How to disable only SIMD auto-vectorization optimization in Visual Studio 2015 (for C++)?

Question

My question is simply how can I disable only the SIMD auto-vectorization optimization (keeping other optimizations of Release mode) in Visual Studio 2015 for:

1) the whole project being compiled;

2) for parts of the code.

In the first case, I would like to learn how to disable it for the whole project. For the second case, I would like to know whether it is also possible to do it for specific areas of the code, similarly to what is possible for all optimizations when using #pragma optimize("", off) and #pragma optimize("", on).

The purpose of this is performance comparison of some manually optimized code against the compiler's automatic SIMD vectorization.

Answer 1

The Visual C++ auto-vectorizer is automatically enabled when building with /O2 or /Ox.

To see what it is doing, build with /Qvec-report:1 or /Qvec-report:2.

You can disable it for specific loops by using #pragma loop(no_vector)

See MSDN

There's no documented way to disable the auto-vectorizer globally while keeping standard optimizations enabled.

For more information, see this blog series, this video, and the Auto-Vectorization Cookbook