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 /* If the exception does not match EH_FILTER_TYPES, we will
295 execute EH_FILTER_FAILURE, and we will fall through if that
296 falls through. If the exception does match EH_FILTER_TYPES,
297 we will fall through. We don't know which exceptions may be
298 generated, so we just check for EH_FILTER_TYPES being NULL,
299 in which case we know that that the exception does not
301 return (EH_FILTER_TYPES (tsi_stmt (i)) != NULL
302 || block_may_fallthru (EH_FILTER_FAILURE (tsi_stmt (i))));
305 /* This case represents statements to be executed when an
306 exception occurs. Those statements are implicitly followed
307 by a RESX_EXPR to resume execution after the exception. So
308 in this case the TRY_CATCH never falls through. */
313 /* Try to determine if we can fall out of the bottom of BLOCK. This guess
314 need not be 100% accurate; simply be conservative and return true if we
315 don't know. This is used only to avoid stupidly generating extra code.
316 If we're wrong, we'll just delete the extra code later. */
319 block_may_fallthru (tree block)
321 tree stmt = expr_last (block);
323 switch (stmt ? TREE_CODE (stmt) : ERROR_MARK)
328 /* Easy cases. If the last statement of the block implies
329 control transfer, then we can't fall through. */
333 /* If SWITCH_LABELS is set, this is lowered, and represents a
334 branch to a selected label and hence can not fall through.
335 Otherwise SWITCH_BODY is set, and the switch can fall
337 return SWITCH_LABELS (stmt) == NULL_TREE;
340 if (block_may_fallthru (COND_EXPR_THEN (stmt)))
342 return block_may_fallthru (COND_EXPR_ELSE (stmt));
345 return block_may_fallthru (BIND_EXPR_BODY (stmt));
348 return try_catch_may_fallthru (stmt);
350 case TRY_FINALLY_EXPR:
351 return block_may_fallthru (TREE_OPERAND (stmt, 1));
354 if (TREE_CODE (TREE_OPERAND (stmt, 1)) == CALL_EXPR)
355 stmt = TREE_OPERAND (stmt, 1);
361 /* Functions that do not return do not fall through. */
362 return (call_expr_flags (stmt) & ECF_NORETURN) == 0;
369 /* Lowers a cond_expr TSI. DATA is passed through the recursion. */
372 lower_cond_expr (tree_stmt_iterator *tsi, struct lower_data *data)
374 tree stmt = tsi_stmt (*tsi);
375 bool then_is_goto, else_is_goto;
376 tree then_branch, else_branch;
377 tree then_goto, else_goto;
379 then_branch = COND_EXPR_THEN (stmt);
380 else_branch = COND_EXPR_ELSE (stmt);
382 lower_stmt_body (then_branch, data);
383 lower_stmt_body (else_branch, data);
385 then_goto = expr_only (then_branch);
386 then_is_goto = then_goto && simple_goto_p (then_goto);
388 else_goto = expr_only (else_branch);
389 else_is_goto = else_goto && simple_goto_p (else_goto);
391 if (!then_is_goto || !else_is_goto)
393 tree then_label, else_label, end_label, t;
395 then_label = NULL_TREE;
396 else_label = NULL_TREE;
397 end_label = NULL_TREE;
399 /* Replace the cond_expr with explicit gotos. */
402 t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
403 if (TREE_SIDE_EFFECTS (then_branch))
407 then_goto = build_and_jump (&LABEL_EXPR_LABEL (t));
412 t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
413 if (TREE_SIDE_EFFECTS (else_branch))
417 /* Both THEN and ELSE can be no-ops if one or both contained an
418 empty BIND_EXPR that was associated with the toplevel block
419 of an inlined function. In that case remove_useless_stmts
420 can't have cleaned things up for us; kill the whole
430 else_goto = build_and_jump (&LABEL_EXPR_LABEL (t));
435 bool may_fallthru = block_may_fallthru (then_branch);
437 tsi_link_after (tsi, then_label, TSI_CONTINUE_LINKING);
438 tsi_link_after (tsi, then_branch, TSI_CONTINUE_LINKING);
440 if (else_label && may_fallthru)
442 end_label = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
443 t = build_and_jump (&LABEL_EXPR_LABEL (end_label));
444 tsi_link_after (tsi, t, TSI_CONTINUE_LINKING);
450 tsi_link_after (tsi, else_label, TSI_CONTINUE_LINKING);
451 tsi_link_after (tsi, else_branch, TSI_CONTINUE_LINKING);
455 tsi_link_after (tsi, end_label, TSI_CONTINUE_LINKING);
458 COND_EXPR_THEN (stmt) = then_goto;
459 COND_EXPR_ELSE (stmt) = else_goto;
465 lower_return_expr (tree_stmt_iterator *tsi, struct lower_data *data)
467 tree stmt = tsi_stmt (*tsi);
468 tree value, t, label;
470 /* Extract the value being returned. */
471 value = TREE_OPERAND (stmt, 0);
472 if (value && TREE_CODE (value) == MODIFY_EXPR)
473 value = TREE_OPERAND (value, 1);
475 /* Match this up with an existing return statement that's been created. */
476 for (t = data->return_statements; t ; t = TREE_CHAIN (t))
478 tree tvalue = TREE_OPERAND (TREE_VALUE (t), 0);
479 if (tvalue && TREE_CODE (tvalue) == MODIFY_EXPR)
480 tvalue = TREE_OPERAND (tvalue, 1);
484 label = TREE_PURPOSE (t);
489 /* Not found. Create a new label and record the return statement. */
490 label = create_artificial_label ();
491 data->return_statements = tree_cons (label, stmt, data->return_statements);
493 /* Generate a goto statement and remove the return statement. */
495 t = build (GOTO_EXPR, void_type_node, label);
496 SET_EXPR_LOCUS (t, EXPR_LOCUS (stmt));
497 tsi_link_before (tsi, t, TSI_SAME_STMT);
502 /* Record the variables in VARS. */
505 record_vars (tree vars)
507 for (; vars; vars = TREE_CHAIN (vars))
511 /* Nothing to do in this case. */
512 if (DECL_EXTERNAL (var))
514 if (TREE_CODE (var) == FUNCTION_DECL)
517 /* Record the variable. */
518 cfun->unexpanded_var_list = tree_cons (NULL_TREE, var,
519 cfun->unexpanded_var_list);
523 /* Check whether to expand a variable VAR. */
526 expand_var_p (tree var)
528 struct var_ann_d *ann;
530 if (TREE_CODE (var) != VAR_DECL)
533 /* Leave statics and externals alone. */
534 if (TREE_STATIC (var) || DECL_EXTERNAL (var))
537 /* Remove all unused local variables. */
539 if (!ann || !ann->used)
545 /* Throw away variables that are unused. */
548 remove_useless_vars (void)
553 if (dump_file && (dump_flags & TDF_DETAILS))
556 fputs ("Discarding as unused:\n", df);
559 for (cell = &cfun->unexpanded_var_list; *cell; )
561 var = TREE_VALUE (*cell);
563 if (!expand_var_p (var))
568 print_generic_expr (df, var, dump_flags);
572 *cell = TREE_CHAIN (*cell);
576 cell = &TREE_CHAIN (*cell);
583 struct tree_opt_pass pass_remove_useless_vars =
587 remove_useless_vars, /* execute */
590 0, /* static_pass_number */
592 0, /* properties_required */
593 0, /* properties_provided */
594 0, /* properties_destroyed */
595 0, /* todo_flags_start */
596 TODO_dump_func, /* todo_flags_finish */
600 /* Mark BLOCK used if it has a used variable in it, then recurse over its
604 mark_blocks_with_used_vars (tree block)
609 if (!TREE_USED (block))
611 for (var = BLOCK_VARS (block);
613 var = TREE_CHAIN (var))
617 TREE_USED (block) = true;
622 for (subblock = BLOCK_SUBBLOCKS (block);
624 subblock = BLOCK_CHAIN (subblock))
625 mark_blocks_with_used_vars (subblock);
628 /* Mark the used attribute on blocks correctly. */
631 mark_used_blocks (void)
633 mark_blocks_with_used_vars (DECL_INITIAL (current_function_decl));
637 struct tree_opt_pass pass_mark_used_blocks =
641 mark_used_blocks, /* execute */
644 0, /* static_pass_number */
646 0, /* properties_required */
647 0, /* properties_provided */
648 0, /* properties_destroyed */
649 0, /* todo_flags_start */
650 TODO_dump_func, /* todo_flags_finish */