On Tue, Nov 21, 2017 at 11:01:52AM +1000, Nicholas Piggin wrote:

I just wonder are you doing this because there is some worthwhile
performance gain? Or to enable more testing and development of LTO?
Any clues for why a user would want to enable it.

I'm primarily interested in CFI, which with clang requires LTO; not
for the optimizations, but for source visibility. We do expect to see
performance improvements with LTO though, especially if combined with
PGO.

Thanks, if you could. Possibly file a request with LLVMgold too, it
seems to be that toolchain support for archives is quite strong, so it
will be good to keep pushing for that.

It turns out LLVMgold is fine with mixed IR/object archives, but we need
to use llvm-ar to generate symbol tables for them, and there are some
compatibility issues with objdump that I had to work around. I'll send
v3 for review once I receive some feedback for the clang/gold patches we
need first.

Sami