1 /* Conditional constant propagation pass for the GNU compiler.
2 Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005
3 Free Software Foundation, Inc.
4 Adapted from original RTL SSA-CCP by Daniel Berlin <dberlin@dberlin.org>
5 Adapted to GIMPLE trees by Diego Novillo <dnovillo@redhat.com>
7 This file is part of GCC.
9 GCC is free software; you can redistribute it and/or modify it
10 under the terms of the GNU General Public License as published by the
11 Free Software Foundation; either version 2, or (at your option) any
14 GCC is distributed in the hope that it will be useful, but WITHOUT
15 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
16 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
19 You should have received a copy of the GNU General Public License
20 along with GCC; see the file COPYING. If not, write to the Free
21 Software Foundation, 59 Temple Place - Suite 330, Boston, MA
24 /* Conditional constant propagation (CCP) is based on the SSA
25 propagation engine (tree-ssa-propagate.c). Constant assignments of
26 the form VAR = CST are propagated from the assignments into uses of
27 VAR, which in turn may generate new constants. The simulation uses
28 a four level lattice to keep track of constant values associated
29 with SSA names. Given an SSA name V_i, it may take one of the
32 UNINITIALIZED -> This is the default starting value. V_i
33 has not been processed yet.
35 UNDEFINED -> V_i is a local variable whose definition
36 has not been processed yet. Therefore we
37 don't yet know if its value is a constant
40 CONSTANT -> V_i has been found to hold a constant
43 VARYING -> V_i cannot take a constant value, or if it
44 does, it is not possible to determine it
47 The core of SSA-CCP is in ccp_visit_stmt and ccp_visit_phi_node:
49 1- In ccp_visit_stmt, we are interested in assignments whose RHS
50 evaluates into a constant and conditional jumps whose predicate
51 evaluates into a boolean true or false. When an assignment of
52 the form V_i = CONST is found, V_i's lattice value is set to
53 CONSTANT and CONST is associated with it. This causes the
54 propagation engine to add all the SSA edges coming out the
55 assignment into the worklists, so that statements that use V_i
58 If the statement is a conditional with a constant predicate, we
59 mark the outgoing edges as executable or not executable
60 depending on the predicate's value. This is then used when
61 visiting PHI nodes to know when a PHI argument can be ignored.
64 2- In ccp_visit_phi_node, if all the PHI arguments evaluate to the
65 same constant C, then the LHS of the PHI is set to C. This
66 evaluation is known as the "meet operation". Since one of the
67 goals of this evaluation is to optimistically return constant
68 values as often as possible, it uses two main short cuts:
70 - If an argument is flowing in through a non-executable edge, it
71 is ignored. This is useful in cases like this:
77 a_11 = PHI (a_9, a_10)
79 If PRED is known to always evaluate to false, then we can
80 assume that a_11 will always take its value from a_10, meaning
81 that instead of consider it VARYING (a_9 and a_10 have
82 different values), we can consider it CONSTANT 100.
84 - If an argument has an UNDEFINED value, then it does not affect
85 the outcome of the meet operation. If a variable V_i has an
86 UNDEFINED value, it means that either its defining statement
87 hasn't been visited yet or V_i has no defining statement, in
88 which case the original symbol 'V' is being used
89 uninitialized. Since 'V' is a local variable, the compiler
90 may assume any initial value for it.
93 After propagation, every variable V_i that ends up with a lattice
94 value of CONSTANT will have the associated constant value in the
95 array CONST_VAL[i].VALUE. That is fed into substitute_and_fold for
96 final substitution and folding.
99 Constant propagation in stores and loads (STORE-CCP)
100 ----------------------------------------------------
102 While CCP has all the logic to propagate constants in GIMPLE
103 registers, it is missing the ability to associate constants with
104 stores and loads (i.e., pointer dereferences, structures and
105 global/aliased variables). We don't keep loads and stores in
106 SSA, but we do build a factored use-def web for them (in the
109 For instance, consider the following code fragment:
128 We should be able to deduce that the predicate 'a.a != B' is always
129 false. To achieve this, we associate constant values to the SSA
130 names in the V_MAY_DEF and V_MUST_DEF operands for each store.
131 Additionally, since we also glob partial loads/stores with the base
132 symbol, we also keep track of the memory reference where the
133 constant value was stored (in the MEM_REF field of PROP_VALUE_T).
136 # a_5 = V_MAY_DEF <a_4>
142 In the example above, CCP will associate value '2' with 'a_5', but
143 it would be wrong to replace the load from 'a.b' with '2', because
144 '2' had been stored into a.a.
146 To support STORE-CCP, it is necessary to add a new value to the
147 constant propagation lattice. When evaluating a load for a memory
148 reference we can no longer assume a value of UNDEFINED if we
149 haven't seen a preceding store to the same memory location.
150 Consider, for instance global variables:
158 # A_5 = PHI (A_4, A_2);
166 The value of A_2 cannot be assumed to be UNDEFINED, as it may have
167 been defined outside of foo. If we were to assume it UNDEFINED, we
168 would erroneously optimize the above into 'return 3;'. Therefore,
169 when doing STORE-CCP, we introduce a fifth lattice value
170 (UNKNOWN_VAL), which overrides any other value when computing the
171 meet operation in PHI nodes.
173 Though STORE-CCP is not too expensive, it does have to do more work
174 than regular CCP, so it is only enabled at -O2. Both regular CCP
175 and STORE-CCP use the exact same algorithm. The only distinction
176 is that when doing STORE-CCP, the boolean variable DO_STORE_CCP is
177 set to true. This affects the evaluation of statements and PHI
182 Constant propagation with conditional branches,
183 Wegman and Zadeck, ACM TOPLAS 13(2):181-210.
185 Building an Optimizing Compiler,
186 Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9.
188 Advanced Compiler Design and Implementation,
189 Steven Muchnick, Morgan Kaufmann, 1997, Section 12.6 */
193 #include "coretypes.h"
200 #include "basic-block.h"
204 #include "function.h"
205 #include "diagnostic.h"
207 #include "tree-dump.h"
208 #include "tree-flow.h"
209 #include "tree-pass.h"
210 #include "tree-ssa-propagate.h"
211 #include "langhooks.h"
214 /* Possible lattice values. */
224 /* Array of propagated constant values. After propagation,
225 CONST_VAL[I].VALUE holds the constant value for SSA_NAME(I). If
226 the constant is held in an SSA name representing a memory store
227 (i.e., a V_MAY_DEF or V_MUST_DEF), CONST_VAL[I].MEM_REF will
228 contain the actual memory reference used to store (i.e., the LHS of
229 the assignment doing the store). */
230 prop_value_t *const_val;
232 /* True if we are also propagating constants in stores and loads. */
233 static bool do_store_ccp;
235 /* Dump constant propagation value VAL to file OUTF prefixed by PREFIX. */
238 dump_lattice_value (FILE *outf, const char *prefix, prop_value_t val)
240 switch (val.lattice_val)
243 fprintf (outf, "%sUNINITIALIZED", prefix);
246 fprintf (outf, "%sUNDEFINED", prefix);
249 fprintf (outf, "%sVARYING", prefix);
252 fprintf (outf, "%sUNKNOWN_VAL", prefix);
255 fprintf (outf, "%sCONSTANT ", prefix);
256 print_generic_expr (outf, val.value, dump_flags);
264 /* Print lattice value VAL to stderr. */
266 void debug_lattice_value (prop_value_t val);
269 debug_lattice_value (prop_value_t val)
271 dump_lattice_value (stderr, "", val);
272 fprintf (stderr, "\n");
276 /* Compute a default value for variable VAR and store it in the
277 CONST_VAL array. The following rules are used to get default
280 1- Global and static variables that are declared constant are
283 2- Any other value is considered UNDEFINED. This is useful when
284 considering PHI nodes. PHI arguments that are undefined do not
285 change the constant value of the PHI node, which allows for more
286 constants to be propagated.
288 3- If SSA_NAME_VALUE is set and it is a constant, its value is
291 4- Variables defined by statements other than assignments and PHI
292 nodes are considered VARYING.
294 5- Variables that are not GIMPLE registers are considered
295 UNKNOWN_VAL, which is really a stronger version of UNDEFINED.
296 It's used to avoid the short circuit evaluation implied by
297 UNDEFINED in ccp_lattice_meet. */
300 get_default_value (tree var)
302 tree sym = SSA_NAME_VAR (var);
303 prop_value_t val = { UNINITIALIZED, NULL_TREE, NULL_TREE };
305 if (!do_store_ccp && !is_gimple_reg (var))
307 /* Short circuit for regular CCP. We are not interested in any
308 non-register when DO_STORE_CCP is false. */
309 val.lattice_val = VARYING;
311 else if (SSA_NAME_VALUE (var)
312 && is_gimple_min_invariant (SSA_NAME_VALUE (var)))
314 val.lattice_val = CONSTANT;
315 val.value = SSA_NAME_VALUE (var);
317 else if (TREE_STATIC (sym)
318 && TREE_READONLY (sym)
319 && DECL_INITIAL (sym)
320 && is_gimple_min_invariant (DECL_INITIAL (sym)))
322 /* Globals and static variables declared 'const' take their
324 val.lattice_val = CONSTANT;
325 val.value = DECL_INITIAL (sym);
330 tree stmt = SSA_NAME_DEF_STMT (var);
332 if (IS_EMPTY_STMT (stmt))
334 /* Variables defined by an empty statement are those used
335 before being initialized. If VAR is a local variable, we
336 can assume initially that it is UNDEFINED. If we are
337 doing STORE-CCP, function arguments and non-register
338 variables are initially UNKNOWN_VAL, because we cannot
339 discard the value incoming from outside of this function
340 (see ccp_lattice_meet for details). */
341 if (is_gimple_reg (sym) && TREE_CODE (sym) != PARM_DECL)
342 val.lattice_val = UNDEFINED;
343 else if (do_store_ccp)
344 val.lattice_val = UNKNOWN_VAL;
346 val.lattice_val = VARYING;
348 else if (TREE_CODE (stmt) == MODIFY_EXPR
349 || TREE_CODE (stmt) == PHI_NODE)
351 /* Any other variable defined by an assignment or a PHI node
352 is considered UNDEFINED (or UNKNOWN_VAL if VAR is not a
354 val.lattice_val = is_gimple_reg (sym) ? UNDEFINED : UNKNOWN_VAL;
358 /* Otherwise, VAR will never take on a constant value. */
359 val.lattice_val = VARYING;
367 /* Get the constant value associated with variable VAR. If
368 MAY_USE_DEFAULT_P is true, call get_default_value on variables that
369 have the lattice value UNINITIALIZED. */
371 static prop_value_t *
372 get_value (tree var, bool may_use_default_p)
374 prop_value_t *val = &const_val[SSA_NAME_VERSION (var)];
375 if (may_use_default_p && val->lattice_val == UNINITIALIZED)
376 *val = get_default_value (var);
382 /* Set the value for variable VAR to NEW_VAL. Return true if the new
383 value is different from VAR's previous value. */
386 set_lattice_value (tree var, prop_value_t new_val)
388 prop_value_t *old_val = get_value (var, false);
390 /* Lattice transitions must always be monotonically increasing in
391 value. We allow two exceptions:
393 1- If *OLD_VAL and NEW_VAL are the same, return false to
394 inform the caller that this was a non-transition.
396 2- If we are doing store-ccp (i.e., DOING_STORE_CCP is true),
397 allow CONSTANT->UNKNOWN_VAL. The UNKNOWN_VAL state is a
398 special type of UNDEFINED state which prevents the short
399 circuit evaluation of PHI arguments (see ccp_visit_phi_node
400 and ccp_lattice_meet). */
401 gcc_assert (old_val->lattice_val <= new_val.lattice_val
402 || (old_val->lattice_val == new_val.lattice_val
403 && old_val->value == new_val.value
404 && old_val->mem_ref == new_val.mem_ref)
406 && old_val->lattice_val == CONSTANT
407 && new_val.lattice_val == UNKNOWN_VAL));
409 if (old_val->lattice_val != new_val.lattice_val)
411 if (dump_file && (dump_flags & TDF_DETAILS))
413 dump_lattice_value (dump_file, "Lattice value changed to ", new_val);
414 fprintf (dump_file, ". %sdding SSA edges to worklist.\n",
415 new_val.lattice_val != UNDEFINED ? "A" : "Not a");
420 /* Transitions UNINITIALIZED -> UNDEFINED are never interesting
421 for propagation purposes. In these cases return false to
422 avoid doing useless work. */
423 return (new_val.lattice_val != UNDEFINED);
430 /* Return the likely CCP lattice value for STMT.
432 If STMT has no operands, then return CONSTANT.
434 Else if any operands of STMT are undefined, then return UNDEFINED.
436 Else if any operands of STMT are constants, then return CONSTANT.
438 Else return VARYING. */
441 likely_value (tree stmt)
448 ann = stmt_ann (stmt);
450 /* If the statement has volatile operands, it won't fold to a
452 if (ann->has_volatile_ops)
455 /* If we are not doing store-ccp, statements with loads
456 and/or stores will never fold into a constant. */
458 && (ann->makes_aliased_stores
459 || ann->makes_aliased_loads
460 || !ZERO_SSA_OPERANDS (stmt, SSA_OP_ALL_VIRTUALS)))
464 /* A CALL_EXPR is assumed to be varying. NOTE: This may be overly
465 conservative, in the presence of const and pure calls. */
466 if (get_call_expr_in (stmt) != NULL_TREE)
469 /* Anything other than assignments and conditional jumps are not
470 interesting for CCP. */
471 if (TREE_CODE (stmt) != MODIFY_EXPR
472 && TREE_CODE (stmt) != COND_EXPR
473 && TREE_CODE (stmt) != SWITCH_EXPR)
476 found_constant = false;
477 FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE|SSA_OP_VUSE)
479 prop_value_t *val = get_value (use, true);
481 if (val->lattice_val == VARYING)
484 if (val->lattice_val == UNKNOWN_VAL)
486 /* UNKNOWN_VAL is invalid when not doing STORE-CCP. */
487 gcc_assert (do_store_ccp);
491 if (val->lattice_val == CONSTANT)
492 found_constant = true;
496 || ZERO_SSA_OPERANDS (stmt, SSA_OP_USE)
497 || ZERO_SSA_OPERANDS (stmt, SSA_OP_VUSE))
504 /* Initialize local data structures for CCP. */
507 ccp_initialize (void)
511 const_val = xmalloc (num_ssa_names * sizeof (*const_val));
512 memset (const_val, 0, num_ssa_names * sizeof (*const_val));
514 /* Initialize simulation flags for PHI nodes and statements. */
517 block_stmt_iterator i;
519 for (i = bsi_start (bb); !bsi_end_p (i); bsi_next (&i))
521 bool is_varying = false;
522 tree stmt = bsi_stmt (i);
524 if (likely_value (stmt) == VARYING)
530 /* If the statement will not produce a constant, mark
531 all its outputs VARYING. */
532 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
533 get_value (def, false)->lattice_val = VARYING;
535 /* Never mark conditional jumps with DONT_SIMULATE_AGAIN,
536 otherwise the propagator will never add the outgoing
538 if (TREE_CODE (stmt) != COND_EXPR
539 && TREE_CODE (stmt) != SWITCH_EXPR)
543 DONT_SIMULATE_AGAIN (stmt) = is_varying;
547 /* Now process PHI nodes. */
552 for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
556 prop_value_t *val = get_value (PHI_RESULT (phi), false);
558 for (i = 0; i < PHI_NUM_ARGS (phi); i++)
560 arg = PHI_ARG_DEF (phi, i);
562 if (TREE_CODE (arg) == SSA_NAME
563 && get_value (arg, false)->lattice_val == VARYING)
565 val->lattice_val = VARYING;
570 DONT_SIMULATE_AGAIN (phi) = (val->lattice_val == VARYING);
576 /* Do final substitution of propagated values, cleanup the flowgraph and
577 free allocated storage. */
582 /* Perform substitutions based on the known constant values. */
583 substitute_and_fold (const_val);
589 /* Compute the meet operator between *VAL1 and *VAL2. Store the result
592 any M UNDEFINED = any
593 any M UNKNOWN_VAL = UNKNOWN_VAL
594 any M VARYING = VARYING
595 Ci M Cj = Ci if (i == j)
596 Ci M Cj = VARYING if (i != j)
598 Lattice values UNKNOWN_VAL and UNDEFINED are similar but have
599 different semantics at PHI nodes. Both values imply that we don't
600 know whether the variable is constant or not. However, UNKNOWN_VAL
601 values override all others. For instance, suppose that A is a
611 | A_3 = PHI (A_2, A_1)
616 If the edge into A_2 is not executable, the first visit to A_3 will
617 yield the constant 4. But the second visit to A_3 will be with A_2
618 in state UNKNOWN_VAL. We can no longer conclude that A_3 is 4
619 because A_2 may have been set in another function. If we had used
620 the lattice value UNDEFINED, we would have had wrongly concluded
625 ccp_lattice_meet (prop_value_t *val1, prop_value_t *val2)
627 if (val1->lattice_val == UNDEFINED)
629 /* UNDEFINED M any = any */
632 else if (val2->lattice_val == UNDEFINED)
634 /* any M UNDEFINED = any
635 Nothing to do. VAL1 already contains the value we want. */
638 else if (val1->lattice_val == UNKNOWN_VAL
639 || val2->lattice_val == UNKNOWN_VAL)
641 /* UNKNOWN_VAL values are invalid if we are not doing STORE-CCP. */
642 gcc_assert (do_store_ccp);
644 /* any M UNKNOWN_VAL = UNKNOWN_VAL. */
645 val1->lattice_val = UNKNOWN_VAL;
646 val1->value = NULL_TREE;
647 val1->mem_ref = NULL_TREE;
649 else if (val1->lattice_val == VARYING
650 || val2->lattice_val == VARYING)
652 /* any M VARYING = VARYING. */
653 val1->lattice_val = VARYING;
654 val1->value = NULL_TREE;
655 val1->mem_ref = NULL_TREE;
657 else if (val1->lattice_val == CONSTANT
658 && val2->lattice_val == CONSTANT
659 && simple_cst_equal (val1->value, val2->value) == 1
661 || simple_cst_equal (val1->mem_ref, val2->mem_ref) == 1))
663 /* Ci M Cj = Ci if (i == j)
664 Ci M Cj = VARYING if (i != j)
666 If these two values come from memory stores, make sure that
667 they come from the same memory reference. */
668 val1->lattice_val = CONSTANT;
669 val1->value = val1->value;
670 val1->mem_ref = val1->mem_ref;
674 /* Any other combination is VARYING. */
675 val1->lattice_val = VARYING;
676 val1->value = NULL_TREE;
677 val1->mem_ref = NULL_TREE;
682 /* Loop through the PHI_NODE's parameters for BLOCK and compare their
683 lattice values to determine PHI_NODE's lattice value. The value of a
684 PHI node is determined calling ccp_lattice_meet with all the arguments
685 of the PHI node that are incoming via executable edges. */
687 static enum ssa_prop_result
688 ccp_visit_phi_node (tree phi)
691 prop_value_t *old_val, new_val;
693 if (dump_file && (dump_flags & TDF_DETAILS))
695 fprintf (dump_file, "\nVisiting PHI node: ");
696 print_generic_expr (dump_file, phi, dump_flags);
699 old_val = get_value (PHI_RESULT (phi), false);
700 switch (old_val->lattice_val)
703 return SSA_PROP_VARYING;
710 /* To avoid the default value of UNKNOWN_VAL overriding
711 that of its possible constant arguments, temporarily
712 set the PHI node's default lattice value to be
713 UNDEFINED. If the PHI node's old value was UNKNOWN_VAL and
714 the new value is UNDEFINED, then we prevent the invalid
715 transition by not calling set_lattice_value. */
716 gcc_assert (do_store_ccp);
722 new_val.lattice_val = UNDEFINED;
723 new_val.value = NULL_TREE;
724 new_val.mem_ref = NULL_TREE;
731 for (i = 0; i < PHI_NUM_ARGS (phi); i++)
733 /* Compute the meet operator over all the PHI arguments flowing
734 through executable edges. */
735 edge e = PHI_ARG_EDGE (phi, i);
737 if (dump_file && (dump_flags & TDF_DETAILS))
740 "\n Argument #%d (%d -> %d %sexecutable)\n",
741 i, e->src->index, e->dest->index,
742 (e->flags & EDGE_EXECUTABLE) ? "" : "not ");
745 /* If the incoming edge is executable, Compute the meet operator for
746 the existing value of the PHI node and the current PHI argument. */
747 if (e->flags & EDGE_EXECUTABLE)
749 tree arg = PHI_ARG_DEF (phi, i);
750 prop_value_t arg_val;
752 if (is_gimple_min_invariant (arg))
754 arg_val.lattice_val = CONSTANT;
756 arg_val.mem_ref = NULL_TREE;
759 arg_val = *(get_value (arg, true));
761 ccp_lattice_meet (&new_val, &arg_val);
763 if (dump_file && (dump_flags & TDF_DETAILS))
765 fprintf (dump_file, "\t");
766 print_generic_expr (dump_file, arg, dump_flags);
767 dump_lattice_value (dump_file, "\tValue: ", arg_val);
768 fprintf (dump_file, "\n");
771 if (new_val.lattice_val == VARYING)
776 if (dump_file && (dump_flags & TDF_DETAILS))
778 dump_lattice_value (dump_file, "\n PHI node value: ", new_val);
779 fprintf (dump_file, "\n\n");
782 /* Check for an invalid change from UNKNOWN_VAL to UNDEFINED. */
784 && old_val->lattice_val == UNKNOWN_VAL
785 && new_val.lattice_val == UNDEFINED)
786 return SSA_PROP_NOT_INTERESTING;
788 /* Otherwise, make the transition to the new value. */
789 if (set_lattice_value (PHI_RESULT (phi), new_val))
791 if (new_val.lattice_val == VARYING)
792 return SSA_PROP_VARYING;
794 return SSA_PROP_INTERESTING;
797 return SSA_PROP_NOT_INTERESTING;
801 /* CCP specific front-end to the non-destructive constant folding
804 Attempt to simplify the RHS of STMT knowing that one or more
805 operands are constants.
807 If simplification is possible, return the simplified RHS,
808 otherwise return the original RHS. */
813 tree rhs = get_rhs (stmt);
814 enum tree_code code = TREE_CODE (rhs);
815 enum tree_code_class kind = TREE_CODE_CLASS (code);
816 tree retval = NULL_TREE;
818 if (TREE_CODE (rhs) == SSA_NAME)
820 /* If the RHS is an SSA_NAME, return its known constant value,
822 return get_value (rhs, true)->value;
824 else if (do_store_ccp && stmt_makes_single_load (stmt))
826 /* If the RHS is a memory load, see if the VUSEs associated with
827 it are a valid constant for that memory load. */
828 prop_value_t *val = get_value_loaded_by (stmt, const_val);
829 if (val && simple_cst_equal (val->mem_ref, rhs) == 1)
835 /* Unary operators. Note that we know the single operand must
836 be a constant. So this should almost always return a
838 if (kind == tcc_unary)
840 /* Handle unary operators which can appear in GIMPLE form. */
841 tree op0 = TREE_OPERAND (rhs, 0);
843 /* Simplify the operand down to a constant. */
844 if (TREE_CODE (op0) == SSA_NAME)
846 prop_value_t *val = get_value (op0, true);
847 if (val->lattice_val == CONSTANT)
848 op0 = get_value (op0, true)->value;
851 retval = fold_unary_to_constant (code, TREE_TYPE (rhs), op0);
853 /* If we folded, but did not create an invariant, then we can not
854 use this expression. */
855 if (retval && ! is_gimple_min_invariant (retval))
858 /* If we could not fold the expression, but the arguments are all
859 constants and gimple values, then build and return the new
862 In some cases the new expression is still something we can
863 use as a replacement for an argument. This happens with
864 NOP conversions of types for example.
866 In other cases the new expression can not be used as a
867 replacement for an argument (as it would create non-gimple
868 code). But the new expression can still be used to derive
870 if (! retval && is_gimple_min_invariant (op0))
871 return build1 (code, TREE_TYPE (rhs), op0);
874 /* Binary and comparison operators. We know one or both of the
875 operands are constants. */
876 else if (kind == tcc_binary
877 || kind == tcc_comparison
878 || code == TRUTH_AND_EXPR
879 || code == TRUTH_OR_EXPR
880 || code == TRUTH_XOR_EXPR)
882 /* Handle binary and comparison operators that can appear in
884 tree op0 = TREE_OPERAND (rhs, 0);
885 tree op1 = TREE_OPERAND (rhs, 1);
887 /* Simplify the operands down to constants when appropriate. */
888 if (TREE_CODE (op0) == SSA_NAME)
890 prop_value_t *val = get_value (op0, true);
891 if (val->lattice_val == CONSTANT)
895 if (TREE_CODE (op1) == SSA_NAME)
897 prop_value_t *val = get_value (op1, true);
898 if (val->lattice_val == CONSTANT)
902 retval = fold_binary_to_constant (code, TREE_TYPE (rhs), op0, op1);
904 /* If we folded, but did not create an invariant, then we can not
905 use this expression. */
906 if (retval && ! is_gimple_min_invariant (retval))
909 /* If we could not fold the expression, but the arguments are all
910 constants and gimple values, then build and return the new
913 In some cases the new expression is still something we can
914 use as a replacement for an argument. This happens with
915 NOP conversions of types for example.
917 In other cases the new expression can not be used as a
918 replacement for an argument (as it would create non-gimple
919 code). But the new expression can still be used to derive
922 && is_gimple_min_invariant (op0)
923 && is_gimple_min_invariant (op1))
924 return build (code, TREE_TYPE (rhs), op0, op1);
927 /* We may be able to fold away calls to builtin functions if their
928 arguments are constants. */
929 else if (code == CALL_EXPR
930 && TREE_CODE (TREE_OPERAND (rhs, 0)) == ADDR_EXPR
931 && (TREE_CODE (TREE_OPERAND (TREE_OPERAND (rhs, 0), 0))
933 && DECL_BUILT_IN (TREE_OPERAND (TREE_OPERAND (rhs, 0), 0)))
935 if (!ZERO_SSA_OPERANDS (stmt, SSA_OP_USE))
938 tree fndecl, arglist;
943 /* Preserve the original values of every operand. */
944 orig = xmalloc (sizeof (tree) * NUM_SSA_OPERANDS (stmt, SSA_OP_USE));
945 FOR_EACH_SSA_TREE_OPERAND (var, stmt, iter, SSA_OP_USE)
948 /* Substitute operands with their values and try to fold. */
949 replace_uses_in (stmt, NULL, const_val);
950 fndecl = get_callee_fndecl (rhs);
951 arglist = TREE_OPERAND (rhs, 1);
952 retval = fold_builtin (fndecl, arglist, false);
954 /* Restore operands to their original form. */
956 FOR_EACH_SSA_USE_OPERAND (var_p, stmt, iter, SSA_OP_USE)
957 SET_USE (var_p, orig[i++]);
964 /* If we got a simplified form, see if we need to convert its type. */
966 return fold_convert (TREE_TYPE (rhs), retval);
968 /* No simplification was possible. */
973 /* Evaluate statement STMT. */
976 evaluate_stmt (tree stmt)
980 ccp_lattice_t likelyvalue = likely_value (stmt);
982 val.mem_ref = NULL_TREE;
984 /* If the statement is likely to have a CONSTANT result, then try
985 to fold the statement to determine the constant value. */
986 if (likelyvalue == CONSTANT)
987 simplified = ccp_fold (stmt);
988 /* If the statement is likely to have a VARYING result, then do not
989 bother folding the statement. */
990 else if (likelyvalue == VARYING)
991 simplified = get_rhs (stmt);
992 /* Otherwise the statement is likely to have an UNDEFINED value and
993 there will be nothing to do. */
995 simplified = NULL_TREE;
997 if (simplified && is_gimple_min_invariant (simplified))
999 /* The statement produced a constant value. */
1000 val.lattice_val = CONSTANT;
1001 val.value = simplified;
1005 /* The statement produced a nonconstant value. If the statement
1006 had UNDEFINED operands, then the result of the statement
1007 should be UNDEFINED. Otherwise, the statement is VARYING. */
1008 val.lattice_val = (likelyvalue == UNDEFINED) ? UNDEFINED : VARYING;
1009 val.value = NULL_TREE;
1016 /* Visit the assignment statement STMT. Set the value of its LHS to the
1017 value computed by the RHS and store LHS in *OUTPUT_P. If STMT
1018 creates virtual definitions, set the value of each new name to that
1019 of the RHS (if we can derive a constant out of the RHS). */
1021 static enum ssa_prop_result
1022 visit_assignment (tree stmt, tree *output_p)
1026 enum ssa_prop_result retval;
1028 lhs = TREE_OPERAND (stmt, 0);
1029 rhs = TREE_OPERAND (stmt, 1);
1031 if (TREE_CODE (rhs) == SSA_NAME)
1033 /* For a simple copy operation, we copy the lattice values. */
1034 prop_value_t *nval = get_value (rhs, true);
1037 else if (do_store_ccp && stmt_makes_single_load (stmt))
1039 /* Same as above, but the RHS is not a gimple register and yet
1040 has a known VUSE. If STMT is loading from the same memory
1041 location that created the SSA_NAMEs for the virtual operands,
1042 we can propagate the value on the RHS. */
1043 prop_value_t *nval = get_value_loaded_by (stmt, const_val);
1045 if (nval && simple_cst_equal (nval->mem_ref, rhs) == 1)
1048 val = evaluate_stmt (stmt);
1051 /* Evaluate the statement. */
1052 val = evaluate_stmt (stmt);
1054 /* If the original LHS was a VIEW_CONVERT_EXPR, modify the constant
1055 value to be a VIEW_CONVERT_EXPR of the old constant value.
1057 ??? Also, if this was a definition of a bitfield, we need to widen
1058 the constant value into the type of the destination variable. This
1059 should not be necessary if GCC represented bitfields properly. */
1061 tree orig_lhs = TREE_OPERAND (stmt, 0);
1063 if (TREE_CODE (orig_lhs) == VIEW_CONVERT_EXPR
1064 && val.lattice_val == CONSTANT)
1066 tree w = fold (build1 (VIEW_CONVERT_EXPR,
1067 TREE_TYPE (TREE_OPERAND (orig_lhs, 0)),
1070 orig_lhs = TREE_OPERAND (orig_lhs, 0);
1071 if (w && is_gimple_min_invariant (w))
1075 val.lattice_val = VARYING;
1080 if (val.lattice_val == CONSTANT
1081 && TREE_CODE (orig_lhs) == COMPONENT_REF
1082 && DECL_BIT_FIELD (TREE_OPERAND (orig_lhs, 1)))
1084 tree w = widen_bitfield (val.value, TREE_OPERAND (orig_lhs, 1),
1087 if (w && is_gimple_min_invariant (w))
1091 val.lattice_val = VARYING;
1092 val.value = NULL_TREE;
1093 val.mem_ref = NULL_TREE;
1098 retval = SSA_PROP_NOT_INTERESTING;
1100 /* Set the lattice value of the statement's output. */
1101 if (TREE_CODE (lhs) == SSA_NAME)
1103 /* If STMT is an assignment to an SSA_NAME, we only have one
1105 if (set_lattice_value (lhs, val))
1108 if (val.lattice_val == VARYING)
1109 retval = SSA_PROP_VARYING;
1111 retval = SSA_PROP_INTERESTING;
1114 else if (do_store_ccp && stmt_makes_single_store (stmt))
1116 /* Otherwise, set the names in V_MAY_DEF/V_MUST_DEF operands
1117 to the new constant value and mark the LHS as the memory
1118 reference associated with VAL. */
1123 /* Stores cannot take on an UNDEFINED value. */
1124 if (val.lattice_val == UNDEFINED)
1125 val.lattice_val = UNKNOWN_VAL;
1127 /* Mark VAL as stored in the LHS of this assignment. */
1130 /* Set the value of every VDEF to VAL. */
1132 FOR_EACH_SSA_TREE_OPERAND (vdef, stmt, i, SSA_OP_VIRTUAL_DEFS)
1133 changed |= set_lattice_value (vdef, val);
1135 /* Note that for propagation purposes, we are only interested in
1136 visiting statements that load the exact same memory reference
1137 stored here. Those statements will have the exact same list
1138 of virtual uses, so it is enough to set the output of this
1139 statement to be its first virtual definition. */
1140 *output_p = first_vdef (stmt);
1143 if (val.lattice_val == VARYING)
1144 retval = SSA_PROP_VARYING;
1146 retval = SSA_PROP_INTERESTING;
1154 /* Visit the conditional statement STMT. Return SSA_PROP_INTERESTING
1155 if it can determine which edge will be taken. Otherwise, return
1156 SSA_PROP_VARYING. */
1158 static enum ssa_prop_result
1159 visit_cond_stmt (tree stmt, edge *taken_edge_p)
1164 block = bb_for_stmt (stmt);
1165 val = evaluate_stmt (stmt);
1167 /* Find which edge out of the conditional block will be taken and add it
1168 to the worklist. If no single edge can be determined statically,
1169 return SSA_PROP_VARYING to feed all the outgoing edges to the
1170 propagation engine. */
1171 *taken_edge_p = val.value ? find_taken_edge (block, val.value) : 0;
1173 return SSA_PROP_INTERESTING;
1175 return SSA_PROP_VARYING;
1179 /* Evaluate statement STMT. If the statement produces an output value and
1180 its evaluation changes the lattice value of its output, return
1181 SSA_PROP_INTERESTING and set *OUTPUT_P to the SSA_NAME holding the
1184 If STMT is a conditional branch and we can determine its truth
1185 value, set *TAKEN_EDGE_P accordingly. If STMT produces a varying
1186 value, return SSA_PROP_VARYING. */
1188 static enum ssa_prop_result
1189 ccp_visit_stmt (tree stmt, edge *taken_edge_p, tree *output_p)
1194 if (dump_file && (dump_flags & TDF_DETAILS))
1196 fprintf (dump_file, "\nVisiting statement:\n");
1197 print_generic_stmt (dump_file, stmt, dump_flags);
1198 fprintf (dump_file, "\n");
1201 if (TREE_CODE (stmt) == MODIFY_EXPR)
1203 /* If the statement is an assignment that produces a single
1204 output value, evaluate its RHS to see if the lattice value of
1205 its output has changed. */
1206 return visit_assignment (stmt, output_p);
1208 else if (TREE_CODE (stmt) == COND_EXPR || TREE_CODE (stmt) == SWITCH_EXPR)
1210 /* If STMT is a conditional branch, see if we can determine
1211 which branch will be taken. */
1212 return visit_cond_stmt (stmt, taken_edge_p);
1215 /* Any other kind of statement is not interesting for constant
1216 propagation and, therefore, not worth simulating. */
1217 if (dump_file && (dump_flags & TDF_DETAILS))
1218 fprintf (dump_file, "No interesting values produced. Marked VARYING.\n");
1220 /* Definitions made by statements other than assignments to
1221 SSA_NAMEs represent unknown modifications to their outputs.
1222 Mark them VARYING. */
1223 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
1225 prop_value_t v = { VARYING, NULL_TREE, NULL_TREE };
1226 set_lattice_value (def, v);
1229 return SSA_PROP_VARYING;
1233 /* Main entry point for SSA Conditional Constant Propagation. */
1236 execute_ssa_ccp (bool store_ccp)
1238 do_store_ccp = store_ccp;
1240 ssa_propagate (ccp_visit_stmt, ccp_visit_phi_node);
1248 execute_ssa_ccp (false);
1255 return flag_tree_ccp != 0;
1259 struct tree_opt_pass pass_ccp =
1262 gate_ccp, /* gate */
1263 do_ssa_ccp, /* execute */
1266 0, /* static_pass_number */
1267 TV_TREE_CCP, /* tv_id */
1268 PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */
1269 0, /* properties_provided */
1270 0, /* properties_destroyed */
1271 0, /* todo_flags_start */
1272 TODO_cleanup_cfg | TODO_dump_func | TODO_update_ssa
1273 | TODO_ggc_collect | TODO_verify_ssa
1274 | TODO_verify_stmts, /* todo_flags_finish */
1280 do_ssa_store_ccp (void)
1282 /* If STORE-CCP is not enabled, we just run regular CCP. */
1283 execute_ssa_ccp (flag_tree_store_ccp != 0);
1287 gate_store_ccp (void)
1289 /* STORE-CCP is enabled only with -ftree-store-ccp, but when
1290 -fno-tree-store-ccp is specified, we should run regular CCP.
1291 That's why the pass is enabled with either flag. */
1292 return flag_tree_store_ccp != 0 || flag_tree_ccp != 0;
1296 struct tree_opt_pass pass_store_ccp =
1298 "store_ccp", /* name */
1299 gate_store_ccp, /* gate */
1300 do_ssa_store_ccp, /* execute */
1303 0, /* static_pass_number */
1304 TV_TREE_STORE_CCP, /* tv_id */
1305 PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */
1306 0, /* properties_provided */
1307 0, /* properties_destroyed */
1308 0, /* todo_flags_start */
1309 TODO_dump_func | TODO_update_ssa
1310 | TODO_ggc_collect | TODO_verify_ssa
1312 | TODO_verify_stmts, /* todo_flags_finish */
1316 /* Given a constant value VAL for bitfield FIELD, and a destination
1317 variable VAR, return VAL appropriately widened to fit into VAR. If
1318 FIELD is wider than HOST_WIDE_INT, NULL is returned. */
1321 widen_bitfield (tree val, tree field, tree var)
1323 unsigned HOST_WIDE_INT var_size, field_size;
1325 unsigned HOST_WIDE_INT mask;
1328 /* We can only do this if the size of the type and field and VAL are
1329 all constants representable in HOST_WIDE_INT. */
1330 if (!host_integerp (TYPE_SIZE (TREE_TYPE (var)), 1)
1331 || !host_integerp (DECL_SIZE (field), 1)
1332 || !host_integerp (val, 0))
1335 var_size = tree_low_cst (TYPE_SIZE (TREE_TYPE (var)), 1);
1336 field_size = tree_low_cst (DECL_SIZE (field), 1);
1338 /* Give up if either the bitfield or the variable are too wide. */
1339 if (field_size > HOST_BITS_PER_WIDE_INT || var_size > HOST_BITS_PER_WIDE_INT)
1342 gcc_assert (var_size >= field_size);
1344 /* If the sign bit of the value is not set or the field's type is unsigned,
1345 just mask off the high order bits of the value. */
1346 if (DECL_UNSIGNED (field)
1347 || !(tree_low_cst (val, 0) & (((HOST_WIDE_INT)1) << (field_size - 1))))
1349 /* Zero extension. Build a mask with the lower 'field_size' bits
1350 set and a BIT_AND_EXPR node to clear the high order bits of
1352 for (i = 0, mask = 0; i < field_size; i++)
1353 mask |= ((HOST_WIDE_INT) 1) << i;
1355 wide_val = build2 (BIT_AND_EXPR, TREE_TYPE (var), val,
1356 build_int_cst (TREE_TYPE (var), mask));
1360 /* Sign extension. Create a mask with the upper 'field_size'
1361 bits set and a BIT_IOR_EXPR to set the high order bits of the
1363 for (i = 0, mask = 0; i < (var_size - field_size); i++)
1364 mask |= ((HOST_WIDE_INT) 1) << (var_size - i - 1);
1366 wide_val = build2 (BIT_IOR_EXPR, TREE_TYPE (var), val,
1367 build_int_cst (TREE_TYPE (var), mask));
1370 return fold (wide_val);
1374 /* A subroutine of fold_stmt_r. Attempts to fold *(A+O) to A[X].
1375 BASE is an array type. OFFSET is a byte displacement. ORIG_TYPE
1376 is the desired result type. */
1379 maybe_fold_offset_to_array_ref (tree base, tree offset, tree orig_type)
1381 tree min_idx, idx, elt_offset = integer_zero_node;
1382 tree array_type, elt_type, elt_size;
1384 /* If BASE is an ARRAY_REF, we can pick up another offset (this time
1385 measured in units of the size of elements type) from that ARRAY_REF).
1386 We can't do anything if either is variable.
1388 The case we handle here is *(&A[N]+O). */
1389 if (TREE_CODE (base) == ARRAY_REF)
1391 tree low_bound = array_ref_low_bound (base);
1393 elt_offset = TREE_OPERAND (base, 1);
1394 if (TREE_CODE (low_bound) != INTEGER_CST
1395 || TREE_CODE (elt_offset) != INTEGER_CST)
1398 elt_offset = int_const_binop (MINUS_EXPR, elt_offset, low_bound, 0);
1399 base = TREE_OPERAND (base, 0);
1402 /* Ignore stupid user tricks of indexing non-array variables. */
1403 array_type = TREE_TYPE (base);
1404 if (TREE_CODE (array_type) != ARRAY_TYPE)
1406 elt_type = TREE_TYPE (array_type);
1407 if (!lang_hooks.types_compatible_p (orig_type, elt_type))
1410 /* If OFFSET and ELT_OFFSET are zero, we don't care about the size of the
1411 element type (so we can use the alignment if it's not constant).
1412 Otherwise, compute the offset as an index by using a division. If the
1413 division isn't exact, then don't do anything. */
1414 elt_size = TYPE_SIZE_UNIT (elt_type);
1415 if (integer_zerop (offset))
1417 if (TREE_CODE (elt_size) != INTEGER_CST)
1418 elt_size = size_int (TYPE_ALIGN (elt_type));
1420 idx = integer_zero_node;
1424 unsigned HOST_WIDE_INT lquo, lrem;
1425 HOST_WIDE_INT hquo, hrem;
1427 if (TREE_CODE (elt_size) != INTEGER_CST
1428 || div_and_round_double (TRUNC_DIV_EXPR, 1,
1429 TREE_INT_CST_LOW (offset),
1430 TREE_INT_CST_HIGH (offset),
1431 TREE_INT_CST_LOW (elt_size),
1432 TREE_INT_CST_HIGH (elt_size),
1433 &lquo, &hquo, &lrem, &hrem)
1437 idx = build_int_cst_wide (NULL_TREE, lquo, hquo);
1440 /* Assume the low bound is zero. If there is a domain type, get the
1441 low bound, if any, convert the index into that type, and add the
1443 min_idx = integer_zero_node;
1444 if (TYPE_DOMAIN (array_type))
1446 if (TYPE_MIN_VALUE (TYPE_DOMAIN (array_type)))
1447 min_idx = TYPE_MIN_VALUE (TYPE_DOMAIN (array_type));
1449 min_idx = fold_convert (TYPE_DOMAIN (array_type), min_idx);
1451 if (TREE_CODE (min_idx) != INTEGER_CST)
1454 idx = fold_convert (TYPE_DOMAIN (array_type), idx);
1455 elt_offset = fold_convert (TYPE_DOMAIN (array_type), elt_offset);
1458 if (!integer_zerop (min_idx))
1459 idx = int_const_binop (PLUS_EXPR, idx, min_idx, 0);
1460 if (!integer_zerop (elt_offset))
1461 idx = int_const_binop (PLUS_EXPR, idx, elt_offset, 0);
1463 return build (ARRAY_REF, orig_type, base, idx, min_idx,
1464 size_int (tree_low_cst (elt_size, 1)
1465 / (TYPE_ALIGN_UNIT (elt_type))));
1469 /* A subroutine of fold_stmt_r. Attempts to fold *(S+O) to S.X.
1470 BASE is a record type. OFFSET is a byte displacement. ORIG_TYPE
1471 is the desired result type. */
1472 /* ??? This doesn't handle class inheritance. */
1475 maybe_fold_offset_to_component_ref (tree record_type, tree base, tree offset,
1476 tree orig_type, bool base_is_ptr)
1478 tree f, t, field_type, tail_array_field, field_offset;
1480 if (TREE_CODE (record_type) != RECORD_TYPE
1481 && TREE_CODE (record_type) != UNION_TYPE
1482 && TREE_CODE (record_type) != QUAL_UNION_TYPE)
1485 /* Short-circuit silly cases. */
1486 if (lang_hooks.types_compatible_p (record_type, orig_type))
1489 tail_array_field = NULL_TREE;
1490 for (f = TYPE_FIELDS (record_type); f ; f = TREE_CHAIN (f))
1494 if (TREE_CODE (f) != FIELD_DECL)
1496 if (DECL_BIT_FIELD (f))
1499 field_offset = byte_position (f);
1500 if (TREE_CODE (field_offset) != INTEGER_CST)
1503 /* ??? Java creates "interesting" fields for representing base classes.
1504 They have no name, and have no context. With no context, we get into
1505 trouble with nonoverlapping_component_refs_p. Skip them. */
1506 if (!DECL_FIELD_CONTEXT (f))
1509 /* The previous array field isn't at the end. */
1510 tail_array_field = NULL_TREE;
1512 /* Check to see if this offset overlaps with the field. */
1513 cmp = tree_int_cst_compare (field_offset, offset);
1517 field_type = TREE_TYPE (f);
1519 /* Here we exactly match the offset being checked. If the types match,
1520 then we can return that field. */
1522 && lang_hooks.types_compatible_p (orig_type, field_type))
1525 base = build1 (INDIRECT_REF, record_type, base);
1526 t = build (COMPONENT_REF, field_type, base, f, NULL_TREE);
1530 /* Don't care about offsets into the middle of scalars. */
1531 if (!AGGREGATE_TYPE_P (field_type))
1534 /* Check for array at the end of the struct. This is often
1535 used as for flexible array members. We should be able to
1536 turn this into an array access anyway. */
1537 if (TREE_CODE (field_type) == ARRAY_TYPE)
1538 tail_array_field = f;
1540 /* Check the end of the field against the offset. */
1541 if (!DECL_SIZE_UNIT (f)
1542 || TREE_CODE (DECL_SIZE_UNIT (f)) != INTEGER_CST)
1544 t = int_const_binop (MINUS_EXPR, offset, field_offset, 1);
1545 if (!tree_int_cst_lt (t, DECL_SIZE_UNIT (f)))
1548 /* If we matched, then set offset to the displacement into
1554 if (!tail_array_field)
1557 f = tail_array_field;
1558 field_type = TREE_TYPE (f);
1559 offset = int_const_binop (MINUS_EXPR, offset, byte_position (f), 1);
1562 /* If we get here, we've got an aggregate field, and a possibly
1563 nonzero offset into them. Recurse and hope for a valid match. */
1565 base = build1 (INDIRECT_REF, record_type, base);
1566 base = build (COMPONENT_REF, field_type, base, f, NULL_TREE);
1568 t = maybe_fold_offset_to_array_ref (base, offset, orig_type);
1571 return maybe_fold_offset_to_component_ref (field_type, base, offset,
1576 /* A subroutine of fold_stmt_r. Attempt to simplify *(BASE+OFFSET).
1577 Return the simplified expression, or NULL if nothing could be done. */
1580 maybe_fold_stmt_indirect (tree expr, tree base, tree offset)
1584 /* We may well have constructed a double-nested PLUS_EXPR via multiple
1585 substitutions. Fold that down to one. Remove NON_LVALUE_EXPRs that
1586 are sometimes added. */
1589 TREE_OPERAND (expr, 0) = base;
1591 /* One possibility is that the address reduces to a string constant. */
1592 t = fold_read_from_constant_string (expr);
1596 /* Add in any offset from a PLUS_EXPR. */
1597 if (TREE_CODE (base) == PLUS_EXPR)
1601 offset2 = TREE_OPERAND (base, 1);
1602 if (TREE_CODE (offset2) != INTEGER_CST)
1604 base = TREE_OPERAND (base, 0);
1606 offset = int_const_binop (PLUS_EXPR, offset, offset2, 1);
1609 if (TREE_CODE (base) == ADDR_EXPR)
1611 /* Strip the ADDR_EXPR. */
1612 base = TREE_OPERAND (base, 0);
1614 /* Fold away CONST_DECL to its value, if the type is scalar. */
1615 if (TREE_CODE (base) == CONST_DECL
1616 && is_gimple_min_invariant (DECL_INITIAL (base)))
1617 return DECL_INITIAL (base);
1619 /* Try folding *(&B+O) to B[X]. */
1620 t = maybe_fold_offset_to_array_ref (base, offset, TREE_TYPE (expr));
1624 /* Try folding *(&B+O) to B.X. */
1625 t = maybe_fold_offset_to_component_ref (TREE_TYPE (base), base, offset,
1626 TREE_TYPE (expr), false);
1630 /* Fold *&B to B. We can only do this if EXPR is the same type
1631 as BASE. We can't do this if EXPR is the element type of an array
1632 and BASE is the array. */
1633 if (integer_zerop (offset)
1634 && lang_hooks.types_compatible_p (TREE_TYPE (base),
1640 /* We can get here for out-of-range string constant accesses,
1641 such as "_"[3]. Bail out of the entire substitution search
1642 and arrange for the entire statement to be replaced by a
1643 call to __builtin_trap. In all likelihood this will all be
1644 constant-folded away, but in the meantime we can't leave with
1645 something that get_expr_operands can't understand. */
1649 if (TREE_CODE (t) == ADDR_EXPR
1650 && TREE_CODE (TREE_OPERAND (t, 0)) == STRING_CST)
1652 /* FIXME: Except that this causes problems elsewhere with dead
1653 code not being deleted, and we die in the rtl expanders
1654 because we failed to remove some ssa_name. In the meantime,
1655 just return zero. */
1656 /* FIXME2: This condition should be signaled by
1657 fold_read_from_constant_string directly, rather than
1658 re-checking for it here. */
1659 return integer_zero_node;
1662 /* Try folding *(B+O) to B->X. Still an improvement. */
1663 if (POINTER_TYPE_P (TREE_TYPE (base)))
1665 t = maybe_fold_offset_to_component_ref (TREE_TYPE (TREE_TYPE (base)),
1667 TREE_TYPE (expr), true);
1673 /* Otherwise we had an offset that we could not simplify. */
1678 /* A subroutine of fold_stmt_r. EXPR is a PLUS_EXPR.
1680 A quaint feature extant in our address arithmetic is that there
1681 can be hidden type changes here. The type of the result need
1682 not be the same as the type of the input pointer.
1684 What we're after here is an expression of the form
1685 (T *)(&array + const)
1686 where the cast doesn't actually exist, but is implicit in the
1687 type of the PLUS_EXPR. We'd like to turn this into
1689 which may be able to propagate further. */
1692 maybe_fold_stmt_addition (tree expr)
1694 tree op0 = TREE_OPERAND (expr, 0);
1695 tree op1 = TREE_OPERAND (expr, 1);
1696 tree ptr_type = TREE_TYPE (expr);
1699 bool subtract = (TREE_CODE (expr) == MINUS_EXPR);
1701 /* We're only interested in pointer arithmetic. */
1702 if (!POINTER_TYPE_P (ptr_type))
1704 /* Canonicalize the integral operand to op1. */
1705 if (INTEGRAL_TYPE_P (TREE_TYPE (op0)))
1709 t = op0, op0 = op1, op1 = t;
1711 /* It had better be a constant. */
1712 if (TREE_CODE (op1) != INTEGER_CST)
1714 /* The first operand should be an ADDR_EXPR. */
1715 if (TREE_CODE (op0) != ADDR_EXPR)
1717 op0 = TREE_OPERAND (op0, 0);
1719 /* If the first operand is an ARRAY_REF, expand it so that we can fold
1720 the offset into it. */
1721 while (TREE_CODE (op0) == ARRAY_REF)
1723 tree array_obj = TREE_OPERAND (op0, 0);
1724 tree array_idx = TREE_OPERAND (op0, 1);
1725 tree elt_type = TREE_TYPE (op0);
1726 tree elt_size = TYPE_SIZE_UNIT (elt_type);
1729 if (TREE_CODE (array_idx) != INTEGER_CST)
1731 if (TREE_CODE (elt_size) != INTEGER_CST)
1734 /* Un-bias the index by the min index of the array type. */
1735 min_idx = TYPE_DOMAIN (TREE_TYPE (array_obj));
1738 min_idx = TYPE_MIN_VALUE (min_idx);
1741 if (TREE_CODE (min_idx) != INTEGER_CST)
1744 array_idx = convert (TREE_TYPE (min_idx), array_idx);
1745 if (!integer_zerop (min_idx))
1746 array_idx = int_const_binop (MINUS_EXPR, array_idx,
1751 /* Convert the index to a byte offset. */
1752 array_idx = convert (sizetype, array_idx);
1753 array_idx = int_const_binop (MULT_EXPR, array_idx, elt_size, 0);
1755 /* Update the operands for the next round, or for folding. */
1756 /* If we're manipulating unsigned types, then folding into negative
1757 values can produce incorrect results. Particularly if the type
1758 is smaller than the width of the pointer. */
1760 && TYPE_UNSIGNED (TREE_TYPE (op1))
1761 && tree_int_cst_lt (array_idx, op1))
1763 op1 = int_const_binop (subtract ? MINUS_EXPR : PLUS_EXPR,
1769 /* If we weren't able to fold the subtraction into another array reference,
1770 canonicalize the integer for passing to the array and component ref
1771 simplification functions. */
1774 if (TYPE_UNSIGNED (TREE_TYPE (op1)))
1776 op1 = fold (build1 (NEGATE_EXPR, TREE_TYPE (op1), op1));
1777 /* ??? In theory fold should always produce another integer. */
1778 if (TREE_CODE (op1) != INTEGER_CST)
1782 ptd_type = TREE_TYPE (ptr_type);
1784 /* At which point we can try some of the same things as for indirects. */
1785 t = maybe_fold_offset_to_array_ref (op0, op1, ptd_type);
1787 t = maybe_fold_offset_to_component_ref (TREE_TYPE (op0), op0, op1,
1790 t = build1 (ADDR_EXPR, ptr_type, t);
1796 /* Subroutine of fold_stmt called via walk_tree. We perform several
1797 simplifications of EXPR_P, mostly having to do with pointer arithmetic. */
1800 fold_stmt_r (tree *expr_p, int *walk_subtrees, void *data)
1802 bool *changed_p = data;
1803 tree expr = *expr_p, t;
1805 /* ??? It'd be nice if walk_tree had a pre-order option. */
1806 switch (TREE_CODE (expr))
1809 t = walk_tree (&TREE_OPERAND (expr, 0), fold_stmt_r, data, NULL);
1814 t = maybe_fold_stmt_indirect (expr, TREE_OPERAND (expr, 0),
1818 /* ??? Could handle ARRAY_REF here, as a variant of INDIRECT_REF.
1819 We'd only want to bother decomposing an existing ARRAY_REF if
1820 the base array is found to have another offset contained within.
1821 Otherwise we'd be wasting time. */
1824 t = walk_tree (&TREE_OPERAND (expr, 0), fold_stmt_r, data, NULL);
1829 /* Set TREE_INVARIANT properly so that the value is properly
1830 considered constant, and so gets propagated as expected. */
1832 recompute_tree_invarant_for_addr_expr (expr);
1837 t = walk_tree (&TREE_OPERAND (expr, 0), fold_stmt_r, data, NULL);
1840 t = walk_tree (&TREE_OPERAND (expr, 1), fold_stmt_r, data, NULL);
1845 t = maybe_fold_stmt_addition (expr);
1849 t = walk_tree (&TREE_OPERAND (expr, 0), fold_stmt_r, data, NULL);
1854 /* Make sure the FIELD_DECL is actually a field in the type on the lhs.
1855 We've already checked that the records are compatible, so we should
1856 come up with a set of compatible fields. */
1858 tree expr_record = TREE_TYPE (TREE_OPERAND (expr, 0));
1859 tree expr_field = TREE_OPERAND (expr, 1);
1861 if (DECL_FIELD_CONTEXT (expr_field) != TYPE_MAIN_VARIANT (expr_record))
1863 expr_field = find_compatible_field (expr_record, expr_field);
1864 TREE_OPERAND (expr, 1) = expr_field;
1883 /* Return the string length of ARG in LENGTH. If ARG is an SSA name variable,
1884 follow its use-def chains. If LENGTH is not NULL and its value is not
1885 equal to the length we determine, or if we are unable to determine the
1886 length, return false. VISITED is a bitmap of visited variables. */
1889 get_strlen (tree arg, tree *length, bitmap visited)
1891 tree var, def_stmt, val;
1893 if (TREE_CODE (arg) != SSA_NAME)
1895 val = c_strlen (arg, 1);
1899 if (*length && simple_cst_equal (val, *length) != 1)
1906 /* If we were already here, break the infinite cycle. */
1907 if (bitmap_bit_p (visited, SSA_NAME_VERSION (arg)))
1909 bitmap_set_bit (visited, SSA_NAME_VERSION (arg));
1912 def_stmt = SSA_NAME_DEF_STMT (var);
1914 switch (TREE_CODE (def_stmt))
1920 /* The RHS of the statement defining VAR must either have a
1921 constant length or come from another SSA_NAME with a constant
1923 rhs = TREE_OPERAND (def_stmt, 1);
1925 if (TREE_CODE (rhs) == SSA_NAME)
1926 return get_strlen (rhs, length, visited);
1928 /* See if the RHS is a constant length. */
1929 len = c_strlen (rhs, 1);
1932 if (*length && simple_cst_equal (len, *length) != 1)
1944 /* All the arguments of the PHI node must have the same constant
1948 for (i = 0; i < PHI_NUM_ARGS (def_stmt); i++)
1950 tree arg = PHI_ARG_DEF (def_stmt, i);
1952 /* If this PHI has itself as an argument, we cannot
1953 determine the string length of this argument. However,
1954 if we can find a constant string length for the other
1955 PHI args then we can still be sure that this is a
1956 constant string length. So be optimistic and just
1957 continue with the next argument. */
1958 if (arg == PHI_RESULT (def_stmt))
1961 if (!get_strlen (arg, length, visited))
1977 /* Fold builtin call FN in statement STMT. If it cannot be folded into a
1978 constant, return NULL_TREE. Otherwise, return its constant value. */
1981 ccp_fold_builtin (tree stmt, tree fn)
1983 tree result, strlen_val[2];
1984 tree callee, arglist, a;
1989 ignore = TREE_CODE (stmt) != MODIFY_EXPR;
1991 /* First try the generic builtin folder. If that succeeds, return the
1993 callee = get_callee_fndecl (fn);
1994 arglist = TREE_OPERAND (fn, 1);
1995 result = fold_builtin (callee, arglist, ignore);
1999 STRIP_NOPS (result);
2003 /* Ignore MD builtins. */
2004 if (DECL_BUILT_IN_CLASS (callee) == BUILT_IN_MD)
2007 /* If the builtin could not be folded, and it has no argument list,
2012 /* Limit the work only for builtins we know how to simplify. */
2013 switch (DECL_FUNCTION_CODE (callee))
2015 case BUILT_IN_STRLEN:
2016 case BUILT_IN_FPUTS:
2017 case BUILT_IN_FPUTS_UNLOCKED:
2020 case BUILT_IN_STRCPY:
2021 case BUILT_IN_STRNCPY:
2028 /* Try to use the dataflow information gathered by the CCP process. */
2029 visited = BITMAP_ALLOC (NULL);
2031 memset (strlen_val, 0, sizeof (strlen_val));
2032 for (i = 0, a = arglist;
2034 i++, strlen_arg >>= 1, a = TREE_CHAIN (a))
2037 bitmap_clear (visited);
2038 if (!get_strlen (TREE_VALUE (a), &strlen_val[i], visited))
2039 strlen_val[i] = NULL_TREE;
2042 BITMAP_FREE (visited);
2045 switch (DECL_FUNCTION_CODE (callee))
2047 case BUILT_IN_STRLEN:
2050 tree new = fold_convert (TREE_TYPE (fn), strlen_val[0]);
2052 /* If the result is not a valid gimple value, or not a cast
2053 of a valid gimple value, then we can not use the result. */
2054 if (is_gimple_val (new)
2055 || (is_gimple_cast (new)
2056 && is_gimple_val (TREE_OPERAND (new, 0))))
2061 case BUILT_IN_STRCPY:
2062 if (strlen_val[1] && is_gimple_val (strlen_val[1]))
2064 tree fndecl = get_callee_fndecl (fn);
2065 tree arglist = TREE_OPERAND (fn, 1);
2066 result = fold_builtin_strcpy (fndecl, arglist, strlen_val[1]);
2070 case BUILT_IN_STRNCPY:
2071 if (strlen_val[1] && is_gimple_val (strlen_val[1]))
2073 tree fndecl = get_callee_fndecl (fn);
2074 tree arglist = TREE_OPERAND (fn, 1);
2075 result = fold_builtin_strncpy (fndecl, arglist, strlen_val[1]);
2079 case BUILT_IN_FPUTS:
2080 result = fold_builtin_fputs (arglist,
2081 TREE_CODE (stmt) != MODIFY_EXPR, 0,
2085 case BUILT_IN_FPUTS_UNLOCKED:
2086 result = fold_builtin_fputs (arglist,
2087 TREE_CODE (stmt) != MODIFY_EXPR, 1,
2095 if (result && ignore)
2096 result = fold_ignored_result (result);
2101 /* Fold the statement pointed by STMT_P. In some cases, this function may
2102 replace the whole statement with a new one. Returns true iff folding
2103 makes any changes. */
2106 fold_stmt (tree *stmt_p)
2108 tree rhs, result, stmt;
2109 bool changed = false;
2113 /* If we replaced constants and the statement makes pointer dereferences,
2114 then we may need to fold instances of *&VAR into VAR, etc. */
2115 if (walk_tree (stmt_p, fold_stmt_r, &changed, NULL))
2118 = build_function_call_expr (implicit_built_in_decls[BUILT_IN_TRAP],
2123 rhs = get_rhs (stmt);
2128 if (TREE_CODE (rhs) == CALL_EXPR)
2132 /* Check for builtins that CCP can handle using information not
2133 available in the generic fold routines. */
2134 callee = get_callee_fndecl (rhs);
2135 if (callee && DECL_BUILT_IN (callee))
2136 result = ccp_fold_builtin (stmt, rhs);
2139 /* Check for resolvable OBJ_TYPE_REF. The only sorts we can resolve
2140 here are when we've propagated the address of a decl into the
2142 /* ??? Should perhaps do this in fold proper. However, doing it
2143 there requires that we create a new CALL_EXPR, and that requires
2144 copying EH region info to the new node. Easier to just do it
2145 here where we can just smash the call operand. */
2146 callee = TREE_OPERAND (rhs, 0);
2147 if (TREE_CODE (callee) == OBJ_TYPE_REF
2148 && lang_hooks.fold_obj_type_ref
2149 && TREE_CODE (OBJ_TYPE_REF_OBJECT (callee)) == ADDR_EXPR
2150 && DECL_P (TREE_OPERAND
2151 (OBJ_TYPE_REF_OBJECT (callee), 0)))
2155 /* ??? Caution: Broken ADDR_EXPR semantics means that
2156 looking at the type of the operand of the addr_expr
2157 can yield an array type. See silly exception in
2158 check_pointer_types_r. */
2160 t = TREE_TYPE (TREE_TYPE (OBJ_TYPE_REF_OBJECT (callee)));
2161 t = lang_hooks.fold_obj_type_ref (callee, t);
2164 TREE_OPERAND (rhs, 0) = t;
2171 /* If we couldn't fold the RHS, hand over to the generic fold routines. */
2172 if (result == NULL_TREE)
2173 result = fold (rhs);
2175 /* Strip away useless type conversions. Both the NON_LVALUE_EXPR that
2176 may have been added by fold, and "useless" type conversions that might
2177 now be apparent due to propagation. */
2178 STRIP_USELESS_TYPE_CONVERSION (result);
2181 changed |= set_rhs (stmt_p, result);
2187 /* Convert EXPR into a GIMPLE value suitable for substitution on the
2188 RHS of an assignment. Insert the necessary statements before
2192 convert_to_gimple_builtin (block_stmt_iterator *si_p, tree expr)
2194 tree_stmt_iterator ti;
2195 tree stmt = bsi_stmt (*si_p);
2196 tree tmp, stmts = NULL;
2198 push_gimplify_context ();
2199 tmp = get_initialized_tmp_var (expr, &stmts, NULL);
2200 pop_gimplify_context (NULL);
2202 if (EXPR_HAS_LOCATION (stmt))
2203 annotate_all_with_locus (&stmts, EXPR_LOCATION (stmt));
2205 /* The replacement can expose previously unreferenced variables. */
2206 for (ti = tsi_start (stmts); !tsi_end_p (ti); tsi_next (&ti))
2208 tree new_stmt = tsi_stmt (ti);
2209 find_new_referenced_vars (tsi_stmt_ptr (ti));
2210 bsi_insert_before (si_p, new_stmt, BSI_NEW_STMT);
2211 mark_new_vars_to_rename (bsi_stmt (*si_p));
2219 /* A simple pass that attempts to fold all builtin functions. This pass
2220 is run after we've propagated as many constants as we can. */
2223 execute_fold_all_builtins (void)
2225 bool cfg_changed = false;
2229 block_stmt_iterator i;
2230 for (i = bsi_start (bb); !bsi_end_p (i); bsi_next (&i))
2232 tree *stmtp = bsi_stmt_ptr (i);
2233 tree call = get_rhs (*stmtp);
2234 tree callee, result;
2236 if (!call || TREE_CODE (call) != CALL_EXPR)
2238 callee = get_callee_fndecl (call);
2239 if (!callee || DECL_BUILT_IN_CLASS (callee) != BUILT_IN_NORMAL)
2242 result = ccp_fold_builtin (*stmtp, call);
2244 switch (DECL_FUNCTION_CODE (callee))
2246 case BUILT_IN_CONSTANT_P:
2247 /* Resolve __builtin_constant_p. If it hasn't been
2248 folded to integer_one_node by now, it's fairly
2249 certain that the value simply isn't constant. */
2250 result = integer_zero_node;
2257 if (dump_file && (dump_flags & TDF_DETAILS))
2259 fprintf (dump_file, "Simplified\n ");
2260 print_generic_stmt (dump_file, *stmtp, dump_flags);
2263 if (!set_rhs (stmtp, result))
2265 result = convert_to_gimple_builtin (&i, result);
2268 bool ok = set_rhs (stmtp, result);
2273 update_stmt (*stmtp);
2274 if (maybe_clean_eh_stmt (*stmtp)
2275 && tree_purge_dead_eh_edges (bb))
2278 if (dump_file && (dump_flags & TDF_DETAILS))
2280 fprintf (dump_file, "to\n ");
2281 print_generic_stmt (dump_file, *stmtp, dump_flags);
2282 fprintf (dump_file, "\n");
2287 /* Delete unreachable blocks. */
2289 cleanup_tree_cfg ();
2293 struct tree_opt_pass pass_fold_builtins =
2297 execute_fold_all_builtins, /* execute */
2300 0, /* static_pass_number */
2302 PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */
2303 0, /* properties_provided */
2304 0, /* properties_destroyed */
2305 0, /* todo_flags_start */
2308 | TODO_update_ssa, /* todo_flags_finish */