except.h (in_same_eh_region): New prototype.

[thirdparty/gcc.git] / gcc / except.c

/* Implements exception handling.
   Copyright (C) 1989, 92-96, 1997 Free Software Foundation, Inc.
   Contributed by Mike Stump <mrs@cygnus.com>.

This file is part of GNU CC.

GNU CC 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 2, or (at your option)
any later version.

GNU CC 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 GNU CC; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */


/* An exception is an event that can be signaled from within a
   function. This event can then be "caught" or "trapped" by the
   callers of this function. This potentially allows program flow to
   be transferred to any arbitrary code associated with a function call
   several levels up the stack.

   The intended use for this mechanism is for signaling "exceptional
   events" in an out-of-band fashion, hence its name. The C++ language
   (and many other OO-styled or functional languages) practically
   requires such a mechanism, as otherwise it becomes very difficult
   or even impossible to signal failure conditions in complex
   situations.  The traditional C++ example is when an error occurs in
   the process of constructing an object; without such a mechanism, it
   is impossible to signal that the error occurs without adding global
   state variables and error checks around every object construction.

   The act of causing this event to occur is referred to as "throwing
   an exception". (Alternate terms include "raising an exception" or
   "signaling an exception".) The term "throw" is used because control
   is returned to the callers of the function that is signaling the
   exception, and thus there is the concept of "throwing" the
   exception up the call stack.

   There are two major codegen options for exception handling.  The
   flag -fsjlj-exceptions can be used to select the setjmp/longjmp
   approach, which is the default.  -fno-sjlj-exceptions can be used to
   get the PC range table approach.  While this is a compile time
   flag, an entire application must be compiled with the same codegen
   option.  The first is a PC range table approach, the second is a
   setjmp/longjmp based scheme.  We will first discuss the PC range
   table approach, after that, we will discuss the setjmp/longjmp
   based approach.

   It is appropriate to speak of the "context of a throw". This
   context refers to the address where the exception is thrown from,
   and is used to determine which exception region will handle the
   exception.

   Regions of code within a function can be marked such that if it
   contains the context of a throw, control will be passed to a
   designated "exception handler". These areas are known as "exception
   regions".  Exception regions cannot overlap, but they can be nested
   to any arbitrary depth. Also, exception regions cannot cross
   function boundaries.

   Exception handlers can either be specified by the user (which we
   will call a "user-defined handler") or generated by the compiler
   (which we will designate as a "cleanup"). Cleanups are used to
   perform tasks such as destruction of objects allocated on the
   stack.

   In the current implementation, cleanups are handled by allocating an
   exception region for the area that the cleanup is designated for,
   and the handler for the region performs the cleanup and then
   rethrows the exception to the outer exception region. From the
   standpoint of the current implementation, there is little
   distinction made between a cleanup and a user-defined handler, and
   the phrase "exception handler" can be used to refer to either one
   equally well. (The section "Future Directions" below discusses how
   this will change).

   Each object file that is compiled with exception handling contains
   a static array of exception handlers named __EXCEPTION_TABLE__.
   Each entry contains the starting and ending addresses of the
   exception region, and the address of the handler designated for
   that region.

   If the target does not use the DWARF 2 frame unwind information, at
   program startup each object file invokes a function named
   __register_exceptions with the address of its local
   __EXCEPTION_TABLE__. __register_exceptions is defined in libgcc2.c, and
   is responsible for recording all of the exception regions into one list
   (which is kept in a static variable named exception_table_list).

   On targets that support crtstuff.c, the unwind information
   is stored in a section named .eh_frame and the information for the
   entire shared object or program is registered with a call to
   __register_frame_info.  On other targets, the information for each
   translation unit is registered from the file generated by collect2.
   __register_frame_info is defined in frame.c, and is responsible for
   recording all of the unwind regions into one list (which is kept in a
   static variable named unwind_table_list).

   The function __throw is actually responsible for doing the
   throw. On machines that have unwind info support, __throw is generated
   by code in libgcc2.c, otherwise __throw is generated on a
   per-object-file basis for each source file compiled with
   -fexceptions by the the C++ frontend.  Before __throw is invoked,
   the current context of the throw needs to be placed in the global
   variable __eh_pc.

   __throw attempts to find the appropriate exception handler for the 
   PC value stored in __eh_pc by calling __find_first_exception_table_match
   (which is defined in libgcc2.c). If __find_first_exception_table_match
   finds a relevant handler, __throw transfers control directly to it.

   If a handler for the context being thrown from can't be found, __throw
   walks (see Walking the stack below) the stack up the dynamic call chain to
   continue searching for an appropriate exception handler based upon the
   caller of the function it last sought a exception handler for.  It stops
   then either an exception handler is found, or when the top of the
   call chain is reached.

   If no handler is found, an external library function named
   __terminate is called.  If a handler is found, then we restart
   our search for a handler at the end of the call chain, and repeat
   the search process, but instead of just walking up the call chain,
   we unwind the call chain as we walk up it.

   Internal implementation details:

   To associate a user-defined handler with a block of statements, the
   function expand_start_try_stmts is used to mark the start of the
   block of statements with which the handler is to be associated
   (which is known as a "try block"). All statements that appear
   afterwards will be associated with the try block.

   A call to expand_start_all_catch marks the end of the try block,
   and also marks the start of the "catch block" (the user-defined
   handler) associated with the try block.

   This user-defined handler will be invoked for *every* exception
   thrown with the context of the try block. It is up to the handler
   to decide whether or not it wishes to handle any given exception,
   as there is currently no mechanism in this implementation for doing
   this. (There are plans for conditionally processing an exception
   based on its "type", which will provide a language-independent
   mechanism).

   If the handler chooses not to process the exception (perhaps by
   looking at an "exception type" or some other additional data
   supplied with the exception), it can fall through to the end of the
   handler. expand_end_all_catch and expand_leftover_cleanups
   add additional code to the end of each handler to take care of
   rethrowing to the outer exception handler.

   The handler also has the option to continue with "normal flow of
   code", or in other words to resume executing at the statement
   immediately after the end of the exception region. The variable
   caught_return_label_stack contains a stack of labels, and jumping
   to the topmost entry's label via expand_goto will resume normal
   flow to the statement immediately after the end of the exception
   region. If the handler falls through to the end, the exception will
   be rethrown to the outer exception region.

   The instructions for the catch block are kept as a separate
   sequence, and will be emitted at the end of the function along with
   the handlers specified via expand_eh_region_end. The end of the
   catch block is marked with expand_end_all_catch.

   Any data associated with the exception must currently be handled by
   some external mechanism maintained in the frontend.  For example,
   the C++ exception mechanism passes an arbitrary value along with
   the exception, and this is handled in the C++ frontend by using a
   global variable to hold the value. (This will be changing in the
   future.)

   The mechanism in C++ for handling data associated with the
   exception is clearly not thread-safe. For a thread-based
   environment, another mechanism must be used (possibly using a
   per-thread allocation mechanism if the size of the area that needs
   to be allocated isn't known at compile time.)

   Internally-generated exception regions (cleanups) are marked by
   calling expand_eh_region_start to mark the start of the region,
   and expand_eh_region_end (handler) is used to both designate the
   end of the region and to associate a specified handler/cleanup with
   the region. The rtl code in HANDLER will be invoked whenever an
   exception occurs in the region between the calls to
   expand_eh_region_start and expand_eh_region_end. After HANDLER is
   executed, additional code is emitted to handle rethrowing the
   exception to the outer exception handler. The code for HANDLER will
   be emitted at the end of the function.

   TARGET_EXPRs can also be used to designate exception regions. A
   TARGET_EXPR gives an unwind-protect style interface commonly used
   in functional languages such as LISP. The associated expression is
   evaluated, and whether or not it (or any of the functions that it
   calls) throws an exception, the protect expression is always
   invoked. This implementation takes care of the details of
   associating an exception table entry with the expression and
   generating the necessary code (it actually emits the protect
   expression twice, once for normal flow and once for the exception
   case). As for the other handlers, the code for the exception case
   will be emitted at the end of the function.

   Cleanups can also be specified by using add_partial_entry (handler)
   and end_protect_partials. add_partial_entry creates the start of
   a new exception region; HANDLER will be invoked if an exception is
   thrown with the context of the region between the calls to
   add_partial_entry and end_protect_partials. end_protect_partials is
   used to mark the end of these regions. add_partial_entry can be
   called as many times as needed before calling end_protect_partials.
   However, end_protect_partials should only be invoked once for each
   group of calls to add_partial_entry as the entries are queued
   and all of the outstanding entries are processed simultaneously
   when end_protect_partials is invoked. Similarly to the other
   handlers, the code for HANDLER will be emitted at the end of the
   function.

   The generated RTL for an exception region includes
   NOTE_INSN_EH_REGION_BEG and NOTE_INSN_EH_REGION_END notes that mark
   the start and end of the exception region. A unique label is also
   generated at the start of the exception region, which is available
   by looking at the ehstack variable. The topmost entry corresponds
   to the current region.

   In the current implementation, an exception can only be thrown from
   a function call (since the mechanism used to actually throw an
   exception involves calling __throw).  If an exception region is
   created but no function calls occur within that region, the region
   can be safely optimized away (along with its exception handlers)
   since no exceptions can ever be caught in that region.  This
   optimization is performed unless -fasynchronous-exceptions is
   given.  If the user wishes to throw from a signal handler, or other
   asynchronous place, -fasynchronous-exceptions should be used when
   compiling for maximally correct code, at the cost of additional
   exception regions.  Using -fasynchronous-exceptions only produces
   code that is reasonably safe in such situations, but a correct
   program cannot rely upon this working.  It can be used in failsafe
   code, where trying to continue on, and proceeding with potentially
   incorrect results is better than halting the program.


   Walking the stack:

   The stack is walked by starting with a pointer to the current
   frame, and finding the pointer to the callers frame.  The unwind info
   tells __throw how to find it.

   Unwinding the stack:

   When we use the term unwinding the stack, we mean undoing the
   effects of the function prologue in a controlled fashion so that we
   still have the flow of control.  Otherwise, we could just return
   (jump to the normal end of function epilogue).

   This is done in __throw in libgcc2.c when we know that a handler exists
   in a frame higher up the call stack than its immediate caller.

   To unwind, we find the unwind data associated with the frame, if any.
   If we don't find any, we call the library routine __terminate.  If we do
   find it, we use the information to copy the saved register values from
   that frame into the register save area in the frame for __throw, return
   into a stub which updates the stack pointer, and jump to the handler.
   The normal function epilogue for __throw handles restoring the saved
   values into registers.

   When unwinding, we use this method if we know it will
   work (if DWARF2_UNWIND_INFO is defined).  Otherwise, we know that
   an inline unwinder will have been emitted for any function that
   __unwind_function cannot unwind.  The inline unwinder appears as a
   normal exception handler for the entire function, for any function
   that we know cannot be unwound by __unwind_function.  We inform the
   compiler of whether a function can be unwound with
   __unwind_function by having DOESNT_NEED_UNWINDER evaluate to true
   when the unwinder isn't needed.  __unwind_function is used as an
   action of last resort.  If no other method can be used for
   unwinding, __unwind_function is used.  If it cannot unwind, it
   should call __terminate.

   By default, if the target-specific backend doesn't supply a definition
   for __unwind_function and doesn't support DWARF2_UNWIND_INFO, inlined
   unwinders will be used instead. The main tradeoff here is in text space
   utilization.  Obviously, if inline unwinders have to be generated
   repeatedly, this uses much more space than if a single routine is used.

   However, it is simply not possible on some platforms to write a
   generalized routine for doing stack unwinding without having some
   form of additional data associated with each function.  The current
   implementation can encode this data in the form of additional
   machine instructions or as static data in tabular form.  The later
   is called the unwind data.

   The backend macro DOESNT_NEED_UNWINDER is used to conditionalize whether
   or not per-function unwinders are needed. If DOESNT_NEED_UNWINDER is
   defined and has a non-zero value, a per-function unwinder is not emitted
   for the current function.  If the static unwind data is supported, then
   a per-function unwinder is not emitted.

   On some platforms it is possible that neither __unwind_function
   nor inlined unwinders are available. For these platforms it is not
   possible to throw through a function call, and abort will be
   invoked instead of performing the throw. 

   The reason the unwind data may be needed is that on some platforms
   the order and types of data stored on the stack can vary depending
   on the type of function, its arguments and returned values, and the
   compilation options used (optimization versus non-optimization,
   -fomit-frame-pointer, processor variations, etc).

   Unfortunately, this also means that throwing through functions that
   aren't compiled with exception handling support will still not be
   possible on some platforms. This problem is currently being
   investigated, but no solutions have been found that do not imply
   some unacceptable performance penalties.

   Future directions:

   Currently __throw makes no differentiation between cleanups and
   user-defined exception regions. While this makes the implementation
   simple, it also implies that it is impossible to determine if a
   user-defined exception handler exists for a given exception without
   completely unwinding the stack in the process. This is undesirable
   from the standpoint of debugging, as ideally it would be possible
   to trap unhandled exceptions in the debugger before the process of
   unwinding has even started.

   This problem can be solved by marking user-defined handlers in a
   special way (probably by adding additional bits to exception_table_list).
   A two-pass scheme could then be used by __throw to iterate
   through the table. The first pass would search for a relevant
   user-defined handler for the current context of the throw, and if
   one is found, the second pass would then invoke all needed cleanups
   before jumping to the user-defined handler.

   Many languages (including C++ and Ada) make execution of a
   user-defined handler conditional on the "type" of the exception
   thrown. (The type of the exception is actually the type of the data
   that is thrown with the exception.) It will thus be necessary for
   __throw to be able to determine if a given user-defined
   exception handler will actually be executed, given the type of
   exception.

   One scheme is to add additional information to exception_table_list
   as to the types of exceptions accepted by each handler. __throw
   can do the type comparisons and then determine if the handler is
   actually going to be executed.

   There is currently no significant level of debugging support
   available, other than to place a breakpoint on __throw. While
   this is sufficient in most cases, it would be helpful to be able to
   know where a given exception was going to be thrown to before it is
   actually thrown, and to be able to choose between stopping before
   every exception region (including cleanups), or just user-defined
   exception regions. This should be possible to do in the two-pass
   scheme by adding additional labels to __throw for appropriate
   breakpoints, and additional debugger commands could be added to
   query various state variables to determine what actions are to be
   performed next.

   Another major problem that is being worked on is the issue with stack
   unwinding on various platforms. Currently the only platforms that have
   support for the generation of a generic unwinder are the SPARC and MIPS.
   All other ports require per-function unwinders, which produce large
   amounts of code bloat.

   For setjmp/longjmp based exception handling, some of the details
   are as above, but there are some additional details.  This section
   discusses the details.

   We don't use NOTE_INSN_EH_REGION_{BEG,END} pairs.  We don't
   optimize EH regions yet.  We don't have to worry about machine
   specific issues with unwinding the stack, as we rely upon longjmp
   for all the machine specific details.  There is no variable context
   of a throw, just the one implied by the dynamic handler stack
   pointed to by the dynamic handler chain.  There is no exception
   table, and no calls to __register_exceptions.  __sjthrow is used
   instead of __throw, and it works by using the dynamic handler
   chain, and longjmp.  -fasynchronous-exceptions has no effect, as
   the elimination of trivial exception regions is not yet performed.

   A frontend can set protect_cleanup_actions_with_terminate when all
   the cleanup actions should be protected with an EH region that
   calls terminate when an unhandled exception is throw.  C++ does
   this, Ada does not.  */


#include "config.h"
#include "defaults.h"
#include <stdio.h>
#include "rtl.h"
#include "tree.h"
#include "flags.h"
#include "except.h"
#include "function.h"
#include "insn-flags.h"
#include "expr.h"
#include "insn-codes.h"
#include "regs.h"
#include "hard-reg-set.h"
#include "insn-config.h"
#include "recog.h"
#include "output.h"

#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif

/* One to use setjmp/longjmp method of generating code for exception
   handling.  */

int exceptions_via_longjmp = 2;

/* One to enable asynchronous exception support.  */

int asynchronous_exceptions = 0;

/* One to protect cleanup actions with a handler that calls
   __terminate, zero otherwise.  */

int protect_cleanup_actions_with_terminate;

/* A list of labels used for exception handlers.  Created by
   find_exception_handler_labels for the optimization passes.  */

rtx exception_handler_labels;

/* The EH context.  Nonzero if the function has already
   fetched a pointer to the EH context  for exception handling.  */

rtx current_function_ehc;

/* A stack used for keeping track of the currently active exception
   handling region.  As each exception region is started, an entry
   describing the region is pushed onto this stack.  The current
   region can be found by looking at the top of the stack, and as we
   exit regions, the corresponding entries are popped. 

   Entries cannot overlap; they can be nested. So there is only one
   entry at most that corresponds to the current instruction, and that
   is the entry on the top of the stack.  */

static struct eh_stack ehstack;

/* A queue used for tracking which exception regions have closed but
   whose handlers have not yet been expanded. Regions are emitted in
   groups in an attempt to improve paging performance.

   As we exit a region, we enqueue a new entry. The entries are then
   dequeued during expand_leftover_cleanups and expand_start_all_catch,

   We should redo things so that we either take RTL for the handler,
   or we expand the handler expressed as a tree immediately at region
   end time.  */

static struct eh_queue ehqueue;

/* Insns for all of the exception handlers for the current function.
   They are currently emitted by the frontend code.  */

rtx catch_clauses;

/* A TREE_CHAINed list of handlers for regions that are not yet
   closed. The TREE_VALUE of each entry contains the handler for the
   corresponding entry on the ehstack.  */

static tree protect_list;

/* Stacks to keep track of various labels.  */

/* Keeps track of the label to resume to should one want to resume
   normal control flow out of a handler (instead of, say, returning to
   the caller of the current function or exiting the program).  */

struct label_node *caught_return_label_stack = NULL;

/* Keeps track of the label used as the context of a throw to rethrow an
   exception to the outer exception region.  */

struct label_node *outer_context_label_stack = NULL;

/* A random data area for the front end's own use.  */

struct label_node *false_label_stack = NULL;

rtx expand_builtin_return_addr	PROTO((enum built_in_function, int, rtx));
static void expand_rethrow	PROTO((rtx));

\f
/* Various support routines to manipulate the various data structures
   used by the exception handling code.  */

/* Push a label entry onto the given STACK.  */

void
push_label_entry (stack, rlabel, tlabel)
     struct label_node **stack;
     rtx rlabel;
     tree tlabel;
{
  struct label_node *newnode
    = (struct label_node *) xmalloc (sizeof (struct label_node));

  if (rlabel)
    newnode->u.rlabel = rlabel;
  else
    newnode->u.tlabel = tlabel;
  newnode->chain = *stack;
  *stack = newnode;
}

/* Pop a label entry from the given STACK.  */

rtx
pop_label_entry (stack)
     struct label_node **stack;
{
  rtx label;
  struct label_node *tempnode;

  if (! *stack)
    return NULL_RTX;

  tempnode = *stack;
  label = tempnode->u.rlabel;
  *stack = (*stack)->chain;
  free (tempnode);

  return label;
}

/* Return the top element of the given STACK.  */

tree
top_label_entry (stack)
     struct label_node **stack;
{
  if (! *stack)
    return NULL_TREE;

  return (*stack)->u.tlabel;
}

/* Push a new eh_node entry onto STACK.  */

static void
push_eh_entry (stack)
     struct eh_stack *stack;
{
  struct eh_node *node = (struct eh_node *) xmalloc (sizeof (struct eh_node));
  struct eh_entry *entry = (struct eh_entry *) xmalloc (sizeof (struct eh_entry));

  entry->outer_context = gen_label_rtx ();
  entry->exception_handler_label = gen_label_rtx ();
  entry->finalization = NULL_TREE;

  node->entry = entry;
  node->chain = stack->top;
  stack->top = node;
}

/* Pop an entry from the given STACK.  */

static struct eh_entry *
pop_eh_entry (stack)
     struct eh_stack *stack;
{
  struct eh_node *tempnode;
  struct eh_entry *tempentry;
  
  tempnode = stack->top;
  tempentry = tempnode->entry;
  stack->top = stack->top->chain;
  free (tempnode);

  return tempentry;
}

/* Enqueue an ENTRY onto the given QUEUE.  */

static void
enqueue_eh_entry (queue, entry)
     struct eh_queue *queue;
     struct eh_entry *entry;
{
  struct eh_node *node = (struct eh_node *) xmalloc (sizeof (struct eh_node));

  node->entry = entry;
  node->chain = NULL;

  if (queue->head == NULL)
    {
      queue->head = node;
    }
  else
    {
      queue->tail->chain = node;
    }
  queue->tail = node;
}

/* Dequeue an entry from the given QUEUE.  */

static struct eh_entry *
dequeue_eh_entry (queue)
     struct eh_queue *queue;
{
  struct eh_node *tempnode;
  struct eh_entry *tempentry;

  if (queue->head == NULL)
    return NULL;

  tempnode = queue->head;
  queue->head = queue->head->chain;

  tempentry = tempnode->entry;
  free (tempnode);

  return tempentry;
}
\f
/* Routine to see if exception exception handling is turned on.
   DO_WARN is non-zero if we want to inform the user that exception
   handling is turned off. 

   This is used to ensure that -fexceptions has been specified if the
   compiler tries to use any exception-specific functions.  */

int
doing_eh (do_warn)
     int do_warn;
{
  if (! flag_exceptions)
    {
      static int warned = 0;
      if (! warned && do_warn)
	{
	  error ("exception handling disabled, use -fexceptions to enable");
	  warned = 1;
	}
      return 0;
    }
  return 1;
}

/* Given a return address in ADDR, determine the address we should use
   to find the corresponding EH region.  */

rtx
eh_outer_context (addr)
     rtx addr;
{
  /* First mask out any unwanted bits.  */
#ifdef MASK_RETURN_ADDR
  expand_and (addr, MASK_RETURN_ADDR, addr);
#endif

  /* Then adjust to find the real return address.  */
#if defined (RETURN_ADDR_OFFSET)
  addr = plus_constant (addr, RETURN_ADDR_OFFSET);
#endif

  return addr;
}

/* Start a new exception region for a region of code that has a
   cleanup action and push the HANDLER for the region onto
   protect_list. All of the regions created with add_partial_entry
   will be ended when end_protect_partials is invoked.  */

void
add_partial_entry (handler)
     tree handler;
{
  expand_eh_region_start ();

  /* Make sure the entry is on the correct obstack.  */
  push_obstacks_nochange ();
  resume_temporary_allocation ();

  /* Because this is a cleanup action, we may have to protect the handler
     with __terminate.  */
  handler = protect_with_terminate (handler);

  protect_list = tree_cons (NULL_TREE, handler, protect_list);
  pop_obstacks ();
}

/* Emit code to get EH context to current function.  */

static rtx
call_get_eh_context ()
{
  static tree fn;
  tree expr;

  if (fn == NULL_TREE)
    {
      tree fntype;
      fn = get_identifier ("__get_eh_context");
      push_obstacks_nochange ();
      end_temporary_allocation ();
      fntype = build_pointer_type (build_pointer_type
				   (build_pointer_type (void_type_node)));
      fntype = build_function_type (fntype, NULL_TREE);
      fn = build_decl (FUNCTION_DECL, fn, fntype);
      DECL_EXTERNAL (fn) = 1;
      TREE_PUBLIC (fn) = 1;
      DECL_ARTIFICIAL (fn) = 1;
      TREE_READONLY (fn) = 1;
      make_decl_rtl (fn, NULL_PTR, 1);
      assemble_external (fn);
      pop_obstacks ();
    }

  expr = build1 (ADDR_EXPR, build_pointer_type (TREE_TYPE (fn)), fn);
  expr = build (CALL_EXPR, TREE_TYPE (TREE_TYPE (fn)),
		expr, NULL_TREE, NULL_TREE);
  TREE_SIDE_EFFECTS (expr) = 1;

  return copy_to_reg (expand_expr (expr, NULL_RTX, VOIDmode, 0));
}

/* Get a reference to the EH context.
   We will only generate a register for the current function EH context here,
   and emit a USE insn to mark that this is a EH context register.

   Later, emit_eh_context will emit needed call to __get_eh_context
   in libgcc2, and copy the value to the register we have generated. */

rtx
get_eh_context ()
{
  if (current_function_ehc == 0)
    {
      rtx insn;

      current_function_ehc = gen_reg_rtx (Pmode);
      
      insn = gen_rtx_USE (GET_MODE (current_function_ehc),
			  current_function_ehc);
      insn = emit_insn_before (insn, get_first_nonparm_insn ());

      REG_NOTES (insn)
	= gen_rtx_EXPR_LIST (REG_EH_CONTEXT, current_function_ehc,
			     REG_NOTES (insn));
    }
  return current_function_ehc;
}
     
/* Get a reference to the dynamic handler chain.  It points to the
   pointer to the next element in the dynamic handler chain.  It ends
   when there are no more elements in the dynamic handler chain, when
   the value is &top_elt from libgcc2.c.  Immediately after the
   pointer, is an area suitable for setjmp/longjmp when
   DONT_USE_BUILTIN_SETJMP is defined, and an area suitable for
   __builtin_setjmp/__builtin_longjmp when DONT_USE_BUILTIN_SETJMP
   isn't defined. */

rtx
get_dynamic_handler_chain ()
{
  rtx ehc, dhc, result;

  ehc = get_eh_context ();
  dhc = ehc;

  result = copy_to_reg (dhc);

  /* We don't want a copy of the dcc, but rather, the single dcc.  */
  return gen_rtx_MEM (Pmode, result);
}

/* Get a reference to the dynamic cleanup chain.  It points to the
   pointer to the next element in the dynamic cleanup chain.
   Immediately after the pointer, are two Pmode variables, one for a
   pointer to a function that performs the cleanup action, and the
   second, the argument to pass to that function.  */

rtx
get_dynamic_cleanup_chain ()
{
  rtx dhc, dcc, result;

  dhc = get_dynamic_handler_chain ();
  dcc = plus_constant (dhc, GET_MODE_SIZE (Pmode));

  result = copy_to_reg (dcc);

  /* We don't want a copy of the dcc, but rather, the single dcc.  */
  return gen_rtx_MEM (Pmode, result);
}

/* Generate code to evaluate X and jump to LABEL if the value is nonzero.
   LABEL is an rtx of code CODE_LABEL, in this function.  */

void
jumpif_rtx (x, label)
     rtx x;
     rtx label;
{
  jumpif (make_tree (type_for_mode (GET_MODE (x), 0), x), label);
}

/* Generate code to evaluate X and jump to LABEL if the value is zero.
   LABEL is an rtx of code CODE_LABEL, in this function.  */

void
jumpifnot_rtx (x, label)
     rtx x;
     rtx label;
{
  jumpifnot (make_tree (type_for_mode (GET_MODE (x), 0), x), label);
}

/* Start a dynamic cleanup on the EH runtime dynamic cleanup stack.
   We just need to create an element for the cleanup list, and push it
   into the chain.

   A dynamic cleanup is a cleanup action implied by the presence of an
   element on the EH runtime dynamic cleanup stack that is to be
   performed when an exception is thrown.  The cleanup action is
   performed by __sjthrow when an exception is thrown.  Only certain
   actions can be optimized into dynamic cleanup actions.  For the
   restrictions on what actions can be performed using this routine,
   see expand_eh_region_start_tree.  */

static void
start_dynamic_cleanup (func, arg)
     tree func;
     tree arg;
{
  rtx dcc;
  rtx new_func, new_arg;
  rtx x, buf;
  int size;

  /* We allocate enough room for a pointer to the function, and
     one argument.  */
  size = 2;

  /* XXX, FIXME: The stack space allocated this way is too long lived,
     but there is no allocation routine that allocates at the level of
     the last binding contour.  */
  buf = assign_stack_local (BLKmode,
			    GET_MODE_SIZE (Pmode)*(size+1),
			    0);

  buf = change_address (buf, Pmode, NULL_RTX);

  /* Store dcc into the first word of the newly allocated buffer.  */

  dcc = get_dynamic_cleanup_chain ();
  emit_move_insn (buf, dcc);

  /* Store func and arg into the cleanup list element.  */

  new_func = gen_rtx_MEM (Pmode, plus_constant (XEXP (buf, 0),
						GET_MODE_SIZE (Pmode)));
  new_arg = gen_rtx_MEM (Pmode, plus_constant (XEXP (buf, 0),
					       GET_MODE_SIZE (Pmode)*2));
  x = expand_expr (func, new_func, Pmode, 0);
  if (x != new_func)
    emit_move_insn (new_func, x);

  x = expand_expr (arg, new_arg, Pmode, 0);
  if (x != new_arg)
    emit_move_insn (new_arg, x);

  /* Update the cleanup chain.  */

  emit_move_insn (dcc, XEXP (buf, 0));
}

/* Emit RTL to start a dynamic handler on the EH runtime dynamic
   handler stack.  This should only be used by expand_eh_region_start
   or expand_eh_region_start_tree.  */

static void
start_dynamic_handler ()
{
  rtx dhc, dcc;
  rtx x, arg, buf;
  int size;

#ifndef DONT_USE_BUILTIN_SETJMP
  /* The number of Pmode words for the setjmp buffer, when using the
     builtin setjmp/longjmp, see expand_builtin, case
     BUILT_IN_LONGJMP.  */
  size = 5;
#else
#ifdef JMP_BUF_SIZE
  size = JMP_BUF_SIZE;
#else
  /* Should be large enough for most systems, if it is not,
     JMP_BUF_SIZE should be defined with the proper value.  It will
     also tend to be larger than necessary for most systems, a more
     optimal port will define JMP_BUF_SIZE.  */
  size = FIRST_PSEUDO_REGISTER+2;
#endif
#endif
  /* XXX, FIXME: The stack space allocated this way is too long lived,
     but there is no allocation routine that allocates at the level of
     the last binding contour.  */
  arg = assign_stack_local (BLKmode,
			    GET_MODE_SIZE (Pmode)*(size+1),
			    0);

  arg = change_address (arg, Pmode, NULL_RTX);

  /* Store dhc into the first word of the newly allocated buffer.  */

  dhc = get_dynamic_handler_chain ();
  dcc = gen_rtx_MEM (Pmode, plus_constant (XEXP (arg, 0),
					   GET_MODE_SIZE (Pmode)));
  emit_move_insn (arg, dhc);

  /* Zero out the start of the cleanup chain.  */
  emit_move_insn (dcc, const0_rtx);

  /* The jmpbuf starts two words into the area allocated.  */
  buf = plus_constant (XEXP (arg, 0), GET_MODE_SIZE (Pmode)*2);

#ifdef DONT_USE_BUILTIN_SETJMP
  x = emit_library_call_value (setjmp_libfunc, NULL_RTX, 1, SImode, 1,
			       buf, Pmode);
  /* If we come back here for a catch, transfer control to the handler.  */
  jumpif_rtx (x, ehstack.top->entry->exception_handler_label);
#else
  {
    /* A label to continue execution for the no exception case.  */
    rtx noex = gen_label_rtx();
    x = expand_builtin_setjmp (buf, NULL_RTX, noex,
			       ehstack.top->entry->exception_handler_label);
    emit_label (noex);
  }
#endif

  /* We are committed to this, so update the handler chain.  */

  emit_move_insn (dhc, XEXP (arg, 0));
}

/* Start an exception handling region for the given cleanup action.
   All instructions emitted after this point are considered to be part
   of the region until expand_eh_region_end is invoked.  CLEANUP is
   the cleanup action to perform.  The return value is true if the
   exception region was optimized away.  If that case,
   expand_eh_region_end does not need to be called for this cleanup,
   nor should it be.

   This routine notices one particular common case in C++ code
   generation, and optimizes it so as to not need the exception
   region.  It works by creating a dynamic cleanup action, instead of
   of a using an exception region.  */

int
expand_eh_region_start_tree (decl, cleanup)
     tree decl;
     tree cleanup;
{
  /* This is the old code.  */
  if (! doing_eh (0))
    return 0;

  /* The optimization only applies to actions protected with
     terminate, and only applies if we are using the setjmp/longjmp
     codegen method.  */
  if (exceptions_via_longjmp
      && protect_cleanup_actions_with_terminate)
    {
      tree func, arg;
      tree args;

      /* Ignore any UNSAVE_EXPR.  */
      if (TREE_CODE (cleanup) == UNSAVE_EXPR)
	cleanup = TREE_OPERAND (cleanup, 0);
      
      /* Further, it only applies if the action is a call, if there
	 are 2 arguments, and if the second argument is 2.  */

      if (TREE_CODE (cleanup) == CALL_EXPR
	  && (args = TREE_OPERAND (cleanup, 1))
	  && (func = TREE_OPERAND (cleanup, 0))
	  && (arg = TREE_VALUE (args))
	  && (args = TREE_CHAIN (args))

	  /* is the second argument 2?  */
	  && TREE_CODE (TREE_VALUE (args)) == INTEGER_CST
	  && TREE_INT_CST_LOW (TREE_VALUE (args)) == 2
	  && TREE_INT_CST_HIGH (TREE_VALUE (args)) == 0

	  /* Make sure there are no other arguments.  */
	  && TREE_CHAIN (args) == NULL_TREE)
	{
	  /* Arrange for returns and gotos to pop the entry we make on the
	     dynamic cleanup stack.  */
	  expand_dcc_cleanup (decl);
	  start_dynamic_cleanup (func, arg);
	  return 1;
	}
    }

  expand_eh_region_start_for_decl (decl);
  ehstack.top->entry->finalization = cleanup;

  return 0;
}

/* Just like expand_eh_region_start, except if a cleanup action is
   entered on the cleanup chain, the TREE_PURPOSE of the element put
   on the chain is DECL.  DECL should be the associated VAR_DECL, if
   any, otherwise it should be NULL_TREE.  */

void
expand_eh_region_start_for_decl (decl)
     tree decl;
{
  rtx note;

  /* This is the old code.  */
  if (! doing_eh (0))
    return;

  if (exceptions_via_longjmp)
    {
      /* We need a new block to record the start and end of the
	 dynamic handler chain.  We could always do this, but we
	 really want to permit jumping into such a block, and we want
	 to avoid any errors or performance impact in the SJ EH code
	 for now.  */
      expand_start_bindings (0);

      /* But we don't need or want a new temporary level.  */
      pop_temp_slots ();

      /* Mark this block as created by expand_eh_region_start.  This
	 is so that we can pop the block with expand_end_bindings
	 automatically.  */
      mark_block_as_eh_region ();

      /* Arrange for returns and gotos to pop the entry we make on the
	 dynamic handler stack.  */
      expand_dhc_cleanup (decl);
    }

  push_eh_entry (&ehstack);
  note = emit_note (NULL_PTR, NOTE_INSN_EH_REGION_BEG);
  NOTE_BLOCK_NUMBER (note)
    = CODE_LABEL_NUMBER (ehstack.top->entry->exception_handler_label);
  if (exceptions_via_longjmp)
    start_dynamic_handler ();
}

/* Start an exception handling region.  All instructions emitted after
   this point are considered to be part of the region until
   expand_eh_region_end is invoked.  */

void
expand_eh_region_start ()
{
  expand_eh_region_start_for_decl (NULL_TREE);
}

/* End an exception handling region.  The information about the region
   is found on the top of ehstack.

   HANDLER is either the cleanup for the exception region, or if we're
   marking the end of a try block, HANDLER is integer_zero_node.

   HANDLER will be transformed to rtl when expand_leftover_cleanups
   is invoked.  */

void
expand_eh_region_end (handler)
     tree handler;
{
  struct eh_entry *entry;
  rtx note;

  if (! doing_eh (0))
    return;

  entry = pop_eh_entry (&ehstack);

  note = emit_note (NULL_PTR, NOTE_INSN_EH_REGION_END);
  NOTE_BLOCK_NUMBER (note)
    = CODE_LABEL_NUMBER (entry->exception_handler_label);
  if (exceptions_via_longjmp == 0
      /* We share outer_context between regions; only emit it once.  */
      && INSN_UID (entry->outer_context) == 0)
    {
      rtx label;

      label = gen_label_rtx ();
      emit_jump (label);

      /* Emit a label marking the end of this exception region that
	 is used for rethrowing into the outer context.  */
      emit_label (entry->outer_context);
      expand_internal_throw ();

      emit_label (label);
    }

  entry->finalization = handler;

  enqueue_eh_entry (&ehqueue, entry);

  /* If we have already started ending the bindings, don't recurse.
     This only happens when exceptions_via_longjmp is true.  */
  if (is_eh_region ())
    {
      /* Because we don't need or want a new temporary level and
	 because we didn't create one in expand_eh_region_start,
	 create a fake one now to avoid removing one in
	 expand_end_bindings.  */
      push_temp_slots ();

      mark_block_as_not_eh_region ();

      /* Maybe do this to prevent jumping in and so on...  */
      expand_end_bindings (NULL_TREE, 0, 0);
    }
}

/* End the EH region for a goto fixup.  We only need them in the region-based
   EH scheme.  */

void
expand_fixup_region_start ()
{
  if (! doing_eh (0) || exceptions_via_longjmp)
    return;

  expand_eh_region_start ();
}

/* End the EH region for a goto fixup.  CLEANUP is the cleanup we just
   expanded; to avoid running it twice if it throws, we look through the
   ehqueue for a matching region and rethrow from its outer_context.  */

void
expand_fixup_region_end (cleanup)
     tree cleanup;
{
  struct eh_node *node;

  if (! doing_eh (0) || exceptions_via_longjmp)
    return;

  for (node = ehstack.top; node && node->entry->finalization != cleanup; )
    node = node->chain;
  if (node == 0)
    for (node = ehqueue.head; node && node->entry->finalization != cleanup; )
      node = node->chain;
  if (node == 0)
    abort ();

  ehstack.top->entry->outer_context = node->entry->outer_context;

  /* Just rethrow.  size_zero_node is just a NOP.  */
  expand_eh_region_end (size_zero_node);
}

/* If we are using the setjmp/longjmp EH codegen method, we emit a
   call to __sjthrow.

   Otherwise, we emit a call to __throw and note that we threw
   something, so we know we need to generate the necessary code for
   __throw.

   Before invoking throw, the __eh_pc variable must have been set up
   to contain the PC being thrown from. This address is used by
   __throw to determine which exception region (if any) is
   responsible for handling the exception.  */

void
emit_throw ()
{
  if (exceptions_via_longjmp)
    {
      emit_library_call (sjthrow_libfunc, 0, VOIDmode, 0);
    }
  else
    {
#ifdef JUMP_TO_THROW
      emit_indirect_jump (throw_libfunc);
#else
      emit_library_call (throw_libfunc, 0, VOIDmode, 0);
#endif
    }
  emit_barrier ();
}

/* Throw the current exception.  If appropriate, this is done by jumping
   to the next handler.  */

void
expand_internal_throw ()
{
  emit_throw ();
}

/* Called from expand_exception_blocks and expand_end_catch_block to
   emit any pending handlers/cleanups queued from expand_eh_region_end.  */

void
expand_leftover_cleanups ()
{
  struct eh_entry *entry;

  while ((entry = dequeue_eh_entry (&ehqueue)) != 0)
    {
      rtx prev;

      /* A leftover try block. Shouldn't be one here.  */
      if (entry->finalization == integer_zero_node)
	abort ();

      /* Output the label for the start of the exception handler.  */
      emit_label (entry->exception_handler_label);

#ifdef HAVE_exception_receiver
      if (! exceptions_via_longjmp)
	if (HAVE_exception_receiver)
	  emit_insn (gen_exception_receiver ());
#endif

#ifdef HAVE_nonlocal_goto_receiver
      if (! exceptions_via_longjmp)
	if (HAVE_nonlocal_goto_receiver)
	  emit_insn (gen_nonlocal_goto_receiver ());
#endif

      /* And now generate the insns for the handler.  */
      expand_expr (entry->finalization, const0_rtx, VOIDmode, 0);

      prev = get_last_insn ();
      if (prev == NULL || GET_CODE (prev) != BARRIER)
	/* Emit code to throw to the outer context if we fall off
	   the end of the handler.  */
	expand_rethrow (entry->outer_context);

      do_pending_stack_adjust ();
      free (entry);
    }
}

/* Called at the start of a block of try statements.  */
void
expand_start_try_stmts ()
{
  if (! doing_eh (1))
    return;

  expand_eh_region_start ();
}

/* Generate RTL for the start of a group of catch clauses. 

   It is responsible for starting a new instruction sequence for the
   instructions in the catch block, and expanding the handlers for the
   internally-generated exception regions nested within the try block
   corresponding to this catch block.  */

void
expand_start_all_catch ()
{
  struct eh_entry *entry;
  tree label;
  rtx outer_context;

  if (! doing_eh (1))
    return;

  outer_context = ehstack.top->entry->outer_context;

  /* End the try block.  */
  expand_eh_region_end (integer_zero_node);

  emit_line_note (input_filename, lineno);
  label = build_decl (LABEL_DECL, NULL_TREE, NULL_TREE);

  /* The label for the exception handling block that we will save.
     This is Lresume in the documentation.  */
  expand_label (label);
  
  /* Push the label that points to where normal flow is resumed onto
     the top of the label stack.  */
  push_label_entry (&caught_return_label_stack, NULL_RTX, label);

  /* Start a new sequence for all the catch blocks.  We will add this
     to the global sequence catch_clauses when we have completed all
     the handlers in this handler-seq.  */
  start_sequence ();

  while (1)
    {
      rtx prev;

      entry = dequeue_eh_entry (&ehqueue);
      /* Emit the label for the exception handler for this region, and
	 expand the code for the handler. 

	 Note that a catch region is handled as a side-effect here;
	 for a try block, entry->finalization will contain
	 integer_zero_node, so no code will be generated in the
	 expand_expr call below. But, the label for the handler will
	 still be emitted, so any code emitted after this point will
	 end up being the handler.  */
      emit_label (entry->exception_handler_label);

#ifdef HAVE_exception_receiver
      if (! exceptions_via_longjmp)
	if (HAVE_exception_receiver)
	  emit_insn (gen_exception_receiver ());
#endif

#ifdef HAVE_nonlocal_goto_receiver
      if (! exceptions_via_longjmp)
	if (HAVE_nonlocal_goto_receiver)
	  emit_insn (gen_nonlocal_goto_receiver ());
#endif

      /* When we get down to the matching entry for this try block, stop.  */
      if (entry->finalization == integer_zero_node)
	{
	  /* Don't forget to free this entry.  */
	  free (entry);
	  break;
	}

      /* And now generate the insns for the handler.  */
      expand_expr (entry->finalization, const0_rtx, VOIDmode, 0);

      prev = get_last_insn ();
      if (prev == NULL || GET_CODE (prev) != BARRIER)
	/* Code to throw out to outer context when we fall off end
	   of the handler. We can't do this here for catch blocks,
	   so it's done in expand_end_all_catch instead.  */
	expand_rethrow (entry->outer_context);

      do_pending_stack_adjust ();
      free (entry);
    }

  /* If we are not doing setjmp/longjmp EH, because we are reordered
     out of line, we arrange to rethrow in the outer context.  We need to
     do this because we are not physically within the region, if any, that
     logically contains this catch block.  */
  if (! exceptions_via_longjmp)
    {
      expand_eh_region_start ();
      ehstack.top->entry->outer_context = outer_context;
    }
}

/* Finish up the catch block.  At this point all the insns for the
   catch clauses have already been generated, so we only have to add
   them to the catch_clauses list. We also want to make sure that if
   we fall off the end of the catch clauses that we rethrow to the
   outer EH region.  */

void
expand_end_all_catch ()
{
  rtx new_catch_clause, outer_context = NULL_RTX;

  if (! doing_eh (1))
    return;

  if (! exceptions_via_longjmp)
    {
      outer_context = ehstack.top->entry->outer_context;

      /* Finish the rethrow region.  size_zero_node is just a NOP.  */
      expand_eh_region_end (size_zero_node);
    }

  /* Code to throw out to outer context, if we fall off end of catch
     handlers.  This is rethrow (Lresume, same id, same obj) in the
     documentation. We use Lresume because we know that it will throw
     to the correct context.

     In other words, if the catch handler doesn't exit or return, we
     do a "throw" (using the address of Lresume as the point being
     thrown from) so that the outer EH region can then try to process
     the exception.  */
  expand_rethrow (outer_context);

  /* Now we have the complete catch sequence.  */
  new_catch_clause = get_insns ();
  end_sequence ();
  
  /* This level of catch blocks is done, so set up the successful
     catch jump label for the next layer of catch blocks.  */
  pop_label_entry (&caught_return_label_stack);
  pop_label_entry (&outer_context_label_stack);

  /* Add the new sequence of catches to the main one for this function.  */
  push_to_sequence (catch_clauses);
  emit_insns (new_catch_clause);
  catch_clauses = get_insns ();
  end_sequence ();
  
  /* Here we fall through into the continuation code.  */
}

/* Rethrow from the outer context LABEL.  */

static void
expand_rethrow (label)
     rtx label;
{
  if (exceptions_via_longjmp)
    emit_throw ();
  else
    emit_jump (label);
}

/* End all the pending exception regions on protect_list. The handlers
   will be emitted when expand_leftover_cleanups is invoked.  */

void
end_protect_partials ()
{
  while (protect_list)
    {
      expand_eh_region_end (TREE_VALUE (protect_list));
      protect_list = TREE_CHAIN (protect_list);
    }
}

/* Arrange for __terminate to be called if there is an unhandled throw
   from within E.  */

tree
protect_with_terminate (e)
     tree e;
{
  /* We only need to do this when using setjmp/longjmp EH and the
     language requires it, as otherwise we protect all of the handlers
     at once, if we need to.  */
  if (exceptions_via_longjmp && protect_cleanup_actions_with_terminate)
    {
      tree handler, result;

      /* All cleanups must be on the function_obstack.  */
      push_obstacks_nochange ();
      resume_temporary_allocation ();

      handler = make_node (RTL_EXPR);
      TREE_TYPE (handler) = void_type_node;
      RTL_EXPR_RTL (handler) = const0_rtx;
      TREE_SIDE_EFFECTS (handler) = 1;
      start_sequence_for_rtl_expr (handler);

      emit_library_call (terminate_libfunc, 0, VOIDmode, 0);
      emit_barrier ();

      RTL_EXPR_SEQUENCE (handler) = get_insns ();
      end_sequence ();
	
      result = build (TRY_CATCH_EXPR, TREE_TYPE (e), e, handler);
      TREE_SIDE_EFFECTS (result) = TREE_SIDE_EFFECTS (e);
      TREE_THIS_VOLATILE (result) = TREE_THIS_VOLATILE (e);
      TREE_READONLY (result) = TREE_READONLY (e);

      pop_obstacks ();

      e = result;
    }

  return e;
}
\f
/* The exception table that we build that is used for looking up and
   dispatching exceptions, the current number of entries, and its
   maximum size before we have to extend it. 

   The number in eh_table is the code label number of the exception
   handler for the region. This is added by add_eh_table_entry and
   used by output_exception_table_entry.  */

static int *eh_table;
static int eh_table_size;
static int eh_table_max_size;

/* Note the need for an exception table entry for region N.  If we
   don't need to output an explicit exception table, avoid all of the
   extra work.

   Called from final_scan_insn when a NOTE_INSN_EH_REGION_BEG is seen.
   N is the NOTE_BLOCK_NUMBER of the note, which comes from the code
   label number of the exception handler for the region.  */

void
add_eh_table_entry (n)
     int n;
{
#ifndef OMIT_EH_TABLE
  if (eh_table_size >= eh_table_max_size)
    {
      if (eh_table)
	{
	  eh_table_max_size += eh_table_max_size>>1;

	  if (eh_table_max_size < 0)
	    abort ();

	  eh_table = (int *) xrealloc (eh_table,
				       eh_table_max_size * sizeof (int));
	}
      else
	{
	  eh_table_max_size = 252;
	  eh_table = (int *) xmalloc (eh_table_max_size * sizeof (int));
	}
    }
  eh_table[eh_table_size++] = n;
#endif
}

/* Return a non-zero value if we need to output an exception table.

   On some platforms, we don't have to output a table explicitly.
   This routine doesn't mean we don't have one.  */

int
exception_table_p ()
{
  if (eh_table)
    return 1;

  return 0;
}

/* Output the entry of the exception table corresponding to to the
   exception region numbered N to file FILE. 

   N is the code label number corresponding to the handler of the
   region.  */

static void
output_exception_table_entry (file, n)
     FILE *file;
     int n;
{
  char buf[256];
  rtx sym;

  ASM_GENERATE_INTERNAL_LABEL (buf, "LEHB", n);
  sym = gen_rtx_SYMBOL_REF (Pmode, buf);
  assemble_integer (sym, POINTER_SIZE / BITS_PER_UNIT, 1);

  ASM_GENERATE_INTERNAL_LABEL (buf, "LEHE", n);
  sym = gen_rtx_SYMBOL_REF (Pmode, buf);
  assemble_integer (sym, POINTER_SIZE / BITS_PER_UNIT, 1);

  ASM_GENERATE_INTERNAL_LABEL (buf, "L", n);
  sym = gen_rtx_SYMBOL_REF (Pmode, buf);
  assemble_integer (sym, POINTER_SIZE / BITS_PER_UNIT, 1);

  putc ('\n', file);		/* blank line */
}

/* Output the exception table if we have and need one.  */

void
output_exception_table ()
{
  int i;
  extern FILE *asm_out_file;

  if (! doing_eh (0) || ! eh_table)
    return;

  exception_section ();

  /* Beginning marker for table.  */
  assemble_align (GET_MODE_ALIGNMENT (ptr_mode));
  assemble_label ("__EXCEPTION_TABLE__");

  for (i = 0; i < eh_table_size; ++i)
    output_exception_table_entry (asm_out_file, eh_table[i]);

  free (eh_table);

  /* Ending marker for table.  */
  assemble_integer (constm1_rtx, POINTER_SIZE / BITS_PER_UNIT, 1);
  assemble_integer (constm1_rtx, POINTER_SIZE / BITS_PER_UNIT, 1);
  assemble_integer (constm1_rtx, POINTER_SIZE / BITS_PER_UNIT, 1);
  putc ('\n', asm_out_file);		/* blank line */
}
\f
/* Emit code to get EH context.
   
   We have to scan thru the code to find possible EH context registers.
   Inlined functions may use it too, and thus we'll have to be able
   to change them too.

   This is done only if using exceptions_via_longjmp. */

void
emit_eh_context ()
{
  rtx insn;
  rtx ehc = 0;

  if (! doing_eh (0))
    return;

  for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
    if (GET_CODE (insn) == INSN
	&& GET_CODE (PATTERN (insn)) == USE)
      {
	rtx reg = find_reg_note (insn, REG_EH_CONTEXT, 0);
	if (reg)
	  {
	    rtx insns;
	    
	    start_sequence ();

	    /* If this is the first use insn, emit the call here.  This
	       will always be at the top of our function, because if
	       expand_inline_function notices a REG_EH_CONTEXT note, it
	       adds a use insn to this function as well.  */
	    if (ehc == 0)
	      ehc = call_get_eh_context ();

	    emit_move_insn (XEXP (reg, 0), ehc);
	    insns = get_insns ();
	    end_sequence ();

	    emit_insns_before (insns, insn);
	  }
      }
}

/* Scan the current insns and build a list of handler labels. The
   resulting list is placed in the global variable exception_handler_labels.

   It is called after the last exception handling region is added to
   the current function (when the rtl is almost all built for the
   current function) and before the jump optimization pass.  */

void
find_exception_handler_labels ()
{
  rtx insn;
  int max_labelno = max_label_num ();
  int min_labelno = get_first_label_num ();
  rtx *labels;

  exception_handler_labels = NULL_RTX;

  /* If we aren't doing exception handling, there isn't much to check.  */
  if (! doing_eh (0))
    return;

  /* Generate a handy reference to each label.  */

  /* We call xmalloc here instead of alloca; we did the latter in the past,
     but found that it can sometimes end up being asked to allocate space
     for more than 1 million labels.  */
  labels = (rtx *) xmalloc ((max_labelno - min_labelno) * sizeof (rtx));
  bzero ((char *) labels, (max_labelno - min_labelno) * sizeof (rtx));

  /* Arrange for labels to be indexed directly by CODE_LABEL_NUMBER.  */
  labels -= min_labelno;

  for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
    {
      if (GET_CODE (insn) == CODE_LABEL)
	if (CODE_LABEL_NUMBER (insn) >= min_labelno
	    && CODE_LABEL_NUMBER (insn) < max_labelno)
	  labels[CODE_LABEL_NUMBER (insn)] = insn;
    }

  /* For each start of a region, add its label to the list.  */

  for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
    {
      if (GET_CODE (insn) == NOTE
	  && NOTE_LINE_NUMBER (insn) == NOTE_INSN_EH_REGION_BEG)
	{
	  rtx label = NULL_RTX;

	  if (NOTE_BLOCK_NUMBER (insn) >= min_labelno
	      && NOTE_BLOCK_NUMBER (insn) < max_labelno)
	    {
	      label = labels[NOTE_BLOCK_NUMBER (insn)];

	      if (label)
		exception_handler_labels
		  = gen_rtx_EXPR_LIST (VOIDmode,
				       label, exception_handler_labels);
	      else
		warning ("didn't find handler for EH region %d",
			 NOTE_BLOCK_NUMBER (insn));
	    }
	  else
	    warning ("mismatched EH region %d", NOTE_BLOCK_NUMBER (insn));
	}
    }

  free (labels + min_labelno);
}

/* Perform sanity checking on the exception_handler_labels list.

   Can be called after find_exception_handler_labels is called to
   build the list of exception handlers for the current function and
   before we finish processing the current function.  */

void
check_exception_handler_labels ()
{
  rtx insn, handler;

  /* If we aren't doing exception handling, there isn't much to check.  */
  if (! doing_eh (0))
    return;

  /* Ensure that the CODE_LABEL_NUMBER for the CODE_LABEL entry point
     in each handler corresponds to the CODE_LABEL_NUMBER of the
     handler.  */

  for (handler = exception_handler_labels;
       handler;
       handler = XEXP (handler, 1))
    {
      for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
	{
	  if (GET_CODE (insn) == CODE_LABEL)
	    {
	      if (CODE_LABEL_NUMBER (insn)
		  == CODE_LABEL_NUMBER (XEXP (handler, 0)))
		{
		  if (insn != XEXP (handler, 0))
		    warning ("mismatched handler %d",
			     CODE_LABEL_NUMBER (insn));
		  break;
		}
	    }
	}
      if (insn == NULL_RTX)
	warning ("handler not found %d",
		 CODE_LABEL_NUMBER (XEXP (handler, 0)));
    }

  /* Now go through and make sure that for each region there is a
     corresponding label.  */
  for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
    {
      if (GET_CODE (insn) == NOTE
	  && (NOTE_LINE_NUMBER (insn) == NOTE_INSN_EH_REGION_BEG
	      || NOTE_LINE_NUMBER (insn) == NOTE_INSN_EH_REGION_END))
	{
	  for (handler = exception_handler_labels;
	       handler;
	       handler = XEXP (handler, 1))
	    {
	      if (CODE_LABEL_NUMBER (XEXP (handler, 0))
		  == NOTE_BLOCK_NUMBER (insn))
		break;
	    }
	  if (handler == NULL_RTX && !flag_syntax_only)
	    warning ("region exists, no handler %d",
		     NOTE_BLOCK_NUMBER (insn));
	}
    }
}
\f
/* This group of functions initializes the exception handling data
   structures at the start of the compilation, initializes the data
   structures at the start of a function, and saves and restores the
   exception handling data structures for the start/end of a nested
   function.  */

/* Toplevel initialization for EH things.  */ 

void
init_eh ()
{
  /* Generate rtl to reference the variable in which the PC of the
     current context is saved.  */
  (void) build_pointer_type (make_node (VOID_TYPE));
}

/* Initialize the per-function EH information.  */

void
init_eh_for_function ()
{
  ehstack.top = 0;
  ehqueue.head = ehqueue.tail = 0;
  catch_clauses = NULL_RTX;
  false_label_stack = 0;
  caught_return_label_stack = 0;
  protect_list = NULL_TREE;
  current_function_ehc = NULL_RTX;
}

/* Save some of the per-function EH info into the save area denoted by
   P. 

   This is currently called from save_stmt_status.  */

void
save_eh_status (p)
     struct function *p;
{
  if (p == NULL)
    abort ();

  p->ehstack = ehstack;
  p->ehqueue = ehqueue;
  p->catch_clauses = catch_clauses;
  p->false_label_stack = false_label_stack;
  p->caught_return_label_stack = caught_return_label_stack;
  p->protect_list = protect_list;
  p->ehc = current_function_ehc;

  init_eh ();
}

/* Restore the per-function EH info saved into the area denoted by P.  

   This is currently called from restore_stmt_status.  */

void
restore_eh_status (p)
     struct function *p;
{
  if (p == NULL)
    abort ();

  protect_list = p->protect_list;
  caught_return_label_stack = p->caught_return_label_stack;
  false_label_stack = p->false_label_stack;
  catch_clauses	= p->catch_clauses;
  ehqueue = p->ehqueue;
  ehstack = p->ehstack;
  current_function_ehc = p->ehc;
}
\f
/* This section is for the exception handling specific optimization
   pass.  First are the internal routines, and then the main
   optimization pass.  */

/* Determine if the given INSN can throw an exception.  */

static int
can_throw (insn)
     rtx insn;
{
  /* Calls can always potentially throw exceptions.  */
  if (GET_CODE (insn) == CALL_INSN)
    return 1;

  if (asynchronous_exceptions)
    {
      /* If we wanted asynchronous exceptions, then everything but NOTEs
	 and CODE_LABELs could throw.  */
      if (GET_CODE (insn) != NOTE && GET_CODE (insn) != CODE_LABEL)
	return 1;
    }

  return 0;
}

/* Scan a exception region looking for the matching end and then
   remove it if possible. INSN is the start of the region, N is the
   region number, and DELETE_OUTER is to note if anything in this
   region can throw.

   Regions are removed if they cannot possibly catch an exception.
   This is determined by invoking can_throw on each insn within the
   region; if can_throw returns true for any of the instructions, the
   region can catch an exception, since there is an insn within the
   region that is capable of throwing an exception.

   Returns the NOTE_INSN_EH_REGION_END corresponding to this region, or
   calls abort if it can't find one.

   Can abort if INSN is not a NOTE_INSN_EH_REGION_BEGIN, or if N doesn't
   correspond to the region number, or if DELETE_OUTER is NULL.  */

static rtx
scan_region (insn, n, delete_outer)
     rtx insn;
     int n;
     int *delete_outer;
{
  rtx start = insn;

  /* Assume we can delete the region.  */
  int delete = 1;

  if (insn == NULL_RTX
      || GET_CODE (insn) != NOTE
      || NOTE_LINE_NUMBER (insn) != NOTE_INSN_EH_REGION_BEG
      || NOTE_BLOCK_NUMBER (insn) != n
      || delete_outer == NULL)
    abort ();

  insn = NEXT_INSN (insn);

  /* Look for the matching end.  */
  while (! (GET_CODE (insn) == NOTE
	    && NOTE_LINE_NUMBER (insn) == NOTE_INSN_EH_REGION_END))
    {
      /* If anything can throw, we can't remove the region.  */
      if (delete && can_throw (insn))
	{
	  delete = 0;
	}

      /* Watch out for and handle nested regions.  */
      if (GET_CODE (insn) == NOTE
	  && NOTE_LINE_NUMBER (insn) == NOTE_INSN_EH_REGION_BEG)
	{
	  insn = scan_region (insn, NOTE_BLOCK_NUMBER (insn), &delete);
	}

      insn = NEXT_INSN (insn);
    }

  /* The _BEG/_END NOTEs must match and nest.  */
  if (NOTE_BLOCK_NUMBER (insn) != n)
    abort ();

  /* If anything in this exception region can throw, we can throw.  */
  if (! delete)
    *delete_outer = 0;
  else
    {
      /* Delete the start and end of the region.  */
      delete_insn (start);
      delete_insn (insn);

      /* Only do this part if we have built the exception handler
         labels.  */
      if (exception_handler_labels)
	{
	  rtx x, *prev = &exception_handler_labels;

	  /* Find it in the list of handlers.  */
	  for (x = exception_handler_labels; x; x = XEXP (x, 1))
	    {
	      rtx label = XEXP (x, 0);
	      if (CODE_LABEL_NUMBER (label) == n)
		{
		  /* If we are the last reference to the handler,
                     delete it.  */
		  if (--LABEL_NUSES (label) == 0)
		    delete_insn (label);

		  if (optimize)
		    {
		      /* Remove it from the list of exception handler
			 labels, if we are optimizing.  If we are not, then
			 leave it in the list, as we are not really going to
			 remove the region.  */
		      *prev = XEXP (x, 1);
		      XEXP (x, 1) = 0;
		      XEXP (x, 0) = 0;
		    }

		  break;
		}
	      prev = &XEXP (x, 1);
	    }
	}
    }
  return insn;
}

/* Perform various interesting optimizations for exception handling
   code.

   We look for empty exception regions and make them go (away). The
   jump optimization code will remove the handler if nothing else uses
   it.  */

void
exception_optimize ()
{
  rtx insn;
  int n;

  /* Remove empty regions.  */
  for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
    {
      if (GET_CODE (insn) == NOTE
	  && NOTE_LINE_NUMBER (insn) == NOTE_INSN_EH_REGION_BEG)
	{
	  /* Since scan_region will return the NOTE_INSN_EH_REGION_END
	     insn, we will indirectly skip through all the insns
	     inbetween. We are also guaranteed that the value of insn
	     returned will be valid, as otherwise scan_region won't
	     return.  */
	  insn = scan_region (insn, NOTE_BLOCK_NUMBER (insn), &n);
	}
    }
}
\f
/* Various hooks for the DWARF 2 __throw routine.  */

/* Do any necessary initialization to access arbitrary stack frames.
   On the SPARC, this means flushing the register windows.  */

void
expand_builtin_unwind_init ()
{
  /* Set this so all the registers get saved in our frame; we need to be
     able to copy the saved values for any registers from frames we unwind. */
  current_function_has_nonlocal_label = 1;

#ifdef SETUP_FRAME_ADDRESSES
  SETUP_FRAME_ADDRESSES ();
#endif
}

/* Given a value extracted from the return address register or stack slot,
   return the actual address encoded in that value.  */

rtx
expand_builtin_extract_return_addr (addr_tree)
     tree addr_tree;
{
  rtx addr = expand_expr (addr_tree, NULL_RTX, Pmode, 0);
  return eh_outer_context (addr);
}

/* Given an actual address in addr_tree, do any necessary encoding
   and return the value to be stored in the return address register or
   stack slot so the epilogue will return to that address.  */

rtx
expand_builtin_frob_return_addr (addr_tree)
     tree addr_tree;
{
  rtx addr = expand_expr (addr_tree, NULL_RTX, Pmode, 0);
#ifdef RETURN_ADDR_OFFSET
  addr = plus_constant (addr, -RETURN_ADDR_OFFSET);
#endif
  return addr;
}

/* Given an actual address in addr_tree, set the return address register up
   so the epilogue will return to that address.  If the return address is
   not in a register, do nothing.  */

void
expand_builtin_set_return_addr_reg (addr_tree)
     tree addr_tree;
{
  rtx tmp;
  rtx ra = expand_builtin_return_addr (BUILT_IN_RETURN_ADDRESS,
				       0, hard_frame_pointer_rtx);

  if (GET_CODE (ra) != REG || REGNO (ra) >= FIRST_PSEUDO_REGISTER)
    return;

  tmp = force_operand (expand_builtin_frob_return_addr (addr_tree), ra);
  if (tmp != ra)
    emit_move_insn (ra, tmp);
}

/* Choose two registers for communication between the main body of
   __throw and the stub for adjusting the stack pointer.  The first register
   is used to pass the address of the exception handler; the second register
   is used to pass the stack pointer offset.

   For register 1 we use the return value register for a void *.
   For register 2 we use the static chain register if it exists and is
     different from register 1, otherwise some arbitrary call-clobbered
     register.  */

static void
eh_regs (r1, r2, outgoing)
     rtx *r1, *r2;
     int outgoing;
{
  rtx reg1, reg2;

#ifdef FUNCTION_OUTGOING_VALUE
  if (outgoing)
    reg1 = FUNCTION_OUTGOING_VALUE (build_pointer_type (void_type_node),
				    current_function_decl);
  else
#endif
    reg1 = FUNCTION_VALUE (build_pointer_type (void_type_node),
			   current_function_decl);

#ifdef STATIC_CHAIN_REGNUM
  if (outgoing)
    reg2 = static_chain_incoming_rtx;
  else
    reg2 = static_chain_rtx;
  if (REGNO (reg2) == REGNO (reg1))
#endif /* STATIC_CHAIN_REGNUM */
    reg2 = NULL_RTX;

  if (reg2 == NULL_RTX)
    {
      int i;
      for (i = 0; i < FIRST_PSEUDO_REGISTER; ++i)
	if (call_used_regs[i] && ! fixed_regs[i] && i != REGNO (reg1))
	  {
	    reg2 = gen_rtx_REG (Pmode, i);
	    break;
	  }

      if (reg2 == NULL_RTX)
	abort ();
    }

  *r1 = reg1;
  *r2 = reg2;
}

/* Emit inside of __throw a stub which adjusts the stack pointer and jumps
   to the exception handler.  __throw will set up the necessary values
   and then return to the stub.  */

rtx
expand_builtin_eh_stub ()
{
  rtx stub_start = gen_label_rtx ();
  rtx after_stub = gen_label_rtx ();
  rtx handler, offset;

  emit_jump (after_stub);
  emit_label (stub_start);

  eh_regs (&handler, &offset, 0);

  adjust_stack (offset);
  emit_indirect_jump (handler);

  emit_label (after_stub);
  return gen_rtx_LABEL_REF (Pmode, stub_start);
}

/* Set up the registers for passing the handler address and stack offset
   to the stub above.  */

void
expand_builtin_set_eh_regs (handler, offset)
     tree handler, offset;
{
  rtx reg1, reg2;

  eh_regs (&reg1, &reg2, 1);

  store_expr (offset,  reg2, 0);
  store_expr (handler, reg1, 0);

  /* These will be used by the stub.  */
  emit_insn (gen_rtx_USE (VOIDmode, reg1));
  emit_insn (gen_rtx_USE (VOIDmode, reg2));
}