cpu: make local zero_val const, to avoid internal compiler error vs2019

[N-Dekker]

Declared the local variable zero_val within the function body of
im2col const, to avoid the following error from a Release build of
Visual Studio 2019 version 16.7.1 (compiler version 19.27.29111 for x64):

D:\oneDNN\src\cpu\gemm_convolution_utils.cpp(401): fatal error C1001: Internal compiler error.
(compiler file 'd:\agent_work\7\s\src\vctools\Compiler\Utc\src\p2\main.c', line 195)
To work around this problem, try simplifying or changing the program near the locations listed above.
If possible please provide a repro here: https://developercommunity.visualstudio.com
Please choose the Technical Support command on the Visual C++
Help menu, or open the Technical Support help file for more information
CL!RaiseException()+0x69
CL!RaiseException()+0x69
CL!CloseTypeServerPDB()+0x22e6b
CL!CloseTypeServerPDB()+0xcd30a
Done building project "dnnl_cpu.vcxproj" -- FAILED.

Related compiler problem report: "VS2019 Internal compiler error using
__restrict keyword in Release build"
https://developercommunity.visualstudio.com/content/problem/1145942/vs2019-internal-compiler-error-using-restrict-keyw.html

[emfomenk]

LGTM. Not sure why GitHub CI is unhappy.
Will check and merge this PR along with the changes from #580

Thank you!

[N-Dekker]

LGTM. Not sure why GitHub CI is unhappy.
Will check and merge this PR along with the changes from #580

Thanks @emfomenk ! The changes from #580? I guess you mean #801 😃

Did you or anyone else also get this internal compiler error in gemm_convolution_utils.cpp? It seems to me that it is a compiler bug introduced with a very recent update of VS2019 (Version 16.7 or 16.7.1, Compiler Version 19.27.29110 or 19.27.29111)

The compiler error could also be avoided by removing the __restrict keywords, but I guess that isn't what you would want!

[emfomenk]

Thanks @emfomenk ! The changes from #580? I guess you mean #801 😃

Oops, yeah, you are right.

Did you or anyone else also get this internal compiler error in gemm_convolution_utils.cpp? It seems to me that it is a compiler bug introduced with a very recent update of VS2019 (Version 16.7 or 16.7.1, Compiler Version 19.27.29110 or 19.27.29111)

No, we haven't seen such issue. But maybe we would once updated the version of cl. Currently we use 19.25.28612.

The compiler error could also be avoided by removing the __restrict keywords, but I guess that isn't what you would want!

Yeah, restrict helps with performance a bit. Let's keep it!

[N-Dekker]

By the way, this PR might even improve the runtime performance, as zero_val may not need to be captured anymore by the lambda's that access the variable, once it is declared const! As can be seen in the following example:

int main()
{
    const int zero_int = 0;
    // Empty capture list!
    return []{ return zero_int; }();
}

https://godbolt.org/z/7q1T7x

[emfomenk]

Merged!
Thank you for preventing us and out users to face the issue with VS 2019 :)

[N-Dekker]

Thank you for preventing us and our users to face the issue with VS 2019 :)

You're welcome @emfomenk! By the way, the current vs2019 version also gets an internal compiler error on the latest oneDNN release, v.1.6.1. If you're intending to still maintain oneDNN 1.6.x for a while, you might as well cherry-pick this very little commit onto your rls-v1.6 branch :)

And of course, if you agree that this is a serious compiler bug, you may vote or leave a comment at Visual Studio problem 1145942 - VS2019 Internal compiler error using __restrict keyword in Release build

[emfomenk]

If you're intending to still maintain oneDNN 1.6.x for a while, you might as well cherry-pick this very little commit onto your rls-v1.6 branch :)

Yeah, will do (I am currently working on some other fix for master and v1.6, so will cherry-pick your fix along with mine).
Thanks for the heads-up!

[N-Dekker]

As far as I can see, the compiler bug Visual Studio problem 1145942 - VS2019 Internal compiler error using __restrict keyword in Release build is fixed now, with VS2019 version 16.8.0, released on November 10, 2020.

I think so, because I just did a successful Release build of oneDNN-1.6.1 by VS2019 version 16.8.0. 😃 oneDNN-1.6.1 did not yet include this pull request, so it got an internal compiler error from VS2019 version 16.7.x.

Note that the compiler bug fix is not yet officially confirmed by Microsoft.