Chen, Thank you. When I replaced gcc by clang, how do I ensure that the clang use the LLVM backend that is already modified by myself? I am trying to modified the source code for the register allocator of the llvm and want to apply this modification to the clang compiler. I see that when I compile the whole modified llvm project from scratch, it does not produce a Clang executable. The clang that exists in my computer is from the package I downloaded from the internet (I downloaded this in need of compiling the llvm project. ). Regards, Z. Wu -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20120703/688b95ad/attachment.html>