1 /* Backward propagation of indirect loads through PHIs.
2 Copyright (C) 2007, 2008, 2009, 2010 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"
28 #include "gimple-pretty-print.h"
29 #include "tree-flow.h"
30 #include "tree-pass.h"
31 #include "langhooks.h"
34 /* This pass propagates indirect loads through the PHI node for its
35 address to make the load source possibly non-addressable and to
36 allow for PHI optimization to trigger.
38 For example the pass changes
40 # addr_1 = PHI <&a, &b>
47 but also handles more complex scenarios like
49 D.2077_2 = &this_1(D)->a1;
52 # b_12 = PHI <&c(2), D.2077_2(3)>
56 # b_15 = PHI <b_12(4), &b(5)>
57 D.2080_5 = &this_1(D)->a0;
60 # b_18 = PHI <D.2080_5(6), &c(7)>
63 # b_21 = PHI <b_15(8), b_18(9)>
66 where the addresses loaded are defined by PHIs itself.
69 std::max(std::min(a0, c), std::min(std::max(a1, c), b))
71 where this pass transforms it to a form later PHI optimization
72 recognizes and transforms it to the simple
74 D.2109_10 = this_1(D)->a1;
76 D.2114_31 = MAX_EXPR <D.2109_10, D.2110_11>;
78 D.2125_17 = MIN_EXPR <D.2115_14, D.2114_31>;
79 D.2119_16 = this_1(D)->a0;
80 D.2124_32 = MIN_EXPR <D.2110_11, D.2119_16>;
81 D.2076_33 = MAX_EXPR <D.2125_17, D.2124_32>;
83 The pass does a dominator walk processing loads using a basic-block
84 local analysis and stores the result for use by transformations on
85 dominated basic-blocks. */
88 /* Structure to keep track of the value of a dereferenced PHI result
89 and the virtual operand used for that dereference. */
97 /* Verify if the value recorded for NAME in PHIVN is still valid at
98 the start of basic block BB. */
101 phivn_valid_p (struct phiprop_d *phivn, tree name, basic_block bb)
103 tree vuse = phivn[SSA_NAME_VERSION (name)].vuse;
105 imm_use_iterator ui2;
108 /* The def stmts of the virtual uses need to be dominated by bb. */
109 gcc_assert (vuse != NULL_TREE);
111 FOR_EACH_IMM_USE_STMT (use_stmt, ui2, vuse)
113 /* If BB does not dominate a VDEF, the value is invalid. */
114 if ((gimple_vdef (use_stmt) != NULL_TREE
115 || gimple_code (use_stmt) == GIMPLE_PHI)
116 && !dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), bb))
119 BREAK_FROM_IMM_USE_STMT (ui2);
126 /* Insert a new phi node for the dereference of PHI at basic_block
127 BB with the virtual operands from USE_STMT. */
130 phiprop_insert_phi (basic_block bb, gimple phi, gimple use_stmt,
131 struct phiprop_d *phivn, size_t n)
138 gcc_assert (is_gimple_assign (use_stmt)
139 && gimple_assign_rhs_code (use_stmt) == MEM_REF);
141 /* Build a new PHI node to replace the definition of
142 the indirect reference lhs. */
143 res = gimple_assign_lhs (use_stmt);
144 SSA_NAME_DEF_STMT (res) = new_phi = create_phi_node (res, bb);
146 if (dump_file && (dump_flags & TDF_DETAILS))
148 fprintf (dump_file, "Inserting PHI for result of load ");
149 print_gimple_stmt (dump_file, use_stmt, 0, 0);
152 /* Add PHI arguments for each edge inserting loads of the
153 addressable operands. */
154 FOR_EACH_EDGE (e, ei, bb->preds)
156 tree old_arg, new_var;
158 source_location locus;
160 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
161 locus = gimple_phi_arg_location_from_edge (phi, e);
162 while (TREE_CODE (old_arg) == SSA_NAME
163 && (SSA_NAME_VERSION (old_arg) >= n
164 || phivn[SSA_NAME_VERSION (old_arg)].value == NULL_TREE))
166 gimple def_stmt = SSA_NAME_DEF_STMT (old_arg);
167 old_arg = gimple_assign_rhs1 (def_stmt);
168 locus = gimple_location (def_stmt);
171 if (TREE_CODE (old_arg) == SSA_NAME)
173 if (dump_file && (dump_flags & TDF_DETAILS))
175 fprintf (dump_file, " for edge defining ");
176 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
177 fprintf (dump_file, " reusing PHI result ");
178 print_generic_expr (dump_file,
179 phivn[SSA_NAME_VERSION (old_arg)].value, 0);
180 fprintf (dump_file, "\n");
182 /* Reuse a formerly created dereference. */
183 new_var = phivn[SSA_NAME_VERSION (old_arg)].value;
187 tree rhs = gimple_assign_rhs1 (use_stmt);
188 gcc_assert (TREE_CODE (old_arg) == ADDR_EXPR);
189 new_var = create_tmp_reg (TREE_TYPE (rhs), NULL);
190 if (!is_gimple_min_invariant (old_arg))
191 old_arg = PHI_ARG_DEF_FROM_EDGE (phi, e);
193 old_arg = unshare_expr (old_arg);
194 tmp = gimple_build_assign (new_var,
195 fold_build2 (MEM_REF, TREE_TYPE (rhs),
197 TREE_OPERAND (rhs, 1)));
198 gcc_assert (is_gimple_reg (new_var));
199 new_var = make_ssa_name (new_var, tmp);
200 gimple_assign_set_lhs (tmp, new_var);
201 gimple_set_location (tmp, locus);
203 gsi_insert_on_edge (e, tmp);
206 if (dump_file && (dump_flags & TDF_DETAILS))
208 fprintf (dump_file, " for edge defining ");
209 print_generic_expr (dump_file, PHI_ARG_DEF_FROM_EDGE (phi, e), 0);
210 fprintf (dump_file, " inserting load ");
211 print_gimple_stmt (dump_file, tmp, 0, 0);
215 add_phi_arg (new_phi, new_var, e, locus);
218 update_stmt (new_phi);
220 if (dump_file && (dump_flags & TDF_DETAILS))
221 print_gimple_stmt (dump_file, new_phi, 0, 0);
226 /* Propagate between the phi node arguments of PHI in BB and phi result
227 users. For now this matches
235 Returns true if a transformation was done and edge insertions
236 need to be committed. Global data PHIVN and N is used to track
237 past transformation results. We need to be especially careful here
238 with aliasing issues as we are moving memory reads. */
241 propagate_with_phi (basic_block bb, gimple phi, struct phiprop_d *phivn,
244 tree ptr = PHI_RESULT (phi);
246 tree res = NULL_TREE;
247 gimple_stmt_iterator gsi;
249 use_operand_p arg_p, use;
252 tree type = NULL_TREE;
253 bool one_invariant = false;
255 if (!POINTER_TYPE_P (TREE_TYPE (ptr))
256 || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr))))
259 /* Check if we can "cheaply" dereference all phi arguments. */
260 FOR_EACH_PHI_ARG (arg_p, phi, i, SSA_OP_USE)
262 tree arg = USE_FROM_PTR (arg_p);
263 /* Walk the ssa chain until we reach a ssa name we already
264 created a value for or we reach a definition of the form
265 ssa_name_n = &var; */
266 while (TREE_CODE (arg) == SSA_NAME
267 && !SSA_NAME_IS_DEFAULT_DEF (arg)
268 && (SSA_NAME_VERSION (arg) >= n
269 || phivn[SSA_NAME_VERSION (arg)].value == NULL_TREE))
271 gimple def_stmt = SSA_NAME_DEF_STMT (arg);
272 if (!gimple_assign_single_p (def_stmt))
274 arg = gimple_assign_rhs1 (def_stmt);
276 if (TREE_CODE (arg) != ADDR_EXPR
277 && !(TREE_CODE (arg) == SSA_NAME
278 && SSA_NAME_VERSION (arg) < n
279 && phivn[SSA_NAME_VERSION (arg)].value != NULL_TREE
281 || types_compatible_p
282 (type, TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value)))
283 && phivn_valid_p (phivn, arg, bb)))
286 && TREE_CODE (arg) == SSA_NAME)
287 type = TREE_TYPE (phivn[SSA_NAME_VERSION (arg)].value);
288 if (TREE_CODE (arg) == ADDR_EXPR
289 && is_gimple_min_invariant (arg))
290 one_invariant = true;
293 /* If we neither have an address of a decl nor can reuse a previously
294 inserted load, do not hoist anything. */
299 /* Find a dereferencing use. First follow (single use) ssa
300 copy chains for ptr. */
301 while (single_imm_use (ptr, &use, &use_stmt)
302 && gimple_assign_ssa_name_copy_p (use_stmt))
303 ptr = gimple_assign_lhs (use_stmt);
305 /* Replace the first dereference of *ptr if there is one and if we
306 can move the loads to the place of the ptr phi node. */
307 phi_inserted = false;
308 FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr)
313 /* Check whether this is a load of *ptr. */
314 if (!(is_gimple_assign (use_stmt)
315 && TREE_CODE (gimple_assign_lhs (use_stmt)) == SSA_NAME
316 && gimple_assign_rhs_code (use_stmt) == MEM_REF
317 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == ptr
318 && integer_zerop (TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 1))
320 || types_compatible_p
321 (TREE_TYPE (gimple_assign_lhs (use_stmt)), type))
322 /* We cannot replace a load that may throw or is volatile. */
323 && !stmt_can_throw_internal (use_stmt)))
326 /* Check if we can move the loads. The def stmt of the virtual use
327 needs to be in a different basic block dominating bb. */
328 vuse = gimple_vuse (use_stmt);
329 def_stmt = SSA_NAME_DEF_STMT (vuse);
330 if (!SSA_NAME_IS_DEFAULT_DEF (vuse)
331 && (gimple_bb (def_stmt) == bb
332 || !dominated_by_p (CDI_DOMINATORS,
333 bb, gimple_bb (def_stmt))))
336 /* Found a proper dereference. Insert a phi node if this
337 is the first load transformation. */
340 res = phiprop_insert_phi (bb, phi, use_stmt, phivn, n);
341 type = TREE_TYPE (res);
343 /* Remember the value we created for *ptr. */
344 phivn[SSA_NAME_VERSION (ptr)].value = res;
345 phivn[SSA_NAME_VERSION (ptr)].vuse = vuse;
347 /* Remove old stmt. The phi is taken care of by DCE, if we
348 want to delete it here we also have to delete all intermediate
350 gsi = gsi_for_stmt (use_stmt);
351 gsi_remove (&gsi, true);
357 /* Further replacements are easy, just make a copy out of the
359 gimple_assign_set_rhs1 (use_stmt, res);
360 update_stmt (use_stmt);
364 /* Continue searching for a proper dereference. */
370 /* Main entry for phiprop pass. */
373 tree_ssa_phiprop (void)
375 VEC(basic_block, heap) *bbs;
376 struct phiprop_d *phivn;
377 bool did_something = false;
379 gimple_stmt_iterator gsi;
383 calculate_dominance_info (CDI_DOMINATORS);
386 phivn = XCNEWVEC (struct phiprop_d, n);
388 /* Walk the dominator tree in preorder. */
389 bbs = get_all_dominated_blocks (CDI_DOMINATORS,
390 single_succ (ENTRY_BLOCK_PTR));
391 FOR_EACH_VEC_ELT (basic_block, bbs, i, bb)
392 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
393 did_something |= propagate_with_phi (bb, gsi_stmt (gsi), phivn, n);
396 gsi_commit_edge_inserts ();
398 VEC_free (basic_block, heap, bbs);
407 return flag_tree_phiprop;
410 struct gimple_opt_pass pass_phiprop =
414 "phiprop", /* name */
415 gate_phiprop, /* gate */
416 tree_ssa_phiprop, /* execute */
419 0, /* static_pass_number */
420 TV_TREE_PHIPROP, /* tv_id */
421 PROP_cfg | PROP_ssa, /* properties_required */
422 0, /* properties_provided */
423 0, /* properties_destroyed */
424 0, /* todo_flags_start */
427 | TODO_verify_ssa /* todo_flags_finish */