cmd/compile: binary size increase from generics

[andig]

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

$ go version
go version go1.23.2 darwin/arm64

Does this issue reproduce with the latest release?

yes

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

go env Output

$ go env
GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/andig/Library/Caches/go-build'
GOENV='/Users/andig/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/andig/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/andig/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/homebrew/Cellar/go/1.23.2/libexec'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/opt/homebrew/Cellar/go/1.23.2/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.23.2'
GODEBUG=''
GOTELEMETRY='on'
GOTELEMETRYDIR='/Users/andig/Library/Application Support/go/telemetry'
GCCGO='gccgo'
GOARM64='v8.0'
AR='ar'
CC='cc'
CXX='c++'
CGO_ENABLED='1'
GOMOD='/Users/andig/htdocs/evcc/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/sv/rs_453y57xj86xsbz3kw1mbc0000gn/T/go-build1030719432=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOROOT/bin/go version: go version go1.23.2 darwin/arm64
GOROOT/bin/go tool compile -V: compile version go1.23.2
uname -v: Darwin Kernel Version 24.0.0: Tue Sep 24 23:36:26 PDT 2024; root:xnu-11215.1.12~1/RELEASE_ARM64_T8103
ProductName:		macOS
ProductVersion:		15.0.1
BuildVersion:		24A348
lldb --version: lldb-1600.0.36.3
Apple Swift version 6.0 (swiftlang-6.0.0.9.10 clang-1600.0.26.2)

What did you do?

Replace for loop with generic function.

Before:

func (vv *vehicles) Instances() []api.Vehicle {
	devs := config.Vehicles().Devices()

	res := make([]api.Vehicle, 0, len(devs))
	for _, dev := range devs {
		res = append(res, dev.Instance())
	}

	return res
}

After:

func (vv *vehicles) Instances() []api.Vehicle {
	return lo.Map(config.Vehicles().Devices(), func(dev config.Device[api.Vehicle], _ int) api.Vehicle {
		return dev.Instance()
	})
}

with lo.Map simply being (samber/lo):

func Map[T any, R any](collection []T, iteratee func(item T, index int) R) []R {
	result := make([]R, len(collection))

	for i := range collection {
		result[i] = iteratee(collection[i], i)
	}

	return result
}

What did you expect to see?

Similar or smaller binary size

What did you see instead?

Binary size increased by 14kib for a single function call.

Before:

97417010

After:

97433586

[gabyhelp]

Related Issues and Documentation

• cmd/compile: long symbol names for instantiated generics => large object files (though not executables) #50438
• cmd/compile: generics add significant build time and build size overhead #65605
• cmd/compile: does not inline method of generic type across packages when there are multiple instantiations #59070
• cmd/compile: Go 1.19 might make generic types slower #54238 (closed)
• cmd/compile: code generated by generics seems inefficient #64699 (closed)
• encoding/json: Unmarshal to a typed struct uses 50% more bytes in go 1.21 (and current versions) vs go 1.20 #69828 (closed)
• Demo #66258 (closed)
• cmd/compile: stack overflow #52201 (closed)
• cmd/link: binary on darwin takes up more space on disk #39044 (closed)
• run #70024 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[seankhliao]

do you have a self contained reproducer?

[andig]

The repo is open source but a bit complex. Synthetic example yields additional 400 bytes, not sure that's relevant?

package main

import _ "github.com/samber/lo"

type element struct {
	value string
}

func (c *element) Value() string {
	return c.value
}

func main() {
	var list []element

	// 2953986 bytes
	res := make([]string, 0, len(list))
	for _, el := range list {
		res = append(res, el.Value())
	}

	// 2954306 bytes
	// res := lo.Map(list, func(el element, _ int) string {
	// 	return el.Value()
	// })

	_ = res
}

Could I produce any kind of export data that might be helpful?

[andig]

Another attempt (replacing main.go of https://github.com/evcc-io/evcc):

package main

import (
	"github.com/evcc-io/evcc/api"
	"github.com/evcc-io/evcc/util/config"
	"github.com/samber/lo"
)

type vehicles struct{}

// 9960802 bytes
// func (vv *vehicles) Instances() []api.Vehicle {
// 	devs := config.Vehicles().Devices()

// 	res := make([]api.Vehicle, 0, len(devs))
// 	for _, dev := range devs {
// 		res = append(res, dev.Instance())
// 	}

// 	return res
// }

// 9961538 bytes
func (vv *vehicles) Instances() []api.Vehicle {
	return lo.Map(config.Vehicles().Devices(), func(dev config.Device[api.Vehicle], _ int) api.Vehicle {
		return dev.Instance()
	})
}

func main() {
	var vv vehicles
	_ = vv.Instances()
}

Again only a 700 bytes difference.

[seankhliao]

looks like you have something other than generics that's increasing your binary size

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For questions please refer to https://github.com/golang/go/wiki/Questions

[andig]

Appreciate the feedback. If you want to take the time- any idea what could increase binary size when only this single function is being updated? Is there any AST or similar of the compiled program that I could export for inspection? Thank you!