518 lines
11 KiB
C
518 lines
11 KiB
C
/* Simple garbage collection for the GNU compiler.
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Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GCC is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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License for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING. If not, write to the Free
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Software Foundation, 59 Temple Place - Suite 330, Boston, MA
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02111-1307, USA. */
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#include "config.h"
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#include "system.h"
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#include "rtl.h"
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#include "tree.h"
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#include "tm_p.h"
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#include "flags.h"
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#include "varray.h"
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#include "ggc.h"
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#include "timevar.h"
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/* Debugging flags. */
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/* Zap memory before freeing to catch dangling pointers. */
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#define GGC_POISON
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/* Collect statistics on how bushy the search tree is. */
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#undef GGC_BALANCE
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/* Perform collection every time ggc_collect is invoked. Otherwise,
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collection is performed only when a significant amount of memory
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has been allocated since the last collection. */
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#undef GGC_ALWAYS_COLLECT
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/* Always verify that the to-be-marked memory is collectable. */
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#undef GGC_ALWAYS_VERIFY
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#ifdef ENABLE_GC_CHECKING
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#define GGC_POISON
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#define GGC_ALWAYS_VERIFY
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#endif
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#ifdef ENABLE_GC_ALWAYS_COLLECT
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#define GGC_ALWAYS_COLLECT
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#endif
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#ifndef HOST_BITS_PER_PTR
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#define HOST_BITS_PER_PTR HOST_BITS_PER_LONG
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#endif
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/* We'd like a balanced tree, but we don't really want to pay for the
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cost of keeping the tree balanced. We'll settle for the next best
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thing -- nearly balanced.
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In this context, the most natural key is the node pointer itself,
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but due to the way memory managers work, we'd be virtually certain
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to wind up with a completely degenerate straight line. What's needed
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is to make something more variable, and yet predictable, be more
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significant in the comparison.
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The handiest source of variability is the low bits of the pointer
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value itself. Any sort of bit/byte swap would do, but such machine
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specific operations are not handy, and we don't want to put that much
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effort into it. */
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#define PTR_KEY(p) ((size_t)p << (HOST_BITS_PER_PTR - 8) \
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| ((size_t)p & 0xff00) << (HOST_BITS_PER_PTR - 24) \
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| (size_t)p >> 16)
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/* GC'able memory; a node in a binary search tree. */
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struct ggc_mem
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{
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/* A combination of the standard left/right nodes, indexable by `<'. */
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struct ggc_mem *sub[2];
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unsigned int mark : 1;
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unsigned int context : 7;
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unsigned int size : 24;
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/* Make sure the data is reasonably aligned. */
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union {
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HOST_WIDEST_INT i;
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#ifdef HAVE_LONG_DOUBLE
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long double d;
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#else
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double d;
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#endif
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} u;
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};
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static struct globals
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{
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/* Root of the object tree. */
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struct ggc_mem *root;
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/* Data bytes currently allocated. */
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size_t allocated;
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/* Data objects currently allocated. */
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size_t objects;
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/* Data bytes allocated at time of last GC. */
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size_t allocated_last_gc;
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/* Current context level. */
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int context;
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} G;
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/* Skip garbage collection if the current allocation is not at least
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this factor times the allocation at the end of the last collection.
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In other words, total allocation must expand by (this factor minus
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one) before collection is performed. */
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#define GGC_MIN_EXPAND_FOR_GC (1.3)
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/* Bound `allocated_last_gc' to 4MB, to prevent the memory expansion
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test from triggering too often when the heap is small. */
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#define GGC_MIN_LAST_ALLOCATED (4 * 1024 * 1024)
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/* Local function prototypes. */
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static void tree_insert PARAMS ((struct ggc_mem *));
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static int tree_lookup PARAMS ((struct ggc_mem *));
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static void clear_marks PARAMS ((struct ggc_mem *));
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static void sweep_objs PARAMS ((struct ggc_mem **));
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static void ggc_pop_context_1 PARAMS ((struct ggc_mem *, int));
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/* For use from debugger. */
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extern void debug_ggc_tree PARAMS ((struct ggc_mem *, int));
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#ifdef GGC_BALANCE
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extern void debug_ggc_balance PARAMS ((void));
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#endif
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static void tally_leaves PARAMS ((struct ggc_mem *, int, size_t *, size_t *));
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/* Insert V into the search tree. */
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static inline void
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tree_insert (v)
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struct ggc_mem *v;
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{
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size_t v_key = PTR_KEY (v);
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struct ggc_mem *p, **pp;
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for (pp = &G.root, p = *pp; p ; p = *pp)
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{
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size_t p_key = PTR_KEY (p);
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pp = &p->sub[v_key < p_key];
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}
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*pp = v;
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}
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/* Return true if V is in the tree. */
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static inline int
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tree_lookup (v)
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struct ggc_mem *v;
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{
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size_t v_key = PTR_KEY (v);
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struct ggc_mem *p = G.root;
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while (p)
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{
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size_t p_key = PTR_KEY (p);
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if (p == v)
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return 1;
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p = p->sub[v_key < p_key];
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}
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return 0;
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}
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/* Alloc SIZE bytes of GC'able memory. If ZERO, clear the memory. */
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void *
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ggc_alloc (size)
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size_t size;
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{
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struct ggc_mem *x;
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x = (struct ggc_mem *) xmalloc (offsetof (struct ggc_mem, u) + size);
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x->sub[0] = NULL;
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x->sub[1] = NULL;
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x->mark = 0;
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x->context = G.context;
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x->size = size;
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#ifdef GGC_POISON
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memset (&x->u, 0xaf, size);
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#endif
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tree_insert (x);
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G.allocated += size;
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G.objects += 1;
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return &x->u;
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}
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/* Mark a node. */
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int
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ggc_set_mark (p)
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const void *p;
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{
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struct ggc_mem *x;
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x = (struct ggc_mem *) ((const char *)p - offsetof (struct ggc_mem, u));
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#ifdef GGC_ALWAYS_VERIFY
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if (! tree_lookup (x))
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abort ();
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#endif
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if (x->mark)
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return 1;
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x->mark = 1;
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G.allocated += x->size;
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G.objects += 1;
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return 0;
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}
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/* Return 1 if P has been marked, zero otherwise. */
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int
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ggc_marked_p (p)
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const void *p;
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{
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struct ggc_mem *x;
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x = (struct ggc_mem *) ((const char *)p - offsetof (struct ggc_mem, u));
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#ifdef GGC_ALWAYS_VERIFY
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if (! tree_lookup (x))
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abort ();
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#endif
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return x->mark;
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}
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/* Return the size of the gc-able object P. */
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size_t
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ggc_get_size (p)
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const void *p;
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{
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struct ggc_mem *x
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= (struct ggc_mem *) ((const char *)p - offsetof (struct ggc_mem, u));
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return x->size;
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}
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/* Unmark all objects. */
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static void
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clear_marks (x)
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struct ggc_mem *x;
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{
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x->mark = 0;
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if (x->sub[0])
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clear_marks (x->sub[0]);
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if (x->sub[1])
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clear_marks (x->sub[1]);
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}
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/* Free all objects in the current context that are not marked. */
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static void
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sweep_objs (root)
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struct ggc_mem **root;
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{
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struct ggc_mem *x = *root;
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if (!x)
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return;
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sweep_objs (&x->sub[0]);
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sweep_objs (&x->sub[1]);
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if (! x->mark && x->context >= G.context)
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{
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struct ggc_mem *l, *r;
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l = x->sub[0];
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r = x->sub[1];
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if (!l)
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*root = r;
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else if (!r)
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*root = l;
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else if (!l->sub[1])
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{
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*root = l;
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l->sub[1] = r;
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}
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else if (!r->sub[0])
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{
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*root = r;
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r->sub[0] = l;
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}
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else
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{
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*root = l;
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do {
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root = &l->sub[1];
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} while ((l = *root) != NULL);
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*root = r;
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}
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#ifdef GGC_POISON
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memset (&x->u, 0xA5, x->size);
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#endif
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free (x);
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}
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}
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/* The top level mark-and-sweep routine. */
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void
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ggc_collect ()
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{
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#ifndef GGC_ALWAYS_COLLECT
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if (G.allocated < GGC_MIN_EXPAND_FOR_GC * G.allocated_last_gc)
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return;
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#endif
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#ifdef GGC_BALANCE
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debug_ggc_balance ();
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#endif
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timevar_push (TV_GC);
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if (!quiet_flag)
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fprintf (stderr, " {GC %luk -> ", (unsigned long)G.allocated / 1024);
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G.allocated = 0;
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G.objects = 0;
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clear_marks (G.root);
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ggc_mark_roots ();
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sweep_objs (&G.root);
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G.allocated_last_gc = G.allocated;
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if (G.allocated_last_gc < GGC_MIN_LAST_ALLOCATED)
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G.allocated_last_gc = GGC_MIN_LAST_ALLOCATED;
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timevar_pop (TV_GC);
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if (!quiet_flag)
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fprintf (stderr, "%luk}", (unsigned long) G.allocated / 1024);
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#ifdef GGC_BALANCE
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debug_ggc_balance ();
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#endif
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}
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/* Called once to initialize the garbage collector. */
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void
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init_ggc ()
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{
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G.allocated_last_gc = GGC_MIN_LAST_ALLOCATED;
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}
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/* Start a new GGC context. Memory allocated in previous contexts
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will not be collected while the new context is active. */
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void
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ggc_push_context ()
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{
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G.context++;
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/* We only allocated 7 bits in the node for the context. This
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should be more than enough. */
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if (G.context >= 128)
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abort ();
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}
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/* Finish a GC context. Any uncollected memory in the new context
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will be merged with the old context. */
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void
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ggc_pop_context ()
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{
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G.context--;
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if (G.root)
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ggc_pop_context_1 (G.root, G.context);
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}
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static void
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ggc_pop_context_1 (x, c)
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struct ggc_mem *x;
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int c;
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{
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if (x->context > c)
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x->context = c;
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if (x->sub[0])
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ggc_pop_context_1 (x->sub[0], c);
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if (x->sub[1])
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ggc_pop_context_1 (x->sub[1], c);
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}
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/* Dump a tree. */
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void
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debug_ggc_tree (p, indent)
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struct ggc_mem *p;
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int indent;
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{
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int i;
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if (!p)
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{
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fputs ("(nil)\n", stderr);
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return;
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}
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if (p->sub[0])
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debug_ggc_tree (p->sub[0], indent + 1);
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for (i = 0; i < indent; ++i)
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putc (' ', stderr);
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fprintf (stderr, "%lx %p\n", (unsigned long)PTR_KEY (p), p);
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if (p->sub[1])
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debug_ggc_tree (p->sub[1], indent + 1);
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}
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#ifdef GGC_BALANCE
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/* Collect tree balance metrics */
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#include <math.h>
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void
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debug_ggc_balance ()
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{
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size_t nleaf, sumdepth;
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nleaf = sumdepth = 0;
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tally_leaves (G.root, 0, &nleaf, &sumdepth);
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fprintf (stderr, " {B %.2f,%.1f,%.1f}",
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/* In a balanced tree, leaf/node should approach 1/2. */
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(float)nleaf / (float)G.objects,
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/* In a balanced tree, average leaf depth should approach lg(n). */
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(float)sumdepth / (float)nleaf,
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log ((double) G.objects) / M_LN2);
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}
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#endif
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/* Used by debug_ggc_balance, and also by ggc_print_statistics. */
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static void
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tally_leaves (x, depth, nleaf, sumdepth)
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struct ggc_mem *x;
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int depth;
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size_t *nleaf;
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size_t *sumdepth;
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{
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if (! x->sub[0] && !x->sub[1])
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{
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*nleaf += 1;
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*sumdepth += depth;
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}
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else
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{
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if (x->sub[0])
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tally_leaves (x->sub[0], depth + 1, nleaf, sumdepth);
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if (x->sub[1])
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tally_leaves (x->sub[1], depth + 1, nleaf, sumdepth);
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}
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}
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#define SCALE(x) ((unsigned long) ((x) < 1024*10 \
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? (x) \
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: ((x) < 1024*1024*10 \
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? (x) / 1024 \
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: (x) / (1024*1024))))
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#define LABEL(x) ((x) < 1024*10 ? ' ' : ((x) < 1024*1024*10 ? 'k' : 'M'))
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/* Report on GC memory usage. */
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void
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ggc_print_statistics ()
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{
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struct ggc_statistics stats;
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size_t nleaf = 0, sumdepth = 0;
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/* Clear the statistics. */
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memset (&stats, 0, sizeof (stats));
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/* Make sure collection will really occur. */
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G.allocated_last_gc = 0;
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/* Collect and print the statistics common across collectors. */
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ggc_print_common_statistics (stderr, &stats);
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/* Report on tree balancing. */
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tally_leaves (G.root, 0, &nleaf, &sumdepth);
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fprintf (stderr, "\n\
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Total internal data (bytes)\t%ld%c\n\
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Number of leaves in tree\t%d\n\
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Average leaf depth\t\t%.1f\n",
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SCALE(G.objects * offsetof (struct ggc_mem, u)),
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LABEL(G.objects * offsetof (struct ggc_mem, u)),
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nleaf, (double)sumdepth / (double)nleaf);
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/* Report overall memory usage. */
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fprintf (stderr, "\n\
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Total objects allocated\t\t%d\n\
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Total memory in GC arena\t%ld%c\n",
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G.objects,
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SCALE(G.allocated), LABEL(G.allocated));
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}
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