有什么方法可以在不需要合成的情况下进行面积估算

这是非常可能的。
为了获得准确的估计，有必要了解FPGA将要执行的功能以及如何在FPGA架构中实现它们。
例如，可以估计简单设计具有单个8状态机，三个8位比较器和8×512 FIFO。
使用该信息以及您使用的特定FPGA中将需要多少寄存器和查找表（LUT）将为您提供粗略的使用估计。
除非您能够完全理解设计及其实现的方式，否则明智的做法是将其视为保守估计并将其乘以一个因子来确定您的部分。
速度也是一个因素，因为高度利用的部分难以以最大频率运行，并且将影响用于不同逻辑的架构（例如状态机）。
-DD



以下为原文

It is very possible. 
 
To get an accurate estimation it is necessary to understand the functions the FPGA will be performing and how they will be implemented in the FPGA fabric.  For instance a simple design may be estimated to have a single 8 state state machine, three 8-bit comparators, and a 8x512 FIFO.  Using that information and how many registers and look  up tables (LUT) will be required in the specific FPGA you are using will give you a rough estimate of the usage.  Unless you can fully understand the design and the way it implements it is wise to treat this as a conservative estimate and multiply it by a factor to size your part.  The speed is also a factor as a part that is highly utilized is harder to make run at the maximum frequency and will affect what architecture is used for different logic (for example state machines).
 
-DD