看看内层循环的j是否有问题，一定要在第一层循环内初始化！
应该只有本蒟蒻用x，y当变量调了一天吧……

void update(int x, int y, T c) {
	for (; x <= n; x += lowbit(x)) {
		for (; y <= m; y += lowbit(y)) {
			t[x][y] += c;
		}
	}
}

应为：

void update(int x, int y, T c) {
	for (int i = x; i <= n; i += lowbit(i)) {
		for (int j = y; j <= m; j += lowbit(j)) {
			t[i][j] += c;
		}
	}
}