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[official-gcc.git] / gcc / tree-ssa-phiprop.c
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1 /* Backward propagation of indirect loads through PHIs.
2 Copyright (C) 2007-2018 Free Software Foundation, Inc.
3 Contributed by Richard Guenther <rguenther@suse.de>
5 This file is part of GCC.
7 GCC is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 3, or (at your option)
10 any later version.
12 GCC is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with GCC; see the file COPYING3. If not see
19 <http://www.gnu.org/licenses/>. */
21 #include "config.h"
22 #include "system.h"
23 #include "coretypes.h"
24 #include "backend.h"
25 #include "tree.h"
26 #include "gimple.h"
27 #include "tree-pass.h"
28 #include "ssa.h"
29 #include "gimple-pretty-print.h"
30 #include "fold-const.h"
31 #include "tree-eh.h"
32 #include "gimplify.h"
33 #include "gimple-iterator.h"
34 #include "stor-layout.h"
35 #include "tree-ssa-loop.h"
37 /* This pass propagates indirect loads through the PHI node for its
38 address to make the load source possibly non-addressable and to
39 allow for PHI optimization to trigger.
41 For example the pass changes
43 # addr_1 = PHI <&a, &b>
44 tmp_1 = *addr_1;
48 # tmp_1 = PHI <a, b>
50 but also handles more complex scenarios like
52 D.2077_2 = &this_1(D)->a1;
53 ...
55 # b_12 = PHI <&c(2), D.2077_2(3)>
56 D.2114_13 = *b_12;
57 ...
59 # b_15 = PHI <b_12(4), &b(5)>
60 D.2080_5 = &this_1(D)->a0;
61 ...
63 # b_18 = PHI <D.2080_5(6), &c(7)>
64 ...
66 # b_21 = PHI <b_15(8), b_18(9)>
67 D.2076_8 = *b_21;
69 where the addresses loaded are defined by PHIs itself.
70 The above happens for
72 std::max(std::min(a0, c), std::min(std::max(a1, c), b))
74 where this pass transforms it to a form later PHI optimization
75 recognizes and transforms it to the simple
77 D.2109_10 = this_1(D)->a1;
78 D.2110_11 = c;
79 D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>;
80 D.2115_14 = b;
81 D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>;
82 D.2119_16 = this_1(D)->a0;
83 D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>;
84 D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>;
86 The pass does a dominator walk processing loads using a basic-block
87 local analysis and stores the result for use by transformations on
88 dominated basic-blocks. */
91 /* Structure to keep track of the value of a dereferenced PHI result
92 and the virtual operand used for that dereference. */
94 struct phiprop_d
96 tree value;
97 tree vuse;
100 /* Verify if the value recorded for NAME in PHIVN is still valid at
101 the start of basic block BB. */
103 static bool
104 phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb)
106 tree vuse = phivn[SSA_NAME_VERSION (name)].vuse;
107 gimple *use_stmt;
108 imm_use_iterator ui2;
109 bool ok = true;
111 /* The def stmts of the virtual uses need to be dominated by bb. */
112 gcc_assert (vuse != NULL_TREE);
114 FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse)
116 /* If BB does not dominate a VDEF, the value is invalid. */
117 if ((gimple_vdef (use_stmt) != NULL_TREE
118 || gimple_code (use_stmt) == GIMPLE_PHI)
119 && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb))
121 ok = false;
122 BREAK_FROM_IMM_USE_STMT (ui2);
126 return ok;
129 /* Insert a new phi node for the dereference of PHI at basic_block
130 BB with the virtual operands from USE_STMT. */
132 static tree
133 phiprop_insert_phi (basic_block bb, gphi *phi, gimple *use_stmt,
134 struct phiprop_d *phivn, size_t n)
136 tree res;
137 gphi *new_phi = NULL;
138 edge_iterator ei;
139 edge e;
141 gcc_assert (is_gimple_assign (use_stmt)
142 && gimple_assign_rhs_code (use_stmt) == MEM_REF);
144 /* Build a new PHI node to replace the definition of
145 the indirect reference lhs. */
146 res = gimple_assign_lhs (use_stmt);
147 if (TREE_CODE (res) == SSA_NAME)
148 new_phi = create_phi_node (res, bb);
150 if (dump_file && (dump_flags & TDF_DETAILS))
152 fprintf (dump_file, "Inserting PHI for result of load ");
153 print_gimple_stmt (dump_file, use_stmt, 0);
156 /* Add PHI arguments for each edge inserting loads of the
157 addressable operands. */
158 FOR_EACH_EDGE (e, ei, bb->preds)
160 tree old_arg, new_var;
161 gassign *tmp;
162 source_location locus;
164 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
165 locus = gimple_phi_arg_location_from_edge (phi, e);
166 while (TREE_CODE (old_arg) == SSA_NAME
167 && (SSA_NAME_VERSION (old_arg) >= n
168 || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE))
170 gimple *def_stmt = SSA_NAME_DEF_STMT (old_arg);
171 old_arg = gimple_assign_rhs1 (def_stmt);
172 locus = gimple_location (def_stmt);
175 if (TREE_CODE (old_arg) == SSA_NAME)
177 if (dump_file && (dump_flags & TDF_DETAILS))
179 fprintf (dump_file, " for edge defining ");
180 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e));
181 fprintf (dump_file, " reusing PHI result ");
182 print_generic_expr (dump_file,
183 phivn[SSA_NAME_VERSION (old_arg)].value);
184 fprintf (dump_file, "\n");
186 /* Reuse a formerly created dereference. */
187 new_var = phivn[SSA_NAME_VERSION (old_arg)].value;
189 else
191 tree rhs = gimple_assign_rhs1 (use_stmt);
192 gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR);
193 if (TREE_CODE (res) == SSA_NAME)
194 new_var = make_ssa_name (TREE_TYPE (rhs));
195 else
196 new_var = unshare_expr (res);
197 if (!is_gimple_min_invariant (old_arg))
198 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
199 else
200 old_arg = unshare_expr (old_arg);
201 tmp = gimple_build_assign (new_var,
202 fold_build2 (MEM_REF, TREE_TYPE (rhs),
203 old_arg,
204 TREE_OPERAND (rhs, 1)));
205 gimple_set_location (tmp, locus);
207 gsi_insert_on_edge (e, tmp);
208 update_stmt (tmp);
210 if (dump_file && (dump_flags & TDF_DETAILS))
212 fprintf (dump_file, " for edge defining ");
213 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e));
214 fprintf (dump_file, " inserting load ");
215 print_gimple_stmt (dump_file, tmp, 0);
219 if (new_phi)
220 add_phi_arg (new_phi, new_var, e, locus);
223 if (new_phi)
225 update_stmt (new_phi);
227 if (dump_file && (dump_flags & TDF_DETAILS))
228 print_gimple_stmt (dump_file, new_phi, 0);
231 return res;
234 /* Verify if *idx is available at *DATA. */
236 static bool
237 chk_uses (tree, tree *idx, void *data)
239 basic_block dom = (basic_block) data;
240 if (TREE_CODE (*idx) == SSA_NAME)
241 return (SSA_NAME_IS_DEFAULT_DEF (*idx)
242 || ! dominated_by_p (CDI_DOMINATORS,
243 gimple_bb (SSA_NAME_DEF_STMT (*idx)), dom));
244 return true;
247 /* Propagate between the phi node arguments of PHI in BB and phi result
248 users. For now this matches
249 # p_2 = PHI <&x, &y>
250 <Lx>:;
251 p_3 = p_2;
252 z_2 = *p_3;
253 and converts it to
254 # z_2 = PHI <x, y>
255 <Lx>:;
256 Returns true if a transformation was done and edge insertions
257 need to be committed. Global data PHIVN and N is used to track
258 past transformation results. We need to be especially careful here
259 with aliasing issues as we are moving memory reads. */
261 static bool
262 propagate_with_phi (basic_block bb, gphi *phi, struct phiprop_d *phivn,
263 size_t n)
265 tree ptr = PHI_RESULT (phi);
266 gimple *use_stmt;
267 tree res = NULL_TREE;
268 gimple_stmt_iterator gsi;
269 imm_use_iterator ui;
270 use_operand_p arg_p, use;
271 ssa_op_iter i;
272 bool phi_inserted;
273 tree type = NULL_TREE;
275 if (!POINTER_TYPE_P (TREE_TYPE (ptr))
276 || (!is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr)))
277 && TYPE_MODE (TREE_TYPE (TREE_TYPE (ptr))) == BLKmode))
278 return false;
280 /* Check if we can "cheaply" dereference all phi arguments. */
281 FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE)
283 tree arg = USE_FROM_PTR (arg_p);
284 /* Walk the ssa chain until we reach a ssa name we already
285 created a value for or we reach a definition of the form
286 ssa_name_n = &var; */
287 while (TREE_CODE (arg) == SSA_NAME
288 && !SSA_NAME_IS_DEFAULT_DEF (arg)
289 && (SSA_NAME_VERSION (arg) >= n
290 || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE))
292 gimple *def_stmt = SSA_NAME_DEF_STMT (arg);
293 if (!gimple_assign_single_p (def_stmt))
294 return false;
295 arg = gimple_assign_rhs1 (def_stmt);
297 if (TREE_CODE (arg) != ADDR_EXPR
298 && !(TREE_CODE (arg) == SSA_NAME
299 && SSA_NAME_VERSION (arg) < n
300 && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE
301 && (!type
302 || types_compatible_p
303 (type, TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value)))
304 && phivn_valid_p (phivn, arg, bb)))
305 return false;
306 if (!type
307 && TREE_CODE (arg) == SSA_NAME)
308 type = TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value);
311 /* Find a dereferencing use. First follow (single use) ssa
312 copy chains for ptr. */
313 while (single_imm_use (ptr, &use, &use_stmt)
314 && gimple_assign_ssa_name_copy_p (use_stmt))
315 ptr = gimple_assign_lhs (use_stmt);
317 /* Replace the first dereference of *ptr if there is one and if we
318 can move the loads to the place of the ptr phi node. */
319 phi_inserted = false;
320 FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr)
322 gimple *def_stmt;
323 tree vuse;
325 /* Only replace loads in blocks that post-dominate the PHI node. That
326 makes sure we don't end up speculating loads. */
327 if (!dominated_by_p (CDI_POST_DOMINATORS,
328 bb, gimple_bb (use_stmt)))
329 continue;
331 /* Check whether this is a load of *ptr. */
332 if (!(is_gimple_assign (use_stmt)
333 && gimple_assign_rhs_code (use_stmt) == MEM_REF
334 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr
335 && integer_zerop (TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 1))
336 && (!type
337 || types_compatible_p
338 (TREE_TYPE (gimple_assign_lhs (use_stmt)), type))
339 /* We cannot replace a load that may throw or is volatile. */
340 && !stmt_can_throw_internal (use_stmt)))
341 continue;
343 /* Check if we can move the loads. The def stmt of the virtual use
344 needs to be in a different basic block dominating bb. When the
345 def is an edge-inserted one we know it dominates us. */
346 vuse = gimple_vuse (use_stmt);
347 def_stmt = SSA_NAME_DEF_STMT (vuse);
348 if (!SSA_NAME_IS_DEFAULT_DEF (vuse)
349 && (gimple_bb (def_stmt) == bb
350 || (gimple_bb (def_stmt)
351 && !dominated_by_p (CDI_DOMINATORS,
352 bb, gimple_bb (def_stmt)))))
353 goto next;
355 /* Found a proper dereference with an aggregate copy. Just
356 insert aggregate copies on the edges instead. */
357 if (!is_gimple_reg_type (TREE_TYPE (gimple_assign_lhs (use_stmt))))
359 if (!gimple_vdef (use_stmt))
360 goto next;
362 /* As we replicate the lhs on each incoming edge all
363 used SSA names have to be available there. */
364 if (! for_each_index (gimple_assign_lhs_ptr (use_stmt),
365 chk_uses,
366 get_immediate_dominator (CDI_DOMINATORS,
367 gimple_bb (phi))))
368 goto next;
370 gimple *vuse_stmt;
371 imm_use_iterator vui;
372 use_operand_p vuse_p;
373 /* In order to move the aggregate copies earlier, make sure
374 there are no statements that could read from memory
375 aliasing the lhs in between the start of bb and use_stmt.
376 As we require use_stmt to have a VDEF above, loads after
377 use_stmt will use a different virtual SSA_NAME. */
378 FOR_EACH_IMM_USE_FAST (vuse_p, vui, vuse)
380 vuse_stmt = USE_STMT (vuse_p);
381 if (vuse_stmt == use_stmt)
382 continue;
383 if (!dominated_by_p (CDI_DOMINATORS,
384 gimple_bb (vuse_stmt), bb))
385 continue;
386 if (ref_maybe_used_by_stmt_p (vuse_stmt,
387 gimple_assign_lhs (use_stmt)))
388 goto next;
391 phiprop_insert_phi (bb, phi, use_stmt, phivn, n);
393 /* Remove old stmt. The phi is taken care of by DCE. */
394 gsi = gsi_for_stmt (use_stmt);
395 /* Unlinking the VDEF here is fine as we are sure that we process
396 stmts in execution order due to aggregate copies having VDEFs
397 and we emit loads on the edges in the very same order.
398 We get multiple copies (or intermediate register loads) handled
399 only by walking PHIs or immediate uses in a lucky order though,
400 so we could signal the caller to re-start iterating over PHIs
401 when we come here which would make it quadratic in the number
402 of PHIs. */
403 unlink_stmt_vdef (use_stmt);
404 gsi_remove (&gsi, true);
406 phi_inserted = true;
409 /* Found a proper dereference. Insert a phi node if this
410 is the first load transformation. */
411 else if (!phi_inserted)
413 res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n);
414 type = TREE_TYPE (res);
416 /* Remember the value we created for *ptr. */
417 phivn[SSA_NAME_VERSION (ptr)].value = res;
418 phivn[SSA_NAME_VERSION (ptr)].vuse = vuse;
420 /* Remove old stmt. The phi is taken care of by DCE, if we
421 want to delete it here we also have to delete all intermediate
422 copies. */
423 gsi = gsi_for_stmt (use_stmt);
424 gsi_remove (&gsi, true);
426 phi_inserted = true;
428 else
430 /* Further replacements are easy, just make a copy out of the
431 load. */
432 gimple_assign_set_rhs1 (use_stmt, res);
433 update_stmt (use_stmt);
436 next:;
437 /* Continue searching for a proper dereference. */
440 return phi_inserted;
443 /* Main entry for phiprop pass. */
445 namespace {
447 const pass_data pass_data_phiprop =
449 GIMPLE_PASS, /* type */
450 "phiprop", /* name */
451 OPTGROUP_NONE, /* optinfo_flags */
452 TV_TREE_PHIPROP, /* tv_id */
453 ( PROP_cfg | PROP_ssa ), /* properties_required */
454 0, /* properties_provided */
455 0, /* properties_destroyed */
456 0, /* todo_flags_start */
457 TODO_update_ssa, /* todo_flags_finish */
460 class pass_phiprop : public gimple_opt_pass
462 public:
463 pass_phiprop (gcc::context *ctxt)
464 : gimple_opt_pass (pass_data_phiprop, ctxt)
467 /* opt_pass methods: */
468 virtual bool gate (function *) { return flag_tree_phiprop; }
469 virtual unsigned int execute (function *);
471 }; // class pass_phiprop
473 unsigned int
474 pass_phiprop::execute (function *fun)
476 vec<basic_block> bbs;
477 struct phiprop_d *phivn;
478 bool did_something = false;
479 basic_block bb;
480 gphi_iterator gsi;
481 unsigned i;
482 size_t n;
484 calculate_dominance_info (CDI_DOMINATORS);
485 calculate_dominance_info (CDI_POST_DOMINATORS);
487 n = num_ssa_names;
488 phivn = XCNEWVEC (struct phiprop_d, n);
490 /* Walk the dominator tree in preorder. */
491 bbs = get_all_dominated_blocks (CDI_DOMINATORS,
492 single_succ (ENTRY_BLOCK_PTR_FOR_FN (fun)));
493 FOR_EACH_VEC_ELT (bbs, i, bb)
494 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
495 did_something |= propagate_with_phi (bb, gsi.phi (), phivn, n);
497 if (did_something)
498 gsi_commit_edge_inserts ();
500 bbs.release ();
501 free (phivn);
503 free_dominance_info (CDI_POST_DOMINATORS);
505 return 0;
508 } // anon namespace
510 gimple_opt_pass *
511 make_pass_phiprop (gcc::context *ctxt)
513 return new pass_phiprop (ctxt);