File : par-labl.adb
1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT COMPILER COMPONENTS --
4 -- --
5 -- P A R . L A B L --
6 -- --
7 -- B o d y --
8 -- --
9 -- Copyright (C) 1992-2013, Free Software Foundation, Inc. --
10 -- --
11 -- GNAT is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 3, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING3. If not, go to --
19 -- http://www.gnu.org/licenses for a complete copy of the license. --
20 -- --
21 -- GNAT was originally developed by the GNAT team at New York University. --
22 -- Extensive contributions were provided by Ada Core Technologies Inc. --
23 -- --
24 ------------------------------------------------------------------------------
25
26 separate (Par)
27 procedure Labl is
28 Enclosing_Body_Or_Block : Node_Id;
29 -- Innermost enclosing body or block statement
30
31 Label_Decl_Node : Node_Id;
32 -- Implicit label declaration node
33
34 Defining_Ident_Node : Node_Id;
35 -- Defining identifier node for implicit label declaration
36
37 Next_Label_Elmt : Elmt_Id;
38 -- Next element on label element list
39
40 Label_Node : Node_Id;
41 -- Next label node to process
42
43 function Find_Enclosing_Body_Or_Block (N : Node_Id) return Node_Id;
44 -- Find the innermost body or block that encloses N
45
46 function Find_Enclosing_Body (N : Node_Id) return Node_Id;
47 -- Find the innermost body that encloses N
48
49 procedure Check_Distinct_Labels;
50 -- Checks the rule in RM-5.1(11), which requires distinct identifiers
51 -- for all the labels in a given body.
52
53 procedure Find_Natural_Loops;
54 -- Recognizes loops created by backward gotos, and rewrites the
55 -- corresponding statements into a proper loop, for optimization
56 -- purposes (for example, to control reclaiming local storage).
57
58 ---------------------------
59 -- Check_Distinct_Labels --
60 ---------------------------
61
62 procedure Check_Distinct_Labels is
63 Label_Id : constant Node_Id := Identifier (Label_Node);
64
65 Enclosing_Body : constant Node_Id :=
66 Find_Enclosing_Body (Enclosing_Body_Or_Block);
67 -- Innermost enclosing body
68
69 Next_Other_Label_Elmt : Elmt_Id := First_Elmt (Label_List);
70 -- Next element on label element list
71
72 Other_Label : Node_Id;
73 -- Next label node to process
74
75 begin
76 -- Loop through all the labels, and if we find some other label
77 -- (i.e. not Label_Node) that has the same identifier,
78 -- and whose innermost enclosing body is the same,
79 -- then we have an error.
80
81 -- Note that in the worst case, this is quadratic in the number
82 -- of labels. However, labels are not all that common, and this
83 -- is only called for explicit labels.
84
85 -- ???Nonetheless, the efficiency could be improved. For example,
86 -- call Labl for each body, rather than once per compilation.
87
88 while Present (Next_Other_Label_Elmt) loop
89 Other_Label := Node (Next_Other_Label_Elmt);
90
91 exit when Label_Node = Other_Label;
92
93 if Chars (Label_Id) = Chars (Identifier (Other_Label))
94 and then Enclosing_Body = Find_Enclosing_Body (Other_Label)
95 then
96 Error_Msg_Sloc := Sloc (Other_Label);
97 Error_Msg_N ("& conflicts with label#", Label_Id);
98 exit;
99 end if;
100
101 Next_Elmt (Next_Other_Label_Elmt);
102 end loop;
103 end Check_Distinct_Labels;
104
105 -------------------------
106 -- Find_Enclosing_Body --
107 -------------------------
108
109 function Find_Enclosing_Body (N : Node_Id) return Node_Id is
110 Result : Node_Id := N;
111
112 begin
113 -- This is the same as Find_Enclosing_Body_Or_Block, except
114 -- that we skip block statements and accept statements, instead
115 -- of stopping at them.
116
117 while Present (Result)
118 and then Nkind (Result) /= N_Entry_Body
119 and then Nkind (Result) /= N_Task_Body
120 and then Nkind (Result) /= N_Package_Body
121 and then Nkind (Result) /= N_Subprogram_Body
122 loop
123 Result := Parent (Result);
124 end loop;
125
126 return Result;
127 end Find_Enclosing_Body;
128
129 ----------------------------------
130 -- Find_Enclosing_Body_Or_Block --
131 ----------------------------------
132
133 function Find_Enclosing_Body_Or_Block (N : Node_Id) return Node_Id is
134 Result : Node_Id := Parent (N);
135
136 begin
137 -- Climb up the parent chain until we find a body or block
138
139 while Present (Result)
140 and then Nkind (Result) /= N_Accept_Statement
141 and then Nkind (Result) /= N_Entry_Body
142 and then Nkind (Result) /= N_Task_Body
143 and then Nkind (Result) /= N_Package_Body
144 and then Nkind (Result) /= N_Subprogram_Body
145 and then Nkind (Result) /= N_Block_Statement
146 loop
147 Result := Parent (Result);
148 end loop;
149
150 return Result;
151 end Find_Enclosing_Body_Or_Block;
152
153 ------------------------
154 -- Find_Natural_Loops --
155 ------------------------
156
157 procedure Find_Natural_Loops is
158 Node_List : constant Elist_Id := New_Elmt_List;
159 N : Elmt_Id;
160 Succ : Elmt_Id;
161
162 function Goto_Id (Goto_Node : Node_Id) return Name_Id;
163 -- Find Name_Id of goto statement, which may be an expanded name
164
165 function Matches
166 (Label_Node : Node_Id;
167 Goto_Node : Node_Id) return Boolean;
168 -- A label and a goto are candidates for a loop if the names match,
169 -- and both nodes appear in the same body. In addition, both must
170 -- appear in the same statement list. If they are not in the same
171 -- statement list, the goto is from within an nested structure, and
172 -- the label is not a header. We ignore the case where the goto is
173 -- within a conditional structure, and capture only infinite loops.
174
175 procedure Merge;
176 -- Merge labels and goto statements in order of increasing sloc value.
177 -- Discard labels of loop and block statements.
178
179 procedure No_Header (N : Elmt_Id);
180 -- The label N is known not to be a loop header. Scan forward and
181 -- remove all subsequent gotos that may have this node as a target.
182
183 procedure Process_Goto (N : Elmt_Id);
184 -- N is a forward jump. Scan forward and remove all subsequent gotos
185 -- that may have the same target, to preclude spurious loops.
186
187 procedure Rewrite_As_Loop
188 (Loop_Header : Node_Id;
189 Loop_End : Node_Id);
190 -- Given a label and a backwards goto, rewrite intervening statements
191 -- as a loop. Remove the label from the node list, and rewrite the
192 -- goto with the body of the new loop.
193
194 procedure Try_Loop (N : Elmt_Id);
195 -- N is a label that may be a loop header. Scan forward to find some
196 -- backwards goto with which to make a loop. Do nothing if there is
197 -- an intervening label that is not part of a loop, or more than one
198 -- goto with this target.
199
200 -------------
201 -- Goto_Id --
202 -------------
203
204 function Goto_Id (Goto_Node : Node_Id) return Name_Id is
205 begin
206 if Nkind (Name (Goto_Node)) = N_Identifier then
207 return Chars (Name (Goto_Node));
208
209 elsif Nkind (Name (Goto_Node)) = N_Selected_Component then
210 return Chars (Selector_Name (Name (Goto_Node)));
211 else
212
213 -- In case of error, return Id that can't match anything
214
215 return Name_Null;
216 end if;
217 end Goto_Id;
218
219 -------------
220 -- Matches --
221 -------------
222
223 function Matches
224 (Label_Node : Node_Id;
225 Goto_Node : Node_Id) return Boolean
226 is
227 begin
228 return Chars (Identifier (Label_Node)) = Goto_Id (Goto_Node)
229 and then Find_Enclosing_Body (Label_Node) =
230 Find_Enclosing_Body (Goto_Node);
231 end Matches;
232
233 -----------
234 -- Merge --
235 -----------
236
237 procedure Merge is
238 L1 : Elmt_Id;
239 G1 : Elmt_Id;
240
241 begin
242 L1 := First_Elmt (Label_List);
243 G1 := First_Elmt (Goto_List);
244
245 while Present (L1)
246 and then Present (G1)
247 loop
248 if Sloc (Node (L1)) < Sloc (Node (G1)) then
249
250 -- Optimization: remove labels of loops and blocks, which
251 -- play no role in what follows.
252
253 if Nkind (Node (L1)) /= N_Loop_Statement
254 and then Nkind (Node (L1)) /= N_Block_Statement
255 then
256 Append_Elmt (Node (L1), Node_List);
257 end if;
258
259 Next_Elmt (L1);
260
261 else
262 Append_Elmt (Node (G1), Node_List);
263 Next_Elmt (G1);
264 end if;
265 end loop;
266
267 while Present (L1) loop
268 Append_Elmt (Node (L1), Node_List);
269 Next_Elmt (L1);
270 end loop;
271
272 while Present (G1) loop
273 Append_Elmt (Node (G1), Node_List);
274 Next_Elmt (G1);
275 end loop;
276 end Merge;
277
278 ---------------
279 -- No_Header --
280 ---------------
281
282 procedure No_Header (N : Elmt_Id) is
283 S1, S2 : Elmt_Id;
284
285 begin
286 S1 := Next_Elmt (N);
287 while Present (S1) loop
288 S2 := Next_Elmt (S1);
289 if Nkind (Node (S1)) = N_Goto_Statement
290 and then Matches (Node (N), Node (S1))
291 then
292 Remove_Elmt (Node_List, S1);
293 end if;
294
295 S1 := S2;
296 end loop;
297 end No_Header;
298
299 ------------------
300 -- Process_Goto --
301 ------------------
302
303 procedure Process_Goto (N : Elmt_Id) is
304 Goto1 : constant Node_Id := Node (N);
305 Goto2 : Node_Id;
306 S, S1 : Elmt_Id;
307
308 begin
309 S := Next_Elmt (N);
310
311 while Present (S) loop
312 S1 := Next_Elmt (S);
313 Goto2 := Node (S);
314
315 if Nkind (Goto2) = N_Goto_Statement
316 and then Goto_Id (Goto1) = Goto_Id (Goto2)
317 and then Find_Enclosing_Body (Goto1) =
318 Find_Enclosing_Body (Goto2)
319 then
320
321 -- Goto2 may have the same target, remove it from
322 -- consideration.
323
324 Remove_Elmt (Node_List, S);
325 end if;
326
327 S := S1;
328 end loop;
329 end Process_Goto;
330
331 ---------------------
332 -- Rewrite_As_Loop --
333 ---------------------
334
335 procedure Rewrite_As_Loop
336 (Loop_Header : Node_Id;
337 Loop_End : Node_Id)
338 is
339 Loop_Body : constant List_Id := New_List;
340 Loop_Stmt : constant Node_Id :=
341 New_Node (N_Loop_Statement, Sloc (Loop_Header));
342 Stat : Node_Id;
343 Next_Stat : Node_Id;
344
345 begin
346 Stat := Next (Loop_Header);
347 while Stat /= Loop_End loop
348 Next_Stat := Next (Stat);
349 Remove (Stat);
350 Append (Stat, Loop_Body);
351 Stat := Next_Stat;
352 end loop;
353
354 Set_Statements (Loop_Stmt, Loop_Body);
355 Set_Identifier (Loop_Stmt, Identifier (Loop_Header));
356
357 Remove (Loop_Header);
358 Rewrite (Loop_End, Loop_Stmt);
359 Error_Msg_N
360 ("info: code between label and backwards goto rewritten as loop??",
361 Loop_End);
362 end Rewrite_As_Loop;
363
364 --------------
365 -- Try_Loop --
366 --------------
367
368 procedure Try_Loop (N : Elmt_Id) is
369 Source : Elmt_Id;
370 Found : Boolean := False;
371 S1 : Elmt_Id;
372
373 begin
374 S1 := Next_Elmt (N);
375 while Present (S1) loop
376 if Nkind (Node (S1)) = N_Goto_Statement
377 and then Matches (Node (N), Node (S1))
378 then
379 if not Found then
380
381 -- If the label and the goto are both in the same statement
382 -- list, then we've found a loop. Note that labels and goto
383 -- statements are always part of some list, so In_Same_List
384 -- always makes sense.
385
386 if In_Same_List (Node (N), Node (S1)) then
387 Source := S1;
388 Found := True;
389
390 -- The goto is within some nested structure
391
392 else
393 No_Header (N);
394 return;
395 end if;
396
397 else
398 -- More than one goto with the same target
399
400 No_Header (N);
401 return;
402 end if;
403
404 elsif Nkind (Node (S1)) = N_Label
405 and then not Found
406 then
407 -- Intervening label before possible end of loop. Current
408 -- label is not a candidate. This is conservative, because
409 -- the label might not be the target of any jumps, but not
410 -- worth dealing with useless labels.
411
412 No_Header (N);
413 return;
414
415 else
416 -- If the node is a loop_statement, it corresponds to a
417 -- label-goto pair rewritten as a loop. Continue forward scan.
418
419 null;
420 end if;
421
422 Next_Elmt (S1);
423 end loop;
424
425 if Found then
426 Rewrite_As_Loop (Node (N), Node (Source));
427 Remove_Elmt (Node_List, N);
428 Remove_Elmt (Node_List, Source);
429 end if;
430 end Try_Loop;
431
432 begin
433 -- Start of processing for Find_Natural_Loops
434
435 Merge;
436
437 N := First_Elmt (Node_List);
438 while Present (N) loop
439 Succ := Next_Elmt (N);
440
441 if Nkind (Node (N)) = N_Label then
442 if No (Succ) then
443 exit;
444
445 elsif Nkind (Node (Succ)) = N_Label then
446 Try_Loop (Succ);
447
448 -- If a loop was found, the label has been removed, and
449 -- the following goto rewritten as the loop body.
450
451 Succ := Next_Elmt (N);
452
453 if Nkind (Node (Succ)) = N_Label then
454
455 -- Following label was not removed, so current label
456 -- is not a candidate header.
457
458 No_Header (N);
459
460 else
461
462 -- Following label was part of inner loop. Current
463 -- label is still a candidate.
464
465 Try_Loop (N);
466 Succ := Next_Elmt (N);
467 end if;
468
469 elsif Nkind (Node (Succ)) = N_Goto_Statement then
470 Try_Loop (N);
471 Succ := Next_Elmt (N);
472 end if;
473
474 elsif Nkind (Node (N)) = N_Goto_Statement then
475 Process_Goto (N);
476 Succ := Next_Elmt (N);
477 end if;
478
479 N := Succ;
480 end loop;
481 end Find_Natural_Loops;
482
483 -- Start of processing for Par.Labl
484
485 begin
486 Next_Label_Elmt := First_Elmt (Label_List);
487 while Present (Next_Label_Elmt) loop
488 Label_Node := Node (Next_Label_Elmt);
489
490 if not Comes_From_Source (Label_Node) then
491 goto Next_Label;
492 end if;
493
494 -- Find the innermost enclosing body or block, which is where
495 -- we need to implicitly declare this label
496
497 Enclosing_Body_Or_Block := Find_Enclosing_Body_Or_Block (Label_Node);
498
499 -- If we didn't find a parent, then the label in question never got
500 -- hooked into a reasonable declarative part. This happens only in
501 -- error situations, and we simply ignore the entry (we aren't going
502 -- to get into the semantics in any case given the error).
503
504 if Present (Enclosing_Body_Or_Block) then
505 Check_Distinct_Labels;
506
507 -- Now create the implicit label declaration node and its
508 -- corresponding defining identifier. Note that the defining
509 -- occurrence of a label is the implicit label declaration that
510 -- we are creating. The label itself is an applied occurrence.
511
512 Label_Decl_Node :=
513 New_Node (N_Implicit_Label_Declaration, Sloc (Label_Node));
514 Defining_Ident_Node :=
515 New_Entity (N_Defining_Identifier, Sloc (Identifier (Label_Node)));
516 Set_Chars (Defining_Ident_Node, Chars (Identifier (Label_Node)));
517 Set_Defining_Identifier (Label_Decl_Node, Defining_Ident_Node);
518 Set_Label_Construct (Label_Decl_Node, Label_Node);
519
520 -- The following makes sure that Comes_From_Source is appropriately
521 -- set for the entity, depending on whether the label appeared in
522 -- the source explicitly or not.
523
524 Set_Comes_From_Source
525 (Defining_Ident_Node, Comes_From_Source (Identifier (Label_Node)));
526
527 -- Now attach the implicit label declaration to the appropriate
528 -- declarative region, creating a declaration list if none exists
529
530 if No (Declarations (Enclosing_Body_Or_Block)) then
531 Set_Declarations (Enclosing_Body_Or_Block, New_List);
532 end if;
533
534 Append (Label_Decl_Node, Declarations (Enclosing_Body_Or_Block));
535 end if;
536
537 <<Next_Label>>
538 Next_Elmt (Next_Label_Elmt);
539 end loop;
540
541 Find_Natural_Loops;
542
543 end Labl;