/* Alias analysis for GNU C Copyright (C) 1997, 1998, 1999, 2000 Free Software Foundation, Inc. Contributed by John Carr (jfc@mit.edu). This file is part of GNU CC. GNU CC is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU CC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU CC; see the file COPYING. If not, write to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ #include "config.h" #include "system.h" #include "rtl.h" #include "tree.h" #include "tm_p.h" #include "function.h" #include "insn-flags.h" #include "expr.h" #include "regs.h" #include "hard-reg-set.h" #include "basic-block.h" #include "flags.h" #include "output.h" #include "toplev.h" #include "cselib.h" #include "splay-tree.h" #include "ggc.h" /* The alias sets assigned to MEMs assist the back-end in determining which MEMs can alias which other MEMs. In general, two MEMs in different alias sets cannot alias each other, with one important exception. Consider something like: struct S {int i; double d; }; a store to an `S' can alias something of either type `int' or type `double'. (However, a store to an `int' cannot alias a `double' and vice versa.) We indicate this via a tree structure that looks like: struct S / \ / \ |/_ _\| int double (The arrows are directed and point downwards.) In this situation we say the alias set for `struct S' is the `superset' and that those for `int' and `double' are `subsets'. To see whether two alias sets can point to the same memory, we must see if either alias set is a subset of the other. We need not trace past immediate decendents, however, since we propagate all grandchildren up one level. Alias set zero is implicitly a superset of all other alias sets. However, this is no actual entry for alias set zero. It is an error to attempt to explicitly construct a subset of zero. */ typedef struct alias_set_entry { /* The alias set number, as stored in MEM_ALIAS_SET. */ HOST_WIDE_INT alias_set; /* The children of the alias set. These are not just the immediate children, but, in fact, all decendents. So, if we have: struct T { struct S s; float f; } continuing our example above, the children here will be all of `int', `double', `float', and `struct S'. */ splay_tree children; /* Nonzero if would have a child of zero: this effectively makes this alias set the same as alias set zero. */ int has_zero_child; } *alias_set_entry; static int rtx_equal_for_memref_p PARAMS ((rtx, rtx)); static rtx find_symbolic_term PARAMS ((rtx)); static rtx get_addr PARAMS ((rtx)); static int memrefs_conflict_p PARAMS ((int, rtx, int, rtx, HOST_WIDE_INT)); static void record_set PARAMS ((rtx, rtx, void *)); static rtx find_base_term PARAMS ((rtx)); static int base_alias_check PARAMS ((rtx, rtx, enum machine_mode, enum machine_mode)); static rtx find_base_value PARAMS ((rtx)); static int mems_in_disjoint_alias_sets_p PARAMS ((rtx, rtx)); static int insert_subset_children PARAMS ((splay_tree_node, void*)); static tree find_base_decl PARAMS ((tree)); static alias_set_entry get_alias_set_entry PARAMS ((HOST_WIDE_INT)); static rtx fixed_scalar_and_varying_struct_p PARAMS ((rtx, rtx, rtx, rtx, int (*) (rtx, int))); static int aliases_everything_p PARAMS ((rtx)); static int write_dependence_p PARAMS ((rtx, rtx, int)); static int nonlocal_mentioned_p PARAMS ((rtx)); static int loop_p PARAMS ((void)); /* Set up all info needed to perform alias analysis on memory references. */ /* Returns the size in bytes of the mode of X. */ #define SIZE_FOR_MODE(X) (GET_MODE_SIZE (GET_MODE (X))) /* Returns nonzero if MEM1 and MEM2 do not alias because they are in different alias sets. We ignore alias sets in functions making use of variable arguments because the va_arg macros on some systems are not legal ANSI C. */ #define DIFFERENT_ALIAS_SETS_P(MEM1, MEM2) \ mems_in_disjoint_alias_sets_p (MEM1, MEM2) /* Cap the number of passes we make over the insns propagating alias information through set chains. 10 is a completely arbitrary choice. */ #define MAX_ALIAS_LOOP_PASSES 10 /* reg_base_value[N] gives an address to which register N is related. If all sets after the first add or subtract to the current value or otherwise modify it so it does not point to a different top level object, reg_base_value[N] is equal to the address part of the source of the first set. A base address can be an ADDRESS, SYMBOL_REF, or LABEL_REF. ADDRESS expressions represent certain special values: function arguments and the stack, frame, and argument pointers. The contents of an ADDRESS is not normally used, the mode of the ADDRESS determines whether the ADDRESS is a function argument or some other special value. Pointer equality, not rtx_equal_p, determines whether two ADDRESS expressions refer to the same base address. The only use of the contents of an ADDRESS is for determining if the current function performs nonlocal memory memory references for the purposes of marking the function as a constant function. */ static rtx *reg_base_value; static rtx *new_reg_base_value; static unsigned int reg_base_value_size; /* size of reg_base_value array */ #define REG_BASE_VALUE(X) \ (REGNO (X) < reg_base_value_size \ ? reg_base_value[REGNO (X)] : 0) /* Vector of known invariant relationships between registers. Set in loop unrolling. Indexed by register number, if nonzero the value is an expression describing this register in terms of another. The length of this array is REG_BASE_VALUE_SIZE. Because this array contains only pseudo registers it has no effect after reload. */ static rtx *alias_invariant; /* Vector indexed by N giving the initial (unchanging) value known for pseudo-register N. This array is initialized in init_alias_analysis, and does not change until end_alias_analysis is called. */ rtx *reg_known_value; /* Indicates number of valid entries in reg_known_value. */ static unsigned int reg_known_value_size; /* Vector recording for each reg_known_value whether it is due to a REG_EQUIV note. Future passes (viz., reload) may replace the pseudo with the equivalent expression and so we account for the dependences that would be introduced if that happens. The REG_EQUIV notes created in assign_parms may mention the arg pointer, and there are explicit insns in the RTL that modify the arg pointer. Thus we must ensure that such insns don't get scheduled across each other because that would invalidate the REG_EQUIV notes. One could argue that the REG_EQUIV notes are wrong, but solving the problem in the scheduler will likely give better code, so we do it here. */ char *reg_known_equiv_p; /* True when scanning insns from the start of the rtl to the NOTE_INSN_FUNCTION_BEG note. */ static int copying_arguments; /* The splay-tree used to store the various alias set entries. */ static splay_tree alias_sets; /* Returns a pointer to the alias set entry for ALIAS_SET, if there is such an entry, or NULL otherwise. */ static alias_set_entry get_alias_set_entry (alias_set) HOST_WIDE_INT alias_set; { splay_tree_node sn = splay_tree_lookup (alias_sets, (splay_tree_key) alias_set); return sn != 0 ? ((alias_set_entry) sn->value) : 0; } /* Returns nonzero if the alias sets for MEM1 and MEM2 are such that the two MEMs cannot alias each other. */ static int mems_in_disjoint_alias_sets_p (mem1, mem2) rtx mem1; rtx mem2; { #ifdef ENABLE_CHECKING /* Perform a basic sanity check. Namely, that there are no alias sets if we're not using strict aliasing. This helps to catch bugs whereby someone uses PUT_CODE, but doesn't clear MEM_ALIAS_SET, or where a MEM is allocated in some way other than by the use of gen_rtx_MEM, and the MEM_ALIAS_SET is not cleared. If we begin to use alias sets to indicate that spilled registers cannot alias each other, we might need to remove this check. */ if (! flag_strict_aliasing && (MEM_ALIAS_SET (mem1) != 0 || MEM_ALIAS_SET (mem2) != 0)) abort (); #endif return ! alias_sets_conflict_p (MEM_ALIAS_SET (mem1), MEM_ALIAS_SET (mem2)); } /* Insert the NODE into the splay tree given by DATA. Used by record_alias_subset via splay_tree_foreach. */ static int insert_subset_children (node, data) splay_tree_node node; void *data; { splay_tree_insert ((splay_tree) data, node->key, node->value); return 0; } /* Return 1 if the two specified alias sets may conflict. */ int alias_sets_conflict_p (set1, set2) HOST_WIDE_INT set1, set2; { alias_set_entry ase; /* If have no alias set information for one of the operands, we have to assume it can alias anything. */ if (set1 == 0 || set2 == 0 /* If the two alias sets are the same, they may alias. */ || set1 == set2) return 1; /* See if the first alias set is a subset of the second. */ ase = get_alias_set_entry (set1); if (ase != 0 && (ase->has_zero_child || splay_tree_lookup (ase->children, (splay_tree_key) set2))) return 1; /* Now do the same, but with the alias sets reversed. */ ase = get_alias_set_entry (set2); if (ase != 0 && (ase->has_zero_child || splay_tree_lookup (ase->children, (splay_tree_key) set1))) return 1; /* The two alias sets are distinct and neither one is the child of the other. Therefore, they cannot alias. */ return 0; } /* Return 1 if TYPE is a RECORD_TYPE, UNION_TYPE, or QUAL_UNION_TYPE and has has any readonly fields. If any of the fields have types that contain readonly fields, return true as well. */ int readonly_fields_p (type) tree type; { tree field; if (TREE_CODE (type) != RECORD_TYPE && TREE_CODE (type) != UNION_TYPE && TREE_CODE (type) != QUAL_UNION_TYPE) return 0; for (field = TYPE_FIELDS (type); field != 0; field = TREE_CHAIN (field)) if (TREE_CODE (field) == FIELD_DECL && (TREE_READONLY (field) || readonly_fields_p (TREE_TYPE (field)))) return 1; return 0; } /* Return 1 if any MEM object of type T1 will always conflict (using the dependency routines in this file) with any MEM object of type T2. This is used when allocating temporary storage. If T1 and/or T2 are NULL_TREE, it means we know nothing about the storage. */ int objects_must_conflict_p (t1, t2) tree t1, t2; { /* If one or the other has readonly fields or is readonly, then they may not conflict. */ if ((t1 != 0 && readonly_fields_p (t1)) || (t2 != 0 && readonly_fields_p (t2)) || (t1 != 0 && TYPE_READONLY (t1)) || (t2 != 0 && TYPE_READONLY (t2))) return 0; /* If they are the same type, they must conflict. */ if (t1 == t2 /* Likewise if both are volatile. */ || (t1 != 0 && TYPE_VOLATILE (t1) && t2 != 0 && TYPE_VOLATILE (t2))) return 1; /* If one is aggregate and the other is scalar then they may not conflict. */ if ((t1 != 0 && AGGREGATE_TYPE_P (t1)) != (t2 != 0 && AGGREGATE_TYPE_P (t2))) return 0; /* Otherwise they conflict only if the alias sets conflict. */ return alias_sets_conflict_p (t1 ? get_alias_set (t1) : 0, t2 ? get_alias_set (t2) : 0); } /* T is an expression with pointer type. Find the DECL on which this expression is based. (For example, in `a[i]' this would be `a'.) If there is no such DECL, or a unique decl cannot be determined, NULL_TREE is retured. */ static tree find_base_decl (t) tree t; { tree d0, d1, d2; if (t == 0 || t == error_mark_node || ! POINTER_TYPE_P (TREE_TYPE (t))) return 0; /* If this is a declaration, return it. */ if (TREE_CODE_CLASS (TREE_CODE (t)) == 'd') return t; /* Handle general expressions. It would be nice to deal with COMPONENT_REFs here. If we could tell that `a' and `b' were the same, then `a->f' and `b->f' are also the same. */ switch (TREE_CODE_CLASS (TREE_CODE (t))) { case '1': return find_base_decl (TREE_OPERAND (t, 0)); case '2': /* Return 0 if found in neither or both are the same. */ d0 = find_base_decl (TREE_OPERAND (t, 0)); d1 = find_base_decl (TREE_OPERAND (t, 1)); if (d0 == d1) return d0; else if (d0 == 0) return d1; else if (d1 == 0) return d0; else return 0; case '3': d0 = find_base_decl (TREE_OPERAND (t, 0)); d1 = find_base_decl (TREE_OPERAND (t, 1)); d0 = find_base_decl (TREE_OPERAND (t, 0)); d2 = find_base_decl (TREE_OPERAND (t, 2)); /* Set any nonzero values from the last, then from the first. */ if (d1 == 0) d1 = d2; if (d0 == 0) d0 = d1; if (d1 == 0) d1 = d0; if (d2 == 0) d2 = d1; /* At this point all are nonzero or all are zero. If all three are the same, return it. Otherwise, return zero. */ return (d0 == d1 && d1 == d2) ? d0 : 0; default: return 0; } } /* Return the alias set for T, which may be either a type or an expression. Call language-specific routine for help, if needed. */ HOST_WIDE_INT get_alias_set (t) tree t; { tree orig_t; HOST_WIDE_INT set; /* If we're not doing any alias analysis, just assume everything aliases everything else. Also return 0 if this or its type is an error. */ if (! flag_strict_aliasing || t == error_mark_node || (! TYPE_P (t) && (TREE_TYPE (t) == 0 || TREE_TYPE (t) == error_mark_node))) return 0; /* We can be passed either an expression or a type. This and the language-specific routine may make mutually-recursive calls to each other to figure out what to do. At each juncture, we see if this is a tree that the language may need to handle specially. First handle things that aren't types and start by removing nops since we care only about the actual object. */ if (! TYPE_P (t)) { while (TREE_CODE (t) == NOP_EXPR || TREE_CODE (t) == CONVERT_EXPR || TREE_CODE (t) == NON_LVALUE_EXPR) t = TREE_OPERAND (t, 0); /* Now give the language a chance to do something but record what we gave it this time. */ orig_t = t; if ((set = lang_get_alias_set (t)) != -1) return set; /* Now loop the same way as get_inner_reference and get the alias set to use. Pick up the outermost object that we could have a pointer to. */ while (1) { /* Unnamed bitfields are not an addressable object. */ if (TREE_CODE (t) == BIT_FIELD_REF) ; else if (TREE_CODE (t) == COMPONENT_REF) { if (! DECL_NONADDRESSABLE_P (TREE_OPERAND (t, 1))) /* Stop at an adressable decl. */ break; } else if (TREE_CODE (t) == ARRAY_REF) { if (! TYPE_NONALIASED_COMPONENT (TREE_TYPE (TREE_OPERAND (t, 0)))) /* Stop at an addresssable array element. */ break; } else if (TREE_CODE (t) != NON_LVALUE_EXPR && ! ((TREE_CODE (t) == NOP_EXPR || TREE_CODE (t) == CONVERT_EXPR) && (TYPE_MODE (TREE_TYPE (t)) == TYPE_MODE (TREE_TYPE (TREE_OPERAND (t, 0)))))) /* Stop if not one of above and not mode-preserving conversion. */ break; t = TREE_OPERAND (t, 0); } if (TREE_CODE (t) == INDIRECT_REF) { /* Check for accesses through restrict-qualified pointers. */ tree decl = find_base_decl (TREE_OPERAND (t, 0)); if (decl && DECL_POINTER_ALIAS_SET_KNOWN_P (decl)) /* We use the alias set indicated in the declaration. */ return DECL_POINTER_ALIAS_SET (decl); /* If we have an INDIRECT_REF via a void pointer, we don't know anything about what that might alias. */ if (TREE_CODE (TREE_TYPE (t)) == VOID_TYPE) return 0; } /* Give the language another chance to do something special. */ if (orig_t != t && (set = lang_get_alias_set (t)) != -1) return set; /* Now all we care about is the type. */ t = TREE_TYPE (t); } /* Variant qualifiers don't affect the alias set, so get the main variant. If this is a type with a known alias set, return it. */ t = TYPE_MAIN_VARIANT (t); if (TYPE_P (t) && TYPE_ALIAS_SET_KNOWN_P (t)) return TYPE_ALIAS_SET (t); /* See if the language has special handling for this type. */ if ((set = lang_get_alias_set (t)) != -1) { /* If the alias set is now known, we are done. */ if (TYPE_ALIAS_SET_KNOWN_P (t)) return TYPE_ALIAS_SET (t); } /* There are no objects of FUNCTION_TYPE, so there's no point in using up an alias set for them. (There are, of course, pointers and references to functions, but that's different.) */ else if (TREE_CODE (t) == FUNCTION_TYPE) set = 0; else /* Otherwise make a new alias set for this type. */ set = new_alias_set (); TYPE_ALIAS_SET (t) = set; /* If this is an aggregate type, we must record any component aliasing information. */ if (AGGREGATE_TYPE_P (t) || TREE_CODE (t) == COMPLEX_TYPE) record_component_aliases (t); return set; } /* Return a brand-new alias set. */ HOST_WIDE_INT new_alias_set () { static HOST_WIDE_INT last_alias_set; if (flag_strict_aliasing) return ++last_alias_set; else return 0; } /* Indicate that things in SUBSET can alias things in SUPERSET, but not vice versa. For example, in C, a store to an `int' can alias a structure containing an `int', but not vice versa. Here, the structure would be the SUPERSET and `int' the SUBSET. This function should be called only once per SUPERSET/SUBSET pair. It is illegal for SUPERSET to be zero; everything is implicitly a subset of alias set zero. */ void record_alias_subset (superset, subset) HOST_WIDE_INT superset; HOST_WIDE_INT subset; { alias_set_entry superset_entry; alias_set_entry subset_entry; if (superset == 0) abort (); superset_entry = get_alias_set_entry (superset); if (superset_entry == 0) { /* Create an entry for the SUPERSET, so that we have a place to attach the SUBSET. */ superset_entry = (alias_set_entry) xmalloc (sizeof (struct alias_set_entry)); superset_entry->alias_set = superset; superset_entry->children = splay_tree_new (splay_tree_compare_ints, 0, 0); superset_entry->has_zero_child = 0; splay_tree_insert (alias_sets, (splay_tree_key) superset, (splay_tree_value) superset_entry); } if (subset == 0) superset_entry->has_zero_child = 1; else { subset_entry = get_alias_set_entry (subset); /* If there is an entry for the subset, enter all of its children (if they are not already present) as children of the SUPERSET. */ if (subset_entry) { if (subset_entry->has_zero_child) superset_entry->has_zero_child = 1; splay_tree_foreach (subset_entry->children, insert_subset_children, superset_entry->children); } /* Enter the SUBSET itself as a child of the SUPERSET. */ splay_tree_insert (superset_entry->children, (splay_tree_key) subset, 0); } } /* Record that component types of TYPE, if any, are part of that type for aliasing purposes. For record types, we only record component types for fields that are marked addressable. For array types, we always record the component types, so the front end should not call this function if the individual component aren't addressable. */ void record_component_aliases (type) tree type; { HOST_WIDE_INT superset = get_alias_set (type); tree field; if (superset == 0) return; switch (TREE_CODE (type)) { case ARRAY_TYPE: if (! TYPE_NONALIASED_COMPONENT (type)) record_alias_subset (superset, get_alias_set (TREE_TYPE (type))); break; case RECORD_TYPE: case UNION_TYPE: case QUAL_UNION_TYPE: for (field = TYPE_FIELDS (type); field != 0; field = TREE_CHAIN (field)) if (TREE_CODE (field) == FIELD_DECL && ! DECL_NONADDRESSABLE_P (field)) record_alias_subset (superset, get_alias_set (TREE_TYPE (field))); break; case COMPLEX_TYPE: record_alias_subset (superset, get_alias_set (TREE_TYPE (type))); break; default: break; } } /* Allocate an alias set for use in storing and reading from the varargs spill area. */ HOST_WIDE_INT get_varargs_alias_set () { static HOST_WIDE_INT set = -1; if (set == -1) set = new_alias_set (); return set; } /* Likewise, but used for the fixed portions of the frame, e.g., register save areas. */ HOST_WIDE_INT get_frame_alias_set () { static HOST_WIDE_INT set = -1; if (set == -1) set = new_alias_set (); return set; } /* Inside SRC, the source of a SET, find a base address. */ static rtx find_base_value (src) register rtx src; { unsigned int regno; switch (GET_CODE (src)) { case SYMBOL_REF: case LABEL_REF: return src; case REG: regno = REGNO (src); /* At the start of a function, argument registers have known base values which may be lost later. Returning an ADDRESS expression here allows optimization based on argument values even when the argument registers are used for other purposes. */ if (regno < FIRST_PSEUDO_REGISTER && copying_arguments) return new_reg_base_value[regno]; /* If a pseudo has a known base value, return it. Do not do this for hard regs since it can result in a circular dependency chain for registers which have values at function entry. The test above is not sufficient because the scheduler may move a copy out of an arg reg past the NOTE_INSN_FUNCTION_BEGIN. */ if (regno >= FIRST_PSEUDO_REGISTER && regno < reg_base_value_size && reg_base_value[regno]) return reg_base_value[regno]; return src; case MEM: /* Check for an argument passed in memory. Only record in the copying-arguments block; it is too hard to track changes otherwise. */ if (copying_arguments && (XEXP (src, 0) == arg_pointer_rtx || (GET_CODE (XEXP (src, 0)) == PLUS && XEXP (XEXP (src, 0), 0) == arg_pointer_rtx))) return gen_rtx_ADDRESS (VOIDmode, src); return 0; case CONST: src = XEXP (src, 0); if (GET_CODE (src) != PLUS && GET_CODE (src) != MINUS) break; /* ... fall through ... */ case PLUS: case MINUS: { rtx temp, src_0 = XEXP (src, 0), src_1 = XEXP (src, 1); /* If either operand is a REG, then see if we already have a known value for it. */ if (GET_CODE (src_0) == REG) { temp = find_base_value (src_0); if (temp != 0) src_0 = temp; } if (GET_CODE (src_1) == REG) { temp = find_base_value (src_1); if (temp!= 0) src_1 = temp; } /* Guess which operand is the base address: If either operand is a symbol, then it is the base. If either operand is a CONST_INT, then the other is the base. */ if (GET_CODE (src_1) == CONST_INT || CONSTANT_P (src_0)) return find_base_value (src_0); else if (GET_CODE (src_0) == CONST_INT || CONSTANT_P (src_1)) return find_base_value (src_1); /* This might not be necessary anymore: If either operand is a REG that is a known pointer, then it is the base. */ else if (GET_CODE (src_0) == REG && REG_POINTER (src_0)) return find_base_value (src_0); else if (GET_CODE (src_1) == REG && REG_POINTER (src_1)) return find_base_value (src_1); return 0; } case LO_SUM: /* The standard form is (lo_sum reg sym) so look only at the second operand. */ return find_base_value (XEXP (src, 1)); case AND: /* If the second operand is constant set the base address to the first operand. */ if (GET_CODE (XEXP (src, 1)) == CONST_INT && INTVAL (XEXP (src, 1)) != 0) return find_base_value (XEXP (src, 0)); return 0; case TRUNCATE: if (GET_MODE_SIZE (GET_MODE (src)) < GET_MODE_SIZE (Pmode)) break; /* Fall through. */ case ZERO_EXTEND: case SIGN_EXTEND: /* used for NT/Alpha pointers */ case HIGH: return find_base_value (XEXP (src, 0)); default: break; } return 0; } /* Called from init_alias_analysis indirectly through note_stores. */ /* While scanning insns to find base values, reg_seen[N] is nonzero if register N has been set in this function. */ static char *reg_seen; /* Addresses which are known not to alias anything else are identified by a unique integer. */ static int unique_id; static void record_set (dest, set, data) rtx dest, set; void *data ATTRIBUTE_UNUSED; { register unsigned regno; rtx src; if (GET_CODE (dest) != REG) return; regno = REGNO (dest); if (regno >= reg_base_value_size) abort (); if (set) { /* A CLOBBER wipes out any old value but does not prevent a previously unset register from acquiring a base address (i.e. reg_seen is not set). */ if (GET_CODE (set) == CLOBBER) { new_reg_base_value[regno] = 0; return; } src = SET_SRC (set); } else { if (reg_seen[regno]) { new_reg_base_value[regno] = 0; return; } reg_seen[regno] = 1; new_reg_base_value[regno] = gen_rtx_ADDRESS (Pmode, GEN_INT (unique_id++)); return; } /* This is not the first set. If the new value is not related to the old value, forget the base value. Note that the following code is not detected: extern int x, y; int *p = &x; p += (&y-&x); ANSI C does not allow computing the difference of addresses of distinct top level objects. */ if (new_reg_base_value[regno]) switch (GET_CODE (src)) { case LO_SUM: case MINUS: if (XEXP (src, 0) != dest && XEXP (src, 1) != dest) new_reg_base_value[regno] = 0; break; case PLUS: /* If the value we add in the PLUS is also a valid base value, this might be the actual base value, and the original value an index. */ { rtx other = NULL_RTX; if (XEXP (src, 0) == dest) other = XEXP (src, 1); else if (XEXP (src, 1) == dest) other = XEXP (src, 0); if (! other || find_base_value (other)) new_reg_base_value[regno] = 0; break; } case AND: if (XEXP (src, 0) != dest || GET_CODE (XEXP (src, 1)) != CONST_INT) new_reg_base_value[regno] = 0; break; default: new_reg_base_value[regno] = 0; break; } /* If this is the first set of a register, record the value. */ else if ((regno >= FIRST_PSEUDO_REGISTER || ! fixed_regs[regno]) && ! reg_seen[regno] && new_reg_base_value[regno] == 0) new_reg_base_value[regno] = find_base_value (src); reg_seen[regno] = 1; } /* Called from loop optimization when a new pseudo-register is created. It indicates that REGNO is being set to VAL. f INVARIANT is true then this value also describes an invariant relationship which can be used to deduce that two registers with unknown values are different. */ void record_base_value (regno, val, invariant) unsigned int regno; rtx val; int invariant; { if (regno >= reg_base_value_size) return; if (invariant && alias_invariant) alias_invariant[regno] = val; if (GET_CODE (val) == REG) { if (REGNO (val) < reg_base_value_size) reg_base_value[regno] = reg_base_value[REGNO (val)]; return; } reg_base_value[regno] = find_base_value (val); } /* Returns a canonical version of X, from the point of view alias analysis. (For example, if X is a MEM whose address is a register, and the register has a known value (say a SYMBOL_REF), then a MEM whose address is the SYMBOL_REF is returned.) */ rtx canon_rtx (x) rtx x; { /* Recursively look for equivalences. */ if (GET_CODE (x) == REG && REGNO (x) >= FIRST_PSEUDO_REGISTER && REGNO (x) < reg_known_value_size) return reg_known_value[REGNO (x)] == x ? x : canon_rtx (reg_known_value[REGNO (x)]); else if (GET_CODE (x) == PLUS) { rtx x0 = canon_rtx (XEXP (x, 0)); rtx x1 = canon_rtx (XEXP (x, 1)); if (x0 != XEXP (x, 0) || x1 != XEXP (x, 1)) { /* We can tolerate LO_SUMs being offset here; these rtl are used for nothing other than comparisons. */ if (GET_CODE (x0) == CONST_INT) return plus_constant_for_output (x1, INTVAL (x0)); else if (GET_CODE (x1) == CONST_INT) return plus_constant_for_output (x0, INTVAL (x1)); return gen_rtx_PLUS (GET_MODE (x), x0, x1); } } /* This gives us much better alias analysis when called from the loop optimizer. Note we want to leave the original MEM alone, but need to return the canonicalized MEM with all the flags with their original values. */ else if (GET_CODE (x) == MEM) { rtx addr = canon_rtx (XEXP (x, 0)); if (addr != XEXP (x, 0)) { rtx new = gen_rtx_MEM (GET_MODE (x), addr); MEM_COPY_ATTRIBUTES (new, x); x = new; } } return x; } /* Return 1 if X and Y are identical-looking rtx's. We use the data in reg_known_value above to see if two registers with different numbers are, in fact, equivalent. */ static int rtx_equal_for_memref_p (x, y) rtx x, y; { register int i; register int j; register enum rtx_code code; register const char *fmt; if (x == 0 && y == 0) return 1; if (x == 0 || y == 0) return 0; x = canon_rtx (x); y = canon_rtx (y); if (x == y) return 1; code = GET_CODE (x); /* Rtx's of different codes cannot be equal. */ if (code != GET_CODE (y)) return 0; /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent. (REG:SI x) and (REG:HI x) are NOT equivalent. */ if (GET_MODE (x) != GET_MODE (y)) return 0; /* Some RTL can be compared without a recursive examination. */ switch (code) { case REG: return REGNO (x) == REGNO (y); case LABEL_REF: return XEXP (x, 0) == XEXP (y, 0); case SYMBOL_REF: return XSTR (x, 0) == XSTR (y, 0); case CONST_INT: case CONST_DOUBLE: /* There's no need to compare the contents of CONST_DOUBLEs or CONST_INTs because pointer equality is a good enough comparison for these nodes. */ return 0; case ADDRESSOF: return (XINT (x, 1) == XINT (y, 1) && rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0))); default: break; } /* For commutative operations, the RTX match if the operand match in any order. Also handle the simple binary and unary cases without a loop. */ if (code == EQ || code == NE || GET_RTX_CLASS (code) == 'c') return ((rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0)) && rtx_equal_for_memref_p (XEXP (x, 1), XEXP (y, 1))) || (rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 1)) && rtx_equal_for_memref_p (XEXP (x, 1), XEXP (y, 0)))); else if (GET_RTX_CLASS (code) == '<' || GET_RTX_CLASS (code) == '2') return (rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0)) && rtx_equal_for_memref_p (XEXP (x, 1), XEXP (y, 1))); else if (GET_RTX_CLASS (code) == '1') return rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0)); /* Compare the elements. If any pair of corresponding elements fail to match, return 0 for the whole things. Limit cases to types which actually appear in addresses. */ fmt = GET_RTX_FORMAT (code); for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--) { switch (fmt[i]) { case 'i': if (XINT (x, i) != XINT (y, i)) return 0; break; case 'E': /* Two vectors must have the same length. */ if (XVECLEN (x, i) != XVECLEN (y, i)) return 0; /* And the corresponding elements must match. */ for (j = 0; j < XVECLEN (x, i); j++) if (rtx_equal_for_memref_p (XVECEXP (x, i, j), XVECEXP (y, i, j)) == 0) return 0; break; case 'e': if (rtx_equal_for_memref_p (XEXP (x, i), XEXP (y, i)) == 0) return 0; break; /* This can happen for an asm which clobbers memory. */ case '0': break; /* It is believed that rtx's at this level will never contain anything but integers and other rtx's, except for within LABEL_REFs and SYMBOL_REFs. */ default: abort (); } } return 1; } /* Given an rtx X, find a SYMBOL_REF or LABEL_REF within X and return it, or return 0 if none found. */ static rtx find_symbolic_term (x) rtx x; { register int i; register enum rtx_code code; register const char *fmt; code = GET_CODE (x); if (code == SYMBOL_REF || code == LABEL_REF) return x; if (GET_RTX_CLASS (code) == 'o') return 0; fmt = GET_RTX_FORMAT (code); for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--) { rtx t; if (fmt[i] == 'e') { t = find_symbolic_term (XEXP (x, i)); if (t != 0) return t; } else if (fmt[i] == 'E') break; } return 0; } static rtx find_base_term (x) register rtx x; { cselib_val *val; struct elt_loc_list *l; #if defined (FIND_BASE_TERM) /* Try machine-dependent ways to find the base term. */ x = FIND_BASE_TERM (x); #endif switch (GET_CODE (x)) { case REG: return REG_BASE_VALUE (x); case ZERO_EXTEND: case SIGN_EXTEND: /* Used for Alpha/NT pointers */ case HIGH: case PRE_INC: case PRE_DEC: case POST_INC: case POST_DEC: return find_base_term (XEXP (x, 0)); case VALUE: val = CSELIB_VAL_PTR (x); for (l = val->locs; l; l = l->next) if ((x = find_base_term (l->loc)) != 0) return x; return 0; case CONST: x = XEXP (x, 0); if (GET_CODE (x) != PLUS && GET_CODE (x) != MINUS) return 0; /* fall through */ case LO_SUM: case PLUS: case MINUS: { rtx tmp1 = XEXP (x, 0); rtx tmp2 = XEXP (x, 1); /* This is a litle bit tricky since we have to determine which of the two operands represents the real base address. Otherwise this routine may return the index register instead of the base register. That may cause us to believe no aliasing was possible, when in fact aliasing is possible. We use a few simple tests to guess the base register. Additional tests can certainly be added. For example, if one of the operands is a shift or multiply, then it must be the index register and the other operand is the base register. */ if (tmp1 == pic_offset_table_rtx && CONSTANT_P (tmp2)) return find_base_term (tmp2); /* If either operand is known to be a pointer, then use it to determine the base term. */ if (REG_P (tmp1) && REG_POINTER (tmp1)) return find_base_term (tmp1); if (REG_P (tmp2) && REG_POINTER (tmp2)) return find_base_term (tmp2); /* Neither operand was known to be a pointer. Go ahead and find the base term for both operands. */ tmp1 = find_base_term (tmp1); tmp2 = find_base_term (tmp2); /* If either base term is named object or a special address (like an argument or stack reference), then use it for the base term. */ if (tmp1 != 0 && (GET_CODE (tmp1) == SYMBOL_REF || GET_CODE (tmp1) == LABEL_REF || (GET_CODE (tmp1) == ADDRESS && GET_MODE (tmp1) != VOIDmode))) return tmp1; if (tmp2 != 0 && (GET_CODE (tmp2) == SYMBOL_REF || GET_CODE (tmp2) == LABEL_REF || (GET_CODE (tmp2) == ADDRESS && GET_MODE (tmp2) != VOIDmode))) return tmp2; /* We could not determine which of the two operands was the base register and which was the index. So we can determine nothing from the base alias check. */ return 0; } case AND: if (GET_CODE (XEXP (x, 0)) == REG && GET_CODE (XEXP (x, 1)) == CONST_INT) return REG_BASE_VALUE (XEXP (x, 0)); return 0; case SYMBOL_REF: case LABEL_REF: return x; case ADDRESSOF: return REG_BASE_VALUE (frame_pointer_rtx); default: return 0; } } /* Return 0 if the addresses X and Y are known to point to different objects, 1 if they might be pointers to the same object. */ static int base_alias_check (x, y, x_mode, y_mode) rtx x, y; enum machine_mode x_mode, y_mode; { rtx x_base = find_base_term (x); rtx y_base = find_base_term (y); /* If the address itself has no known base see if a known equivalent value has one. If either address still has no known base, nothing is known about aliasing. */ if (x_base == 0) { rtx x_c; if (! flag_expensive_optimizations || (x_c = canon_rtx (x)) == x) return 1; x_base = find_base_term (x_c); if (x_base == 0) return 1; } if (y_base == 0) { rtx y_c; if (! flag_expensive_optimizations || (y_c = canon_rtx (y)) == y) return 1; y_base = find_base_term (y_c); if (y_base == 0) return 1; } /* If the base addresses are equal nothing is known about aliasing. */ if (rtx_equal_p (x_base, y_base)) return 1; /* The base addresses of the read and write are different expressions. If they are both symbols and they are not accessed via AND, there is no conflict. We can bring knowledge of object alignment into play here. For example, on alpha, "char a, b;" can alias one another, though "char a; long b;" cannot. */ if (GET_CODE (x_base) != ADDRESS && GET_CODE (y_base) != ADDRESS) { if (GET_CODE (x) == AND && GET_CODE (y) == AND) return 1; if (GET_CODE (x) == AND && (GET_CODE (XEXP (x, 1)) != CONST_INT || GET_MODE_UNIT_SIZE (y_mode) < -INTVAL (XEXP (x, 1)))) return 1; if (GET_CODE (y) == AND && (GET_CODE (XEXP (y, 1)) != CONST_INT || GET_MODE_UNIT_SIZE (x_mode) < -INTVAL (XEXP (y, 1)))) return 1; /* Differing symbols never alias. */ return 0; } /* If one address is a stack reference there can be no alias: stack references using different base registers do not alias, a stack reference can not alias a parameter, and a stack reference can not alias a global. */ if ((GET_CODE (x_base) == ADDRESS && GET_MODE (x_base) == Pmode) || (GET_CODE (y_base) == ADDRESS && GET_MODE (y_base) == Pmode)) return 0; if (! flag_argument_noalias) return 1; if (flag_argument_noalias > 1) return 0; /* Weak noalias assertion (arguments are distinct, but may match globals). */ return ! (GET_MODE (x_base) == VOIDmode && GET_MODE (y_base) == VOIDmode); } /* Convert the address X into something we can use. This is done by returning it unchanged unless it is a value; in the latter case we call cselib to get a more useful rtx. */ static rtx get_addr (x) rtx x; { cselib_val *v; struct elt_loc_list *l; if (GET_CODE (x) != VALUE) return x; v = CSELIB_VAL_PTR (x); for (l = v->locs; l; l = l->next) if (CONSTANT_P (l->loc)) return l->loc; for (l = v->locs; l; l = l->next) if (GET_CODE (l->loc) != REG && GET_CODE (l->loc) != MEM) return l->loc; if (v->locs) return v->locs->loc; return x; } /* Return the address of the (N_REFS + 1)th memory reference to ADDR where SIZE is the size in bytes of the memory reference. If ADDR is not modified by the memory reference then ADDR is returned. */ rtx addr_side_effect_eval (addr, size, n_refs) rtx addr; int size; int n_refs; { int offset = 0; switch (GET_CODE (addr)) { case PRE_INC: offset = (n_refs + 1) * size; break; case PRE_DEC: offset = -(n_refs + 1) * size; break; case POST_INC: offset = n_refs * size; break; case POST_DEC: offset = -n_refs * size; break; default: return addr; } if (offset) addr = gen_rtx_PLUS (GET_MODE (addr), XEXP (addr, 0), GEN_INT (offset)); else addr = XEXP (addr, 0); return addr; } /* Return nonzero if X and Y (memory addresses) could reference the same location in memory. C is an offset accumulator. When C is nonzero, we are testing aliases between X and Y + C. XSIZE is the size in bytes of the X reference, similarly YSIZE is the size in bytes for Y. If XSIZE or YSIZE is zero, we do not know the amount of memory being referenced (the reference was BLKmode), so make the most pessimistic assumptions. If XSIZE or YSIZE is negative, we may access memory outside the object being referenced as a side effect. This can happen when using AND to align memory references, as is done on the Alpha. Nice to notice that varying addresses cannot conflict with fp if no local variables had their addresses taken, but that's too hard now. */ static int memrefs_conflict_p (xsize, x, ysize, y, c) register rtx x, y; int xsize, ysize; HOST_WIDE_INT c; { if (GET_CODE (x) == VALUE) x = get_addr (x); if (GET_CODE (y) == VALUE) y = get_addr (y); if (GET_CODE (x) == HIGH) x = XEXP (x, 0); else if (GET_CODE (x) == LO_SUM) x = XEXP (x, 1); else x = canon_rtx (addr_side_effect_eval (x, xsize, 0)); if (GET_CODE (y) == HIGH) y = XEXP (y, 0); else if (GET_CODE (y) == LO_SUM) y = XEXP (y, 1); else y = canon_rtx (addr_side_effect_eval (y, ysize, 0)); if (rtx_equal_for_memref_p (x, y)) { if (xsize <= 0 || ysize <= 0) return 1; if (c >= 0 && xsize > c) return 1; if (c < 0 && ysize+c > 0) return 1; return 0; } /* This code used to check for conflicts involving stack references and globals but the base address alias code now handles these cases. */ if (GET_CODE (x) == PLUS) { /* The fact that X is canonicalized means that this PLUS rtx is canonicalized. */ rtx x0 = XEXP (x, 0); rtx x1 = XEXP (x, 1); if (GET_CODE (y) == PLUS) { /* The fact that Y is canonicalized means that this PLUS rtx is canonicalized. */ rtx y0 = XEXP (y, 0); rtx y1 = XEXP (y, 1); if (rtx_equal_for_memref_p (x1, y1)) return memrefs_conflict_p (xsize, x0, ysize, y0, c); if (rtx_equal_for_memref_p (x0, y0)) return memrefs_conflict_p (xsize, x1, ysize, y1, c); if (GET_CODE (x1) == CONST_INT) { if (GET_CODE (y1) == CONST_INT) return memrefs_conflict_p (xsize, x0, ysize, y0, c - INTVAL (x1) + INTVAL (y1)); else return memrefs_conflict_p (xsize, x0, ysize, y, c - INTVAL (x1)); } else if (GET_CODE (y1) == CONST_INT) return memrefs_conflict_p (xsize, x, ysize, y0, c + INTVAL (y1)); return 1; } else if (GET_CODE (x1) == CONST_INT) return memrefs_conflict_p (xsize, x0, ysize, y, c - INTVAL (x1)); } else if (GET_CODE (y) == PLUS) { /* The fact that Y is canonicalized means that this PLUS rtx is canonicalized. */ rtx y0 = XEXP (y, 0); rtx y1 = XEXP (y, 1); if (GET_CODE (y1) == CONST_INT) return memrefs_conflict_p (xsize, x, ysize, y0, c + INTVAL (y1)); else return 1; } if (GET_CODE (x) == GET_CODE (y)) switch (GET_CODE (x)) { case MULT: { /* Handle cases where we expect the second operands to be the same, and check only whether the first operand would conflict or not. */ rtx x0, y0; rtx x1 = canon_rtx (XEXP (x, 1)); rtx y1 = canon_rtx (XEXP (y, 1)); if (! rtx_equal_for_memref_p (x1, y1)) return 1; x0 = canon_rtx (XEXP (x, 0)); y0 = canon_rtx (XEXP (y, 0)); if (rtx_equal_for_memref_p (x0, y0)) return (xsize == 0 || ysize == 0 || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)); /* Can't properly adjust our sizes. */ if (GET_CODE (x1) != CONST_INT) return 1; xsize /= INTVAL (x1); ysize /= INTVAL (x1); c /= INTVAL (x1); return memrefs_conflict_p (xsize, x0, ysize, y0, c); } case REG: /* Are these registers known not to be equal? */ if (alias_invariant) { unsigned int r_x = REGNO (x), r_y = REGNO (y); rtx i_x, i_y; /* invariant relationships of X and Y */ i_x = r_x >= reg_base_value_size ? 0 : alias_invariant[r_x]; i_y = r_y >= reg_base_value_size ? 0 : alias_invariant[r_y]; if (i_x == 0 && i_y == 0) break; if (! memrefs_conflict_p (xsize, i_x ? i_x : x, ysize, i_y ? i_y : y, c)) return 0; } break; default: break; } /* Treat an access through an AND (e.g. a subword access on an Alpha) as an access with indeterminate size. Assume that references besides AND are aligned, so if the size of the other reference is at least as large as the alignment, assume no other overlap. */ if (GET_CODE (x) == AND && GET_CODE (XEXP (x, 1)) == CONST_INT) { if (GET_CODE (y) == AND || ysize < -INTVAL (XEXP (x, 1))) xsize = -1; return memrefs_conflict_p (xsize, XEXP (x, 0), ysize, y, c); } if (GET_CODE (y) == AND && GET_CODE (XEXP (y, 1)) == CONST_INT) { /* ??? If we are indexing far enough into the array/structure, we may yet be able to determine that we can not overlap. But we also need to that we are far enough from the end not to overlap a following reference, so we do nothing with that for now. */ if (GET_CODE (x) == AND || xsize < -INTVAL (XEXP (y, 1))) ysize = -1; return memrefs_conflict_p (xsize, x, ysize, XEXP (y, 0), c); } if (GET_CODE (x) == ADDRESSOF) { if (y == frame_pointer_rtx || GET_CODE (y) == ADDRESSOF) return xsize <= 0 || ysize <= 0; } if (GET_CODE (y) == ADDRESSOF) { if (x == frame_pointer_rtx) return xsize <= 0 || ysize <= 0; } if (CONSTANT_P (x)) { if (GET_CODE (x) == CONST_INT && GET_CODE (y) == CONST_INT) { c += (INTVAL (y) - INTVAL (x)); return (xsize <= 0 || ysize <= 0 || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)); } if (GET_CODE (x) == CONST) { if (GET_CODE (y) == CONST) return memrefs_conflict_p (xsize, canon_rtx (XEXP (x, 0)), ysize, canon_rtx (XEXP (y, 0)), c); else return memrefs_conflict_p (xsize, canon_rtx (XEXP (x, 0)), ysize, y, c); } if (GET_CODE (y) == CONST) return memrefs_conflict_p (xsize, x, ysize, canon_rtx (XEXP (y, 0)), c); if (CONSTANT_P (y)) return (xsize <= 0 || ysize <= 0 || (rtx_equal_for_memref_p (x, y) && ((c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)))); return 1; } return 1; } /* Functions to compute memory dependencies. Since we process the insns in execution order, we can build tables to keep track of what registers are fixed (and not aliased), what registers are varying in known ways, and what registers are varying in unknown ways. If both memory references are volatile, then there must always be a dependence between the two references, since their order can not be changed. A volatile and non-volatile reference can be interchanged though. A MEM_IN_STRUCT reference at a non-AND varying address can never conflict with a non-MEM_IN_STRUCT reference at a fixed address. We also must allow AND addresses, because they may generate accesses outside the object being referenced. This is used to generate aligned addresses from unaligned addresses, for instance, the alpha storeqi_unaligned pattern. */ /* Read dependence: X is read after read in MEM takes place. There can only be a dependence here if both reads are volatile. */ int read_dependence (mem, x) rtx mem; rtx x; { return MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem); } /* Returns MEM1 if and only if MEM1 is a scalar at a fixed address and MEM2 is a reference to a structure at a varying address, or returns MEM2 if vice versa. Otherwise, returns NULL_RTX. If a non-NULL value is returned MEM1 and MEM2 can never alias. VARIES_P is used to decide whether or not an address may vary; it should return nonzero whenever variation is possible. MEM1_ADDR and MEM2_ADDR are the addresses of MEM1 and MEM2. */ static rtx fixed_scalar_and_varying_struct_p (mem1, mem2, mem1_addr, mem2_addr, varies_p) rtx mem1, mem2; rtx mem1_addr, mem2_addr; int (*varies_p) PARAMS ((rtx, int)); { if (! flag_strict_aliasing) return NULL_RTX; if (MEM_SCALAR_P (mem1) && MEM_IN_STRUCT_P (mem2) && !varies_p (mem1_addr, 1) && varies_p (mem2_addr, 1)) /* MEM1 is a scalar at a fixed address; MEM2 is a struct at a varying address. */ return mem1; if (MEM_IN_STRUCT_P (mem1) && MEM_SCALAR_P (mem2) && varies_p (mem1_addr, 1) && !varies_p (mem2_addr, 1)) /* MEM2 is a scalar at a fixed address; MEM1 is a struct at a varying address. */ return mem2; return NULL_RTX; } /* Returns nonzero if something about the mode or address format MEM1 indicates that it might well alias *anything*. */ static int aliases_everything_p (mem) rtx mem; { if (GET_CODE (XEXP (mem, 0)) == AND) /* If the address is an AND, its very hard to know at what it is actually pointing. */ return 1; return 0; } /* True dependence: X is read after store in MEM takes place. */ int true_dependence (mem, mem_mode, x, varies) rtx mem; enum machine_mode mem_mode; rtx x; int (*varies) PARAMS ((rtx, int)); { register rtx x_addr, mem_addr; rtx base; if (MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem)) return 1; if (DIFFERENT_ALIAS_SETS_P (x, mem)) return 0; /* Unchanging memory can't conflict with non-unchanging memory. A non-unchanging read can conflict with a non-unchanging write. An unchanging read can conflict with an unchanging write since there may be a single store to this address to initialize it. Note that an unchanging store can conflict with a non-unchanging read since we have to make conservative assumptions when we have a record with readonly fields and we are copying the whole thing. Just fall through to the code below to resolve potential conflicts. This won't handle all cases optimally, but the possible performance loss should be negligible. */ if (RTX_UNCHANGING_P (x) && ! RTX_UNCHANGING_P (mem)) return 0; if (mem_mode == VOIDmode) mem_mode = GET_MODE (mem); x_addr = get_addr (XEXP (x, 0)); mem_addr = get_addr (XEXP (mem, 0)); base = find_base_term (x_addr); if (base && (GET_CODE (base) == LABEL_REF || (GET_CODE (base) == SYMBOL_REF && CONSTANT_POOL_ADDRESS_P (base)))) return 0; if (! base_alias_check (x_addr, mem_addr, GET_MODE (x), mem_mode)) return 0; x_addr = canon_rtx (x_addr); mem_addr = canon_rtx (mem_addr); if (! memrefs_conflict_p (GET_MODE_SIZE (mem_mode), mem_addr, SIZE_FOR_MODE (x), x_addr, 0)) return 0; if (aliases_everything_p (x)) return 1; /* We cannot use aliases_everyting_p to test MEM, since we must look at MEM_MODE, rather than GET_MODE (MEM). */ if (mem_mode == QImode || GET_CODE (mem_addr) == AND) return 1; /* In true_dependence we also allow BLKmode to alias anything. Why don't we do this in anti_dependence and output_dependence? */ if (mem_mode == BLKmode || GET_MODE (x) == BLKmode) return 1; return ! fixed_scalar_and_varying_struct_p (mem, x, mem_addr, x_addr, varies); } /* Returns non-zero if a write to X might alias a previous read from (or, if WRITEP is non-zero, a write to) MEM. */ static int write_dependence_p (mem, x, writep) rtx mem; rtx x; int writep; { rtx x_addr, mem_addr; rtx fixed_scalar; rtx base; if (MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem)) return 1; if (DIFFERENT_ALIAS_SETS_P (x, mem)) return 0; /* Unchanging memory can't conflict with non-unchanging memory. */ if (RTX_UNCHANGING_P (x) != RTX_UNCHANGING_P (mem)) return 0; /* If MEM is an unchanging read, then it can't possibly conflict with the store to X, because there is at most one store to MEM, and it must have occurred somewhere before MEM. */ if (! writep && RTX_UNCHANGING_P (mem)) return 0; x_addr = get_addr (XEXP (x, 0)); mem_addr = get_addr (XEXP (mem, 0)); if (! writep) { base = find_base_term (mem_addr); if (base && (GET_CODE (base) == LABEL_REF || (GET_CODE (base) == SYMBOL_REF && CONSTANT_POOL_ADDRESS_P (base)))) return 0; } if (! base_alias_check (x_addr, mem_addr, GET_MODE (x), GET_MODE (mem))) return 0; x_addr = canon_rtx (x_addr); mem_addr = canon_rtx (mem_addr); if (!memrefs_conflict_p (SIZE_FOR_MODE (mem), mem_addr, SIZE_FOR_MODE (x), x_addr, 0)) return 0; fixed_scalar = fixed_scalar_and_varying_struct_p (mem, x, mem_addr, x_addr, rtx_addr_varies_p); return (!(fixed_scalar == mem && !aliases_everything_p (x)) && !(fixed_scalar == x && !aliases_everything_p (mem))); } /* Anti dependence: X is written after read in MEM takes place. */ int anti_dependence (mem, x) rtx mem; rtx x; { return write_dependence_p (mem, x, /*writep=*/0); } /* Output dependence: X is written after store in MEM takes place. */ int output_dependence (mem, x) register rtx mem; register rtx x; { return write_dependence_p (mem, x, /*writep=*/1); } /* Returns non-zero if X mentions something which is not local to the function and is not constant. */ static int nonlocal_mentioned_p (x) rtx x; { rtx base; register RTX_CODE code; int regno; code = GET_CODE (x); if (GET_RTX_CLASS (code) == 'i') { /* Constant functions can be constant if they don't use scratch memory used to mark function w/o side effects. */ if (code == CALL_INSN && CONST_CALL_P (x)) { x = CALL_INSN_FUNCTION_USAGE (x); if (x == 0) return 0; } else x = PATTERN (x); code = GET_CODE (x); } switch (code) { case SUBREG: if (GET_CODE (SUBREG_REG (x)) == REG) { /* Global registers are not local. */ if (REGNO (SUBREG_REG (x)) < FIRST_PSEUDO_REGISTER && global_regs[REGNO (SUBREG_REG (x)) + SUBREG_WORD (x)]) return 1; return 0; } break; case REG: regno = REGNO (x); /* Global registers are not local. */ if (regno < FIRST_PSEUDO_REGISTER && global_regs[regno]) return 1; return 0; case SCRATCH: case PC: case CC0: case CONST_INT: case CONST_DOUBLE: case CONST: case LABEL_REF: return 0; case SYMBOL_REF: /* Constants in the function's constants pool are constant. */ if (CONSTANT_POOL_ADDRESS_P (x)) return 0; return 1; case CALL: /* Non-constant calls and recursion are not local. */ return 1; case MEM: /* Be overly conservative and consider any volatile memory reference as not local. */ if (MEM_VOLATILE_P (x)) return 1; base = find_base_term (XEXP (x, 0)); if (base) { /* A Pmode ADDRESS could be a reference via the structure value address or static chain. Such memory references are nonlocal. Thus, we have to examine the contents of the ADDRESS to find out if this is a local reference or not. */ if (GET_CODE (base) == ADDRESS && GET_MODE (base) == Pmode && (XEXP (base, 0) == stack_pointer_rtx || XEXP (base, 0) == arg_pointer_rtx #if HARD_FRAME_POINTER_REGNUM != FRAME_POINTER_REGNUM || XEXP (base, 0) == hard_frame_pointer_rtx #endif || XEXP (base, 0) == frame_pointer_rtx)) return 0; /* Constants in the function's constant pool are constant. */ if (GET_CODE (base) == SYMBOL_REF && CONSTANT_POOL_ADDRESS_P (base)) return 0; } return 1; case UNSPEC_VOLATILE: case ASM_INPUT: return 1; case ASM_OPERANDS: if (MEM_VOLATILE_P (x)) return 1; /* FALLTHROUGH */ default: break; } /* Recursively scan the operands of this expression. */ { register const char *fmt = GET_RTX_FORMAT (code); register int i; for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--) { if (fmt[i] == 'e' && XEXP (x, i)) { if (nonlocal_mentioned_p (XEXP (x, i))) return 1; } else if (fmt[i] == 'E') { register int j; for (j = 0; j < XVECLEN (x, i); j++) if (nonlocal_mentioned_p (XVECEXP (x, i, j))) return 1; } } } return 0; } /* Return non-zero if a loop (natural or otherwise) is present. Inspired by Depth_First_Search_PP described in: Advanced Compiler Design and Implementation Steven Muchnick Morgan Kaufmann, 1997 and heavily borrowed from flow_depth_first_order_compute. */ static int loop_p () { edge *stack; int *pre; int *post; int sp; int prenum = 1; int postnum = 1; sbitmap visited; /* Allocate the preorder and postorder number arrays. */ pre = (int *) xcalloc (n_basic_blocks, sizeof (int)); post = (int *) xcalloc (n_basic_blocks, sizeof (int)); /* Allocate stack for back-tracking up CFG. */ stack = (edge *) xmalloc ((n_basic_blocks + 1) * sizeof (edge)); sp = 0; /* Allocate bitmap to track nodes that have been visited. */ visited = sbitmap_alloc (n_basic_blocks); /* None of the nodes in the CFG have been visited yet. */ sbitmap_zero (visited); /* Push the first edge on to the stack. */ stack[sp++] = ENTRY_BLOCK_PTR->succ; while (sp) { edge e; basic_block src; basic_block dest; /* Look at the edge on the top of the stack. */ e = stack[sp - 1]; src = e->src; dest = e->dest; /* Check if the edge destination has been visited yet. */ if (dest != EXIT_BLOCK_PTR && ! TEST_BIT (visited, dest->index)) { /* Mark that we have visited the destination. */ SET_BIT (visited, dest->index); pre[dest->index] = prenum++; if (dest->succ) { /* Since the DEST node has been visited for the first time, check its successors. */ stack[sp++] = dest->succ; } else post[dest->index] = postnum++; } else { if (dest != EXIT_BLOCK_PTR && pre[src->index] >= pre[dest->index] && post[dest->index] == 0) break; if (! e->succ_next && src != ENTRY_BLOCK_PTR) post[src->index] = postnum++; if (e->succ_next) stack[sp - 1] = e->succ_next; else sp--; } } free (pre); free (post); free (stack); sbitmap_free (visited); return sp; } /* Mark the function if it is constant. */ void mark_constant_function () { rtx insn; int nonlocal_mentioned; if (TREE_PUBLIC (current_function_decl) || TREE_READONLY (current_function_decl) || DECL_IS_PURE (current_function_decl) || TREE_THIS_VOLATILE (current_function_decl) || TYPE_MODE (TREE_TYPE (current_function_decl)) == VOIDmode) return; /* A loop might not return which counts as a side effect. */ if (loop_p ()) return; nonlocal_mentioned = 0; init_alias_analysis (); /* Determine if this is a constant function. */ for (insn = get_insns (); insn; insn = NEXT_INSN (insn)) if (INSN_P (insn) && nonlocal_mentioned_p (insn)) { nonlocal_mentioned = 1; break; } end_alias_analysis (); /* Mark the function. */ if (! nonlocal_mentioned) TREE_READONLY (current_function_decl) = 1; } static HARD_REG_SET argument_registers; void init_alias_once () { register int i; #ifndef OUTGOING_REGNO #define OUTGOING_REGNO(N) N #endif for (i = 0; i < FIRST_PSEUDO_REGISTER; i++) /* Check whether this register can hold an incoming pointer argument. FUNCTION_ARG_REGNO_P tests outgoing register numbers, so translate if necessary due to register windows. */ if (FUNCTION_ARG_REGNO_P (OUTGOING_REGNO (i)) && HARD_REGNO_MODE_OK (i, Pmode)) SET_HARD_REG_BIT (argument_registers, i); alias_sets = splay_tree_new (splay_tree_compare_ints, 0, 0); } /* Initialize the aliasing machinery. Initialize the REG_KNOWN_VALUE array. */ void init_alias_analysis () { int maxreg = max_reg_num (); int changed, pass; register int i; register unsigned int ui; register rtx insn; reg_known_value_size = maxreg; reg_known_value = (rtx *) xcalloc ((maxreg - FIRST_PSEUDO_REGISTER), sizeof (rtx)) - FIRST_PSEUDO_REGISTER; reg_known_equiv_p = (char*) xcalloc ((maxreg - FIRST_PSEUDO_REGISTER), sizeof (char)) - FIRST_PSEUDO_REGISTER; /* Overallocate reg_base_value to allow some growth during loop optimization. Loop unrolling can create a large number of registers. */ reg_base_value_size = maxreg * 2; reg_base_value = (rtx *) xcalloc (reg_base_value_size, sizeof (rtx)); ggc_add_rtx_root (reg_base_value, reg_base_value_size); new_reg_base_value = (rtx *) xmalloc (reg_base_value_size * sizeof (rtx)); reg_seen = (char *) xmalloc (reg_base_value_size); if (! reload_completed && flag_unroll_loops) { /* ??? Why are we realloc'ing if we're just going to zero it? */ alias_invariant = (rtx *)xrealloc (alias_invariant, reg_base_value_size * sizeof (rtx)); memset ((char *)alias_invariant, 0, reg_base_value_size * sizeof (rtx)); } /* The basic idea is that each pass through this loop will use the "constant" information from the previous pass to propagate alias information through another level of assignments. This could get expensive if the assignment chains are long. Maybe we should throttle the number of iterations, possibly based on the optimization level or flag_expensive_optimizations. We could propagate more information in the first pass by making use of REG_N_SETS to determine immediately that the alias information for a pseudo is "constant". A program with an uninitialized variable can cause an infinite loop here. Instead of doing a full dataflow analysis to detect such problems we just cap the number of iterations for the loop. The state of the arrays for the set chain in question does not matter since the program has undefined behavior. */ pass = 0; do { /* Assume nothing will change this iteration of the loop. */ changed = 0; /* We want to assign the same IDs each iteration of this loop, so start counting from zero each iteration of the loop. */ unique_id = 0; /* We're at the start of the funtion each iteration through the loop, so we're copying arguments. */ copying_arguments = 1; /* Wipe the potential alias information clean for this pass. */ memset ((char *) new_reg_base_value, 0, reg_base_value_size * sizeof (rtx)); /* Wipe the reg_seen array clean. */ memset ((char *) reg_seen, 0, reg_base_value_size); /* Mark all hard registers which may contain an address. The stack, frame and argument pointers may contain an address. An argument register which can hold a Pmode value may contain an address even if it is not in BASE_REGS. The address expression is VOIDmode for an argument and Pmode for other registers. */ for (i = 0; i < FIRST_PSEUDO_REGISTER; i++) if (TEST_HARD_REG_BIT (argument_registers, i)) new_reg_base_value[i] = gen_rtx_ADDRESS (VOIDmode, gen_rtx_REG (Pmode, i)); new_reg_base_value[STACK_POINTER_REGNUM] = gen_rtx_ADDRESS (Pmode, stack_pointer_rtx); new_reg_base_value[ARG_POINTER_REGNUM] = gen_rtx_ADDRESS (Pmode, arg_pointer_rtx); new_reg_base_value[FRAME_POINTER_REGNUM] = gen_rtx_ADDRESS (Pmode, frame_pointer_rtx); #if HARD_FRAME_POINTER_REGNUM != FRAME_POINTER_REGNUM new_reg_base_value[HARD_FRAME_POINTER_REGNUM] = gen_rtx_ADDRESS (Pmode, hard_frame_pointer_rtx); #endif /* Walk the insns adding values to the new_reg_base_value array. */ for (insn = get_insns (); insn; insn = NEXT_INSN (insn)) { if (INSN_P (insn)) { rtx note, set; #if defined (HAVE_prologue) || defined (HAVE_epilogue) /* The prologue/epilouge insns are not threaded onto the insn chain until after reload has completed. Thus, there is no sense wasting time checking if INSN is in the prologue/epilogue until after reload has completed. */ if (reload_completed && prologue_epilogue_contains (insn)) continue; #endif /* If this insn has a noalias note, process it, Otherwise, scan for sets. A simple set will have no side effects which could change the base value of any other register. */ if (GET_CODE (PATTERN (insn)) == SET && REG_NOTES (insn) != 0 && find_reg_note (insn, REG_NOALIAS, NULL_RTX)) record_set (SET_DEST (PATTERN (insn)), NULL_RTX, NULL); else note_stores (PATTERN (insn), record_set, NULL); set = single_set (insn); if (set != 0 && GET_CODE (SET_DEST (set)) == REG && REGNO (SET_DEST (set)) >= FIRST_PSEUDO_REGISTER) { unsigned int regno = REGNO (SET_DEST (set)); rtx src = SET_SRC (set); if (REG_NOTES (insn) != 0 && (((note = find_reg_note (insn, REG_EQUAL, 0)) != 0 && REG_N_SETS (regno) == 1) || (note = find_reg_note (insn, REG_EQUIV, NULL_RTX)) != 0) && GET_CODE (XEXP (note, 0)) != EXPR_LIST && ! reg_overlap_mentioned_p (SET_DEST (set), XEXP (note, 0))) { reg_known_value[regno] = XEXP (note, 0); reg_known_equiv_p[regno] = REG_NOTE_KIND (note) == REG_EQUIV; } else if (REG_N_SETS (regno) == 1 && GET_CODE (src) == PLUS && GET_CODE (XEXP (src, 0)) == REG && REGNO (XEXP (src, 0)) >= FIRST_PSEUDO_REGISTER && (reg_known_value[REGNO (XEXP (src, 0))]) && GET_CODE (XEXP (src, 1)) == CONST_INT) { rtx op0 = XEXP (src, 0); if (reg_known_value[REGNO (op0)]) op0 = reg_known_value[REGNO (op0)]; reg_known_value[regno] = plus_constant_for_output (op0, INTVAL (XEXP (src, 1))); reg_known_equiv_p[regno] = 0; } else if (REG_N_SETS (regno) == 1 && ! rtx_varies_p (src, 1)) { reg_known_value[regno] = src; reg_known_equiv_p[regno] = 0; } } } else if (GET_CODE (insn) == NOTE && NOTE_LINE_NUMBER (insn) == NOTE_INSN_FUNCTION_BEG) copying_arguments = 0; } /* Now propagate values from new_reg_base_value to reg_base_value. */ for (ui = 0; ui < reg_base_value_size; ui++) { if (new_reg_base_value[ui] && new_reg_base_value[ui] != reg_base_value[ui] && ! rtx_equal_p (new_reg_base_value[ui], reg_base_value[ui])) { reg_base_value[ui] = new_reg_base_value[ui]; changed = 1; } } } while (changed && ++pass < MAX_ALIAS_LOOP_PASSES); /* Fill in the remaining entries. */ for (i = FIRST_PSEUDO_REGISTER; i < maxreg; i++) if (reg_known_value[i] == 0) reg_known_value[i] = regno_reg_rtx[i]; /* Simplify the reg_base_value array so that no register refers to another register, except to special registers indirectly through ADDRESS expressions. In theory this loop can take as long as O(registers^2), but unless there are very long dependency chains it will run in close to linear time. This loop may not be needed any longer now that the main loop does a better job at propagating alias information. */ pass = 0; do { changed = 0; pass++; for (ui = 0; ui < reg_base_value_size; ui++) { rtx base = reg_base_value[ui]; if (base && GET_CODE (base) == REG) { unsigned int base_regno = REGNO (base); if (base_regno == ui) /* register set from itself */ reg_base_value[ui] = 0; else reg_base_value[ui] = reg_base_value[base_regno]; changed = 1; } } } while (changed && pass < MAX_ALIAS_LOOP_PASSES); /* Clean up. */ free (new_reg_base_value); new_reg_base_value = 0; free (reg_seen); reg_seen = 0; } void end_alias_analysis () { free (reg_known_value + FIRST_PSEUDO_REGISTER); reg_known_value = 0; reg_known_value_size = 0; free (reg_known_equiv_p + FIRST_PSEUDO_REGISTER); reg_known_equiv_p = 0; if (reg_base_value) { ggc_del_root (reg_base_value); free (reg_base_value); reg_base_value = 0; } reg_base_value_size = 0; if (alias_invariant) { free (alias_invariant); alias_invariant = 0; } }