1 /* Tree lowering pass. Lowers GIMPLE into unstructured form.
3 Copyright (C) 2003, 2005 Free Software Foundation, Inc.
5 This file is part of GCC.
7 GCC is free software; you can redistribute it and/or modify it under
8 the terms of the GNU General Public License as published by the Free
9 Software Foundation; either version 2, or (at your option) any later
12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
17 You should have received a copy of the GNU General Public License
18 along with GCC; see the file COPYING. If not, write to the Free
19 Software Foundation, 59 Temple Place - Suite 330, Boston, MA
24 #include "coretypes.h"
30 #include "tree-gimple.h"
31 #include "tree-inline.h"
32 #include "diagnostic.h"
33 #include "langhooks.h"
34 #include "langhooks-def.h"
35 #include "tree-flow.h"
43 #include "tree-pass.h"
47 /* Block the current statement belongs to. */
50 /* A TREE_LIST of label and return statements to be moved to the end
52 tree return_statements
;
55 static void lower_stmt (tree_stmt_iterator
*, struct lower_data
*);
56 static void lower_bind_expr (tree_stmt_iterator
*, struct lower_data
*);
57 static void lower_cond_expr (tree_stmt_iterator
*, struct lower_data
*);
58 static void lower_return_expr (tree_stmt_iterator
*, struct lower_data
*);
59 static bool expand_var_p (tree
);
61 /* Lowers the body of current_function_decl. */
64 lower_function_body (void)
66 struct lower_data data
;
67 tree
*body_p
= &DECL_SAVED_TREE (current_function_decl
);
72 gcc_assert (TREE_CODE (bind
) == BIND_EXPR
);
74 data
.block
= DECL_INITIAL (current_function_decl
);
75 BLOCK_SUBBLOCKS (data
.block
) = NULL_TREE
;
76 BLOCK_CHAIN (data
.block
) = NULL_TREE
;
77 TREE_ASM_WRITTEN (data
.block
) = 1;
79 data
.return_statements
= NULL_TREE
;
81 *body_p
= alloc_stmt_list ();
82 i
= tsi_start (*body_p
);
83 tsi_link_after (&i
, bind
, TSI_NEW_STMT
);
84 lower_bind_expr (&i
, &data
);
86 i
= tsi_last (*body_p
);
88 /* If the function falls off the end, we need a null return statement.
89 If we've already got one in the return_statements list, we don't
90 need to do anything special. Otherwise build one by hand. */
91 if (block_may_fallthru (*body_p
)
92 && (data
.return_statements
== NULL
93 || TREE_OPERAND (TREE_VALUE (data
.return_statements
), 0) != NULL
))
95 x
= build (RETURN_EXPR
, void_type_node
, NULL
);
96 SET_EXPR_LOCATION (x
, cfun
->function_end_locus
);
97 tsi_link_after (&i
, x
, TSI_CONTINUE_LINKING
);
100 /* If we lowered any return statements, emit the representative
101 at the end of the function. */
102 for (t
= data
.return_statements
; t
; t
= TREE_CHAIN (t
))
104 x
= build (LABEL_EXPR
, void_type_node
, TREE_PURPOSE (t
));
105 tsi_link_after (&i
, x
, TSI_CONTINUE_LINKING
);
107 /* Remove the line number from the representative return statement.
108 It now fills in for many such returns. Failure to remove this
109 will result in incorrect results for coverage analysis. */
111 #ifdef USE_MAPPED_LOCATION
112 SET_EXPR_LOCATION (x
, UNKNOWN_LOCATION
);
114 SET_EXPR_LOCUS (x
, NULL
);
116 tsi_link_after (&i
, x
, TSI_CONTINUE_LINKING
);
119 gcc_assert (data
.block
== DECL_INITIAL (current_function_decl
));
120 BLOCK_SUBBLOCKS (data
.block
)
121 = blocks_nreverse (BLOCK_SUBBLOCKS (data
.block
));
123 clear_block_marks (data
.block
);
126 struct tree_opt_pass pass_lower_cf
=
130 lower_function_body
, /* execute */
133 0, /* static_pass_number */
135 PROP_gimple_any
, /* properties_required */
136 PROP_gimple_lcf
, /* properties_provided */
137 PROP_gimple_any
, /* properties_destroyed */
138 0, /* todo_flags_start */
139 TODO_dump_func
, /* todo_flags_finish */
144 /* Lowers the EXPR. Unlike gimplification the statements are not relowered
145 when they are changed -- if this has to be done, the lowering routine must
146 do it explicitly. DATA is passed through the recursion. */
149 lower_stmt_body (tree expr
, struct lower_data
*data
)
151 tree_stmt_iterator tsi
;
153 for (tsi
= tsi_start (expr
); !tsi_end_p (tsi
); )
154 lower_stmt (&tsi
, data
);
157 /* Lowers statement TSI. DATA is passed through the recursion. */
160 lower_stmt (tree_stmt_iterator
*tsi
, struct lower_data
*data
)
162 tree stmt
= tsi_stmt (*tsi
);
164 if (EXPR_HAS_LOCATION (stmt
) && data
)
165 TREE_BLOCK (stmt
) = data
->block
;
167 switch (TREE_CODE (stmt
))
170 lower_bind_expr (tsi
, data
);
173 lower_cond_expr (tsi
, data
);
176 lower_return_expr (tsi
, data
);
179 case TRY_FINALLY_EXPR
:
181 lower_stmt_body (TREE_OPERAND (stmt
, 0), data
);
182 lower_stmt_body (TREE_OPERAND (stmt
, 1), data
);
185 lower_stmt_body (CATCH_BODY (stmt
), data
);
188 lower_stmt_body (EH_FILTER_FAILURE (stmt
), data
);
201 #ifdef ENABLE_CHECKING
202 print_node_brief (stderr
, "", stmt
, 0);
203 internal_error ("unexpected node");
212 /* Lowers a bind_expr TSI. DATA is passed through the recursion. */
215 lower_bind_expr (tree_stmt_iterator
*tsi
, struct lower_data
*data
)
217 tree old_block
= data
->block
;
218 tree stmt
= tsi_stmt (*tsi
);
219 tree new_block
= BIND_EXPR_BLOCK (stmt
);
223 if (new_block
== old_block
)
225 /* The outermost block of the original function may not be the
226 outermost statement chain of the gimplified function. So we
227 may see the outermost block just inside the function. */
228 gcc_assert (new_block
== DECL_INITIAL (current_function_decl
));
233 /* We do not expect to handle duplicate blocks. */
234 gcc_assert (!TREE_ASM_WRITTEN (new_block
));
235 TREE_ASM_WRITTEN (new_block
) = 1;
237 /* Block tree may get clobbered by inlining. Normally this would
238 be fixed in rest_of_decl_compilation using block notes, but
239 since we are not going to emit them, it is up to us. */
240 BLOCK_CHAIN (new_block
) = BLOCK_SUBBLOCKS (old_block
);
241 BLOCK_SUBBLOCKS (old_block
) = new_block
;
242 BLOCK_SUBBLOCKS (new_block
) = NULL_TREE
;
243 BLOCK_SUPERCONTEXT (new_block
) = old_block
;
245 data
->block
= new_block
;
249 record_vars (BIND_EXPR_VARS (stmt
));
250 lower_stmt_body (BIND_EXPR_BODY (stmt
), data
);
254 gcc_assert (data
->block
== new_block
);
256 BLOCK_SUBBLOCKS (new_block
)
257 = blocks_nreverse (BLOCK_SUBBLOCKS (new_block
));
258 data
->block
= old_block
;
261 /* The BIND_EXPR no longer carries any useful information -- kill it. */
262 tsi_link_before (tsi
, BIND_EXPR_BODY (stmt
), TSI_SAME_STMT
);
266 /* Try to determine whether a TRY_CATCH expression can fall through.
267 This is a subroutine of block_may_fallthru. */
270 try_catch_may_fallthru (tree stmt
)
272 tree_stmt_iterator i
;
274 /* If the TRY block can fall through, the whole TRY_CATCH can
276 if (block_may_fallthru (TREE_OPERAND (stmt
, 0)))
279 i
= tsi_start (TREE_OPERAND (stmt
, 1));
280 switch (TREE_CODE (tsi_stmt (i
)))
283 /* We expect to see a sequence of CATCH_EXPR trees, each with a
284 catch expression and a body. The whole TRY_CATCH may fall
285 through iff any of the catch bodies falls through. */
286 for (; !tsi_end_p (i
); tsi_next (&i
))
288 if (block_may_fallthru (CATCH_BODY (tsi_stmt (i
))))
294 /* The exception filter expression only matters if there is an
295 exception. If the exception does not match EH_FILTER_TYPES,
296 we will execute EH_FILTER_FAILURE, and we will fall through
297 if that falls through. If the exception does match
298 EH_FILTER_TYPES, the stack unwinder will continue up the
299 stack, so we will not fall through. We don't know whether we
300 will throw an exception which matches EH_FILTER_TYPES or not,
301 so we just ignore EH_FILTER_TYPES and assume that we might
302 throw an exception which doesn't match. */
303 return block_may_fallthru (EH_FILTER_FAILURE (tsi_stmt (i
)));
306 /* This case represents statements to be executed when an
307 exception occurs. Those statements are implicitly followed
308 by a RESX_EXPR to resume execution after the exception. So
309 in this case the TRY_CATCH never falls through. */
314 /* Try to determine if we can fall out of the bottom of BLOCK. This guess
315 need not be 100% accurate; simply be conservative and return true if we
316 don't know. This is used only to avoid stupidly generating extra code.
317 If we're wrong, we'll just delete the extra code later. */
320 block_may_fallthru (tree block
)
322 tree stmt
= expr_last (block
);
324 switch (stmt
? TREE_CODE (stmt
) : ERROR_MARK
)
329 /* Easy cases. If the last statement of the block implies
330 control transfer, then we can't fall through. */
334 /* If SWITCH_LABELS is set, this is lowered, and represents a
335 branch to a selected label and hence can not fall through.
336 Otherwise SWITCH_BODY is set, and the switch can fall
338 return SWITCH_LABELS (stmt
) == NULL_TREE
;
341 if (block_may_fallthru (COND_EXPR_THEN (stmt
)))
343 return block_may_fallthru (COND_EXPR_ELSE (stmt
));
346 return block_may_fallthru (BIND_EXPR_BODY (stmt
));
349 return try_catch_may_fallthru (stmt
);
351 case TRY_FINALLY_EXPR
:
352 /* The finally clause is always executed after the try clause,
353 so if it does not fall through, then the try-finally will not
354 fall through. Otherwise, if the try clause does not fall
355 through, then when the finally clause falls through it will
356 resume execution wherever the try clause was going. So the
357 whole try-finally will only fall through if both the try
358 clause and the finally clause fall through. */
359 return (block_may_fallthru (TREE_OPERAND (stmt
, 0))
360 && block_may_fallthru (TREE_OPERAND (stmt
, 1)));
363 if (TREE_CODE (TREE_OPERAND (stmt
, 1)) == CALL_EXPR
)
364 stmt
= TREE_OPERAND (stmt
, 1);
370 /* Functions that do not return do not fall through. */
371 return (call_expr_flags (stmt
) & ECF_NORETURN
) == 0;
373 case CLEANUP_POINT_EXPR
:
374 return block_may_fallthru (TREE_OPERAND (stmt
, 0));
381 /* Lowers a cond_expr TSI. DATA is passed through the recursion. */
384 lower_cond_expr (tree_stmt_iterator
*tsi
, struct lower_data
*data
)
386 tree stmt
= tsi_stmt (*tsi
);
387 bool then_is_goto
, else_is_goto
;
388 tree then_branch
, else_branch
;
389 tree then_goto
, else_goto
;
391 then_branch
= COND_EXPR_THEN (stmt
);
392 else_branch
= COND_EXPR_ELSE (stmt
);
394 lower_stmt_body (then_branch
, data
);
395 lower_stmt_body (else_branch
, data
);
397 then_goto
= expr_only (then_branch
);
398 then_is_goto
= then_goto
&& simple_goto_p (then_goto
);
400 else_goto
= expr_only (else_branch
);
401 else_is_goto
= else_goto
&& simple_goto_p (else_goto
);
403 if (!then_is_goto
|| !else_is_goto
)
405 tree then_label
, else_label
, end_label
, t
;
407 then_label
= NULL_TREE
;
408 else_label
= NULL_TREE
;
409 end_label
= NULL_TREE
;
411 /* Replace the cond_expr with explicit gotos. */
414 t
= build1 (LABEL_EXPR
, void_type_node
, NULL_TREE
);
415 if (TREE_SIDE_EFFECTS (then_branch
))
419 then_goto
= build_and_jump (&LABEL_EXPR_LABEL (t
));
424 t
= build1 (LABEL_EXPR
, void_type_node
, NULL_TREE
);
425 if (TREE_SIDE_EFFECTS (else_branch
))
429 /* Both THEN and ELSE can be no-ops if one or both contained an
430 empty BIND_EXPR that was associated with the toplevel block
431 of an inlined function. In that case remove_useless_stmts
432 can't have cleaned things up for us; kill the whole
442 else_goto
= build_and_jump (&LABEL_EXPR_LABEL (t
));
447 bool may_fallthru
= block_may_fallthru (then_branch
);
449 tsi_link_after (tsi
, then_label
, TSI_CONTINUE_LINKING
);
450 tsi_link_after (tsi
, then_branch
, TSI_CONTINUE_LINKING
);
452 if (else_label
&& may_fallthru
)
454 end_label
= build1 (LABEL_EXPR
, void_type_node
, NULL_TREE
);
455 t
= build_and_jump (&LABEL_EXPR_LABEL (end_label
));
456 tsi_link_after (tsi
, t
, TSI_CONTINUE_LINKING
);
462 tsi_link_after (tsi
, else_label
, TSI_CONTINUE_LINKING
);
463 tsi_link_after (tsi
, else_branch
, TSI_CONTINUE_LINKING
);
467 tsi_link_after (tsi
, end_label
, TSI_CONTINUE_LINKING
);
470 COND_EXPR_THEN (stmt
) = then_goto
;
471 COND_EXPR_ELSE (stmt
) = else_goto
;
477 lower_return_expr (tree_stmt_iterator
*tsi
, struct lower_data
*data
)
479 tree stmt
= tsi_stmt (*tsi
);
480 tree value
, t
, label
;
482 /* Extract the value being returned. */
483 value
= TREE_OPERAND (stmt
, 0);
484 if (value
&& TREE_CODE (value
) == MODIFY_EXPR
)
485 value
= TREE_OPERAND (value
, 1);
487 /* Match this up with an existing return statement that's been created. */
488 for (t
= data
->return_statements
; t
; t
= TREE_CHAIN (t
))
490 tree tvalue
= TREE_OPERAND (TREE_VALUE (t
), 0);
491 if (tvalue
&& TREE_CODE (tvalue
) == MODIFY_EXPR
)
492 tvalue
= TREE_OPERAND (tvalue
, 1);
496 label
= TREE_PURPOSE (t
);
501 /* Not found. Create a new label and record the return statement. */
502 label
= create_artificial_label ();
503 data
->return_statements
= tree_cons (label
, stmt
, data
->return_statements
);
505 /* Generate a goto statement and remove the return statement. */
507 t
= build (GOTO_EXPR
, void_type_node
, label
);
508 SET_EXPR_LOCUS (t
, EXPR_LOCUS (stmt
));
509 tsi_link_before (tsi
, t
, TSI_SAME_STMT
);
514 /* Record the variables in VARS. */
517 record_vars (tree vars
)
519 for (; vars
; vars
= TREE_CHAIN (vars
))
523 /* Nothing to do in this case. */
524 if (DECL_EXTERNAL (var
))
526 if (TREE_CODE (var
) == FUNCTION_DECL
)
529 /* Record the variable. */
530 cfun
->unexpanded_var_list
= tree_cons (NULL_TREE
, var
,
531 cfun
->unexpanded_var_list
);
535 /* Check whether to expand a variable VAR. */
538 expand_var_p (tree var
)
540 struct var_ann_d
*ann
;
542 if (TREE_CODE (var
) != VAR_DECL
)
545 /* Leave statics and externals alone. */
546 if (TREE_STATIC (var
) || DECL_EXTERNAL (var
))
549 /* Remove all unused local variables. */
551 if (!ann
|| !ann
->used
)
557 /* Throw away variables that are unused. */
560 remove_useless_vars (void)
565 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
568 fputs ("Discarding as unused:\n", df
);
571 for (cell
= &cfun
->unexpanded_var_list
; *cell
; )
573 var
= TREE_VALUE (*cell
);
575 if (!expand_var_p (var
))
580 print_generic_expr (df
, var
, dump_flags
);
584 *cell
= TREE_CHAIN (*cell
);
588 cell
= &TREE_CHAIN (*cell
);
595 struct tree_opt_pass pass_remove_useless_vars
=
599 remove_useless_vars
, /* execute */
602 0, /* static_pass_number */
604 0, /* properties_required */
605 0, /* properties_provided */
606 0, /* properties_destroyed */
607 0, /* todo_flags_start */
608 TODO_dump_func
, /* todo_flags_finish */
612 /* Mark BLOCK used if it has a used variable in it, then recurse over its
616 mark_blocks_with_used_vars (tree block
)
621 if (!TREE_USED (block
))
623 for (var
= BLOCK_VARS (block
);
625 var
= TREE_CHAIN (var
))
629 TREE_USED (block
) = true;
634 for (subblock
= BLOCK_SUBBLOCKS (block
);
636 subblock
= BLOCK_CHAIN (subblock
))
637 mark_blocks_with_used_vars (subblock
);
640 /* Mark the used attribute on blocks correctly. */
643 mark_used_blocks (void)
645 mark_blocks_with_used_vars (DECL_INITIAL (current_function_decl
));
649 struct tree_opt_pass pass_mark_used_blocks
=
653 mark_used_blocks
, /* execute */
656 0, /* static_pass_number */
658 0, /* properties_required */
659 0, /* properties_provided */
660 0, /* properties_destroyed */
661 0, /* todo_flags_start */
662 TODO_dump_func
, /* todo_flags_finish */