Getting Started with LLVM System for Microsoft Visual Studio

The Visual Studio port at this time is experimental. It is suitable for use only 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 indirectly create executables by using the C back end.

To emphasize, there is no C/C++ front end currently available. llvm-gcc is based on GCC, which cannot be bootstrapped using VC++. Eventually there should be a llvm-gcc based on Cygwin or MinGW that is usable. There is also the option of generating bitcode files on Unix and copying them over to Windows. But be aware the odds of linking C++ code compiled with llvm-gcc with code compiled with VC++ is essentially zero.

The LLVM test suite cannot be run on the Visual Studio port at this time.

Most of the tools build and work. llvm-db does not build at this time. bugpoint does build, but does not work.

Additional information about the LLVM directory structure and tool chain can be found on the main Getting Started page.

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:
  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
Start Visual Studio
1. Simply double click on the solution file llvm/win32/llvm.sln.
Build the LLVM Suite:
1. Simply build the solution.
2. The Fibonacci project is a sample program that uses the JIT. Modify the project's debugging properties to provide a numeric command line argument. The program will print the corresponding fibonacci value.

It is strongly encouraged that you get the latest version from Subversion as changes are continually making the VS support better.

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 2003 is fine. The LLVM source tree and object files, libraries and executables will consume approximately 3GB.

You will need Visual Studio .NET 2003. Earlier versions cannot open the solution/project files. The VS 2005 beta can, but will migrate these files to its own format in the process. While it should work with the VS 2005 beta, there are no guarantees and there is no support for it at this time. It has been reported that VC++ Express also works.

If you plan to modify any .y or .l files, you will need to have bison and/or flex installed where Visual Studio can find them. Otherwise, you do not need them and the pre-generated files that come with the source tree will be used.

The remainder of this guide is meant to get you up and running with LLVM using Visual Studio and to give you some basic information about the LLVM environment.

Throughout this manual, the following names are used to denote paths specific to the local system and working environment. These are not environment variables you need to set but just strings used in the rest of this document below. In any of the examples below, simply replace each of these names with the appropriate pathname on your local system. All these paths are absolute:

SRC_ROOT: This is the top level directory of the LLVM source tree.
OBJ_ROOT: This is the top level directory of the LLVM object tree (i.e. the tree where object files and compiled programs will be placed. It is fixed at SRC_ROOT/win32).

The object files are placed under OBJ_ROOT/Debug for debug builds and OBJ_ROOT/Release for release (optimized) builds. These include both executables and libararies that your application can link against.

The files that configure would create when building on Unix are created by the Configure project and placed in OBJ_ROOT/llvm. You application must have OBJ_ROOT in its include search path just before SRC_ROOT/include.

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 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: while you cannot do this step on Windows, you can do it on a Unix system and transfer hello.bc to Windows. Important: transfer as a binary file!
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.
Use the llvm-dis utility to take a look at the LLVM assembly code:
```
% llvm-dis < hello.bc | more
```
Compile the program to C using the LLC code generator:
```
% llc -march=c hello.bc
```
Compile to binary using Microsoft C:
```
% cl hello.cbe.c
```
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.
Execute the native code program:
```
% hello.cbe.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: