Compiling Multiple Files

Clang Frontend
1

Clangers,

What’s the best way to compile multiple files in one LLVM IR file? It doesn’t appear that clang supports the gcc -combine feature.

2

Hi Ryan,

I would just compile to multiple IR files then link them together with llvm-link.

Would that work for you?

Cheers,

James

3

I believe it might actually. Do you know if it’s possible to inline functions without an external node? It doesn’t appear to be so.

4

Hi Ryan,

Do you know if it's possible to inline functions without an external node?

Sorry, I don't know to what you're referring here. Could you please rephrase? what do you mean be "external node"?

Cheers,

James

5

James,

Sure. I want to inline functions in a C program that has no external node, or “main”. So the “top” function is not main and there does not exist a main in the file.

Thanks.

6

Hi Ryan,

I see. Well, that shouldn't be an issue. If you link the bitcode files together with llvm-link you can then do several things:

(1) Run clang on it as you normally would with -O3 for maximum inlining
(2) Run 'llc' manually with -O3 and LTO, which will do the maximum link time optimisations.
(3) Run 'opt' manually with -O3, LTO which will produce another bitcode file, which you can then again give to Clang to codegen.

Cheers,

James

7

James,

Thanks. It wouldn’t take the LTO option; however, I can get it to inline using -cppgen=inline.

However, when I run clang the second time it gives me an error, stating that it expects a top level entity. I think I’ve run into this issue before. Any ideas?

8

Hi Ryan,

Well, when linking, it'll need a top level entity. Else what is it going to link to? (unless you're building a shared library?)