/* $OpenBSD: optimize.c,v 1.5 1996/09/16 02:33:07 tholo Exp $ */ /* * 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 char rcsid[] = "@(#) Header: optimize.c,v 1.58 96/06/16 22:36:59 leres Exp (LBL)"; #endif #include #include #include #include #include #include #ifdef HAVE_OS_PROTO_H #include "os-proto.h" #endif #include "pcap-int.h" #include "gencode.h" #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