1 /* Alias analysis for GNU C
2 Copyright (C) 1997, 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
3 Contributed by John Carr (jfc@mit.edu).
5 This file is part of GNU CC.
7 GNU CC 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 2, or (at your option)
12 GNU CC 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 GNU CC; see the file COPYING. If not, write to
19 the Free Software Foundation, 59 Temple Place - Suite 330,
20 Boston, MA 02111-1307, USA. */
30 #include "hard-reg-set.h"
31 #include "basic-block.h"
36 #include "splay-tree.h"
39 /* The alias sets assigned to MEMs assist the back-end in determining
40 which MEMs can alias which other MEMs. In general, two MEMs in
41 different alias sets cannot alias each other, with one important
42 exception. Consider something like:
44 struct S {int i; double d; };
46 a store to an `S' can alias something of either type `int' or type
47 `double'. (However, a store to an `int' cannot alias a `double'
48 and vice versa.) We indicate this via a tree structure that looks
56 (The arrows are directed and point downwards.)
57 In this situation we say the alias set for `struct S' is the
58 `superset' and that those for `int' and `double' are `subsets'.
60 To see whether two alias sets can point to the same memory, we must
61 see if either alias set is a subset of the other. We need not trace
62 past immediate decendents, however, since we propagate all
63 grandchildren up one level.
65 Alias set zero is implicitly a superset of all other alias sets.
66 However, this is no actual entry for alias set zero. It is an
67 error to attempt to explicitly construct a subset of zero. */
69 typedef struct alias_set_entry
71 /* The alias set number, as stored in MEM_ALIAS_SET. */
72 HOST_WIDE_INT alias_set
;
74 /* The children of the alias set. These are not just the immediate
75 children, but, in fact, all decendents. So, if we have:
77 struct T { struct S s; float f; }
79 continuing our example above, the children here will be all of
80 `int', `double', `float', and `struct S'. */
83 /* Nonzero if would have a child of zero: this effectively makes this
84 alias set the same as alias set zero. */
88 static int rtx_equal_for_memref_p
PARAMS ((rtx
, rtx
));
89 static rtx find_symbolic_term
PARAMS ((rtx
));
90 rtx get_addr
PARAMS ((rtx
));
91 static int memrefs_conflict_p
PARAMS ((int, rtx
, int, rtx
,
93 static void record_set
PARAMS ((rtx
, rtx
, void *));
94 static rtx find_base_term
PARAMS ((rtx
));
95 static int base_alias_check
PARAMS ((rtx
, rtx
, enum machine_mode
,
97 static int handled_component_p
PARAMS ((tree
));
98 static int can_address_p
PARAMS ((tree
));
99 static rtx find_base_value
PARAMS ((rtx
));
100 static int mems_in_disjoint_alias_sets_p
PARAMS ((rtx
, rtx
));
101 static int insert_subset_children
PARAMS ((splay_tree_node
, void*));
102 static tree find_base_decl
PARAMS ((tree
));
103 static alias_set_entry get_alias_set_entry
PARAMS ((HOST_WIDE_INT
));
104 static rtx fixed_scalar_and_varying_struct_p
PARAMS ((rtx
, rtx
, rtx
, rtx
,
105 int (*) (rtx
, int)));
106 static int aliases_everything_p
PARAMS ((rtx
));
107 static int write_dependence_p
PARAMS ((rtx
, rtx
, int));
108 static int nonlocal_mentioned_p
PARAMS ((rtx
));
110 /* Set up all info needed to perform alias analysis on memory references. */
112 /* Returns the size in bytes of the mode of X. */
113 #define SIZE_FOR_MODE(X) (GET_MODE_SIZE (GET_MODE (X)))
115 /* Returns nonzero if MEM1 and MEM2 do not alias because they are in
116 different alias sets. We ignore alias sets in functions making use
117 of variable arguments because the va_arg macros on some systems are
119 #define DIFFERENT_ALIAS_SETS_P(MEM1, MEM2) \
120 mems_in_disjoint_alias_sets_p (MEM1, MEM2)
122 /* Cap the number of passes we make over the insns propagating alias
123 information through set chains. 10 is a completely arbitrary choice. */
124 #define MAX_ALIAS_LOOP_PASSES 10
126 /* reg_base_value[N] gives an address to which register N is related.
127 If all sets after the first add or subtract to the current value
128 or otherwise modify it so it does not point to a different top level
129 object, reg_base_value[N] is equal to the address part of the source
132 A base address can be an ADDRESS, SYMBOL_REF, or LABEL_REF. ADDRESS
133 expressions represent certain special values: function arguments and
134 the stack, frame, and argument pointers.
136 The contents of an ADDRESS is not normally used, the mode of the
137 ADDRESS determines whether the ADDRESS is a function argument or some
138 other special value. Pointer equality, not rtx_equal_p, determines whether
139 two ADDRESS expressions refer to the same base address.
141 The only use of the contents of an ADDRESS is for determining if the
142 current function performs nonlocal memory memory references for the
143 purposes of marking the function as a constant function. */
145 static rtx
*reg_base_value
;
146 static rtx
*new_reg_base_value
;
147 static unsigned int reg_base_value_size
; /* size of reg_base_value array */
149 #define REG_BASE_VALUE(X) \
150 (REGNO (X) < reg_base_value_size \
151 ? reg_base_value[REGNO (X)] : 0)
153 /* Vector of known invariant relationships between registers. Set in
154 loop unrolling. Indexed by register number, if nonzero the value
155 is an expression describing this register in terms of another.
157 The length of this array is REG_BASE_VALUE_SIZE.
159 Because this array contains only pseudo registers it has no effect
161 static rtx
*alias_invariant
;
163 /* Vector indexed by N giving the initial (unchanging) value known for
164 pseudo-register N. This array is initialized in
165 init_alias_analysis, and does not change until end_alias_analysis
167 rtx
*reg_known_value
;
169 /* Indicates number of valid entries in reg_known_value. */
170 static unsigned int reg_known_value_size
;
172 /* Vector recording for each reg_known_value whether it is due to a
173 REG_EQUIV note. Future passes (viz., reload) may replace the
174 pseudo with the equivalent expression and so we account for the
175 dependences that would be introduced if that happens.
177 The REG_EQUIV notes created in assign_parms may mention the arg
178 pointer, and there are explicit insns in the RTL that modify the
179 arg pointer. Thus we must ensure that such insns don't get
180 scheduled across each other because that would invalidate the
181 REG_EQUIV notes. One could argue that the REG_EQUIV notes are
182 wrong, but solving the problem in the scheduler will likely give
183 better code, so we do it here. */
184 char *reg_known_equiv_p
;
186 /* True when scanning insns from the start of the rtl to the
187 NOTE_INSN_FUNCTION_BEG note. */
188 static int copying_arguments
;
190 /* The splay-tree used to store the various alias set entries. */
191 static splay_tree alias_sets
;
193 /* Returns a pointer to the alias set entry for ALIAS_SET, if there is
194 such an entry, or NULL otherwise. */
196 static alias_set_entry
197 get_alias_set_entry (alias_set
)
198 HOST_WIDE_INT alias_set
;
201 = splay_tree_lookup (alias_sets
, (splay_tree_key
) alias_set
);
203 return sn
!= 0 ? ((alias_set_entry
) sn
->value
) : 0;
206 /* Returns nonzero if the alias sets for MEM1 and MEM2 are such that
207 the two MEMs cannot alias each other. */
210 mems_in_disjoint_alias_sets_p (mem1
, mem2
)
214 #ifdef ENABLE_CHECKING
215 /* Perform a basic sanity check. Namely, that there are no alias sets
216 if we're not using strict aliasing. This helps to catch bugs
217 whereby someone uses PUT_CODE, but doesn't clear MEM_ALIAS_SET, or
218 where a MEM is allocated in some way other than by the use of
219 gen_rtx_MEM, and the MEM_ALIAS_SET is not cleared. If we begin to
220 use alias sets to indicate that spilled registers cannot alias each
221 other, we might need to remove this check. */
222 if (! flag_strict_aliasing
223 && (MEM_ALIAS_SET (mem1
) != 0 || MEM_ALIAS_SET (mem2
) != 0))
227 return ! alias_sets_conflict_p (MEM_ALIAS_SET (mem1
), MEM_ALIAS_SET (mem2
));
230 /* Insert the NODE into the splay tree given by DATA. Used by
231 record_alias_subset via splay_tree_foreach. */
234 insert_subset_children (node
, data
)
235 splay_tree_node node
;
238 splay_tree_insert ((splay_tree
) data
, node
->key
, node
->value
);
243 /* Return 1 if the two specified alias sets may conflict. */
246 alias_sets_conflict_p (set1
, set2
)
247 HOST_WIDE_INT set1
, set2
;
251 /* If have no alias set information for one of the operands, we have
252 to assume it can alias anything. */
253 if (set1
== 0 || set2
== 0
254 /* If the two alias sets are the same, they may alias. */
258 /* See if the first alias set is a subset of the second. */
259 ase
= get_alias_set_entry (set1
);
261 && (ase
->has_zero_child
262 || splay_tree_lookup (ase
->children
,
263 (splay_tree_key
) set2
)))
266 /* Now do the same, but with the alias sets reversed. */
267 ase
= get_alias_set_entry (set2
);
269 && (ase
->has_zero_child
270 || splay_tree_lookup (ase
->children
,
271 (splay_tree_key
) set1
)))
274 /* The two alias sets are distinct and neither one is the
275 child of the other. Therefore, they cannot alias. */
279 /* Set the alias set of MEM to SET. */
282 set_mem_alias_set (mem
, set
)
286 /* We would like to do this test but can't yet since when converting a
287 REG to a MEM, the alias set field is undefined. */
289 /* If the new and old alias sets don't conflict, something is wrong. */
290 if (!alias_sets_conflict_p (set
, MEM_ALIAS_SET (mem
)))
294 MEM_ALIAS_SET (mem
) = set
;
297 /* Return 1 if TYPE is a RECORD_TYPE, UNION_TYPE, or QUAL_UNION_TYPE and has
298 has any readonly fields. If any of the fields have types that
299 contain readonly fields, return true as well. */
302 readonly_fields_p (type
)
307 if (TREE_CODE (type
) != RECORD_TYPE
&& TREE_CODE (type
) != UNION_TYPE
308 && TREE_CODE (type
) != QUAL_UNION_TYPE
)
311 for (field
= TYPE_FIELDS (type
); field
!= 0; field
= TREE_CHAIN (field
))
312 if (TREE_CODE (field
) == FIELD_DECL
313 && (TREE_READONLY (field
)
314 || readonly_fields_p (TREE_TYPE (field
))))
320 /* Return 1 if any MEM object of type T1 will always conflict (using the
321 dependency routines in this file) with any MEM object of type T2.
322 This is used when allocating temporary storage. If T1 and/or T2 are
323 NULL_TREE, it means we know nothing about the storage. */
326 objects_must_conflict_p (t1
, t2
)
329 /* If neither has a type specified, we don't know if they'll conflict
330 because we may be using them to store objects of various types, for
331 example the argument and local variables areas of inlined functions. */
332 if (t1
== 0 && t2
== 0)
335 /* If one or the other has readonly fields or is readonly,
336 then they may not conflict. */
337 if ((t1
!= 0 && readonly_fields_p (t1
))
338 || (t2
!= 0 && readonly_fields_p (t2
))
339 || (t1
!= 0 && TYPE_READONLY (t1
))
340 || (t2
!= 0 && TYPE_READONLY (t2
)))
343 /* If they are the same type, they must conflict. */
345 /* Likewise if both are volatile. */
346 || (t1
!= 0 && TYPE_VOLATILE (t1
) && t2
!= 0 && TYPE_VOLATILE (t2
)))
349 /* If one is aggregate and the other is scalar then they may not
351 if ((t1
!= 0 && AGGREGATE_TYPE_P (t1
))
352 != (t2
!= 0 && AGGREGATE_TYPE_P (t2
)))
355 /* Otherwise they conflict only if the alias sets conflict. */
356 return alias_sets_conflict_p (t1
? get_alias_set (t1
) : 0,
357 t2
? get_alias_set (t2
) : 0);
360 /* T is an expression with pointer type. Find the DECL on which this
361 expression is based. (For example, in `a[i]' this would be `a'.)
362 If there is no such DECL, or a unique decl cannot be determined,
363 NULL_TREE is retured. */
371 if (t
== 0 || t
== error_mark_node
|| ! POINTER_TYPE_P (TREE_TYPE (t
)))
374 /* If this is a declaration, return it. */
375 if (TREE_CODE_CLASS (TREE_CODE (t
)) == 'd')
378 /* Handle general expressions. It would be nice to deal with
379 COMPONENT_REFs here. If we could tell that `a' and `b' were the
380 same, then `a->f' and `b->f' are also the same. */
381 switch (TREE_CODE_CLASS (TREE_CODE (t
)))
384 return find_base_decl (TREE_OPERAND (t
, 0));
387 /* Return 0 if found in neither or both are the same. */
388 d0
= find_base_decl (TREE_OPERAND (t
, 0));
389 d1
= find_base_decl (TREE_OPERAND (t
, 1));
400 d0
= find_base_decl (TREE_OPERAND (t
, 0));
401 d1
= find_base_decl (TREE_OPERAND (t
, 1));
402 d2
= find_base_decl (TREE_OPERAND (t
, 2));
404 /* Set any nonzero values from the last, then from the first. */
405 if (d1
== 0) d1
= d2
;
406 if (d0
== 0) d0
= d1
;
407 if (d1
== 0) d1
= d0
;
408 if (d2
== 0) d2
= d1
;
410 /* At this point all are nonzero or all are zero. If all three are the
411 same, return it. Otherwise, return zero. */
412 return (d0
== d1
&& d1
== d2
) ? d0
: 0;
419 /* Return 1 if T is an expression that get_inner_reference handles. */
422 handled_component_p (t
)
425 switch (TREE_CODE (t
))
430 case ARRAY_RANGE_REF
:
431 case NON_LVALUE_EXPR
:
436 return (TYPE_MODE (TREE_TYPE (t
))
437 == TYPE_MODE (TREE_TYPE (TREE_OPERAND (t
, 0))));
444 /* Return 1 if all the nested component references handled by
445 get_inner_reference in T are such that we can address the object in T. */
451 /* If we're at the end, it is vacuously addressable. */
452 if (! handled_component_p (t
))
455 /* Bitfields are never addressable. */
456 else if (TREE_CODE (t
) == BIT_FIELD_REF
)
459 else if (TREE_CODE (t
) == COMPONENT_REF
460 && ! DECL_NONADDRESSABLE_P (TREE_OPERAND (t
, 1))
461 && can_address_p (TREE_OPERAND (t
, 0)))
464 else if ((TREE_CODE (t
) == ARRAY_REF
|| TREE_CODE (t
) == ARRAY_RANGE_REF
)
465 && ! TYPE_NONALIASED_COMPONENT (TREE_TYPE (TREE_OPERAND (t
, 0)))
466 && can_address_p (TREE_OPERAND (t
, 0)))
472 /* Return the alias set for T, which may be either a type or an
473 expression. Call language-specific routine for help, if needed. */
482 /* If we're not doing any alias analysis, just assume everything
483 aliases everything else. Also return 0 if this or its type is
485 if (! flag_strict_aliasing
|| t
== error_mark_node
487 && (TREE_TYPE (t
) == 0 || TREE_TYPE (t
) == error_mark_node
)))
490 /* We can be passed either an expression or a type. This and the
491 language-specific routine may make mutually-recursive calls to
492 each other to figure out what to do. At each juncture, we see if
493 this is a tree that the language may need to handle specially.
494 First handle things that aren't types and start by removing nops
495 since we care only about the actual object. */
498 while (TREE_CODE (t
) == NOP_EXPR
|| TREE_CODE (t
) == CONVERT_EXPR
499 || TREE_CODE (t
) == NON_LVALUE_EXPR
)
500 t
= TREE_OPERAND (t
, 0);
502 /* Now give the language a chance to do something but record what we
503 gave it this time. */
505 if ((set
= lang_get_alias_set (t
)) != -1)
508 /* Now loop the same way as get_inner_reference and get the alias
509 set to use. Pick up the outermost object that we could have
511 while (handled_component_p (t
) && ! can_address_p (t
))
512 t
= TREE_OPERAND (t
, 0);
514 if (TREE_CODE (t
) == INDIRECT_REF
)
516 /* Check for accesses through restrict-qualified pointers. */
517 tree decl
= find_base_decl (TREE_OPERAND (t
, 0));
519 if (decl
&& DECL_POINTER_ALIAS_SET_KNOWN_P (decl
))
520 /* We use the alias set indicated in the declaration. */
521 return DECL_POINTER_ALIAS_SET (decl
);
523 /* If we have an INDIRECT_REF via a void pointer, we don't
524 know anything about what that might alias. */
525 if (TREE_CODE (TREE_TYPE (t
)) == VOID_TYPE
)
529 /* If we've already determined the alias set for this decl, just
530 return it. This is necessary for C++ anonymous unions, whose
531 component variables don't look like union members (boo!). */
532 if (TREE_CODE (t
) == VAR_DECL
533 && DECL_RTL_SET_P (t
) && GET_CODE (DECL_RTL (t
)) == MEM
)
534 return MEM_ALIAS_SET (DECL_RTL (t
));
536 /* Give the language another chance to do something special. */
538 && (set
= lang_get_alias_set (t
)) != -1)
541 /* Now all we care about is the type. */
545 /* Variant qualifiers don't affect the alias set, so get the main
546 variant. If this is a type with a known alias set, return it. */
547 t
= TYPE_MAIN_VARIANT (t
);
548 if (TYPE_P (t
) && TYPE_ALIAS_SET_KNOWN_P (t
))
549 return TYPE_ALIAS_SET (t
);
551 /* See if the language has special handling for this type. */
552 if ((set
= lang_get_alias_set (t
)) != -1)
554 /* If the alias set is now known, we are done. */
555 if (TYPE_ALIAS_SET_KNOWN_P (t
))
556 return TYPE_ALIAS_SET (t
);
559 /* There are no objects of FUNCTION_TYPE, so there's no point in
560 using up an alias set for them. (There are, of course, pointers
561 and references to functions, but that's different.) */
562 else if (TREE_CODE (t
) == FUNCTION_TYPE
)
565 /* Otherwise make a new alias set for this type. */
566 set
= new_alias_set ();
568 TYPE_ALIAS_SET (t
) = set
;
570 /* If this is an aggregate type, we must record any component aliasing
572 if (AGGREGATE_TYPE_P (t
) || TREE_CODE (t
) == COMPLEX_TYPE
)
573 record_component_aliases (t
);
578 /* Return a brand-new alias set. */
583 static HOST_WIDE_INT last_alias_set
;
585 if (flag_strict_aliasing
)
586 return ++last_alias_set
;
591 /* Indicate that things in SUBSET can alias things in SUPERSET, but
592 not vice versa. For example, in C, a store to an `int' can alias a
593 structure containing an `int', but not vice versa. Here, the
594 structure would be the SUPERSET and `int' the SUBSET. This
595 function should be called only once per SUPERSET/SUBSET pair.
597 It is illegal for SUPERSET to be zero; everything is implicitly a
598 subset of alias set zero. */
601 record_alias_subset (superset
, subset
)
602 HOST_WIDE_INT superset
;
603 HOST_WIDE_INT subset
;
605 alias_set_entry superset_entry
;
606 alias_set_entry subset_entry
;
611 superset_entry
= get_alias_set_entry (superset
);
612 if (superset_entry
== 0)
614 /* Create an entry for the SUPERSET, so that we have a place to
615 attach the SUBSET. */
617 = (alias_set_entry
) xmalloc (sizeof (struct alias_set_entry
));
618 superset_entry
->alias_set
= superset
;
619 superset_entry
->children
620 = splay_tree_new (splay_tree_compare_ints
, 0, 0);
621 superset_entry
->has_zero_child
= 0;
622 splay_tree_insert (alias_sets
, (splay_tree_key
) superset
,
623 (splay_tree_value
) superset_entry
);
627 superset_entry
->has_zero_child
= 1;
630 subset_entry
= get_alias_set_entry (subset
);
631 /* If there is an entry for the subset, enter all of its children
632 (if they are not already present) as children of the SUPERSET. */
635 if (subset_entry
->has_zero_child
)
636 superset_entry
->has_zero_child
= 1;
638 splay_tree_foreach (subset_entry
->children
, insert_subset_children
,
639 superset_entry
->children
);
642 /* Enter the SUBSET itself as a child of the SUPERSET. */
643 splay_tree_insert (superset_entry
->children
,
644 (splay_tree_key
) subset
, 0);
648 /* Record that component types of TYPE, if any, are part of that type for
649 aliasing purposes. For record types, we only record component types
650 for fields that are marked addressable. For array types, we always
651 record the component types, so the front end should not call this
652 function if the individual component aren't addressable. */
655 record_component_aliases (type
)
658 HOST_WIDE_INT superset
= get_alias_set (type
);
664 switch (TREE_CODE (type
))
667 if (! TYPE_NONALIASED_COMPONENT (type
))
668 record_alias_subset (superset
, get_alias_set (TREE_TYPE (type
)));
673 case QUAL_UNION_TYPE
:
674 for (field
= TYPE_FIELDS (type
); field
!= 0; field
= TREE_CHAIN (field
))
675 if (TREE_CODE (field
) == FIELD_DECL
&& ! DECL_NONADDRESSABLE_P (field
))
676 record_alias_subset (superset
, get_alias_set (TREE_TYPE (field
)));
680 record_alias_subset (superset
, get_alias_set (TREE_TYPE (type
)));
688 /* Allocate an alias set for use in storing and reading from the varargs
692 get_varargs_alias_set ()
694 static HOST_WIDE_INT set
= -1;
697 set
= new_alias_set ();
702 /* Likewise, but used for the fixed portions of the frame, e.g., register
706 get_frame_alias_set ()
708 static HOST_WIDE_INT set
= -1;
711 set
= new_alias_set ();
716 /* Inside SRC, the source of a SET, find a base address. */
719 find_base_value (src
)
723 switch (GET_CODE (src
))
731 /* At the start of a function, argument registers have known base
732 values which may be lost later. Returning an ADDRESS
733 expression here allows optimization based on argument values
734 even when the argument registers are used for other purposes. */
735 if (regno
< FIRST_PSEUDO_REGISTER
&& copying_arguments
)
736 return new_reg_base_value
[regno
];
738 /* If a pseudo has a known base value, return it. Do not do this
739 for hard regs since it can result in a circular dependency
740 chain for registers which have values at function entry.
742 The test above is not sufficient because the scheduler may move
743 a copy out of an arg reg past the NOTE_INSN_FUNCTION_BEGIN. */
744 if (regno
>= FIRST_PSEUDO_REGISTER
745 && regno
< reg_base_value_size
746 && reg_base_value
[regno
])
747 return reg_base_value
[regno
];
752 /* Check for an argument passed in memory. Only record in the
753 copying-arguments block; it is too hard to track changes
755 if (copying_arguments
756 && (XEXP (src
, 0) == arg_pointer_rtx
757 || (GET_CODE (XEXP (src
, 0)) == PLUS
758 && XEXP (XEXP (src
, 0), 0) == arg_pointer_rtx
)))
759 return gen_rtx_ADDRESS (VOIDmode
, src
);
764 if (GET_CODE (src
) != PLUS
&& GET_CODE (src
) != MINUS
)
767 /* ... fall through ... */
772 rtx temp
, src_0
= XEXP (src
, 0), src_1
= XEXP (src
, 1);
774 /* If either operand is a REG, then see if we already have
775 a known value for it. */
776 if (GET_CODE (src_0
) == REG
)
778 temp
= find_base_value (src_0
);
783 if (GET_CODE (src_1
) == REG
)
785 temp
= find_base_value (src_1
);
790 /* Guess which operand is the base address:
791 If either operand is a symbol, then it is the base. If
792 either operand is a CONST_INT, then the other is the base. */
793 if (GET_CODE (src_1
) == CONST_INT
|| CONSTANT_P (src_0
))
794 return find_base_value (src_0
);
795 else if (GET_CODE (src_0
) == CONST_INT
|| CONSTANT_P (src_1
))
796 return find_base_value (src_1
);
798 /* This might not be necessary anymore:
799 If either operand is a REG that is a known pointer, then it
801 else if (GET_CODE (src_0
) == REG
&& REG_POINTER (src_0
))
802 return find_base_value (src_0
);
803 else if (GET_CODE (src_1
) == REG
&& REG_POINTER (src_1
))
804 return find_base_value (src_1
);
810 /* The standard form is (lo_sum reg sym) so look only at the
812 return find_base_value (XEXP (src
, 1));
815 /* If the second operand is constant set the base
816 address to the first operand. */
817 if (GET_CODE (XEXP (src
, 1)) == CONST_INT
&& INTVAL (XEXP (src
, 1)) != 0)
818 return find_base_value (XEXP (src
, 0));
822 if (GET_MODE_SIZE (GET_MODE (src
)) < GET_MODE_SIZE (Pmode
))
826 case SIGN_EXTEND
: /* used for NT/Alpha pointers */
828 return find_base_value (XEXP (src
, 0));
837 /* Called from init_alias_analysis indirectly through note_stores. */
839 /* While scanning insns to find base values, reg_seen[N] is nonzero if
840 register N has been set in this function. */
841 static char *reg_seen
;
843 /* Addresses which are known not to alias anything else are identified
844 by a unique integer. */
845 static int unique_id
;
848 record_set (dest
, set
, data
)
850 void *data ATTRIBUTE_UNUSED
;
852 register unsigned regno
;
855 if (GET_CODE (dest
) != REG
)
858 regno
= REGNO (dest
);
860 if (regno
>= reg_base_value_size
)
865 /* A CLOBBER wipes out any old value but does not prevent a previously
866 unset register from acquiring a base address (i.e. reg_seen is not
868 if (GET_CODE (set
) == CLOBBER
)
870 new_reg_base_value
[regno
] = 0;
879 new_reg_base_value
[regno
] = 0;
883 new_reg_base_value
[regno
] = gen_rtx_ADDRESS (Pmode
,
884 GEN_INT (unique_id
++));
888 /* This is not the first set. If the new value is not related to the
889 old value, forget the base value. Note that the following code is
891 extern int x, y; int *p = &x; p += (&y-&x);
892 ANSI C does not allow computing the difference of addresses
893 of distinct top level objects. */
894 if (new_reg_base_value
[regno
])
895 switch (GET_CODE (src
))
899 if (XEXP (src
, 0) != dest
&& XEXP (src
, 1) != dest
)
900 new_reg_base_value
[regno
] = 0;
903 /* If the value we add in the PLUS is also a valid base value,
904 this might be the actual base value, and the original value
907 rtx other
= NULL_RTX
;
909 if (XEXP (src
, 0) == dest
)
910 other
= XEXP (src
, 1);
911 else if (XEXP (src
, 1) == dest
)
912 other
= XEXP (src
, 0);
914 if (! other
|| find_base_value (other
))
915 new_reg_base_value
[regno
] = 0;
919 if (XEXP (src
, 0) != dest
|| GET_CODE (XEXP (src
, 1)) != CONST_INT
)
920 new_reg_base_value
[regno
] = 0;
923 new_reg_base_value
[regno
] = 0;
926 /* If this is the first set of a register, record the value. */
927 else if ((regno
>= FIRST_PSEUDO_REGISTER
|| ! fixed_regs
[regno
])
928 && ! reg_seen
[regno
] && new_reg_base_value
[regno
] == 0)
929 new_reg_base_value
[regno
] = find_base_value (src
);
934 /* Called from loop optimization when a new pseudo-register is
935 created. It indicates that REGNO is being set to VAL. f INVARIANT
936 is true then this value also describes an invariant relationship
937 which can be used to deduce that two registers with unknown values
941 record_base_value (regno
, val
, invariant
)
946 if (regno
>= reg_base_value_size
)
949 if (invariant
&& alias_invariant
)
950 alias_invariant
[regno
] = val
;
952 if (GET_CODE (val
) == REG
)
954 if (REGNO (val
) < reg_base_value_size
)
955 reg_base_value
[regno
] = reg_base_value
[REGNO (val
)];
960 reg_base_value
[regno
] = find_base_value (val
);
963 /* Returns a canonical version of X, from the point of view alias
964 analysis. (For example, if X is a MEM whose address is a register,
965 and the register has a known value (say a SYMBOL_REF), then a MEM
966 whose address is the SYMBOL_REF is returned.) */
972 /* Recursively look for equivalences. */
973 if (GET_CODE (x
) == REG
&& REGNO (x
) >= FIRST_PSEUDO_REGISTER
974 && REGNO (x
) < reg_known_value_size
)
975 return reg_known_value
[REGNO (x
)] == x
976 ? x
: canon_rtx (reg_known_value
[REGNO (x
)]);
977 else if (GET_CODE (x
) == PLUS
)
979 rtx x0
= canon_rtx (XEXP (x
, 0));
980 rtx x1
= canon_rtx (XEXP (x
, 1));
982 if (x0
!= XEXP (x
, 0) || x1
!= XEXP (x
, 1))
984 if (GET_CODE (x0
) == CONST_INT
)
985 return plus_constant (x1
, INTVAL (x0
));
986 else if (GET_CODE (x1
) == CONST_INT
)
987 return plus_constant (x0
, INTVAL (x1
));
988 return gen_rtx_PLUS (GET_MODE (x
), x0
, x1
);
992 /* This gives us much better alias analysis when called from
993 the loop optimizer. Note we want to leave the original
994 MEM alone, but need to return the canonicalized MEM with
995 all the flags with their original values. */
996 else if (GET_CODE (x
) == MEM
)
997 x
= replace_equiv_address_nv (x
, canon_rtx (XEXP (x
, 0)));
1002 /* Return 1 if X and Y are identical-looking rtx's.
1004 We use the data in reg_known_value above to see if two registers with
1005 different numbers are, in fact, equivalent. */
1008 rtx_equal_for_memref_p (x
, y
)
1013 register enum rtx_code code
;
1014 register const char *fmt
;
1016 if (x
== 0 && y
== 0)
1018 if (x
== 0 || y
== 0)
1027 code
= GET_CODE (x
);
1028 /* Rtx's of different codes cannot be equal. */
1029 if (code
!= GET_CODE (y
))
1032 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent.
1033 (REG:SI x) and (REG:HI x) are NOT equivalent. */
1035 if (GET_MODE (x
) != GET_MODE (y
))
1038 /* Some RTL can be compared without a recursive examination. */
1042 return CSELIB_VAL_PTR (x
) == CSELIB_VAL_PTR (y
);
1045 return REGNO (x
) == REGNO (y
);
1048 return XEXP (x
, 0) == XEXP (y
, 0);
1051 return XSTR (x
, 0) == XSTR (y
, 0);
1055 /* There's no need to compare the contents of CONST_DOUBLEs or
1056 CONST_INTs because pointer equality is a good enough
1057 comparison for these nodes. */
1061 return (XINT (x
, 1) == XINT (y
, 1)
1062 && rtx_equal_for_memref_p (XEXP (x
, 0), XEXP (y
, 0)));
1068 /* For commutative operations, the RTX match if the operand match in any
1069 order. Also handle the simple binary and unary cases without a loop. */
1070 if (code
== EQ
|| code
== NE
|| GET_RTX_CLASS (code
) == 'c')
1071 return ((rtx_equal_for_memref_p (XEXP (x
, 0), XEXP (y
, 0))
1072 && rtx_equal_for_memref_p (XEXP (x
, 1), XEXP (y
, 1)))
1073 || (rtx_equal_for_memref_p (XEXP (x
, 0), XEXP (y
, 1))
1074 && rtx_equal_for_memref_p (XEXP (x
, 1), XEXP (y
, 0))));
1075 else if (GET_RTX_CLASS (code
) == '<' || GET_RTX_CLASS (code
) == '2')
1076 return (rtx_equal_for_memref_p (XEXP (x
, 0), XEXP (y
, 0))
1077 && rtx_equal_for_memref_p (XEXP (x
, 1), XEXP (y
, 1)));
1078 else if (GET_RTX_CLASS (code
) == '1')
1079 return rtx_equal_for_memref_p (XEXP (x
, 0), XEXP (y
, 0));
1081 /* Compare the elements. If any pair of corresponding elements
1082 fail to match, return 0 for the whole things.
1084 Limit cases to types which actually appear in addresses. */
1086 fmt
= GET_RTX_FORMAT (code
);
1087 for (i
= GET_RTX_LENGTH (code
) - 1; i
>= 0; i
--)
1092 if (XINT (x
, i
) != XINT (y
, i
))
1097 /* Two vectors must have the same length. */
1098 if (XVECLEN (x
, i
) != XVECLEN (y
, i
))
1101 /* And the corresponding elements must match. */
1102 for (j
= 0; j
< XVECLEN (x
, i
); j
++)
1103 if (rtx_equal_for_memref_p (XVECEXP (x
, i
, j
),
1104 XVECEXP (y
, i
, j
)) == 0)
1109 if (rtx_equal_for_memref_p (XEXP (x
, i
), XEXP (y
, i
)) == 0)
1113 /* This can happen for asm operands. */
1115 if (strcmp (XSTR (x
, i
), XSTR (y
, i
)))
1119 /* This can happen for an asm which clobbers memory. */
1123 /* It is believed that rtx's at this level will never
1124 contain anything but integers and other rtx's,
1125 except for within LABEL_REFs and SYMBOL_REFs. */
1133 /* Given an rtx X, find a SYMBOL_REF or LABEL_REF within
1134 X and return it, or return 0 if none found. */
1137 find_symbolic_term (x
)
1141 register enum rtx_code code
;
1142 register const char *fmt
;
1144 code
= GET_CODE (x
);
1145 if (code
== SYMBOL_REF
|| code
== LABEL_REF
)
1147 if (GET_RTX_CLASS (code
) == 'o')
1150 fmt
= GET_RTX_FORMAT (code
);
1151 for (i
= GET_RTX_LENGTH (code
) - 1; i
>= 0; i
--)
1157 t
= find_symbolic_term (XEXP (x
, i
));
1161 else if (fmt
[i
] == 'E')
1172 struct elt_loc_list
*l
;
1174 #if defined (FIND_BASE_TERM)
1175 /* Try machine-dependent ways to find the base term. */
1176 x
= FIND_BASE_TERM (x
);
1179 switch (GET_CODE (x
))
1182 return REG_BASE_VALUE (x
);
1185 case SIGN_EXTEND
: /* Used for Alpha/NT pointers */
1191 return find_base_term (XEXP (x
, 0));
1194 val
= CSELIB_VAL_PTR (x
);
1195 for (l
= val
->locs
; l
; l
= l
->next
)
1196 if ((x
= find_base_term (l
->loc
)) != 0)
1202 if (GET_CODE (x
) != PLUS
&& GET_CODE (x
) != MINUS
)
1209 rtx tmp1
= XEXP (x
, 0);
1210 rtx tmp2
= XEXP (x
, 1);
1212 /* This is a litle bit tricky since we have to determine which of
1213 the two operands represents the real base address. Otherwise this
1214 routine may return the index register instead of the base register.
1216 That may cause us to believe no aliasing was possible, when in
1217 fact aliasing is possible.
1219 We use a few simple tests to guess the base register. Additional
1220 tests can certainly be added. For example, if one of the operands
1221 is a shift or multiply, then it must be the index register and the
1222 other operand is the base register. */
1224 if (tmp1
== pic_offset_table_rtx
&& CONSTANT_P (tmp2
))
1225 return find_base_term (tmp2
);
1227 /* If either operand is known to be a pointer, then use it
1228 to determine the base term. */
1229 if (REG_P (tmp1
) && REG_POINTER (tmp1
))
1230 return find_base_term (tmp1
);
1232 if (REG_P (tmp2
) && REG_POINTER (tmp2
))
1233 return find_base_term (tmp2
);
1235 /* Neither operand was known to be a pointer. Go ahead and find the
1236 base term for both operands. */
1237 tmp1
= find_base_term (tmp1
);
1238 tmp2
= find_base_term (tmp2
);
1240 /* If either base term is named object or a special address
1241 (like an argument or stack reference), then use it for the
1244 && (GET_CODE (tmp1
) == SYMBOL_REF
1245 || GET_CODE (tmp1
) == LABEL_REF
1246 || (GET_CODE (tmp1
) == ADDRESS
1247 && GET_MODE (tmp1
) != VOIDmode
)))
1251 && (GET_CODE (tmp2
) == SYMBOL_REF
1252 || GET_CODE (tmp2
) == LABEL_REF
1253 || (GET_CODE (tmp2
) == ADDRESS
1254 && GET_MODE (tmp2
) != VOIDmode
)))
1257 /* We could not determine which of the two operands was the
1258 base register and which was the index. So we can determine
1259 nothing from the base alias check. */
1264 if (GET_CODE (XEXP (x
, 0)) == REG
&& GET_CODE (XEXP (x
, 1)) == CONST_INT
)
1265 return REG_BASE_VALUE (XEXP (x
, 0));
1273 return REG_BASE_VALUE (frame_pointer_rtx
);
1280 /* Return 0 if the addresses X and Y are known to point to different
1281 objects, 1 if they might be pointers to the same object. */
1284 base_alias_check (x
, y
, x_mode
, y_mode
)
1286 enum machine_mode x_mode
, y_mode
;
1288 rtx x_base
= find_base_term (x
);
1289 rtx y_base
= find_base_term (y
);
1291 /* If the address itself has no known base see if a known equivalent
1292 value has one. If either address still has no known base, nothing
1293 is known about aliasing. */
1298 if (! flag_expensive_optimizations
|| (x_c
= canon_rtx (x
)) == x
)
1301 x_base
= find_base_term (x_c
);
1309 if (! flag_expensive_optimizations
|| (y_c
= canon_rtx (y
)) == y
)
1312 y_base
= find_base_term (y_c
);
1317 /* If the base addresses are equal nothing is known about aliasing. */
1318 if (rtx_equal_p (x_base
, y_base
))
1321 /* The base addresses of the read and write are different expressions.
1322 If they are both symbols and they are not accessed via AND, there is
1323 no conflict. We can bring knowledge of object alignment into play
1324 here. For example, on alpha, "char a, b;" can alias one another,
1325 though "char a; long b;" cannot. */
1326 if (GET_CODE (x_base
) != ADDRESS
&& GET_CODE (y_base
) != ADDRESS
)
1328 if (GET_CODE (x
) == AND
&& GET_CODE (y
) == AND
)
1330 if (GET_CODE (x
) == AND
1331 && (GET_CODE (XEXP (x
, 1)) != CONST_INT
1332 || (int) GET_MODE_UNIT_SIZE (y_mode
) < -INTVAL (XEXP (x
, 1))))
1334 if (GET_CODE (y
) == AND
1335 && (GET_CODE (XEXP (y
, 1)) != CONST_INT
1336 || (int) GET_MODE_UNIT_SIZE (x_mode
) < -INTVAL (XEXP (y
, 1))))
1338 /* Differing symbols never alias. */
1342 /* If one address is a stack reference there can be no alias:
1343 stack references using different base registers do not alias,
1344 a stack reference can not alias a parameter, and a stack reference
1345 can not alias a global. */
1346 if ((GET_CODE (x_base
) == ADDRESS
&& GET_MODE (x_base
) == Pmode
)
1347 || (GET_CODE (y_base
) == ADDRESS
&& GET_MODE (y_base
) == Pmode
))
1350 if (! flag_argument_noalias
)
1353 if (flag_argument_noalias
> 1)
1356 /* Weak noalias assertion (arguments are distinct, but may match globals). */
1357 return ! (GET_MODE (x_base
) == VOIDmode
&& GET_MODE (y_base
) == VOIDmode
);
1360 /* Convert the address X into something we can use. This is done by returning
1361 it unchanged unless it is a value; in the latter case we call cselib to get
1362 a more useful rtx. */
1369 struct elt_loc_list
*l
;
1371 if (GET_CODE (x
) != VALUE
)
1373 v
= CSELIB_VAL_PTR (x
);
1374 for (l
= v
->locs
; l
; l
= l
->next
)
1375 if (CONSTANT_P (l
->loc
))
1377 for (l
= v
->locs
; l
; l
= l
->next
)
1378 if (GET_CODE (l
->loc
) != REG
&& GET_CODE (l
->loc
) != MEM
)
1381 return v
->locs
->loc
;
1385 /* Return the address of the (N_REFS + 1)th memory reference to ADDR
1386 where SIZE is the size in bytes of the memory reference. If ADDR
1387 is not modified by the memory reference then ADDR is returned. */
1390 addr_side_effect_eval (addr
, size
, n_refs
)
1397 switch (GET_CODE (addr
))
1400 offset
= (n_refs
+ 1) * size
;
1403 offset
= -(n_refs
+ 1) * size
;
1406 offset
= n_refs
* size
;
1409 offset
= -n_refs
* size
;
1417 addr
= gen_rtx_PLUS (GET_MODE (addr
), XEXP (addr
, 0), GEN_INT (offset
));
1419 addr
= XEXP (addr
, 0);
1424 /* Return nonzero if X and Y (memory addresses) could reference the
1425 same location in memory. C is an offset accumulator. When
1426 C is nonzero, we are testing aliases between X and Y + C.
1427 XSIZE is the size in bytes of the X reference,
1428 similarly YSIZE is the size in bytes for Y.
1430 If XSIZE or YSIZE is zero, we do not know the amount of memory being
1431 referenced (the reference was BLKmode), so make the most pessimistic
1434 If XSIZE or YSIZE is negative, we may access memory outside the object
1435 being referenced as a side effect. This can happen when using AND to
1436 align memory references, as is done on the Alpha.
1438 Nice to notice that varying addresses cannot conflict with fp if no
1439 local variables had their addresses taken, but that's too hard now. */
1442 memrefs_conflict_p (xsize
, x
, ysize
, y
, c
)
1447 if (GET_CODE (x
) == VALUE
)
1449 if (GET_CODE (y
) == VALUE
)
1451 if (GET_CODE (x
) == HIGH
)
1453 else if (GET_CODE (x
) == LO_SUM
)
1456 x
= canon_rtx (addr_side_effect_eval (x
, xsize
, 0));
1457 if (GET_CODE (y
) == HIGH
)
1459 else if (GET_CODE (y
) == LO_SUM
)
1462 y
= canon_rtx (addr_side_effect_eval (y
, ysize
, 0));
1464 if (rtx_equal_for_memref_p (x
, y
))
1466 if (xsize
<= 0 || ysize
<= 0)
1468 if (c
>= 0 && xsize
> c
)
1470 if (c
< 0 && ysize
+c
> 0)
1475 /* This code used to check for conflicts involving stack references and
1476 globals but the base address alias code now handles these cases. */
1478 if (GET_CODE (x
) == PLUS
)
1480 /* The fact that X is canonicalized means that this
1481 PLUS rtx is canonicalized. */
1482 rtx x0
= XEXP (x
, 0);
1483 rtx x1
= XEXP (x
, 1);
1485 if (GET_CODE (y
) == PLUS
)
1487 /* The fact that Y is canonicalized means that this
1488 PLUS rtx is canonicalized. */
1489 rtx y0
= XEXP (y
, 0);
1490 rtx y1
= XEXP (y
, 1);
1492 if (rtx_equal_for_memref_p (x1
, y1
))
1493 return memrefs_conflict_p (xsize
, x0
, ysize
, y0
, c
);
1494 if (rtx_equal_for_memref_p (x0
, y0
))
1495 return memrefs_conflict_p (xsize
, x1
, ysize
, y1
, c
);
1496 if (GET_CODE (x1
) == CONST_INT
)
1498 if (GET_CODE (y1
) == CONST_INT
)
1499 return memrefs_conflict_p (xsize
, x0
, ysize
, y0
,
1500 c
- INTVAL (x1
) + INTVAL (y1
));
1502 return memrefs_conflict_p (xsize
, x0
, ysize
, y
,
1505 else if (GET_CODE (y1
) == CONST_INT
)
1506 return memrefs_conflict_p (xsize
, x
, ysize
, y0
, c
+ INTVAL (y1
));
1510 else if (GET_CODE (x1
) == CONST_INT
)
1511 return memrefs_conflict_p (xsize
, x0
, ysize
, y
, c
- INTVAL (x1
));
1513 else if (GET_CODE (y
) == PLUS
)
1515 /* The fact that Y is canonicalized means that this
1516 PLUS rtx is canonicalized. */
1517 rtx y0
= XEXP (y
, 0);
1518 rtx y1
= XEXP (y
, 1);
1520 if (GET_CODE (y1
) == CONST_INT
)
1521 return memrefs_conflict_p (xsize
, x
, ysize
, y0
, c
+ INTVAL (y1
));
1526 if (GET_CODE (x
) == GET_CODE (y
))
1527 switch (GET_CODE (x
))
1531 /* Handle cases where we expect the second operands to be the
1532 same, and check only whether the first operand would conflict
1535 rtx x1
= canon_rtx (XEXP (x
, 1));
1536 rtx y1
= canon_rtx (XEXP (y
, 1));
1537 if (! rtx_equal_for_memref_p (x1
, y1
))
1539 x0
= canon_rtx (XEXP (x
, 0));
1540 y0
= canon_rtx (XEXP (y
, 0));
1541 if (rtx_equal_for_memref_p (x0
, y0
))
1542 return (xsize
== 0 || ysize
== 0
1543 || (c
>= 0 && xsize
> c
) || (c
< 0 && ysize
+c
> 0));
1545 /* Can't properly adjust our sizes. */
1546 if (GET_CODE (x1
) != CONST_INT
)
1548 xsize
/= INTVAL (x1
);
1549 ysize
/= INTVAL (x1
);
1551 return memrefs_conflict_p (xsize
, x0
, ysize
, y0
, c
);
1555 /* Are these registers known not to be equal? */
1556 if (alias_invariant
)
1558 unsigned int r_x
= REGNO (x
), r_y
= REGNO (y
);
1559 rtx i_x
, i_y
; /* invariant relationships of X and Y */
1561 i_x
= r_x
>= reg_base_value_size
? 0 : alias_invariant
[r_x
];
1562 i_y
= r_y
>= reg_base_value_size
? 0 : alias_invariant
[r_y
];
1564 if (i_x
== 0 && i_y
== 0)
1567 if (! memrefs_conflict_p (xsize
, i_x
? i_x
: x
,
1568 ysize
, i_y
? i_y
: y
, c
))
1577 /* Treat an access through an AND (e.g. a subword access on an Alpha)
1578 as an access with indeterminate size. Assume that references
1579 besides AND are aligned, so if the size of the other reference is
1580 at least as large as the alignment, assume no other overlap. */
1581 if (GET_CODE (x
) == AND
&& GET_CODE (XEXP (x
, 1)) == CONST_INT
)
1583 if (GET_CODE (y
) == AND
|| ysize
< -INTVAL (XEXP (x
, 1)))
1585 return memrefs_conflict_p (xsize
, XEXP (x
, 0), ysize
, y
, c
);
1587 if (GET_CODE (y
) == AND
&& GET_CODE (XEXP (y
, 1)) == CONST_INT
)
1589 /* ??? If we are indexing far enough into the array/structure, we
1590 may yet be able to determine that we can not overlap. But we
1591 also need to that we are far enough from the end not to overlap
1592 a following reference, so we do nothing with that for now. */
1593 if (GET_CODE (x
) == AND
|| xsize
< -INTVAL (XEXP (y
, 1)))
1595 return memrefs_conflict_p (xsize
, x
, ysize
, XEXP (y
, 0), c
);
1598 if (GET_CODE (x
) == ADDRESSOF
)
1600 if (y
== frame_pointer_rtx
1601 || GET_CODE (y
) == ADDRESSOF
)
1602 return xsize
<= 0 || ysize
<= 0;
1604 if (GET_CODE (y
) == ADDRESSOF
)
1606 if (x
== frame_pointer_rtx
)
1607 return xsize
<= 0 || ysize
<= 0;
1612 if (GET_CODE (x
) == CONST_INT
&& GET_CODE (y
) == CONST_INT
)
1614 c
+= (INTVAL (y
) - INTVAL (x
));
1615 return (xsize
<= 0 || ysize
<= 0
1616 || (c
>= 0 && xsize
> c
) || (c
< 0 && ysize
+c
> 0));
1619 if (GET_CODE (x
) == CONST
)
1621 if (GET_CODE (y
) == CONST
)
1622 return memrefs_conflict_p (xsize
, canon_rtx (XEXP (x
, 0)),
1623 ysize
, canon_rtx (XEXP (y
, 0)), c
);
1625 return memrefs_conflict_p (xsize
, canon_rtx (XEXP (x
, 0)),
1628 if (GET_CODE (y
) == CONST
)
1629 return memrefs_conflict_p (xsize
, x
, ysize
,
1630 canon_rtx (XEXP (y
, 0)), c
);
1633 return (xsize
<= 0 || ysize
<= 0
1634 || (rtx_equal_for_memref_p (x
, y
)
1635 && ((c
>= 0 && xsize
> c
) || (c
< 0 && ysize
+c
> 0))));
1642 /* Functions to compute memory dependencies.
1644 Since we process the insns in execution order, we can build tables
1645 to keep track of what registers are fixed (and not aliased), what registers
1646 are varying in known ways, and what registers are varying in unknown
1649 If both memory references are volatile, then there must always be a
1650 dependence between the two references, since their order can not be
1651 changed. A volatile and non-volatile reference can be interchanged
1654 A MEM_IN_STRUCT reference at a non-AND varying address can never
1655 conflict with a non-MEM_IN_STRUCT reference at a fixed address. We
1656 also must allow AND addresses, because they may generate accesses
1657 outside the object being referenced. This is used to generate
1658 aligned addresses from unaligned addresses, for instance, the alpha
1659 storeqi_unaligned pattern. */
1661 /* Read dependence: X is read after read in MEM takes place. There can
1662 only be a dependence here if both reads are volatile. */
1665 read_dependence (mem
, x
)
1669 return MEM_VOLATILE_P (x
) && MEM_VOLATILE_P (mem
);
1672 /* Returns MEM1 if and only if MEM1 is a scalar at a fixed address and
1673 MEM2 is a reference to a structure at a varying address, or returns
1674 MEM2 if vice versa. Otherwise, returns NULL_RTX. If a non-NULL
1675 value is returned MEM1 and MEM2 can never alias. VARIES_P is used
1676 to decide whether or not an address may vary; it should return
1677 nonzero whenever variation is possible.
1678 MEM1_ADDR and MEM2_ADDR are the addresses of MEM1 and MEM2. */
1681 fixed_scalar_and_varying_struct_p (mem1
, mem2
, mem1_addr
, mem2_addr
, varies_p
)
1683 rtx mem1_addr
, mem2_addr
;
1684 int (*varies_p
) PARAMS ((rtx
, int));
1686 if (! flag_strict_aliasing
)
1689 if (MEM_SCALAR_P (mem1
) && MEM_IN_STRUCT_P (mem2
)
1690 && !varies_p (mem1_addr
, 1) && varies_p (mem2_addr
, 1))
1691 /* MEM1 is a scalar at a fixed address; MEM2 is a struct at a
1695 if (MEM_IN_STRUCT_P (mem1
) && MEM_SCALAR_P (mem2
)
1696 && varies_p (mem1_addr
, 1) && !varies_p (mem2_addr
, 1))
1697 /* MEM2 is a scalar at a fixed address; MEM1 is a struct at a
1704 /* Returns nonzero if something about the mode or address format MEM1
1705 indicates that it might well alias *anything*. */
1708 aliases_everything_p (mem
)
1711 if (GET_CODE (XEXP (mem
, 0)) == AND
)
1712 /* If the address is an AND, its very hard to know at what it is
1713 actually pointing. */
1719 /* True dependence: X is read after store in MEM takes place. */
1722 true_dependence (mem
, mem_mode
, x
, varies
)
1724 enum machine_mode mem_mode
;
1726 int (*varies
) PARAMS ((rtx
, int));
1728 register rtx x_addr
, mem_addr
;
1731 if (MEM_VOLATILE_P (x
) && MEM_VOLATILE_P (mem
))
1734 if (DIFFERENT_ALIAS_SETS_P (x
, mem
))
1737 /* Unchanging memory can't conflict with non-unchanging memory.
1738 A non-unchanging read can conflict with a non-unchanging write.
1739 An unchanging read can conflict with an unchanging write since
1740 there may be a single store to this address to initialize it.
1741 Note that an unchanging store can conflict with a non-unchanging read
1742 since we have to make conservative assumptions when we have a
1743 record with readonly fields and we are copying the whole thing.
1744 Just fall through to the code below to resolve potential conflicts.
1745 This won't handle all cases optimally, but the possible performance
1746 loss should be negligible. */
1747 if (RTX_UNCHANGING_P (x
) && ! RTX_UNCHANGING_P (mem
))
1750 if (mem_mode
== VOIDmode
)
1751 mem_mode
= GET_MODE (mem
);
1753 x_addr
= get_addr (XEXP (x
, 0));
1754 mem_addr
= get_addr (XEXP (mem
, 0));
1756 base
= find_base_term (x_addr
);
1757 if (base
&& (GET_CODE (base
) == LABEL_REF
1758 || (GET_CODE (base
) == SYMBOL_REF
1759 && CONSTANT_POOL_ADDRESS_P (base
))))
1762 if (! base_alias_check (x_addr
, mem_addr
, GET_MODE (x
), mem_mode
))
1765 x_addr
= canon_rtx (x_addr
);
1766 mem_addr
= canon_rtx (mem_addr
);
1768 if (! memrefs_conflict_p (GET_MODE_SIZE (mem_mode
), mem_addr
,
1769 SIZE_FOR_MODE (x
), x_addr
, 0))
1772 if (aliases_everything_p (x
))
1775 /* We cannot use aliases_everyting_p to test MEM, since we must look
1776 at MEM_MODE, rather than GET_MODE (MEM). */
1777 if (mem_mode
== QImode
|| GET_CODE (mem_addr
) == AND
)
1780 /* In true_dependence we also allow BLKmode to alias anything. Why
1781 don't we do this in anti_dependence and output_dependence? */
1782 if (mem_mode
== BLKmode
|| GET_MODE (x
) == BLKmode
)
1785 return ! fixed_scalar_and_varying_struct_p (mem
, x
, mem_addr
, x_addr
,
1789 /* Canonical true dependence: X is read after store in MEM takes place.
1790 Variant of true_dependece which assumes MEM has already been
1791 canonicalized (hence we no longer do that here).
1792 The mem_addr argument has been added, since true_dependence computed
1793 this value prior to canonicalizing. */
1796 canon_true_dependence (mem
, mem_mode
, mem_addr
, x
, varies
)
1797 rtx mem
, mem_addr
, x
;
1798 enum machine_mode mem_mode
;
1799 int (*varies
) PARAMS ((rtx
, int));
1801 register rtx x_addr
;
1803 if (MEM_VOLATILE_P (x
) && MEM_VOLATILE_P (mem
))
1806 if (DIFFERENT_ALIAS_SETS_P (x
, mem
))
1809 /* If X is an unchanging read, then it can't possibly conflict with any
1810 non-unchanging store. It may conflict with an unchanging write though,
1811 because there may be a single store to this address to initialize it.
1812 Just fall through to the code below to resolve the case where we have
1813 both an unchanging read and an unchanging write. This won't handle all
1814 cases optimally, but the possible performance loss should be
1816 if (RTX_UNCHANGING_P (x
) && ! RTX_UNCHANGING_P (mem
))
1819 x_addr
= get_addr (XEXP (x
, 0));
1821 if (! base_alias_check (x_addr
, mem_addr
, GET_MODE (x
), mem_mode
))
1824 x_addr
= canon_rtx (x_addr
);
1825 if (! memrefs_conflict_p (GET_MODE_SIZE (mem_mode
), mem_addr
,
1826 SIZE_FOR_MODE (x
), x_addr
, 0))
1829 if (aliases_everything_p (x
))
1832 /* We cannot use aliases_everyting_p to test MEM, since we must look
1833 at MEM_MODE, rather than GET_MODE (MEM). */
1834 if (mem_mode
== QImode
|| GET_CODE (mem_addr
) == AND
)
1837 /* In true_dependence we also allow BLKmode to alias anything. Why
1838 don't we do this in anti_dependence and output_dependence? */
1839 if (mem_mode
== BLKmode
|| GET_MODE (x
) == BLKmode
)
1842 return ! fixed_scalar_and_varying_struct_p (mem
, x
, mem_addr
, x_addr
,
1846 /* Returns non-zero if a write to X might alias a previous read from
1847 (or, if WRITEP is non-zero, a write to) MEM. */
1850 write_dependence_p (mem
, x
, writep
)
1855 rtx x_addr
, mem_addr
;
1859 if (MEM_VOLATILE_P (x
) && MEM_VOLATILE_P (mem
))
1862 if (DIFFERENT_ALIAS_SETS_P (x
, mem
))
1865 /* Unchanging memory can't conflict with non-unchanging memory. */
1866 if (RTX_UNCHANGING_P (x
) != RTX_UNCHANGING_P (mem
))
1869 /* If MEM is an unchanging read, then it can't possibly conflict with
1870 the store to X, because there is at most one store to MEM, and it must
1871 have occurred somewhere before MEM. */
1872 if (! writep
&& RTX_UNCHANGING_P (mem
))
1875 x_addr
= get_addr (XEXP (x
, 0));
1876 mem_addr
= get_addr (XEXP (mem
, 0));
1880 base
= find_base_term (mem_addr
);
1881 if (base
&& (GET_CODE (base
) == LABEL_REF
1882 || (GET_CODE (base
) == SYMBOL_REF
1883 && CONSTANT_POOL_ADDRESS_P (base
))))
1887 if (! base_alias_check (x_addr
, mem_addr
, GET_MODE (x
),
1891 x_addr
= canon_rtx (x_addr
);
1892 mem_addr
= canon_rtx (mem_addr
);
1894 if (!memrefs_conflict_p (SIZE_FOR_MODE (mem
), mem_addr
,
1895 SIZE_FOR_MODE (x
), x_addr
, 0))
1899 = fixed_scalar_and_varying_struct_p (mem
, x
, mem_addr
, x_addr
,
1902 return (!(fixed_scalar
== mem
&& !aliases_everything_p (x
))
1903 && !(fixed_scalar
== x
&& !aliases_everything_p (mem
)));
1906 /* Anti dependence: X is written after read in MEM takes place. */
1909 anti_dependence (mem
, x
)
1913 return write_dependence_p (mem
, x
, /*writep=*/0);
1916 /* Output dependence: X is written after store in MEM takes place. */
1919 output_dependence (mem
, x
)
1923 return write_dependence_p (mem
, x
, /*writep=*/1);
1926 /* Returns non-zero if X mentions something which is not
1927 local to the function and is not constant. */
1930 nonlocal_mentioned_p (x
)
1934 register RTX_CODE code
;
1937 code
= GET_CODE (x
);
1939 if (GET_RTX_CLASS (code
) == 'i')
1941 /* Constant functions can be constant if they don't use
1942 scratch memory used to mark function w/o side effects. */
1943 if (code
== CALL_INSN
&& CONST_OR_PURE_CALL_P (x
))
1945 x
= CALL_INSN_FUNCTION_USAGE (x
);
1951 code
= GET_CODE (x
);
1957 if (GET_CODE (SUBREG_REG (x
)) == REG
)
1959 /* Global registers are not local. */
1960 if (REGNO (SUBREG_REG (x
)) < FIRST_PSEUDO_REGISTER
1961 && global_regs
[subreg_regno (x
)])
1969 /* Global registers are not local. */
1970 if (regno
< FIRST_PSEUDO_REGISTER
&& global_regs
[regno
])
1984 /* Constants in the function's constants pool are constant. */
1985 if (CONSTANT_POOL_ADDRESS_P (x
))
1990 /* Non-constant calls and recursion are not local. */
1994 /* Be overly conservative and consider any volatile memory
1995 reference as not local. */
1996 if (MEM_VOLATILE_P (x
))
1998 base
= find_base_term (XEXP (x
, 0));
2001 /* A Pmode ADDRESS could be a reference via the structure value
2002 address or static chain. Such memory references are nonlocal.
2004 Thus, we have to examine the contents of the ADDRESS to find
2005 out if this is a local reference or not. */
2006 if (GET_CODE (base
) == ADDRESS
2007 && GET_MODE (base
) == Pmode
2008 && (XEXP (base
, 0) == stack_pointer_rtx
2009 || XEXP (base
, 0) == arg_pointer_rtx
2010 #if HARD_FRAME_POINTER_REGNUM != FRAME_POINTER_REGNUM
2011 || XEXP (base
, 0) == hard_frame_pointer_rtx
2013 || XEXP (base
, 0) == frame_pointer_rtx
))
2015 /* Constants in the function's constant pool are constant. */
2016 if (GET_CODE (base
) == SYMBOL_REF
&& CONSTANT_POOL_ADDRESS_P (base
))
2021 case UNSPEC_VOLATILE
:
2026 if (MEM_VOLATILE_P (x
))
2035 /* Recursively scan the operands of this expression. */
2038 register const char *fmt
= GET_RTX_FORMAT (code
);
2041 for (i
= GET_RTX_LENGTH (code
) - 1; i
>= 0; i
--)
2043 if (fmt
[i
] == 'e' && XEXP (x
, i
))
2045 if (nonlocal_mentioned_p (XEXP (x
, i
)))
2048 else if (fmt
[i
] == 'E')
2051 for (j
= 0; j
< XVECLEN (x
, i
); j
++)
2052 if (nonlocal_mentioned_p (XVECEXP (x
, i
, j
)))
2061 /* Mark the function if it is constant. */
2064 mark_constant_function ()
2067 int nonlocal_mentioned
;
2069 if (TREE_PUBLIC (current_function_decl
)
2070 || TREE_READONLY (current_function_decl
)
2071 || DECL_IS_PURE (current_function_decl
)
2072 || TREE_THIS_VOLATILE (current_function_decl
)
2073 || TYPE_MODE (TREE_TYPE (current_function_decl
)) == VOIDmode
)
2076 /* A loop might not return which counts as a side effect. */
2077 if (mark_dfs_back_edges ())
2080 nonlocal_mentioned
= 0;
2082 init_alias_analysis ();
2084 /* Determine if this is a constant function. */
2086 for (insn
= get_insns (); insn
; insn
= NEXT_INSN (insn
))
2087 if (INSN_P (insn
) && nonlocal_mentioned_p (insn
))
2089 nonlocal_mentioned
= 1;
2093 end_alias_analysis ();
2095 /* Mark the function. */
2097 if (! nonlocal_mentioned
)
2098 TREE_READONLY (current_function_decl
) = 1;
2102 static HARD_REG_SET argument_registers
;
2109 #ifndef OUTGOING_REGNO
2110 #define OUTGOING_REGNO(N) N
2112 for (i
= 0; i
< FIRST_PSEUDO_REGISTER
; i
++)
2113 /* Check whether this register can hold an incoming pointer
2114 argument. FUNCTION_ARG_REGNO_P tests outgoing register
2115 numbers, so translate if necessary due to register windows. */
2116 if (FUNCTION_ARG_REGNO_P (OUTGOING_REGNO (i
))
2117 && HARD_REGNO_MODE_OK (i
, Pmode
))
2118 SET_HARD_REG_BIT (argument_registers
, i
);
2120 alias_sets
= splay_tree_new (splay_tree_compare_ints
, 0, 0);
2123 /* Initialize the aliasing machinery. Initialize the REG_KNOWN_VALUE
2127 init_alias_analysis ()
2129 int maxreg
= max_reg_num ();
2132 register unsigned int ui
;
2135 reg_known_value_size
= maxreg
;
2138 = (rtx
*) xcalloc ((maxreg
- FIRST_PSEUDO_REGISTER
), sizeof (rtx
))
2139 - FIRST_PSEUDO_REGISTER
;
2141 = (char*) xcalloc ((maxreg
- FIRST_PSEUDO_REGISTER
), sizeof (char))
2142 - FIRST_PSEUDO_REGISTER
;
2144 /* Overallocate reg_base_value to allow some growth during loop
2145 optimization. Loop unrolling can create a large number of
2147 reg_base_value_size
= maxreg
* 2;
2148 reg_base_value
= (rtx
*) xcalloc (reg_base_value_size
, sizeof (rtx
));
2149 ggc_add_rtx_root (reg_base_value
, reg_base_value_size
);
2151 new_reg_base_value
= (rtx
*) xmalloc (reg_base_value_size
* sizeof (rtx
));
2152 reg_seen
= (char *) xmalloc (reg_base_value_size
);
2153 if (! reload_completed
&& flag_unroll_loops
)
2155 /* ??? Why are we realloc'ing if we're just going to zero it? */
2156 alias_invariant
= (rtx
*)xrealloc (alias_invariant
,
2157 reg_base_value_size
* sizeof (rtx
));
2158 memset ((char *)alias_invariant
, 0, reg_base_value_size
* sizeof (rtx
));
2161 /* The basic idea is that each pass through this loop will use the
2162 "constant" information from the previous pass to propagate alias
2163 information through another level of assignments.
2165 This could get expensive if the assignment chains are long. Maybe
2166 we should throttle the number of iterations, possibly based on
2167 the optimization level or flag_expensive_optimizations.
2169 We could propagate more information in the first pass by making use
2170 of REG_N_SETS to determine immediately that the alias information
2171 for a pseudo is "constant".
2173 A program with an uninitialized variable can cause an infinite loop
2174 here. Instead of doing a full dataflow analysis to detect such problems
2175 we just cap the number of iterations for the loop.
2177 The state of the arrays for the set chain in question does not matter
2178 since the program has undefined behavior. */
2183 /* Assume nothing will change this iteration of the loop. */
2186 /* We want to assign the same IDs each iteration of this loop, so
2187 start counting from zero each iteration of the loop. */
2190 /* We're at the start of the funtion each iteration through the
2191 loop, so we're copying arguments. */
2192 copying_arguments
= 1;
2194 /* Wipe the potential alias information clean for this pass. */
2195 memset ((char *) new_reg_base_value
, 0, reg_base_value_size
* sizeof (rtx
));
2197 /* Wipe the reg_seen array clean. */
2198 memset ((char *) reg_seen
, 0, reg_base_value_size
);
2200 /* Mark all hard registers which may contain an address.
2201 The stack, frame and argument pointers may contain an address.
2202 An argument register which can hold a Pmode value may contain
2203 an address even if it is not in BASE_REGS.
2205 The address expression is VOIDmode for an argument and
2206 Pmode for other registers. */
2208 for (i
= 0; i
< FIRST_PSEUDO_REGISTER
; i
++)
2209 if (TEST_HARD_REG_BIT (argument_registers
, i
))
2210 new_reg_base_value
[i
] = gen_rtx_ADDRESS (VOIDmode
,
2211 gen_rtx_REG (Pmode
, i
));
2213 new_reg_base_value
[STACK_POINTER_REGNUM
]
2214 = gen_rtx_ADDRESS (Pmode
, stack_pointer_rtx
);
2215 new_reg_base_value
[ARG_POINTER_REGNUM
]
2216 = gen_rtx_ADDRESS (Pmode
, arg_pointer_rtx
);
2217 new_reg_base_value
[FRAME_POINTER_REGNUM
]
2218 = gen_rtx_ADDRESS (Pmode
, frame_pointer_rtx
);
2219 #if HARD_FRAME_POINTER_REGNUM != FRAME_POINTER_REGNUM
2220 new_reg_base_value
[HARD_FRAME_POINTER_REGNUM
]
2221 = gen_rtx_ADDRESS (Pmode
, hard_frame_pointer_rtx
);
2224 /* Walk the insns adding values to the new_reg_base_value array. */
2225 for (insn
= get_insns (); insn
; insn
= NEXT_INSN (insn
))
2231 #if defined (HAVE_prologue) || defined (HAVE_epilogue)
2232 /* The prologue/epilouge insns are not threaded onto the
2233 insn chain until after reload has completed. Thus,
2234 there is no sense wasting time checking if INSN is in
2235 the prologue/epilogue until after reload has completed. */
2236 if (reload_completed
2237 && prologue_epilogue_contains (insn
))
2241 /* If this insn has a noalias note, process it, Otherwise,
2242 scan for sets. A simple set will have no side effects
2243 which could change the base value of any other register. */
2245 if (GET_CODE (PATTERN (insn
)) == SET
2246 && REG_NOTES (insn
) != 0
2247 && find_reg_note (insn
, REG_NOALIAS
, NULL_RTX
))
2248 record_set (SET_DEST (PATTERN (insn
)), NULL_RTX
, NULL
);
2250 note_stores (PATTERN (insn
), record_set
, NULL
);
2252 set
= single_set (insn
);
2255 && GET_CODE (SET_DEST (set
)) == REG
2256 && REGNO (SET_DEST (set
)) >= FIRST_PSEUDO_REGISTER
)
2258 unsigned int regno
= REGNO (SET_DEST (set
));
2259 rtx src
= SET_SRC (set
);
2261 if (REG_NOTES (insn
) != 0
2262 && (((note
= find_reg_note (insn
, REG_EQUAL
, 0)) != 0
2263 && REG_N_SETS (regno
) == 1)
2264 || (note
= find_reg_note (insn
, REG_EQUIV
, NULL_RTX
)) != 0)
2265 && GET_CODE (XEXP (note
, 0)) != EXPR_LIST
2266 && ! rtx_varies_p (XEXP (note
, 0), 1)
2267 && ! reg_overlap_mentioned_p (SET_DEST (set
), XEXP (note
, 0)))
2269 reg_known_value
[regno
] = XEXP (note
, 0);
2270 reg_known_equiv_p
[regno
] = REG_NOTE_KIND (note
) == REG_EQUIV
;
2272 else if (REG_N_SETS (regno
) == 1
2273 && GET_CODE (src
) == PLUS
2274 && GET_CODE (XEXP (src
, 0)) == REG
2275 && REGNO (XEXP (src
, 0)) >= FIRST_PSEUDO_REGISTER
2276 && (reg_known_value
[REGNO (XEXP (src
, 0))])
2277 && GET_CODE (XEXP (src
, 1)) == CONST_INT
)
2279 rtx op0
= XEXP (src
, 0);
2280 op0
= reg_known_value
[REGNO (op0
)];
2281 reg_known_value
[regno
]
2282 = plus_constant (op0
, INTVAL (XEXP (src
, 1)));
2283 reg_known_equiv_p
[regno
] = 0;
2285 else if (REG_N_SETS (regno
) == 1
2286 && ! rtx_varies_p (src
, 1))
2288 reg_known_value
[regno
] = src
;
2289 reg_known_equiv_p
[regno
] = 0;
2293 else if (GET_CODE (insn
) == NOTE
2294 && NOTE_LINE_NUMBER (insn
) == NOTE_INSN_FUNCTION_BEG
)
2295 copying_arguments
= 0;
2298 /* Now propagate values from new_reg_base_value to reg_base_value. */
2299 for (ui
= 0; ui
< reg_base_value_size
; ui
++)
2301 if (new_reg_base_value
[ui
]
2302 && new_reg_base_value
[ui
] != reg_base_value
[ui
]
2303 && ! rtx_equal_p (new_reg_base_value
[ui
], reg_base_value
[ui
]))
2305 reg_base_value
[ui
] = new_reg_base_value
[ui
];
2310 while (changed
&& ++pass
< MAX_ALIAS_LOOP_PASSES
);
2312 /* Fill in the remaining entries. */
2313 for (i
= FIRST_PSEUDO_REGISTER
; i
< maxreg
; i
++)
2314 if (reg_known_value
[i
] == 0)
2315 reg_known_value
[i
] = regno_reg_rtx
[i
];
2317 /* Simplify the reg_base_value array so that no register refers to
2318 another register, except to special registers indirectly through
2319 ADDRESS expressions.
2321 In theory this loop can take as long as O(registers^2), but unless
2322 there are very long dependency chains it will run in close to linear
2325 This loop may not be needed any longer now that the main loop does
2326 a better job at propagating alias information. */
2332 for (ui
= 0; ui
< reg_base_value_size
; ui
++)
2334 rtx base
= reg_base_value
[ui
];
2335 if (base
&& GET_CODE (base
) == REG
)
2337 unsigned int base_regno
= REGNO (base
);
2338 if (base_regno
== ui
) /* register set from itself */
2339 reg_base_value
[ui
] = 0;
2341 reg_base_value
[ui
] = reg_base_value
[base_regno
];
2346 while (changed
&& pass
< MAX_ALIAS_LOOP_PASSES
);
2349 free (new_reg_base_value
);
2350 new_reg_base_value
= 0;
2356 end_alias_analysis ()
2358 free (reg_known_value
+ FIRST_PSEUDO_REGISTER
);
2359 reg_known_value
= 0;
2360 reg_known_value_size
= 0;
2361 free (reg_known_equiv_p
+ FIRST_PSEUDO_REGISTER
);
2362 reg_known_equiv_p
= 0;
2365 ggc_del_root (reg_base_value
);
2366 free (reg_base_value
);
2369 reg_base_value_size
= 0;
2370 if (alias_invariant
)
2372 free (alias_invariant
);
2373 alias_invariant
= 0;