llvm-link issues when combining BC files.

[DStaelens]

I am working on some opt transforms that require a monolithic ir file. Compiling the two simple .cpp files to .bc files and linking them with llvm-link causes the MSVC linker to fail with the error below. I do not have this issue if I use a compiled version of clang with MINGW, but for release I need the MSVC version.

Steps to reproduce:

clang.exe -emit-llvm -c one.cpp two.cpp
llvm-link.exe one.bc two.bc -o combined.bc
clang.exe combined.bc -o test3.exe
combined-2b91e8.o : fatal error LNK1243: invalid or corrupt file: COMDAT section 0x17B associated with following section 0x17E clang.exe: error: linker command failed with exit code 1243 (use -v to see invocation)

Note that if I just clang.exe the two bc files out to an executable it works.
one.cpp.txt
two.cpp.txt
two.h.txt

[aaronsm]

Try clang-cl instead of clang since you are using the VS linker.

[DStaelens]

Seems to have the same issue, but maybe I'm doing something wrong.. Here's what I did:
clang-cl.exe -Xclang -emit-llvm -c one.cpp two.cpp
The above command created one.obj and two.obj, but they did seem to be bc files.
llvm-link.exe one.obj two.obj -o combined.bc
I could not figure out how to directly compile bc files with clang-cl, so I did..
llc.exe -filetype=obj combined.bc -o combined.obj
clang-cl.exe combined.obj -o test.exe
Received same COMDAT error as before.

[aaronsm]

Your command line looks okay. If you use clang-cl it will generate bc files. If you use /FA it will generate ll files but clang-cl will also error out because its not setup properly to do that.

I was able to reproduce your problem but I don't think this is a VS linker issue. This is most likely a problem in llvm-link. You'd probably get a better response on the LLVM developer mailing list since Microsoft doesn't develop clang-cl or llvm-link or llc.