How Can I Remove Unused Code in Go at Compile Time?

Removing Unused Code in Go at Compile Time

Go packages are often used by multiple modules or programs. Despite only requiring a small subset of functionality, the entire package can end up being compiled into each executable. This can result in large binaries that include unused functions and strings.

Unfortunately, unlike some other programming languages, Go does not currently offer a way to explicitly remove unused code at compile time. The compiler optimizes and removes unreachable code to some extent, but it cannot determine unused code that is potentially reachable, even if it is never explicitly called.

This behavior can be demonstrated with the following code:

// play/subplay.go
package subplay

func A() {
    fmt.Printf("this is function A()")
}

func B() {
    fmt.Printf("secret string")
}

In the main module, we import the subplay package but only call function A():

// main.go
package main

import "play/subplay"

func main() {
    subplay.A()
}

Despite B() never being called, the string "secret string" is still included in the resulting binary.

As noted in the responses to this question, one workaround is to be mindful of the dependencies introduced by imported packages. For example, importing net/http will also import 39 other packages, which can significantly increase the binary size, even if none of those packages are used.

While the compiler may not be able to remove unused code, it is still essential to optimize code for efficiency. Avoiding unnecessary function calls, keeping data structures lean, and minimizing string allocations can all help reduce binary size.

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