Clang/LLVM static analyzer that detects microarchitectural hazards

2 days ago

lshaz is a Clang/LLVM-based static analysis tool for detecting microarchitectural latency hazards in C++ code at compile time.
The tool aims to move the performance feedback loop earlier in the development process, from production profiling to code writing.
lshaz analyzes struct field geometry, atomic ordering choices, thread escape, and NUMA placement using runtime-relevant information like byte offsets and cache line boundaries.
When run against Abseil-C++, lshaz produced 256 diagnostics, highlighting potential performance issues.
Key findings include the ThreadIdentity struct, which has deliberate hardware trade-offs involving cache line sharing and atomic fields.
ThreadIdentity triggers a Compound Hazard Amplification due to multiple co-occurring hazards like cache spanning and false sharing.
Another significant finding is HashtablezInfo, a sampling struct with high atomic field density across cache lines.
The 256 diagnostics are categorized into Proven, Likely, and Speculative tiers based on evidence strength.
lshaz uniquely generates formal hypotheses and experiment bundles for validating its predictions using hardware performance counters.
The tool is available on GitHub and integrates with CI systems via SARIF output for GitHub Code Scanning.

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