Thin and fat LTO share the same pre-link pipeline, keeping PGO counts intact
charliermarsh · x · 2026-10-10
Charlie Marsh continues his PGO + thin LTO experiment: thin and fat LTO share the same pre-link pipeline, backed by a link into the Rust compiler source (PassWrapper.cpp).
Key detail: turning off LTO can change the optimizations that run before instrumentation and therefore what gets counted; thin and fat LTO behave identically pre-instrumentation, so counts stay equivalent.
Related event: Ruff Author Finds ThinLTO Dramatically Speeds Up PGO Builds(4 posts)→
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