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e18a6d14 AB |
1 | /* This file is part of GCC. |
2 | ||
3 | GCC is free software; you can redistribute it and/or modify | |
4 | it under the terms of the GNU General Public License as published by | |
5 | the Free Software Foundation; either version 3, or (at your option) | |
6 | any later version. | |
7 | ||
8 | GCC is distributed in the hope that it will be useful, | |
9 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
10 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
11 | GNU General Public License for more details. | |
12 | ||
13 | You should have received a copy of the GNU General Public License | |
14 | along with GCC; see the file COPYING3. If not see | |
15 | <http://www.gnu.org/licenses/>. */ | |
16 | ||
17 | /* This file contains code aimed at optimizing function generated with the | |
18 | use of '-msave-restore. The goal is to identify cases where the call | |
19 | out to the save/restore routines are sub-optimal, and remove the calls | |
20 | in this case. | |
21 | ||
22 | As GCC currently makes the choice between using or not using | |
23 | save/restore early on (during the gimple expand pass) once we have | |
24 | selected to use save/restore we are stuck with it. */ | |
25 | ||
26 | #define IN_TARGET_CODE 1 | |
27 | ||
28 | #include "config.h" | |
29 | #include "system.h" | |
30 | #include "coretypes.h" | |
31 | #include "tm.h" | |
32 | #include "rtl.h" | |
33 | #include "function.h" | |
34 | #include "memmodel.h" | |
35 | #include "emit-rtl.h" | |
36 | #include "target.h" | |
37 | #include "basic-block.h" | |
38 | #include "bitmap.h" | |
39 | #include "df.h" | |
40 | #include "tree.h" | |
41 | #include "expr.h" | |
42 | #include "cfg.h" | |
43 | ||
44 | /* This file should be included last. */ | |
45 | #include "hard-reg-set.h" | |
46 | ||
47 | /* Look in the function prologue for a call to the save stub. Ensure that | |
48 | the instruction is as we expect (see detail below) and if the | |
49 | instruction matches return a pointer to it. Otherwise, return NULL. | |
50 | ||
51 | We expect the function prologue to look like this: | |
52 | ||
53 | (note NOTE_INSN_BASIC_BLOCK) | |
54 | (insn (parallel [ | |
55 | (unspec_volatile [ | |
56 | (const_int 2 [0x2]) | |
57 | ] UNSPECV_GPR_SAVE) | |
58 | (clobber (reg:SI 5 t0)) | |
59 | (clobber (reg:SI 6 t1))]) | |
60 | (note NOTE_INSN_PROLOGUE_END) | |
61 | ||
62 | Between the NOTE_INSN_BASIC_BLOCK and the GPR_SAVE insn we might find | |
63 | other notes of type NOTE_INSN_DELETED and/or NOTE_INSN_FUNCTION_BEG. | |
64 | ||
65 | The parameter BODY is updated to point to the first instruction after | |
66 | the NOTE_INSN_PROLOGUE_END or will be updated to NULL if the prologue | |
67 | end note was not found. */ | |
68 | ||
69 | static rtx_insn * | |
70 | riscv_sr_match_prologue (rtx_insn **body) | |
71 | { | |
72 | rtx_insn *insn, *bb_note; | |
73 | *body = NULL; | |
74 | ||
75 | /* Find the prologue end note. */ | |
76 | for (insn = get_insns (); insn != NULL; insn = NEXT_INSN (insn)) | |
77 | if (NOTE_P (insn) && NOTE_KIND (insn) == NOTE_INSN_PROLOGUE_END) | |
78 | { | |
79 | *body = NEXT_INSN (insn); | |
80 | break; | |
81 | } | |
82 | ||
83 | /* If we don't have the prologue end note and at least one instruction | |
84 | before it, then this function doesn't have the structure we expect. */ | |
85 | if (insn == NULL | |
86 | || PREV_INSN (insn) == NULL) | |
87 | return NULL; | |
88 | ||
89 | /* The INSN is the end of prologue note, before this we expect to find | |
90 | one real instruction which makes the prologue, and before that we | |
91 | expect to find some number of notes for deleted instructions, the | |
92 | beginning of the function, and finally a basicblock beginning. The | |
93 | following loop checks that this assumption is true. */ | |
94 | for (bb_note = PREV_INSN (PREV_INSN (insn)); | |
95 | bb_note != NULL; | |
96 | bb_note = PREV_INSN (bb_note)) | |
97 | { | |
98 | if (!NOTE_P (bb_note)) | |
99 | return NULL; | |
100 | if (NOTE_KIND (bb_note) == NOTE_INSN_BASIC_BLOCK) | |
101 | break; | |
102 | if (NOTE_KIND (bb_note) != NOTE_INSN_DELETED | |
103 | && NOTE_KIND (bb_note) != NOTE_INSN_FUNCTION_BEG) | |
104 | return NULL; | |
105 | } | |
106 | if (bb_note == NULL) | |
107 | return NULL; | |
108 | ||
109 | /* Set INSN to point to the actual interesting prologue instruction. */ | |
110 | insn = PREV_INSN (insn); | |
111 | if (INSN_P (insn) | |
112 | && INSN_CODE (insn) == CODE_FOR_gpr_save | |
113 | /* Check this is a call to _riscv_save_0. */ | |
114 | && GET_CODE (PATTERN (insn)) == PARALLEL | |
115 | && GET_CODE (XVECEXP (PATTERN (insn), 0, 0)) == UNSPEC_VOLATILE | |
116 | && (GET_CODE (XVECEXP (XVECEXP (PATTERN (insn), 0, 0), 0, 0)) | |
117 | == CONST_INT) | |
dcf41a4e | 118 | && INTVAL (XVECEXP (XVECEXP (PATTERN (insn), 0, 0), 0, 0)) == 0) |
e18a6d14 AB |
119 | return insn; |
120 | ||
121 | return NULL; | |
122 | } | |
123 | ||
124 | /* Find the first instruction in the epilogue of the current function, and | |
125 | return a pointer to that instruction if, and only if, the epilogue has | |
126 | the correct structure that would allow us to optimize out the call to | |
127 | _riscv_restore_0. */ | |
128 | ||
129 | static rtx_insn * | |
130 | riscv_sr_match_epilogue (void) | |
131 | { | |
132 | /* Find the first instruction in the epilogue. */ | |
133 | rtx_insn *insn, *start; | |
134 | for (insn = get_insns (); insn != NULL; insn = NEXT_INSN (insn)) | |
135 | if (NOTE_P (insn) && NOTE_KIND (insn) == NOTE_INSN_EPILOGUE_BEG) | |
136 | { | |
137 | insn = NEXT_INSN (insn); | |
138 | break; | |
139 | } | |
140 | if (insn == NULL) | |
141 | return NULL; | |
142 | ||
143 | /* At this point INSN is the first instruction in the epilogue. A | |
144 | standard epilogue (of the form we expect to handle) consists of the | |
145 | following instructions: | |
146 | ||
147 | 1. A stack_tiesi or stack_tiedi (for RV32 and RV64 respectively), | |
148 | ||
149 | 2. An optional use instruction for the register holding the return | |
150 | value. This will be missing in functions with no return value, | |
151 | ||
152 | 3. A gpr_restore instruction, and | |
153 | ||
154 | 4. A jump instruction of type gpr_restore_return. */ | |
155 | start = insn; | |
156 | if (INSN_CODE (insn) != CODE_FOR_stack_tiesi | |
157 | && INSN_CODE (insn) != CODE_FOR_stack_tiedi) | |
158 | return NULL; | |
159 | ||
160 | insn = NEXT_INSN (insn); | |
161 | if (INSN_P (insn) && GET_CODE (PATTERN (insn)) == USE) | |
162 | insn = NEXT_INSN (insn); | |
163 | ||
164 | if (!INSN_P (insn) || INSN_CODE (insn) != CODE_FOR_gpr_restore) | |
165 | return NULL; | |
166 | ||
167 | insn = NEXT_INSN (insn); | |
168 | if (!INSN_P (insn) || INSN_CODE (insn) != CODE_FOR_gpr_restore_return) | |
169 | return NULL; | |
170 | ||
171 | return start; | |
172 | } | |
173 | ||
174 | /* Helper for riscv_remove_unneeded_save_restore_calls. If we match the | |
175 | prologue instructions but not the epilogue then we might have the case | |
176 | where the epilogue has been optimized out due to a call to a no-return | |
177 | function. In this case we might be able to remove the prologue too - | |
178 | that's what this function does. PROLOGUE is the matched prolgoue | |
179 | instruction, by the time this function returns the progloue instruction | |
180 | may have been removed. */ | |
181 | ||
182 | static void | |
183 | check_for_no_return_call (rtx_insn *prologue) | |
184 | { | |
185 | /* Check to see if we have the following pattern: | |
186 | ||
187 | PROLOGUE instruction | |
188 | NOTE_INSN_PROLOGUE_END | |
189 | A no-return call instruction | |
190 | ||
191 | If we do, then we can remove the prologue instruction safely. Remember | |
192 | that we've already confirmed by this point that the prologue is a call | |
193 | to riscv_save_0. */ | |
194 | ||
195 | if (dump_file) | |
196 | fprintf (dump_file, | |
197 | "Prologue matched, checking for no-return epilogue.\n"); | |
198 | ||
199 | rtx_insn *tmp = NEXT_INSN (prologue); | |
200 | if (!NOTE_P (tmp) || NOTE_KIND (tmp) != NOTE_INSN_PROLOGUE_END) | |
201 | return; | |
202 | ||
203 | /* Skip any extra notes in here, they're most likely just debug. */ | |
204 | do | |
205 | { | |
206 | tmp = NEXT_INSN (tmp); | |
207 | } | |
208 | while (tmp != NULL && NOTE_P (tmp)); | |
209 | ||
210 | if (tmp == NULL || !INSN_P (tmp)) | |
211 | return; | |
212 | ||
213 | bool noreturn_p = find_reg_note (tmp, REG_NORETURN, NULL_RTX) != NULL_RTX; | |
214 | if (!CALL_P (tmp) || !noreturn_p) | |
215 | return; | |
216 | ||
217 | if (dump_file) | |
218 | fprintf (dump_file, | |
219 | "Prologue call to riscv_save_0 followed by noreturn call, " | |
220 | "removing prologue.\n"); | |
221 | remove_insn (prologue); | |
222 | } | |
223 | ||
224 | /* Entry point called from riscv_reorg to remove some unneeded calls to | |
225 | the save and restore stubs. This should only be called when | |
226 | -msave-restore is in use. | |
227 | ||
228 | We identify some simple cases where the function looks like this: | |
229 | ||
230 | call t0,__riscv_save_0 | |
231 | <other-code> | |
232 | call foo | |
233 | tail __riscv_restore_0 | |
234 | ||
235 | And transform it into something like this: | |
236 | ||
237 | <other-code> | |
238 | tail foo | |
239 | ||
240 | In the above examples, what can appear in <other-code> is pretty | |
241 | restricted; only caller saved registers can be touched, this prevents | |
242 | any additional calls (as they would write to 'ra'). */ | |
243 | ||
244 | void | |
245 | riscv_remove_unneeded_save_restore_calls (void) | |
246 | { | |
4c0d1322 KC |
247 | /* We'll adjust stack size after this optimization, that require update every |
248 | sp use site, which could be unsafe, so we decide to turn off this | |
249 | optimization if there are any arguments put on stack. */ | |
3496ca4e | 250 | if (known_ne (crtl->args.size, 0)) |
4c0d1322 KC |
251 | return; |
252 | ||
e18a6d14 AB |
253 | /* Will point to the first instruction of the function body, after the |
254 | prologue end note. */ | |
255 | rtx_insn *body = NULL; | |
256 | ||
257 | /* Should only be called with -msave-restore is in use. */ | |
258 | gcc_assert (TARGET_SAVE_RESTORE); | |
259 | ||
260 | /* Match the expected prologue and epilogue patterns. If either of these | |
261 | fail to match then we abandon our attempt to optimize this function. */ | |
262 | rtx_insn *prologue_matched = riscv_sr_match_prologue (&body); | |
263 | if (prologue_matched == NULL || body == NULL) | |
264 | return; | |
265 | ||
266 | rtx_insn *epilogue_matched = riscv_sr_match_epilogue (); | |
267 | if (epilogue_matched == NULL) | |
268 | { | |
269 | check_for_no_return_call (prologue_matched); | |
270 | return; | |
271 | } | |
272 | ||
273 | if (dump_file) | |
274 | fprintf (dump_file, | |
275 | "Could be a candidate for save/restore removal\n"); | |
276 | ||
277 | /* We want to check which registers this function uses. */ | |
278 | df_analyze (); | |
279 | ||
280 | int call_count = 0; | |
281 | bool good_use = true; | |
282 | int epilogue_count = 0; | |
283 | ||
284 | /* Now examine all of the instructions that make up this function, we're | |
285 | looking for call instructions and also double checking register usage | |
286 | while we're at it (see comments below). */ | |
287 | basic_block bb; | |
288 | FOR_EACH_BB_FN (bb, cfun) | |
289 | { | |
290 | rtx_insn *insn; | |
291 | ||
292 | FOR_BB_INSNS (bb, insn) | |
293 | { | |
294 | if (dump_file) | |
295 | fprintf (dump_file, | |
296 | "Block %d, Insn %d\n", bb->index, INSN_UID (insn)); | |
297 | ||
298 | /* If we scan the epilogue we will fall foul of our register | |
299 | usage check below (due to it's use of the return address), so | |
300 | once we spot we're at the epilogue, just skip the rest of this | |
301 | block. Scanning the prologue instructions again (if they | |
302 | match the expected pattern) is harmless. */ | |
303 | if (NOTE_P (insn) | |
304 | && NOTE_KIND (insn) == NOTE_INSN_EPILOGUE_BEG) | |
305 | { | |
306 | ++epilogue_count; | |
307 | break; | |
308 | } | |
309 | ||
310 | if (!INSN_P (insn)) | |
311 | continue; | |
312 | ||
313 | if (CALL_P (insn)) | |
314 | ++call_count; | |
d0e0c130 KC |
315 | /* Ignore any USEs in the gpr_save pattern. They don't prevent us |
316 | from optimizing away the save call. */ | |
317 | else if (insn == prologue_matched) | |
318 | ; | |
e18a6d14 AB |
319 | else |
320 | { | |
321 | df_ref use; | |
322 | ||
323 | FOR_EACH_INSN_USE (use, insn) | |
324 | { | |
325 | /* If the function makes use of any registers that are | |
326 | callee saved then we should be saving them in this | |
327 | function, which would suggest that a call to the save | |
328 | and restore functions is required. This would seem to | |
329 | indicate that something has gone wrong above, as we | |
330 | should only get here if we are saving zero registers. | |
331 | ||
332 | The one exception to this rule is the return address | |
333 | register used within a call instruction. We can | |
334 | optimize a single call within a function (by making it | |
335 | a tail call), so we skip call instructions here. */ | |
336 | if (!call_used_regs[DF_REF_REGNO (use)]) | |
337 | { | |
338 | if (dump_file) | |
339 | fprintf (dump_file, | |
340 | "Found unsupported use of callee saved " | |
341 | "register in instruction %d\n", | |
342 | INSN_UID (insn)); | |
343 | good_use = false; | |
344 | break; | |
345 | } | |
346 | } | |
347 | if (!good_use) | |
348 | break; | |
349 | } | |
350 | } | |
351 | } | |
352 | ||
353 | /* If we used any registers that would indicate a need for a call to a | |
354 | save/restore stub then don't optimize. */ | |
355 | if (!good_use) | |
356 | return; | |
357 | ||
358 | /* If this function has multiple epilogues, then for now we don't try to | |
359 | optimize it. */ | |
360 | if (epilogue_count != 1) | |
361 | return; | |
362 | ||
363 | /* We can only optimize functions containing a single call, any more | |
364 | would require us to add instructions to store the return address on | |
365 | the stack (and restore it before we return). We could do this in the | |
366 | future, but for now we don't. A single call can be transformed into | |
367 | a tail call reasonably easily. */ | |
368 | if (call_count > 1) | |
369 | { | |
370 | if (dump_file) | |
371 | fprintf (dump_file, | |
372 | "Found too many call instructions\n"); | |
373 | return; | |
374 | } | |
375 | ||
376 | rtx_insn *epilogue_begin_note = PREV_INSN (epilogue_matched); | |
377 | gcc_assert (NOTE_P (epilogue_begin_note) | |
378 | && NOTE_KIND (epilogue_begin_note) == NOTE_INSN_EPILOGUE_BEG); | |
379 | ||
380 | df_finish_pass (false); | |
381 | ||
382 | /* Find the first instruction before the function epilogue. */ | |
383 | rtx_insn *insn_before_epilogue; | |
384 | for (insn_before_epilogue = PREV_INSN (epilogue_begin_note); | |
385 | NOTE_P (insn_before_epilogue); | |
386 | insn_before_epilogue = PREV_INSN (insn_before_epilogue)) | |
387 | ; | |
388 | ||
389 | /* Leaf functions will not generate calls to the save/restore stubs, so | |
390 | there's no need for this optimization there. We know this function | |
391 | has no more than 1 call (checked above). To convert this single call | |
392 | into a tail call we rely on the call being the last thing before the | |
393 | epilogue. */ | |
394 | if (GET_CODE (insn_before_epilogue) != CALL_INSN) | |
395 | return; | |
396 | ||
397 | /* The last instruction in this block, just before the epilogue is a | |
398 | call. We can potentially change this call into a tail call. */ | |
399 | rtx_insn *call = insn_before_epilogue; | |
400 | ||
401 | /* Transform call in insn to a sibcall, this will only be done if the | |
402 | last thing in the function is a call. */ | |
403 | rtx callpat = PATTERN (call); | |
404 | gcc_assert (GET_CODE (callpat) == PARALLEL); | |
405 | ||
406 | /* Extract from CALLPAT the information we need to build the sibcall. */ | |
407 | rtx target_call = NULL; | |
408 | rtx tmp_rtx = XVECEXP (callpat, 0, 0); | |
409 | rtx set_target = NULL; | |
410 | switch (GET_CODE (tmp_rtx)) | |
411 | { | |
412 | case CALL: | |
413 | target_call = tmp_rtx; | |
414 | break; | |
415 | ||
416 | case SET: | |
417 | { | |
418 | set_target = XEXP (tmp_rtx, 0); | |
419 | tmp_rtx = XEXP (tmp_rtx, 1); | |
420 | if (GET_CODE (tmp_rtx) != CALL) | |
421 | return; | |
422 | target_call = tmp_rtx; | |
423 | break; | |
424 | } | |
425 | ||
426 | default: | |
427 | return; | |
428 | } | |
429 | ||
430 | rtx target_mem = XEXP (target_call, 0); | |
431 | if (GET_CODE (target_mem) != MEM) | |
432 | return; | |
433 | ||
434 | rtx target = XEXP (target_mem, 0); | |
435 | if (GET_CODE (target) != SYMBOL_REF && GET_CODE (target) != REG) | |
436 | return; | |
437 | ||
438 | /* The sibcall instructions can only use a specific subset of | |
439 | registers, we're about to (possibly) move a call through a | |
440 | register from the function body and make it a sibcall. If we're | |
441 | not using an appropriate register then we can't make this change. | |
442 | ||
443 | Maybe in some future iteration we could actually scan the | |
444 | function, find a suitable sibcall register, and switch over the | |
445 | registers. But we don't do that yet. */ | |
446 | if (GET_CODE (target) == REG | |
447 | && !SIBCALL_REG_P (REGNO (target))) | |
448 | return; | |
449 | ||
450 | rtx sibcall = NULL; | |
451 | if (set_target != NULL) | |
452 | sibcall | |
453 | = gen_sibcall_value_internal (set_target, target, const0_rtx); | |
454 | else | |
455 | sibcall = gen_sibcall_internal (target, const0_rtx); | |
456 | ||
457 | rtx_insn *before_call = PREV_INSN (call); | |
458 | remove_insn (call); | |
459 | rtx_insn *insn = emit_call_insn_after_setloc (sibcall, before_call, | |
460 | INSN_LOCATION (call)); | |
461 | REG_NOTES (insn) = REG_NOTES (call); | |
462 | SIBLING_CALL_P (insn) = 1; | |
463 | ||
464 | /* Now update the prologue and epilogue to take account of the | |
465 | changes within the function body. */ | |
466 | remove_insn (prologue_matched); | |
467 | remove_insn (NEXT_INSN (NEXT_INSN (NEXT_INSN (epilogue_matched)))); | |
468 | remove_insn (NEXT_INSN (NEXT_INSN (epilogue_matched))); | |
469 | remove_insn (NEXT_INSN (epilogue_matched)); | |
470 | remove_insn (epilogue_matched); | |
471 | ||
472 | if (dump_file) | |
473 | fprintf (dump_file, | |
474 | "Save/restore successfully removed\n"); | |
475 | } |