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"
29 #include "basic-block.h"
31 #include "diagnostic.h"
32 #include "tree-flow.h"
33 #include "tree-pass.h"
34 #include "tree-dump.h"
35 #include "langhooks.h"
38 /* This pass propagates indirect loads through the PHI node for its
39 address to make the load source possibly non-addressable and to
40 allow for PHI optimization to trigger.
42 For example the pass changes
44 # addr_1 = PHI <&a, &b>
51 but also handles more complex scenarios like
53 D.2077_2 = &this_1(D)->a1;
56 # b_12 = PHI <&c(2), D.2077_2(3)>
60 # b_15 = PHI <b_12(4), &b(5)>
61 D.2080_5 = &this_1(D)->a0;
64 # b_18 = PHI <D.2080_5(6), &c(7)>
67 # b_21 = PHI <b_15(8), b_18(9)>
70 where the addresses loaded are defined by PHIs itself.
73 std::max(std::min(a0, c), std::min(std::max(a1, c), b))
75 where this pass transforms it to a form later PHI optimization
76 recognizes and transforms it to the simple
78 D.2109_10 = this_1(D)->a1;
80 D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>;
82 D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>;
83 D.2119_16 = this_1(D)->a0;
84 D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>;
85 D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>;
87 The pass does a dominator walk processing loads using a basic-block
88 local analysis and stores the result for use by transformations on
89 dominated basic-blocks. */
92 /* Structure to keep track of the value of a dereferenced PHI result
93 and the set of virtual operands used for that dereference. */
101 /* Verify if the value recorded for NAME in PHIVN is still valid at
102 the start of basic block BB. */
105 phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb)
107 gimple vop_stmt = phivn[SSA_NAME_VERSION (name)].vop_stmt;
111 /* The def stmts of all virtual uses need to be post-dominated
113 FOR_EACH_SSA_TREE_OPERAND (vuse, vop_stmt, ui, SSA_OP_VUSE)
116 imm_use_iterator ui2;
119 FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse)
121 /* If BB does not dominate a VDEF, the value is invalid. */
122 if ((!ZERO_SSA_OPERANDS (use_stmt, SSA_OP_VDEF)
123 || gimple_code (use_stmt) == GIMPLE_PHI)
124 && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb))
127 BREAK_FROM_IMM_USE_STMT (ui2);
137 /* Insert a new phi node for the dereference of PHI at basic_block
138 BB with the virtual operands from USE_STMT. */
141 phiprop_insert_phi (basic_block bb, gimple phi, gimple use_stmt,
142 struct phiprop_d *phivn, size_t n)
149 gcc_assert (is_gimple_assign (use_stmt)
150 && gimple_assign_rhs_code (use_stmt) == INDIRECT_REF);
152 /* Build a new PHI node to replace the definition of
153 the indirect reference lhs. */
154 res = gimple_assign_lhs (use_stmt);
155 SSA_NAME_DEF_STMT (res) = new_phi = create_phi_node (res, bb);
157 /* Add PHI arguments for each edge inserting loads of the
158 addressable operands. */
159 FOR_EACH_EDGE (e, ei, bb->preds)
161 tree old_arg, new_var;
164 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
165 while (TREE_CODE (old_arg) == SSA_NAME
166 && (SSA_NAME_VERSION (old_arg) >= n
167 || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE))
169 gimple def_stmt = SSA_NAME_DEF_STMT (old_arg);
170 old_arg = gimple_assign_rhs1 (def_stmt);
173 if (TREE_CODE (old_arg) == SSA_NAME)
174 /* Reuse a formerly created dereference. */
175 new_var = phivn[SSA_NAME_VERSION (old_arg)].value;
178 gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR);
179 old_arg = TREE_OPERAND (old_arg, 0);
180 new_var = create_tmp_var (TREE_TYPE (old_arg), NULL);
181 tmp = gimple_build_assign (new_var, unshare_expr (old_arg));
182 if (TREE_CODE (TREE_TYPE (old_arg)) == COMPLEX_TYPE
183 || TREE_CODE (TREE_TYPE (old_arg)) == VECTOR_TYPE)
184 DECL_GIMPLE_REG_P (new_var) = 1;
185 gcc_assert (is_gimple_reg (new_var));
186 add_referenced_var (new_var);
187 new_var = make_ssa_name (new_var, tmp);
188 gimple_assign_set_lhs (tmp, new_var);
190 gsi_insert_on_edge (e, tmp);
193 mark_symbols_for_renaming (tmp);
196 add_phi_arg (new_phi, new_var, e);
199 update_stmt (new_phi);
204 /* Propagate between the phi node arguments of PHI in BB and phi result
205 users. For now this matches
213 Returns true if a transformation was done and edge insertions
214 need to be committed. Global data PHIVN and N is used to track
215 past transformation results. We need to be especially careful here
216 with aliasing issues as we are moving memory reads. */
219 propagate_with_phi (basic_block bb, gimple phi, struct phiprop_d *phivn,
222 tree ptr = PHI_RESULT (phi);
224 tree res = NULL_TREE;
225 gimple_stmt_iterator gsi;
227 use_operand_p arg_p, use;
231 if (MTAG_P (SSA_NAME_VAR (ptr))
232 || !POINTER_TYPE_P (TREE_TYPE (ptr))
233 || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr))))
236 /* Check if we can "cheaply" dereference all phi arguments. */
237 FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE)
239 tree arg = USE_FROM_PTR (arg_p);
240 /* Walk the ssa chain until we reach a ssa name we already
241 created a value for or we reach a definition of the form
242 ssa_name_n = &var; */
243 while (TREE_CODE (arg) == SSA_NAME
244 && !SSA_NAME_IS_DEFAULT_DEF (arg)
245 && (SSA_NAME_VERSION (arg) >= n
246 || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE))
248 gimple def_stmt = SSA_NAME_DEF_STMT (arg);
249 if (!gimple_assign_single_p (def_stmt))
251 arg = gimple_assign_rhs1 (def_stmt);
253 if ((TREE_CODE (arg) != ADDR_EXPR
254 /* Avoid to have to decay *&a to a[0] later. */
255 || !is_gimple_reg_type (TREE_TYPE (TREE_OPERAND (arg, 0))))
256 && !(TREE_CODE (arg) == SSA_NAME
257 && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE
258 && phivn_valid_p (phivn, arg, bb)))
262 /* Find a dereferencing use. First follow (single use) ssa
263 copy chains for ptr. */
264 while (single_imm_use (ptr, &use, &use_stmt)
265 && gimple_assign_ssa_name_copy_p (use_stmt))
266 ptr = gimple_assign_lhs (use_stmt);
268 /* Replace the first dereference of *ptr if there is one and if we
269 can move the loads to the place of the ptr phi node. */
270 phi_inserted = false;
271 FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr)
276 /* Check whether this is a load of *ptr. */
277 if (!(is_gimple_assign (use_stmt)
278 && TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME
279 && gimple_assign_rhs_code (use_stmt) == INDIRECT_REF
280 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr
281 /* We cannot replace a load that may throw or is volatile. */
282 && !stmt_can_throw_internal (use_stmt)))
285 /* Check if we can move the loads. The def stmts of all virtual uses
286 need to be post-dominated by bb. */
287 FOR_EACH_SSA_TREE_OPERAND (vuse, use_stmt, ui2, SSA_OP_VUSE)
289 gimple def_stmt = SSA_NAME_DEF_STMT (vuse);
290 if (!SSA_NAME_IS_DEFAULT_DEF (vuse)
291 && (gimple_bb (def_stmt) == bb
292 || !dominated_by_p (CDI_DOMINATORS,
293 bb, gimple_bb (def_stmt))))
297 /* Found a proper dereference. Insert a phi node if this
298 is the first load transformation. */
301 res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n);
303 /* Remember the value we created for *ptr. */
304 phivn[SSA_NAME_VERSION (ptr)].value = res;
305 phivn[SSA_NAME_VERSION (ptr)].vop_stmt = use_stmt;
307 /* Remove old stmt. The phi is taken care of by DCE, if we
308 want to delete it here we also have to delete all intermediate
310 gsi = gsi_for_stmt (use_stmt);
311 gsi_remove (&gsi, false);
317 /* Further replacements are easy, just make a copy out of the
319 gimple_assign_set_rhs1 (use_stmt, res);
320 update_stmt (use_stmt);
324 /* Continue searching for a proper dereference. */
330 /* Helper walking the dominator tree starting from BB and processing
331 phi nodes with global data PHIVN and N. */
334 tree_ssa_phiprop_1 (basic_block bb, struct phiprop_d *phivn, size_t n)
336 bool did_something = false;
338 gimple_stmt_iterator gsi;
340 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
341 did_something |= propagate_with_phi (bb, gsi_stmt (gsi), phivn, n);
343 for (son = first_dom_son (CDI_DOMINATORS, bb);
345 son = next_dom_son (CDI_DOMINATORS, son))
346 did_something |= tree_ssa_phiprop_1 (son, phivn, n);
348 return did_something;
351 /* Main entry for phiprop pass. */
354 tree_ssa_phiprop (void)
356 struct phiprop_d *phivn;
358 calculate_dominance_info (CDI_DOMINATORS);
360 phivn = XCNEWVEC (struct phiprop_d, num_ssa_names);
362 if (tree_ssa_phiprop_1 (ENTRY_BLOCK_PTR, phivn, num_ssa_names))
363 gsi_commit_edge_inserts ();
376 struct gimple_opt_pass pass_phiprop =
380 "phiprop", /* name */
381 gate_phiprop, /* gate */
382 tree_ssa_phiprop, /* execute */
385 0, /* static_pass_number */
386 TV_TREE_PHIPROP, /* tv_id */
387 PROP_cfg | PROP_ssa, /* properties_required */
388 0, /* properties_provided */
389 0, /* properties_destroyed */
390 0, /* todo_flags_start */
394 | TODO_verify_ssa /* todo_flags_finish */