[LLVMdev] Compile programs with the LLVM Compiler as a gsoc project

[Andrew Lenharth]

On Sun, Mar 30, 2008 at 11:34 PM, Kumaripaba Miyurusara Atukorala
<paba50 at gmail.com> wrote:
> 1) I thought of taking the gcc compiler and compiling it with llvm since it
> is easier to make test cases to test the system. Is gcc compiler already
> built with llvm? if so I have the linux kernel as the second option. What is
> your openion on this ?

We rutinely compile linux with llvm (and do LTO and custom transforms
on it).  So that would be novel.  However, several existing
optimizations break the linux kernel (and several bits of the linux
kernel are buggy and just happen to work with gcc (aka their
correctness depends on getting a pseudo random value from reading an
unitinialized variable)).  Tracking down and distilling minimal test
cases for the broken optimizations would be really useful (and very
painful).

There are really 2 ways to do this.  First is to do it manually.  find
the optimization that breaks the kernel, find the function, see what
it does that causes the breakage, etc.  OR, you could extend bugpoint
to be able to launch an external tool that performed the final linking
and testing of the bytecode.  This would be nice because then bugpoint
would give the tool two pieces, the tool would assemble the two pieces
into a booting kernel, run the kernel in an emulator and report back
to bugpoint on whether it suceeded or failed.

Obviously the second one would be a more useful addition to the llvm
too chain, whereas the first method would be invaluable hard manual
debugging.

Andrew