Looks like the reverted commit broke the windows build.

Windows build was broken because of unrelated to commit issue - linker falls back (because it runs out of memory) to another linker that didn't support a command line option.

@peterjc123 / @yf225 have you seen the error on https://ci.pytorch.org/jenkins/job/pytorch-builds/job/pytorch-win-ws2016-cuda9-cudnn7-py3-build/23709//console before? In particular what @ilia-cher is referring to is this:

06:02:02 LINK : the 32-bit linker (C:\PROGRA~2\MIB055~1\2017\COMMUN~1\VC\Tools\MSVC\1411~1.255\bin\Hostx86\x64\link.exe) ran out of heap space; restarting link with the 64-bit linker (C:\Program Files\Git\usr\bin\link.exe)
06:02:02 link: unknown option -- L

is this an actual problem with the commit or do we need to change the build / build config?

cc. @Yangqing

I'm pretty sure it is a build script issue and not the commit, but I can accept and send a new pr and lets recheck everything

leaving this open for discussion, but don't commit because phabricator diff isn't valid.

@gchanan According to this post, this problem can be solved by setting the environmental variable PreferredToolArchitecture to x64.

I'm a little confused by the discussion here, because the CI results seem to claim the Windows builds passed?

@ezyang I guess that this PR reverts the change that may cause the aforementioned error. Let's switch the default to the x64 toolchain and then it'll be fine.

06:02:02 LINK : the 32-bit linker (C:\PROGRA~2\MIB055~1\2017\COMMUN~1\VC\Tools\MSVC\1411~1.255\bin\Hostx86\x64\link.exe) ran out of heap space; restarting link with the 64-bit linker (C:\Program Files\Git\usr\bin\link.exe)

Isn't a build error. The build will succeed, but it will take longer to link, as it's basically trying to link with the 32-bit hosted linker, which fails because the 32-bit address space is too small to be able to link successfully, so it runs the 64-bit hosted linker which then links successfully.

TLDR; The x86_amd64 MSVC toolchain is 32-bit binaries cross-compiling for amd64, and if the linker runs out of memory, it starts the linker from the amd64 (aka. amd64_amd64) toolchain, which is a 64-bit binary and has enough memory to complete.

@Orvid Yes, you are right. But the alternative x64 linker C:\Program Files\Git\usr\bin\link.exe is not what we want here. So #12446 is created.