Welcome to LLVM on Windows! This document only covers LLVM on Windows using Visual Studio, not mingw or cygwin. In order to get started, you first need to know some basic information.
There are many different projects that compose LLVM. The first piece is the LLVM suite. This contains all of the tools, libraries, and header files needed to use LLVM. It contains an assembler, disassembler, bitcode analyzer and bitcode optimizer. It also contains basic regression tests that can be used to test the LLVM tools and the Clang front end.
The second piece is the Clang front end. This component compiles C, C++, Objective C, and Objective C++ code into LLVM bitcode. Clang typically uses LLVM libraries to optimize the bitcode and emit machine code. LLVM fully supports the COFF object file format, which is compatible with all other existing Windows toolchains.
The last major part of LLVM, the execution Test Suite, does not run on Windows, and this document does not discuss it.
Additional information about the LLVM directory structure and tool chain can be found on the main Getting Started with the LLVM System page.
Before you begin to use the LLVM system, review the requirements given below. This may save you some trouble by knowing ahead of time what hardware and software you will need.
Any system that can adequately run Visual Studio 2015 is fine. The LLVM source tree and object files, libraries and executables will consume approximately 3GB.
You will need Visual Studio 2015 or higher, with the latest Update installed.
You will also need the CMake build system since it generates the project files you will use to build with.
If you would like to run the LLVM tests you will need Python. Version 2.7 and newer are known to work. You will need GnuWin32 tools, too.
Do not install the LLVM directory tree into a path containing spaces (e.g. C:\Documents and Settings\...) as the configure step will fail.
Here’s the short story for getting up and running quickly with LLVM:
Read the documentation.
Seriously, read the documentation.
Remember that you were warned twice about reading the documentation.
Get the Source Code
With the distributed files:
- cd <where-you-want-llvm-to-live>
- gunzip --stdout llvm-VERSION.tar.gz | tar -xvf - (or use WinZip)
- cd llvm
With anonymous Subversion access:
- cd <where-you-want-llvm-to-live>
- svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm
- cd llvm
Use CMake to generate up-to-date project files:
Start Visual Studio
Build the LLVM Suite:
Test LLVM in Visual Studio:
Test LLVM on the command line:
The LLVM tests can be run by changing directory to the llvm source directory and running:
C:\..\llvm> python ..\build\bin\llvm-lit --param build_config=Win32 --param build_mode=Debug --param llvm_site_config=../build/test/lit.site.cfg test
This example assumes that Python is in your PATH variable, you have built a Win32 Debug version of llvm with a standard out of line build. You should not see any unexpected failures, but will see many unsupported tests and expected failures.
A specific test or test directory can be run with:
C:\..\llvm> python ..\build\bin\llvm-lit --param build_config=Win32 --param build_mode=Debug --param llvm_site_config=../build/test/lit.site.cfg test/path/to/test
First, create a simple C file, name it ‘hello.c‘:
#include <stdio.h>
int main() {
printf("hello world\n");
return 0;
}
Next, compile the C file into an LLVM bitcode file:
C:\..> clang -c hello.c -emit-llvm -o hello.bc
This will create the result file hello.bc which is the LLVM bitcode that corresponds the compiled program and the library facilities that it required. You can execute this file directly using lli tool, compile it to native assembly with the llc, optimize or analyze it further with the opt tool, etc.
Alternatively you can directly output an executable with clang with:
C:\..> clang hello.c -o hello.exe
The -o hello.exe is required because clang currently outputs a.out when neither -o nor -c are given.
Run the program using the just-in-time compiler:
C:\..> lli hello.bc
Use the llvm-dis utility to take a look at the LLVM assembly code:
C:\..> llvm-dis < hello.bc | more
Compile the program to object code using the LLC code generator:
C:\..> llc -filetype=obj hello.bc
Link to binary using Microsoft link:
C:\..> link hello.obj -defaultlib:libcmt
Execute the native code program:
C:\..> hello.exe
If you are having problems building or using LLVM, or if you have any other general questions about LLVM, please consult the Frequently Asked Questions page.
This document is just an introduction to how to use LLVM to do some simple things... there are many more interesting and complicated things that you can do that aren’t documented here (but we’ll gladly accept a patch if you want to write something up!). For more information about LLVM, check out: