Optimize ZSTD_decodeSequence when ofBits==0 #3651
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This patch adds a branch to a previously branchless code in decompress hot loop handling the case where `ofBits == 0`. Even though a branch is added, the branch saves on instructions that introduce memory dependency an unneeded memory operations when the condition isn't met. Testing on intel Skylake shows positive decompression speed improvements across different corpora and compilers, with speed improvements of 1% to 7%. On M1 Macbook Pro performance is mostly neutral with a possible very small regression.
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Seems reasonable for most data, since we probably almost never use |
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I will run benchmarks on my server as well |
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This patch adds a branch to a previously branchless code in decompress hot loop handling the case where
ofBits == 0.Even though a branch is added, the branch saves on instructions that introduce memory dependency an unneeded memory operations when the condition isn't met.
Testing on intel Skylake shows positive decompression speed improvements across different corpora and compilers, with speed improvements of 1% to 7%.
On M1 Macbook Pro performance is mostly neutral with a possible very small regression.
Full benchmark results - https://docs.google.com/spreadsheets/d/1hEUY5Gkf6Ebz6Gq5X9U5mURC_SsI43BhIFpE7uBDVsw/edit?usp=sharing