Instructions to build Glow tools for win x86 using the MSYS environme…

…nt (#3640)

Summary:
**Summary**
Add documentation with instructions to build Glow for Windows x86 using the MSYS MINGW environment.
This is oriented more towards delivering the Glow front-end tools (e.g. image-classifier) on the windows side for an out-of-the-box experience with Glow for Windows users (and not developers).
If users are happy with the user experience and functionality, they might become contributors (like myself).

**Documentation**
Added GlowWindowsBuildx86.md

**Fixes**
In order for the windows build to work some Cmake fixes were required.
Also the msys build signaled a warning in Type.h which is a potential bug (fixed that).

**Test Plan**
None. I guess you should try to follow the instructions and verify the build works.
You might also have a look on the compile warnings and see if there are some serious problems there (like I spotted the problem from Type.h).

**Proposal**
To reach more to end-users which are non-experts and want to give Glow a try using their Windows machine (very common case) using an out-of-the-box deliverable, I propose:

1. Automatize the windows build using the instructions I gave and insert the windows build as a stage in the CI pipeline. All that is required is a windows server on your side, setup the msys environment once, and run some automated script to build (the build itself takes only a couple of minutes)
2. Provide a link on the Glow front page to the latest Windows build (personally I would find that extremely useful - other might as well).

I attached a sketch of the bash script which does the build and package it. The package should also contain the "dot.exe" utility which I find extremely useful for converting the dot file generated with "-dump-graph-DAG" option to PDF for graph inspection with the command:
`dot -Tpdf graph.dot -o graph.pdf -Nfontname="Times New Roman,"`
[glow-build-win-x64.sh.txt](https://github.com/pytorch/glow/files/3743728/glow-build-win-x64.sh.txt)
The bash script can be called from the Windows cmd without entering the msys2 shell like this:
`C:/msys64/msys2_shell.cmd  -mingw64  -where C:/msys64/mingw64  -c "./glow-build-win-x64.sh"`
assuming the script is located in _C:/msys64/mingw64/glow-build-win-x64.sh_
Pull Request resolved: #3640

Differential Revision: D18375939

Pulled By: jfix71

fbshipit-source-id: 65339f78e61f7a0da8eb116550f74183bc388ed4

CMakeLists.txt

@@ -82,18 +82,18 @@ add_custom_target(CollectHeaders SOURCES ${header_files})
 find_package(Git)
 # Get the commit's short SHA1
 execute_process(COMMAND
-  "${GIT_EXECUTABLE}" log -1 --pretty=format:"%h"
+  "${GIT_EXECUTABLE}" log -1 --pretty=format:%h
   WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
   OUTPUT_VARIABLE GIT_SHA1
   ERROR_QUIET OUTPUT_STRIP_TRAILING_WHITESPACE)
-add_definitions("-DGIT_SHA1=${GIT_SHA1}")
+add_definitions("-DGIT_SHA1=\"${GIT_SHA1}\"")
 # Get the date of the commit
 execute_process(COMMAND
-  "${GIT_EXECUTABLE}" log -1 --pretty=format:"%ad" --date=short
+  "${GIT_EXECUTABLE}" log -1 --pretty=format:%ad --date=short
   WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
   OUTPUT_VARIABLE GIT_DATE
   ERROR_QUIET OUTPUT_STRIP_TRAILING_WHITESPACE)
-add_definitions("-DGIT_DATE=${GIT_DATE}")
+add_definitions("-DGIT_DATE=\"${GIT_DATE}\"")
 
 find_package(PNG)
 if(PNG_FOUND)

docs/GlowWindowsBuildx86.md

@@ -0,0 +1,98 @@
+## Build Glow for Windows x86:
+------------------------------
+
+This document provides a short description about how to build Glow for Windows
+using the MSYS2 MINGW build environment. The instructions below apply for the
+**x86_64** build (64 bit). For the **x86** target build (32 bit) the instructions
+are similar (replace *mingw64* with *mingw32* in all the instructions below).
+
+### Setup the MSYS2 build environment:
+1. Download and install Msys2 from the following location:
+
+   http://repo.msys2.org/distrib/x86_64/msys2-x86_64-20190524.exe
+
+2. Start the Msys2 MinGW64 shell from the windows command prompt.
+   All the subsequent commands will be executed in the Msys2 shell.
+
+   ```
+   C:\msys64\msys2_shell.cmd -mingw64
+   ```
+
+3. Install LLVM 8.0.1 manually (make sure NOT to install the latest available LLVM).
+   Do NOT use the command "**pacman -Su**" for updating all the installed packages since 
+   Glow requires a specific LLVM version. Execute the commands below one at a time.
+
+   ```
+   wget http://repo.msys2.org/mingw/x86_64/mingw-w64-x86_64-llvm-8.0.1-1-any.pkg.tar.xz
+   wget http://repo.msys2.org/mingw/x86_64/mingw-w64-x86_64-clang-8.0.1-1-any.pkg.tar.xz
+   wget http://repo.msys2.org/mingw/x86_64/mingw-w64-x86_64-polly-8.0.1-1-any.pkg.tar.xz
+   pacman -U mingw-w64-x86_64-llvm-8.0.1-1-any.pkg.tar.xz
+   pacman -U mingw-w64-x86_64-clang-8.0.1-1-any.pkg.tar.xz
+   pacman -U mingw-w64-x86_64-polly-8.0.1-1-any.pkg.tar.xz
+   rm mingw-w64-x86_64-llvm-8.0.1-1-any.pkg.tar.xz
+   rm mingw-w64-x86_64-clang-8.0.1-1-any.pkg.tar.xz
+   rm mingw-w64-x86_64-polly-8.0.1-1-any.pkg.tar.xz
+   ```
+
+4. Install the dependencies required for Glow. During package installation it might be
+   required to restart the Msys2 shell. Execute the commands below one at a time.
+
+   ```
+   pacman -Sy
+   pacman -S base-devel zip git mingw-w64-x86_64-toolchain
+   pacman -S make mingw-w64-x86_64-cmake mingw-w64-x86_64-protobuf
+   pacman -S mingw-w64-x86_64-libpng mingw-w64-x86_64-graphviz mingw-w64-x86_64-python3
+   pacman -S mingw-w64-x86_64-glog
+   ```
+
+### Build Glow:
+1. Restart the Msys2 MinGW64 shell from the windows command prompt:
+
+   ```
+   C:\msys64\msys2_shell.cmd -mingw64
+   ```
+
+2. Clone the Glow repository:
+
+   ```
+   cd /mingw64
+   git clone https://github.com/pytorch/glow.git
+   ```
+
+3. Update the submodules:
+
+   ```
+   cd glow
+   git submodule update --init --recursive
+   cd ..
+   ```
+
+4. Configure Cmake:
+
+   ```
+   mkdir glow_build
+   cd glow_build
+   cmake -G "MSYS Makefiles" -DCMAKE_BUILD_TYPE=Release ../glow/
+   ```
+
+5. Build the project:
+
+   ```
+   make -j 8
+   cd ..
+   ```
+
+6. Package Glow (apart from the executables some DLL dependencies are required from the Msys2 environment):
+
+   ```
+   mkdir glow_package
+   cp glow_build/bin/model-compiler.exe glow_package
+   cp glow_build/bin/model-runner.exe glow_package
+   cp glow_build/bin/text-translator.exe glow_package
+   cp /mingw64/bin/libstdc++-6.dll glow_package
+   cp /mingw64/bin/zlib1.dll glow_package
+   cp /mingw64/bin/libwinpthread-1.dll glow_package
+   cp /mingw64/bin/libgcc_s_seh-1.dll glow_package
+   cp /mingw64/bin/libprotobuf.dll glow_package
+   cp /mingw64/bin/libpng16-16.dll glow_package
+   ```

lib/Backends/CPU/CMakeLists.txt

@@ -13,7 +13,10 @@ if(NOT LLVM_LINK_BIN)
   if(MSVC)
     set(LLVM_LINK_BIN ${LLVM_BINARY_DIR}/$(Configuration)/bin/llvm-link)
   else()
-    set(LLVM_LINK_BIN ${LLVM_BINARY_DIR}/bin/llvm-link)
+    find_program(LLVM_LINK_BIN NAMES llvm-link)
+    if(NOT EXISTS ${LLVM_LINK_BIN})
+      set(LLVM_LINK_BIN ${LLVM_BINARY_DIR}/bin/llvm-link)
+    endif()
   endif()
 endif()
 if(NOT EXISTS ${LLVM_LINK_BIN} AND NOT MSVC)