8000 cmd/compile: stronger constant propagation around closures · Issue #73601 · golang/go · GitHub
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adonovan opened this issue May 5, 2025 · 1 comment
Open

cmd/compile: stronger constant propagation around closures #73601

adonovan opened this issue May 5, 2025 · 1 comment
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compiler/runtime Issues related to the Go compiler and/or runtime. FeatureRequest Issues asking for a new feature that does not need a proposal. NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. Performance
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@adonovan
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adonovan commented May 5, 2025

I notice that the use of a local variable to hold a function (e.g. for brevity) doesn't prevent the compiler from treating the variable as an alias for the function, and dispatching calls statically. However, if the variable is referenced from an inner closure, it is treated as a true variable, resulting in a dynamic call:

func f() any {
	escape := html.EscapeString
	println(escape("foo")) // static call
	return func() {
		println(escape("foo")) // dynamic call
	}
}

The closure may be latent, in the case of a range-over-func:

func f(seq iter.Seq[string]) {
	escape := html.EscapeString
	println(escape("foo")) // static call
	for s := range seq {
		println(escape(s)) // dynamic call
	}
}

This is another facet of #73524 (comment), where closures defeat constant propagation of outer single-assignment variables.
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label May 5, 2025
@adonovan adonovan added the FeatureRequest Issues asking for a new feature that does not need a proposal. label May 5, 2025
@cherrymui
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cc @dr2chase @golang/compiler

@cherrymui cherrymui added this to the Backlog milestone May 6, 2025
@cherrymui cherrymui added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label May 6, 2025
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