1 /* Generic SSA value propagation engine.
2 Copyright (C) 2004, 2005 Free Software Foundation, Inc.
3 Contributed by Diego Novillo <dnovillo@redhat.com>
5 This file is part of GCC.
7 GCC is free software; you can redistribute it and/or modify it
8 under the terms of the GNU General Public License as published by the
9 Free Software Foundation; either version 2, or (at your option) any
12 GCC is distributed in the hope that it will be useful, but WITHOUT
13 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
17 You should have received a copy of the GNU General Public License
18 along with GCC; see the file COPYING. If not, write to the Free
19 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
24 #include "coretypes.h"
31 #include "basic-block.h"
35 #include "diagnostic.h"
37 #include "tree-dump.h"
38 #include "tree-flow.h"
39 #include "tree-pass.h"
40 #include "tree-ssa-propagate.h"
41 #include "langhooks.h"
45 /* This file implements a generic value propagation engine based on
46 the same propagation used by the SSA-CCP algorithm [1].
48 Propagation is performed by simulating the execution of every
49 statement that produces the value being propagated. Simulation
52 1- Initially, all edges of the CFG are marked not executable and
53 the CFG worklist is seeded with all the statements in the entry
54 basic block (block 0).
56 2- Every statement S is simulated with a call to the call-back
57 function SSA_PROP_VISIT_STMT. This evaluation may produce 3
60 SSA_PROP_NOT_INTERESTING: Statement S produces nothing of
61 interest and does not affect any of the work lists.
63 SSA_PROP_VARYING: The value produced by S cannot be determined
64 at compile time. Further simulation of S is not required.
65 If S is a conditional jump, all the outgoing edges for the
66 block are considered executable and added to the work
69 SSA_PROP_INTERESTING: S produces a value that can be computed
70 at compile time. Its result can be propagated into the
71 statements that feed from S. Furthermore, if S is a
72 conditional jump, only the edge known to be taken is added
73 to the work list. Edges that are known not to execute are
76 3- PHI nodes are simulated with a call to SSA_PROP_VISIT_PHI. The
77 return value from SSA_PROP_VISIT_PHI has the same semantics as
80 4- Three work lists are kept. Statements are only added to these
81 lists if they produce one of SSA_PROP_INTERESTING or
84 CFG_BLOCKS contains the list of blocks to be simulated.
85 Blocks are added to this list if their incoming edges are
88 VARYING_SSA_EDGES contains the list of statements that feed
89 from statements that produce an SSA_PROP_VARYING result.
90 These are simulated first to speed up processing.
92 INTERESTING_SSA_EDGES contains the list of statements that
93 feed from statements that produce an SSA_PROP_INTERESTING
96 5- Simulation terminates when all three work lists are drained.
98 Before calling ssa_propagate, it is important to clear
99 DONT_SIMULATE_AGAIN for all the statements in the program that
100 should be simulated. This initialization allows an implementation
101 to specify which statements should never be simulated.
103 It is also important to compute def-use information before calling
108 [1] Constant propagation with conditional branches,
109 Wegman and Zadeck, ACM TOPLAS 13(2):181-210.
111 [2] Building an Optimizing Compiler,
112 Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9.
114 [3] Advanced Compiler Design and Implementation,
115 Steven Muchnick, Morgan Kaufmann, 1997, Section 12.6 */
117 /* Function pointers used to parameterize the propagation engine. */
118 static ssa_prop_visit_stmt_fn ssa_prop_visit_stmt
;
119 static ssa_prop_visit_phi_fn ssa_prop_visit_phi
;
121 /* Use the TREE_DEPRECATED bitflag to mark statements that have been
122 added to one of the SSA edges worklists. This flag is used to
123 avoid visiting statements unnecessarily when draining an SSA edge
124 worklist. If while simulating a basic block, we find a statement with
125 STMT_IN_SSA_EDGE_WORKLIST set, we clear it to prevent SSA edge
126 processing from visiting it again. */
127 #define STMT_IN_SSA_EDGE_WORKLIST(T) TREE_DEPRECATED (T)
129 /* A bitmap to keep track of executable blocks in the CFG. */
130 static sbitmap executable_blocks
;
132 /* Array of control flow edges on the worklist. */
133 static GTY(()) varray_type cfg_blocks
= NULL
;
135 static unsigned int cfg_blocks_num
= 0;
136 static int cfg_blocks_tail
;
137 static int cfg_blocks_head
;
139 static sbitmap bb_in_list
;
141 /* Worklist of SSA edges which will need reexamination as their
142 definition has changed. SSA edges are def-use edges in the SSA
143 web. For each D-U edge, we store the target statement or PHI node
145 static GTY(()) VEC(tree
,gc
) *interesting_ssa_edges
;
147 /* Identical to INTERESTING_SSA_EDGES. For performance reasons, the
148 list of SSA edges is split into two. One contains all SSA edges
149 who need to be reexamined because their lattice value changed to
150 varying (this worklist), and the other contains all other SSA edges
151 to be reexamined (INTERESTING_SSA_EDGES).
153 Since most values in the program are VARYING, the ideal situation
154 is to move them to that lattice value as quickly as possible.
155 Thus, it doesn't make sense to process any other type of lattice
156 value until all VARYING values are propagated fully, which is one
157 thing using the VARYING worklist achieves. In addition, if we
158 don't use a separate worklist for VARYING edges, we end up with
159 situations where lattice values move from
160 UNDEFINED->INTERESTING->VARYING instead of UNDEFINED->VARYING. */
161 static GTY(()) VEC(tree
,gc
) *varying_ssa_edges
;
164 /* Return true if the block worklist empty. */
167 cfg_blocks_empty_p (void)
169 return (cfg_blocks_num
== 0);
173 /* Add a basic block to the worklist. The block must not be already
174 in the worklist, and it must not be the ENTRY or EXIT block. */
177 cfg_blocks_add (basic_block bb
)
179 gcc_assert (bb
!= ENTRY_BLOCK_PTR
&& bb
!= EXIT_BLOCK_PTR
);
180 gcc_assert (!TEST_BIT (bb_in_list
, bb
->index
));
182 if (cfg_blocks_empty_p ())
184 cfg_blocks_tail
= cfg_blocks_head
= 0;
190 if (cfg_blocks_num
> VARRAY_SIZE (cfg_blocks
))
192 /* We have to grow the array now. Adjust to queue to occupy the
193 full space of the original array. */
194 cfg_blocks_tail
= VARRAY_SIZE (cfg_blocks
);
196 VARRAY_GROW (cfg_blocks
, 2 * VARRAY_SIZE (cfg_blocks
));
199 cfg_blocks_tail
= (cfg_blocks_tail
+ 1) % VARRAY_SIZE (cfg_blocks
);
202 VARRAY_BB (cfg_blocks
, cfg_blocks_tail
) = bb
;
203 SET_BIT (bb_in_list
, bb
->index
);
207 /* Remove a block from the worklist. */
210 cfg_blocks_get (void)
214 bb
= VARRAY_BB (cfg_blocks
, cfg_blocks_head
);
216 gcc_assert (!cfg_blocks_empty_p ());
219 cfg_blocks_head
= (cfg_blocks_head
+ 1) % VARRAY_SIZE (cfg_blocks
);
221 RESET_BIT (bb_in_list
, bb
->index
);
227 /* We have just defined a new value for VAR. If IS_VARYING is true,
228 add all immediate uses of VAR to VARYING_SSA_EDGES, otherwise add
229 them to INTERESTING_SSA_EDGES. */
232 add_ssa_edge (tree var
, bool is_varying
)
234 imm_use_iterator iter
;
237 FOR_EACH_IMM_USE_FAST (use_p
, iter
, var
)
239 tree use_stmt
= USE_STMT (use_p
);
241 if (!DONT_SIMULATE_AGAIN (use_stmt
)
242 && !STMT_IN_SSA_EDGE_WORKLIST (use_stmt
))
244 STMT_IN_SSA_EDGE_WORKLIST (use_stmt
) = 1;
246 VEC_safe_push (tree
, gc
, varying_ssa_edges
, use_stmt
);
248 VEC_safe_push (tree
, gc
, interesting_ssa_edges
, use_stmt
);
254 /* Add edge E to the control flow worklist. */
257 add_control_edge (edge e
)
259 basic_block bb
= e
->dest
;
260 if (bb
== EXIT_BLOCK_PTR
)
263 /* If the edge had already been executed, skip it. */
264 if (e
->flags
& EDGE_EXECUTABLE
)
267 e
->flags
|= EDGE_EXECUTABLE
;
269 /* If the block is already in the list, we're done. */
270 if (TEST_BIT (bb_in_list
, bb
->index
))
275 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
276 fprintf (dump_file
, "Adding Destination of edge (%d -> %d) to worklist\n\n",
277 e
->src
->index
, e
->dest
->index
);
281 /* Simulate the execution of STMT and update the work lists accordingly. */
284 simulate_stmt (tree stmt
)
286 enum ssa_prop_result val
= SSA_PROP_NOT_INTERESTING
;
287 edge taken_edge
= NULL
;
288 tree output_name
= NULL_TREE
;
290 /* Don't bother visiting statements that are already
291 considered varying by the propagator. */
292 if (DONT_SIMULATE_AGAIN (stmt
))
295 if (TREE_CODE (stmt
) == PHI_NODE
)
297 val
= ssa_prop_visit_phi (stmt
);
298 output_name
= PHI_RESULT (stmt
);
301 val
= ssa_prop_visit_stmt (stmt
, &taken_edge
, &output_name
);
303 if (val
== SSA_PROP_VARYING
)
305 DONT_SIMULATE_AGAIN (stmt
) = 1;
307 /* If the statement produced a new varying value, add the SSA
308 edges coming out of OUTPUT_NAME. */
310 add_ssa_edge (output_name
, true);
312 /* If STMT transfers control out of its basic block, add
313 all outgoing edges to the work list. */
314 if (stmt_ends_bb_p (stmt
))
318 basic_block bb
= bb_for_stmt (stmt
);
319 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
320 add_control_edge (e
);
323 else if (val
== SSA_PROP_INTERESTING
)
325 /* If the statement produced new value, add the SSA edges coming
326 out of OUTPUT_NAME. */
328 add_ssa_edge (output_name
, false);
330 /* If we know which edge is going to be taken out of this block,
331 add it to the CFG work list. */
333 add_control_edge (taken_edge
);
337 /* Process an SSA edge worklist. WORKLIST is the SSA edge worklist to
338 drain. This pops statements off the given WORKLIST and processes
339 them until there are no more statements on WORKLIST.
340 We take a pointer to WORKLIST because it may be reallocated when an
341 SSA edge is added to it in simulate_stmt. */
344 process_ssa_edge_worklist (VEC(tree
,gc
) **worklist
)
346 /* Drain the entire worklist. */
347 while (VEC_length (tree
, *worklist
) > 0)
351 /* Pull the statement to simulate off the worklist. */
352 tree stmt
= VEC_pop (tree
, *worklist
);
354 /* If this statement was already visited by simulate_block, then
355 we don't need to visit it again here. */
356 if (!STMT_IN_SSA_EDGE_WORKLIST (stmt
))
359 /* STMT is no longer in a worklist. */
360 STMT_IN_SSA_EDGE_WORKLIST (stmt
) = 0;
362 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
364 fprintf (dump_file
, "\nSimulating statement (from ssa_edges): ");
365 print_generic_stmt (dump_file
, stmt
, dump_flags
);
368 bb
= bb_for_stmt (stmt
);
370 /* PHI nodes are always visited, regardless of whether or not
371 the destination block is executable. Otherwise, visit the
372 statement only if its block is marked executable. */
373 if (TREE_CODE (stmt
) == PHI_NODE
374 || TEST_BIT (executable_blocks
, bb
->index
))
375 simulate_stmt (stmt
);
380 /* Simulate the execution of BLOCK. Evaluate the statement associated
381 with each variable reference inside the block. */
384 simulate_block (basic_block block
)
388 /* There is nothing to do for the exit block. */
389 if (block
== EXIT_BLOCK_PTR
)
392 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
393 fprintf (dump_file
, "\nSimulating block %d\n", block
->index
);
395 /* Always simulate PHI nodes, even if we have simulated this block
397 for (phi
= phi_nodes (block
); phi
; phi
= PHI_CHAIN (phi
))
400 /* If this is the first time we've simulated this block, then we
401 must simulate each of its statements. */
402 if (!TEST_BIT (executable_blocks
, block
->index
))
404 block_stmt_iterator j
;
405 unsigned int normal_edge_count
;
409 /* Note that we have simulated this block. */
410 SET_BIT (executable_blocks
, block
->index
);
412 for (j
= bsi_start (block
); !bsi_end_p (j
); bsi_next (&j
))
414 tree stmt
= bsi_stmt (j
);
416 /* If this statement is already in the worklist then
417 "cancel" it. The reevaluation implied by the worklist
418 entry will produce the same value we generate here and
419 thus reevaluating it again from the worklist is
421 if (STMT_IN_SSA_EDGE_WORKLIST (stmt
))
422 STMT_IN_SSA_EDGE_WORKLIST (stmt
) = 0;
424 simulate_stmt (stmt
);
427 /* We can not predict when abnormal edges will be executed, so
428 once a block is considered executable, we consider any
429 outgoing abnormal edges as executable.
431 At the same time, if this block has only one successor that is
432 reached by non-abnormal edges, then add that successor to the
434 normal_edge_count
= 0;
436 FOR_EACH_EDGE (e
, ei
, block
->succs
)
438 if (e
->flags
& EDGE_ABNORMAL
)
439 add_control_edge (e
);
447 if (normal_edge_count
== 1)
448 add_control_edge (normal_edge
);
453 /* Initialize local data structures and work lists. */
463 /* Worklists of SSA edges. */
464 interesting_ssa_edges
= VEC_alloc (tree
, gc
, 20);
465 varying_ssa_edges
= VEC_alloc (tree
, gc
, 20);
467 executable_blocks
= sbitmap_alloc (last_basic_block
);
468 sbitmap_zero (executable_blocks
);
470 bb_in_list
= sbitmap_alloc (last_basic_block
);
471 sbitmap_zero (bb_in_list
);
473 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
474 dump_immediate_uses (dump_file
);
476 VARRAY_BB_INIT (cfg_blocks
, 20, "cfg_blocks");
478 /* Initialize the values for every SSA_NAME. */
479 for (i
= 1; i
< num_ssa_names
; i
++)
481 SSA_NAME_VALUE (ssa_name (i
)) = NULL_TREE
;
483 /* Initially assume that every edge in the CFG is not executable.
484 (including the edges coming out of ENTRY_BLOCK_PTR). */
487 block_stmt_iterator si
;
489 for (si
= bsi_start (bb
); !bsi_end_p (si
); bsi_next (&si
))
490 STMT_IN_SSA_EDGE_WORKLIST (bsi_stmt (si
)) = 0;
492 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
493 e
->flags
&= ~EDGE_EXECUTABLE
;
496 /* Seed the algorithm by adding the successors of the entry block to the
498 FOR_EACH_EDGE (e
, ei
, ENTRY_BLOCK_PTR
->succs
)
499 add_control_edge (e
);
503 /* Free allocated storage. */
508 VEC_free (tree
, gc
, interesting_ssa_edges
);
509 VEC_free (tree
, gc
, varying_ssa_edges
);
511 sbitmap_free (bb_in_list
);
512 sbitmap_free (executable_blocks
);
516 /* Get the main expression from statement STMT. */
521 enum tree_code code
= TREE_CODE (stmt
);
526 stmt
= TREE_OPERAND (stmt
, 0);
527 if (!stmt
|| TREE_CODE (stmt
) != MODIFY_EXPR
)
532 stmt
= TREE_OPERAND (stmt
, 1);
533 if (TREE_CODE (stmt
) == WITH_SIZE_EXPR
)
534 return TREE_OPERAND (stmt
, 0);
539 return COND_EXPR_COND (stmt
);
541 return SWITCH_COND (stmt
);
543 return GOTO_DESTINATION (stmt
);
545 return LABEL_EXPR_LABEL (stmt
);
553 /* Set the main expression of *STMT_P to EXPR. If EXPR is not a valid
554 GIMPLE expression no changes are done and the function returns
558 set_rhs (tree
*stmt_p
, tree expr
)
560 tree stmt
= *stmt_p
, op
;
561 enum tree_code code
= TREE_CODE (expr
);
566 /* Verify the constant folded result is valid gimple. */
567 if (TREE_CODE_CLASS (code
) == tcc_binary
)
569 if (!is_gimple_val (TREE_OPERAND (expr
, 0))
570 || !is_gimple_val (TREE_OPERAND (expr
, 1)))
573 else if (TREE_CODE_CLASS (code
) == tcc_unary
)
575 if (!is_gimple_val (TREE_OPERAND (expr
, 0)))
578 else if (code
== ADDR_EXPR
)
580 if (TREE_CODE (TREE_OPERAND (expr
, 0)) == ARRAY_REF
581 && !is_gimple_val (TREE_OPERAND (TREE_OPERAND (expr
, 0), 1)))
584 else if (code
== COMPOUND_EXPR
)
587 switch (TREE_CODE (stmt
))
590 op
= TREE_OPERAND (stmt
, 0);
591 if (TREE_CODE (op
) != MODIFY_EXPR
)
593 TREE_OPERAND (stmt
, 0) = expr
;
600 op
= TREE_OPERAND (stmt
, 1);
601 if (TREE_CODE (op
) == WITH_SIZE_EXPR
)
603 TREE_OPERAND (stmt
, 1) = expr
;
607 COND_EXPR_COND (stmt
) = expr
;
610 SWITCH_COND (stmt
) = expr
;
613 GOTO_DESTINATION (stmt
) = expr
;
616 LABEL_EXPR_LABEL (stmt
) = expr
;
620 /* Replace the whole statement with EXPR. If EXPR has no side
621 effects, then replace *STMT_P with an empty statement. */
622 ann
= stmt_ann (stmt
);
623 *stmt_p
= TREE_SIDE_EFFECTS (expr
) ? expr
: build_empty_stmt ();
624 (*stmt_p
)->common
.ann
= (tree_ann_t
) ann
;
626 if (TREE_SIDE_EFFECTS (expr
))
628 /* Fix all the SSA_NAMEs created by *STMT_P to point to its new
630 FOR_EACH_SSA_TREE_OPERAND (var
, stmt
, iter
, SSA_OP_ALL_DEFS
)
632 if (TREE_CODE (var
) == SSA_NAME
)
633 SSA_NAME_DEF_STMT (var
) = *stmt_p
;
643 /* Entry point to the propagation engine.
645 VISIT_STMT is called for every statement visited.
646 VISIT_PHI is called for every PHI node visited. */
649 ssa_propagate (ssa_prop_visit_stmt_fn visit_stmt
,
650 ssa_prop_visit_phi_fn visit_phi
)
652 ssa_prop_visit_stmt
= visit_stmt
;
653 ssa_prop_visit_phi
= visit_phi
;
657 /* Iterate until the worklists are empty. */
658 while (!cfg_blocks_empty_p ()
659 || VEC_length (tree
, interesting_ssa_edges
) > 0
660 || VEC_length (tree
, varying_ssa_edges
) > 0)
662 if (!cfg_blocks_empty_p ())
664 /* Pull the next block to simulate off the worklist. */
665 basic_block dest_block
= cfg_blocks_get ();
666 simulate_block (dest_block
);
669 /* In order to move things to varying as quickly as
670 possible,process the VARYING_SSA_EDGES worklist first. */
671 process_ssa_edge_worklist (&varying_ssa_edges
);
673 /* Now process the INTERESTING_SSA_EDGES worklist. */
674 process_ssa_edge_worklist (&interesting_ssa_edges
);
681 /* Return the first V_MAY_DEF or V_MUST_DEF operand for STMT. */
684 first_vdef (tree stmt
)
689 /* Simply return the first operand we arrive at. */
690 FOR_EACH_SSA_TREE_OPERAND (op
, stmt
, iter
, SSA_OP_VIRTUAL_DEFS
)
697 /* Return true if STMT is of the form 'LHS = mem_ref', where 'mem_ref'
698 is a non-volatile pointer dereference, a structure reference or a
699 reference to a single _DECL. Ignore volatile memory references
700 because they are not interesting for the optimizers. */
703 stmt_makes_single_load (tree stmt
)
707 if (TREE_CODE (stmt
) != MODIFY_EXPR
)
710 if (ZERO_SSA_OPERANDS (stmt
, SSA_OP_VMAYDEF
|SSA_OP_VUSE
))
713 rhs
= TREE_OPERAND (stmt
, 1);
716 return (!TREE_THIS_VOLATILE (rhs
)
718 || REFERENCE_CLASS_P (rhs
)));
722 /* Return true if STMT is of the form 'mem_ref = RHS', where 'mem_ref'
723 is a non-volatile pointer dereference, a structure reference or a
724 reference to a single _DECL. Ignore volatile memory references
725 because they are not interesting for the optimizers. */
728 stmt_makes_single_store (tree stmt
)
732 if (TREE_CODE (stmt
) != MODIFY_EXPR
)
735 if (ZERO_SSA_OPERANDS (stmt
, SSA_OP_VMAYDEF
|SSA_OP_VMUSTDEF
))
738 lhs
= TREE_OPERAND (stmt
, 0);
741 return (!TREE_THIS_VOLATILE (lhs
)
743 || REFERENCE_CLASS_P (lhs
)));
747 /* If STMT makes a single memory load and all the virtual use operands
748 have the same value in array VALUES, return it. Otherwise, return
752 get_value_loaded_by (tree stmt
, prop_value_t
*values
)
756 prop_value_t
*prev_val
= NULL
;
757 prop_value_t
*val
= NULL
;
759 FOR_EACH_SSA_TREE_OPERAND (vuse
, stmt
, i
, SSA_OP_VIRTUAL_USES
)
761 val
= &values
[SSA_NAME_VERSION (vuse
)];
762 if (prev_val
&& prev_val
->value
!= val
->value
)
771 /* Propagation statistics. */
776 long num_pred_folded
;
779 static struct prop_stats_d prop_stats
;
781 /* Replace USE references in statement STMT with the values stored in
782 PROP_VALUE. Return true if at least one reference was replaced. If
783 REPLACED_ADDRESSES_P is given, it will be set to true if an address
784 constant was replaced. */
787 replace_uses_in (tree stmt
, bool *replaced_addresses_p
,
788 prop_value_t
*prop_value
)
790 bool replaced
= false;
794 FOR_EACH_SSA_USE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
796 tree tuse
= USE_FROM_PTR (use
);
797 tree val
= prop_value
[SSA_NAME_VERSION (tuse
)].value
;
799 if (val
== tuse
|| val
== NULL_TREE
)
802 if (TREE_CODE (stmt
) == ASM_EXPR
803 && !may_propagate_copy_into_asm (tuse
))
806 if (!may_propagate_copy (tuse
, val
))
809 if (TREE_CODE (val
) != SSA_NAME
)
810 prop_stats
.num_const_prop
++;
812 prop_stats
.num_copy_prop
++;
814 propagate_value (use
, val
);
817 if (POINTER_TYPE_P (TREE_TYPE (tuse
)) && replaced_addresses_p
)
818 *replaced_addresses_p
= true;
825 /* Replace the VUSE references in statement STMT with the values
826 stored in PROP_VALUE. Return true if a reference was replaced. If
827 REPLACED_ADDRESSES_P is given, it will be set to true if an address
828 constant was replaced.
830 Replacing VUSE operands is slightly more complex than replacing
831 regular USEs. We are only interested in two types of replacements
834 1- If the value to be replaced is a constant or an SSA name for a
835 GIMPLE register, then we are making a copy/constant propagation
836 from a memory store. For instance,
838 # a_3 = V_MAY_DEF <a_2>
844 This replacement is only possible iff STMT is an assignment
845 whose RHS is identical to the LHS of the statement that created
846 the VUSE(s) that we are replacing. Otherwise, we may do the
849 # a_3 = V_MAY_DEF <a_2>
850 # b_5 = V_MAY_DEF <b_4>
856 Even though 'b_5' acquires the value '10' during propagation,
857 there is no way for the propagator to tell whether the
858 replacement is correct in every reached use, because values are
859 computed at definition sites. Therefore, when doing final
860 substitution of propagated values, we have to check each use
861 site. Since the RHS of STMT ('b') is different from the LHS of
862 the originating statement ('*p'), we cannot replace 'b' with
865 Similarly, when merging values from PHI node arguments,
866 propagators need to take care not to merge the same values
867 stored in different locations:
870 # a_3 = V_MAY_DEF <a_2>
873 # a_4 = V_MAY_DEF <a_2>
875 # a_5 = PHI <a_3, a_4>
877 It would be wrong to propagate '3' into 'a_5' because that
878 operation merges two stores to different memory locations.
881 2- If the value to be replaced is an SSA name for a virtual
882 register, then we simply replace each VUSE operand with its
883 value from PROP_VALUE. This is the same replacement done by
887 replace_vuses_in (tree stmt
, bool *replaced_addresses_p
,
888 prop_value_t
*prop_value
)
890 bool replaced
= false;
894 if (stmt_makes_single_load (stmt
))
896 /* If STMT is an assignment whose RHS is a single memory load,
897 see if we are trying to propagate a constant or a GIMPLE
898 register (case #1 above). */
899 prop_value_t
*val
= get_value_loaded_by (stmt
, prop_value
);
900 tree rhs
= TREE_OPERAND (stmt
, 1);
904 && (is_gimple_reg (val
->value
)
905 || is_gimple_min_invariant (val
->value
))
906 && simple_cst_equal (rhs
, val
->mem_ref
) == 1)
909 /* If we are replacing a constant address, inform our
911 if (TREE_CODE (val
->value
) != SSA_NAME
912 && POINTER_TYPE_P (TREE_TYPE (TREE_OPERAND (stmt
, 1)))
913 && replaced_addresses_p
)
914 *replaced_addresses_p
= true;
916 /* We can only perform the substitution if the load is done
917 from the same memory location as the original store.
918 Since we already know that there are no intervening
919 stores between DEF_STMT and STMT, we only need to check
920 that the RHS of STMT is the same as the memory reference
921 propagated together with the value. */
922 TREE_OPERAND (stmt
, 1) = val
->value
;
924 if (TREE_CODE (val
->value
) != SSA_NAME
)
925 prop_stats
.num_const_prop
++;
927 prop_stats
.num_copy_prop
++;
929 /* Since we have replaced the whole RHS of STMT, there
930 is no point in checking the other VUSEs, as they will
931 all have the same value. */
936 /* Otherwise, the values for every VUSE operand must be other
937 SSA_NAMEs that can be propagated into STMT. */
938 FOR_EACH_SSA_USE_OPERAND (vuse
, stmt
, iter
, SSA_OP_VIRTUAL_USES
)
940 tree var
= USE_FROM_PTR (vuse
);
941 tree val
= prop_value
[SSA_NAME_VERSION (var
)].value
;
943 if (val
== NULL_TREE
|| var
== val
)
946 /* Constants and copies propagated between real and virtual
947 operands are only possible in the cases handled above. They
948 should be ignored in any other context. */
949 if (is_gimple_min_invariant (val
) || is_gimple_reg (val
))
952 propagate_value (vuse
, val
);
953 prop_stats
.num_copy_prop
++;
961 /* Replace propagated values into all the arguments for PHI using the
962 values from PROP_VALUE. */
965 replace_phi_args_in (tree phi
, prop_value_t
*prop_value
)
968 bool replaced
= false;
969 tree prev_phi
= NULL
;
971 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
972 prev_phi
= unshare_expr (phi
);
974 for (i
= 0; i
< PHI_NUM_ARGS (phi
); i
++)
976 tree arg
= PHI_ARG_DEF (phi
, i
);
978 if (TREE_CODE (arg
) == SSA_NAME
)
980 tree val
= prop_value
[SSA_NAME_VERSION (arg
)].value
;
982 if (val
&& val
!= arg
&& may_propagate_copy (arg
, val
))
984 if (TREE_CODE (val
) != SSA_NAME
)
985 prop_stats
.num_const_prop
++;
987 prop_stats
.num_copy_prop
++;
989 propagate_value (PHI_ARG_DEF_PTR (phi
, i
), val
);
992 /* If we propagated a copy and this argument flows
993 through an abnormal edge, update the replacement
995 if (TREE_CODE (val
) == SSA_NAME
996 && PHI_ARG_EDGE (phi
, i
)->flags
& EDGE_ABNORMAL
)
997 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (val
) = 1;
1002 if (replaced
&& dump_file
&& (dump_flags
& TDF_DETAILS
))
1004 fprintf (dump_file
, "Folded PHI node: ");
1005 print_generic_stmt (dump_file
, prev_phi
, TDF_SLIM
);
1006 fprintf (dump_file
, " into: ");
1007 print_generic_stmt (dump_file
, phi
, TDF_SLIM
);
1008 fprintf (dump_file
, "\n");
1013 /* If STMT has a predicate whose value can be computed using the value
1014 range information computed by VRP, compute its value and return true.
1015 Otherwise, return false. */
1018 fold_predicate_in (tree stmt
)
1020 tree
*pred_p
= NULL
;
1023 if (TREE_CODE (stmt
) == MODIFY_EXPR
1024 && COMPARISON_CLASS_P (TREE_OPERAND (stmt
, 1)))
1025 pred_p
= &TREE_OPERAND (stmt
, 1);
1026 else if (TREE_CODE (stmt
) == COND_EXPR
)
1027 pred_p
= &COND_EXPR_COND (stmt
);
1031 val
= vrp_evaluate_conditional (*pred_p
, true);
1036 fprintf (dump_file
, "Folding predicate ");
1037 print_generic_expr (dump_file
, *pred_p
, 0);
1038 fprintf (dump_file
, " to ");
1039 print_generic_expr (dump_file
, val
, 0);
1040 fprintf (dump_file
, "\n");
1043 prop_stats
.num_pred_folded
++;
1052 /* Perform final substitution and folding of propagated values.
1054 PROP_VALUE[I] contains the single value that should be substituted
1055 at every use of SSA name N_I. If PROP_VALUE is NULL, no values are
1058 If USE_RANGES_P is true, statements that contain predicate
1059 expressions are evaluated with a call to vrp_evaluate_conditional.
1060 This will only give meaningful results when called from tree-vrp.c
1061 (the information used by vrp_evaluate_conditional is built by the
1065 substitute_and_fold (prop_value_t
*prop_value
, bool use_ranges_p
)
1069 if (prop_value
== NULL
&& !use_ranges_p
)
1072 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1073 fprintf (dump_file
, "\nSubstituing values and folding statements\n\n");
1075 memset (&prop_stats
, 0, sizeof (prop_stats
));
1077 /* Substitute values in every statement of every basic block. */
1080 block_stmt_iterator i
;
1083 /* Propagate known values into PHI nodes. */
1085 for (phi
= phi_nodes (bb
); phi
; phi
= PHI_CHAIN (phi
))
1086 replace_phi_args_in (phi
, prop_value
);
1088 for (i
= bsi_start (bb
); !bsi_end_p (i
); bsi_next (&i
))
1090 bool replaced_address
, did_replace
;
1091 tree prev_stmt
= NULL
;
1092 tree stmt
= bsi_stmt (i
);
1094 /* Ignore ASSERT_EXPRs. They are used by VRP to generate
1095 range information for names and they are discarded
1097 if (TREE_CODE (stmt
) == MODIFY_EXPR
1098 && TREE_CODE (TREE_OPERAND (stmt
, 1)) == ASSERT_EXPR
)
1101 /* Replace the statement with its folded version and mark it
1103 did_replace
= false;
1104 replaced_address
= false;
1105 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1106 prev_stmt
= unshare_expr (stmt
);
1108 /* If we have range information, see if we can fold
1109 predicate expressions. */
1112 did_replace
= fold_predicate_in (stmt
);
1114 /* Some statements may be simplified using ranges. For
1115 example, division may be replaced by shifts, modulo
1116 replaced with bitwise and, etc. */
1117 simplify_stmt_using_ranges (stmt
);
1122 /* Only replace real uses if we couldn't fold the
1123 statement using value range information (value range
1124 information is not collected on virtuals, so we only
1125 need to check this for real uses). */
1127 did_replace
|= replace_uses_in (stmt
, &replaced_address
,
1130 did_replace
|= replace_vuses_in (stmt
, &replaced_address
,
1134 /* If we made a replacement, fold and cleanup the statement. */
1137 tree old_stmt
= stmt
;
1140 fold_stmt (bsi_stmt_ptr (i
));
1141 stmt
= bsi_stmt (i
);
1143 /* If we folded a builtin function, we'll likely
1144 need to rename VDEFs. */
1145 mark_new_vars_to_rename (stmt
);
1147 /* If we cleaned up EH information from the statement,
1149 if (maybe_clean_or_replace_eh_stmt (old_stmt
, stmt
))
1150 tree_purge_dead_eh_edges (bb
);
1152 rhs
= get_rhs (stmt
);
1153 if (TREE_CODE (rhs
) == ADDR_EXPR
)
1154 recompute_tree_invarant_for_addr_expr (rhs
);
1156 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1158 fprintf (dump_file
, "Folded statement: ");
1159 print_generic_stmt (dump_file
, prev_stmt
, TDF_SLIM
);
1160 fprintf (dump_file
, " into: ");
1161 print_generic_stmt (dump_file
, stmt
, TDF_SLIM
);
1162 fprintf (dump_file
, "\n");
1168 if (dump_file
&& (dump_flags
& TDF_STATS
))
1170 fprintf (dump_file
, "Constants propagated: %6ld\n",
1171 prop_stats
.num_const_prop
);
1172 fprintf (dump_file
, "Copies propagated: %6ld\n",
1173 prop_stats
.num_copy_prop
);
1174 fprintf (dump_file
, "Predicates folded: %6ld\n",
1175 prop_stats
.num_pred_folded
);
1179 #include "gt-tree-ssa-propagate.h"