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gcc-papermario/except.c
Ethan Roseman 57261bd1c1 Initial commit of GCC 2.8.1
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/* Implements exception handling.
Copyright (C) 1989, 92-97, 1998 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"
/* 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 = 0;
/* A list of labels used for exception handlers. Created by
find_exception_handler_labels for the optimization passes. */
rtx exception_handler_labels;
/* Nonzero means that __throw was invoked.
This is used by the C++ frontend to know if code needs to be emitted
for __throw or not. */
int throw_used;
/* The dynamic handler chain. Nonzero if the function has already
fetched a pointer to the dynamic handler chain for exception
handling. */
rtx current_function_dhc;
/* The dynamic cleanup chain. Nonzero if the function has already
fetched a pointer to the dynamic cleanup chain for exception
handling. */
rtx current_function_dcc;
/* 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;
/* The rtx and the tree for the saved PC value. */
rtx eh_saved_pc_rtx;
tree eh_saved_pc;
rtx expand_builtin_return_addr PROTO((enum built_in_function, int, rtx));
/* 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;
}
/* Make a copy of ENTRY using xmalloc to allocate the space. */
static struct eh_entry *
copy_eh_entry (entry)
struct eh_entry *entry;
{
struct eh_entry *newentry;
newentry = (struct eh_entry *) xmalloc (sizeof (struct eh_entry));
bcopy ((char *) entry, (char *) newentry, sizeof (struct eh_entry));
return newentry;
}
/* 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;
}
/* 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 ();
}
/* 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.
This routine is here to facilitate the porting of this code to
systems with threads. One can either replace the routine we emit a
call for here in libgcc2.c, or one can modify this routine to work
with their thread system.
Ideally, we really only want one per real function, not one
per inlined function. */
rtx
get_dynamic_handler_chain ()
{
static tree fn;
tree expr;
rtx insns;
if (current_function_dhc)
return current_function_dhc;
if (fn == NULL_TREE)
{
tree fntype;
fn = get_identifier ("__get_dynamic_handler_chain");
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;
expr = build1 (INDIRECT_REF, TREE_TYPE (TREE_TYPE (expr)), expr);
start_sequence ();
current_function_dhc = expand_expr (expr, NULL_RTX, VOIDmode, 0);
insns = get_insns ();
end_sequence ();
emit_insns_before (insns, get_first_nonparm_insn ());
return current_function_dhc;
}
/* 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;
dhc = get_dynamic_handler_chain ();
dcc = plus_constant (dhc, GET_MODE_SIZE (Pmode));
current_function_dcc = copy_to_reg (dcc);
/* We don't want a copy of the dcc, but rather, the single dcc. */
return gen_rtx (MEM, Pmode, current_function_dcc);
}
/* 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 dhc, 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);
#else
x = expand_builtin_setjmp (buf, NULL_RTX);
#endif
/* If we come back here for a catch, transfer control to the
handler. */
jumpif_rtx (x, ehstack.top->entry->exception_handler_label);
/* 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;
{
rtx note;
/* 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);
}
if (exceptions_via_longjmp == 0)
note = emit_note (NULL_PTR, NOTE_INSN_EH_REGION_BEG);
push_eh_entry (&ehstack);
if (exceptions_via_longjmp == 0)
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;
if (! doing_eh (0))
return;
entry = pop_eh_entry (&ehstack);
if (exceptions_via_longjmp == 0)
{
rtx label;
rtx note = emit_note (NULL_PTR, NOTE_INSN_EH_REGION_END);
NOTE_BLOCK_NUMBER (note) = CODE_LABEL_NUMBER (entry->exception_handler_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);
/* Put in something that takes up space, as otherwise the end
address for this EH region could have the exact same address as
its outer region. This would cause us to miss the fact that
resuming exception handling with this PC value would be inside
the outer region. */
emit_insn (gen_nop ());
emit_barrier ();
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;
{
tree t;
struct eh_node *node;
int yes;
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 ();
yes = suspend_momentary ();
t = build (RTL_EXPR, void_type_node, NULL_RTX, const0_rtx);
TREE_SIDE_EFFECTS (t) = 1;
do_pending_stack_adjust ();
start_sequence_for_rtl_expr (t);
expand_internal_throw (node->entry->outer_context);
do_pending_stack_adjust ();
RTL_EXPR_SEQUENCE (t) = get_insns ();
end_sequence ();
resume_momentary (yes);
expand_eh_region_end (t);
}
/* 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
#ifndef DWARF2_UNWIND_INFO
/* Prevent assemble_external from doing anything with this symbol. */
SYMBOL_REF_USED (throw_libfunc) = 1;
#endif
emit_library_call (throw_libfunc, 0, VOIDmode, 0);
#endif
throw_used = 1;
}
emit_barrier ();
}
/* An internal throw with an indirect CONTEXT we want to throw from.
CONTEXT evaluates to the context of the throw. */
static void
expand_internal_throw_indirect (context)
rtx context;
{
assemble_external (eh_saved_pc);
emit_move_insn (eh_saved_pc_rtx, context);
emit_throw ();
}
/* An internal throw with a direct CONTEXT we want to throw from.
CONTEXT must be a label; its address will be used as the context of
the throw. */
void
expand_internal_throw (context)
rtx context;
{
expand_internal_throw_indirect (gen_rtx (LABEL_REF, Pmode, context));
}
/* 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)
{
if (exceptions_via_longjmp)
emit_throw ();
else
{
/* The below can be optimized away, and we could just
fall into the next EH handler, if we are certain they
are nested. */
/* Emit code to throw to the outer context if we fall off
the end of the handler. */
expand_internal_throw (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;
if (! doing_eh (1))
return;
push_label_entry (&outer_context_label_stack,
ehstack.top->entry->outer_context, NULL_TREE);
/* 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);
if (exceptions_via_longjmp == 0)
{
/* Put in something that takes up space, as otherwise the end
address for the EH region could have the exact same address as
the outer region, causing us to miss the fact that resuming
exception handling with this PC value would be inside the outer
region. */
emit_insn (gen_nop ());
}
/* 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)
{
if (exceptions_via_longjmp)
emit_throw ();
else
{
/* 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.
The below can be optimized away (and we could just fall
into the next EH handler) if we are certain they are
nested. */
expand_internal_throw (entry->outer_context);
}
}
do_pending_stack_adjust ();
free (entry);
}
}
/* 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;
if (! doing_eh (1))
return;
if (exceptions_via_longjmp)
emit_throw ();
else
{
/* 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_internal_throw (outer_context_label_stack->u.rlabel);
}
/* 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. */
}
/* 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;
}
/* 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;
}
/* 1 if we need a static constructor to register EH table info. */
int
register_exception_table_p ()
{
#if defined (DWARF2_UNWIND_INFO)
return 0;
#endif
return exception_table_p ();
}
/* 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_label ("__EXCEPTION_END__");
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 */
}
/* Generate code to initialize the exception table at program startup
time. */
void
register_exception_table ()
{
emit_library_call (gen_rtx (SYMBOL_REF, Pmode, "__register_exceptions"), 0,
VOIDmode, 1,
gen_rtx (SYMBOL_REF, Pmode, "__EXCEPTION_TABLE__"),
Pmode);
}
/* Emit the RTL for the start of the per-function unwinder for the
current function. See emit_unwinder for further information.
DOESNT_NEED_UNWINDER is a target-specific macro that determines if
the current function actually needs a per-function unwinder or not.
By default, all functions need one. */
void
start_eh_unwinder ()
{
#ifdef DOESNT_NEED_UNWINDER
if (DOESNT_NEED_UNWINDER)
return;
#endif
/* If we are using the setjmp/longjmp implementation, we don't need a
per function unwinder. */
if (exceptions_via_longjmp)
return;
#ifdef DWARF2_UNWIND_INFO
return;
#endif
expand_eh_region_start ();
}
/* Emit insns for the end of the per-function unwinder for the
current function. */
void
end_eh_unwinder ()
{
tree expr;
rtx return_val_rtx, ret_val, label, end, insns;
if (! doing_eh (0))
return;
#ifdef DOESNT_NEED_UNWINDER
if (DOESNT_NEED_UNWINDER)
return;
#endif
/* If we are using the setjmp/longjmp implementation, we don't need a
per function unwinder. */
if (exceptions_via_longjmp)
return;
#ifdef DWARF2_UNWIND_INFO
return;
#else /* DWARF2_UNWIND_INFO */
assemble_external (eh_saved_pc);
expr = make_node (RTL_EXPR);
TREE_TYPE (expr) = void_type_node;
RTL_EXPR_RTL (expr) = const0_rtx;
TREE_SIDE_EFFECTS (expr) = 1;
start_sequence_for_rtl_expr (expr);
/* ret_val will contain the address of the code where the call
to the current function occurred. */
ret_val = expand_builtin_return_addr (BUILT_IN_RETURN_ADDRESS,
0, hard_frame_pointer_rtx);
return_val_rtx = copy_to_reg (ret_val);
/* Get the address we need to use to determine what exception
handler should be invoked, and store it in __eh_pc. */
return_val_rtx = eh_outer_context (return_val_rtx);
return_val_rtx = expand_binop (Pmode, sub_optab, return_val_rtx, GEN_INT (1),
NULL_RTX, 0, OPTAB_LIB_WIDEN);
emit_move_insn (eh_saved_pc_rtx, return_val_rtx);
/* Either set things up so we do a return directly to __throw, or
we return here instead. */
#ifdef JUMP_TO_THROW
emit_move_insn (ret_val, throw_libfunc);
#else
label = gen_label_rtx ();
emit_move_insn (ret_val, gen_rtx (LABEL_REF, Pmode, label));
#endif
#ifdef RETURN_ADDR_OFFSET
return_val_rtx = plus_constant (ret_val, -RETURN_ADDR_OFFSET);
if (return_val_rtx != ret_val)
emit_move_insn (ret_val, return_val_rtx);
#endif
end = gen_label_rtx ();
emit_jump (end);
RTL_EXPR_SEQUENCE (expr) = get_insns ();
end_sequence ();
expand_eh_region_end (expr);
emit_jump (end);
#ifndef JUMP_TO_THROW
emit_label (label);
emit_throw ();
#endif
expand_leftover_cleanups ();
emit_label (end);
#ifdef HAVE_return
if (HAVE_return)
{
emit_jump_insn (gen_return ());
emit_barrier ();
}
#endif
#endif /* DWARF2_UNWIND_INFO */
}
/* If necessary, emit insns for the per function unwinder for the
current function. Called after all the code that needs unwind
protection is output.
The unwinder takes care of catching any exceptions that have not
been previously caught within the function, unwinding the stack to
the next frame, and rethrowing using the address of the current
function's caller as the context of the throw.
On some platforms __throw can do this by itself (or with the help
of __unwind_function) so the per-function unwinder is
unnecessary.
We cannot place the unwinder into the function until after we know
we are done inlining, as we don't want to have more than one
unwinder per non-inlined function. */
void
emit_unwinder ()
{
rtx insns, insn;
start_sequence ();
start_eh_unwinder ();
insns = get_insns ();
end_sequence ();
/* We place the start of the exception region associated with the
per function unwinder at the top of the function. */
if (insns)
emit_insns_after (insns, get_insns ());
start_sequence ();
end_eh_unwinder ();
insns = get_insns ();
end_sequence ();
/* And we place the end of the exception region before the USE and
CLOBBER insns that may come at the end of the function. */
if (insns == 0)
return;
insn = get_last_insn ();
while (GET_CODE (insn) == NOTE
|| (GET_CODE (insn) == INSN
&& (GET_CODE (PATTERN (insn)) == USE
|| GET_CODE (PATTERN (insn)) == CLOBBER)))
insn = PREV_INSN (insn);
if (GET_CODE (insn) == CODE_LABEL
&& GET_CODE (PREV_INSN (insn)) == BARRIER)
{
insn = PREV_INSN (insn);
}
else
{
rtx label = gen_label_rtx ();
emit_label_after (label, insn);
insn = emit_jump_insn_after (gen_jump (label), insn);
insn = emit_barrier_after (insn);
}
emit_insns_after (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)
warning ("region exists, no handler %d",
NOTE_BLOCK_NUMBER (insn));
}
}
}
/* 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. */
tree type = build_pointer_type (make_node (VOID_TYPE));
eh_saved_pc = build_decl (VAR_DECL, get_identifier ("__eh_pc"), type);
DECL_EXTERNAL (eh_saved_pc) = 1;
TREE_PUBLIC (eh_saved_pc) = 1;
make_decl_rtl (eh_saved_pc, NULL_PTR, 1);
eh_saved_pc_rtx = DECL_RTL (eh_saved_pc);
}
/* 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_dhc = NULL_RTX;
current_function_dcc = 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;
{
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->dhc = current_function_dhc;
p->dcc = current_function_dcc;
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;
{
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_dhc = p->dhc;
current_function_dcc = p->dcc;
}
/* 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 (! (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, regions = NULL_RTX;
int n;
/* The below doesn't apply to setjmp/longjmp EH. */
if (exceptions_via_longjmp)
return;
/* 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);
}
}
}
/* 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, temp;
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));
}
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