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      "text": "Pass 1 — Instrument\ncompile with profile counters\n\n-fprofile-generate\n-fno-omit-frame-pointer\n      ↓\n  instrumented binary\n  ~10% slower than baseline\n\nembedded counters track\nbranch taken/not-taken,\nfunction entries, etc.",
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      "text": "Pass 2 — Profile\nrun against representative load\n\n./instrumented_binary\n  with realistic workload\n      ↓\n  .profraw files\n  merged with llvm-profdata\n\n→ merged.profdata\nthe entire feedback loop:\n'what the binary actually does'",
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      "text": "What PGO does to your binary, given the profile:\n• inline aggressively in hot functions   • keep cold paths out of the I-cache\n• reorder branches for the common case   • lay out functions to fit working set in pages\n• apply __builtin_expect implicitly       • better register allocation",
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