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 virtual operand 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 tree vuse
= phivn
[SSA_NAME_VERSION (name
)].vuse
;
109 imm_use_iterator ui2
;
112 /* The def stmts of the virtual uses need to be dominated by bb. */
113 gcc_assert (vuse
!= NULL_TREE
);
115 FOR_EACH_IMM_USE_STMT (use_stmt
, ui2
, vuse
)
117 /* If BB does not dominate a VDEF, the value is invalid. */
118 if ((gimple_vdef (use_stmt
) != NULL_TREE
119 || gimple_code (use_stmt
) == GIMPLE_PHI
)
120 && !dominated_by_p (CDI_DOMINATORS
, gimple_bb (use_stmt
), bb
))
123 BREAK_FROM_IMM_USE_STMT (ui2
);
130 /* Insert a new phi node for the dereference of PHI at basic_block
131 BB with the virtual operands from USE_STMT. */
134 phiprop_insert_phi (basic_block bb
, gimple phi
, gimple use_stmt
,
135 struct phiprop_d
*phivn
, size_t n
)
142 gcc_assert (is_gimple_assign (use_stmt
)
143 && gimple_assign_rhs_code (use_stmt
) == INDIRECT_REF
);
145 /* Build a new PHI node to replace the definition of
146 the indirect reference lhs. */
147 res
= gimple_assign_lhs (use_stmt
);
148 SSA_NAME_DEF_STMT (res
) = new_phi
= create_phi_node (res
, bb
);
150 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
152 fprintf (dump_file
, "Inserting PHI for result of load ");
153 print_gimple_stmt (dump_file
, use_stmt
, 0, 0);
156 /* Add PHI arguments for each edge inserting loads of the
157 addressable operands. */
158 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
160 tree old_arg
, new_var
;
163 old_arg
= PHI_ARG_DEF_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
);
172 if (TREE_CODE (old_arg
) == SSA_NAME
)
174 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
176 fprintf (dump_file
, " for edge defining ");
177 print_generic_expr (dump_file
, PHI_ARG_DEF_FROM_EDGE (phi
, e
), 0);
178 fprintf (dump_file
, " reusing PHI result ");
179 print_generic_expr (dump_file
,
180 phivn
[SSA_NAME_VERSION (old_arg
)].value
, 0);
181 fprintf (dump_file
, "\n");
183 /* Reuse a formerly created dereference. */
184 new_var
= phivn
[SSA_NAME_VERSION (old_arg
)].value
;
188 gcc_assert (TREE_CODE (old_arg
) == ADDR_EXPR
);
189 old_arg
= TREE_OPERAND (old_arg
, 0);
190 new_var
= create_tmp_var (TREE_TYPE (old_arg
), NULL
);
191 tmp
= gimple_build_assign (new_var
, unshare_expr (old_arg
));
192 if (TREE_CODE (TREE_TYPE (old_arg
)) == COMPLEX_TYPE
193 || TREE_CODE (TREE_TYPE (old_arg
)) == VECTOR_TYPE
)
194 DECL_GIMPLE_REG_P (new_var
) = 1;
195 gcc_assert (is_gimple_reg (new_var
));
196 add_referenced_var (new_var
);
197 new_var
= make_ssa_name (new_var
, tmp
);
198 gimple_assign_set_lhs (tmp
, new_var
);
200 gsi_insert_on_edge (e
, tmp
);
203 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
205 fprintf (dump_file
, " for edge defining ");
206 print_generic_expr (dump_file
, PHI_ARG_DEF_FROM_EDGE (phi
, e
), 0);
207 fprintf (dump_file
, " inserting load ");
208 print_gimple_stmt (dump_file
, tmp
, 0, 0);
212 add_phi_arg (new_phi
, new_var
, e
);
215 update_stmt (new_phi
);
217 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
218 print_gimple_stmt (dump_file
, new_phi
, 0, 0);
223 /* Propagate between the phi node arguments of PHI in BB and phi result
224 users. For now this matches
232 Returns true if a transformation was done and edge insertions
233 need to be committed. Global data PHIVN and N is used to track
234 past transformation results. We need to be especially careful here
235 with aliasing issues as we are moving memory reads. */
238 propagate_with_phi (basic_block bb
, gimple phi
, struct phiprop_d
*phivn
,
241 tree ptr
= PHI_RESULT (phi
);
243 tree res
= NULL_TREE
;
244 gimple_stmt_iterator gsi
;
246 use_operand_p arg_p
, use
;
250 if (!POINTER_TYPE_P (TREE_TYPE (ptr
))
251 || !is_gimple_reg_type (TREE_TYPE (TREE_TYPE (ptr
))))
254 /* Check if we can "cheaply" dereference all phi arguments. */
255 FOR_EACH_PHI_ARG (arg_p
, phi
, i
, SSA_OP_USE
)
257 tree arg
= USE_FROM_PTR (arg_p
);
258 /* Walk the ssa chain until we reach a ssa name we already
259 created a value for or we reach a definition of the form
260 ssa_name_n = &var; */
261 while (TREE_CODE (arg
) == SSA_NAME
262 && !SSA_NAME_IS_DEFAULT_DEF (arg
)
263 && (SSA_NAME_VERSION (arg
) >= n
264 || phivn
[SSA_NAME_VERSION (arg
)].value
== NULL_TREE
))
266 gimple def_stmt
= SSA_NAME_DEF_STMT (arg
);
267 if (!gimple_assign_single_p (def_stmt
))
269 arg
= gimple_assign_rhs1 (def_stmt
);
271 if ((TREE_CODE (arg
) != ADDR_EXPR
272 /* Avoid to have to decay *&a to a[0] later. */
273 || !is_gimple_reg_type (TREE_TYPE (TREE_OPERAND (arg
, 0))))
274 && !(TREE_CODE (arg
) == SSA_NAME
275 && SSA_NAME_VERSION (arg
) < n
276 && phivn
[SSA_NAME_VERSION (arg
)].value
!= NULL_TREE
277 && phivn_valid_p (phivn
, arg
, bb
)))
281 /* Find a dereferencing use. First follow (single use) ssa
282 copy chains for ptr. */
283 while (single_imm_use (ptr
, &use
, &use_stmt
)
284 && gimple_assign_ssa_name_copy_p (use_stmt
))
285 ptr
= gimple_assign_lhs (use_stmt
);
287 /* Replace the first dereference of *ptr if there is one and if we
288 can move the loads to the place of the ptr phi node. */
289 phi_inserted
= false;
290 FOR_EACH_IMM_USE_STMT (use_stmt
, ui
, ptr
)
295 /* Check whether this is a load of *ptr. */
296 if (!(is_gimple_assign (use_stmt
)
297 && TREE_CODE (gimple_assign_lhs (use_stmt
)) == SSA_NAME
298 && gimple_assign_rhs_code (use_stmt
) == INDIRECT_REF
299 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt
), 0) == ptr
300 /* We cannot replace a load that may throw or is volatile. */
301 && !stmt_can_throw_internal (use_stmt
)))
304 /* Check if we can move the loads. The def stmt of the virtual use
305 needs to be in a different basic block dominating bb. */
306 vuse
= gimple_vuse (use_stmt
);
307 def_stmt
= SSA_NAME_DEF_STMT (vuse
);
308 if (!SSA_NAME_IS_DEFAULT_DEF (vuse
)
309 && (gimple_bb (def_stmt
) == bb
310 || !dominated_by_p (CDI_DOMINATORS
,
311 bb
, gimple_bb (def_stmt
))))
314 /* Found a proper dereference. Insert a phi node if this
315 is the first load transformation. */
318 res
= phiprop_insert_phi (bb
, phi
, use_stmt
, phivn
, n
);
320 /* Remember the value we created for *ptr. */
321 phivn
[SSA_NAME_VERSION (ptr
)].value
= res
;
322 phivn
[SSA_NAME_VERSION (ptr
)].vuse
= vuse
;
324 /* Remove old stmt. The phi is taken care of by DCE, if we
325 want to delete it here we also have to delete all intermediate
327 gsi
= gsi_for_stmt (use_stmt
);
328 gsi_remove (&gsi
, false);
334 /* Further replacements are easy, just make a copy out of the
336 gimple_assign_set_rhs1 (use_stmt
, res
);
337 update_stmt (use_stmt
);
341 /* Continue searching for a proper dereference. */
347 /* Main entry for phiprop pass. */
350 tree_ssa_phiprop (void)
352 VEC(basic_block
, heap
) *bbs
;
353 struct phiprop_d
*phivn
;
354 bool did_something
= false;
356 gimple_stmt_iterator gsi
;
360 calculate_dominance_info (CDI_DOMINATORS
);
363 phivn
= XCNEWVEC (struct phiprop_d
, n
);
365 /* Walk the dominator tree in preorder. */
366 bbs
= get_all_dominated_blocks (CDI_DOMINATORS
,
367 single_succ (ENTRY_BLOCK_PTR
));
368 for (i
= 0; VEC_iterate (basic_block
, bbs
, i
, bb
); ++i
)
369 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
370 did_something
|= propagate_with_phi (bb
, gsi_stmt (gsi
), phivn
, n
);
373 gsi_commit_edge_inserts ();
375 VEC_free (basic_block
, heap
, bbs
);
387 struct gimple_opt_pass pass_phiprop
=
391 "phiprop", /* name */
392 gate_phiprop
, /* gate */
393 tree_ssa_phiprop
, /* execute */
396 0, /* static_pass_number */
397 TV_TREE_PHIPROP
, /* tv_id */
398 PROP_cfg
| PROP_ssa
, /* properties_required */
399 0, /* properties_provided */
400 0, /* properties_destroyed */
401 0, /* todo_flags_start */
405 | TODO_verify_ssa
/* todo_flags_finish */