summaryrefslogtreecommitdiff
path: root/gcc/tree-ssa-phiprop.c
blob: 96d48b142e7db5cf79db5ea2dd23e3d65e88aaae (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
/* Backward propagation of indirect loads through PHIs.
   Copyright (C) 2007-2014 Free Software Foundation, Inc.
   Contributed by Richard Guenther <rguenther@suse.de>

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.

GCC is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "tm_p.h"
#include "predict.h"
#include "vec.h"
#include "hashtab.h"
#include "hash-set.h"
#include "machmode.h"
#include "hard-reg-set.h"
#include "input.h"
#include "function.h"
#include "dominance.h"
#include "cfg.h"
#include "basic-block.h"
#include "gimple-pretty-print.h"
#include "tree-ssa-alias.h"
#include "internal-fn.h"
#include "tree-eh.h"
#include "gimple-expr.h"
#include "is-a.h"
#include "gimple.h"
#include "gimplify.h"
#include "gimple-iterator.h"
#include "gimple-ssa.h"
#include "tree-phinodes.h"
#include "ssa-iterators.h"
#include "stringpool.h"
#include "tree-ssanames.h"
#include "tree-pass.h"
#include "langhooks.h"
#include "flags.h"

/* This pass propagates indirect loads through the PHI node for its
   address to make the load source possibly non-addressable and to
   allow for PHI optimization to trigger.

   For example the pass changes

     # addr_1 = PHI <&a, &b>
     tmp_1 = *addr_1;

   to

     # tmp_1 = PHI <a, b>

   but also handles more complex scenarios like

     D.2077_2 = &this_1(D)->a1;
     ...

     # b_12 = PHI <&c(2), D.2077_2(3)>
     D.2114_13 = *b_12;
     ...

     # b_15 = PHI <b_12(4), &b(5)>
     D.2080_5 = &this_1(D)->a0;
     ...

     # b_18 = PHI <D.2080_5(6), &c(7)>
     ...

     # b_21 = PHI <b_15(8), b_18(9)>
     D.2076_8 = *b_21;

   where the addresses loaded are defined by PHIs itself.
   The above happens for

     std::max(std::min(a0, c), std::min(std::max(a1, c), b))

   where this pass transforms it to a form later PHI optimization
   recognizes and transforms it to the simple

     D.2109_10 = this_1(D)->a1;
     D.2110_11 = c;
     D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>;
     D.2115_14 = b;
     D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>;
     D.2119_16 = this_1(D)->a0;
     D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>;
     D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>;

   The pass does a dominator walk processing loads using a basic-block
   local analysis and stores the result for use by transformations on
   dominated basic-blocks.  */


/* Structure to keep track of the value of a dereferenced PHI result
   and the virtual operand used for that dereference.  */

struct phiprop_d
{
  tree value;
  tree vuse;
};

/* Verify if the value recorded for NAME in PHIVN is still valid at
   the start of basic block BB.  */

static bool
phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb)
{
  tree vuse = phivn[SSA_NAME_VERSION (name)].vuse;
  gimple use_stmt;
  imm_use_iterator ui2;
  bool ok = true;

  /* The def stmts of the virtual uses need to be dominated by bb.  */
  gcc_assert (vuse != NULL_TREE);

  FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse)
    {
      /* If BB does not dominate a VDEF, the value is invalid.  */
      if ((gimple_vdef (use_stmt) != NULL_TREE
	   || gimple_code (use_stmt) == GIMPLE_PHI)
	  && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb))
	{
	  ok = false;
	  BREAK_FROM_IMM_USE_STMT (ui2);
	}
    }

  return ok;
}

/* Insert a new phi node for the dereference of PHI at basic_block
   BB with the virtual operands from USE_STMT.  */

static tree
phiprop_insert_phi (basic_block bb, gimple phi, gimple use_stmt,
		    struct phiprop_d *phivn, size_t n)
{
  tree res;
  gimple new_phi;
  edge_iterator ei;
  edge e;

  gcc_assert (is_gimple_assign (use_stmt)
	      && gimple_assign_rhs_code (use_stmt) == MEM_REF);

  /* Build a new PHI node to replace the definition of
     the indirect reference lhs.  */
  res = gimple_assign_lhs (use_stmt);
  new_phi = create_phi_node (res, bb);

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "Inserting PHI for result of load ");
      print_gimple_stmt (dump_file, use_stmt, 0, 0);
    }

  /* Add PHI arguments for each edge inserting loads of the
     addressable operands.  */
  FOR_EACH_EDGE (e, ei, bb->preds)
    {
      tree old_arg, new_var;
      gimple tmp;
      source_location locus;

      old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
      locus = gimple_phi_arg_location_from_edge (phi, e);
      while (TREE_CODE (old_arg) == SSA_NAME
	     && (SSA_NAME_VERSION (old_arg) >= n
	         || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE))
	{
	  gimple def_stmt = SSA_NAME_DEF_STMT (old_arg);
	  old_arg = gimple_assign_rhs1 (def_stmt);
	  locus = gimple_location (def_stmt);
	}

      if (TREE_CODE (old_arg) == SSA_NAME)
	{
	  if (dump_file && (dump_flags & TDF_DETAILS))
	    {
	      fprintf (dump_file, "  for edge defining ");
	      print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
	      fprintf (dump_file, " reusing PHI result ");
	      print_generic_expr (dump_file,
				  phivn[SSA_NAME_VERSION (old_arg)].value, 0);
	      fprintf (dump_file, "\n");
	    }
	  /* Reuse a formerly created dereference.  */
	  new_var = phivn[SSA_NAME_VERSION (old_arg)].value;
	}
      else
	{
	  tree rhs = gimple_assign_rhs1 (use_stmt);
	  gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR);
	  new_var = make_ssa_name (TREE_TYPE (rhs), NULL);
	  if (!is_gimple_min_invariant (old_arg))
	    old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
	  else
	    old_arg = unshare_expr (old_arg);
	  tmp = gimple_build_assign (new_var,
				     fold_build2 (MEM_REF, TREE_TYPE (rhs),
						  old_arg,
						  TREE_OPERAND (rhs, 1)));
	  gimple_set_location (tmp, locus);

	  gsi_insert_on_edge (e, tmp);
	  update_stmt (tmp);

	  if (dump_file && (dump_flags & TDF_DETAILS))
	    {
	      fprintf (dump_file, "  for edge defining ");
	      print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
	      fprintf (dump_file, " inserting load ");
	      print_gimple_stmt (dump_file, tmp, 0, 0);
	    }
	}

      add_phi_arg (new_phi, new_var, e, locus);
    }

  update_stmt (new_phi);

  if (dump_file && (dump_flags & TDF_DETAILS))
    print_gimple_stmt (dump_file, new_phi, 0, 0);

  return res;
}

/* Propagate between the phi node arguments of PHI in BB and phi result
   users.  For now this matches
        # p_2 = PHI <&x, &y>
      <Lx>:;
	p_3 = p_2;
	z_2 = *p_3;
   and converts it to
	# z_2 = PHI <x, y>
      <Lx>:;
   Returns true if a transformation was done and edge insertions
   need to be committed.  Global data PHIVN and N is used to track
   past transformation results.  We need to be especially careful here
   with aliasing issues as we are moving memory reads.  */

static bool
propagate_with_phi (basic_block bb, gimple phi, struct phiprop_d *phivn,
		    size_t n)
{
  tree ptr = PHI_RESULT (phi);
  gimple use_stmt;
  tree res = NULL_TREE;
  gimple_stmt_iterator gsi;
  imm_use_iterator ui;
  use_operand_p arg_p, use;
  ssa_op_iter i;
  bool phi_inserted;
  tree type = NULL_TREE;

  if (!POINTER_TYPE_P (TREE_TYPE (ptr))
      || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr))))
    return false;

  /* Check if we can "cheaply" dereference all phi arguments.  */
  FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE)
    {
      tree arg = USE_FROM_PTR (arg_p);
      /* Walk the ssa chain until we reach a ssa name we already
	 created a value for or we reach a definition of the form
	 ssa_name_n = &var;  */
      while (TREE_CODE (arg) == SSA_NAME
	     && !SSA_NAME_IS_DEFAULT_DEF (arg)
	     && (SSA_NAME_VERSION (arg) >= n
	         || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE))
	{
	  gimple def_stmt = SSA_NAME_DEF_STMT (arg);
	  if (!gimple_assign_single_p (def_stmt))
	    return false;
	  arg = gimple_assign_rhs1 (def_stmt);
	}
      if (TREE_CODE (arg) != ADDR_EXPR
	  && !(TREE_CODE (arg) == SSA_NAME
	       && SSA_NAME_VERSION (arg) < n
	       && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE
	       && (!type
		   || types_compatible_p
		       (type, TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value)))
	       && phivn_valid_p (phivn, arg, bb)))
	return false;
      if (!type
	  && TREE_CODE (arg) == SSA_NAME)
	type = TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value);
    }

  /* Find a dereferencing use.  First follow (single use) ssa
     copy chains for ptr.  */
  while (single_imm_use (ptr, &use, &use_stmt)
	 && gimple_assign_ssa_name_copy_p (use_stmt))
    ptr = gimple_assign_lhs (use_stmt);

  /* Replace the first dereference of *ptr if there is one and if we
     can move the loads to the place of the ptr phi node.  */
  phi_inserted = false;
  FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr)
    {
      gimple def_stmt;
      tree vuse;

      /* Only replace loads in blocks that post-dominate the PHI node.  That
         makes sure we don't end up speculating loads.  */
      if (!dominated_by_p (CDI_POST_DOMINATORS,
			   bb, gimple_bb (use_stmt)))
	continue;
         
      /* Check whether this is a load of *ptr.  */
      if (!(is_gimple_assign (use_stmt)
	    && TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME
	    && gimple_assign_rhs_code (use_stmt) == MEM_REF
	    && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr
	    && integer_zerop (TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 1))
	    && (!type
		|| types_compatible_p
		     (TREE_TYPE (gimple_assign_lhs (use_stmt)), type))
	    /* We cannot replace a load that may throw or is volatile.  */
	    && !stmt_can_throw_internal (use_stmt)))
	continue;

      /* Check if we can move the loads.  The def stmt of the virtual use
	 needs to be in a different basic block dominating bb.  */
      vuse = gimple_vuse (use_stmt);
      def_stmt = SSA_NAME_DEF_STMT (vuse);
      if (!SSA_NAME_IS_DEFAULT_DEF (vuse)
	  && (gimple_bb (def_stmt) == bb
	      || !dominated_by_p (CDI_DOMINATORS,
				  bb, gimple_bb (def_stmt))))
	goto next;

      /* Found a proper dereference.  Insert a phi node if this
	 is the first load transformation.  */
      if (!phi_inserted)
	{
	  res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n);
	  type = TREE_TYPE (res);

	  /* Remember the value we created for *ptr.  */
	  phivn[SSA_NAME_VERSION (ptr)].value = res;
	  phivn[SSA_NAME_VERSION (ptr)].vuse = vuse;

	  /* Remove old stmt.  The phi is taken care of by DCE, if we
	     want to delete it here we also have to delete all intermediate
	     copies.  */
	  gsi = gsi_for_stmt (use_stmt);
	  gsi_remove (&gsi, true);

	  phi_inserted = true;
	}
      else
	{
	  /* Further replacements are easy, just make a copy out of the
	     load.  */
	  gimple_assign_set_rhs1 (use_stmt, res);
	  update_stmt (use_stmt);
	}

next:;
      /* Continue searching for a proper dereference.  */
    }

  return phi_inserted;
}

/* Main entry for phiprop pass.  */

namespace {

const pass_data pass_data_phiprop =
{
  GIMPLE_PASS, /* type */
  "phiprop", /* name */
  OPTGROUP_NONE, /* optinfo_flags */
  TV_TREE_PHIPROP, /* tv_id */
  ( PROP_cfg | PROP_ssa ), /* properties_required */
  0, /* properties_provided */
  0, /* properties_destroyed */
  0, /* todo_flags_start */
  TODO_update_ssa, /* todo_flags_finish */
};

class pass_phiprop : public gimple_opt_pass
{
public:
  pass_phiprop (gcc::context *ctxt)
    : gimple_opt_pass (pass_data_phiprop, ctxt)
  {}

  /* opt_pass methods: */
  virtual bool gate (function *) { return flag_tree_phiprop; }
  virtual unsigned int execute (function *);

}; // class pass_phiprop

unsigned int
pass_phiprop::execute (function *fun)
{
  vec<basic_block> bbs;
  struct phiprop_d *phivn;
  bool did_something = false;
  basic_block bb;
  gimple_stmt_iterator gsi;
  unsigned i;
  size_t n;

  calculate_dominance_info (CDI_DOMINATORS);
  calculate_dominance_info (CDI_POST_DOMINATORS);

  n = num_ssa_names;
  phivn = XCNEWVEC (struct phiprop_d, n);

  /* Walk the dominator tree in preorder.  */
  bbs = get_all_dominated_blocks (CDI_DOMINATORS,
				  single_succ (ENTRY_BLOCK_PTR_FOR_FN (fun)));
  FOR_EACH_VEC_ELT (bbs, i, bb)
    for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
      did_something |= propagate_with_phi (bb, gsi_stmt (gsi), phivn, n);

  if (did_something)
    gsi_commit_edge_inserts ();

  bbs.release ();
  free (phivn);

  free_dominance_info (CDI_POST_DOMINATORS);

  return 0;
}

} // anon namespace

gimple_opt_pass *
make_pass_phiprop (gcc::context *ctxt)
{
  return new pass_phiprop (ctxt);
}