MINOR: vars: remove the emptiness tests in callers before pruning

All callers of vars_prune_* currently check the list for emptiness.
Let's leave that to vars_prune() itself, it will ease some changes in
the code. Thanks to the previous inlining of the vars_prune() function,
there's no performance loss, and even a very tiny 0.1% gain.

include/haproxy/vars.h

@@ -85,6 +85,9 @@ static inline void vars_prune(struct vars *vars, struct session *sess, struct st
 		size += var_clear(var, 1);
 	}
 
+	if (!size)
+		return;
+
 	var_accounting_diff(vars, sess, strm, -size);
 }
 

src/http_ana.c

@@ -2967,8 +2967,7 @@ int http_eval_after_res_rules(struct stream *s)
 
 	/* prune the request variables if not already done and swap to the response variables. */
 	if (s->vars_reqres.scope != SCOPE_RES) {
-		if (!LIST_ISEMPTY(&s->vars_reqres.head))
-			vars_prune(&s->vars_reqres, s->sess, s);
+		vars_prune(&s->vars_reqres, s->sess, s);
 		vars_init_head(&s->vars_reqres, SCOPE_RES);
 	}
 
@@ -5094,10 +5093,8 @@ void http_destroy_txn(struct stream *s)
 	txn->srv_cookie = NULL;
 	txn->cli_cookie = NULL;
 
-	if (!LIST_ISEMPTY(&s->vars_txn.head))
-		vars_prune(&s->vars_txn, s->sess, s);
-	if (!LIST_ISEMPTY(&s->vars_reqres.head))
-		vars_prune(&s->vars_reqres, s->sess, s);
+	vars_prune(&s->vars_txn, s->sess, s);
+	vars_prune(&s->vars_reqres, s->sess, s);
 
 	b_free(&txn->l7_buffer);
 

src/stream.c

@@ -695,10 +695,8 @@ void stream_free(struct stream *s)
 	}
 
 	/* Cleanup all variable contexts. */
-	if (!LIST_ISEMPTY(&s->vars_txn.head))
-		vars_prune(&s->vars_txn, s->sess, s);
-	if (!LIST_ISEMPTY(&s->vars_reqres.head))
-		vars_prune(&s->vars_reqres, s->sess, s);
+	vars_prune(&s->vars_txn, s->sess, s);
+	vars_prune(&s->vars_reqres, s->sess, s);
 
 	stream_store_counters(s);
 	pool_free(pool_head_stk_ctr, s->stkctr);
@@ -2309,8 +2307,7 @@ struct task *process_stream(struct task *t, void *context, unsigned int state)
 	if (sc_state_in(scb->state, SC_SB_REQ|SC_SB_QUE|SC_SB_TAR|SC_SB_ASS)) {
 		/* prune the request variables and swap to the response variables. */
 		if (s->vars_reqres.scope != SCOPE_RES) {
-			if (!LIST_ISEMPTY(&s->vars_reqres.head))
-				vars_prune(&s->vars_reqres, s->sess, s);
+			vars_prune(&s->vars_reqres, s->sess, s);
 			vars_init_head(&s->vars_reqres, SCOPE_RES);
 		}
 

src/vars.c

@@ -207,6 +207,9 @@ void vars_prune_per_sess(struct vars *vars)
 		size += var_clear(var, 1);
 	}
 
+	if (!size)
+		return;
+
 	if (var_sess_limit)
 		_HA_ATOMIC_SUB(&vars->size, size);
 	if (var_proc_limit || var_global_limit)