bpf: clean up visit_insn()'s instruction processing

Instead of referencing processed instruction repeatedly as insns[t]
throughout entire visit_insn() function, take a local insn pointer and
work with it in a cleaner way.

It makes enhancing this function further a bit easier as well.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230302235015.2044271-7-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/verifier.c

@@ -13484,44 +13484,43 @@ static int visit_func_call_insn(int t, struct bpf_insn *insns,
  */
 static int visit_insn(int t, struct bpf_verifier_env *env)
 {
-	struct bpf_insn *insns = env->prog->insnsi;
+	struct bpf_insn *insns = env->prog->insnsi, *insn = &insns[t];
 	int ret;
 
-	if (bpf_pseudo_func(insns + t))
+	if (bpf_pseudo_func(insn))
 		return visit_func_call_insn(t, insns, env, true);
 
 	/* All non-branch instructions have a single fall-through edge. */
-	if (BPF_CLASS(insns[t].code) != BPF_JMP &&
-	    BPF_CLASS(insns[t].code) != BPF_JMP32)
+	if (BPF_CLASS(insn->code) != BPF_JMP &&
+	    BPF_CLASS(insn->code) != BPF_JMP32)
 		return push_insn(t, t + 1, FALLTHROUGH, env, false);
 
-	switch (BPF_OP(insns[t].code)) {
+	switch (BPF_OP(insn->code)) {
 	case BPF_EXIT:
 		return DONE_EXPLORING;
 
 	case BPF_CALL:
-		if (insns[t].imm == BPF_FUNC_timer_set_callback)
+		if (insn->imm == BPF_FUNC_timer_set_callback)
 			/* Mark this call insn as a prune point to trigger
 			 * is_state_visited() check before call itself is
 			 * processed by __check_func_call(). Otherwise new
 			 * async state will be pushed for further exploration.
 			 */
 			mark_prune_point(env, t);
-		return visit_func_call_insn(t, insns, env,
-					    insns[t].src_reg == BPF_PSEUDO_CALL);
+		return visit_func_call_insn(t, insns, env, insn->src_reg == BPF_PSEUDO_CALL);
 
 	case BPF_JA:
-		if (BPF_SRC(insns[t].code) != BPF_K)
+		if (BPF_SRC(insn->code) != BPF_K)
 			return -EINVAL;
 
 		/* unconditional jump with single edge */
-		ret = push_insn(t, t + insns[t].off + 1, FALLTHROUGH, env,
+		ret = push_insn(t, t + insn->off + 1, FALLTHROUGH, env,
 				true);
 		if (ret)
 			return ret;
 
-		mark_prune_point(env, t + insns[t].off + 1);
-		mark_jmp_point(env, t + insns[t].off + 1);
+		mark_prune_point(env, t + insn->off + 1);
+		mark_jmp_point(env, t + insn->off + 1);
 
 		return ret;
 
@@ -13533,7 +13532,7 @@ static int visit_insn(int t, struct bpf_verifier_env *env)
 		if (ret)
 			return ret;
 
-		return push_insn(t, t + insns[t].off + 1, BRANCH, env, true);
+		return push_insn(t, t + insn->off + 1, BRANCH, env, true);
 	}
 }