What version of Go are you using (go version)?

gccgo tip

$ go version
go version go1.13 gccgo (GCC) 10.0.0 20190916 (experimental) linux/amd64

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

linux/amd64

What did you do?

Compile this package with gccgo:

package c

import "sort"

func init() {
	sort.Sort(byMaskLength(xpolicyTable))
}

type byMaskLength []policyTableEntry

func (s byMaskLength) Len() int           { return len(s) }
func (s byMaskLength) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
func (s byMaskLength) Less(i, j int) bool { return s[i].Label < s[j].Label }

type policyTableEntry struct {
	Label int
}

type policyTable []policyTableEntry

var xpolicyTable = policyTable{}

//go:noinline
func F() int {
	return xpolicyTable[0].Label
}

What did you expect to see?

Expected a single entry

func F () <type -11>

in the export data for the package, since that is the only exported identifier.

What did you see instead?

Export data includes the 'byMaskLength' type and its associated methods, which was a surprise.

I poked around at this and discovered that the lowering phase is running inlinabliity analysis on init functions, and it decides as part of this that the init() function is inlinable. This means that we include the types reachable from it in the export data (even though the init function itself is not emitted as an inline candidate.