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...t reads the call graph from a file. The format would be very similar to what you propose, just weight,caller,callee. In a another patch we can then look at instrumentation: Why it is more convenient for some uses and what performance advantage it might have. I have written a small tool that usesr intel_bts and 'perf script' to construct the callgraph. I am giving it a try with your lld patch and will hopefully post results today. Cheers, Rafael

I've recently implemented profile guided section layout in llvm + lld using the Call-Chain Clustering (C³) heuristic from https://research.fb.com/wp-content/uploads/2017/01/cgo2017-hfsort-final1.pdf . In the programs I've tested it on I've gotten from 0% to 5% performance improvement over standard PGO with zero cases of slowdowns and up to 15% reduction in ITLB misses. There are