initial import of NetBSD tree

1 files changed, 1928 insertions, 0 deletions

diff --git a/lib/libpcap/optimize.c b/lib/libpcap/optimize.c
new file mode 100644
index 00000000000..c416d70ecb7
--- /dev/null
+++ b/lib/libpcap/optimize.c
@@ -0,0 +1,1928 @@
+/*	$NetBSD: optimize.c,v 1.3 1995/04/29 05:42:28 cgd Exp $	*/
+
+/*
+ * Copyright (c) 1988, 1989, 1990, 1991, 1993, 1994
+ *	The Regents of the University of California.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that: (1) source code distributions
+ * retain the above copyright notice and this paragraph in its entirety, (2)
+ * distributions including binary code include the above copyright notice and
+ * this paragraph in its entirety in the documentation or other materials
+ * provided with the distribution, and (3) all advertising materials mentioning
+ * features or use of this software display the following acknowledgement:
+ * ``This product includes software developed by the University of California,
+ * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
+ * the University nor the names of its contributors may be used to endorse
+ * or promote products derived from this software without specific prior
+ * written permission.
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ *  Optimization module for tcpdump intermediate representation.
+ */
+#ifndef lint
+static char rcsid[] =
+    "@(#) Header: optimize.c,v 1.45 94/06/20 19:07:55 leres Exp (LBL)";
+#endif
+
+#include <sys/types.h>
+#include <sys/time.h>
+
+#include <net/bpf.h>
+
+#include <stdio.h>
+#ifdef __osf__
+#include <stdlib.h>
+#include <malloc.h>
+#endif
+#ifdef __NetBSD__
+#include <stdlib.h>
+#endif
+#include <memory.h>
+
+#include "gencode.h"
+
+#ifndef __GNUC__
+#define inline
+#endif
+
+#define A_ATOM BPF_MEMWORDS
+#define X_ATOM (BPF_MEMWORDS+1)
+
+#define NOP -1
+
+/*
+ * This define is used to represent *both* the accumulator and
+ * x register in use-def computations.
+ * Currently, the use-def code assumes only one definition per instruction.
+ */
+#define AX_ATOM N_ATOMS
+
+/*
+ * A flag to indicate that further optimization is needed.
+ * Iterative passes are continued until a given pass yields no
+ * branch movement.
+ */
+static int done;
+
+/*
+ * A block is marked if only if its mark equals the current mark.
+ * Rather than traverse the code array, marking each item, 'cur_mark' is
+ * incremented.  This automatically makes each element unmarked.
+ */
+static int cur_mark;
+#define isMarked(p) ((p)->mark == cur_mark)
+#define unMarkAll() cur_mark += 1
+#define Mark(p) ((p)->mark = cur_mark)
+
+static void opt_init(struct block *);
+static void opt_cleanup(void);
+
+static void make_marks(struct block *);
+static void mark_code(struct block *);
+
+static void intern_blocks(struct block *);
+
+static int eq_slist(struct slist *, struct slist *);
+
+static void find_levels_r(struct block *);
+
+static void find_levels(struct block *);
+static void find_dom(struct block *);
+static void propedom(struct edge *);
+static void find_edom(struct block *);
+static void find_closure(struct block *);
+static int atomuse(struct stmt *);
+static int atomdef(struct stmt *);
+static void compute_local_ud(struct block *);
+static void find_ud(struct block *);
+static void init_val(void);
+static long F(int, long, long);
+static inline void vstore(struct stmt *, long *, long, int);
+static void opt_blk(struct block *, int);
+static int use_conflict(struct block *, struct block *);
+static void opt_j(struct edge *);
+static void or_pullup(struct block *);
+static void and_pullup(struct block *);
+static void opt_blks(struct block *, int);
+static inline void link_inedge(struct edge *, struct block *);
+static void find_inedges(struct block *);
+static void opt_root(struct block **);
+static void opt_loop(struct block *, int);
+static void fold_op(struct stmt *, long, long);
+static inline struct slist *this_op(struct slist *);
+static void opt_not(struct block *);
+static void opt_peep(struct block *);
+static void opt_stmt(struct stmt *, long[], int);
+static void deadstmt(struct stmt *, struct stmt *[]);
+static void opt_deadstores(struct block *);
+static void opt_blk(struct block *, int);
+static int use_conflict(struct block *, struct block *);
+static void opt_j(struct edge *);
+static struct block *fold_edge(struct block *, struct edge *);
+static inline int eq_blk(struct block *, struct block *);
+static int slength(struct slist *);
+static int count_blocks(struct block *);
+static void number_blks_r(struct block *);
+static int count_stmts(struct block *);
+static void convert_code_r(struct block *);
+
+static int n_blocks;
+struct block **blocks;
+static int n_edges;
+struct edge **edges;
+
+/*
+ * A bit vector set representation of the dominators.
+ * We round up the set size to the next power of two.
+ */
+static int nodewords;
+static int edgewords;
+struct block **levels;
+u_long *space;
+#define BITS_PER_WORD (8*sizeof(u_long))
+/*
+ * True if a is in uset {p}
+ */
+#define SET_MEMBER(p, a) \
+((p)[(unsigned)(a) / BITS_PER_WORD] & (1 << ((unsigned)(a) % BITS_PER_WORD)))
+
+/*
+ * Add 'a' to uset p.
+ */
+#define SET_INSERT(p, a) \
+(p)[(unsigned)(a) / BITS_PER_WORD] |= (1 << ((unsigned)(a) % BITS_PER_WORD))
+
+/*
+ * Delete 'a' from uset p.
+ */
+#define SET_DELETE(p, a) \
+(p)[(unsigned)(a) / BITS_PER_WORD] &= ~(1 << ((unsigned)(a) % BITS_PER_WORD))
+
+/*
+ * a := a intersect b
+ */
+#define SET_INTERSECT(a, b, n)\
+{\
+	register u_long *_x = a, *_y = b;\
+	register int _n = n;\
+	while (--_n >= 0) *_x++ &= *_y++;\
+}
+
+/*
+ * a := a - b
+ */
+#define SET_SUBTRACT(a, b, n)\
+{\
+	register u_long *_x = a, *_y = b;\
+	register int _n = n;\
+	while (--_n >= 0) *_x++ &=~ *_y++;\
+}
+
+/*
+ * a := a union b
+ */
+#define SET_UNION(a, b, n)\
+{\
+	register u_long *_x = a, *_y = b;\
+	register int _n = n;\
+	while (--_n >= 0) *_x++ |= *_y++;\
+}
+
+static uset all_dom_sets;
+static uset all_closure_sets;
+static uset all_edge_sets;
+
+#ifndef MAX
+#define MAX(a,b) ((a)>(b)?(a):(b))
+#endif
+
+static void
+find_levels_r(b)
+	struct block *b;
+{
+	int level;
+
+	if (isMarked(b))
+		return;
+
+	Mark(b);
+	b->link = 0;
+
+	if (JT(b)) {
+		find_levels_r(JT(b));
+		find_levels_r(JF(b));
+		level = MAX(JT(b)->level, JF(b)->level) + 1;
+	} else
+		level = 0;
+	b->level = level;
+	b->link = levels[level];
+	levels[level] = b;
+}
+
+/*
+ * Level graph.  The levels go from 0 at the leaves to
+ * N_LEVELS at the root.  The levels[] array points to the
+ * first node of the level list, whose elements are linked
+ * with the 'link' field of the struct block.
+ */
+static void
+find_levels(root)
+	struct block *root;
+{
+	memset((char *)levels, 0, n_blocks * sizeof(*levels));
+	unMarkAll();
+	find_levels_r(root);
+}
+
+/*
+ * Find dominator relationships.
+ * Assumes graph has been leveled.
+ */
+static void
+find_dom(root)
+	struct block *root;
+{
+	int i;
+	struct block *b;
+	u_long *x;
+
+	/*
+	 * Initialize sets to contain all nodes.
+	 */
+	x = all_dom_sets;
+	i = n_blocks * nodewords;
+	while (--i >= 0)
+		*x++ = ~0;
+	/* Root starts off empty. */
+	for (i = nodewords; --i >= 0;)
+		root->dom[i] = 0;
+
+	/* root->level is the highest level no found. */
+	for (i = root->level; i >= 0; --i) {
+		for (b = levels[i]; b; b = b->link) {
+			SET_INSERT(b->dom, b->id);
+			if (JT(b) == 0)
+				continue;
+			SET_INTERSECT(JT(b)->dom, b->dom, nodewords);
+			SET_INTERSECT(JF(b)->dom, b->dom, nodewords);
+		}
+	}
+}
+
+static void
+propedom(ep)
+	struct edge *ep;
+{
+	SET_INSERT(ep->edom, ep->id);
+	if (ep->succ) {
+		SET_INTERSECT(ep->succ->et.edom, ep->edom, edgewords);
+		SET_INTERSECT(ep->succ->ef.edom, ep->edom, edgewords);
+	}
+}
+
+/*
+ * Compute edge dominators.
+ * Assumes graph has been leveled and predecessors established.
+ */
+static void
+find_edom(root)
+	struct block *root;
+{
+	int i;
+	uset x;
+	struct block *b;
+
+	x = all_edge_sets;
+	for (i = n_edges * edgewords; --i >= 0; )
+		x[i] = ~0;
+
+	/* root->level is the highest level no found. */
+	memset(root->et.edom, 0, edgewords * sizeof(*(uset)0));
+	memset(root->ef.edom, 0, edgewords * sizeof(*(uset)0));
+	for (i = root->level; i >= 0; --i) {
+		for (b = levels[i]; b != 0; b = b->link) {
+			propedom(&b->et);
+			propedom(&b->ef);
+		}
+	}
+}
+
+/*
+ * Find the backwards transitive closure of the flow graph.  These sets
+ * are backwards in the sense that we find the set of nodes that reach
+ * a given node, not the set of nodes that can be reached by a node.
+ *
+ * Assumes graph has been leveled.
+ */
+static void
+find_closure(root)
+	struct block *root;
+{
+	int i;
+	struct block *b;
+
+	/*
+	 * Initialize sets to contain no nodes.
+	 */
+	memset((char *)all_closure_sets, 0,
+	      n_blocks * nodewords * sizeof(*all_closure_sets));
+
+	/* root->level is the highest level no found. */
+	for (i = root->level; i >= 0; --i) {
+		for (b = levels[i]; b; b = b->link) {
+			SET_INSERT(b->closure, b->id);
+			if (JT(b) == 0)
+				continue;
+			SET_UNION(JT(b)->closure, b->closure, nodewords);
+			SET_UNION(JF(b)->closure, b->closure, nodewords);
+		}
+	}
+}
+
+/*
+ * Return the register number that is used by s.  If A and X are both
+ * used, return AX_ATOM.  If no register is used, return -1.
+ *
+ * The implementation should probably change to an array access.
+ */
+static int
+atomuse(s)
+	struct stmt *s;
+{
+	register int c = s->code;
+
+	if (c == NOP)
+		return -1;
+
+	switch (BPF_CLASS(c)) {
+
+	case BPF_RET:
+		return (BPF_RVAL(c) == BPF_A) ? A_ATOM :
+			(BPF_RVAL(c) == BPF_X) ? X_ATOM : -1;
+
+	case BPF_LD:
+	case BPF_LDX:
+		return (BPF_MODE(c) == BPF_IND) ? X_ATOM :
+			(BPF_MODE(c) == BPF_MEM) ? s->k : -1;
+
+	case BPF_ST:
+		return A_ATOM;
+
+	case BPF_STX:
+		return X_ATOM;
+
+	case BPF_JMP:
+	case BPF_ALU:
+		if (BPF_SRC(c) == BPF_X)
+			return AX_ATOM;
+		return A_ATOM;
+
+	case BPF_MISC:
+		return BPF_MISCOP(c) == BPF_TXA ? X_ATOM : A_ATOM;
+	}
+	abort();
+	/* NOTREACHED */
+}
+
+/*
+ * Return the register number that is defined by 's'.  We assume that
+ * a single stmt cannot define more than one register.  If no register
+ * is defined, return -1.
+ *
+ * The implementation should probably change to an array access.
+ */
+static int
+atomdef(s)
+	struct stmt *s;
+{
+	if (s->code == NOP)
+		return -1;
+
+	switch (BPF_CLASS(s->code)) {
+
+	case BPF_LD:
+	case BPF_ALU:
+		return A_ATOM;
+
+	case BPF_LDX:
+		return X_ATOM;
+
+	case BPF_ST:
+	case BPF_STX:
+		return s->k;
+
+	case BPF_MISC:
+		return BPF_MISCOP(s->code) == BPF_TAX ? X_ATOM : A_ATOM;
+	}
+	return -1;
+}
+
+static void
+compute_local_ud(b)
+	struct block *b;
+{
+	struct slist *s;
+	atomset def = 0, use = 0, kill = 0;
+	int atom;
+
+	for (s = b->stmts; s; s = s->next) {
+		if (s->s.code == NOP)
+			continue;
+		atom = atomuse(&s->s);
+		if (atom >= 0) {
+			if (atom == AX_ATOM) {
+				if (!ATOMELEM(def, X_ATOM))
+					use |= ATOMMASK(X_ATOM);
+				if (!ATOMELEM(def, A_ATOM))
+					use |= ATOMMASK(A_ATOM);
+			}
+			else if (atom < N_ATOMS) {
+				if (!ATOMELEM(def, atom))
+					use |= ATOMMASK(atom);
+			}
+			else
+				abort();
+		}
+		atom = atomdef(&s->s);
+		if (atom >= 0) {
+			if (!ATOMELEM(use, atom))
+				kill |= ATOMMASK(atom);
+			def |= ATOMMASK(atom);
+		}
+	}
+	if (!ATOMELEM(def, A_ATOM) && BPF_CLASS(b->s.code) == BPF_JMP)
+		use |= ATOMMASK(A_ATOM);
+
+	b->def = def;
+	b->kill = kill;
+	b->in_use = use;
+}
+
+/*
+ * Assume graph is already leveled.
+ */
+static void
+find_ud(root)
+	struct block *root;
+{
+	int i, maxlevel;
+	struct block *p;
+
+	/*
+	 * root->level is the highest level no found;
+	 * count down from there.
+	 */
+	maxlevel = root->level;
+	for (i = maxlevel; i >= 0; --i)
+		for (p = levels[i]; p; p = p->link) {
+			compute_local_ud(p);
+			p->out_use = 0;
+		}
+
+	for (i = 1; i <= maxlevel; ++i) {
+		for (p = levels[i]; p; p = p->link) {
+			p->out_use |= JT(p)->in_use | JF(p)->in_use;
+			p->in_use |= p->out_use &~ p->kill;
+		}
+	}
+}
+
+/*
+ * These data structures are used in a Cocke and Shwarz style
+ * value numbering scheme.  Since the flowgraph is acyclic,
+ * exit values can be propagated from a node's predecessors
+ * provided it is uniquely defined.
+ */
+struct valnode {
+	int code;
+	long v0, v1;
+	long val;
+	struct valnode *next;
+};
+
+#define MODULUS 213
+static struct valnode *hashtbl[MODULUS];
+static int curval;
+static int maxval;
+
+/* Integer constants mapped with the load immediate opcode. */
+#define K(i) F(BPF_LD|BPF_IMM|BPF_W, i, 0L)
+
+struct vmapinfo {
+	int is_const;
+	long const_val;
+};
+
+struct vmapinfo *vmap;
+struct valnode *vnode_base;
+struct valnode *next_vnode;
+
+static void
+init_val()
+{
+	curval = 0;
+	next_vnode = vnode_base;
+	memset((char *)vmap, 0, maxval * sizeof(*vmap));
+	memset((char *)hashtbl, 0, sizeof hashtbl);
+}
+
+/* Because we really don't have an IR, this stuff is a little messy. */
+static long
+F(code, v0, v1)
+	int code;
+	long v0, v1;
+{
+	u_int hash;
+	int val;
+	struct valnode *p;
+
+	hash = (u_int)code ^ (v0 << 4) ^ (v1 << 8);
+	hash %= MODULUS;
+
+	for (p = hashtbl[hash]; p; p = p->next)
+		if (p->code == code && p->v0 == v0 && p->v1 == v1)
+			return p->val;
+
+	val = ++curval;
+	if (BPF_MODE(code) == BPF_IMM &&
+	    (BPF_CLASS(code) == BPF_LD || BPF_CLASS(code) == BPF_LDX)) {
+		vmap[val].const_val = v0;
+		vmap[val].is_const = 1;
+	}
+	p = next_vnode++;
+	p->val = val;
+	p->code = code;
+	p->v0 = v0;
+	p->v1 = v1;
+	p->next = hashtbl[hash];
+	hashtbl[hash] = p;
+
+	return val;
+}
+
+static inline void
+vstore(s, valp, newval, alter)
+	struct stmt *s;
+	long *valp;
+	long newval;
+	int alter;
+{
+	if (alter && *valp == newval)
+		s->code = NOP;
+	else
+		*valp = newval;
+}
+
+static void
+fold_op(s, v0, v1)
+	struct stmt *s;
+	long v0, v1;
+{
+	long a, b;
+
+	a = vmap[v0].const_val;
+	b = vmap[v1].const_val;
+
+	switch (BPF_OP(s->code)) {
+	case BPF_ADD:
+		a += b;
+		break;
+
+	case BPF_SUB:
+		a -= b;
+		break;
+
+	case BPF_MUL:
+		a *= b;
+		break;
+
+	case BPF_DIV:
+		if (b == 0)
+			bpf_error("division by zero");
+		a /= b;
+		break;
+
+	case BPF_AND:
+		a &= b;
+		break;
+
+	case BPF_OR:
+		a |= b;
+		break;
+
+	case BPF_LSH:
+		a <<= b;
+		break;
+
+	case BPF_RSH:
+		a >>= b;
+		break;
+
+	case BPF_NEG:
+		a = -a;
+		break;
+
+	default:
+		abort();
+	}
+	s->k = a;
+	s->code = BPF_LD|BPF_IMM;
+	done = 0;
+}
+
+static inline struct slist *
+this_op(s)
+	struct slist *s;
+{
+	while (s != 0 && s->s.code == NOP)
+		s = s->next;
+	return s;
+}
+
+static void
+opt_not(b)
+	struct block *b;
+{
+	struct block *tmp = JT(b);
+
+	JT(b) = JF(b);
+	JF(b) = tmp;
+}
+
+static void
+opt_peep(b)
+	struct block *b;
+{
+	struct slist *s;
+	struct slist *next, *last;
+	int val;
+	long v;
+
+	s = b->stmts;
+	if (s == 0)
+		return;
+
+	last = s;
+	while (1) {
+		s = this_op(s);
+		if (s == 0)
+			break;
+		next = this_op(s->next);
+		if (next == 0)
+			break;
+		last = next;
+
+		/*
+		 * st  M[k]	-->	st  M[k]
+		 * ldx M[k]		tax
+		 */
+		if (s->s.code == BPF_ST &&
+		    next->s.code == (BPF_LDX|BPF_MEM) &&
+		    s->s.k == next->s.k) {
+			done = 0;
+			next->s.code = BPF_MISC|BPF_TAX;
+		}
+		/*
+		 * ld  #k	-->	ldx  #k
+		 * tax			txa
+		 */
+		if (s->s.code == (BPF_LD|BPF_IMM) &&
+		    next->s.code == (BPF_MISC|BPF_TAX)) {
+			s->s.code = BPF_LDX|BPF_IMM;
+			next->s.code = BPF_MISC|BPF_TXA;
+			done = 0;
+		}
+		/*
+		 * This is an ugly special case, but it happens
+		 * when you say tcp[k] or udp[k] where k is a constant.
+		 */
+		if (s->s.code == (BPF_LD|BPF_IMM)) {
+			struct slist *add, *tax, *ild;
+
+			/*
+			 * Check that X isn't used on exit from this
+			 * block (which the optimizer might cause).
+			 * We know the code generator won't generate
+			 * any local dependencies.
+			 */
+			if (ATOMELEM(b->out_use, X_ATOM))
+				break;
+
+			if (next->s.code != (BPF_LDX|BPF_MSH|BPF_B))
+				add = next;
+			else
+				add = this_op(next->next);
+			if (add == 0 || add->s.code != (BPF_ALU|BPF_ADD|BPF_X))
+				break;
+
+			tax = this_op(add->next);
+			if (tax == 0 || tax->s.code != (BPF_MISC|BPF_TAX))
+				break;
+
+			ild = this_op(tax->next);
+			if (ild == 0 || BPF_CLASS(ild->s.code) != BPF_LD ||
+			    BPF_MODE(ild->s.code) != BPF_IND)
+				break;
+			/*
+			 * XXX We need to check that X is not
+			 * subsequently used.  We know we can eliminate the
+			 * accumulator modifications since it is defined
+			 * by the last stmt of this sequence.
+			 *
+			 * We want to turn this sequence:
+			 *
+			 * (004) ldi     #0x2		{s}
+			 * (005) ldxms   [14]		{next}  -- optional
+			 * (006) addx			{add}
+			 * (007) tax			{tax}
+			 * (008) ild     [x+0]		{ild}
+			 *
+			 * into this sequence:
+			 *
+			 * (004) nop
+			 * (005) ldxms   [14]
+			 * (006) nop
+			 * (007) nop
+			 * (008) ild     [x+2]
+			 *
+			 */
+			ild->s.k += s->s.k;
+			s->s.code = NOP;
+			add->s.code = NOP;
+			tax->s.code = NOP;
+			done = 0;
+		}
+		s = next;
+	}
+	/*
+	 * If we have a subtract to do a comparison, and the X register
+	 * is a known constant, we can merge this value into the
+	 * comparison.
+	 */
+	if (last->s.code == (BPF_ALU|BPF_SUB|BPF_X) &&
+	    !ATOMELEM(b->out_use, A_ATOM)) {
+		val = b->val[X_ATOM];
+		if (vmap[val].is_const) {
+			b->s.k += vmap[val].const_val;
+			last->s.code = NOP;
+			done = 0;
+		} else if (b->s.k == 0) {
+			/*
+			 * sub x  ->	nop
+			 * j  #0	j  x
+			 */
+			last->s.code = NOP;
+			b->s.code = BPF_CLASS(b->s.code) | BPF_OP(b->s.code) |
+				BPF_X;
+			done = 0;
+		}
+	}
+	/*
+	 * Likewise, a constant subtract can be simplified.
+	 */
+	else if (last->s.code == (BPF_ALU|BPF_SUB|BPF_K) &&
+		 !ATOMELEM(b->out_use, A_ATOM)) {
+		b->s.k += last->s.k;
+		last->s.code = NOP;
+		done = 0;
+	}
+	/*
+	 * and #k	nop
+	 * jeq #0  ->	jset #k
+	 */
+	if (last->s.code == (BPF_ALU|BPF_AND|BPF_K) &&
+	    !ATOMELEM(b->out_use, A_ATOM) && b->s.k == 0) {
+		b->s.k = last->s.k;
+		b->s.code = BPF_JMP|BPF_K|BPF_JSET;
+		last->s.code = NOP;
+		done = 0;
+		opt_not(b);
+	}
+	/*
+	 * If the accumulator is a known constant, we can compute the
+	 * comparison result.
+	 */
+	val = b->val[A_ATOM];
+	if (vmap[val].is_const && BPF_SRC(b->s.code) == BPF_K) {
+		v = vmap[val].const_val;
+		switch (BPF_OP(b->s.code)) {
+
+		case BPF_JEQ:
+			v = v == b->s.k;
+			break;
+
+		case BPF_JGT:
+			v = v > b->s.k;
+			break;
+
+		case BPF_JGE:
+			v = v >= b->s.k;
+			break;
+
+		case BPF_JSET:
+			v &= b->s.k;
+			break;
+
+		default:
+			abort();
+		}
+		if (JF(b) != JT(b))
+			done = 0;
+		if (v)
+			JF(b) = JT(b);
+		else
+			JT(b) = JF(b);
+	}
+}
+
+/*
+ * Compute the symbolic value of expression of 's', and update
+ * anything it defines in the value table 'val'.  If 'alter' is true,
+ * do various optimizations.  This code would be cleaner if symbolic
+ * evaluation and code transformations weren't folded together.
+ */
+static void
+opt_stmt(s, val, alter)
+	struct stmt *s;
+	long val[];
+	int alter;
+{
+	int op;
+	long v;
+
+	switch (s->code) {
+
+	case BPF_LD|BPF_ABS|BPF_W:
+	case BPF_LD|BPF_ABS|BPF_H:
+	case BPF_LD|BPF_ABS|BPF_B:
+		v = F(s->code, s->k, 0L);
+		vstore(s, &val[A_ATOM], v, alter);
+		break;
+
+	case BPF_LD|BPF_IND|BPF_W:
+	case BPF_LD|BPF_IND|BPF_H:
+	case BPF_LD|BPF_IND|BPF_B:
+		v = val[X_ATOM];
+		if (alter && vmap[v].is_const) {
+			s->code = BPF_LD|BPF_ABS|BPF_SIZE(s->code);
+			s->k += vmap[v].const_val;
+			v = F(s->code, s->k, 0L);
+			done = 0;
+		}
+		else
+			v = F(s->code, s->k, v);
+		vstore(s, &val[A_ATOM], v, alter);
+		break;
+
+	case BPF_LD|BPF_LEN:
+		v = F(s->code, 0L, 0L);
+		vstore(s, &val[A_ATOM], v, alter);
+		break;
+
+	case BPF_LD|BPF_IMM:
+		v = K(s->k);
+		vstore(s, &val[A_ATOM], v, alter);
+		break;
+
+	case BPF_LDX|BPF_IMM:
+		v = K(s->k);
+		vstore(s, &val[X_ATOM], v, alter);
+		break;
+
+	case BPF_LDX|BPF_MSH|BPF_B:
+		v = F(s->code, s->k, 0L);
+		vstore(s, &val[X_ATOM], v, alter);
+		break;
+
+	case BPF_ALU|BPF_NEG:
+		if (alter && vmap[val[A_ATOM]].is_const) {
+			s->code = BPF_LD|BPF_IMM;
+			s->k = -vmap[val[A_ATOM]].const_val;
+			val[A_ATOM] = K(s->k);
+		}
+		else
+			val[A_ATOM] = F(s->code, val[A_ATOM], 0L);
+		break;
+
+	case BPF_ALU|BPF_ADD|BPF_K:
+	case BPF_ALU|BPF_SUB|BPF_K:
+	case BPF_ALU|BPF_MUL|BPF_K:
+	case BPF_ALU|BPF_DIV|BPF_K:
+	case BPF_ALU|BPF_AND|BPF_K:
+	case BPF_ALU|BPF_OR|BPF_K:
+	case BPF_ALU|BPF_LSH|BPF_K:
+	case BPF_ALU|BPF_RSH|BPF_K:
+		op = BPF_OP(s->code);
+		if (alter) {
+			if (s->k == 0) {
+				if (op == BPF_ADD || op == BPF_SUB ||
+				    op == BPF_LSH || op == BPF_RSH ||
+				    op == BPF_OR) {
+					s->code = NOP;
+					break;
+				}
+				if (op == BPF_MUL || op == BPF_AND) {
+					s->code = BPF_LD|BPF_IMM;
+					val[A_ATOM] = K(s->k);
+					break;
+				}
+			}
+			if (vmap[val[A_ATOM]].is_const) {
+				fold_op(s, val[A_ATOM], K(s->k));
+				val[A_ATOM] = K(s->k);
+				break;
+			}
+		}
+		val[A_ATOM] = F(s->code, val[A_ATOM], K(s->k));
+		break;
+
+	case BPF_ALU|BPF_ADD|BPF_X:
+	case BPF_ALU|BPF_SUB|BPF_X:
+	case BPF_ALU|BPF_MUL|BPF_X:
+	case BPF_ALU|BPF_DIV|BPF_X:
+	case BPF_ALU|BPF_AND|BPF_X:
+	case BPF_ALU|BPF_OR|BPF_X:
+	case BPF_ALU|BPF_LSH|BPF_X:
+	case BPF_ALU|BPF_RSH|BPF_X:
+		op = BPF_OP(s->code);
+		if (alter && vmap[val[X_ATOM]].is_const) {
+			if (vmap[val[A_ATOM]].is_const) {
+				fold_op(s, val[A_ATOM], val[X_ATOM]);
+				val[A_ATOM] = K(s->k);
+			}
+			else {
+				s->code = BPF_ALU|BPF_K|op;
+				s->k = vmap[val[X_ATOM]].const_val;
+				done = 0;
+				val[A_ATOM] =
+					F(s->code, val[A_ATOM], K(s->k));
+			}
+			break;
+		}
+		/*
+		 * Check if we're doing something to an accumulator
+		 * that is 0, and simplify.  This may not seem like
+		 * much of a simplification but it could open up further
+		 * optimizations.
+		 * XXX We could also check for mul by 1, and -1, etc.
+		 */
+		if (alter && vmap[val[A_ATOM]].is_const
+		    && vmap[val[A_ATOM]].const_val == 0) {
+			if (op == BPF_ADD || op == BPF_OR ||
+			    op == BPF_LSH || op == BPF_RSH || op == BPF_SUB) {
+				s->code = BPF_MISC|BPF_TXA;
+				vstore(s, &val[A_ATOM], val[X_ATOM], alter);
+				break;
+			}
+			else if (op == BPF_MUL || op == BPF_DIV ||
+				 op == BPF_AND) {
+				s->code = BPF_LD|BPF_IMM;
+				s->k = 0;
+				vstore(s, &val[A_ATOM], K(s->k), alter);
+				break;
+			}
+			else if (op == BPF_NEG) {
+				s->code = NOP;
+				break;
+			}
+		}
+		val[A_ATOM] = F(s->code, val[A_ATOM], val[X_ATOM]);
+		break;
+
+	case BPF_MISC|BPF_TXA:
+		vstore(s, &val[A_ATOM], val[X_ATOM], alter);
+		break;
+
+	case BPF_LD|BPF_MEM:
+		v = val[s->k];
+		if (alter && vmap[v].is_const) {
+			s->code = BPF_LD|BPF_IMM;
+			s->k = vmap[v].const_val;
+			done = 0;
+		}
+		vstore(s, &val[A_ATOM], v, alter);
+		break;
+
+	case BPF_MISC|BPF_TAX:
+		vstore(s, &val[X_ATOM], val[A_ATOM], alter);
+		break;
+
+	case BPF_LDX|BPF_MEM:
+		v = val[s->k];
+		if (alter && vmap[v].is_const) {
+			s->code = BPF_LDX|BPF_IMM;
+			s->k = vmap[v].const_val;
+			done = 0;
+		}
+		vstore(s, &val[X_ATOM], v, alter);
+		break;
+
+	case BPF_ST:
+		vstore(s, &val[s->k], val[A_ATOM], alter);
+		break;
+
+	case BPF_STX:
+		vstore(s, &val[s->k], val[X_ATOM], alter);
+		break;
+	}
+}
+
+static void
+deadstmt(s, last)
+	register struct stmt *s;
+	register struct stmt *last[];
+{
+	register int atom;
+
+	atom = atomuse(s);
+	if (atom >= 0) {
+		if (atom == AX_ATOM) {
+			last[X_ATOM] = 0;
+			last[A_ATOM] = 0;
+		}
+		else
+			last[atom] = 0;
+	}
+	atom = atomdef(s);
+	if (atom >= 0) {
+		if (last[atom]) {
+			done = 0;
+			last[atom]->code = NOP;
+		}
+		last[atom] = s;
+	}
+}
+
+static void
+opt_deadstores(b)
+	register struct block *b;
+{
+	register struct slist *s;
+	register int atom;
+	struct stmt *last[N_ATOMS];
+
+	memset((char *)last, 0, sizeof last);
+
+	for (s = b->stmts; s != 0; s = s->next)
+		deadstmt(&s->s, last);
+	deadstmt(&b->s, last);
+
+	for (atom = 0; atom < N_ATOMS; ++atom)
+		if (last[atom] && !ATOMELEM(b->out_use, atom)) {
+			last[atom]->code = NOP;
+			done = 0;
+		}
+}
+
+static void
+opt_blk(b, do_stmts)
+	struct block *b;
+	int do_stmts;
+{
+	struct slist *s;
+	struct edge *p;
+	int i;
+	long aval;
+
+	/*
+	 * Initialize the atom values.
+	 * If we have no predecessors, everything is undefined.
+	 * Otherwise, we inherent our values from our predecessors.
+	 * If any register has an ambiguous value (i.e. control paths are
+	 * merging) give it the undefined value of 0.
+	 */
+	p = b->in_edges;
+	if (p == 0)
+		memset((char *)b->val, 0, sizeof(b->val));
+	else {
+		memcpy((char *)b->val, (char *)p->pred->val, sizeof(b->val));
+		while ((p = p->next) != NULL) {
+			for (i = 0; i < N_ATOMS; ++i)
+				if (b->val[i] != p->pred->val[i])
+					b->val[i] = 0;
+		}
+	}
+	aval = b->val[A_ATOM];
+	for (s = b->stmts; s; s = s->next)
+		opt_stmt(&s->s, b->val, do_stmts);
+
+	/*
+	 * This is a special case: if we don't use anything from this
+	 * block, and we load the accumulator with value that is
+	 * already there, eliminate all the statements.
+	 */
+	if (do_stmts && b->out_use == 0 && aval != 0 &&
+	    b->val[A_ATOM] == aval)
+		b->stmts = 0;
+	else {
+		opt_peep(b);
+		opt_deadstores(b);
+	}
+	/*
+	 * Set up values for branch optimizer.
+	 */
+	if (BPF_SRC(b->s.code) == BPF_K)
+		b->oval = K(b->s.k);
+	else
+		b->oval = b->val[X_ATOM];
+	b->et.code = b->s.code;
+	b->ef.code = -b->s.code;
+}
+
+/*
+ * Return true if any register that is used on exit from 'succ', has
+ * an exit value that is different from the corresponding exit value
+ * from 'b'.
+ */
+static int
+use_conflict(b, succ)
+	struct block *b, *succ;
+{
+	int atom;
+	atomset use = succ->out_use;
+
+	if (use == 0)
+		return 0;
+
+	for (atom = 0; atom < N_ATOMS; ++atom)
+		if (ATOMELEM(use, atom))
+			if (b->val[atom] != succ->val[atom])
+				return 1;
+	return 0;
+}
+
+static struct block *
+fold_edge(child, ep)
+	struct block *child;
+	struct edge *ep;
+{
+	int sense;
+	int aval0, aval1, oval0, oval1;
+	int code = ep->code;
+
+	if (code < 0) {
+		code = -code;
+		sense = 0;
+	} else
+		sense = 1;
+
+	if (child->s.code != code)
+		return 0;
+
+	aval0 = child->val[A_ATOM];
+	oval0 = child->oval;
+	aval1 = ep->pred->val[A_ATOM];
+	oval1 = ep->pred->oval;
+
+	if (aval0 != aval1)
+		return 0;
+
+	if (oval0 == oval1)
+		/*
+		 * The operands are identical, so the
+		 * result is true if a true branch was
+		 * taken to get here, otherwise false.
+		 */
+		return sense ? JT(child) : JF(child);
+
+	if (sense && code == (BPF_JMP|BPF_JEQ|BPF_K))
+		/*
+		 * At this point, we only know the comparison if we
+		 * came down the true branch, and it was an equality
+		 * comparison with a constant.  We rely on the fact that
+		 * distinct constants have distinct value numbers.
+		 */
+		return JF(child);
+
+	return 0;
+}
+
+static void
+opt_j(ep)
+	struct edge *ep;
+{
+	register int i, k;
+	register struct block *target;
+
+	if (JT(ep->succ) == 0)
+		return;
+
+	if (JT(ep->succ) == JF(ep->succ)) {
+		/*
+		 * Common branch targets can be eliminated, provided
+		 * there is no data dependency.
+		 */
+		if (!use_conflict(ep->pred, ep->succ->et.succ)) {
+			done = 0;
+			ep->succ = JT(ep->succ);
+		}
+	}
+	/*
+	 * For each edge dominator that matches the successor of this
+	 * edge, promote the edge successor to the its grandchild.
+	 *
+	 * XXX We violate the set abstraction here in favor a reasonably
+	 * efficient loop.
+	 */
+ top:
+	for (i = 0; i < edgewords; ++i) {
+		register u_long x = ep->edom[i];
+
+		while (x != 0) {
+			k = ffs(x) - 1;
+			x &=~ (1 << k);
+			k += i * BITS_PER_WORD;
+
+			target = fold_edge(ep->succ, edges[k]);
+			/*
+			 * Check that there is no data dependency between
+			 * nodes that will be violated if we move the edge.
+			 */
+			if (target != 0 && !use_conflict(ep->pred, target)) {
+				done = 0;
+				ep->succ = target;
+				if (JT(target) != 0)
+					/*
+					 * Start over unless we hit a leaf.
+					 */
+					goto top;
+				return;
+			}
+		}
+	}
+}
+
+
+static void
+or_pullup(b)
+	struct block *b;
+{
+	int val, at_top;
+	struct block *pull;
+	struct block **diffp, **samep;
+	struct edge *ep;
+
+	ep = b->in_edges;
+	if (ep == 0)
+		return;
+
+	/*
+	 * Make sure each predecessor loads the same value.
+	 * XXX why?
+	 */
+	val = ep->pred->val[A_ATOM];
+	for (ep = ep->next; ep != 0; ep = ep->next)
+		if (val != ep->pred->val[A_ATOM])
+			return;
+
+	if (JT(b->in_edges->pred) == b)
+		diffp = &JT(b->in_edges->pred);
+	else
+		diffp = &JF(b->in_edges->pred);
+
+	at_top = 1;
+	while (1) {
+		if (*diffp == 0)
+			return;
+
+		if (JT(*diffp) != JT(b))
+			return;
+
+		if (!SET_MEMBER((*diffp)->dom, b->id))
+			return;
+
+		if ((*diffp)->val[A_ATOM] != val)
+			break;
+
+		diffp = &JF(*diffp);
+		at_top = 0;
+	}
+	samep = &JF(*diffp);
+	while (1) {
+		if (*samep == 0)
+			return;
+
+		if (JT(*samep) != JT(b))
+			return;
+
+		if (!SET_MEMBER((*samep)->dom, b->id))
+			return;
+
+		if ((*samep)->val[A_ATOM] == val)
+			break;
+
+		/* XXX Need to check that there are no data dependencies
+		   between dp0 and dp1.  Currently, the code generator
+		   will not produce such dependencies. */
+		samep = &JF(*samep);
+	}
+#ifdef notdef
+	/* XXX This doesn't cover everything. */
+	for (i = 0; i < N_ATOMS; ++i)
+		if ((*samep)->val[i] != pred->val[i])
+			return;
+#endif
+	/* Pull up the node. */
+	pull = *samep;
+	*samep = JF(pull);
+	JF(pull) = *diffp;
+
+	/*
+	 * At the top of the chain, each predecessor needs to point at the
+	 * pulled up node.  Inside the chain, there is only one predecessor
+	 * to worry about.
+	 */
+	if (at_top) {
+		for (ep = b->in_edges; ep != 0; ep = ep->next) {
+			if (JT(ep->pred) == b)
+				JT(ep->pred) = pull;
+			else
+				JF(ep->pred) = pull;
+		}
+	}
+	else
+		*diffp = pull;
+
+	done = 0;
+}
+
+static void
+and_pullup(b)
+	struct block *b;
+{
+	int val, at_top;
+	struct block *pull;
+	struct block **diffp, **samep;
+	struct edge *ep;
+
+	ep = b->in_edges;
+	if (ep == 0)
+		return;
+
+	/*
+	 * Make sure each predecessor loads the same value.
+	 */
+	val = ep->pred->val[A_ATOM];
+	for (ep = ep->next; ep != 0; ep = ep->next)
+		if (val != ep->pred->val[A_ATOM])
+			return;
+
+	if (JT(b->in_edges->pred) == b)
+		diffp = &JT(b->in_edges->pred);
+	else
+		diffp = &JF(b->in_edges->pred);
+
+	at_top = 1;
+	while (1) {
+		if (*diffp == 0)
+			return;
+
+		if (JF(*diffp) != JF(b))
+			return;
+
+		if (!SET_MEMBER((*diffp)->dom, b->id))
+			return;
+
+		if ((*diffp)->val[A_ATOM] != val)
+			break;
+
+		diffp = &JT(*diffp);
+		at_top = 0;
+	}
+	samep = &JT(*diffp);
+	while (1) {
+		if (*samep == 0)
+			return;
+
+		if (JF(*samep) != JF(b))
+			return;
+
+		if (!SET_MEMBER((*samep)->dom, b->id))
+			return;
+
+		if ((*samep)->val[A_ATOM] == val)
+			break;
+
+		/* XXX Need to check that there are no data dependencies
+		   between diffp and samep.  Currently, the code generator
+		   will not produce such dependencies. */
+		samep = &JT(*samep);
+	}
+#ifdef notdef
+	/* XXX This doesn't cover everything. */
+	for (i = 0; i < N_ATOMS; ++i)
+		if ((*samep)->val[i] != pred->val[i])
+			return;
+#endif
+	/* Pull up the node. */
+	pull = *samep;
+	*samep = JT(pull);
+	JT(pull) = *diffp;
+
+	/*
+	 * At the top of the chain, each predecessor needs to point at the
+	 * pulled up node.  Inside the chain, there is only one predecessor
+	 * to worry about.
+	 */
+	if (at_top) {
+		for (ep = b->in_edges; ep != 0; ep = ep->next) {
+			if (JT(ep->pred) == b)
+				JT(ep->pred) = pull;
+			else
+				JF(ep->pred) = pull;
+		}
+	}
+	else
+		*diffp = pull;
+
+	done = 0;
+}
+
+static void
+opt_blks(root, do_stmts)
+	struct block *root;
+	int do_stmts;
+{
+	int i, maxlevel;
+	struct block *p;
+
+	init_val();
+	maxlevel = root->level;
+	for (i = maxlevel; i >= 0; --i)
+		for (p = levels[i]; p; p = p->link)
+			opt_blk(p, do_stmts);
+
+	if (do_stmts)
+		/*
+		 * No point trying to move branches; it can't possibly
+		 * make a difference at this point.
+		 */
+		return;
+
+	for (i = 1; i <= maxlevel; ++i) {
+		for (p = levels[i]; p; p = p->link) {
+			opt_j(&p->et);
+			opt_j(&p->ef);
+		}
+	}
+	for (i = 1; i <= maxlevel; ++i) {
+		for (p = levels[i]; p; p = p->link) {
+			or_pullup(p);
+			and_pullup(p);
+		}
+	}
+}
+
+static inline void
+link_inedge(parent, child)
+	struct edge *parent;
+	struct block *child;
+{
+	parent->next = child->in_edges;
+	child->in_edges = parent;
+}
+
+static void
+find_inedges(root)
+	struct block *root;
+{
+	int i;
+	struct block *b;
+
+	for (i = 0; i < n_blocks; ++i)
+		blocks[i]->in_edges = 0;
+
+	/*
+	 * Traverse the graph, adding each edge to the predecessor
+	 * list of its successors.  Skip the leaves (i.e. level 0).
+	 */
+	for (i = root->level; i > 0; --i) {
+		for (b = levels[i]; b != 0; b = b->link) {
+			link_inedge(&b->et, JT(b));
+			link_inedge(&b->ef, JF(b));
+		}
+	}
+}
+
+static void
+opt_root(b)
+	struct block **b;
+{
+	struct slist *tmp, *s;
+
+	s = (*b)->stmts;
+	(*b)->stmts = 0;
+	while (BPF_CLASS((*b)->s.code) == BPF_JMP && JT(*b) == JF(*b))
+		*b = JT(*b);
+
+	tmp = (*b)->stmts;
+	if (tmp != 0)
+		sappend(s, tmp);
+	(*b)->stmts = s;
+}
+
+static void
+opt_loop(root, do_stmts)
+	struct block *root;
+	int do_stmts;
+{
+
+#ifdef BDEBUG
+	if (dflag > 1)
+		opt_dump(root);
+#endif
+	do {
+		done = 1;
+		find_levels(root);
+		find_dom(root);
+		find_closure(root);
+		find_inedges(root);
+		find_ud(root);
+		find_edom(root);
+		opt_blks(root, do_stmts);
+#ifdef BDEBUG
+		if (dflag > 1)
+			opt_dump(root);
+#endif
+	} while (!done);
+}
+
+/*
+ * Optimize the filter code in its dag representation.
+ */
+void
+bpf_optimize(rootp)
+	struct block **rootp;
+{
+	struct block *root;
+
+	root = *rootp;
+
+	opt_init(root);
+	opt_loop(root, 0);
+	opt_loop(root, 1);
+	intern_blocks(root);
+	opt_root(rootp);
+	opt_cleanup();
+}
+
+static void
+make_marks(p)
+	struct block *p;
+{
+	if (!isMarked(p)) {
+		Mark(p);
+		if (BPF_CLASS(p->s.code) != BPF_RET) {
+			make_marks(JT(p));
+			make_marks(JF(p));
+		}
+	}
+}
+
+/*
+ * Mark code array such that isMarked(i) is true
+ * only for nodes that are alive.
+ */
+static void
+mark_code(p)
+	struct block *p;
+{
+	cur_mark += 1;
+	make_marks(p);
+}
+
+/*
+ * True iff the two stmt lists load the same value from the packet into
+ * the accumulator.
+ */
+static int
+eq_slist(x, y)
+	struct slist *x, *y;
+{
+	while (1) {
+		while (x && x->s.code == NOP)
+			x = x->next;
+		while (y && y->s.code == NOP)
+			y = y->next;
+		if (x == 0)
+			return y == 0;
+		if (y == 0)
+			return x == 0;
+		if (x->s.code != y->s.code || x->s.k != y->s.k)
+			return 0;
+		x = x->next;
+		y = y->next;
+	}
+}
+
+static inline int
+eq_blk(b0, b1)
+	struct block *b0, *b1;
+{
+	if (b0->s.code == b1->s.code &&
+	    b0->s.k == b1->s.k &&
+	    b0->et.succ == b1->et.succ &&
+	    b0->ef.succ == b1->ef.succ)
+		return eq_slist(b0->stmts, b1->stmts);
+	return 0;
+}
+
+static void
+intern_blocks(root)
+	struct block *root;
+{
+	struct block *p;
+	int i, j;
+	int done;
+ top:
+	done = 1;
+	for (i = 0; i < n_blocks; ++i)
+		blocks[i]->link = 0;
+
+	mark_code(root);
+
+	for (i = n_blocks - 1; --i >= 0; ) {
+		if (!isMarked(blocks[i]))
+			continue;
+		for (j = i + 1; j < n_blocks; ++j) {
+			if (!isMarked(blocks[j]))
+				continue;
+			if (eq_blk(blocks[i], blocks[j])) {
+				blocks[i]->link = blocks[j]->link ?
+					blocks[j]->link : blocks[j];
+				break;
+			}
+		}
+	}
+	for (i = 0; i < n_blocks; ++i) {
+		p = blocks[i];
+		if (JT(p) == 0)
+			continue;
+		if (JT(p)->link) {
+			done = 0;
+			JT(p) = JT(p)->link;
+		}
+		if (JF(p)->link) {
+			done = 0;
+			JF(p) = JF(p)->link;
+		}
+	}
+	if (!done)
+		goto top;
+}
+
+static void
+opt_cleanup()
+{
+	free((void *)vnode_base);
+	free((void *)vmap);
+	free((void *)edges);
+	free((void *)space);
+	free((void *)levels);
+	free((void *)blocks);
+}
+
+/*
+ * Return the number of stmts in 's'.
+ */
+static int
+slength(s)
+	struct slist *s;
+{
+	int n = 0;
+
+	for (; s; s = s->next)
+		if (s->s.code != NOP)
+			++n;
+	return n;
+}
+
+/*
+ * Return the number of nodes reachable by 'p'.
+ * All nodes should be initially unmarked.
+ */
+static int
+count_blocks(p)
+	struct block *p;
+{
+	if (p == 0 || isMarked(p))
+		return 0;
+	Mark(p);
+	return count_blocks(JT(p)) + count_blocks(JF(p)) + 1;
+}
+
+/*
+ * Do a depth first search on the flow graph, numbering the
+ * the basic blocks, and entering them into the 'blocks' array.`
+ */
+static void
+number_blks_r(p)
+	struct block *p;
+{
+	int n;
+
+	if (p == 0 || isMarked(p))
+		return;
+
+	Mark(p);
+	n = n_blocks++;
+	p->id = n;
+	blocks[n] = p;
+
+	number_blks_r(JT(p));
+	number_blks_r(JF(p));
+}
+
+/*
+ * Return the number of stmts in the flowgraph reachable by 'p'.
+ * The nodes should be unmarked before calling.
+ */
+static int
+count_stmts(p)
+	struct block *p;
+{
+	int n;
+
+	if (p == 0 || isMarked(p))
+		return 0;
+	Mark(p);
+	n = count_stmts(JT(p)) + count_stmts(JF(p));
+	return slength(p->stmts) + n + 1;
+}
+
+/*
+ * Allocate memory.  All allocation is done before optimization
+ * is begun.  A linear bound on the size of all data structures is computed
+ * from the total number of blocks and/or statements.
+ */
+static void
+opt_init(root)
+	struct block *root;
+{
+	u_long *p;
+	int i, n, max_stmts;
+
+	/*
+	 * First, count the blocks, so we can malloc an array to map
+	 * block number to block.  Then, put the blocks into the array.
+	 */
+	unMarkAll();
+	n = count_blocks(root);
+	blocks = (struct block **)malloc(n * sizeof(*blocks));
+	unMarkAll();
+	n_blocks = 0;
+	number_blks_r(root);
+
+	n_edges = 2 * n_blocks;
+	edges = (struct edge **)malloc(n_edges * sizeof(*edges));
+
+	/*
+	 * The number of levels is bounded by the number of nodes.
+	 */
+	levels = (struct block **)malloc(n_blocks * sizeof(*levels));
+
+	edgewords = n_edges / (8 * sizeof(u_long)) + 1;
+	nodewords = n_blocks / (8 * sizeof(u_long)) + 1;
+
+	/* XXX */
+	space = (u_long *)malloc(2 * n_blocks * nodewords * sizeof(*space)
+				 + n_edges * edgewords * sizeof(*space));
+	p = space;
+	all_dom_sets = p;
+	for (i = 0; i < n; ++i) {
+		blocks[i]->dom = p;
+		p += nodewords;
+	}
+	all_closure_sets = p;
+	for (i = 0; i < n; ++i) {
+		blocks[i]->closure = p;
+		p += nodewords;
+	}
+	all_edge_sets = p;
+	for (i = 0; i < n; ++i) {
+		register struct block *b = blocks[i];
+
+		b->et.edom = p;
+		p += edgewords;
+		b->ef.edom = p;
+		p += edgewords;
+		b->et.id = i;
+		edges[i] = &b->et;
+		b->ef.id = n_blocks + i;
+		edges[n_blocks + i] = &b->ef;
+		b->et.pred = b;
+		b->ef.pred = b;
+	}
+	max_stmts = 0;
+	for (i = 0; i < n; ++i)
+		max_stmts += slength(blocks[i]->stmts) + 1;
+	/*
+	 * We allocate at most 3 value numbers per statement,
+	 * so this is an upper bound on the number of valnodes
+	 * we'll need.
+	 */
+	maxval = 3 * max_stmts;
+	vmap = (struct vmapinfo *)malloc(maxval * sizeof(*vmap));
+	vnode_base = (struct valnode *)malloc(maxval * sizeof(*vmap));
+}
+
+/*
+ * Some pointers used to convert the basic block form of the code,
+ * into the array form that BPF requires.  'fstart' will point to
+ * the malloc'd array while 'ftail' is used during the recursive traversal.
+ */
+static struct bpf_insn *fstart;
+static struct bpf_insn *ftail;
+
+#ifdef BDEBUG
+int bids[1000];
+#endif
+
+static void
+convert_code_r(p)
+	struct block *p;
+{
+	struct bpf_insn *dst;
+	struct slist *src;
+	int slen;
+	u_int off;
+
+	if (p == 0 || isMarked(p))
+		return;
+	Mark(p);
+
+	convert_code_r(JF(p));
+	convert_code_r(JT(p));
+
+	slen = slength(p->stmts);
+	dst = ftail -= slen + 1;
+
+	p->offset = dst - fstart;
+
+	for (src = p->stmts; src; src = src->next) {
+		if (src->s.code == NOP)
+			continue;
+		dst->code = (u_short)src->s.code;
+		dst->k = src->s.k;
+		++dst;
+	}
+#ifdef BDEBUG
+	bids[dst - fstart] = p->id + 1;
+#endif
+	dst->code = (u_short)p->s.code;
+	dst->k = p->s.k;
+	if (JT(p)) {
+		off = JT(p)->offset - (p->offset + slen) - 1;
+		if (off >= 256)
+			bpf_error("long jumps not supported");
+		dst->jt = off;
+		off = JF(p)->offset - (p->offset + slen) - 1;
+		if (off >= 256)
+			bpf_error("long jumps not supported");
+		dst->jf = off;
+	}
+}
+
+
+/*
+ * Convert flowgraph intermediate representation to the
+ * BPF array representation.  Set *lenp to the number of instructions.
+ */
+struct bpf_insn *
+icode_to_fcode(root, lenp)
+	struct block *root;
+	int *lenp;
+{
+	int n;
+	struct bpf_insn *fp;
+
+	unMarkAll();
+	n = *lenp = count_stmts(root);
+
+	fp = (struct bpf_insn *)malloc(sizeof(*fp) * n);
+	memset((char *)fp, 0, sizeof(*fp) * n);
+	fstart = fp;
+	ftail = fp + n;
+
+	unMarkAll();
+	convert_code_r(root);
+
+	return fp;
+}
+
+#ifdef BDEBUG
+opt_dump(root)
+	struct block *root;
+{
+	struct bpf_program f;
+
+	memset(bids, 0, sizeof bids);
+	f.bf_insns = icode_to_fcode(root, &f.bf_len);
+	bpf_dump(&f, 1);
+	putchar('\n');
+	free((char *)f.bf_insns);
+}
+#endif