PGO or not PGO this is the dilemma. Step 2

Automated excerpt

Second pass recompiles using those counts to drive inlining decisions, branch layout (hot path falls through, cold path jumps away), hot/cold function splitting, code ordering for icache/iTLB locality, loop unrolling, and indirect-call promotion. So for every branch, every loop back-edge, every call site, there’s a counter that increments each time execution takes that path. Hot code gets compiled favoring speed, more aggressive unrolling, more registers dedicated to hot-path values.

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