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antcc's -O2 build runs 1.4× slower than -O1 on a Lua benchmark

386s.org 13 min read Editor score 7/10

The compiler's Lua benchmark ran in 1.410 seconds at -O2 versus 1.077 seconds at -O1; disabling inlining appeared to remove the slowdown. The investigation highlights how compiler optimizations can regress performance and why benchmarks need scrutiny.

What

An investigation traces why antcc's -O2 build runs slower than -O1 on a simple Lua benchmark.

How

Inlining was suspected, but -O2 IR was only 11% larger while luaV_execute grew to about 43 KB, 2.4× its -O1 size.

Why it matters

The case shows how small IR growth can become large machine-code growth in a hot interpreter loop, making later compiler passes worth inspecting.

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