How can I run the MSVC preprocessor and compiler in two separate steps?

Question

I'd like to run the Microsoft Visual Studio Compiler cl.exe without invoking the preprocessor. Is this possible? I thought that simply compiling preprocessed source code (using the /c flag) would make the preprocessor run being a no-op, but apparently that's not the case. I did a bit of benchmarking. Here's a little source file (main.cpp) which just includes some code:

#include <iostream>
#include <string>
#include <windows.h>

Here are some different compiler invocations and their timings:

1: cl /c main.cpp                             ~1.02s
2: cl /EP main.cpp > main-preprocessed.cpp    ~0.5s
3: cl /c main-preprocessed.cpp                ~0.75s

It seems that compiling preprocessed source code is already a bit faster (the preprocessor doesn't need to do anything). However, the difference between 1 and 2 suggests that the actual compiler and assembler just needs a bit more 0.5s. So compiling the preprocessed source code (as done in step 3) is a bit slower than I hoped.

Is there any way to just run the compiler and assembler, without invoking the preprocessor? I'm interested in solutions for MSVC6 up to MSVC10.

Answer 1

To my knowledge there is no way to run the compiler without the preprocessor (regardless of the fact that it doesn't do anything.

However seperating the 2 stages will obviously be slower as you are adding a write to file and then read back of that file. If it doesn't need to do those writes it can hold it in memory and you save a tonne of time waiting for the disk to be written to & read from.

ie Even if you could disable the pre-processor it would still be slower than running both stages simultaneously.