- Generated by
1.8.1.1
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GCC Middle and Back End API Reference
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Data Structures | |
| struct | max_alignment |
| struct | page_entry |
| struct | page_group |
| struct | page_table_chain |
| struct | free_object |
| struct | globals |
| struct | ggc_pch_ondisk |
| struct | ggc_pch_data |
Typedefs | |
| typedef struct page_entry | page_entry |
| typedef struct page_group | page_group |
| typedef page_entry ** | page_table [PAGE_L1_SIZE] |
Functions | |
| static int | ggc_allocated_p (const void *) |
| static page_entry * | lookup_page_table_entry (const void *) |
| static void | set_page_table_entry (void *, page_entry *) |
| static char * | alloc_anon (char *, size_t, bool check) |
| static size_t | page_group_index (char *, char *) |
| static void | set_page_group_in_use (page_group *, char *) |
| static void | clear_page_group_in_use (page_group *, char *) |
| static struct page_entry * | alloc_page (unsigned) |
| static void | free_page (struct page_entry *) |
| static void | release_pages (void) |
| static void | clear_marks (void) |
| static void | sweep_pages (void) |
| static void | ggc_recalculate_in_use_p (page_entry *) |
| static void | compute_inverse (unsigned) |
| static void | adjust_depth (void) |
| static void | move_ptes_to_front (int, int) |
| void | debug_print_page_list (int) |
| static void | push_depth (unsigned int) |
| static void | push_by_depth (page_entry *, unsigned long *) |
| static void | push_depth () |
| static void | push_by_depth () |
| static int | ggc_allocated_p () |
| static page_entry * | lookup_page_table_entry () |
| static void | set_page_table_entry () |
| DEBUG_FUNCTION void | debug_print_page_list () |
| static char * | alloc_anon () |
| static size_t | page_group_index () |
| static void | set_page_group_in_use () |
| static void | clear_page_group_in_use () |
| static struct page_entry * | alloc_page () |
| static void | free_page () |
| static void | ggc_round_alloc_size_1 (size_t requested_size, size_t *size_order, size_t *alloced_size) |
| size_t | ggc_round_alloc_size () |
| void * | ggc_internal_alloc_stat () |
| void | gt_ggc_m_S () |
| void | gt_ggc_mx () |
| int | ggc_set_mark () |
| int | ggc_marked_p () |
| size_t | ggc_get_size () |
| void | ggc_free () |
| static void | compute_inverse () |
| void | init_ggc () |
| static void | ggc_recalculate_in_use_p () |
| static void | poison_pages () |
| static void | validate_free_objects () |
| void | ggc_collect () |
| void | ggc_print_statistics () |
| struct ggc_pch_data * | init_ggc_pch () |
| void | ggc_pch_count_object (struct ggc_pch_data *d, void *x, size_t size, bool is_string) |
| size_t | ggc_pch_total_size () |
| void | ggc_pch_this_base () |
| char * | ggc_pch_alloc_object (struct ggc_pch_data *d, void *x, size_t size, bool is_string) |
| void | ggc_pch_prepare_write (struct ggc_pch_data *d, FILE *f) |
| void | ggc_pch_write_object (struct ggc_pch_data *d, FILE *f, void *x, void *newx, size_t size, bool is_string) |
| void | ggc_pch_finish () |
| static void | move_ptes_to_front () |
| void | ggc_pch_read () |
Variables | |
| static const size_t | extra_order_size_table [] |
| static unsigned | objects_per_page_table [NUM_ORDERS] |
| static size_t | object_size_table [NUM_ORDERS] |
| struct { | |
| size_t mult | |
| unsigned int shift | |
| } | inverse_table [NUM_ORDERS] |
| static struct globals | G |
| static unsigned char | size_lookup [NUM_SIZE_LOOKUP] |
| typedef struct page_entry page_entry |
A page_entry records the status of an allocation page. This structure is dynamically sized to fit the bitmap in_use_p.
| typedef struct page_group page_group |
A page_group describes a large allocation from malloc, from which we parcel out aligned pages.
| typedef struct page_table_chain * page_table |
On 32-bit hosts, we use a two level page table, as pictured above.
On 64-bit hosts, we use the same two level page tables plus a linked list that disambiguates the top 32-bits. There will almost always be exactly one entry in the list.
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Adjust the size of G.depth so that no index greater than the one used by the top of the G.by_depth is used.
Peel back indices in depth that index into by_depth, so that
as new elements are added to by_depth, we note the indices
of those elements, if they are for new context depths.
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Referenced by page_group_index().
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Allocate SIZE bytes of anonymous memory, preferably near PREF, (if non-null). The ifdef structure here is intended to cause a compile error unless exactly one of the HAVE_* is defined.
Remember that we allocated this memory.
Pretend we don't have access to the allocated pages. We'll enable
access to smaller pieces of the area in ggc_internal_alloc. Discard the
handle to avoid handle leak.
References page_entry::bytes, globals::bytes_mapped, page_entry::discarded, free(), G, page_entry::group, memset(), page_entry::next, page_entry::order, and page_entry::page.
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Allocate a new page for allocating objects of size 2^ORDER, and return an entry for it. The entry is not added to the appropriate page_table list.
Check the list of free pages for one we can use.
Recycle the allocated memory from this page ...
... and, if possible, the page entry itself.
We want just one page. Allocate a bunch of them and put the
extras on the freelist. (Can only do this optimization with
mmap for backing store.) This loop counts down so that the chain will be in ascending
memory order. Allocate a large block of memory and serve out the aligned
pages therein. This results in much less memory wastage
than the traditional implementation of valloc. We allocated N pages, which are likely not aligned, leaving
us with N-1 usable pages. We plan to place the page_group
structure somewhere in the slop. We magically got an aligned allocation. Too bad, we have
to waste a page anyway. Remember that we allocated this memory.
If we allocated multiple pages, put the rest on the free list.
Set the one-past-the-end in-use bit. This acts as a sentry as we
increment the hint.
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Unmark all objects.
The data should be page-aligned.
Pages that aren't in the topmost context are not collected;
nevertheless, we need their in-use bit vectors to store GC
marks. So, back them up first. Reset reset the number of free objects and clear the
in-use bits. These will be adjusted by mark_obj. Make sure the one-past-the-end bit is always set.
References page_entry::context_depth, globals::context_depth, G, HOST_BITS_PER_LONG, page_entry::in_use_p, memset(), page_entry::next, page_entry::page, and globals::pages.
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Subroutine of init_ggc which computes the pair of numbers used to perform division by OBJECT_SIZE (order) and fills in inverse_table[]. This algorithm is taken from Granlund and Montgomery's paper "Division by Invariant Integers using Multiplication" (Proc. SIGPLAN PLDI, 1994), section 9 (Exact division by constants).
References page_entry::context_depth, globals::context_depth, G, page_entry::in_use_p, memcpy(), memset(), page_entry::num_free_objects, page_entry::page, and globals::pagesize.
| void debug_print_page_list | ( | int | ) |
| DEBUG_FUNCTION void debug_print_page_list | ( | ) |
Prints the page-entry for object size ORDER, for debugging.
References G, page_entry::group, page_entry::page, and globals::pagesize.
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For a page that is no longer needed, put it on the free page list.
Mark the page as inaccessible. Discard the handle to avoid handle
leak. We cannot free a page from a context deeper than the current
one. Put top element into freed slot.
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Returns nonzero if P was allocated in GC'able memory.
Extract the level 1 and 2 indices.
| void ggc_collect | ( | void | ) |
Top level mark-and-sweep routine.
Avoid frequent unnecessary work by skipping collection if the
total allocations haven't expanded much since the last
collection. Zero the total allocated bytes. This will be recalculated in the
sweep phase. Release the pages we freed the last time we collected, but didn't
reuse in the interim. Indicate that we've seen collections at this context depth.
References ggc_pch_data::base, ggc_pch_data::d, and ggc_pch_ondisk::totals.
Referenced by ggc_splay_alloc(), and gcc::pass_manager::pass_manager().
| void ggc_free | ( | ) |
Release the memory for object P.
Poison the data, to indicate the data is garbage.
Let valgrind know the object is free.
In the completely-anal-checking mode, we do *not* immediately free
the data, but instead verify that the data is *actually* not
reachable the next time we collect. Mark the object not-in-use.
If the page is completely full, then it's supposed to
be after all pages that aren't. Since we've freed one
object from a page that was full, we need to move the
page to the head of the list.
PE is the node we want to move. Q is the previous node
and P is the next node in the list. If PE was at the end of the list, then Q becomes the
new end of the list. If PE was not the end of the
list, then we need to update the PREV field for P. Move PE to the head of the list.
Reset the hint bit to point to the only free object.
| size_t ggc_get_size | ( | ) |
Return the size of the gc-able object P.
| void* ggc_internal_alloc_stat | ( | ) |
Allocate a chunk of memory of SIZE bytes. Its contents are undefined.
If there are non-full pages for this size allocation, they are at
the head of the list. If there is no page for this object size, or all pages in this
context are full, allocate a new page. We can skip context depths, if we do, make sure we go all the
way to the new depth. If this is the only entry, it's also the tail. If it is not
the only entry, then we must update the PREV pointer of the
ENTRY (G.pages[order]) to point to our new page entry. Put new pages at the head of the page list. By definition the
entry at the head of the list always has a NULL pointer. For a new page, we know the word and bit positions (in the
in_use bitmap) of the first available object -- they're zero. First try to use the hint left from the previous allocation
to locate a clear bit in the in-use bitmap. We've made sure
that the one-past-the-end bit is always set, so if the hint
has run over, this test will fail. If the hint didn't work, scan the bitmap from the beginning.
Next time, try the next bit.
Set the in-use bit.
Keep a running total of the number of free objects. If this page
fills up, we may have to move it to the end of the list if the
next page isn't full. If the next page is full, all subsequent
pages are full, so there's no need to move it. We have a new head for the list.
We are moving ENTRY to the end of the page table list.
The new page at the head of the list will have NULL in
its PREV field and ENTRY will have NULL in its NEXT field. Append ENTRY to the tail of the list.
Calculate the object's address.
Keep poisoning-by-writing-0xaf the object, in an attempt to keep the
exact same semantics in presence of memory bugs, regardless of
ENABLE_VALGRIND_CHECKING. We override this request below. Drop the
handle to avoid handle leak. `Poison' the entire allocated object, including any padding at
the end. Make the bytes after the end of the object unaccessible. Discard the
handle to avoid handle leak. Tell Valgrind that the memory is there, but its content isn't
defined. The bytes at the end of the object are still marked
unaccessible. Keep track of how many bytes are being allocated. This
information is used in deciding when to collect. For timevar statistics.
| int ggc_marked_p | ( | ) |
Return 1 if P has been marked, zero otherwise. P must have been allocated by the GC allocator; it mustn't point to static objects, stack variables, or memory allocated with malloc.
Look up the page on which the object is alloced. If the object
wasn't allocated by the collector, we'll probably die. Calculate the index of the object on the page; this is its bit
position in the in_use_p bitmap.
Referenced by stringpool_statistics().
| char* ggc_pch_alloc_object | ( | struct ggc_pch_data * | , |
| void * | , | ||
| size_t | , | ||
| bool | |||
| ) |
Assuming that the objects really do end up at the address passed to ggc_pch_this_base, return the address of this object. The bool argument should be true if the object is a string.
| void ggc_pch_count_object | ( | struct ggc_pch_data * | , |
| void * | , | ||
| size_t | , | ||
| bool | |||
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The second parameter and third parameters give the address and size of an object. Update the ggc_pch_data structure with as much of that information as is necessary. The bool argument should be true if the object is a string.
| void ggc_pch_finish | ( | ) |
| void ggc_pch_prepare_write | ( | struct ggc_pch_data * | , |
| FILE * | |||
| ) |
Write out any initial information required.
Nothing to do.
| void ggc_pch_read | ( | ) |
We've just read in a PCH file. So, every object that used to be
allocated is now free. Since we free all the allocated objects, the free list becomes
useless. Validate it now, which will also clear it. No object read from a PCH file should ever be freed. So, set the
context depth to 1, and set the depth of all the currently-allocated
pages to be 1 too. PCH pages will have depth 0. Allocate the appropriate page-table entries for the pages read from
the PCH file. We start off by just adding all the new information to the
end of the varrays, later, we will move the new information
to the front of the varrays, as the PCH page tables are at
context 0. Now, we update the various data structures that speed page table
handling. Update the statistics.
| void ggc_pch_this_base | ( | ) |
| size_t ggc_pch_total_size | ( | ) |
| void ggc_pch_write_object | ( | struct ggc_pch_data * | , |
| FILE * | , | ||
| void * | , | ||
| void * | , | ||
| size_t | , | ||
| bool | |||
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Write out this object, including any padding. The last argument should be true if the object is a string.
If SIZE is not the same as OBJECT_SIZE(order), then we need to pad the
object out to OBJECT_SIZE(order). This happens for strings. To speed small writes, we use a nulled-out array that's larger
than most padding requests as the source for our null bytes. This
permits us to do the padding with fwrite() rather than fseek(), and
limits the chance the OS may try to flush any outstanding writes. Larger than our buffer? Just default to fseek.
| void ggc_print_statistics | ( | void | ) |
Statistics.
Print allocation statistics.
Clear the statistics.
Make sure collection will really occur.
Collect and print the statistics common across collectors.
Release free pages so that we will not count the bytes allocated
there as part of the total allocated memory. Collect some information about the various sizes of
allocation. Skip empty entries.
Figure out the total number of bytes allocated for objects of
this size, and how many of them are actually in use. Also figure
out how much memory the page table is using.
References fatal_error().
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Merge the SAVE_IN_USE_P and IN_USE_P arrays in P so that IN_USE_P reflects reality. Recalculate NUM_FREE_OBJECTS as well.
Because the past-the-end bit in in_use_p is always set, we
pretend there is one additional object. Reset the free object count.
Combine the IN_USE_P and SAVE_IN_USE_P arrays.
Something is in use if it is marked, or if it was in use in a
context further down the context stack. Decrement the free object count for every object allocated.
| size_t ggc_round_alloc_size | ( | ) |
For a given size of memory requested for allocation, return the actual size that is going to be allocated.
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For a given size of memory requested for allocation, return the actual size that is going to be allocated, as well as the size order.
| int ggc_set_mark | ( | ) |
If P is not marked, marks it and return false. Otherwise return true. P must have been allocated by the GC allocator; it mustn't point to static objects, stack variables, or memory allocated with malloc.
Look up the page on which the object is alloced. If the object
wasn't allocated by the collector, we'll probably die. Calculate the index of the object on the page; this is its bit
position in the in_use_p bitmap. If the bit was previously set, skip it.
Otherwise set it, and decrement the free object count.
Referenced by ggc_register_cache_tab().
| void gt_ggc_m_S | ( | ) |
Mark function for strings.
Look up the page on which the object is alloced. .
Calculate the index of the object on the page; this is its bit
position in the in_use_p bitmap. Note that because a char* might
point to the middle of an object, we need special code here to
make sure P points to the start of an object. Here we've seen a char* which does not point to the beginning
of an allocated object. We assume it points to the middle of
a STRING_CST. If the bit was previously set, skip it.
Otherwise set it, and decrement the free object count.
References globals::allocated, globals::debug_file, globals::free_object_list, G, ggc_free_overhead(), HOST_BITS_PER_LONG, page_entry::in_use_p, lookup_page_table_entry(), memset(), free_object::next, page_entry::num_free_objects, free_object::object, page_entry::order, page_entry::page, and page_entry::prev.
| void gt_ggc_mx | ( | ) |
User-callable entry points for marking string X.
Nothing to do. Vectors of atomic types wrt GC do not need to
be traversed.
References G, page_entry::next, order, globals::page_tails, globals::pages, and page_entry::prev.
| void init_ggc | ( | void | ) |
Initialize the ggc-mmap allocator.
StunOS has an amazing off-by-one error for the first mmap allocation
after fiddling with RLIMIT_STACK. The result, as hard as it is to
believe, is an unaligned page allocation, which would cause us to
hork badly if we tried to use it. How losing. Discard this one and try another. If we still
can't get something useful, give up. We have a good page, might as well hold onto it...
Initialize the object size table.
If S is not a multiple of the MAX_ALIGNMENT, then round it up
so that we're sure of getting aligned memory. Initialize the objects-per-page and inverse tables.
Reset the size_lookup array to put appropriately sized objects in
the special orders. All objects bigger than the previous power
of two, but no greater than the special size, should go in the
new order.
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Return a new ggc_pch_data structure.
References page_entry::bytes.
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Referenced by gt_ggc_m_S(), and sweep_pages().
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Traverse the page table and find the entry for a page. Die (probably) if the object wasn't allocated via GC.
Extract the level 1 and 2 indices.
References globals::bytes_mapped, globals::dev_zero_fd, G, page_entry::page, and pref.
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Move the PCH PTE entries just added to the end of by_depth, to the front.
First, we swap the new entries to the front of the varrays.
Now update all the index_by_depth fields.
And last, we update the depth pointers in G.depth. The first
entry is already 0, and context 0 entries always start at index
0, so there is nothing to update in the first slot. We need a
second slot, only if we have old ptes, and if we do, they start
at index count_new_page_tables.
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Compute the index for this page into the page group.
References alloc_anon(), G, and globals::pagesize.
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Clobber all free objects.
Since we don't do any collection for pages in pushed
contexts, there's no need to do any poisoning. And
besides, the IN_USE_P array isn't valid until we pop
contexts. Keep poison-by-write when we expect to use Valgrind,
so the exact same memory semantics is kept, in case
there are memory errors. We override this request
below. Drop the handle to avoid handle leak.
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Push an entry onto G.by_depth and G.save_in_use.
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Push an entry onto G.depth.
References G, and globals::lookup.
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Release the free page cache to the system.
First free larger continuous areas to the OS.
This allows other allocators to grab these areas if needed.
This is only done on larger chunks to avoid fragmentation.
This does not always work because the free_pages list is only
approximately sorted. Now give back the fragmented pages to the OS, but keep the address
space to reuse it next time. Give the page back to the kernel, but don't free the mapping.
This avoids fragmentation in the virtual memory map of the
process. Next time we can reuse it by just touching it. Don't count those pages as mapped to not touch the garbage collector
unnecessarily. Gather up adjacent pages so they are unmapped together.
Remove all pages from free page groups from the list.
Remove all free page groups, and release the storage.
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Set and clear the in_use bit for this page in the page group.
References page_entry::bytes, G, globals::lg_pagesize, page_entry::next, page_entry::order, order, page_entry::page, and globals::pagesize.
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Set the page table entry for a page.
Not found -- allocate a new table.
Extract the level 1 and 2 indices.
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Free all empty pages. Partially empty pages need no attention because the `mark' bit doubles as an `unused' bit.
The last page-entry to consider, regardless of entries
placed at the end of the list. Loop until all entries have been examined.
Add all live objects on this page to the count of
allocated memory. Only objects on pages in the topmost context should get
collected. Remove the page if it's empty.
If P was the first page in the list, then NEXT
becomes the new first page in the list, otherwise
splice P out of the forward pointers. Splice P out of the back pointers too.
Are we removing the last element?
If the page is full, move it to the end.
Don't move it if it's already at the end.
Move p to the end of the list.
Update the tail pointer...
... and the head pointer, if necessary.
And update the backpointer in NEXT if necessary.
If we've fallen through to here, it's a page in the
topmost context that is neither full nor empty. Such a
page must precede pages at lesser context depth in the
list, so move it to the head. Update the backchain in the next node if it exists.
Move P to the head of the list.
Update the head pointer.
Are we moving the last element?
Now, restore the in_use_p vectors for any pages from contexts
other than the current one.
References page_entry::context_depth, globals::context_depth, free(), globals::free_object_list, G, HOST_BITS_PER_LONG, page_entry::in_use_p, lookup_page_table_entry(), free_object::next, free_object::object, page_entry::order, and page_entry::page.
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Validate that the reportedly free objects actually are.
Make certain it isn't visible from any root. Notice that we
do this check before sweep_pages merges save_in_use_p. If the object comes from an outer context, then retain the
free_object entry, so that we can verify that the address
isn't live on the stack in some outer context.
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The Ith entry is the maximum size of an object to be stored in the Ith extra order. Adding a new entry to this array is the *only* thing you need to do to add a new special allocation size.
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| struct { ... } inverse_table[NUM_ORDERS] |
The Ith entry is a pair of numbers (mult, shift) such that ((k * mult) >> shift) mod 2^32 == (k / OBJECT_SIZE(I)) mod 2^32, for all k evenly divisible by OBJECT_SIZE(I).
| size_t mult |
Referenced by coalesce_cost_bb(), and update_costs_from_allocno().
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The Ith entry is the size of an object on a page of order I.
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The Ith entry is the number of objects on a page or order I.
| unsigned int shift |
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1.8.1.1