1 /* Backward propagation of indirect loads through PHIs.
2 Copyright (C) 2007, 2008 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)
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/>. */
23 #include "coretypes.h"
27 #include "basic-block.h"
29 #include "diagnostic.h"
30 #include "tree-flow.h"
31 #include "tree-pass.h"
32 #include "tree-dump.h"
33 #include "langhooks.h"
36 /* This pass propagates indirect loads through the PHI node for its
37 address to make the load source possibly non-addressable and to
38 allow for PHI optimization to trigger.
40 For example the pass changes
42 # addr_1 = PHI <&a, &b>
49 but also handles more complex scenarios like
51 D.2077_2 = &this_1(D)->a1;
54 # b_12 = PHI <&c(2), D.2077_2(3)>
58 # b_15 = PHI <b_12(4), &b(5)>
59 D.2080_5 = &this_1(D)->a0;
62 # b_18 = PHI <D.2080_5(6), &c(7)>
65 # b_21 = PHI <b_15(8), b_18(9)>
68 where the addresses loaded are defined by PHIs itself.
71 std::max(std::min(a0, c), std::min(std::max(a1, c), b))
73 where this pass transforms it to a form later PHI optimization
74 recognizes and transforms it to the simple
76 D.2109_10 = this_1(D)->a1;
78 D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>;
80 D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>;
81 D.2119_16 = this_1(D)->a0;
82 D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>;
83 D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>;
85 The pass does a dominator walk processing loads using a basic-block
86 local analysis and stores the result for use by transformations on
87 dominated basic-blocks. */
90 /* Structure to keep track of the value of a dereferenced PHI result
91 and the virtual operand used for that dereference. */
99 /* Verify if the value recorded for NAME in PHIVN is still valid at
100 the start of basic block BB. */
103 phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb)
105 tree vuse = phivn[SSA_NAME_VERSION (name)].vuse;
107 imm_use_iterator ui2;
110 /* The def stmts of the virtual uses need to be dominated by bb. */
111 gcc_assert (vuse != NULL_TREE);
113 FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse)
115 /* If BB does not dominate a VDEF, the value is invalid. */
116 if ((gimple_vdef (use_stmt) != NULL_TREE
117 || gimple_code (use_stmt) == GIMPLE_PHI)
118 && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb))
121 BREAK_FROM_IMM_USE_STMT (ui2);
128 /* Insert a new phi node for the dereference of PHI at basic_block
129 BB with the virtual operands from USE_STMT. */
132 phiprop_insert_phi (basic_block bb, gimple phi, gimple use_stmt,
133 struct phiprop_d *phivn, size_t n)
140 gcc_assert (is_gimple_assign (use_stmt)
141 && gimple_assign_rhs_code (use_stmt) == INDIRECT_REF);
143 /* Build a new PHI node to replace the definition of
144 the indirect reference lhs. */
145 res = gimple_assign_lhs (use_stmt);
146 SSA_NAME_DEF_STMT (res) = new_phi = create_phi_node (res, bb);
148 if (dump_file && (dump_flags & TDF_DETAILS))
150 fprintf (dump_file, "Inserting PHI for result of load ");
151 print_gimple_stmt (dump_file, use_stmt, 0, 0);
154 /* Add PHI arguments for each edge inserting loads of the
155 addressable operands. */
156 FOR_EACH_EDGE (e, ei, bb->preds)
158 tree old_arg, new_var;
160 source_location locus;
162 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
163 locus = gimple_phi_arg_location_from_edge (phi, e);
164 while (TREE_CODE (old_arg) == SSA_NAME
165 && (SSA_NAME_VERSION (old_arg) >= n
166 || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE))
168 gimple def_stmt = SSA_NAME_DEF_STMT (old_arg);
169 old_arg = gimple_assign_rhs1 (def_stmt);
170 locus = gimple_location (def_stmt);
173 if (TREE_CODE (old_arg) == SSA_NAME)
175 if (dump_file && (dump_flags & TDF_DETAILS))
177 fprintf (dump_file, " for edge defining ");
178 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
179 fprintf (dump_file, " reusing PHI result ");
180 print_generic_expr (dump_file,
181 phivn[SSA_NAME_VERSION (old_arg)].value, 0);
182 fprintf (dump_file, "\n");
184 /* Reuse a formerly created dereference. */
185 new_var = phivn[SSA_NAME_VERSION (old_arg)].value;
189 gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR);
190 old_arg = TREE_OPERAND (old_arg, 0);
191 new_var = create_tmp_reg (TREE_TYPE (old_arg), NULL);
192 tmp = gimple_build_assign (new_var, unshare_expr (old_arg));
193 gcc_assert (is_gimple_reg (new_var));
194 add_referenced_var (new_var);
195 new_var = make_ssa_name (new_var, tmp);
196 gimple_assign_set_lhs (tmp, new_var);
197 gimple_set_location (tmp, locus);
199 gsi_insert_on_edge (e, tmp);
202 if (dump_file && (dump_flags & TDF_DETAILS))
204 fprintf (dump_file, " for edge defining ");
205 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
206 fprintf (dump_file, " inserting load ");
207 print_gimple_stmt (dump_file, tmp, 0, 0);
211 add_phi_arg (new_phi, new_var, e, locus);
214 update_stmt (new_phi);
216 if (dump_file && (dump_flags & TDF_DETAILS))
217 print_gimple_stmt (dump_file, new_phi, 0, 0);
222 /* Propagate between the phi node arguments of PHI in BB and phi result
223 users. For now this matches
231 Returns true if a transformation was done and edge insertions
232 need to be committed. Global data PHIVN and N is used to track
233 past transformation results. We need to be especially careful here
234 with aliasing issues as we are moving memory reads. */
237 propagate_with_phi (basic_block bb, gimple phi, struct phiprop_d *phivn,
240 tree ptr = PHI_RESULT (phi);
242 tree res = NULL_TREE;
243 gimple_stmt_iterator gsi;
245 use_operand_p arg_p, use;
249 if (!POINTER_TYPE_P (TREE_TYPE (ptr))
250 || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr))))
253 /* Check if we can "cheaply" dereference all phi arguments. */
254 FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE)
256 tree arg = USE_FROM_PTR (arg_p);
257 /* Walk the ssa chain until we reach a ssa name we already
258 created a value for or we reach a definition of the form
259 ssa_name_n = &var; */
260 while (TREE_CODE (arg) == SSA_NAME
261 && !SSA_NAME_IS_DEFAULT_DEF (arg)
262 && (SSA_NAME_VERSION (arg) >= n
263 || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE))
265 gimple def_stmt = SSA_NAME_DEF_STMT (arg);
266 if (!gimple_assign_single_p (def_stmt))
268 arg = gimple_assign_rhs1 (def_stmt);
270 if ((TREE_CODE (arg) != ADDR_EXPR
271 /* Avoid to have to decay *&a to a[0] later. */
272 || !is_gimple_reg_type (TREE_TYPE (TREE_OPERAND (arg, 0))))
273 && !(TREE_CODE (arg) == SSA_NAME
274 && SSA_NAME_VERSION (arg) < n
275 && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE
276 && phivn_valid_p (phivn, arg, bb)))
280 /* Find a dereferencing use. First follow (single use) ssa
281 copy chains for ptr. */
282 while (single_imm_use (ptr, &use, &use_stmt)
283 && gimple_assign_ssa_name_copy_p (use_stmt))
284 ptr = gimple_assign_lhs (use_stmt);
286 /* Replace the first dereference of *ptr if there is one and if we
287 can move the loads to the place of the ptr phi node. */
288 phi_inserted = false;
289 FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr)
294 /* Check whether this is a load of *ptr. */
295 if (!(is_gimple_assign (use_stmt)
296 && TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME
297 && gimple_assign_rhs_code (use_stmt) == INDIRECT_REF
298 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr
299 /* We cannot replace a load that may throw or is volatile. */
300 && !stmt_can_throw_internal (use_stmt)))
303 /* Check if we can move the loads. The def stmt of the virtual use
304 needs to be in a different basic block dominating bb. */
305 vuse = gimple_vuse (use_stmt);
306 def_stmt = SSA_NAME_DEF_STMT (vuse);
307 if (!SSA_NAME_IS_DEFAULT_DEF (vuse)
308 && (gimple_bb (def_stmt) == bb
309 || !dominated_by_p (CDI_DOMINATORS,
310 bb, gimple_bb (def_stmt))))
313 /* Found a proper dereference. Insert a phi node if this
314 is the first load transformation. */
317 res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n);
319 /* Remember the value we created for *ptr. */
320 phivn[SSA_NAME_VERSION (ptr)].value = res;
321 phivn[SSA_NAME_VERSION (ptr)].vuse = vuse;
323 /* Remove old stmt. The phi is taken care of by DCE, if we
324 want to delete it here we also have to delete all intermediate
326 gsi = gsi_for_stmt (use_stmt);
327 gsi_remove (&gsi, false);
333 /* Further replacements are easy, just make a copy out of the
335 gimple_assign_set_rhs1 (use_stmt, res);
336 update_stmt (use_stmt);
340 /* Continue searching for a proper dereference. */
346 /* Main entry for phiprop pass. */
349 tree_ssa_phiprop (void)
351 VEC(basic_block, heap) *bbs;
352 struct phiprop_d *phivn;
353 bool did_something = false;
355 gimple_stmt_iterator gsi;
359 calculate_dominance_info (CDI_DOMINATORS);
362 phivn = XCNEWVEC (struct phiprop_d, n);
364 /* Walk the dominator tree in preorder. */
365 bbs = get_all_dominated_blocks (CDI_DOMINATORS,
366 single_succ (ENTRY_BLOCK_PTR));
367 for (i = 0; VEC_iterate (basic_block, bbs, i, bb); ++i)
368 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
369 did_something |= propagate_with_phi (bb, gsi_stmt (gsi), phivn, n);
372 gsi_commit_edge_inserts ();
374 VEC_free (basic_block, heap, bbs);
383 return flag_tree_phiprop;
386 struct gimple_opt_pass pass_phiprop =
390 "phiprop", /* name */
391 gate_phiprop, /* gate */
392 tree_ssa_phiprop, /* execute */
395 0, /* static_pass_number */
396 TV_TREE_PHIPROP, /* tv_id */
397 PROP_cfg | PROP_ssa, /* properties_required */
398 0, /* properties_provided */
399 0, /* properties_destroyed */
400 0, /* todo_flags_start */
404 | TODO_verify_ssa /* todo_flags_finish */