mirror of
https://github.com/facebook/zstd.git
synced 2025-03-06 16:56:49 +02:00
e6dccbf482
Inlining `BIT_reloadDStream` provided >3% decompression speed improvement for clang PGO-optimized zstd binary, measured using the Silesia corpus with compression level 1. The win comes from improved register allocation which leads to fewer spills and reloads. Take a look at this comparison of profile-annotated hot assembly before and after this change: https://www.diffchecker.com/UjDGIyLz/. The diff is a bit messy, but notice three fewer moves after inlining. In general LLVM's register allocator works better when it can see more code. For example, when the register allocator sees a call instruction, it partitions the registers into caller registers and callee registers, and it is not free to do whatever it wants with all the registers for the current function. Inlining the callee lets the register allocation access all registers and use them more flexsibly.