[llvm] r234535 - Simplify use of formatted_raw_ostream.

[Rafael Espíndola]

> Thanks for the patch!
> The slowdown is non-negligible,  but I’m not sure I understand what you mean by "The outer caching is
> non-virtual”.

The write call in raw_ostream in non-virtual and writes to a buffer.
If buffering is disable, it just calls write_impl, which is virtual.
In the case of formatted_raw_ostream that then puts data in a buffer.

> Can you try "llvm-mc all-of-clang-lto.s -o - > /dev/null”?

That still puts the output in a file and will buffer the same.

BTW, at which point do you need to access the generated assembly?
Could MCAsmStreamer::FinishImpl flush the stream?

Cheers,
Rafael