rt: Don't hit TLS on upcall_vec_push unless necessary

src/rt/rust_util.h

@@ -189,6 +189,18 @@ inline void reserve_vec(rust_task* task, rust_vec** vpp, size_t size) {
     reserve_vec_exact(task, vpp, next_power_of_two(size));
 }
 
+// Call this when you don't already have a task pointer and it will
+// avoid hitting the TLS if it doesn't have to
+inline void reserve_vec_fast(rust_vec **vpp, size_t size) {
+    size_t new_size = next_power_of_two(size);
+    if (new_size > (*vpp)->alloc) {
+        rust_task *task = rust_task_thread::get_task();
+        size_t alloc_size = new_size + sizeof(rust_vec);
+        *vpp = (rust_vec*)task->kernel->realloc(*vpp, alloc_size);
+        (*vpp)->alloc = new_size;
+    }
+}
+
 typedef rust_vec rust_str;
 
 inline rust_str *