On 6/19/19 3:21 AM, Martin Liška wrote: > Hi. > > I've written a patch draft that replaces zlib with the zstd compression > algorithm ([1]) > in LTO. I'm also sending statistics that are collected for couple of quite > big C++ source > files. Observation I did: > > - LTO stream compression takes 3-4% of LGEN compile time > - zstd in default compression level (3) generated slighly smaller LTO elf > files > - zstd compression is 4-8x faster > - decompression is quite negligible, but for a bigger project (godot) I can > reduction from 1.37 to 0.53 seconds > - ZSTD API is much simpler to use > > Suggestion based on the observation: > - I would suggest to make zstd optional (--enable-zstd) and one would > use #include <zstd> + -lzstd > - I like the default level as we want to mainly speed up LTO compilation > - we can provide an option to control algorithm (-flto-compression-algorithm), > similarly to -flto-compression-level > - we can discuss possible compression of LTO bytecode that is distributed > between WPA > stage and individual LTRANS phases. Presumably the reason we're not being more aggressive about switching is the build/run time dependency on zstd? I wonder if we could default to zstd and fallback to zlib when zstd isn't available?
jeff
