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 GCC.
7 GCC is free software; you can redistribute it and/or modify it under
8 the terms of the GNU General Public License as published by the Free
9 Software Foundation; either version 2, or (at your option) any later
12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
17 You should have received a copy of the GNU General Public License
18 along with GCC; see the file COPYING. If not, write to the Free
19 Software Foundation, 59 Temple Place - Suite 330, Boston, MA
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 descendents, 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 descendents. 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 rtx find_base_value PARAMS ((rtx));
99 static int mems_in_disjoint_alias_sets_p PARAMS ((rtx, rtx));
100 static int insert_subset_children PARAMS ((splay_tree_node, void*));
101 static tree find_base_decl PARAMS ((tree));
102 static alias_set_entry get_alias_set_entry PARAMS ((HOST_WIDE_INT));
103 static rtx fixed_scalar_and_varying_struct_p PARAMS ((rtx, rtx, rtx, rtx,
104 int (*) (rtx, int)));
105 static int aliases_everything_p PARAMS ((rtx));
106 static int write_dependence_p PARAMS ((rtx, rtx, int));
107 static int nonlocal_mentioned_p PARAMS ((rtx));
109 /* Set up all info needed to perform alias analysis on memory references. */
111 /* Returns the size in bytes of the mode of X. */
112 #define SIZE_FOR_MODE(X) (GET_MODE_SIZE (GET_MODE (X)))
114 /* Returns nonzero if MEM1 and MEM2 do not alias because they are in
115 different alias sets. We ignore alias sets in functions making use
116 of variable arguments because the va_arg macros on some systems are
118 #define DIFFERENT_ALIAS_SETS_P(MEM1, MEM2) \
119 mems_in_disjoint_alias_sets_p (MEM1, MEM2)
121 /* Cap the number of passes we make over the insns propagating alias
122 information through set chains. 10 is a completely arbitrary choice. */
123 #define MAX_ALIAS_LOOP_PASSES 10
125 /* reg_base_value[N] gives an address to which register N is related.
126 If all sets after the first add or subtract to the current value
127 or otherwise modify it so it does not point to a different top level
128 object, reg_base_value[N] is equal to the address part of the source
131 A base address can be an ADDRESS, SYMBOL_REF, or LABEL_REF. ADDRESS
132 expressions represent certain special values: function arguments and
133 the stack, frame, and argument pointers.
135 The contents of an ADDRESS is not normally used, the mode of the
136 ADDRESS determines whether the ADDRESS is a function argument or some
137 other special value. Pointer equality, not rtx_equal_p, determines whether
138 two ADDRESS expressions refer to the same base address.
140 The only use of the contents of an ADDRESS is for determining if the
141 current function performs nonlocal memory memory references for the
142 purposes of marking the function as a constant function. */
144 static rtx *reg_base_value;
145 static rtx *new_reg_base_value;
146 static unsigned int reg_base_value_size; /* size of reg_base_value array */
148 #define REG_BASE_VALUE(X) \
149 (REGNO (X) < reg_base_value_size \
150 ? reg_base_value[REGNO (X)] : 0)
152 /* Vector of known invariant relationships between registers. Set in
153 loop unrolling. Indexed by register number, if nonzero the value
154 is an expression describing this register in terms of another.
156 The length of this array is REG_BASE_VALUE_SIZE.
158 Because this array contains only pseudo registers it has no effect
160 static rtx *alias_invariant;
162 /* Vector indexed by N giving the initial (unchanging) value known for
163 pseudo-register N. This array is initialized in
164 init_alias_analysis, and does not change until end_alias_analysis
166 rtx *reg_known_value;
168 /* Indicates number of valid entries in reg_known_value. */
169 static unsigned int reg_known_value_size;
171 /* Vector recording for each reg_known_value whether it is due to a
172 REG_EQUIV note. Future passes (viz., reload) may replace the
173 pseudo with the equivalent expression and so we account for the
174 dependences that would be introduced if that happens.
176 The REG_EQUIV notes created in assign_parms may mention the arg
177 pointer, and there are explicit insns in the RTL that modify the
178 arg pointer. Thus we must ensure that such insns don't get
179 scheduled across each other because that would invalidate the
180 REG_EQUIV notes. One could argue that the REG_EQUIV notes are
181 wrong, but solving the problem in the scheduler will likely give
182 better code, so we do it here. */
183 char *reg_known_equiv_p;
185 /* True when scanning insns from the start of the rtl to the
186 NOTE_INSN_FUNCTION_BEG note. */
187 static int copying_arguments;
189 /* The splay-tree used to store the various alias set entries. */
190 static splay_tree alias_sets;
192 /* Returns a pointer to the alias set entry for ALIAS_SET, if there is
193 such an entry, or NULL otherwise. */
195 static alias_set_entry
196 get_alias_set_entry (alias_set)
197 HOST_WIDE_INT alias_set;
200 = splay_tree_lookup (alias_sets, (splay_tree_key) alias_set);
202 return sn != 0 ? ((alias_set_entry) sn->value) : 0;
205 /* Returns nonzero if the alias sets for MEM1 and MEM2 are such that
206 the two MEMs cannot alias each other. */
209 mems_in_disjoint_alias_sets_p (mem1, mem2)
213 #ifdef ENABLE_CHECKING
214 /* Perform a basic sanity check. Namely, that there are no alias sets
215 if we're not using strict aliasing. This helps to catch bugs
216 whereby someone uses PUT_CODE, but doesn't clear MEM_ALIAS_SET, or
217 where a MEM is allocated in some way other than by the use of
218 gen_rtx_MEM, and the MEM_ALIAS_SET is not cleared. If we begin to
219 use alias sets to indicate that spilled registers cannot alias each
220 other, we might need to remove this check. */
221 if (! flag_strict_aliasing
222 && (MEM_ALIAS_SET (mem1) != 0 || MEM_ALIAS_SET (mem2) != 0))
226 return ! alias_sets_conflict_p (MEM_ALIAS_SET (mem1), MEM_ALIAS_SET (mem2));
229 /* Insert the NODE into the splay tree given by DATA. Used by
230 record_alias_subset via splay_tree_foreach. */
233 insert_subset_children (node, data)
234 splay_tree_node node;
237 splay_tree_insert ((splay_tree) data, node->key, node->value);
242 /* Return 1 if the two specified alias sets may conflict. */
245 alias_sets_conflict_p (set1, set2)
246 HOST_WIDE_INT set1, set2;
250 /* If have no alias set information for one of the operands, we have
251 to assume it can alias anything. */
252 if (set1 == 0 || set2 == 0
253 /* If the two alias sets are the same, they may alias. */
257 /* See if the first alias set is a subset of the second. */
258 ase = get_alias_set_entry (set1);
260 && (ase->has_zero_child
261 || splay_tree_lookup (ase->children,
262 (splay_tree_key) set2)))
265 /* Now do the same, but with the alias sets reversed. */
266 ase = get_alias_set_entry (set2);
268 && (ase->has_zero_child
269 || splay_tree_lookup (ase->children,
270 (splay_tree_key) set1)))
273 /* The two alias sets are distinct and neither one is the
274 child of the other. Therefore, they cannot alias. */
278 /* Return 1 if TYPE is a RECORD_TYPE, UNION_TYPE, or QUAL_UNION_TYPE and has
279 has any readonly fields. If any of the fields have types that
280 contain readonly fields, return true as well. */
283 readonly_fields_p (type)
288 if (TREE_CODE (type) != RECORD_TYPE && TREE_CODE (type) != UNION_TYPE
289 && TREE_CODE (type) != QUAL_UNION_TYPE)
292 for (field = TYPE_FIELDS (type); field != 0; field = TREE_CHAIN (field))
293 if (TREE_CODE (field) == FIELD_DECL
294 && (TREE_READONLY (field)
295 || readonly_fields_p (TREE_TYPE (field))))
301 /* Return 1 if any MEM object of type T1 will always conflict (using the
302 dependency routines in this file) with any MEM object of type T2.
303 This is used when allocating temporary storage. If T1 and/or T2 are
304 NULL_TREE, it means we know nothing about the storage. */
307 objects_must_conflict_p (t1, t2)
310 /* If neither has a type specified, we don't know if they'll conflict
311 because we may be using them to store objects of various types, for
312 example the argument and local variables areas of inlined functions. */
313 if (t1 == 0 && t2 == 0)
316 /* If one or the other has readonly fields or is readonly,
317 then they may not conflict. */
318 if ((t1 != 0 && readonly_fields_p (t1))
319 || (t2 != 0 && readonly_fields_p (t2))
320 || (t1 != 0 && TYPE_READONLY (t1))
321 || (t2 != 0 && TYPE_READONLY (t2)))
324 /* If they are the same type, they must conflict. */
326 /* Likewise if both are volatile. */
327 || (t1 != 0 && TYPE_VOLATILE (t1) && t2 != 0 && TYPE_VOLATILE (t2)))
330 /* If one is aggregate and the other is scalar then they may not
332 if ((t1 != 0 && AGGREGATE_TYPE_P (t1))
333 != (t2 != 0 && AGGREGATE_TYPE_P (t2)))
336 /* Otherwise they conflict only if the alias sets conflict. */
337 return alias_sets_conflict_p (t1 ? get_alias_set (t1) : 0,
338 t2 ? get_alias_set (t2) : 0);
341 /* T is an expression with pointer type. Find the DECL on which this
342 expression is based. (For example, in `a[i]' this would be `a'.)
343 If there is no such DECL, or a unique decl cannot be determined,
344 NULL_TREE is retured. */
352 if (t == 0 || t == error_mark_node || ! POINTER_TYPE_P (TREE_TYPE (t)))
355 /* If this is a declaration, return it. */
356 if (TREE_CODE_CLASS (TREE_CODE (t)) == 'd')
359 /* Handle general expressions. It would be nice to deal with
360 COMPONENT_REFs here. If we could tell that `a' and `b' were the
361 same, then `a->f' and `b->f' are also the same. */
362 switch (TREE_CODE_CLASS (TREE_CODE (t)))
365 return find_base_decl (TREE_OPERAND (t, 0));
368 /* Return 0 if found in neither or both are the same. */
369 d0 = find_base_decl (TREE_OPERAND (t, 0));
370 d1 = find_base_decl (TREE_OPERAND (t, 1));
381 d0 = find_base_decl (TREE_OPERAND (t, 0));
382 d1 = find_base_decl (TREE_OPERAND (t, 1));
383 d2 = find_base_decl (TREE_OPERAND (t, 2));
385 /* Set any nonzero values from the last, then from the first. */
386 if (d1 == 0) d1 = d2;
387 if (d0 == 0) d0 = d1;
388 if (d1 == 0) d1 = d0;
389 if (d2 == 0) d2 = d1;
391 /* At this point all are nonzero or all are zero. If all three are the
392 same, return it. Otherwise, return zero. */
393 return (d0 == d1 && d1 == d2) ? d0 : 0;
400 /* Return 1 if T is an expression that get_inner_reference handles. */
403 handled_component_p (t)
406 switch (TREE_CODE (t))
411 case ARRAY_RANGE_REF:
412 case NON_LVALUE_EXPR:
417 return (TYPE_MODE (TREE_TYPE (t))
418 == TYPE_MODE (TREE_TYPE (TREE_OPERAND (t, 0))));
425 /* Return 1 if all the nested component references handled by
426 get_inner_reference in T are such that we can address the object in T. */
432 /* If we're at the end, it is vacuously addressable. */
433 if (! handled_component_p (t))
436 /* Bitfields are never addressable. */
437 else if (TREE_CODE (t) == BIT_FIELD_REF)
440 /* Fields are addressable unless they are marked as nonaddressable or
441 the containing type has alias set 0. */
442 else if (TREE_CODE (t) == COMPONENT_REF
443 && ! DECL_NONADDRESSABLE_P (TREE_OPERAND (t, 1))
444 && get_alias_set (TREE_TYPE (TREE_OPERAND (t, 0))) != 0
445 && can_address_p (TREE_OPERAND (t, 0)))
448 /* Likewise for arrays. */
449 else if ((TREE_CODE (t) == ARRAY_REF || TREE_CODE (t) == ARRAY_RANGE_REF)
450 && ! TYPE_NONALIASED_COMPONENT (TREE_TYPE (TREE_OPERAND (t, 0)))
451 && get_alias_set (TREE_TYPE (TREE_OPERAND (t, 0))) != 0
452 && can_address_p (TREE_OPERAND (t, 0)))
458 /* Return the alias set for T, which may be either a type or an
459 expression. Call language-specific routine for help, if needed. */
467 /* If we're not doing any alias analysis, just assume everything
468 aliases everything else. Also return 0 if this or its type is
470 if (! flag_strict_aliasing || t == error_mark_node
472 && (TREE_TYPE (t) == 0 || TREE_TYPE (t) == error_mark_node)))
475 /* We can be passed either an expression or a type. This and the
476 language-specific routine may make mutually-recursive calls to each other
477 to figure out what to do. At each juncture, we see if this is a tree
478 that the language may need to handle specially. First handle things that
483 tree placeholder_ptr = 0;
485 /* Remove any nops, then give the language a chance to do
486 something with this tree before we look at it. */
488 set = (*lang_hooks.get_alias_set) (t);
492 /* First see if the actual object referenced is an INDIRECT_REF from a
493 restrict-qualified pointer or a "void *". Replace
494 PLACEHOLDER_EXPRs. */
495 while (TREE_CODE (inner) == PLACEHOLDER_EXPR
496 || handled_component_p (inner))
498 if (TREE_CODE (inner) == PLACEHOLDER_EXPR)
499 inner = find_placeholder (inner, &placeholder_ptr);
501 inner = TREE_OPERAND (inner, 0);
506 /* Check for accesses through restrict-qualified pointers. */
507 if (TREE_CODE (inner) == INDIRECT_REF)
509 tree decl = find_base_decl (TREE_OPERAND (inner, 0));
511 if (decl && DECL_POINTER_ALIAS_SET_KNOWN_P (decl))
513 /* If we haven't computed the actual alias set, do it now. */
514 if (DECL_POINTER_ALIAS_SET (decl) == -2)
516 /* No two restricted pointers can point at the same thing.
517 However, a restricted pointer can point at the same thing
518 as an unrestricted pointer, if that unrestricted pointer
519 is based on the restricted pointer. So, we make the
520 alias set for the restricted pointer a subset of the
521 alias set for the type pointed to by the type of the
523 HOST_WIDE_INT pointed_to_alias_set
524 = get_alias_set (TREE_TYPE (TREE_TYPE (decl)));
526 if (pointed_to_alias_set == 0)
527 /* It's not legal to make a subset of alias set zero. */
531 DECL_POINTER_ALIAS_SET (decl) = new_alias_set ();
532 record_alias_subset (pointed_to_alias_set,
533 DECL_POINTER_ALIAS_SET (decl));
537 /* We use the alias set indicated in the declaration. */
538 return DECL_POINTER_ALIAS_SET (decl);
541 /* If we have an INDIRECT_REF via a void pointer, we don't
542 know anything about what that might alias. */
543 else if (TREE_CODE (TREE_TYPE (inner)) == VOID_TYPE)
547 /* Otherwise, pick up the outermost object that we could have a pointer
548 to, processing conversion and PLACEHOLDER_EXPR as above. */
550 while (TREE_CODE (t) == PLACEHOLDER_EXPR
551 || (handled_component_p (t) && ! can_address_p (t)))
553 if (TREE_CODE (t) == PLACEHOLDER_EXPR)
554 t = find_placeholder (t, &placeholder_ptr);
556 t = TREE_OPERAND (t, 0);
561 /* If we've already determined the alias set for a decl, just return
562 it. This is necessary for C++ anonymous unions, whose component
563 variables don't look like union members (boo!). */
564 if (TREE_CODE (t) == VAR_DECL
565 && DECL_RTL_SET_P (t) && GET_CODE (DECL_RTL (t)) == MEM)
566 return MEM_ALIAS_SET (DECL_RTL (t));
568 /* Now all we care about is the type. */
572 /* Variant qualifiers don't affect the alias set, so get the main
573 variant. If this is a type with a known alias set, return it. */
574 t = TYPE_MAIN_VARIANT (t);
575 if (TYPE_ALIAS_SET_KNOWN_P (t))
576 return TYPE_ALIAS_SET (t);
578 /* See if the language has special handling for this type. */
579 set = (*lang_hooks.get_alias_set) (t);
583 /* There are no objects of FUNCTION_TYPE, so there's no point in
584 using up an alias set for them. (There are, of course, pointers
585 and references to functions, but that's different.) */
586 else if (TREE_CODE (t) == FUNCTION_TYPE)
589 /* Otherwise make a new alias set for this type. */
590 set = new_alias_set ();
592 TYPE_ALIAS_SET (t) = set;
594 /* If this is an aggregate type, we must record any component aliasing
596 if (AGGREGATE_TYPE_P (t) || TREE_CODE (t) == COMPLEX_TYPE)
597 record_component_aliases (t);
602 /* Return a brand-new alias set. */
607 static HOST_WIDE_INT last_alias_set;
609 if (flag_strict_aliasing)
610 return ++last_alias_set;
615 /* Indicate that things in SUBSET can alias things in SUPERSET, but
616 not vice versa. For example, in C, a store to an `int' can alias a
617 structure containing an `int', but not vice versa. Here, the
618 structure would be the SUPERSET and `int' the SUBSET. This
619 function should be called only once per SUPERSET/SUBSET pair.
621 It is illegal for SUPERSET to be zero; everything is implicitly a
622 subset of alias set zero. */
625 record_alias_subset (superset, subset)
626 HOST_WIDE_INT superset;
627 HOST_WIDE_INT subset;
629 alias_set_entry superset_entry;
630 alias_set_entry subset_entry;
632 /* It is possible in complex type situations for both sets to be the same,
633 in which case we can ignore this operation. */
634 if (superset == subset)
640 superset_entry = get_alias_set_entry (superset);
641 if (superset_entry == 0)
643 /* Create an entry for the SUPERSET, so that we have a place to
644 attach the SUBSET. */
646 = (alias_set_entry) xmalloc (sizeof (struct alias_set_entry));
647 superset_entry->alias_set = superset;
648 superset_entry->children
649 = splay_tree_new (splay_tree_compare_ints, 0, 0);
650 superset_entry->has_zero_child = 0;
651 splay_tree_insert (alias_sets, (splay_tree_key) superset,
652 (splay_tree_value) superset_entry);
656 superset_entry->has_zero_child = 1;
659 subset_entry = get_alias_set_entry (subset);
660 /* If there is an entry for the subset, enter all of its children
661 (if they are not already present) as children of the SUPERSET. */
664 if (subset_entry->has_zero_child)
665 superset_entry->has_zero_child = 1;
667 splay_tree_foreach (subset_entry->children, insert_subset_children,
668 superset_entry->children);
671 /* Enter the SUBSET itself as a child of the SUPERSET. */
672 splay_tree_insert (superset_entry->children,
673 (splay_tree_key) subset, 0);
677 /* Record that component types of TYPE, if any, are part of that type for
678 aliasing purposes. For record types, we only record component types
679 for fields that are marked addressable. For array types, we always
680 record the component types, so the front end should not call this
681 function if the individual component aren't addressable. */
684 record_component_aliases (type)
687 HOST_WIDE_INT superset = get_alias_set (type);
693 switch (TREE_CODE (type))
696 if (! TYPE_NONALIASED_COMPONENT (type))
697 record_alias_subset (superset, get_alias_set (TREE_TYPE (type)));
702 case QUAL_UNION_TYPE:
703 for (field = TYPE_FIELDS (type); field != 0; field = TREE_CHAIN (field))
704 if (TREE_CODE (field) == FIELD_DECL && ! DECL_NONADDRESSABLE_P (field))
705 record_alias_subset (superset, get_alias_set (TREE_TYPE (field)));
709 record_alias_subset (superset, get_alias_set (TREE_TYPE (type)));
717 /* Allocate an alias set for use in storing and reading from the varargs
721 get_varargs_alias_set ()
723 static HOST_WIDE_INT set = -1;
726 set = new_alias_set ();
731 /* Likewise, but used for the fixed portions of the frame, e.g., register
735 get_frame_alias_set ()
737 static HOST_WIDE_INT set = -1;
740 set = new_alias_set ();
745 /* Inside SRC, the source of a SET, find a base address. */
748 find_base_value (src)
752 switch (GET_CODE (src))
760 /* At the start of a function, argument registers have known base
761 values which may be lost later. Returning an ADDRESS
762 expression here allows optimization based on argument values
763 even when the argument registers are used for other purposes. */
764 if (regno < FIRST_PSEUDO_REGISTER && copying_arguments)
765 return new_reg_base_value[regno];
767 /* If a pseudo has a known base value, return it. Do not do this
768 for hard regs since it can result in a circular dependency
769 chain for registers which have values at function entry.
771 The test above is not sufficient because the scheduler may move
772 a copy out of an arg reg past the NOTE_INSN_FUNCTION_BEGIN. */
773 if (regno >= FIRST_PSEUDO_REGISTER
774 && regno < reg_base_value_size
775 && reg_base_value[regno])
776 return reg_base_value[regno];
781 /* Check for an argument passed in memory. Only record in the
782 copying-arguments block; it is too hard to track changes
784 if (copying_arguments
785 && (XEXP (src, 0) == arg_pointer_rtx
786 || (GET_CODE (XEXP (src, 0)) == PLUS
787 && XEXP (XEXP (src, 0), 0) == arg_pointer_rtx)))
788 return gen_rtx_ADDRESS (VOIDmode, src);
793 if (GET_CODE (src) != PLUS && GET_CODE (src) != MINUS)
796 /* ... fall through ... */
801 rtx temp, src_0 = XEXP (src, 0), src_1 = XEXP (src, 1);
803 /* If either operand is a REG, then see if we already have
804 a known value for it. */
805 if (GET_CODE (src_0) == REG)
807 temp = find_base_value (src_0);
812 if (GET_CODE (src_1) == REG)
814 temp = find_base_value (src_1);
819 /* Guess which operand is the base address:
820 If either operand is a symbol, then it is the base. If
821 either operand is a CONST_INT, then the other is the base. */
822 if (GET_CODE (src_1) == CONST_INT || CONSTANT_P (src_0))
823 return find_base_value (src_0);
824 else if (GET_CODE (src_0) == CONST_INT || CONSTANT_P (src_1))
825 return find_base_value (src_1);
827 /* This might not be necessary anymore:
828 If either operand is a REG that is a known pointer, then it
830 else if (GET_CODE (src_0) == REG && REG_POINTER (src_0))
831 return find_base_value (src_0);
832 else if (GET_CODE (src_1) == REG && REG_POINTER (src_1))
833 return find_base_value (src_1);
839 /* The standard form is (lo_sum reg sym) so look only at the
841 return find_base_value (XEXP (src, 1));
844 /* If the second operand is constant set the base
845 address to the first operand. */
846 if (GET_CODE (XEXP (src, 1)) == CONST_INT && INTVAL (XEXP (src, 1)) != 0)
847 return find_base_value (XEXP (src, 0));
851 if (GET_MODE_SIZE (GET_MODE (src)) < GET_MODE_SIZE (Pmode))
855 case SIGN_EXTEND: /* used for NT/Alpha pointers */
857 return find_base_value (XEXP (src, 0));
866 /* Called from init_alias_analysis indirectly through note_stores. */
868 /* While scanning insns to find base values, reg_seen[N] is nonzero if
869 register N has been set in this function. */
870 static char *reg_seen;
872 /* Addresses which are known not to alias anything else are identified
873 by a unique integer. */
874 static int unique_id;
877 record_set (dest, set, data)
879 void *data ATTRIBUTE_UNUSED;
884 if (GET_CODE (dest) != REG)
887 regno = REGNO (dest);
889 if (regno >= reg_base_value_size)
894 /* A CLOBBER wipes out any old value but does not prevent a previously
895 unset register from acquiring a base address (i.e. reg_seen is not
897 if (GET_CODE (set) == CLOBBER)
899 new_reg_base_value[regno] = 0;
908 new_reg_base_value[regno] = 0;
912 new_reg_base_value[regno] = gen_rtx_ADDRESS (Pmode,
913 GEN_INT (unique_id++));
917 /* This is not the first set. If the new value is not related to the
918 old value, forget the base value. Note that the following code is
920 extern int x, y; int *p = &x; p += (&y-&x);
921 ANSI C does not allow computing the difference of addresses
922 of distinct top level objects. */
923 if (new_reg_base_value[regno])
924 switch (GET_CODE (src))
928 if (XEXP (src, 0) != dest && XEXP (src, 1) != dest)
929 new_reg_base_value[regno] = 0;
932 /* If the value we add in the PLUS is also a valid base value,
933 this might be the actual base value, and the original value
936 rtx other = NULL_RTX;
938 if (XEXP (src, 0) == dest)
939 other = XEXP (src, 1);
940 else if (XEXP (src, 1) == dest)
941 other = XEXP (src, 0);
943 if (! other || find_base_value (other))
944 new_reg_base_value[regno] = 0;
948 if (XEXP (src, 0) != dest || GET_CODE (XEXP (src, 1)) != CONST_INT)
949 new_reg_base_value[regno] = 0;
952 new_reg_base_value[regno] = 0;
955 /* If this is the first set of a register, record the value. */
956 else if ((regno >= FIRST_PSEUDO_REGISTER || ! fixed_regs[regno])
957 && ! reg_seen[regno] && new_reg_base_value[regno] == 0)
958 new_reg_base_value[regno] = find_base_value (src);
963 /* Called from loop optimization when a new pseudo-register is
964 created. It indicates that REGNO is being set to VAL. f INVARIANT
965 is true then this value also describes an invariant relationship
966 which can be used to deduce that two registers with unknown values
970 record_base_value (regno, val, invariant)
975 if (regno >= reg_base_value_size)
978 if (invariant && alias_invariant)
979 alias_invariant[regno] = val;
981 if (GET_CODE (val) == REG)
983 if (REGNO (val) < reg_base_value_size)
984 reg_base_value[regno] = reg_base_value[REGNO (val)];
989 reg_base_value[regno] = find_base_value (val);
992 /* Clear alias info for a register. This is used if an RTL transformation
993 changes the value of a register. This is used in flow by AUTO_INC_DEC
994 optimizations. We don't need to clear reg_base_value, since flow only
995 changes the offset. */
998 clear_reg_alias_info (reg)
1001 unsigned int regno = REGNO (reg);
1003 if (regno < reg_known_value_size && regno >= FIRST_PSEUDO_REGISTER)
1004 reg_known_value[regno] = reg;
1007 /* Returns a canonical version of X, from the point of view alias
1008 analysis. (For example, if X is a MEM whose address is a register,
1009 and the register has a known value (say a SYMBOL_REF), then a MEM
1010 whose address is the SYMBOL_REF is returned.) */
1016 /* Recursively look for equivalences. */
1017 if (GET_CODE (x) == REG && REGNO (x) >= FIRST_PSEUDO_REGISTER
1018 && REGNO (x) < reg_known_value_size)
1019 return reg_known_value[REGNO (x)] == x
1020 ? x : canon_rtx (reg_known_value[REGNO (x)]);
1021 else if (GET_CODE (x) == PLUS)
1023 rtx x0 = canon_rtx (XEXP (x, 0));
1024 rtx x1 = canon_rtx (XEXP (x, 1));
1026 if (x0 != XEXP (x, 0) || x1 != XEXP (x, 1))
1028 if (GET_CODE (x0) == CONST_INT)
1029 return plus_constant (x1, INTVAL (x0));
1030 else if (GET_CODE (x1) == CONST_INT)
1031 return plus_constant (x0, INTVAL (x1));
1032 return gen_rtx_PLUS (GET_MODE (x), x0, x1);
1036 /* This gives us much better alias analysis when called from
1037 the loop optimizer. Note we want to leave the original
1038 MEM alone, but need to return the canonicalized MEM with
1039 all the flags with their original values. */
1040 else if (GET_CODE (x) == MEM)
1041 x = replace_equiv_address_nv (x, canon_rtx (XEXP (x, 0)));
1046 /* Return 1 if X and Y are identical-looking rtx's.
1048 We use the data in reg_known_value above to see if two registers with
1049 different numbers are, in fact, equivalent. */
1052 rtx_equal_for_memref_p (x, y)
1060 if (x == 0 && y == 0)
1062 if (x == 0 || y == 0)
1071 code = GET_CODE (x);
1072 /* Rtx's of different codes cannot be equal. */
1073 if (code != GET_CODE (y))
1076 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent.
1077 (REG:SI x) and (REG:HI x) are NOT equivalent. */
1079 if (GET_MODE (x) != GET_MODE (y))
1082 /* Some RTL can be compared without a recursive examination. */
1086 return CSELIB_VAL_PTR (x) == CSELIB_VAL_PTR (y);
1089 return REGNO (x) == REGNO (y);
1092 return XEXP (x, 0) == XEXP (y, 0);
1095 return XSTR (x, 0) == XSTR (y, 0);
1099 /* There's no need to compare the contents of CONST_DOUBLEs or
1100 CONST_INTs because pointer equality is a good enough
1101 comparison for these nodes. */
1105 return (XINT (x, 1) == XINT (y, 1)
1106 && rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0)));
1112 /* For commutative operations, the RTX match if the operand match in any
1113 order. Also handle the simple binary and unary cases without a loop. */
1114 if (code == EQ || code == NE || GET_RTX_CLASS (code) == 'c')
1115 return ((rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0))
1116 && rtx_equal_for_memref_p (XEXP (x, 1), XEXP (y, 1)))
1117 || (rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 1))
1118 && rtx_equal_for_memref_p (XEXP (x, 1), XEXP (y, 0))));
1119 else if (GET_RTX_CLASS (code) == '<' || GET_RTX_CLASS (code) == '2')
1120 return (rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0))
1121 && rtx_equal_for_memref_p (XEXP (x, 1), XEXP (y, 1)));
1122 else if (GET_RTX_CLASS (code) == '1')
1123 return rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0));
1125 /* Compare the elements. If any pair of corresponding elements
1126 fail to match, return 0 for the whole things.
1128 Limit cases to types which actually appear in addresses. */
1130 fmt = GET_RTX_FORMAT (code);
1131 for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
1136 if (XINT (x, i) != XINT (y, i))
1141 /* Two vectors must have the same length. */
1142 if (XVECLEN (x, i) != XVECLEN (y, i))
1145 /* And the corresponding elements must match. */
1146 for (j = 0; j < XVECLEN (x, i); j++)
1147 if (rtx_equal_for_memref_p (XVECEXP (x, i, j),
1148 XVECEXP (y, i, j)) == 0)
1153 if (rtx_equal_for_memref_p (XEXP (x, i), XEXP (y, i)) == 0)
1157 /* This can happen for asm operands. */
1159 if (strcmp (XSTR (x, i), XSTR (y, i)))
1163 /* This can happen for an asm which clobbers memory. */
1167 /* It is believed that rtx's at this level will never
1168 contain anything but integers and other rtx's,
1169 except for within LABEL_REFs and SYMBOL_REFs. */
1177 /* Given an rtx X, find a SYMBOL_REF or LABEL_REF within
1178 X and return it, or return 0 if none found. */
1181 find_symbolic_term (x)
1188 code = GET_CODE (x);
1189 if (code == SYMBOL_REF || code == LABEL_REF)
1191 if (GET_RTX_CLASS (code) == 'o')
1194 fmt = GET_RTX_FORMAT (code);
1195 for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
1201 t = find_symbolic_term (XEXP (x, i));
1205 else if (fmt[i] == 'E')
1216 struct elt_loc_list *l;
1218 #if defined (FIND_BASE_TERM)
1219 /* Try machine-dependent ways to find the base term. */
1220 x = FIND_BASE_TERM (x);
1223 switch (GET_CODE (x))
1226 return REG_BASE_VALUE (x);
1229 case SIGN_EXTEND: /* Used for Alpha/NT pointers */
1235 return find_base_term (XEXP (x, 0));
1238 val = CSELIB_VAL_PTR (x);
1239 for (l = val->locs; l; l = l->next)
1240 if ((x = find_base_term (l->loc)) != 0)
1246 if (GET_CODE (x) != PLUS && GET_CODE (x) != MINUS)
1253 rtx tmp1 = XEXP (x, 0);
1254 rtx tmp2 = XEXP (x, 1);
1256 /* This is a litle bit tricky since we have to determine which of
1257 the two operands represents the real base address. Otherwise this
1258 routine may return the index register instead of the base register.
1260 That may cause us to believe no aliasing was possible, when in
1261 fact aliasing is possible.
1263 We use a few simple tests to guess the base register. Additional
1264 tests can certainly be added. For example, if one of the operands
1265 is a shift or multiply, then it must be the index register and the
1266 other operand is the base register. */
1268 if (tmp1 == pic_offset_table_rtx && CONSTANT_P (tmp2))
1269 return find_base_term (tmp2);
1271 /* If either operand is known to be a pointer, then use it
1272 to determine the base term. */
1273 if (REG_P (tmp1) && REG_POINTER (tmp1))
1274 return find_base_term (tmp1);
1276 if (REG_P (tmp2) && REG_POINTER (tmp2))
1277 return find_base_term (tmp2);
1279 /* Neither operand was known to be a pointer. Go ahead and find the
1280 base term for both operands. */
1281 tmp1 = find_base_term (tmp1);
1282 tmp2 = find_base_term (tmp2);
1284 /* If either base term is named object or a special address
1285 (like an argument or stack reference), then use it for the
1288 && (GET_CODE (tmp1) == SYMBOL_REF
1289 || GET_CODE (tmp1) == LABEL_REF
1290 || (GET_CODE (tmp1) == ADDRESS
1291 && GET_MODE (tmp1) != VOIDmode)))
1295 && (GET_CODE (tmp2) == SYMBOL_REF
1296 || GET_CODE (tmp2) == LABEL_REF
1297 || (GET_CODE (tmp2) == ADDRESS
1298 && GET_MODE (tmp2) != VOIDmode)))
1301 /* We could not determine which of the two operands was the
1302 base register and which was the index. So we can determine
1303 nothing from the base alias check. */
1308 if (GET_CODE (XEXP (x, 0)) == REG && GET_CODE (XEXP (x, 1)) == CONST_INT)
1309 return REG_BASE_VALUE (XEXP (x, 0));
1317 return REG_BASE_VALUE (frame_pointer_rtx);
1324 /* Return 0 if the addresses X and Y are known to point to different
1325 objects, 1 if they might be pointers to the same object. */
1328 base_alias_check (x, y, x_mode, y_mode)
1330 enum machine_mode x_mode, y_mode;
1332 rtx x_base = find_base_term (x);
1333 rtx y_base = find_base_term (y);
1335 /* If the address itself has no known base see if a known equivalent
1336 value has one. If either address still has no known base, nothing
1337 is known about aliasing. */
1342 if (! flag_expensive_optimizations || (x_c = canon_rtx (x)) == x)
1345 x_base = find_base_term (x_c);
1353 if (! flag_expensive_optimizations || (y_c = canon_rtx (y)) == y)
1356 y_base = find_base_term (y_c);
1361 /* If the base addresses are equal nothing is known about aliasing. */
1362 if (rtx_equal_p (x_base, y_base))
1365 /* The base addresses of the read and write are different expressions.
1366 If they are both symbols and they are not accessed via AND, there is
1367 no conflict. We can bring knowledge of object alignment into play
1368 here. For example, on alpha, "char a, b;" can alias one another,
1369 though "char a; long b;" cannot. */
1370 if (GET_CODE (x_base) != ADDRESS && GET_CODE (y_base) != ADDRESS)
1372 if (GET_CODE (x) == AND && GET_CODE (y) == AND)
1374 if (GET_CODE (x) == AND
1375 && (GET_CODE (XEXP (x, 1)) != CONST_INT
1376 || (int) GET_MODE_UNIT_SIZE (y_mode) < -INTVAL (XEXP (x, 1))))
1378 if (GET_CODE (y) == AND
1379 && (GET_CODE (XEXP (y, 1)) != CONST_INT
1380 || (int) GET_MODE_UNIT_SIZE (x_mode) < -INTVAL (XEXP (y, 1))))
1382 /* Differing symbols never alias. */
1386 /* If one address is a stack reference there can be no alias:
1387 stack references using different base registers do not alias,
1388 a stack reference can not alias a parameter, and a stack reference
1389 can not alias a global. */
1390 if ((GET_CODE (x_base) == ADDRESS && GET_MODE (x_base) == Pmode)
1391 || (GET_CODE (y_base) == ADDRESS && GET_MODE (y_base) == Pmode))
1394 if (! flag_argument_noalias)
1397 if (flag_argument_noalias > 1)
1400 /* Weak noalias assertion (arguments are distinct, but may match globals). */
1401 return ! (GET_MODE (x_base) == VOIDmode && GET_MODE (y_base) == VOIDmode);
1404 /* Convert the address X into something we can use. This is done by returning
1405 it unchanged unless it is a value; in the latter case we call cselib to get
1406 a more useful rtx. */
1413 struct elt_loc_list *l;
1415 if (GET_CODE (x) != VALUE)
1417 v = CSELIB_VAL_PTR (x);
1418 for (l = v->locs; l; l = l->next)
1419 if (CONSTANT_P (l->loc))
1421 for (l = v->locs; l; l = l->next)
1422 if (GET_CODE (l->loc) != REG && GET_CODE (l->loc) != MEM)
1425 return v->locs->loc;
1429 /* Return the address of the (N_REFS + 1)th memory reference to ADDR
1430 where SIZE is the size in bytes of the memory reference. If ADDR
1431 is not modified by the memory reference then ADDR is returned. */
1434 addr_side_effect_eval (addr, size, n_refs)
1441 switch (GET_CODE (addr))
1444 offset = (n_refs + 1) * size;
1447 offset = -(n_refs + 1) * size;
1450 offset = n_refs * size;
1453 offset = -n_refs * size;
1461 addr = gen_rtx_PLUS (GET_MODE (addr), XEXP (addr, 0), GEN_INT (offset));
1463 addr = XEXP (addr, 0);
1468 /* Return nonzero if X and Y (memory addresses) could reference the
1469 same location in memory. C is an offset accumulator. When
1470 C is nonzero, we are testing aliases between X and Y + C.
1471 XSIZE is the size in bytes of the X reference,
1472 similarly YSIZE is the size in bytes for Y.
1474 If XSIZE or YSIZE is zero, we do not know the amount of memory being
1475 referenced (the reference was BLKmode), so make the most pessimistic
1478 If XSIZE or YSIZE is negative, we may access memory outside the object
1479 being referenced as a side effect. This can happen when using AND to
1480 align memory references, as is done on the Alpha.
1482 Nice to notice that varying addresses cannot conflict with fp if no
1483 local variables had their addresses taken, but that's too hard now. */
1486 memrefs_conflict_p (xsize, x, ysize, y, c)
1491 if (GET_CODE (x) == VALUE)
1493 if (GET_CODE (y) == VALUE)
1495 if (GET_CODE (x) == HIGH)
1497 else if (GET_CODE (x) == LO_SUM)
1500 x = canon_rtx (addr_side_effect_eval (x, xsize, 0));
1501 if (GET_CODE (y) == HIGH)
1503 else if (GET_CODE (y) == LO_SUM)
1506 y = canon_rtx (addr_side_effect_eval (y, ysize, 0));
1508 if (rtx_equal_for_memref_p (x, y))
1510 if (xsize <= 0 || ysize <= 0)
1512 if (c >= 0 && xsize > c)
1514 if (c < 0 && ysize+c > 0)
1519 /* This code used to check for conflicts involving stack references and
1520 globals but the base address alias code now handles these cases. */
1522 if (GET_CODE (x) == PLUS)
1524 /* The fact that X is canonicalized means that this
1525 PLUS rtx is canonicalized. */
1526 rtx x0 = XEXP (x, 0);
1527 rtx x1 = XEXP (x, 1);
1529 if (GET_CODE (y) == PLUS)
1531 /* The fact that Y is canonicalized means that this
1532 PLUS rtx is canonicalized. */
1533 rtx y0 = XEXP (y, 0);
1534 rtx y1 = XEXP (y, 1);
1536 if (rtx_equal_for_memref_p (x1, y1))
1537 return memrefs_conflict_p (xsize, x0, ysize, y0, c);
1538 if (rtx_equal_for_memref_p (x0, y0))
1539 return memrefs_conflict_p (xsize, x1, ysize, y1, c);
1540 if (GET_CODE (x1) == CONST_INT)
1542 if (GET_CODE (y1) == CONST_INT)
1543 return memrefs_conflict_p (xsize, x0, ysize, y0,
1544 c - INTVAL (x1) + INTVAL (y1));
1546 return memrefs_conflict_p (xsize, x0, ysize, y,
1549 else if (GET_CODE (y1) == CONST_INT)
1550 return memrefs_conflict_p (xsize, x, ysize, y0, c + INTVAL (y1));
1554 else if (GET_CODE (x1) == CONST_INT)
1555 return memrefs_conflict_p (xsize, x0, ysize, y, c - INTVAL (x1));
1557 else if (GET_CODE (y) == PLUS)
1559 /* The fact that Y is canonicalized means that this
1560 PLUS rtx is canonicalized. */
1561 rtx y0 = XEXP (y, 0);
1562 rtx y1 = XEXP (y, 1);
1564 if (GET_CODE (y1) == CONST_INT)
1565 return memrefs_conflict_p (xsize, x, ysize, y0, c + INTVAL (y1));
1570 if (GET_CODE (x) == GET_CODE (y))
1571 switch (GET_CODE (x))
1575 /* Handle cases where we expect the second operands to be the
1576 same, and check only whether the first operand would conflict
1579 rtx x1 = canon_rtx (XEXP (x, 1));
1580 rtx y1 = canon_rtx (XEXP (y, 1));
1581 if (! rtx_equal_for_memref_p (x1, y1))
1583 x0 = canon_rtx (XEXP (x, 0));
1584 y0 = canon_rtx (XEXP (y, 0));
1585 if (rtx_equal_for_memref_p (x0, y0))
1586 return (xsize == 0 || ysize == 0
1587 || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0));
1589 /* Can't properly adjust our sizes. */
1590 if (GET_CODE (x1) != CONST_INT)
1592 xsize /= INTVAL (x1);
1593 ysize /= INTVAL (x1);
1595 return memrefs_conflict_p (xsize, x0, ysize, y0, c);
1599 /* Are these registers known not to be equal? */
1600 if (alias_invariant)
1602 unsigned int r_x = REGNO (x), r_y = REGNO (y);
1603 rtx i_x, i_y; /* invariant relationships of X and Y */
1605 i_x = r_x >= reg_base_value_size ? 0 : alias_invariant[r_x];
1606 i_y = r_y >= reg_base_value_size ? 0 : alias_invariant[r_y];
1608 if (i_x == 0 && i_y == 0)
1611 if (! memrefs_conflict_p (xsize, i_x ? i_x : x,
1612 ysize, i_y ? i_y : y, c))
1621 /* Treat an access through an AND (e.g. a subword access on an Alpha)
1622 as an access with indeterminate size. Assume that references
1623 besides AND are aligned, so if the size of the other reference is
1624 at least as large as the alignment, assume no other overlap. */
1625 if (GET_CODE (x) == AND && GET_CODE (XEXP (x, 1)) == CONST_INT)
1627 if (GET_CODE (y) == AND || ysize < -INTVAL (XEXP (x, 1)))
1629 return memrefs_conflict_p (xsize, XEXP (x, 0), ysize, y, c);
1631 if (GET_CODE (y) == AND && GET_CODE (XEXP (y, 1)) == CONST_INT)
1633 /* ??? If we are indexing far enough into the array/structure, we
1634 may yet be able to determine that we can not overlap. But we
1635 also need to that we are far enough from the end not to overlap
1636 a following reference, so we do nothing with that for now. */
1637 if (GET_CODE (x) == AND || xsize < -INTVAL (XEXP (y, 1)))
1639 return memrefs_conflict_p (xsize, x, ysize, XEXP (y, 0), c);
1642 if (GET_CODE (x) == ADDRESSOF)
1644 if (y == frame_pointer_rtx
1645 || GET_CODE (y) == ADDRESSOF)
1646 return xsize <= 0 || ysize <= 0;
1648 if (GET_CODE (y) == ADDRESSOF)
1650 if (x == frame_pointer_rtx)
1651 return xsize <= 0 || ysize <= 0;
1656 if (GET_CODE (x) == CONST_INT && GET_CODE (y) == CONST_INT)
1658 c += (INTVAL (y) - INTVAL (x));
1659 return (xsize <= 0 || ysize <= 0
1660 || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0));
1663 if (GET_CODE (x) == CONST)
1665 if (GET_CODE (y) == CONST)
1666 return memrefs_conflict_p (xsize, canon_rtx (XEXP (x, 0)),
1667 ysize, canon_rtx (XEXP (y, 0)), c);
1669 return memrefs_conflict_p (xsize, canon_rtx (XEXP (x, 0)),
1672 if (GET_CODE (y) == CONST)
1673 return memrefs_conflict_p (xsize, x, ysize,
1674 canon_rtx (XEXP (y, 0)), c);
1677 return (xsize <= 0 || ysize <= 0
1678 || (rtx_equal_for_memref_p (x, y)
1679 && ((c >= 0 && xsize > c) || (c < 0 && ysize+c > 0))));
1686 /* Functions to compute memory dependencies.
1688 Since we process the insns in execution order, we can build tables
1689 to keep track of what registers are fixed (and not aliased), what registers
1690 are varying in known ways, and what registers are varying in unknown
1693 If both memory references are volatile, then there must always be a
1694 dependence between the two references, since their order can not be
1695 changed. A volatile and non-volatile reference can be interchanged
1698 A MEM_IN_STRUCT reference at a non-AND varying address can never
1699 conflict with a non-MEM_IN_STRUCT reference at a fixed address. We
1700 also must allow AND addresses, because they may generate accesses
1701 outside the object being referenced. This is used to generate
1702 aligned addresses from unaligned addresses, for instance, the alpha
1703 storeqi_unaligned pattern. */
1705 /* Read dependence: X is read after read in MEM takes place. There can
1706 only be a dependence here if both reads are volatile. */
1709 read_dependence (mem, x)
1713 return MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem);
1716 /* Returns MEM1 if and only if MEM1 is a scalar at a fixed address and
1717 MEM2 is a reference to a structure at a varying address, or returns
1718 MEM2 if vice versa. Otherwise, returns NULL_RTX. If a non-NULL
1719 value is returned MEM1 and MEM2 can never alias. VARIES_P is used
1720 to decide whether or not an address may vary; it should return
1721 nonzero whenever variation is possible.
1722 MEM1_ADDR and MEM2_ADDR are the addresses of MEM1 and MEM2. */
1725 fixed_scalar_and_varying_struct_p (mem1, mem2, mem1_addr, mem2_addr, varies_p)
1727 rtx mem1_addr, mem2_addr;
1728 int (*varies_p) PARAMS ((rtx, int));
1730 if (! flag_strict_aliasing)
1733 if (MEM_SCALAR_P (mem1) && MEM_IN_STRUCT_P (mem2)
1734 && !varies_p (mem1_addr, 1) && varies_p (mem2_addr, 1))
1735 /* MEM1 is a scalar at a fixed address; MEM2 is a struct at a
1739 if (MEM_IN_STRUCT_P (mem1) && MEM_SCALAR_P (mem2)
1740 && varies_p (mem1_addr, 1) && !varies_p (mem2_addr, 1))
1741 /* MEM2 is a scalar at a fixed address; MEM1 is a struct at a
1748 /* Returns nonzero if something about the mode or address format MEM1
1749 indicates that it might well alias *anything*. */
1752 aliases_everything_p (mem)
1755 if (GET_CODE (XEXP (mem, 0)) == AND)
1756 /* If the address is an AND, its very hard to know at what it is
1757 actually pointing. */
1763 /* True dependence: X is read after store in MEM takes place. */
1766 true_dependence (mem, mem_mode, x, varies)
1768 enum machine_mode mem_mode;
1770 int (*varies) PARAMS ((rtx, int));
1772 rtx x_addr, mem_addr;
1775 if (MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem))
1778 if (DIFFERENT_ALIAS_SETS_P (x, mem))
1781 /* Unchanging memory can't conflict with non-unchanging memory.
1782 A non-unchanging read can conflict with a non-unchanging write.
1783 An unchanging read can conflict with an unchanging write since
1784 there may be a single store to this address to initialize it.
1785 Note that an unchanging store can conflict with a non-unchanging read
1786 since we have to make conservative assumptions when we have a
1787 record with readonly fields and we are copying the whole thing.
1788 Just fall through to the code below to resolve potential conflicts.
1789 This won't handle all cases optimally, but the possible performance
1790 loss should be negligible. */
1791 if (RTX_UNCHANGING_P (x) && ! RTX_UNCHANGING_P (mem))
1794 if (mem_mode == VOIDmode)
1795 mem_mode = GET_MODE (mem);
1797 x_addr = get_addr (XEXP (x, 0));
1798 mem_addr = get_addr (XEXP (mem, 0));
1800 base = find_base_term (x_addr);
1801 if (base && (GET_CODE (base) == LABEL_REF
1802 || (GET_CODE (base) == SYMBOL_REF
1803 && CONSTANT_POOL_ADDRESS_P (base))))
1806 if (! base_alias_check (x_addr, mem_addr, GET_MODE (x), mem_mode))
1809 x_addr = canon_rtx (x_addr);
1810 mem_addr = canon_rtx (mem_addr);
1812 if (! memrefs_conflict_p (GET_MODE_SIZE (mem_mode), mem_addr,
1813 SIZE_FOR_MODE (x), x_addr, 0))
1816 if (aliases_everything_p (x))
1819 /* We cannot use aliases_everyting_p to test MEM, since we must look
1820 at MEM_MODE, rather than GET_MODE (MEM). */
1821 if (mem_mode == QImode || GET_CODE (mem_addr) == AND)
1824 /* In true_dependence we also allow BLKmode to alias anything. Why
1825 don't we do this in anti_dependence and output_dependence? */
1826 if (mem_mode == BLKmode || GET_MODE (x) == BLKmode)
1829 return ! fixed_scalar_and_varying_struct_p (mem, x, mem_addr, x_addr,
1833 /* Canonical true dependence: X is read after store in MEM takes place.
1834 Variant of true_dependece which assumes MEM has already been
1835 canonicalized (hence we no longer do that here).
1836 The mem_addr argument has been added, since true_dependence computed
1837 this value prior to canonicalizing. */
1840 canon_true_dependence (mem, mem_mode, mem_addr, x, varies)
1841 rtx mem, mem_addr, x;
1842 enum machine_mode mem_mode;
1843 int (*varies) PARAMS ((rtx, int));
1847 if (MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem))
1850 if (DIFFERENT_ALIAS_SETS_P (x, mem))
1853 /* If X is an unchanging read, then it can't possibly conflict with any
1854 non-unchanging store. It may conflict with an unchanging write though,
1855 because there may be a single store to this address to initialize it.
1856 Just fall through to the code below to resolve the case where we have
1857 both an unchanging read and an unchanging write. This won't handle all
1858 cases optimally, but the possible performance loss should be
1860 if (RTX_UNCHANGING_P (x) && ! RTX_UNCHANGING_P (mem))
1863 x_addr = get_addr (XEXP (x, 0));
1865 if (! base_alias_check (x_addr, mem_addr, GET_MODE (x), mem_mode))
1868 x_addr = canon_rtx (x_addr);
1869 if (! memrefs_conflict_p (GET_MODE_SIZE (mem_mode), mem_addr,
1870 SIZE_FOR_MODE (x), x_addr, 0))
1873 if (aliases_everything_p (x))
1876 /* We cannot use aliases_everyting_p to test MEM, since we must look
1877 at MEM_MODE, rather than GET_MODE (MEM). */
1878 if (mem_mode == QImode || GET_CODE (mem_addr) == AND)
1881 /* In true_dependence we also allow BLKmode to alias anything. Why
1882 don't we do this in anti_dependence and output_dependence? */
1883 if (mem_mode == BLKmode || GET_MODE (x) == BLKmode)
1886 return ! fixed_scalar_and_varying_struct_p (mem, x, mem_addr, x_addr,
1890 /* Returns non-zero if a write to X might alias a previous read from
1891 (or, if WRITEP is non-zero, a write to) MEM. */
1894 write_dependence_p (mem, x, writep)
1899 rtx x_addr, mem_addr;
1903 if (MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem))
1906 if (DIFFERENT_ALIAS_SETS_P (x, mem))
1909 /* Unchanging memory can't conflict with non-unchanging memory. */
1910 if (RTX_UNCHANGING_P (x) != RTX_UNCHANGING_P (mem))
1913 /* If MEM is an unchanging read, then it can't possibly conflict with
1914 the store to X, because there is at most one store to MEM, and it must
1915 have occurred somewhere before MEM. */
1916 if (! writep && RTX_UNCHANGING_P (mem))
1919 x_addr = get_addr (XEXP (x, 0));
1920 mem_addr = get_addr (XEXP (mem, 0));
1924 base = find_base_term (mem_addr);
1925 if (base && (GET_CODE (base) == LABEL_REF
1926 || (GET_CODE (base) == SYMBOL_REF
1927 && CONSTANT_POOL_ADDRESS_P (base))))
1931 if (! base_alias_check (x_addr, mem_addr, GET_MODE (x),
1935 x_addr = canon_rtx (x_addr);
1936 mem_addr = canon_rtx (mem_addr);
1938 if (!memrefs_conflict_p (SIZE_FOR_MODE (mem), mem_addr,
1939 SIZE_FOR_MODE (x), x_addr, 0))
1943 = fixed_scalar_and_varying_struct_p (mem, x, mem_addr, x_addr,
1946 return (!(fixed_scalar == mem && !aliases_everything_p (x))
1947 && !(fixed_scalar == x && !aliases_everything_p (mem)));
1950 /* Anti dependence: X is written after read in MEM takes place. */
1953 anti_dependence (mem, x)
1957 return write_dependence_p (mem, x, /*writep=*/0);
1960 /* Output dependence: X is written after store in MEM takes place. */
1963 output_dependence (mem, x)
1967 return write_dependence_p (mem, x, /*writep=*/1);
1970 /* Returns non-zero if X mentions something which is not
1971 local to the function and is not constant. */
1974 nonlocal_mentioned_p (x)
1981 code = GET_CODE (x);
1983 if (GET_RTX_CLASS (code) == 'i')
1985 /* Constant functions can be constant if they don't use
1986 scratch memory used to mark function w/o side effects. */
1987 if (code == CALL_INSN && CONST_OR_PURE_CALL_P (x))
1989 x = CALL_INSN_FUNCTION_USAGE (x);
1995 code = GET_CODE (x);
2001 if (GET_CODE (SUBREG_REG (x)) == REG)
2003 /* Global registers are not local. */
2004 if (REGNO (SUBREG_REG (x)) < FIRST_PSEUDO_REGISTER
2005 && global_regs[subreg_regno (x)])
2013 /* Global registers are not local. */
2014 if (regno < FIRST_PSEUDO_REGISTER && global_regs[regno])
2028 /* Constants in the function's constants pool are constant. */
2029 if (CONSTANT_POOL_ADDRESS_P (x))
2034 /* Non-constant calls and recursion are not local. */
2038 /* Be overly conservative and consider any volatile memory
2039 reference as not local. */
2040 if (MEM_VOLATILE_P (x))
2042 base = find_base_term (XEXP (x, 0));
2045 /* A Pmode ADDRESS could be a reference via the structure value
2046 address or static chain. Such memory references are nonlocal.
2048 Thus, we have to examine the contents of the ADDRESS to find
2049 out if this is a local reference or not. */
2050 if (GET_CODE (base) == ADDRESS
2051 && GET_MODE (base) == Pmode
2052 && (XEXP (base, 0) == stack_pointer_rtx
2053 || XEXP (base, 0) == arg_pointer_rtx
2054 #if HARD_FRAME_POINTER_REGNUM != FRAME_POINTER_REGNUM
2055 || XEXP (base, 0) == hard_frame_pointer_rtx
2057 || XEXP (base, 0) == frame_pointer_rtx))
2059 /* Constants in the function's constant pool are constant. */
2060 if (GET_CODE (base) == SYMBOL_REF && CONSTANT_POOL_ADDRESS_P (base))
2065 case UNSPEC_VOLATILE:
2070 if (MEM_VOLATILE_P (x))
2079 /* Recursively scan the operands of this expression. */
2082 const char *fmt = GET_RTX_FORMAT (code);
2085 for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
2087 if (fmt[i] == 'e' && XEXP (x, i))
2089 if (nonlocal_mentioned_p (XEXP (x, i)))
2092 else if (fmt[i] == 'E')
2095 for (j = 0; j < XVECLEN (x, i); j++)
2096 if (nonlocal_mentioned_p (XVECEXP (x, i, j)))
2105 /* Mark the function if it is constant. */
2108 mark_constant_function ()
2111 int nonlocal_mentioned;
2113 if (TREE_PUBLIC (current_function_decl)
2114 || TREE_READONLY (current_function_decl)
2115 || DECL_IS_PURE (current_function_decl)
2116 || TREE_THIS_VOLATILE (current_function_decl)
2117 || TYPE_MODE (TREE_TYPE (current_function_decl)) == VOIDmode)
2120 /* A loop might not return which counts as a side effect. */
2121 if (mark_dfs_back_edges ())
2124 nonlocal_mentioned = 0;
2126 init_alias_analysis ();
2128 /* Determine if this is a constant function. */
2130 for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
2131 if (INSN_P (insn) && nonlocal_mentioned_p (insn))
2133 nonlocal_mentioned = 1;
2137 end_alias_analysis ();
2139 /* Mark the function. */
2141 if (! nonlocal_mentioned)
2142 TREE_READONLY (current_function_decl) = 1;
2146 static HARD_REG_SET argument_registers;
2153 #ifndef OUTGOING_REGNO
2154 #define OUTGOING_REGNO(N) N
2156 for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
2157 /* Check whether this register can hold an incoming pointer
2158 argument. FUNCTION_ARG_REGNO_P tests outgoing register
2159 numbers, so translate if necessary due to register windows. */
2160 if (FUNCTION_ARG_REGNO_P (OUTGOING_REGNO (i))
2161 && HARD_REGNO_MODE_OK (i, Pmode))
2162 SET_HARD_REG_BIT (argument_registers, i);
2164 alias_sets = splay_tree_new (splay_tree_compare_ints, 0, 0);
2167 /* Initialize the aliasing machinery. Initialize the REG_KNOWN_VALUE
2171 init_alias_analysis ()
2173 int maxreg = max_reg_num ();
2179 reg_known_value_size = maxreg;
2182 = (rtx *) xcalloc ((maxreg - FIRST_PSEUDO_REGISTER), sizeof (rtx))
2183 - FIRST_PSEUDO_REGISTER;
2185 = (char*) xcalloc ((maxreg - FIRST_PSEUDO_REGISTER), sizeof (char))
2186 - FIRST_PSEUDO_REGISTER;
2188 /* Overallocate reg_base_value to allow some growth during loop
2189 optimization. Loop unrolling can create a large number of
2191 reg_base_value_size = maxreg * 2;
2192 reg_base_value = (rtx *) xcalloc (reg_base_value_size, sizeof (rtx));
2193 ggc_add_rtx_root (reg_base_value, reg_base_value_size);
2195 new_reg_base_value = (rtx *) xmalloc (reg_base_value_size * sizeof (rtx));
2196 reg_seen = (char *) xmalloc (reg_base_value_size);
2197 if (! reload_completed && flag_unroll_loops)
2199 /* ??? Why are we realloc'ing if we're just going to zero it? */
2200 alias_invariant = (rtx *)xrealloc (alias_invariant,
2201 reg_base_value_size * sizeof (rtx));
2202 memset ((char *)alias_invariant, 0, reg_base_value_size * sizeof (rtx));
2205 /* The basic idea is that each pass through this loop will use the
2206 "constant" information from the previous pass to propagate alias
2207 information through another level of assignments.
2209 This could get expensive if the assignment chains are long. Maybe
2210 we should throttle the number of iterations, possibly based on
2211 the optimization level or flag_expensive_optimizations.
2213 We could propagate more information in the first pass by making use
2214 of REG_N_SETS to determine immediately that the alias information
2215 for a pseudo is "constant".
2217 A program with an uninitialized variable can cause an infinite loop
2218 here. Instead of doing a full dataflow analysis to detect such problems
2219 we just cap the number of iterations for the loop.
2221 The state of the arrays for the set chain in question does not matter
2222 since the program has undefined behavior. */
2227 /* Assume nothing will change this iteration of the loop. */
2230 /* We want to assign the same IDs each iteration of this loop, so
2231 start counting from zero each iteration of the loop. */
2234 /* We're at the start of the funtion each iteration through the
2235 loop, so we're copying arguments. */
2236 copying_arguments = 1;
2238 /* Wipe the potential alias information clean for this pass. */
2239 memset ((char *) new_reg_base_value, 0, reg_base_value_size * sizeof (rtx));
2241 /* Wipe the reg_seen array clean. */
2242 memset ((char *) reg_seen, 0, reg_base_value_size);
2244 /* Mark all hard registers which may contain an address.
2245 The stack, frame and argument pointers may contain an address.
2246 An argument register which can hold a Pmode value may contain
2247 an address even if it is not in BASE_REGS.
2249 The address expression is VOIDmode for an argument and
2250 Pmode for other registers. */
2252 for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
2253 if (TEST_HARD_REG_BIT (argument_registers, i))
2254 new_reg_base_value[i] = gen_rtx_ADDRESS (VOIDmode,
2255 gen_rtx_REG (Pmode, i));
2257 new_reg_base_value[STACK_POINTER_REGNUM]
2258 = gen_rtx_ADDRESS (Pmode, stack_pointer_rtx);
2259 new_reg_base_value[ARG_POINTER_REGNUM]
2260 = gen_rtx_ADDRESS (Pmode, arg_pointer_rtx);
2261 new_reg_base_value[FRAME_POINTER_REGNUM]
2262 = gen_rtx_ADDRESS (Pmode, frame_pointer_rtx);
2263 #if HARD_FRAME_POINTER_REGNUM != FRAME_POINTER_REGNUM
2264 new_reg_base_value[HARD_FRAME_POINTER_REGNUM]
2265 = gen_rtx_ADDRESS (Pmode, hard_frame_pointer_rtx);
2268 /* Walk the insns adding values to the new_reg_base_value array. */
2269 for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
2275 #if defined (HAVE_prologue) || defined (HAVE_epilogue)
2276 /* The prologue/epilouge insns are not threaded onto the
2277 insn chain until after reload has completed. Thus,
2278 there is no sense wasting time checking if INSN is in
2279 the prologue/epilogue until after reload has completed. */
2280 if (reload_completed
2281 && prologue_epilogue_contains (insn))
2285 /* If this insn has a noalias note, process it, Otherwise,
2286 scan for sets. A simple set will have no side effects
2287 which could change the base value of any other register. */
2289 if (GET_CODE (PATTERN (insn)) == SET
2290 && REG_NOTES (insn) != 0
2291 && find_reg_note (insn, REG_NOALIAS, NULL_RTX))
2292 record_set (SET_DEST (PATTERN (insn)), NULL_RTX, NULL);
2294 note_stores (PATTERN (insn), record_set, NULL);
2296 set = single_set (insn);
2299 && GET_CODE (SET_DEST (set)) == REG
2300 && REGNO (SET_DEST (set)) >= FIRST_PSEUDO_REGISTER)
2302 unsigned int regno = REGNO (SET_DEST (set));
2303 rtx src = SET_SRC (set);
2305 if (REG_NOTES (insn) != 0
2306 && (((note = find_reg_note (insn, REG_EQUAL, 0)) != 0
2307 && REG_N_SETS (regno) == 1)
2308 || (note = find_reg_note (insn, REG_EQUIV, NULL_RTX)) != 0)
2309 && GET_CODE (XEXP (note, 0)) != EXPR_LIST
2310 && ! rtx_varies_p (XEXP (note, 0), 1)
2311 && ! reg_overlap_mentioned_p (SET_DEST (set), XEXP (note, 0)))
2313 reg_known_value[regno] = XEXP (note, 0);
2314 reg_known_equiv_p[regno] = REG_NOTE_KIND (note) == REG_EQUIV;
2316 else if (REG_N_SETS (regno) == 1
2317 && GET_CODE (src) == PLUS
2318 && GET_CODE (XEXP (src, 0)) == REG
2319 && REGNO (XEXP (src, 0)) >= FIRST_PSEUDO_REGISTER
2320 && (reg_known_value[REGNO (XEXP (src, 0))])
2321 && GET_CODE (XEXP (src, 1)) == CONST_INT)
2323 rtx op0 = XEXP (src, 0);
2324 op0 = reg_known_value[REGNO (op0)];
2325 reg_known_value[regno]
2326 = plus_constant (op0, INTVAL (XEXP (src, 1)));
2327 reg_known_equiv_p[regno] = 0;
2329 else if (REG_N_SETS (regno) == 1
2330 && ! rtx_varies_p (src, 1))
2332 reg_known_value[regno] = src;
2333 reg_known_equiv_p[regno] = 0;
2337 else if (GET_CODE (insn) == NOTE
2338 && NOTE_LINE_NUMBER (insn) == NOTE_INSN_FUNCTION_BEG)
2339 copying_arguments = 0;
2342 /* Now propagate values from new_reg_base_value to reg_base_value. */
2343 for (ui = 0; ui < reg_base_value_size; ui++)
2345 if (new_reg_base_value[ui]
2346 && new_reg_base_value[ui] != reg_base_value[ui]
2347 && ! rtx_equal_p (new_reg_base_value[ui], reg_base_value[ui]))
2349 reg_base_value[ui] = new_reg_base_value[ui];
2354 while (changed && ++pass < MAX_ALIAS_LOOP_PASSES);
2356 /* Fill in the remaining entries. */
2357 for (i = FIRST_PSEUDO_REGISTER; i < maxreg; i++)
2358 if (reg_known_value[i] == 0)
2359 reg_known_value[i] = regno_reg_rtx[i];
2361 /* Simplify the reg_base_value array so that no register refers to
2362 another register, except to special registers indirectly through
2363 ADDRESS expressions.
2365 In theory this loop can take as long as O(registers^2), but unless
2366 there are very long dependency chains it will run in close to linear
2369 This loop may not be needed any longer now that the main loop does
2370 a better job at propagating alias information. */
2376 for (ui = 0; ui < reg_base_value_size; ui++)
2378 rtx base = reg_base_value[ui];
2379 if (base && GET_CODE (base) == REG)
2381 unsigned int base_regno = REGNO (base);
2382 if (base_regno == ui) /* register set from itself */
2383 reg_base_value[ui] = 0;
2385 reg_base_value[ui] = reg_base_value[base_regno];
2390 while (changed && pass < MAX_ALIAS_LOOP_PASSES);
2393 free (new_reg_base_value);
2394 new_reg_base_value = 0;
2400 end_alias_analysis ()
2402 free (reg_known_value + FIRST_PSEUDO_REGISTER);
2403 reg_known_value = 0;
2404 reg_known_value_size = 0;
2405 free (reg_known_equiv_p + FIRST_PSEUDO_REGISTER);
2406 reg_known_equiv_p = 0;
2409 ggc_del_root (reg_base_value);
2410 free (reg_base_value);
2413 reg_base_value_size = 0;
2414 if (alias_invariant)
2416 free (alias_invariant);
2417 alias_invariant = 0;