/* * output all code and labels in the peep list. */ void flush_peep() { if (opt_nopeep==FALSE) opt_peep(); /* do the peephole optimizations */ while( peep_head != NULL ) { if( peep_head->opcode == op_label ) put_label((int64_t)peep_head->oper1,"",GetNamespace(),'C'); else put_ocode(peep_head); peep_head = peep_head->fwd; } }
static void opt_blk(struct block *b, int do_stmts) { struct slist *s; struct edge *p; int i; bpf_int32 aval, xval; #if 0 for (s = b->stmts; s && s->next; s = s->next) if (BPF_CLASS(s->s.code) == BPF_JMP) { do_stmts = 0; break; } #endif /* * Initialize the atom values. */ p = b->in_edges; if (p == 0) { /* * We have no predecessors, so everything is undefined * upon entry to this block. */ memset((char *)b->val, 0, sizeof(b->val)); } else { /* * Inherit values from our predecessors. * * First, get the values from the predecessor along the * first edge leading to this node. */ memcpy((char *)b->val, (char *)p->pred->val, sizeof(b->val)); /* * Now look at all the other nodes leading to this node. * If, for the predecessor along that edge, a register * has a different value from the one we have (i.e., * control paths are merging, and the merging paths * assign different values to that register), give the * register the undefined value of 0. */ 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]; xval = b->val[X_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 or index register with a * value that is already there, or if this block is a return, * eliminate all the statements. * * XXX - what if it does a store? * * XXX - why does it matter whether we use anything from this * block? If the accumulator or index register doesn't change * its value, isn't that OK even if we use that value? * * XXX - if we load the accumulator with a different value, * and the block ends with a conditional branch, we obviously * can't eliminate it, as the branch depends on that value. * For the index register, the conditional branch only depends * on the index register value if the test is against the index * register value rather than a constant; if nothing uses the * value we put into the index register, and we're not testing * against the index register's value, and there aren't any * other problems that would keep us from eliminating this * block, can we eliminate it? */ if (do_stmts && ((b->out_use == 0 && aval != 0 && b->val[A_ATOM] == aval && xval != 0 && b->val[X_ATOM] == xval) || 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; }