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1.8.1.1
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GCC Middle and Back End API Reference
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Go to the source code of this file.
Data Structures | |
| struct | bitmap_obstack |
| struct | bitmap_element_def |
| struct | bitmap_head_def |
| struct | bitmap_iterator |
Typedefs | |
| typedef unsigned long | BITMAP_WORD |
| typedef struct bitmap_obstack | bitmap_obstack |
| typedef struct bitmap_element_def | bitmap_element |
| typedef struct bitmap_head_def | bitmap_head |
Variables | |
| bitmap_element | bitmap_zero_bits |
| bitmap_obstack | bitmap_default_obstack |
| typedef struct bitmap_element_def bitmap_element |
Bitmap set element. We use a linked list to hold only the bits that are set. This allows for use to grow the bitset dynamically without having to realloc and copy a giant bit array. The free list is implemented as a list of lists. There is one outer list connected together by prev fields. Each element of that outer is an inner list (that may consist only of the outer list element) that are connected by the next fields. The prev pointer is undefined for interior elements. This allows bitmap_elt_clear_from to be implemented in unit time rather than linear in the number of elements to be freed.
| typedef struct bitmap_head_def bitmap_head |
Head of bitmap linked list. The 'current' member points to something already pointed to by the chain started by first, so it.
| typedef struct bitmap_obstack bitmap_obstack |
Obstack for allocating bitmaps and elements from.
| typedef unsigned long BITMAP_WORD |
Implementation of sparse integer sets as a linked list.
This sparse set representation is suitable for sparse sets with an
unknown (a priori) universe. The set is represented as a double-linked
list of container nodes (struct bitmap_element_def). Each node consists
of an index for the first member that could be held in the container,
a small array of integers that represent the members in the container,
and pointers to the next and previous element in the linked list. The
elements in the list are sorted in ascending order, i.e. the head of
the list holds the element with the smallest member of the set.
For a given member I in the set:
- the element for I will have index is I / (bits per element)
- the position for I within element is I % (bits per element)
This representation is very space-efficient for large sparse sets, and
the size of the set can be changed dynamically without much overhead.
An important parameter is the number of bits per element. In this
implementation, there are 128 bits per element. This results in a
high storage overhead *per element*, but a small overall overhead if
the set is very sparse.
The downside is that many operations are relatively slow because the
linked list has to be traversed to test membership (i.e. member_p/
add_member/remove_member). To improve the performance of this set
representation, the last accessed element and its index are cached.
For membership tests on members close to recently accessed members,
the cached last element improves membership test to a constant-time
operation.
The following operations can always be performed in O(1) time:
* clear : bitmap_clear
* choose_one : (not implemented, but could be
implemented in constant time)
The following operations can be performed in O(E) time worst-case (with
E the number of elements in the linked list), but in O(1) time with a
suitable access patterns:
* member_p : bitmap_bit_p
* add_member : bitmap_set_bit
* remove_member : bitmap_clear_bit
The following operations can be performed in O(E) time:
* cardinality : bitmap_count_bits
* set_size : bitmap_last_set_bit (but this could
in constant time with a pointer to
the last element in the chain)
Additionally, the linked-list sparse set representation supports
enumeration of the members in O(E) time:
* forall : EXECUTE_IF_SET_IN_BITMAP
* set_copy : bitmap_copy
* set_intersection : bitmap_intersect_p /
bitmap_and / bitmap_and_into /
EXECUTE_IF_AND_IN_BITMAP
* set_union : bitmap_ior / bitmap_ior_into
* set_difference : bitmap_intersect_compl_p /
bitmap_and_comp / bitmap_and_comp_into /
EXECUTE_IF_AND_COMPL_IN_BITMAP
* set_disjuction : bitmap_xor_comp / bitmap_xor_comp_into
* set_compare : bitmap_equal_p
Some operations on 3 sets that occur frequently in in data flow problems
are also implemented:
* A | (B & C) : bitmap_ior_and_into
* A | (B & ~C) : bitmap_ior_and_compl /
bitmap_ior_and_compl_into
The storage requirements for linked-list sparse sets are O(E), with E->N
in the worst case (a sparse set with large distances between the values
of the set members).
The linked-list set representation works well for problems involving very
sparse sets. The canonical example in GCC is, of course, the "set of
sets" for some CFG-based data flow problems (liveness analysis, dominance
frontiers, etc.).
This representation also works well for data flow problems where the size
of the set may grow dynamically, but care must be taken that the member_p,
add_member, and remove_member operations occur with a suitable access
pattern.
For random-access sets with a known, relatively small universe size, the
SparseSet or simple bitmap representations may be more efficient than a
linked-list set. For random-access sets of unknown universe, a hash table
or a balanced binary tree representation is likely to be a more suitable
choice.
Traversing linked lists is usually cache-unfriendly, even with the last
accessed element cached.
Cache performance can be improved by keeping the elements in the set
grouped together in memory, using a dedicated obstack for a set (or group
of related sets). Elements allocated on obstacks are released to a
free-list and taken off the free list. If multiple sets are allocated on
the same obstack, elements freed from one set may be re-used for one of
the other sets. This usually helps avoid cache misses.
A single free-list is used for all sets allocated in GGC space. This is
bad for persistent sets, so persistent sets should be allocated on an
obstack whenever possible. Fundamental storage type for bitmap.
| void bitmap_and | ( | bitmap | , |
| const_bitmap | , | ||
| const_bitmap | |||
| ) |
Boolean operations on bitmaps. The _into variants are two operand versions that modify the first source operand. The other variants are three operand versions that to not destroy the source bitmaps. The operations supported are &, & ~, |, ^.
| bool bitmap_and_compl | ( | bitmap | , |
| const_bitmap | , | ||
| const_bitmap | |||
| ) |
| bool bitmap_and_compl_into | ( | bitmap | , |
| const_bitmap | |||
| ) |
| bool bitmap_and_into | ( | bitmap | , |
| const_bitmap | |||
| ) |
| int bitmap_bit_p | ( | bitmap | , |
| int | |||
| ) |
Return true if a register is set in a register set.
| void bitmap_clear | ( | bitmap | ) |
Clear a bitmap by freeing up the linked list.
| bool bitmap_clear_bit | ( | bitmap | , |
| int | |||
| ) |
Clear a single bit in a bitmap. Return true if the bit changed.
| void bitmap_clear_range | ( | bitmap | , |
| unsigned | int, | ||
| unsigned | int | ||
| ) |
| void bitmap_compl_and_into | ( | bitmap | , |
| const_bitmap | |||
| ) |
| void bitmap_copy | ( | bitmap | , |
| const_bitmap | |||
| ) |
Copy a bitmap to another bitmap.
| unsigned long bitmap_count_bits | ( | const_bitmap | ) |
Count the number of bits set in the bitmap.
|
inline |
True if MAP is an empty bitmap.
Referenced by add_to_partition_kill_list(), bitmap_set_and(), compute_builtin_object_size(), dse_step3(), find_replaceable_exprs(), find_uses_to_rename(), get_node_of_insn(), get_stored_val(), prepare_block_for_update(), remove_from_partition_kill_list(), reset_debug_uses(), and setup_reg_equiv().
| bool bitmap_equal_p | ( | const_bitmap | , |
| const_bitmap | |||
| ) |
True if two bitmaps are identical.
| unsigned bitmap_first_set_bit | ( | const_bitmap | ) |
| bitmap bitmap_gc_alloc_stat | ( | ALONE_MEM_STAT_DECL | ) |
| hashval_t bitmap_hash | ( | const_bitmap | ) |
Compute bitmap hash (for purposes of hashing etc.)
|
inlinestatic |
Initialize a bitmap header. OBSTACK indicates the bitmap obstack to allocate from, NULL for GC'd bitmap.
| bool bitmap_intersect_compl_p | ( | const_bitmap | , |
| const_bitmap | |||
| ) |
True if the complement of the second intersects the first (their AND_COMPL is non-empty).
| bool bitmap_intersect_p | ( | const_bitmap | , |
| const_bitmap | |||
| ) |
True if the bitmaps intersect (their AND is non-empty).
| bool bitmap_ior | ( | bitmap | , |
| const_bitmap | , | ||
| const_bitmap | |||
| ) |
| bool bitmap_ior_and_compl | ( | bitmap | DST, |
| const_bitmap | A, | ||
| const_bitmap | B, | ||
| const_bitmap | C | ||
| ) |
DST = A | (B & ~C). Return true if DST changes.
| bool bitmap_ior_and_compl_into | ( | bitmap | A, |
| const_bitmap | B, | ||
| const_bitmap | C | ||
| ) |
A |= (B & ~C). Return true if A changes.
| bool bitmap_ior_and_into | ( | bitmap | DST, |
| const_bitmap | B, | ||
| const_bitmap | C | ||
| ) |
DST = A | (B & C). Return true if DST changes.
| bool bitmap_ior_into | ( | bitmap | , |
| const_bitmap | |||
| ) |
| unsigned bitmap_last_set_bit | ( | const_bitmap | ) |
| bitmap bitmap_obstack_alloc_stat | ( | bitmap_obstack *obstack | MEM_STAT_DECL | ) |
Allocate and free bitmaps from obstack, malloc and gc'd memory.
| void bitmap_obstack_free | ( | bitmap | ) |
| void bitmap_obstack_initialize | ( | bitmap_obstack * | ) |
Initialize and release a bitmap obstack.
| void bitmap_obstack_release | ( | bitmap_obstack * | ) |
| void bitmap_print | ( | FILE * | file, |
| const_bitmap | head, | ||
| const char * | prefix, | ||
| const char * | suffix | ||
| ) |
Print a bitmap.
Function to print out the contents of a bitmap. Unlike debug_bitmap_file, it does not print anything but the bits.
Referenced by df_clear_flags(), and dse_step3().
| void bitmap_register | ( | bitmap | MEM_STAT_DECL | ) |
| bool bitmap_set_bit | ( | bitmap | , |
| int | |||
| ) |
Set a single bit in a bitmap. Return true if the bit changed.
| void bitmap_set_range | ( | bitmap | , |
| unsigned | int, | ||
| unsigned | int | ||
| ) |
| bool bitmap_single_bit_set_p | ( | const_bitmap | ) |
True if the bitmap has only a single bit set.
| void bitmap_xor | ( | bitmap | , |
| const_bitmap | , | ||
| const_bitmap | |||
| ) |
| void bitmap_xor_into | ( | bitmap | , |
| const_bitmap | |||
| ) |
|
inlinestatic |
Advance to the next nonzero bit of an intersecting pair of bitmaps. We will have already advanced past the just iterated bit. Return true if there is a bit to iterate.
If our current word is nonzero, it contains the bit we want.
Round up to the word boundary. We might have just iterated past
the end of the last word, hence the -1. It is not possible for
bit_no to point at the beginning of the now last word. Find the next nonzero word in this elt.
Advance to the next identical element.
Advance elt1 while it is less than elt2. We always want
to advance one elt. Advance elt2 to be no less than elt1. This might not
advance.
|
inlinestatic |
Advance to the next nonzero bit in the intersection of complemented bitmaps. We will have already advanced past the just iterated bit.
If our current word is nonzero, it contains the bit we want.
Round up to the word boundary. We might have just iterated past
the end of the last word, hence the -1. It is not possible for
bit_no to point at the beginning of the now last word. Find the next nonzero word in this elt.
Advance to the next element of elt1.
Advance elt2 until it is no less than elt1.
|
inlinestatic |
Initialize an iterator to iterate over the bits in MAP1 & ~MAP2.
Advance elt1 until it is not before the block containing start_bit.
Advance elt2 until it is not before elt1.
We might have advanced beyond the start_bit, so reinitialize for
that. If this word is zero, we must make sure we're not pointing at the
first bit, otherwise our incrementing to the next word boundary
will fail. It won't matter if this increment moves us into the
next word.
|
inlinestatic |
Initialize an iterator to iterate over the intersection of two bitmaps. START_BIT is the bit to commence from.
Advance elt1 until it is not before the block containing
start_bit. Advance elt2 until it is not before elt1.
If we're at the same index, then we have some intersecting bits.
We might have advanced beyond the start_bit, so reinitialize
for that. Otherwise we must immediately advance elt1, so initialize for
that. If this word is zero, we must make sure we're not pointing at the
first bit, otherwise our incrementing to the next word boundary
will fail. It won't matter if this increment moves us into the
next word.
|
inlinestatic |
Advance to the next bit in BI. We don't advance to the next nonzero bit yet.
|
inlinestatic |
Advance to first set bit in BI.
|
inlinestatic |
Advance to the next nonzero bit of a single bitmap, we will have already advanced past the just iterated bit. Return true if there is a bit to iterate.
If our current word is nonzero, it contains the bit we want.
Round up to the word boundary. We might have just iterated past
the end of the last word, hence the -1. It is not possible for
bit_no to point at the beginning of the now last word. Find the next nonzero word in this elt.
Advance to the next element.
|
inlinestatic |
Initialize a single bitmap iterator. START_BIT is the first bit to iterate from.
Advance elt1 until it is not before the block containing start_bit.
We might have gone past the start bit, so reinitialize it.
Initialize for what is now start_bit.
If this word is zero, we must make sure we're not pointing at the
first bit, otherwise our incrementing to the next word boundary
will fail. It won't matter if this increment moves us into the
next word.
| void debug | ( | const bitmap_head_def & | ref | ) |
| void debug | ( | const bitmap_head_def * | ptr | ) |
| void debug_bitmap | ( | const_bitmap | ) |
Debug functions to print a bitmap linked list.
| void debug_bitmap_file | ( | FILE * | , |
| const_bitmap | |||
| ) |
|
inline |
A few compatibility/functions macros for compatibility with sbitmaps
Referenced by cgraph_redirect_edge_call_stmt_to_callee(), distribute_loop(), and dump_use().
| void dump_bitmap_statistics | ( | void | ) |
Output per-bitmap memory usage statistics.
| bitmap_obstack bitmap_default_obstack |
| bitmap_element bitmap_zero_bits |
Global data
1.8.1.1