How Does Go\'s Compiler Decide When to Inline Functions?

Inlining in Go: Strategies and Factors

Go dynamically determines which functions are suitable for inlining, offering advantages such as improved performance. While declaring inline explicitly is not supported, the compiler's logic considers certain factors for inlining.

Inline Function Candidates

To enhance the likelihood of inlining, the following criteria should be taken into consideration:

• Small Function Size: Functions with fewer lines of code are more likely to be inlined.
• High Frequency of Calls: Functions that are called frequently within the program are good candidates for inlining.
• Pure Functions: Functions without side effects (e.g., do not mutate data or make system calls) are favorable for inlining.
• No Recursion: Recursive functions cannot be inlined.
• No Variables Captured from Outside: Functions that rely on variables defined in their enclosing scope cannot be inlined.

Influencing the Compiler's Decision

While it's generally not advisable to explicitly control inlining, performance concerns may necessitate doing so. In these situations, placing the target function within the same file as its caller can increase the likelihood of inlining.

Additional Resources

• Go compiler documentation on inlining: [$GOROOT/src/cmd/compile/internal/inline/inl.go](https://go.googlesource.com/go/ /master/src/cmd/compile/internal/inline/inl.go)
• Debugging flag for controlling aggressiveness: -l [level]
• Dave Cheney's blog post on Go performance: [Five things that make Go fast](https://dave.cheney.net/2014/06/07/five-things-that-make-go-fast)
• Discussion on inlining improvements: [cmd/compile: improve inlining cost model #17566](https://go-review.googlesource.com/c/go/ /17566)

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