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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) 2007-2015 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 "tm.h"
25 #include "alias.h"
26 #include "symtab.h"
27 #include "tree.h"
28 #include "fold-const.h"
29 #include "tm_p.h"
30 #include "predict.h"
31 #include "hard-reg-set.h"
32 #include "function.h"
33 #include "dominance.h"
34 #include "cfg.h"
35 #include "basic-block.h"
36 #include "gimple-pretty-print.h"
37 #include "tree-ssa-alias.h"
38 #include "internal-fn.h"
39 #include "tree-eh.h"
40 #include "gimple-expr.h"
41 #include "gimple.h"
42 #include "gimplify.h"
43 #include "gimple-iterator.h"
44 #include "gimple-ssa.h"
45 #include "tree-phinodes.h"
46 #include "ssa-iterators.h"
47 #include "stringpool.h"
48 #include "tree-ssanames.h"
49 #include "tree-pass.h"
50 #include "langhooks.h"
51 #include "flags.h"
53 /* This pass propagates indirect loads through the PHI node for its
54 address to make the load source possibly non-addressable and to
55 allow for PHI optimization to trigger.
57 For example the pass changes
59 # addr_1 = PHI <&a, &b>
60 tmp_1 = *addr_1;
64 # tmp_1 = PHI <a, b>
66 but also handles more complex scenarios like
68 D.2077_2 = &this_1(D)->a1;
69 ...
71 # b_12 = PHI <&c(2), D.2077_2(3)>
72 D.2114_13 = *b_12;
73 ...
75 # b_15 = PHI <b_12(4), &b(5)>
76 D.2080_5 = &this_1(D)->a0;
77 ...
79 # b_18 = PHI <D.2080_5(6), &c(7)>
80 ...
82 # b_21 = PHI <b_15(8), b_18(9)>
83 D.2076_8 = *b_21;
85 where the addresses loaded are defined by PHIs itself.
86 The above happens for
88 std::max(std::min(a0, c), std::min(std::max(a1, c), b))
90 where this pass transforms it to a form later PHI optimization
91 recognizes and transforms it to the simple
93 D.2109_10 = this_1(D)->a1;
94 D.2110_11 = c;
95 D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>;
96 D.2115_14 = b;
97 D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>;
98 D.2119_16 = this_1(D)->a0;
99 D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>;
100 D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>;
102 The pass does a dominator walk processing loads using a basic-block
103 local analysis and stores the result for use by transformations on
104 dominated basic-blocks. */
107 /* Structure to keep track of the value of a dereferenced PHI result
108 and the virtual operand used for that dereference. */
110 struct phiprop_d
112 tree value;
113 tree vuse;
116 /* Verify if the value recorded for NAME in PHIVN is still valid at
117 the start of basic block BB. */
119 static bool
120 phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb)
122 tree vuse = phivn[SSA_NAME_VERSION (name)].vuse;
123 gimple use_stmt;
124 imm_use_iterator ui2;
125 bool ok = true;
127 /* The def stmts of the virtual uses need to be dominated by bb. */
128 gcc_assert (vuse != NULL_TREE);
130 FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse)
132 /* If BB does not dominate a VDEF, the value is invalid. */
133 if ((gimple_vdef (use_stmt) != NULL_TREE
134 || gimple_code (use_stmt) == GIMPLE_PHI)
135 && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb))
137 ok = false;
138 BREAK_FROM_IMM_USE_STMT (ui2);
142 return ok;
145 /* Insert a new phi node for the dereference of PHI at basic_block
146 BB with the virtual operands from USE_STMT. */
148 static tree
149 phiprop_insert_phi (basic_block bb, gphi *phi, gimple use_stmt,
150 struct phiprop_d *phivn, size_t n)
152 tree res;
153 gphi *new_phi;
154 edge_iterator ei;
155 edge e;
157 gcc_assert (is_gimple_assign (use_stmt)
158 && gimple_assign_rhs_code (use_stmt) == MEM_REF);
160 /* Build a new PHI node to replace the definition of
161 the indirect reference lhs. */
162 res = gimple_assign_lhs (use_stmt);
163 new_phi = create_phi_node (res, bb);
165 if (dump_file && (dump_flags & TDF_DETAILS))
167 fprintf (dump_file, "Inserting PHI for result of load ");
168 print_gimple_stmt (dump_file, use_stmt, 0, 0);
171 /* Add PHI arguments for each edge inserting loads of the
172 addressable operands. */
173 FOR_EACH_EDGE (e, ei, bb->preds)
175 tree old_arg, new_var;
176 gassign *tmp;
177 source_location locus;
179 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
180 locus = gimple_phi_arg_location_from_edge (phi, e);
181 while (TREE_CODE (old_arg) == SSA_NAME
182 && (SSA_NAME_VERSION (old_arg) >= n
183 || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE))
185 gimple def_stmt = SSA_NAME_DEF_STMT (old_arg);
186 old_arg = gimple_assign_rhs1 (def_stmt);
187 locus = gimple_location (def_stmt);
190 if (TREE_CODE (old_arg) == SSA_NAME)
192 if (dump_file && (dump_flags & TDF_DETAILS))
194 fprintf (dump_file, " for edge defining ");
195 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
196 fprintf (dump_file, " reusing PHI result ");
197 print_generic_expr (dump_file,
198 phivn[SSA_NAME_VERSION (old_arg)].value, 0);
199 fprintf (dump_file, "\n");
201 /* Reuse a formerly created dereference. */
202 new_var = phivn[SSA_NAME_VERSION (old_arg)].value;
204 else
206 tree rhs = gimple_assign_rhs1 (use_stmt);
207 gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR);
208 new_var = make_ssa_name (TREE_TYPE (rhs));
209 if (!is_gimple_min_invariant (old_arg))
210 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
211 else
212 old_arg = unshare_expr (old_arg);
213 tmp = gimple_build_assign (new_var,
214 fold_build2 (MEM_REF, TREE_TYPE (rhs),
215 old_arg,
216 TREE_OPERAND (rhs, 1)));
217 gimple_set_location (tmp, locus);
219 gsi_insert_on_edge (e, tmp);
220 update_stmt (tmp);
222 if (dump_file && (dump_flags & TDF_DETAILS))
224 fprintf (dump_file, " for edge defining ");
225 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
226 fprintf (dump_file, " inserting load ");
227 print_gimple_stmt (dump_file, tmp, 0, 0);
231 add_phi_arg (new_phi, new_var, e, locus);
234 update_stmt (new_phi);
236 if (dump_file && (dump_flags & TDF_DETAILS))
237 print_gimple_stmt (dump_file, new_phi, 0, 0);
239 return res;
242 /* Propagate between the phi node arguments of PHI in BB and phi result
243 users. For now this matches
244 # p_2 = PHI <&x, &y>
245 <Lx>:;
246 p_3 = p_2;
247 z_2 = *p_3;
248 and converts it to
249 # z_2 = PHI <x, y>
250 <Lx>:;
251 Returns true if a transformation was done and edge insertions
252 need to be committed. Global data PHIVN and N is used to track
253 past transformation results. We need to be especially careful here
254 with aliasing issues as we are moving memory reads. */
256 static bool
257 propagate_with_phi (basic_block bb, gphi *phi, struct phiprop_d *phivn,
258 size_t n)
260 tree ptr = PHI_RESULT (phi);
261 gimple use_stmt;
262 tree res = NULL_TREE;
263 gimple_stmt_iterator gsi;
264 imm_use_iterator ui;
265 use_operand_p arg_p, use;
266 ssa_op_iter i;
267 bool phi_inserted;
268 tree type = NULL_TREE;
270 if (!POINTER_TYPE_P (TREE_TYPE (ptr))
271 || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr))))
272 return false;
274 /* Check if we can "cheaply" dereference all phi arguments. */
275 FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE)
277 tree arg = USE_FROM_PTR (arg_p);
278 /* Walk the ssa chain until we reach a ssa name we already
279 created a value for or we reach a definition of the form
280 ssa_name_n = &var; */
281 while (TREE_CODE (arg) == SSA_NAME
282 && !SSA_NAME_IS_DEFAULT_DEF (arg)
283 && (SSA_NAME_VERSION (arg) >= n
284 || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE))
286 gimple def_stmt = SSA_NAME_DEF_STMT (arg);
287 if (!gimple_assign_single_p (def_stmt))
288 return false;
289 arg = gimple_assign_rhs1 (def_stmt);
291 if (TREE_CODE (arg) != ADDR_EXPR
292 && !(TREE_CODE (arg) == SSA_NAME
293 && SSA_NAME_VERSION (arg) < n
294 && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE
295 && (!type
296 || types_compatible_p
297 (type, TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value)))
298 && phivn_valid_p (phivn, arg, bb)))
299 return false;
300 if (!type
301 && TREE_CODE (arg) == SSA_NAME)
302 type = TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value);
305 /* Find a dereferencing use. First follow (single use) ssa
306 copy chains for ptr. */
307 while (single_imm_use (ptr, &use, &use_stmt)
308 && gimple_assign_ssa_name_copy_p (use_stmt))
309 ptr = gimple_assign_lhs (use_stmt);
311 /* Replace the first dereference of *ptr if there is one and if we
312 can move the loads to the place of the ptr phi node. */
313 phi_inserted = false;
314 FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr)
316 gimple def_stmt;
317 tree vuse;
319 /* Only replace loads in blocks that post-dominate the PHI node. That
320 makes sure we don't end up speculating loads. */
321 if (!dominated_by_p (CDI_POST_DOMINATORS,
322 bb, gimple_bb (use_stmt)))
323 continue;
325 /* Check whether this is a load of *ptr. */
326 if (!(is_gimple_assign (use_stmt)
327 && TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME
328 && gimple_assign_rhs_code (use_stmt) == MEM_REF
329 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr
330 && integer_zerop (TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 1))
331 && (!type
332 || types_compatible_p
333 (TREE_TYPE (gimple_assign_lhs (use_stmt)), type))
334 /* We cannot replace a load that may throw or is volatile. */
335 && !stmt_can_throw_internal (use_stmt)))
336 continue;
338 /* Check if we can move the loads. The def stmt of the virtual use
339 needs to be in a different basic block dominating bb. */
340 vuse = gimple_vuse (use_stmt);
341 def_stmt = SSA_NAME_DEF_STMT (vuse);
342 if (!SSA_NAME_IS_DEFAULT_DEF (vuse)
343 && (gimple_bb (def_stmt) == bb
344 || !dominated_by_p (CDI_DOMINATORS,
345 bb, gimple_bb (def_stmt))))
346 goto next;
348 /* Found a proper dereference. Insert a phi node if this
349 is the first load transformation. */
350 if (!phi_inserted)
352 res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n);
353 type = TREE_TYPE (res);
355 /* Remember the value we created for *ptr. */
356 phivn[SSA_NAME_VERSION (ptr)].value = res;
357 phivn[SSA_NAME_VERSION (ptr)].vuse = vuse;
359 /* Remove old stmt. The phi is taken care of by DCE, if we
360 want to delete it here we also have to delete all intermediate
361 copies. */
362 gsi = gsi_for_stmt (use_stmt);
363 gsi_remove (&gsi, true);
365 phi_inserted = true;
367 else
369 /* Further replacements are easy, just make a copy out of the
370 load. */
371 gimple_assign_set_rhs1 (use_stmt, res);
372 update_stmt (use_stmt);
375 next:;
376 /* Continue searching for a proper dereference. */
379 return phi_inserted;
382 /* Main entry for phiprop pass. */
384 namespace {
386 const pass_data pass_data_phiprop =
388 GIMPLE_PASS, /* type */
389 "phiprop", /* name */
390 OPTGROUP_NONE, /* optinfo_flags */
391 TV_TREE_PHIPROP, /* tv_id */
392 ( PROP_cfg | PROP_ssa ), /* properties_required */
393 0, /* properties_provided */
394 0, /* properties_destroyed */
395 0, /* todo_flags_start */
396 TODO_update_ssa, /* todo_flags_finish */
399 class pass_phiprop : public gimple_opt_pass
401 public:
402 pass_phiprop (gcc::context *ctxt)
403 : gimple_opt_pass (pass_data_phiprop, ctxt)
406 /* opt_pass methods: */
407 virtual bool gate (function *) { return flag_tree_phiprop; }
408 virtual unsigned int execute (function *);
410 }; // class pass_phiprop
412 unsigned int
413 pass_phiprop::execute (function *fun)
415 vec<basic_block> bbs;
416 struct phiprop_d *phivn;
417 bool did_something = false;
418 basic_block bb;
419 gphi_iterator gsi;
420 unsigned i;
421 size_t n;
423 calculate_dominance_info (CDI_DOMINATORS);
424 calculate_dominance_info (CDI_POST_DOMINATORS);
426 n = num_ssa_names;
427 phivn = XCNEWVEC (struct phiprop_d, n);
429 /* Walk the dominator tree in preorder. */
430 bbs = get_all_dominated_blocks (CDI_DOMINATORS,
431 single_succ (ENTRY_BLOCK_PTR_FOR_FN (fun)));
432 FOR_EACH_VEC_ELT (bbs, i, bb)
433 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
434 did_something |= propagate_with_phi (bb, gsi.phi (), phivn, n);
436 if (did_something)
437 gsi_commit_edge_inserts ();
439 bbs.release ();
440 free (phivn);
442 free_dominance_info (CDI_POST_DOMINATORS);
444 return 0;
447 } // anon namespace
449 gimple_opt_pass *
450 make_pass_phiprop (gcc::context *ctxt)
452 return new pass_phiprop (ctxt);