encoding/asn1: remove allocation from init

[Thorleon]

asn1 allocates due to reflect.TypeOf(new(big.Int)) in init time. We could replace it with reflect.TypeOf((*big.Int)(nil)).

Before:
init encoding/asn1 @1.0 ms, 0.009 ms clock, 224 bytes, 7 allocs

After:
init encoding/asn1 @0.70 ms, 0.002 ms clock, 192 bytes, 6 allocs

[gopherbot]

Change https://go.dev/cl/435257 mentions this issue: encoding/asn1: remove allocation from init

[mvdan]

No need to file issues for small optimizations, FYI. You can send the CL directly.

[Thorleon]

Sure, I will skip Github issue part in minor tasks, thanks.

[andig]

The standard library has a few more occurences of this pattern reflect.TypeOf(new(foo)). Should they all be replaced?

20 results - 13 files

evcc • vendor/github.com/google/go-querystring/query/encode.go:
35: var encoderType = reflect.TypeOf(new(Encoder)).Elem()

evcc • vendor/github.com/pelletier/go-toml/marshal.go:
76: var marshalerType = reflect.TypeOf(new(Marshaler)).Elem()
77: var unmarshalerType = reflect.TypeOf(new(Unmarshaler)).Elem()
78: var textMarshalerType = reflect.TypeOf(new(encoding.TextMarshaler)).Elem()
79: var textUnmarshalerType = reflect.TypeOf(new(encoding.TextUnmarshaler)).Elem()

evcc • vendor/github.com/pelletier/go-toml/v2/types.go:
10: var textMarshalerType = reflect.TypeOf(new(encoding.TextMarshaler)).Elem()
11: var textUnmarshalerType = reflect.TypeOf(new(encoding.TextUnmarshaler)).Elem()

evcc • vendor/gopkg.in/square/go-jose.v2/json/encode.go:
353: 	marshalerType     = reflect.TypeOf(new(Marshaler)).Elem()
354: 	textMarshalerType = reflect.TypeOf(new(encoding.TextMarshaler)).Elem()

go • src/cmd/compile/internal/base/flag.go:
277: 		ptrBoolType   = reflect.TypeOf(new(bool))
278: 		ptrIntType    = reflect.TypeOf(new(int))
279: 		ptrStringType = reflect.TypeOf(new(string))

go • src/cmd/vendor/golang.org/x/tools/go/analysis/passes/ctrlflow/ctrlflow.go:
28: 	ResultType: reflect.TypeOf(new(CFGs)),

go • src/cmd/vendor/golang.org/x/tools/go/analysis/passes/inspect/inspect.go:
43: 	ResultType:       reflect.TypeOf(new(inspector.Inspector)),

go • src/database/sql/fakedb_test.go:
1269: 		return reflect.TypeOf(new(any)).Elem()

go • src/database/sql/sql.go:
3188: 			ci.scanType = reflect.TypeOf(new(any)).Elem()

go • src/encoding/asn1/asn1.go:
663: 	bigIntType           = reflect.TypeOf(new(big.Int))

go • test/fixedbugs/issue32595.dir/b.go:
11: 	t2 := reflect.TypeOf(new([0]byte)).Elem()

go • test/fixedbugs/issue47068.dir/b.go:
11: 	t2 := reflect.TypeOf(new([30]int)).Elem()

go • test/typeparam/mdempsky/15.go:
17: 	return reflect.TypeOf(new(T)).Elem().String()

[ianlancetaylor]

Probably.

Note that files in $GOROOT/test should not be changed unnecessarily.

Note that files under vendor are copied from upstream sources, and must be changed upstream and then vendored into to the standard library.

[hopehook]

I checked all the code, the memory is allocated on initialization, nowhere else.

@ianlancetaylor @andig
To clarify, do we need to deal with the allocation of memory during the program running phase?

[Thorleon]

I didn't take care of other cases, as I was mainly focused on reducing init time of common binary.

But for the sake of consistency and based on the Ian's comment I will adjust cases below in separate CLs:

go • src/cmd/compile/internal/base/flag.go:
277: 		ptrBoolType   = reflect.TypeOf(new(bool))
278: 		ptrIntType    = reflect.TypeOf(new(int))
279: 		ptrStringType = reflect.TypeOf(new(string))

go • src/cmd/vendor/golang.org/x/tools/go/analysis/passes/ctrlflow/ctrlflow.go:
28: 	ResultType: reflect.TypeOf(new(CFGs)),

go • src/cmd/vendor/golang.org/x/tools/go/analysis/passes/inspect/inspect.go:
43: 	ResultType:       reflect.TypeOf(new(inspector.Inspector)),

go • src/database/sql/sql.go:
3188: 			ci.scanType = reflect.TypeOf(new(any)).Elem()

[mvdan]

Sure, I definitely don't object to improving popular libraries. I think this issue should remain open for cases which would directly benefit the standard library, though, as otherwise its scope would be far too broad.