/* The alias set number, as stored in MEM_ALIAS_SET. */
alias_set_type alias_set;
- /* Nonzero if would have a child of zero: this effectively makes this
- alias set the same as alias set zero. */
- int has_zero_child;
-
/* The children of the alias set. These are not just the immediate
children, but, in fact, all descendants. So, if we have:
continuing our example above, the children here will be all of
`int', `double', `float', and `struct S'. */
hash_map<int, int, alias_set_traits> *children;
+
+ /* Nonzero if would have a child of zero: this effectively makes this
+ alias set the same as alias set zero. */
+ bool has_zero_child;
+ /* Nonzero if alias set corresponds to pointer type itself (i.e. not to
+ aggregate contaiing pointer.
+ This is used for a special case where we need an universal pointer type
+ compatible with all other pointer types. */
+ bool is_pointer;
+ /* Nonzero if is_pointer or if one of childs have has_pointer set. */
+ bool has_pointer;
};
typedef struct alias_set_entry_d *alias_set_entry;
unsigned long long num_same_objects;
unsigned long long num_volatile;
unsigned long long num_dag;
+ unsigned long long num_universal;
unsigned long long num_disambiguated;
} alias_stats;
bool
alias_set_subset_of (alias_set_type set1, alias_set_type set2)
{
- alias_set_entry ase;
+ alias_set_entry ase2;
/* Everything is a subset of the "aliases everything" set. */
if (set2 == 0)
return true;
- /* Otherwise, check if set1 is a subset of set2. */
- ase = get_alias_set_entry (set2);
- if (ase != 0
- && (ase->has_zero_child
- || ase->children->get (set1)))
+ /* Check if set1 is a subset of set2. */
+ ase2 = get_alias_set_entry (set2);
+ if (ase2 != 0
+ && (ase2->has_zero_child
+ || (ase2->children && ase2->children->get (set1))))
return true;
+
+ /* As a special case we consider alias set of "void *" to be both subset
+ and superset of every alias set of a pointer. This extra symmetry does
+ not matter for alias_sets_conflict_p but it makes aliasing_component_refs_p
+ to return true on the following testcase:
+
+ void *ptr;
+ char **ptr2=(char **)&ptr;
+ *ptr2 = ...
+
+ Additionally if a set contains universal pointer, we consider every pointer
+ to be a subset of it, but we do not represent this explicitely - doing so
+ would require us to update transitive closure each time we introduce new
+ pointer type. This makes aliasing_component_refs_p to return true
+ on the following testcase:
+
+ struct a {void *ptr;}
+ char **ptr = (char **)&a.ptr;
+ ptr = ...
+
+ This makes void * truly universal pointer type. See pointer handling in
+ get_alias_set for more details. */
+ if (ase2 && ase2->has_pointer)
+ {
+ alias_set_entry ase1 = get_alias_set_entry (set1);
+
+ if (ase1 && ase1->is_pointer)
+ {
+ alias_set_type voidptr_set = TYPE_ALIAS_SET (ptr_type_node);
+ /* If one is ptr_type_node and other is pointer, then we consider
+ them subset of each other. */
+ if (set1 == voidptr_set || set2 == voidptr_set)
+ return true;
+ /* If SET2 contains universal pointer's alias set, then we consdier
+ every (non-universal) pointer. */
+ if (ase2->children && set1 != voidptr_set
+ && ase2->children->get (voidptr_set))
+ return true;
+ }
+ }
return false;
}
int
alias_sets_conflict_p (alias_set_type set1, alias_set_type set2)
{
- alias_set_entry ase;
+ alias_set_entry ase1;
+ alias_set_entry ase2;
/* The easy case. */
if (alias_sets_must_conflict_p (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->children->get (set2))
+ ase1 = get_alias_set_entry (set1);
+ if (ase1 != 0
+ && ase1->children && ase1->children->get (set2))
{
++alias_stats.num_dag;
return 1;
}
/* Now do the same, but with the alias sets reversed. */
- ase = get_alias_set_entry (set2);
- if (ase != 0
- && ase->children->get (set1))
+ ase2 = get_alias_set_entry (set2);
+ if (ase2 != 0
+ && ase2->children && ase2->children->get (set1))
{
++alias_stats.num_dag;
return 1;
}
+
+ /* We want void * to be compatible with any other pointer without
+ really dropping it to alias set 0. Doing so would make it
+ compatible with all non-pointer types too.
+
+ This is not strictly necessary by the C/C++ language
+ standards, but avoids common type punning mistakes. In
+ addition to that, we need the existence of such universal
+ pointer to implement Fortran's C_PTR type (which is defined as
+ type compatible with all C pointers). */
+ if (ase1 && ase2 && ase1->has_pointer && ase2->has_pointer)
+ {
+ alias_set_type voidptr_set = TYPE_ALIAS_SET (ptr_type_node);
+
+ /* If one of the sets corresponds to universal pointer,
+ we consider it to conflict with anything that is
+ or contains pointer. */
+ if (set1 == voidptr_set || set2 == voidptr_set)
+ {
+ ++alias_stats.num_universal;
+ return true;
+ }
+ /* If one of sets is (non-universal) pointer and the other
+ contains universal pointer, we also get conflict. */
+ if (ase1->is_pointer && set2 != voidptr_set
+ && ase2->children && ase2->children->get (voidptr_set))
+ {
+ ++alias_stats.num_universal;
+ return true;
+ }
+ if (ase2->is_pointer && set1 != voidptr_set
+ && ase1->children && ase1->children->get (voidptr_set))
+ {
+ ++alias_stats.num_universal;
+ return true;
+ }
+ }
+
++alias_stats.num_disambiguated;
/* The two alias sets are distinct and neither one is the
== TYPE_MAIN_VARIANT (TREE_TYPE (t2)));
}
+/* Create emptry alias set entry. */
+
+alias_set_entry
+init_alias_set_entry (alias_set_type set)
+{
+ alias_set_entry ase = ggc_alloc<alias_set_entry_d> ();
+ ase->alias_set = set;
+ ase->children = NULL;
+ ase->has_zero_child = false;
+ ase->is_pointer = false;
+ ase->has_pointer = false;
+ gcc_checking_assert (!get_alias_set_entry (set));
+ (*alias_sets)[set] = ase;
+ return ase;
+}
+
/* Return the alias set for T, which may be either a type or an
expression. Call language-specific routine for help, if needed. */
the pointed-to types. This issue has been reported to the
C++ committee.
- In addition to the above canonicalization issue, with LTO
- we should also canonicalize `T (*)[]' to `T *' avoiding
- alias issues with pointer-to element types and pointer-to
- array types.
-
- Likewise we need to deal with the situation of incomplete
- pointed-to types and make `*(struct X **)&a' and
- `*(struct X {} **)&a' alias. Otherwise we will have to
- guarantee that all pointer-to incomplete type variants
- will be replaced by pointer-to complete type variants if
- they are available.
-
- With LTO the convenient situation of using `void *' to
- access and store any pointer type will also become
- more apparent (and `void *' is just another pointer-to
- incomplete type). Assigning alias-set zero to `void *'
- and all pointer-to incomplete types is a not appealing
- solution. Assigning an effective alias-set zero only
- affecting pointers might be - by recording proper subset
- relationships of all pointer alias-sets.
-
- Pointer-to function types are another grey area which
- needs caution. Globbing them all into one alias-set
- or the above effective zero set would work.
-
- For now just assign the same alias-set to all pointers.
- That's simple and avoids all the above problems. */
- else if (POINTER_TYPE_P (t)
- && t != ptr_type_node)
+ For this reason go to canonical type of the unqalified pointer type.
+ Until GCC 6 this code set all pointers sets to have alias set of
+ ptr_type_node but that is a bad idea, because it prevents disabiguations
+ in between pointers. For Firefox this accounts about 20% of all
+ disambiguations in the program. */
+ else if (POINTER_TYPE_P (t) && t != ptr_type_node && !in_lto_p)
+ {
+ tree p;
+ auto_vec <bool, 8> reference;
+
+ /* Unnest all pointers and references.
+ We also want to make pointer to array equivalent to pointer to its
+ element. So skip all array types, too. */
+ for (p = t; POINTER_TYPE_P (p)
+ || (TREE_CODE (p) == ARRAY_TYPE && !TYPE_NONALIASED_COMPONENT (p));
+ p = TREE_TYPE (p))
+ {
+ if (TREE_CODE (p) == REFERENCE_TYPE)
+ reference.safe_push (true);
+ if (TREE_CODE (p) == POINTER_TYPE)
+ reference.safe_push (false);
+ }
+ p = TYPE_MAIN_VARIANT (p);
+
+ /* Make void * compatible with char * and also void **.
+ Programs are commonly violating TBAA by this.
+
+ We also make void * to conflict with every pointer
+ (see record_component_aliases) and thus it is safe it to use it for
+ pointers to types with TYPE_STRUCTURAL_EQUALITY_P. */
+ if (TREE_CODE (p) == VOID_TYPE || TYPE_STRUCTURAL_EQUALITY_P (p))
+ set = get_alias_set (ptr_type_node);
+ else
+ {
+ /* Rebuild pointer type from starting from canonical types using
+ unqualified pointers and references only. This way all such
+ pointers will have the same alias set and will conflict with
+ each other.
+
+ Most of time we already have pointers or references of a given type.
+ If not we build new one just to be sure that if someone later
+ (probably only middle-end can, as we should assign all alias
+ classes only after finishing translation unit) builds the pointer
+ type, the canonical type will match. */
+ p = TYPE_CANONICAL (p);
+ while (!reference.is_empty ())
+ {
+ if (reference.pop ())
+ p = build_reference_type (p);
+ else
+ p = build_pointer_type (p);
+ p = TYPE_CANONICAL (TYPE_MAIN_VARIANT (p));
+ }
+ gcc_checking_assert (TYPE_CANONICAL (p) == p);
+
+ /* Assign the alias set to both p and t.
+ We can not call get_alias_set (p) here as that would trigger
+ infinite recursion when p == t. In other cases it would just
+ trigger unnecesary legwork of rebuilding the pointer again. */
+ if (TYPE_ALIAS_SET_KNOWN_P (p))
+ set = TYPE_ALIAS_SET (p);
+ else
+ {
+ set = new_alias_set ();
+ TYPE_ALIAS_SET (p) = set;
+ }
+ }
+ }
+ /* In LTO the rules above needs to be part of canonical type machinery.
+ For now just punt. */
+ else if (POINTER_TYPE_P (t) && t != ptr_type_node && in_lto_p)
set = get_alias_set (ptr_type_node);
/* Otherwise make a new alias set for this type. */
if (AGGREGATE_TYPE_P (t) || TREE_CODE (t) == COMPLEX_TYPE)
record_component_aliases (t);
+ /* We treat pointer types specially in alias_set_subset_of. */
+ if (POINTER_TYPE_P (t) && set)
+ {
+ alias_set_entry ase = get_alias_set_entry (set);
+ if (!ase)
+ ase = init_alias_set_entry (set);
+ ase->is_pointer = true;
+ ase->has_pointer = true;
+ }
+
return set;
}
{
/* Create an entry for the SUPERSET, so that we have a place to
attach the SUBSET. */
- superset_entry = ggc_cleared_alloc<alias_set_entry_d> ();
- superset_entry->alias_set = superset;
- superset_entry->children
- = hash_map<int, int, alias_set_traits>::create_ggc (64);
- superset_entry->has_zero_child = 0;
- (*alias_sets)[superset] = superset_entry;
+ superset_entry = init_alias_set_entry (superset);
}
if (subset == 0)
else
{
subset_entry = get_alias_set_entry (subset);
+ if (!superset_entry->children)
+ superset_entry->children
+ = hash_map<int, int, alias_set_traits>::create_ggc (64);
/* 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;
+ superset_entry->has_zero_child = true;
+ if (subset_entry->has_pointer)
+ superset_entry->has_pointer = true;
- hash_map<int, int, alias_set_traits>::iterator iter
- = subset_entry->children->begin ();
- for (; iter != subset_entry->children->end (); ++iter)
- superset_entry->children->put ((*iter).first, (*iter).second);
+ if (subset_entry->children)
+ {
+ hash_map<int, int, alias_set_traits>::iterator iter
+ = subset_entry->children->begin ();
+ for (; iter != subset_entry->children->end (); ++iter)
+ superset_entry->children->put ((*iter).first, (*iter).second);
+ }
}
/* Enter the SUBSET itself as a child of the SUPERSET. */
" %llu queries asked about the same object\n"
" %llu queries asked about the same alias set\n"
" %llu access volatile\n"
- " %llu are dependent in the DAG\n",
+ " %llu are dependent in the DAG\n"
+ " %llu are aritificially in conflict with void *\n",
alias_stats.num_disambiguated,
alias_stats.num_alias_zero + alias_stats.num_same_alias_set
+ alias_stats.num_same_objects + alias_stats.num_volatile
- + alias_stats.num_dag,
+ + alias_stats.num_dag + alias_stats.num_disambiguated
+ + alias_stats.num_universal,
alias_stats.num_alias_zero, alias_stats.num_same_alias_set,
- + alias_stats.num_same_objects, alias_stats.num_volatile,
- + alias_stats.num_dag);
+ alias_stats.num_same_objects, alias_stats.num_volatile,
+ alias_stats.num_dag, alias_stats.num_universal);
}
#include "gt-alias.h"
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