December 18, 2025
Fast lane, slow lane, fight lane
Partial Inlining
Half‑inlining: faster code without the bloat—commenters lose it
TLDR: Compilers can now inline only the quick part of a function and call the heavy part when needed, boosting speed without bloating code. Comments split between applause for smarter optimization and warnings to check the output, with embedded devs cheering size savings and skeptics urging 'trust but verify'.
Today’s nerd fight: the compiler learned a new trick called “partial inlining,” which is just fancy talk for copy-pasting only the easy part of a function while leaving the heavy stuff in a separate side‑quest. The demo shows a fast path for small numbers (just “double it”) and a slow path for big ones. The compiler turns the slow chunk into a helper (the ominous “.part.0”), then inlines the quick check right where it’s needed. Translation: you get speed without bulking up your app. Cue the comment cage match.
One camp is cheering like it’s a sports win: “more speed, less bloat—chef’s kiss!” Another camp fires back that compiler “heuristics” (fancy word for guesses) are roulette and you should peek at the actual assembly in Compiler Explorer. Embedded devs are popping champagne over smaller binaries, while cloud folks shrug: “my server has calories to spare.” Language warriors show up to compare GCC, Clang, MSVC, and Rust like it’s Eurovision. Memes fly: “99 problems but a branch ain’t one,” “.part.0 is my boss fight,” and “trust but verify” becomes the rallying cry. The mood? Equal parts hype, suspicion, and jokes about sending slow code to the naughty corner. It’s optimization theater—and everyone bought tickets.
Key Points
- •Partial inlining inlines only the fast path and keeps the cold, expensive path in a separate outlined function.
- •The compiler outlines the cold path into process(.part.0) and rewrites the original function as a wrapper with a quick range check and simple arithmetic.
- •In the caller, the compiler inlines the wrapper (fast path) and calls the outlined function for values ≥100.
- •This approach reduces function call overhead for common cases while avoiding code bloat from duplicating complex logic.
- •Compiler heuristics decide when to apply outlining and partial inlining; developers can verify results using Compiler Explorer.