/*
* Copyright (c) 1988, 1989, 1990, 1991, 1993, 1994, 1995, 1996
* 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 const char rcsid[] =
"@(#) $Header: optimize.c,v 1.60 96/09/26 23:28:14 leres Exp $ (LBL)";
#endif
#include <sys/types.h>
#include <sys/time.h>
#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include "pcap-int.h"
#include "gencode.h"
#include "gnuc.h"
#ifdef HAVE_OS_PROTO_H
#include "os-proto.h"
#endif
#ifdef BDEBUG
extern int dflag;
#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 int F(int, int, int);
static inline void vstore(struct stmt *, int *, int, 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 *, int, int);
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 *, int[], 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 int convert_code_r(struct block *);
#ifdef BDEBUG
static void opt_dump(struct block *);
#endif
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;
bpf_u_int32 *space;
#define BITS_PER_WORD (8*sizeof(bpf_u_int32))
/*
* 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 bpf_u_int32 *_x = a, *_y = b;\
register int _n = n;\
while (--_n >= 0) *_x++ &= *_y++;\
}
/*
* a := a - b
*/
#define SET_SUBTRACT(a, b, n)\
{\
register bpf_u_int32 *_x = a, *_y = b;\
register int _n = n;\
while (--_n >= 0) *_x++ &=~ *_y++;\
}
/*
* a := a union b
*/
#define SET_UNION(a, b, n)\
{\
register bpf_u_int32 *_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;
bpf_u_int32 *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;
int v0, v1;
int 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;
bpf_int32 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 int
F(code, v0, v1)
int code;
int 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;
int *valp;
int newval;
int alter;
{
if (alter && *valp == newval)
s->code = NOP;
else
*valp = newval;
}
static void
fold_op(s, v0, v1)
struct stmt *s;
int v0, v1;
{
bpf_int32 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;
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) {
int op;
b->s.k += vmap[val].const_val;
op = BPF_OP(b->s.code);
if (op == BPF_JGT || op == BPF_JGE) {
struct block *t = JT(b);
JT(b) = JF(b);
JF(b) = t;
b->s.k += 0x80000000;
}
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)) {
int op;
b->s.k += last->s.k;
last->s.code = NOP;
op = BPF_OP(b->s.code);
if (op == BPF_JGT || op == BPF_JGE) {
struct block *t = JT(b);
JT(b) = JF(b);
JF(b) = t;
b->s.k += 0x80000000;
}
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) {
bpf_int32 v = vmap[val].const_val;
switch (BPF_OP(b->s.code)) {
case BPF_JEQ:
v = v == b->s.k;
break;
case BPF_JGT:
v = (unsigned)v > b->s.k;
break;
case BPF_JGE:
v = (unsigned)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;
int val[];
int alter;
{
int op;
int 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;
bpf_int32 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, or if this block is a return,
* eliminate all the statements.
*/
if (do_stmts &&
((b->out_use == 0 && aval != 0 &&b->val[A_ATOM] == aval) ||
BPF_CLASS(b->s.code) == BPF_RET)) {
if (b->stmts != 0) {
b->stmts = 0;
done = 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 bpf_u_int32 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;
/*
* If the root node is a return, then there is no
* point executing any statements (since the bpf machine
* has no side effects).
*/
if (BPF_CLASS((*b)->s.code) == BPF_RET)
(*b)->stmts = 0;
}
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;
{
bpf_u_int32 *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(bpf_u_int32)) + 1;
nodewords = n_blocks / (8 * sizeof(bpf_u_int32)) + 1;
/* XXX */
space = (bpf_u_int32 *)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
/*
* Returns true if successful. Returns false if a branch has
* an offset that is too large. If so, we have marked that
* branch so that on a subsequent iteration, it will be treated
* properly.
*/
static int
convert_code_r(p)
struct block *p;
{
struct bpf_insn *dst;
struct slist *src;
int slen;
u_int off;
int extrajmps; /* number of extra jumps inserted */
if (p == 0 || isMarked(p))
return (1);
Mark(p);
if (convert_code_r(JF(p)) == 0)
return (0);
if (convert_code_r(JT(p)) == 0)
return (0);
slen = slength(p->stmts);
dst = ftail -= (slen + 1 + p->longjt + p->longjf);
/* inflate length by any extra jumps */
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)) {
extrajmps = 0;
off = JT(p)->offset - (p->offset + slen) - 1;
if (off >= 256) {
/* offset too large for branch, must add a jump */
if (p->longjt == 0) {
/* mark this instruction and retry */
p->longjt++;
return(0);
}
/* branch if T to following jump */
dst->jt = extrajmps;
extrajmps++;
dst[extrajmps].code = BPF_JMP|BPF_JA;
dst[extrajmps].k = off - extrajmps;
}
else
dst->jt = off;
off = JF(p)->offset - (p->offset + slen) - 1;
if (off >= 256) {
/* offset too large for branch, must add a jump */
if (p->longjf == 0) {
/* mark this instruction and retry */
p->longjf++;
return(0);
}
/* branch if F to following jump */
/* if two jumps are inserted, F goes to second one */
dst->jf = extrajmps;
extrajmps++;
dst[extrajmps].code = BPF_JMP|BPF_JA;
dst[extrajmps].k = off - extrajmps;
}
else
dst->jf = off;
}
return (1);
}
/*
* 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;
/*
* Loop doing convert_codr_r() until no branches remain
* with too-large offsets.
*/
while (1) {
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();
if (convert_code_r(root))
break;
free(fp);
}
return fp;
}
#ifdef BDEBUG
static void
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
