The Visual Studio port has some limitations. It is suitable for use if you are writing your own compiler front end or otherwise have a need to dynamically generate machine code. The JIT and interpreter are functional, but it is currently not possible to generate assembly code which is then assembled into an executable. You can output object files in COFF format, though. You can also indirectly create executables by using the C backend.

llvm-gcc is based on GCC, which cannot be bootstrapped using VC++. There are llvm-gcc binaries based on MinGW available on the LLVM download page. Eventually, Clang will be able to produce executables on Windows.

bugpoint does build, but does not work. The other tools 'should' work, but have not been fully tested.

Additional information about the LLVM directory structure and tool chain can be found on the main Getting Started 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 .NET 2005 SP1 is fine. The LLVM source tree and object files, libraries and executables will consume approximately 3GB.

You will need Visual Studio .NET 2005 SP1 or higher. The VS2005 SP1 beta and the normal VS2005 still have bugs that are not completely compatible. VS2003 would work except (at last check) it has a bug with friend classes that you can work-around with some minor code rewriting (and please submit a patch if you do). Earlier versions of Visual Studio do not support the C++ standard well enough and will not work.

You will also need the CMake build system since it generates the project files you will use to build with.

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:

1. Read the documentation.
2. Seriously, read the documentation.
3. Remember that you were warned twice about reading the documentation.
4. Get the Source Code
   • With the distributed files:
     1. cd where-you-want-llvm-to-live
     2. gunzip --stdout llvm-version.tar.gz | tar -xvf -       or use WinZip
     3. cd llvm
   • With anonymous Subversion access:
     1. cd where-you-want-llvm-to-live
     2. svn co http://llvm.org/svn/llvm-project/llvm-top/trunk llvm-top
     3. make checkout MODULE=llvm
     4. cd llvm
5. Use CMake to generate up-to-date project files:
   • Once CMake is installed then the most simple way is to just start the CMake GUI, select the directory where you have LLVM extracted to, and the default options should all be fine. One option you may really want to change, regardless of anything else, might be the CMAKE_INSTALL_PREFIX setting to select a directory to INSTALL to once compiling is complete, although installation is not mandatory for using LLVM. Another important option is LLVM_TARGETS_TO_BUILD, which controls the LLVM target architectures that are included on the build. If you want to run the example described below you must set that variable to "X86;CBackend".
   • See the LLVM CMake guide for detailed information about how to configure the LLVM build.
6. Start Visual Studio
   • In the directory you created the project files will have an llvm.sln file, just double-click on that to open Visual Studio.
7. Build the LLVM Suite:
   • The projects may still be built individually, but to build them all do not just select all of them in batch build (as some are meant as configuration projects), but rather select and build just the ALL_BUILD project to build everything, or the INSTALL project, which first builds the ALL_BUILD project, then installs the LLVM headers, libs, and other useful things to the directory set by the CMAKE_INSTALL_PREFIX setting when you first configured CMake.
   • The Fibonacci project is a sample program that uses the JIT. Modify the project's debugging properties to provide a numeric command line argument or run it from the command line. The program will print the corresponding fibonacci value.

1. First, create a simple C file, name it 'hello.c':

   #include <stdio.h>
   int main() {
     printf("hello world\n");
     return 0;
   }
   

2. Next, compile the C file into a LLVM bitcode file:

   % llvm-gcc -c hello.c -emit-llvm -o hello.bc
   

   This will create the result file hello.bc which is the LLVM bitcode that corresponds the 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.

   Note: you will need the llvm-gcc binaries from the LLVM download page

3. Run the program using the just-in-time compiler:

   % lli hello.bc
   

   Note: this will only work for trivial C programs. Non-trivial programs (and any C++ program) will have dependencies on the GCC runtime that won't be satisfied by the Microsoft runtime libraries.

4. Use the llvm-dis utility to take a look at the LLVM assembly code:

   % llvm-dis < hello.bc | more
   

5. Compile the program to C using the LLC code generator:

   % llc -march=c hello.bc
   

   Note: you need to add the C backend to the LLVM build, which amounts to setting the CMake variable LLVM_TARGETS_TO_BUILD to "X86;CBackend" when you generate the VS solution files. See the LLVM CMake guide for more information about how to configure the LLVM build.

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:

• LLVM homepage
• LLVM doxygen tree
• Starting a Project that Uses LLVM