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 if we can fall out of the bottom of BLOCK. This guess
267 need not be 100% accurate; simply be conservative and return true if we
268 don't know. This is used only to avoid stupidly generating extra code.
269 If we're wrong, we'll just delete the extra code later. */
272 block_may_fallthru (tree block)
274 tree stmt = expr_last (block);
276 switch (stmt ? TREE_CODE (stmt) : ERROR_MARK)
281 /* Easy cases. If the last statement of the block implies
282 control transfer, then we can't fall through. */
286 /* If SWITCH_LABELS is set, this is lowered, and represents a
287 branch to a selected label and hence can not fall through.
288 Otherwise SWITCH_BODY is set, and the switch can fall
290 return SWITCH_LABELS (stmt) != NULL_TREE;
293 if (block_may_fallthru (COND_EXPR_THEN (stmt)))
295 return block_may_fallthru (COND_EXPR_ELSE (stmt));
298 return block_may_fallthru (BIND_EXPR_BODY (stmt));
300 case TRY_FINALLY_EXPR:
301 return block_may_fallthru (TREE_OPERAND (stmt, 1));
304 if (TREE_CODE (TREE_OPERAND (stmt, 1)) == CALL_EXPR)
305 stmt = TREE_OPERAND (stmt, 1);
311 /* Functions that do not return do not fall through. */
312 return (call_expr_flags (stmt) & ECF_NORETURN) == 0;
319 /* Lowers a cond_expr TSI. DATA is passed through the recursion. */
322 lower_cond_expr (tree_stmt_iterator *tsi, struct lower_data *data)
324 tree stmt = tsi_stmt (*tsi);
325 bool then_is_goto, else_is_goto;
326 tree then_branch, else_branch;
327 tree then_goto, else_goto;
329 then_branch = COND_EXPR_THEN (stmt);
330 else_branch = COND_EXPR_ELSE (stmt);
332 lower_stmt_body (then_branch, data);
333 lower_stmt_body (else_branch, data);
335 then_goto = expr_only (then_branch);
336 then_is_goto = then_goto && simple_goto_p (then_goto);
338 else_goto = expr_only (else_branch);
339 else_is_goto = else_goto && simple_goto_p (else_goto);
341 if (!then_is_goto || !else_is_goto)
343 tree then_label, else_label, end_label, t;
345 then_label = NULL_TREE;
346 else_label = NULL_TREE;
347 end_label = NULL_TREE;
349 /* Replace the cond_expr with explicit gotos. */
352 t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
353 if (TREE_SIDE_EFFECTS (then_branch))
357 then_goto = build_and_jump (&LABEL_EXPR_LABEL (t));
362 t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
363 if (TREE_SIDE_EFFECTS (else_branch))
367 /* Both THEN and ELSE can be no-ops if one or both contained an
368 empty BIND_EXPR that was associated with the toplevel block
369 of an inlined function. In that case remove_useless_stmts
370 can't have cleaned things up for us; kill the whole
380 else_goto = build_and_jump (&LABEL_EXPR_LABEL (t));
385 bool may_fallthru = block_may_fallthru (then_branch);
387 tsi_link_after (tsi, then_label, TSI_CONTINUE_LINKING);
388 tsi_link_after (tsi, then_branch, TSI_CONTINUE_LINKING);
390 if (else_label && may_fallthru)
392 end_label = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
393 t = build_and_jump (&LABEL_EXPR_LABEL (end_label));
394 tsi_link_after (tsi, t, TSI_CONTINUE_LINKING);
400 tsi_link_after (tsi, else_label, TSI_CONTINUE_LINKING);
401 tsi_link_after (tsi, else_branch, TSI_CONTINUE_LINKING);
405 tsi_link_after (tsi, end_label, TSI_CONTINUE_LINKING);
408 COND_EXPR_THEN (stmt) = then_goto;
409 COND_EXPR_ELSE (stmt) = else_goto;
415 lower_return_expr (tree_stmt_iterator *tsi, struct lower_data *data)
417 tree stmt = tsi_stmt (*tsi);
418 tree value, t, label;
420 /* Extract the value being returned. */
421 value = TREE_OPERAND (stmt, 0);
422 if (value && TREE_CODE (value) == MODIFY_EXPR)
423 value = TREE_OPERAND (value, 1);
425 /* Match this up with an existing return statement that's been created. */
426 for (t = data->return_statements; t ; t = TREE_CHAIN (t))
428 tree tvalue = TREE_OPERAND (TREE_VALUE (t), 0);
429 if (tvalue && TREE_CODE (tvalue) == MODIFY_EXPR)
430 tvalue = TREE_OPERAND (tvalue, 1);
434 label = TREE_PURPOSE (t);
439 /* Not found. Create a new label and record the return statement. */
440 label = create_artificial_label ();
441 data->return_statements = tree_cons (label, stmt, data->return_statements);
443 /* Generate a goto statement and remove the return statement. */
445 t = build (GOTO_EXPR, void_type_node, label);
446 SET_EXPR_LOCUS (t, EXPR_LOCUS (stmt));
447 tsi_link_before (tsi, t, TSI_SAME_STMT);
452 /* Record the variables in VARS. */
455 record_vars (tree vars)
457 for (; vars; vars = TREE_CHAIN (vars))
461 /* Nothing to do in this case. */
462 if (DECL_EXTERNAL (var))
464 if (TREE_CODE (var) == FUNCTION_DECL)
467 /* Record the variable. */
468 cfun->unexpanded_var_list = tree_cons (NULL_TREE, var,
469 cfun->unexpanded_var_list);
473 /* Check whether to expand a variable VAR. */
476 expand_var_p (tree var)
478 struct var_ann_d *ann;
480 if (TREE_CODE (var) != VAR_DECL)
483 /* Leave statics and externals alone. */
484 if (TREE_STATIC (var) || DECL_EXTERNAL (var))
487 /* Remove all unused local variables. */
489 if (!ann || !ann->used)
495 /* Throw away variables that are unused. */
498 remove_useless_vars (void)
503 if (dump_file && (dump_flags & TDF_DETAILS))
506 fputs ("Discarding as unused:\n", df);
509 for (cell = &cfun->unexpanded_var_list; *cell; )
511 var = TREE_VALUE (*cell);
513 if (!expand_var_p (var))
518 print_generic_expr (df, var, dump_flags);
522 *cell = TREE_CHAIN (*cell);
526 cell = &TREE_CHAIN (*cell);
533 struct tree_opt_pass pass_remove_useless_vars =
537 remove_useless_vars, /* execute */
540 0, /* static_pass_number */
542 0, /* properties_required */
543 0, /* properties_provided */
544 0, /* properties_destroyed */
545 0, /* todo_flags_start */
546 TODO_dump_func, /* todo_flags_finish */
550 /* Mark BLOCK used if it has a used variable in it, then recurse over its
554 mark_blocks_with_used_vars (tree block)
559 if (!TREE_USED (block))
561 for (var = BLOCK_VARS (block);
563 var = TREE_CHAIN (var))
567 TREE_USED (block) = true;
572 for (subblock = BLOCK_SUBBLOCKS (block);
574 subblock = BLOCK_CHAIN (subblock))
575 mark_blocks_with_used_vars (subblock);
578 /* Mark the used attribute on blocks correctly. */
581 mark_used_blocks (void)
583 mark_blocks_with_used_vars (DECL_INITIAL (current_function_decl));
587 struct tree_opt_pass pass_mark_used_blocks =
591 mark_used_blocks, /* execute */
594 0, /* static_pass_number */
596 0, /* properties_required */
597 0, /* properties_provided */
598 0, /* properties_destroyed */
599 0, /* todo_flags_start */
600 TODO_dump_func, /* todo_flags_finish */