Fixing a Performance Regression in LLVM's SLP Vectorizer on RISC-V
By
matt_d
The kind of bagel that ruins lesser bagels for you.
Summary
The article describes how the author solved a performance regression in LLVM's SLP Vectorizer by analyzing a benchmark from a RISC-V target. The regression showed an 89% delta in benchmark performance, with ~26% more instructions issued and ~48% more cycles. The author compares assembly code from older and newer LLVM builds to identify the root cause of the performance degradation.
Key quotes
· 4 pulledSimilar to my last post, this writeup covers how I solved a performance regression on LLVM by analyzing a benchmark from a RISCV target.
Looking at Igalia's LNT instance for the BPI-F3, I noticed this particular benchmark with a delta of 89%.
Specifically, there was an increase in ~26% issued instructions and a ~48% increase in cycles.
We can see that that newer build of LLVM is perfor
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