack
  from within the VM, so that any rewinder sees valid prompt entries.
  (call_cc, tail_call_cc): Adapt to pass the dynstack to
  scm_i_vm_capture_stack.
  (prompt, wind, unwind, wind_fluids, unwind_fluids): Adapt to the new
  interfaces.

* libguile/vm.h (scm_i_capture_current_stack): Rename from
  scm_i_vm_capture_continuation.
  (scm_i_vm_capture_stack): Take a dynstack as an argument.
* libguile/vm.c (vm_reinstate_partial_continuation): Don't wind here, as
  that could result in winders seeing invalid prompts.

* libguile/eval.c:
* libguile/root.c:
* libguile/stacks.c:
* libguile/threads.c:
* libguile/threads.h:
* libguile/throw.c: Adapt other users of dynwinds to use the dynstack.

libguile/stacks.c

@@ -1,5 +1,5 @@
 /* A stack holds a frame chain
- * Copyright (C) 1996,1997,2000,2001, 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation
+ * Copyright (C) 1996,1997,2000,2001, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Free Software Foundation
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -95,19 +95,17 @@ stack_depth (SCM frame)
  * encountered.
  */
 
-static SCM
+static SCM*
 find_prompt (SCM key)
 {
-  SCM winds;
-  for (winds = scm_i_dynwinds (); scm_is_pair (winds); winds = scm_cdr (winds))
-    {
-      SCM elt = scm_car (winds);
-      if (SCM_PROMPT_P (elt) && scm_is_eq (SCM_PROMPT_TAG (elt), key))
-        return elt;
-    }
-  scm_misc_error ("make-stack", "Prompt tag not found while narrowing stack",
-                  scm_list_1 (key));
-  return SCM_BOOL_F; /* not reached */
+  scm_t_prompt_registers *regs;
+
+  if (!scm_dynstack_find_prompt (&SCM_I_CURRENT_THREAD->dynstack, key,
+                                 &regs, NULL))
+    scm_misc_error ("make-stack", "Prompt tag not found while narrowing stack",
+                    scm_list_1 (key));
+
+  return regs->fp;
 }
 
 static void
@@ -136,10 +134,9 @@ narrow_stack (SCM stack, long inner, SCM inner_key, long outer, SCM outer_key)
     {
       /* Cut until the given prompt tag is seen. FIXME, assumes prompt tags are
          symbols. */
-      SCM prompt = find_prompt (inner_key);
+      SCM *fp = find_prompt (inner_key);
       for (; len; len--, frame = scm_frame_previous (frame))
-        if (SCM_PROMPT_REGISTERS (prompt)->fp
-            == SCM_VM_FRAME_FP (frame) - SCM_VM_FRAME_OFFSET (frame))
+        if (fp == SCM_VM_FRAME_FP (frame) - SCM_VM_FRAME_OFFSET (frame))
           break;
     }
   else
@@ -171,13 +168,12 @@ narrow_stack (SCM stack, long inner, SCM inner_key, long outer, SCM outer_key)
     {
       /* Cut until the given prompt tag is seen. FIXME, assumes prompt tags are
          symbols. */
-      SCM prompt = find_prompt (outer_key);
+      SCM *fp = find_prompt (outer_key);
       while (len)
         {
           frame = scm_stack_ref (stack, scm_from_long (len - 1));
           len--;
-          if (SCM_PROMPT_REGISTERS (prompt)->fp
-              == SCM_VM_FRAME_FP (frame) - SCM_VM_FRAME_OFFSET (frame))
+          if (fp == SCM_VM_FRAME_FP (frame) - SCM_VM_FRAME_OFFSET (frame))
             break;
         }
     }
@@ -257,7 +253,7 @@ SCM_DEFINE (scm_make_stack, "make-stack", 1, 0, 1,
       SCM cont;
       struct scm_vm_cont *c;
 
-      cont = scm_i_vm_capture_continuation (scm_the_vm ());
+      cont = scm_i_capture_current_stack ();
       c = SCM_VM_CONT_DATA (cont);
 
       frame = scm_c_make_frame (cont, c->fp + c->reloc,