[eigen] Windows Testing Issues (was: 3.3 branch state)

[Rob Conde <rob.conde@xxxxxxxxxxxxxxxx>]

Starting a new thread as the topic has become more general. 

Thanks David for your test...I'm only seeing the issue on Windows at the moment. I'm on Windows 10, with 16GB RAM, 4 core (8 hyperthreaded) CPU, and an SSD with plenty of space...it's not a powerhouse, but it's a reasonably recent machine.

Ok - so I took the head, made some small alterations to the CMake files to run using C++17 and built the tests with Visual Studio 2017 Win64. Firstly there are several build errors:

• cxx11_tensor_block_access
• This fails to compile because it uses std::random_shuffle which was removed in C++17. Interestingly, msvc seems to be the most standards compliant here. It's a simple fix.
• cxx11_tensor_image_patch_1/2/3/4/5/6/7
  
• Compiler runs out of heap space
• cxx11_tensor_reduction
  
• error C2666: 'Eigen::half_impl::operator /': 14 overloads have similar conversions
  
• error C2672: 'verifyIsApprox': no matching overloaded function found

More problematic are the build times in a release build. I created a summary but unfortunately I found that at least some of the tests which took a long time were quick when compiled alone (this compilation was done through visual studio where they built in parallel). In any case, I went back and ran 3.3.7 using ctest and the default CMake file....which compiles only 1 project at a time. This has been running for about 11 hours now (still on the build part). Obviously this is a visual studio issue, but I'm not sure when it was introduced. We're not seeing anything like this in the our usage of Eigen...although to a smaller degree it might be hard to tease out of the larger picture.

Rob