[llvm-commits] [PATCH] New external2availableexternally pass (issue166075)

[Jeffrey Yasskin]

On Sun, Dec 6, 2009 at 12:35 AM, Duncan Sands <baldrick at free.fr> wrote:
> Hi,
>
>> When we have a runtime library, it's useful to expose that library to
>> the optimizers, but it's bad to ask LLVM to actually codegen the
>> library's code a second time.
>
> I didn't look at the code, but it sounds like it gives functions
> available_externally linkage.

Yes.

> Why not have the front-end output
> the functions with available_externally linkage in the first place?

1. I knew how to write this pass; modifying clang would have required
learning more.
2. It seems useful to be able to compile the runtime library to .bc
with external functions, codegen the .o from that for the real runtime
library, and then convert it to the available_externally form for use
by application optimizers and JITs. A front-end flag would require
compiling from C twice.
3. dgregor endorsed the idea of this patch, although I didn't mention
the possibility of a clang flag.

But let me know if an extra clang flag would be preferable. I'll
probably wind up writing a standalone tool for Unladen instead of
shaving that yak, but I wouldn't object strongly to dropping this
patch.