1 /* Alias analysis for GNU C
2 Copyright (C) 1997, 1998, 1999 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. */
28 #include "insn-flags.h"
31 #include "hard-reg-set.h"
35 #include "splay-tree.h"
38 /* The alias sets assigned to MEMs assist the back-end in determining
39 which MEMs can alias which other MEMs. In general, two MEMs in
40 different alias sets to not alias each other. There is one
41 exception, however. Consider something like:
43 struct S {int i; double d; };
45 a store to an `S' can alias something of either type `int' or type
46 `double'. (However, a store to an `int' cannot alias a `double'
47 and vice versa.) We indicate this via a tree structure that looks
55 (The arrows are directed and point downwards.) If, when comparing
56 two alias sets, we can hold one set fixed, trace the other set
57 downwards, and at some point find the first set, the two MEMs can
58 alias one another. In this situation we say the alias set for
59 `struct S' is the `superset' and that those for `int' and `double'
62 Alias set zero is implicitly a superset of all other alias sets.
63 However, this is no actual entry for alias set zero. It is an
64 error to attempt to explicitly construct a subset of zero. */
66 typedef struct alias_set_entry
68 /* The alias set number, as stored in MEM_ALIAS_SET. */
71 /* The children of the alias set. These are not just the immediate
72 children, but, in fact, all children. So, if we have:
74 struct T { struct S s; float f; }
76 continuing our example above, the children here will be all of
77 `int', `double', `float', and `struct S'. */
81 static rtx canon_rtx PROTO((rtx));
82 static int rtx_equal_for_memref_p PROTO((rtx, rtx));
83 static rtx find_symbolic_term PROTO((rtx));
84 static int memrefs_conflict_p PROTO((int, rtx, int, rtx,
86 static void record_set PROTO((rtx, rtx, void *));
87 static rtx find_base_term PROTO((rtx));
88 static int base_alias_check PROTO((rtx, rtx, enum machine_mode,
90 static rtx find_base_value PROTO((rtx));
91 static int mems_in_disjoint_alias_sets_p PROTO((rtx, rtx));
92 static int insert_subset_children PROTO((splay_tree_node,
94 static alias_set_entry get_alias_set_entry PROTO((int));
95 static rtx fixed_scalar_and_varying_struct_p PROTO((rtx, rtx, int (*)(rtx)));
96 static int aliases_everything_p PROTO((rtx));
97 static int write_dependence_p PROTO((rtx, rtx, int));
98 static int nonlocal_reference_p PROTO((rtx));
100 /* Set up all info needed to perform alias analysis on memory references. */
102 /* Returns the size in bytes of the mode of X. */
103 #define SIZE_FOR_MODE(X) (GET_MODE_SIZE (GET_MODE (X)))
105 /* Returns nonzero if MEM1 and MEM2 do not alias because they are in
106 different alias sets. We ignore alias sets in functions making use
107 of variable arguments because the va_arg macros on some systems are
109 #define DIFFERENT_ALIAS_SETS_P(MEM1, MEM2) \
110 mems_in_disjoint_alias_sets_p (MEM1, MEM2)
112 /* Cap the number of passes we make over the insns propagating alias
113 information through set chains.
115 10 is a completely arbitrary choice. */
116 #define MAX_ALIAS_LOOP_PASSES 10
118 /* reg_base_value[N] gives an address to which register N is related.
119 If all sets after the first add or subtract to the current value
120 or otherwise modify it so it does not point to a different top level
121 object, reg_base_value[N] is equal to the address part of the source
124 A base address can be an ADDRESS, SYMBOL_REF, or LABEL_REF. ADDRESS
125 expressions represent certain special values: function arguments and
126 the stack, frame, and argument pointers.
128 The contents of an ADDRESS is not normally used, the mode of the
129 ADDRESS determines whether the ADDRESS is a function argument or some
130 other special value. Pointer equality, not rtx_equal_p, determines whether
131 two ADDRESS expressions refer to the same base address.
133 The only use of the contents of an ADDRESS is for determining if the
134 current function performs nonlocal memory memory references for the
135 purposes of marking the function as a constant function. */
137 static rtx *reg_base_value;
138 static rtx *new_reg_base_value;
139 static unsigned int reg_base_value_size; /* size of reg_base_value array */
141 #define REG_BASE_VALUE(X) \
142 ((unsigned) REGNO (X) < reg_base_value_size ? reg_base_value[REGNO (X)] : 0)
144 /* Vector of known invariant relationships between registers. Set in
145 loop unrolling. Indexed by register number, if nonzero the value
146 is an expression describing this register in terms of another.
148 The length of this array is REG_BASE_VALUE_SIZE.
150 Because this array contains only pseudo registers it has no effect
152 static rtx *alias_invariant;
154 /* Vector indexed by N giving the initial (unchanging) value known
155 for pseudo-register N. */
156 rtx *reg_known_value;
158 /* Indicates number of valid entries in reg_known_value. */
159 static int reg_known_value_size;
161 /* Vector recording for each reg_known_value whether it is due to a
162 REG_EQUIV note. Future passes (viz., reload) may replace the
163 pseudo with the equivalent expression and so we account for the
164 dependences that would be introduced if that happens. */
165 /* ??? This is a problem only on the Convex. The REG_EQUIV notes created in
166 assign_parms mention the arg pointer, and there are explicit insns in the
167 RTL that modify the arg pointer. Thus we must ensure that such insns don't
168 get scheduled across each other because that would invalidate the REG_EQUIV
169 notes. One could argue that the REG_EQUIV notes are wrong, but solving
170 the problem in the scheduler will likely give better code, so we do it
172 char *reg_known_equiv_p;
174 /* True when scanning insns from the start of the rtl to the
175 NOTE_INSN_FUNCTION_BEG note. */
177 static int copying_arguments;
179 /* The splay-tree used to store the various alias set entries. */
181 static splay_tree alias_sets;
183 /* Returns a pointer to the alias set entry for ALIAS_SET, if there is
184 such an entry, or NULL otherwise. */
186 static alias_set_entry
187 get_alias_set_entry (alias_set)
191 = splay_tree_lookup (alias_sets, (splay_tree_key) alias_set);
193 return sn != 0 ? ((alias_set_entry) sn->value) : 0;
196 /* Returns nonzero value if the alias sets for MEM1 and MEM2 are such
197 that the two MEMs cannot alias each other. */
200 mems_in_disjoint_alias_sets_p (mem1, mem2)
206 #ifdef ENABLE_CHECKING
207 /* Perform a basic sanity check. Namely, that there are no alias sets
208 if we're not using strict aliasing. This helps to catch bugs
209 whereby someone uses PUT_CODE, but doesn't clear MEM_ALIAS_SET, or
210 where a MEM is allocated in some way other than by the use of
211 gen_rtx_MEM, and the MEM_ALIAS_SET is not cleared. If we begin to
212 use alias sets to indicate that spilled registers cannot alias each
213 other, we might need to remove this check. */
214 if (! flag_strict_aliasing
215 && (MEM_ALIAS_SET (mem1) != 0 || MEM_ALIAS_SET (mem2) != 0))
219 /* The code used in varargs macros are often not conforming ANSI C,
220 which can trick the compiler into making incorrect aliasing
221 assumptions in these functions. So, we don't use alias sets in
222 such a function. FIXME: This should be moved into the front-end;
223 it is a language-dependent notion, and there's no reason not to
224 still use these checks to handle globals. */
225 if (current_function_stdarg || current_function_varargs)
228 /* If have no alias set information for one of the MEMs, we have to assume
229 it can alias anything. */
230 if (MEM_ALIAS_SET (mem1) == 0 || MEM_ALIAS_SET (mem2) == 0)
233 /* If the two alias sets are the same, they may alias. */
234 if (MEM_ALIAS_SET (mem1) == MEM_ALIAS_SET (mem2))
237 /* Iterate through each of the children of the first alias set,
238 comparing it with the second alias set. */
239 ase = get_alias_set_entry (MEM_ALIAS_SET (mem1));
240 if (ase != 0 && splay_tree_lookup (ase->children,
241 (splay_tree_key) MEM_ALIAS_SET (mem2)))
244 /* Now do the same, but with the alias sets reversed. */
245 ase = get_alias_set_entry (MEM_ALIAS_SET (mem2));
246 if (ase != 0 && splay_tree_lookup (ase->children,
247 (splay_tree_key) MEM_ALIAS_SET (mem1)))
250 /* The two MEMs are in distinct alias sets, and neither one is the
251 child of the other. Therefore, they cannot alias. */
255 /* Insert the NODE into the splay tree given by DATA. Used by
256 record_alias_subset via splay_tree_foreach. */
259 insert_subset_children (node, data)
260 splay_tree_node node;
263 splay_tree_insert ((splay_tree) data, node->key, node->value);
268 /* Indicate that things in SUBSET can alias things in SUPERSET, but
269 not vice versa. For example, in C, a store to an `int' can alias a
270 structure containing an `int', but not vice versa. Here, the
271 structure would be the SUPERSET and `int' the SUBSET. This
272 function should be called only once per SUPERSET/SUBSET pair. At
273 present any given alias set may only be a subset of one superset.
275 It is illegal for SUPERSET to be zero; everything is implicitly a
276 subset of alias set zero. */
279 record_alias_subset (superset, subset)
283 alias_set_entry superset_entry;
284 alias_set_entry subset_entry;
289 superset_entry = get_alias_set_entry (superset);
290 if (superset_entry == 0)
292 /* Create an entry for the SUPERSET, so that we have a place to
293 attach the SUBSET. */
295 = (alias_set_entry) xmalloc (sizeof (struct alias_set_entry));
296 superset_entry->alias_set = superset;
297 superset_entry->children
298 = splay_tree_new (splay_tree_compare_ints, 0, 0);
299 splay_tree_insert (alias_sets, (splay_tree_key) superset,
300 (splay_tree_value) superset_entry);
304 subset_entry = get_alias_set_entry (subset);
306 /* If there is an entry for the subset, enter all of its children
307 (if they are not already present) as children of the SUPERSET. */
309 splay_tree_foreach (subset_entry->children,
310 insert_subset_children,
311 superset_entry->children);
313 /* Enter the SUBSET itself as a child of the SUPERSET. */
314 splay_tree_insert (superset_entry->children,
315 (splay_tree_key) subset, 0);
318 /* Inside SRC, the source of a SET, find a base address. */
321 find_base_value (src)
324 switch (GET_CODE (src))
331 /* At the start of a function, argument registers have known base
332 values which may be lost later. Returning an ADDRESS
333 expression here allows optimization based on argument values
334 even when the argument registers are used for other purposes. */
335 if (REGNO (src) < FIRST_PSEUDO_REGISTER && copying_arguments)
336 return new_reg_base_value[REGNO (src)];
338 /* If a pseudo has a known base value, return it. Do not do this
339 for hard regs since it can result in a circular dependency
340 chain for registers which have values at function entry.
342 The test above is not sufficient because the scheduler may move
343 a copy out of an arg reg past the NOTE_INSN_FUNCTION_BEGIN. */
344 if (REGNO (src) >= FIRST_PSEUDO_REGISTER
345 && (unsigned) REGNO (src) < reg_base_value_size
346 && reg_base_value[REGNO (src)])
347 return reg_base_value[REGNO (src)];
352 /* Check for an argument passed in memory. Only record in the
353 copying-arguments block; it is too hard to track changes
355 if (copying_arguments
356 && (XEXP (src, 0) == arg_pointer_rtx
357 || (GET_CODE (XEXP (src, 0)) == PLUS
358 && XEXP (XEXP (src, 0), 0) == arg_pointer_rtx)))
359 return gen_rtx_ADDRESS (VOIDmode, src);
364 if (GET_CODE (src) != PLUS && GET_CODE (src) != MINUS)
367 /* ... fall through ... */
372 rtx temp, src_0 = XEXP (src, 0), src_1 = XEXP (src, 1);
374 /* If either operand is a REG, then see if we already have
375 a known value for it. */
376 if (GET_CODE (src_0) == REG)
378 temp = find_base_value (src_0);
383 if (GET_CODE (src_1) == REG)
385 temp = find_base_value (src_1);
390 /* Guess which operand is the base address:
391 If either operand is a symbol, then it is the base. If
392 either operand is a CONST_INT, then the other is the base. */
393 if (GET_CODE (src_1) == CONST_INT || CONSTANT_P (src_0))
394 return find_base_value (src_0);
395 else if (GET_CODE (src_0) == CONST_INT || CONSTANT_P (src_1))
396 return find_base_value (src_1);
398 /* This might not be necessary anymore:
399 If either operand is a REG that is a known pointer, then it
401 else if (GET_CODE (src_0) == REG && REGNO_POINTER_FLAG (REGNO (src_0)))
402 return find_base_value (src_0);
403 else if (GET_CODE (src_1) == REG && REGNO_POINTER_FLAG (REGNO (src_1)))
404 return find_base_value (src_1);
410 /* The standard form is (lo_sum reg sym) so look only at the
412 return find_base_value (XEXP (src, 1));
415 /* If the second operand is constant set the base
416 address to the first operand. */
417 if (GET_CODE (XEXP (src, 1)) == CONST_INT && INTVAL (XEXP (src, 1)) != 0)
418 return find_base_value (XEXP (src, 0));
422 case SIGN_EXTEND: /* used for NT/Alpha pointers */
424 return find_base_value (XEXP (src, 0));
433 /* Called from init_alias_analysis indirectly through note_stores. */
435 /* While scanning insns to find base values, reg_seen[N] is nonzero if
436 register N has been set in this function. */
437 static char *reg_seen;
439 /* Addresses which are known not to alias anything else are identified
440 by a unique integer. */
441 static int unique_id;
444 record_set (dest, set, data)
446 void *data ATTRIBUTE_UNUSED;
448 register unsigned regno;
451 if (GET_CODE (dest) != REG)
454 regno = REGNO (dest);
456 if (regno >= reg_base_value_size)
461 /* A CLOBBER wipes out any old value but does not prevent a previously
462 unset register from acquiring a base address (i.e. reg_seen is not
464 if (GET_CODE (set) == CLOBBER)
466 new_reg_base_value[regno] = 0;
475 new_reg_base_value[regno] = 0;
479 new_reg_base_value[regno] = gen_rtx_ADDRESS (Pmode,
480 GEN_INT (unique_id++));
484 /* This is not the first set. If the new value is not related to the
485 old value, forget the base value. Note that the following code is
487 extern int x, y; int *p = &x; p += (&y-&x);
488 ANSI C does not allow computing the difference of addresses
489 of distinct top level objects. */
490 if (new_reg_base_value[regno])
491 switch (GET_CODE (src))
496 if (XEXP (src, 0) != dest && XEXP (src, 1) != dest)
497 new_reg_base_value[regno] = 0;
500 if (XEXP (src, 0) != dest || GET_CODE (XEXP (src, 1)) != CONST_INT)
501 new_reg_base_value[regno] = 0;
504 new_reg_base_value[regno] = 0;
507 /* If this is the first set of a register, record the value. */
508 else if ((regno >= FIRST_PSEUDO_REGISTER || ! fixed_regs[regno])
509 && ! reg_seen[regno] && new_reg_base_value[regno] == 0)
510 new_reg_base_value[regno] = find_base_value (src);
515 /* Called from loop optimization when a new pseudo-register is created. */
518 record_base_value (regno, val, invariant)
523 if ((unsigned) regno >= reg_base_value_size)
526 /* If INVARIANT is true then this value also describes an invariant
527 relationship which can be used to deduce that two registers with
528 unknown values are different. */
529 if (invariant && alias_invariant)
530 alias_invariant[regno] = val;
532 if (GET_CODE (val) == REG)
534 if ((unsigned) REGNO (val) < reg_base_value_size)
535 reg_base_value[regno] = reg_base_value[REGNO (val)];
540 reg_base_value[regno] = find_base_value (val);
547 /* Recursively look for equivalences. */
548 if (GET_CODE (x) == REG && REGNO (x) >= FIRST_PSEUDO_REGISTER
549 && REGNO (x) < reg_known_value_size)
550 return reg_known_value[REGNO (x)] == x
551 ? x : canon_rtx (reg_known_value[REGNO (x)]);
552 else if (GET_CODE (x) == PLUS)
554 rtx x0 = canon_rtx (XEXP (x, 0));
555 rtx x1 = canon_rtx (XEXP (x, 1));
557 if (x0 != XEXP (x, 0) || x1 != XEXP (x, 1))
559 /* We can tolerate LO_SUMs being offset here; these
560 rtl are used for nothing other than comparisons. */
561 if (GET_CODE (x0) == CONST_INT)
562 return plus_constant_for_output (x1, INTVAL (x0));
563 else if (GET_CODE (x1) == CONST_INT)
564 return plus_constant_for_output (x0, INTVAL (x1));
565 return gen_rtx_PLUS (GET_MODE (x), x0, x1);
569 /* This gives us much better alias analysis when called from
570 the loop optimizer. Note we want to leave the original
571 MEM alone, but need to return the canonicalized MEM with
572 all the flags with their original values. */
573 else if (GET_CODE (x) == MEM)
575 rtx addr = canon_rtx (XEXP (x, 0));
577 if (addr != XEXP (x, 0))
579 rtx new = gen_rtx_MEM (GET_MODE (x), addr);
581 RTX_UNCHANGING_P (new) = RTX_UNCHANGING_P (x);
582 MEM_COPY_ATTRIBUTES (new, x);
583 MEM_ALIAS_SET (new) = MEM_ALIAS_SET (x);
590 /* Return 1 if X and Y are identical-looking rtx's.
592 We use the data in reg_known_value above to see if two registers with
593 different numbers are, in fact, equivalent. */
596 rtx_equal_for_memref_p (x, y)
601 register enum rtx_code code;
602 register const char *fmt;
604 if (x == 0 && y == 0)
606 if (x == 0 || y == 0)
616 /* Rtx's of different codes cannot be equal. */
617 if (code != GET_CODE (y))
620 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent.
621 (REG:SI x) and (REG:HI x) are NOT equivalent. */
623 if (GET_MODE (x) != GET_MODE (y))
626 /* REG, LABEL_REF, and SYMBOL_REF can be compared nonrecursively. */
629 return REGNO (x) == REGNO (y);
630 if (code == LABEL_REF)
631 return XEXP (x, 0) == XEXP (y, 0);
632 if (code == SYMBOL_REF)
633 return XSTR (x, 0) == XSTR (y, 0);
634 if (code == CONST_INT)
635 return INTVAL (x) == INTVAL (y);
636 /* There's no need to compare the contents of CONST_DOUBLEs because
638 if (code == CONST_DOUBLE)
640 if (code == ADDRESSOF)
641 return (REGNO (XEXP (x, 0)) == REGNO (XEXP (y, 0))
642 && XINT (x, 1) == XINT (y, 1));
644 /* For commutative operations, the RTX match if the operand match in any
645 order. Also handle the simple binary and unary cases without a loop. */
646 if (code == EQ || code == NE || GET_RTX_CLASS (code) == 'c')
647 return ((rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0))
648 && rtx_equal_for_memref_p (XEXP (x, 1), XEXP (y, 1)))
649 || (rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 1))
650 && rtx_equal_for_memref_p (XEXP (x, 1), XEXP (y, 0))));
651 else if (GET_RTX_CLASS (code) == '<' || GET_RTX_CLASS (code) == '2')
652 return (rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0))
653 && rtx_equal_for_memref_p (XEXP (x, 1), XEXP (y, 1)));
654 else if (GET_RTX_CLASS (code) == '1')
655 return rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0));
657 /* Compare the elements. If any pair of corresponding elements
658 fail to match, return 0 for the whole things.
660 Limit cases to types which actually appear in addresses. */
662 fmt = GET_RTX_FORMAT (code);
663 for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
668 if (XINT (x, i) != XINT (y, i))
673 /* Two vectors must have the same length. */
674 if (XVECLEN (x, i) != XVECLEN (y, i))
677 /* And the corresponding elements must match. */
678 for (j = 0; j < XVECLEN (x, i); j++)
679 if (rtx_equal_for_memref_p (XVECEXP (x, i, j),
680 XVECEXP (y, i, j)) == 0)
685 if (rtx_equal_for_memref_p (XEXP (x, i), XEXP (y, i)) == 0)
689 /* This can happen for an asm which clobbers memory. */
693 /* It is believed that rtx's at this level will never
694 contain anything but integers and other rtx's,
695 except for within LABEL_REFs and SYMBOL_REFs. */
703 /* Given an rtx X, find a SYMBOL_REF or LABEL_REF within
704 X and return it, or return 0 if none found. */
707 find_symbolic_term (x)
711 register enum rtx_code code;
712 register const char *fmt;
715 if (code == SYMBOL_REF || code == LABEL_REF)
717 if (GET_RTX_CLASS (code) == 'o')
720 fmt = GET_RTX_FORMAT (code);
721 for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
727 t = find_symbolic_term (XEXP (x, i));
731 else if (fmt[i] == 'E')
741 switch (GET_CODE (x))
744 return REG_BASE_VALUE (x);
747 case SIGN_EXTEND: /* Used for Alpha/NT pointers */
753 return find_base_term (XEXP (x, 0));
757 if (GET_CODE (x) != PLUS && GET_CODE (x) != MINUS)
764 rtx tmp1 = XEXP (x, 0);
765 rtx tmp2 = XEXP (x, 1);
767 /* This is a litle bit tricky since we have to determine which of
768 the two operands represents the real base address. Otherwise this
769 routine may return the index register instead of the base register.
771 That may cause us to believe no aliasing was possible, when in
772 fact aliasing is possible.
774 We use a few simple tests to guess the base register. Additional
775 tests can certainly be added. For example, if one of the operands
776 is a shift or multiply, then it must be the index register and the
777 other operand is the base register. */
779 /* If either operand is known to be a pointer, then use it
780 to determine the base term. */
781 if (REG_P (tmp1) && REGNO_POINTER_FLAG (REGNO (tmp1)))
782 return find_base_term (tmp1);
784 if (REG_P (tmp2) && REGNO_POINTER_FLAG (REGNO (tmp2)))
785 return find_base_term (tmp2);
787 /* Neither operand was known to be a pointer. Go ahead and find the
788 base term for both operands. */
789 tmp1 = find_base_term (tmp1);
790 tmp2 = find_base_term (tmp2);
792 /* If either base term is named object or a special address
793 (like an argument or stack reference), then use it for the
796 && (GET_CODE (tmp1) == SYMBOL_REF
797 || GET_CODE (tmp1) == LABEL_REF
798 || (GET_CODE (tmp1) == ADDRESS
799 && GET_MODE (tmp1) != VOIDmode)))
803 && (GET_CODE (tmp2) == SYMBOL_REF
804 || GET_CODE (tmp2) == LABEL_REF
805 || (GET_CODE (tmp2) == ADDRESS
806 && GET_MODE (tmp2) != VOIDmode)))
809 /* We could not determine which of the two operands was the
810 base register and which was the index. So we can determine
811 nothing from the base alias check. */
816 if (GET_CODE (XEXP (x, 0)) == REG && GET_CODE (XEXP (x, 1)) == CONST_INT)
817 return REG_BASE_VALUE (XEXP (x, 0));
829 /* Return 0 if the addresses X and Y are known to point to different
830 objects, 1 if they might be pointers to the same object. */
833 base_alias_check (x, y, x_mode, y_mode)
835 enum machine_mode x_mode, y_mode;
837 rtx x_base = find_base_term (x);
838 rtx y_base = find_base_term (y);
840 /* If the address itself has no known base see if a known equivalent
841 value has one. If either address still has no known base, nothing
842 is known about aliasing. */
847 if (! flag_expensive_optimizations || (x_c = canon_rtx (x)) == x)
850 x_base = find_base_term (x_c);
858 if (! flag_expensive_optimizations || (y_c = canon_rtx (y)) == y)
861 y_base = find_base_term (y_c);
866 /* If the base addresses are equal nothing is known about aliasing. */
867 if (rtx_equal_p (x_base, y_base))
870 /* The base addresses of the read and write are different expressions.
871 If they are both symbols and they are not accessed via AND, there is
872 no conflict. We can bring knowledge of object alignment into play
873 here. For example, on alpha, "char a, b;" can alias one another,
874 though "char a; long b;" cannot. */
875 if (GET_CODE (x_base) != ADDRESS && GET_CODE (y_base) != ADDRESS)
877 if (GET_CODE (x) == AND && GET_CODE (y) == AND)
879 if (GET_CODE (x) == AND
880 && (GET_CODE (XEXP (x, 1)) != CONST_INT
881 || GET_MODE_UNIT_SIZE (y_mode) < -INTVAL (XEXP (x, 1))))
883 if (GET_CODE (y) == AND
884 && (GET_CODE (XEXP (y, 1)) != CONST_INT
885 || GET_MODE_UNIT_SIZE (x_mode) < -INTVAL (XEXP (y, 1))))
887 /* Differing symbols never alias. */
891 /* If one address is a stack reference there can be no alias:
892 stack references using different base registers do not alias,
893 a stack reference can not alias a parameter, and a stack reference
894 can not alias a global. */
895 if ((GET_CODE (x_base) == ADDRESS && GET_MODE (x_base) == Pmode)
896 || (GET_CODE (y_base) == ADDRESS && GET_MODE (y_base) == Pmode))
899 if (! flag_argument_noalias)
902 if (flag_argument_noalias > 1)
905 /* Weak noalias assertion (arguments are distinct, but may match globals). */
906 return ! (GET_MODE (x_base) == VOIDmode && GET_MODE (y_base) == VOIDmode);
909 /* Return the address of the (N_REFS + 1)th memory reference to ADDR
910 where SIZE is the size in bytes of the memory reference. If ADDR
911 is not modified by the memory reference then ADDR is returned. */
914 addr_side_effect_eval (addr, size, n_refs)
921 switch (GET_CODE (addr))
924 offset = (n_refs + 1) * size;
927 offset = -(n_refs + 1) * size;
930 offset = n_refs * size;
933 offset = -n_refs * size;
941 addr = gen_rtx_PLUS (GET_MODE (addr), XEXP (addr, 0), GEN_INT (offset));
943 addr = XEXP (addr, 0);
948 /* Return nonzero if X and Y (memory addresses) could reference the
949 same location in memory. C is an offset accumulator. When
950 C is nonzero, we are testing aliases between X and Y + C.
951 XSIZE is the size in bytes of the X reference,
952 similarly YSIZE is the size in bytes for Y.
954 If XSIZE or YSIZE is zero, we do not know the amount of memory being
955 referenced (the reference was BLKmode), so make the most pessimistic
958 If XSIZE or YSIZE is negative, we may access memory outside the object
959 being referenced as a side effect. This can happen when using AND to
960 align memory references, as is done on the Alpha.
962 Nice to notice that varying addresses cannot conflict with fp if no
963 local variables had their addresses taken, but that's too hard now. */
967 memrefs_conflict_p (xsize, x, ysize, y, c)
972 if (GET_CODE (x) == HIGH)
974 else if (GET_CODE (x) == LO_SUM)
977 x = canon_rtx (addr_side_effect_eval (x, xsize, 0));
978 if (GET_CODE (y) == HIGH)
980 else if (GET_CODE (y) == LO_SUM)
983 y = canon_rtx (addr_side_effect_eval (y, ysize, 0));
985 if (rtx_equal_for_memref_p (x, y))
987 if (xsize <= 0 || ysize <= 0)
989 if (c >= 0 && xsize > c)
991 if (c < 0 && ysize+c > 0)
996 /* This code used to check for conflicts involving stack references and
997 globals but the base address alias code now handles these cases. */
999 if (GET_CODE (x) == PLUS)
1001 /* The fact that X is canonicalized means that this
1002 PLUS rtx is canonicalized. */
1003 rtx x0 = XEXP (x, 0);
1004 rtx x1 = XEXP (x, 1);
1006 if (GET_CODE (y) == PLUS)
1008 /* The fact that Y is canonicalized means that this
1009 PLUS rtx is canonicalized. */
1010 rtx y0 = XEXP (y, 0);
1011 rtx y1 = XEXP (y, 1);
1013 if (rtx_equal_for_memref_p (x1, y1))
1014 return memrefs_conflict_p (xsize, x0, ysize, y0, c);
1015 if (rtx_equal_for_memref_p (x0, y0))
1016 return memrefs_conflict_p (xsize, x1, ysize, y1, c);
1017 if (GET_CODE (x1) == CONST_INT)
1019 if (GET_CODE (y1) == CONST_INT)
1020 return memrefs_conflict_p (xsize, x0, ysize, y0,
1021 c - INTVAL (x1) + INTVAL (y1));
1023 return memrefs_conflict_p (xsize, x0, ysize, y,
1026 else if (GET_CODE (y1) == CONST_INT)
1027 return memrefs_conflict_p (xsize, x, ysize, y0, c + INTVAL (y1));
1031 else if (GET_CODE (x1) == CONST_INT)
1032 return memrefs_conflict_p (xsize, x0, ysize, y, c - INTVAL (x1));
1034 else if (GET_CODE (y) == PLUS)
1036 /* The fact that Y is canonicalized means that this
1037 PLUS rtx is canonicalized. */
1038 rtx y0 = XEXP (y, 0);
1039 rtx y1 = XEXP (y, 1);
1041 if (GET_CODE (y1) == CONST_INT)
1042 return memrefs_conflict_p (xsize, x, ysize, y0, c + INTVAL (y1));
1047 if (GET_CODE (x) == GET_CODE (y))
1048 switch (GET_CODE (x))
1052 /* Handle cases where we expect the second operands to be the
1053 same, and check only whether the first operand would conflict
1056 rtx x1 = canon_rtx (XEXP (x, 1));
1057 rtx y1 = canon_rtx (XEXP (y, 1));
1058 if (! rtx_equal_for_memref_p (x1, y1))
1060 x0 = canon_rtx (XEXP (x, 0));
1061 y0 = canon_rtx (XEXP (y, 0));
1062 if (rtx_equal_for_memref_p (x0, y0))
1063 return (xsize == 0 || ysize == 0
1064 || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0));
1066 /* Can't properly adjust our sizes. */
1067 if (GET_CODE (x1) != CONST_INT)
1069 xsize /= INTVAL (x1);
1070 ysize /= INTVAL (x1);
1072 return memrefs_conflict_p (xsize, x0, ysize, y0, c);
1076 /* Are these registers known not to be equal? */
1077 if (alias_invariant)
1079 unsigned int r_x = REGNO (x), r_y = REGNO (y);
1080 rtx i_x, i_y; /* invariant relationships of X and Y */
1082 i_x = r_x >= reg_base_value_size ? 0 : alias_invariant[r_x];
1083 i_y = r_y >= reg_base_value_size ? 0 : alias_invariant[r_y];
1085 if (i_x == 0 && i_y == 0)
1088 if (! memrefs_conflict_p (xsize, i_x ? i_x : x,
1089 ysize, i_y ? i_y : y, c))
1098 /* Treat an access through an AND (e.g. a subword access on an Alpha)
1099 as an access with indeterminate size. Assume that references
1100 besides AND are aligned, so if the size of the other reference is
1101 at least as large as the alignment, assume no other overlap. */
1102 if (GET_CODE (x) == AND && GET_CODE (XEXP (x, 1)) == CONST_INT)
1104 if (GET_CODE (y) == AND || ysize < -INTVAL (XEXP (x, 1)))
1106 return memrefs_conflict_p (xsize, XEXP (x, 0), ysize, y, c);
1108 if (GET_CODE (y) == AND && GET_CODE (XEXP (y, 1)) == CONST_INT)
1110 /* ??? If we are indexing far enough into the array/structure, we
1111 may yet be able to determine that we can not overlap. But we
1112 also need to that we are far enough from the end not to overlap
1113 a following reference, so we do nothing with that for now. */
1114 if (GET_CODE (x) == AND || xsize < -INTVAL (XEXP (y, 1)))
1116 return memrefs_conflict_p (xsize, x, ysize, XEXP (y, 0), c);
1121 if (GET_CODE (x) == CONST_INT && GET_CODE (y) == CONST_INT)
1123 c += (INTVAL (y) - INTVAL (x));
1124 return (xsize <= 0 || ysize <= 0
1125 || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0));
1128 if (GET_CODE (x) == CONST)
1130 if (GET_CODE (y) == CONST)
1131 return memrefs_conflict_p (xsize, canon_rtx (XEXP (x, 0)),
1132 ysize, canon_rtx (XEXP (y, 0)), c);
1134 return memrefs_conflict_p (xsize, canon_rtx (XEXP (x, 0)),
1137 if (GET_CODE (y) == CONST)
1138 return memrefs_conflict_p (xsize, x, ysize,
1139 canon_rtx (XEXP (y, 0)), c);
1142 return (xsize < 0 || ysize < 0
1143 || (rtx_equal_for_memref_p (x, y)
1144 && (xsize == 0 || ysize == 0
1145 || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0))));
1152 /* Functions to compute memory dependencies.
1154 Since we process the insns in execution order, we can build tables
1155 to keep track of what registers are fixed (and not aliased), what registers
1156 are varying in known ways, and what registers are varying in unknown
1159 If both memory references are volatile, then there must always be a
1160 dependence between the two references, since their order can not be
1161 changed. A volatile and non-volatile reference can be interchanged
1164 A MEM_IN_STRUCT reference at a non-QImode non-AND varying address can never
1165 conflict with a non-MEM_IN_STRUCT reference at a fixed address. We must
1166 allow QImode aliasing because the ANSI C standard allows character
1167 pointers to alias anything. We are assuming that characters are
1168 always QImode here. We also must allow AND addresses, because they may
1169 generate accesses outside the object being referenced. This is used to
1170 generate aligned addresses from unaligned addresses, for instance, the
1171 alpha storeqi_unaligned pattern. */
1173 /* Read dependence: X is read after read in MEM takes place. There can
1174 only be a dependence here if both reads are volatile. */
1177 read_dependence (mem, x)
1181 return MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem);
1184 /* Returns MEM1 if and only if MEM1 is a scalar at a fixed address and
1185 MEM2 is a reference to a structure at a varying address, or returns
1186 MEM2 if vice versa. Otherwise, returns NULL_RTX. If a non-NULL
1187 value is returned MEM1 and MEM2 can never alias. VARIES_P is used
1188 to decide whether or not an address may vary; it should return
1189 nozero whenever variation is possible. */
1192 fixed_scalar_and_varying_struct_p (mem1, mem2, varies_p)
1195 int (*varies_p) PROTO((rtx));
1197 rtx mem1_addr = XEXP (mem1, 0);
1198 rtx mem2_addr = XEXP (mem2, 0);
1200 if (MEM_SCALAR_P (mem1) && MEM_IN_STRUCT_P (mem2)
1201 && !varies_p (mem1_addr) && varies_p (mem2_addr))
1202 /* MEM1 is a scalar at a fixed address; MEM2 is a struct at a
1206 if (MEM_IN_STRUCT_P (mem1) && MEM_SCALAR_P (mem2)
1207 && varies_p (mem1_addr) && !varies_p (mem2_addr))
1208 /* MEM2 is a scalar at a fixed address; MEM1 is a struct at a
1215 /* Returns nonzero if something about the mode or address format MEM1
1216 indicates that it might well alias *anything*. */
1219 aliases_everything_p (mem)
1222 if (GET_MODE (mem) == QImode)
1223 /* ANSI C says that a `char*' can point to anything. */
1226 if (GET_CODE (XEXP (mem, 0)) == AND)
1227 /* If the address is an AND, its very hard to know at what it is
1228 actually pointing. */
1234 /* True dependence: X is read after store in MEM takes place. */
1237 true_dependence (mem, mem_mode, x, varies)
1239 enum machine_mode mem_mode;
1241 int (*varies) PROTO((rtx));
1243 register rtx x_addr, mem_addr;
1245 if (MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem))
1248 if (DIFFERENT_ALIAS_SETS_P (x, mem))
1251 /* If X is an unchanging read, then it can't possibly conflict with any
1252 non-unchanging store. It may conflict with an unchanging write though,
1253 because there may be a single store to this address to initialize it.
1254 Just fall through to the code below to resolve the case where we have
1255 both an unchanging read and an unchanging write. This won't handle all
1256 cases optimally, but the possible performance loss should be
1258 if (RTX_UNCHANGING_P (x) && ! RTX_UNCHANGING_P (mem))
1261 if (mem_mode == VOIDmode)
1262 mem_mode = GET_MODE (mem);
1264 if (! base_alias_check (XEXP (x, 0), XEXP (mem, 0), GET_MODE (x), mem_mode))
1267 x_addr = canon_rtx (XEXP (x, 0));
1268 mem_addr = canon_rtx (XEXP (mem, 0));
1270 if (! memrefs_conflict_p (GET_MODE_SIZE (mem_mode), mem_addr,
1271 SIZE_FOR_MODE (x), x_addr, 0))
1274 if (aliases_everything_p (x))
1277 /* We cannot use aliases_everyting_p to test MEM, since we must look
1278 at MEM_MODE, rather than GET_MODE (MEM). */
1279 if (mem_mode == QImode || GET_CODE (mem_addr) == AND)
1282 /* In true_dependence we also allow BLKmode to alias anything. Why
1283 don't we do this in anti_dependence and output_dependence? */
1284 if (mem_mode == BLKmode || GET_MODE (x) == BLKmode)
1287 return !fixed_scalar_and_varying_struct_p (mem, x, varies);
1290 /* Returns non-zero if a write to X might alias a previous read from
1291 (or, if WRITEP is non-zero, a write to) MEM. */
1294 write_dependence_p (mem, x, writep)
1299 rtx x_addr, mem_addr;
1302 if (MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem))
1305 /* If MEM is an unchanging read, then it can't possibly conflict with
1306 the store to X, because there is at most one store to MEM, and it must
1307 have occurred somewhere before MEM. */
1308 if (!writep && RTX_UNCHANGING_P (mem))
1311 if (! base_alias_check (XEXP (x, 0), XEXP (mem, 0), GET_MODE (x),
1316 mem = canon_rtx (mem);
1318 if (DIFFERENT_ALIAS_SETS_P (x, mem))
1321 x_addr = XEXP (x, 0);
1322 mem_addr = XEXP (mem, 0);
1324 if (!memrefs_conflict_p (SIZE_FOR_MODE (mem), mem_addr,
1325 SIZE_FOR_MODE (x), x_addr, 0))
1329 = fixed_scalar_and_varying_struct_p (mem, x, rtx_addr_varies_p);
1331 return (!(fixed_scalar == mem && !aliases_everything_p (x))
1332 && !(fixed_scalar == x && !aliases_everything_p (mem)));
1335 /* Anti dependence: X is written after read in MEM takes place. */
1338 anti_dependence (mem, x)
1342 return write_dependence_p (mem, x, /*writep=*/0);
1345 /* Output dependence: X is written after store in MEM takes place. */
1348 output_dependence (mem, x)
1352 return write_dependence_p (mem, x, /*writep=*/1);
1355 /* Returns non-zero if X might refer to something which is not
1356 local to the function and is not constant. */
1359 nonlocal_reference_p (x)
1363 register RTX_CODE code;
1366 code = GET_CODE (x);
1368 if (GET_RTX_CLASS (code) == 'i')
1370 /* Constant functions are constant. */
1371 if (code == CALL_INSN && CONST_CALL_P (x))
1374 code = GET_CODE (x);
1380 if (GET_CODE (SUBREG_REG (x)) == REG)
1382 /* Global registers are not local. */
1383 if (REGNO (SUBREG_REG (x)) < FIRST_PSEUDO_REGISTER
1384 && global_regs[REGNO (SUBREG_REG (x)) + SUBREG_WORD (x)])
1392 /* Global registers are not local. */
1393 if (regno < FIRST_PSEUDO_REGISTER && global_regs[regno])
1407 /* Constants in the function's constants pool are constant. */
1408 if (CONSTANT_POOL_ADDRESS_P (x))
1413 /* Recursion introduces no additional considerations. */
1414 if (GET_CODE (XEXP (x, 0)) == MEM
1415 && GET_CODE (XEXP (XEXP (x, 0), 0)) == SYMBOL_REF
1416 && strcmp(XSTR (XEXP (XEXP (x, 0), 0), 0),
1417 IDENTIFIER_POINTER (
1418 DECL_ASSEMBLER_NAME (current_function_decl))) == 0)
1423 /* Be overly conservative and consider any volatile memory
1424 reference as not local. */
1425 if (MEM_VOLATILE_P (x))
1427 base = find_base_term (XEXP (x, 0));
1430 /* A Pmode ADDRESS could be a reference via the structure value
1431 address or static chain. Such memory references are nonlocal.
1433 Thus, we have to examine the contents of the ADDRESS to find
1434 out if this is a local reference or not. */
1435 if (GET_CODE (base) == ADDRESS
1436 && GET_MODE (base) == Pmode
1437 && (XEXP (base, 0) == stack_pointer_rtx
1438 || XEXP (base, 0) == arg_pointer_rtx
1439 #if HARD_FRAME_POINTER_REGNUM != FRAME_POINTER_REGNUM
1440 || XEXP (base, 0) == hard_frame_pointer_rtx
1442 || XEXP (base, 0) == frame_pointer_rtx))
1444 /* Constants in the function's constant pool are constant. */
1445 if (GET_CODE (base) == SYMBOL_REF && CONSTANT_POOL_ADDRESS_P (base))
1458 /* Recursively scan the operands of this expression. */
1461 register const char *fmt = GET_RTX_FORMAT (code);
1464 for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
1468 if (nonlocal_reference_p (XEXP (x, i)))
1471 else if (fmt[i] == 'E')
1474 for (j = 0; j < XVECLEN (x, i); j++)
1475 if (nonlocal_reference_p (XVECEXP (x, i, j)))
1484 /* Mark the function if it is constant. */
1487 mark_constant_function ()
1491 if (TREE_PUBLIC (current_function_decl)
1492 || TREE_READONLY (current_function_decl)
1493 || TREE_THIS_VOLATILE (current_function_decl)
1494 || TYPE_MODE (TREE_TYPE (current_function_decl)) == VOIDmode)
1497 /* Determine if this is a constant function. */
1499 for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
1500 if (GET_RTX_CLASS (GET_CODE (insn)) == 'i'
1501 && nonlocal_reference_p (insn))
1504 /* Mark the function. */
1506 TREE_READONLY (current_function_decl) = 1;
1510 static HARD_REG_SET argument_registers;
1517 #ifndef OUTGOING_REGNO
1518 #define OUTGOING_REGNO(N) N
1520 for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
1521 /* Check whether this register can hold an incoming pointer
1522 argument. FUNCTION_ARG_REGNO_P tests outgoing register
1523 numbers, so translate if necessary due to register windows. */
1524 if (FUNCTION_ARG_REGNO_P (OUTGOING_REGNO (i))
1525 && HARD_REGNO_MODE_OK (i, Pmode))
1526 SET_HARD_REG_BIT (argument_registers, i);
1528 alias_sets = splay_tree_new (splay_tree_compare_ints, 0, 0);
1532 init_alias_analysis ()
1534 int maxreg = max_reg_num ();
1537 register unsigned int ui;
1540 reg_known_value_size = maxreg;
1543 = (rtx *) xcalloc ((maxreg - FIRST_PSEUDO_REGISTER), sizeof (rtx))
1544 - FIRST_PSEUDO_REGISTER;
1546 = (char*) xcalloc ((maxreg - FIRST_PSEUDO_REGISTER), sizeof (char))
1547 - FIRST_PSEUDO_REGISTER;
1549 /* Overallocate reg_base_value to allow some growth during loop
1550 optimization. Loop unrolling can create a large number of
1552 reg_base_value_size = maxreg * 2;
1553 reg_base_value = (rtx *) xcalloc (reg_base_value_size, sizeof (rtx));
1555 ggc_add_rtx_root (reg_base_value, reg_base_value_size);
1557 new_reg_base_value = (rtx *) xmalloc (reg_base_value_size * sizeof (rtx));
1558 reg_seen = (char *) xmalloc (reg_base_value_size);
1559 if (! reload_completed && flag_unroll_loops)
1561 /* ??? Why are we realloc'ing if we're just going to zero it? */
1562 alias_invariant = (rtx *)xrealloc (alias_invariant,
1563 reg_base_value_size * sizeof (rtx));
1564 bzero ((char *)alias_invariant, reg_base_value_size * sizeof (rtx));
1568 /* The basic idea is that each pass through this loop will use the
1569 "constant" information from the previous pass to propagate alias
1570 information through another level of assignments.
1572 This could get expensive if the assignment chains are long. Maybe
1573 we should throttle the number of iterations, possibly based on
1574 the optimization level or flag_expensive_optimizations.
1576 We could propagate more information in the first pass by making use
1577 of REG_N_SETS to determine immediately that the alias information
1578 for a pseudo is "constant".
1580 A program with an uninitialized variable can cause an infinite loop
1581 here. Instead of doing a full dataflow analysis to detect such problems
1582 we just cap the number of iterations for the loop.
1584 The state of the arrays for the set chain in question does not matter
1585 since the program has undefined behavior. */
1590 /* Assume nothing will change this iteration of the loop. */
1593 /* We want to assign the same IDs each iteration of this loop, so
1594 start counting from zero each iteration of the loop. */
1597 /* We're at the start of the funtion each iteration through the
1598 loop, so we're copying arguments. */
1599 copying_arguments = 1;
1601 /* Wipe the potential alias information clean for this pass. */
1602 bzero ((char *) new_reg_base_value, reg_base_value_size * sizeof (rtx));
1604 /* Wipe the reg_seen array clean. */
1605 bzero ((char *) reg_seen, reg_base_value_size);
1607 /* Mark all hard registers which may contain an address.
1608 The stack, frame and argument pointers may contain an address.
1609 An argument register which can hold a Pmode value may contain
1610 an address even if it is not in BASE_REGS.
1612 The address expression is VOIDmode for an argument and
1613 Pmode for other registers. */
1615 for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
1616 if (TEST_HARD_REG_BIT (argument_registers, i))
1617 new_reg_base_value[i] = gen_rtx_ADDRESS (VOIDmode,
1618 gen_rtx_REG (Pmode, i));
1620 new_reg_base_value[STACK_POINTER_REGNUM]
1621 = gen_rtx_ADDRESS (Pmode, stack_pointer_rtx);
1622 new_reg_base_value[ARG_POINTER_REGNUM]
1623 = gen_rtx_ADDRESS (Pmode, arg_pointer_rtx);
1624 new_reg_base_value[FRAME_POINTER_REGNUM]
1625 = gen_rtx_ADDRESS (Pmode, frame_pointer_rtx);
1626 #if HARD_FRAME_POINTER_REGNUM != FRAME_POINTER_REGNUM
1627 new_reg_base_value[HARD_FRAME_POINTER_REGNUM]
1628 = gen_rtx_ADDRESS (Pmode, hard_frame_pointer_rtx);
1630 if (struct_value_incoming_rtx
1631 && GET_CODE (struct_value_incoming_rtx) == REG)
1632 new_reg_base_value[REGNO (struct_value_incoming_rtx)]
1633 = gen_rtx_ADDRESS (Pmode, struct_value_incoming_rtx);
1635 if (static_chain_rtx
1636 && GET_CODE (static_chain_rtx) == REG)
1637 new_reg_base_value[REGNO (static_chain_rtx)]
1638 = gen_rtx_ADDRESS (Pmode, static_chain_rtx);
1640 /* Walk the insns adding values to the new_reg_base_value array. */
1641 for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
1643 #if defined (HAVE_prologue) || defined (HAVE_epilogue)
1644 if (prologue_epilogue_contains (insn))
1647 if (GET_RTX_CLASS (GET_CODE (insn)) == 'i')
1650 /* If this insn has a noalias note, process it, Otherwise,
1651 scan for sets. A simple set will have no side effects
1652 which could change the base value of any other register. */
1654 if (GET_CODE (PATTERN (insn)) == SET
1655 && (find_reg_note (insn, REG_NOALIAS, NULL_RTX)))
1656 record_set (SET_DEST (PATTERN (insn)), NULL_RTX, NULL);
1658 note_stores (PATTERN (insn), record_set, NULL);
1660 set = single_set (insn);
1663 && GET_CODE (SET_DEST (set)) == REG
1664 && REGNO (SET_DEST (set)) >= FIRST_PSEUDO_REGISTER
1665 && (((note = find_reg_note (insn, REG_EQUAL, 0)) != 0
1666 && REG_N_SETS (REGNO (SET_DEST (set))) == 1)
1667 || (note = find_reg_note (insn, REG_EQUIV, NULL_RTX)) != 0)
1668 && GET_CODE (XEXP (note, 0)) != EXPR_LIST
1669 && ! reg_overlap_mentioned_p (SET_DEST (set), XEXP (note, 0)))
1671 int regno = REGNO (SET_DEST (set));
1672 reg_known_value[regno] = XEXP (note, 0);
1673 reg_known_equiv_p[regno] = REG_NOTE_KIND (note) == REG_EQUIV;
1676 else if (GET_CODE (insn) == NOTE
1677 && NOTE_LINE_NUMBER (insn) == NOTE_INSN_FUNCTION_BEG)
1678 copying_arguments = 0;
1681 /* Now propagate values from new_reg_base_value to reg_base_value. */
1682 for (ui = 0; ui < reg_base_value_size; ui++)
1684 if (new_reg_base_value[ui]
1685 && new_reg_base_value[ui] != reg_base_value[ui]
1686 && ! rtx_equal_p (new_reg_base_value[ui], reg_base_value[ui]))
1688 reg_base_value[ui] = new_reg_base_value[ui];
1693 while (changed && ++pass < MAX_ALIAS_LOOP_PASSES);
1695 /* Fill in the remaining entries. */
1696 for (i = FIRST_PSEUDO_REGISTER; i < maxreg; i++)
1697 if (reg_known_value[i] == 0)
1698 reg_known_value[i] = regno_reg_rtx[i];
1700 /* Simplify the reg_base_value array so that no register refers to
1701 another register, except to special registers indirectly through
1702 ADDRESS expressions.
1704 In theory this loop can take as long as O(registers^2), but unless
1705 there are very long dependency chains it will run in close to linear
1708 This loop may not be needed any longer now that the main loop does
1709 a better job at propagating alias information. */
1715 for (ui = 0; ui < reg_base_value_size; ui++)
1717 rtx base = reg_base_value[ui];
1718 if (base && GET_CODE (base) == REG)
1720 unsigned int base_regno = REGNO (base);
1721 if (base_regno == ui) /* register set from itself */
1722 reg_base_value[ui] = 0;
1724 reg_base_value[ui] = reg_base_value[base_regno];
1729 while (changed && pass < MAX_ALIAS_LOOP_PASSES);
1732 free (new_reg_base_value);
1733 new_reg_base_value = 0;
1739 end_alias_analysis ()
1741 free (reg_known_value + FIRST_PSEUDO_REGISTER);
1742 reg_known_value = 0;
1743 reg_known_value_size = 0;
1744 free (reg_known_equiv_p + FIRST_PSEUDO_REGISTER);
1745 reg_known_equiv_p = 0;
1749 ggc_del_root (reg_base_value);
1750 free (reg_base_value);
1753 reg_base_value_size = 0;
1754 if (alias_invariant)
1756 free (alias_invariant);
1757 alias_invariant = 0;