[LLVMdev] Compile a large project with llvm?

[John Criswell]

Wink zhang wrote:
> Hi,
>
> How to compile a large project (such as Apache) by using llvm-gcc?
> I tried to replace CC with llvm-gcc and CFLAGS with -emit-llvm while 
> running configure, but it didn't work.
>   
If you just want to compile the program with llvm-gcc, then Diego's 
instructions are fine.

If, however, you want to do inter-procedural optimization or whole 
program analysis, then there's additional things you need to do.

If you just want to use LLVM's link-time optimizations, you will need to 
use the libLTO library with your linker.  Your linker, in turn, must be 
able to support plugins (like the gold linker, for example).  For 
directions on how to set up libLTO, see 
http://llvm.org/docs/LinkTimeOptimization.html and 
http://llvm.org/docs/GoldPlugin.html.

If you want to write and use your own link-time passes, then you have 
several options:

1) Modify the program's Makefiles to use llvm-ld to link bitcode files 
together.  This will allow you to generate a single bitcode image.

2) Modify libLTO to run your analysis and transform passes.  If you plan 
to work with several large applications, this is probably the way to 
go.  SAFECode has a version of libLTO that does whole-program analysis; 
you can find this tool in the safecode/tools/LTO directory in the 
SAFECode source code (directions for getting SAFECode are at 
http://safecode.cs.illinois.edu/downloads.html).  This approach can 
sometimes alleviate the need for changing the Makefiles.

-- John T.
> Thank you for your help.
>
> -Wink
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