chore: add fast path for ints, fixed ints and floats

Since typed slice appender did not produce enough performance benefit, we try the next thing: this commit implements fast path decoding for slices of primitives. Comparison:
BenchmarkSliceOld
BenchmarkSliceOld-10     	 1591179	       764.2 ns/op	     368 B/op	      10 allocs/op
BenchmarkSlice
BenchmarkSlice-10     	 3551311	       337.7 ns/op	     248 B/op	       5 allocs/op

Signed-off-by: Dmitriy Matrenichev <dmitry.matrenichev@siderolabs.com>

.dockerignore

@@ -1,6 +1,6 @@
 # THIS FILE WAS AUTOMATICALLY GENERATED, PLEASE DO NOT EDIT.
 #
-# Generated on 2022-08-03T15:33:56Z by kres latest.
+# Generated on 2022-08-04T13:22:07Z by kres latest.
 
 **
 !messages
@@ -19,6 +19,7 @@
 !protobuf_test.go
 !type_cache.go
 !unmarshal.go
+!unmarshal_fastpath.go
 !go.mod
 !go.sum
 !.golangci.yml

Dockerfile

@@ -2,7 +2,7 @@
 
 # THIS FILE WAS AUTOMATICALLY GENERATED, PLEASE DO NOT EDIT.
 #
-# Generated on 2022-08-03T15:33:56Z by kres latest.
+# Generated on 2022-08-04T13:22:07Z by kres latest.
 
 ARG TOOLCHAIN
 
@@ -64,6 +64,7 @@ COPY ./predefined_types.go ./predefined_types.go
 COPY ./protobuf_test.go ./protobuf_test.go
 COPY ./type_cache.go ./type_cache.go
 COPY ./unmarshal.go ./unmarshal.go
+COPY ./unmarshal_fastpath.go ./unmarshal_fastpath.go
 RUN --mount=type=cache,target=/go/pkg go list -mod=readonly all >/dev/null
 
 # runs protobuf compiler

benchmarks_test.go

@@ -74,6 +74,8 @@ func BenchmarkCustom(b *testing.B) {
 			b.Fatal(err)
 		}
 	}
+
+	require.Equal(b, o.Field.Value+2, target.Field.Value)
 }
 
 func BenchmarkSlice(b *testing.B) {
@@ -106,6 +108,8 @@ func BenchmarkSlice(b *testing.B) {
 			b.Fatal(err)
 		}
 	}
+
+	require.Equal(b, o, *target)
 }
 
 func BenchmarkString(b *testing.B) {
@@ -138,4 +142,6 @@ func BenchmarkString(b *testing.B) {
 			b.Fatal(err)
 		}
 	}
+
+	require.Equal(b, o, *target)
 }

unmarshal.go

@@ -454,7 +454,7 @@ func (u *unmarshaller) slice(dst reflect.Value, decodedBytes []byte) error {
 	if wiretype < 0 { // Other unpacked repeated types
 		// Just unpack and append one value from decodedBytes.
 		elem := reflect.New(elemType).Elem()
-		if err := u.putInto(elem, protowire.BytesType, 0, decodedBytes); err != nil {
+		if err = u.putInto(elem, protowire.BytesType, 0, decodedBytes); err != nil {
 			return err
 		}
 
@@ -463,6 +463,15 @@ func (u *unmarshaller) slice(dst reflect.Value, decodedBytes []byte) error {
 		return nil
 	}
 
+	ok, err = tryDecodePredefinedSlice(wiretype, decodedBytes, dst)
+	if err != nil {
+		return err
+	}
+
+	if ok {
+		return nil
+	}
+
 	sw := sequenceWrapper{
 		seq: dst,
 	}
@@ -489,7 +498,7 @@ func getWiretypeFor(elemType reflect.Type) (protowire.Type, error) {
 	case reflect.Bool, reflect.Int32, reflect.Int64, reflect.Int,
 		reflect.Uint32, reflect.Uint64, reflect.Uint:
 		if (elemType.Kind() == reflect.Int || elemType.Kind() == reflect.Uint) && elemType.Size() < 8 {
-			return 0, errors.New("detected a 32bit machine, please either use (u)int64 or (u)int32")
+			return -1, errors.New("detected a 32bit machine, please either use (u)int64 or (u)int32")
 		}
 
 		switch elemType {

unmarshal_fastpath.go

@@ -0,0 +1,142 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package protoenc
+
+import (
+	"errors"
+	"math"
+	"reflect"
+	"unsafe"
+
+	"google.golang.org/protobuf/encoding/protowire"
+)
+
+var predefiniedDecoders = map[reflect.Type]func(buf []byte, dst reflect.Value) (bool, error){
+	typeOf[[]int]():      decodeIntSlice[int],
+	typeOf[[]int32]():    decodeIntSlice[int32],
+	typeOf[[]int64]():    decodeIntSlice[int64],
+	typeOf[[]uint]():     decodeIntSlice[uint],
+	typeOf[[]uint32]():   decodeIntSlice[uint32],
+	typeOf[[]uint64]():   decodeIntSlice[uint64],
+	typeOf[[]FixedU32](): decodeFixed32[FixedU32],
+	typeOf[[]FixedS32](): decodeFixed32[FixedS32],
+	typeOf[[]FixedU64](): decodeFixed64[FixedU64],
+	typeOf[[]FixedS64](): decodeFixed64[FixedS64],
+	typeOf[[]float32]():  decodeFloat32,
+	typeOf[[]float64]():  decodeFloat64,
+}
+
+func tryDecodePredefinedSlice(wiretype protowire.Type, buf []byte, dst reflect.Value) (bool, error) {
+	switch wiretype { //nolint:exhaustive
+	case protowire.VarintType, protowire.Fixed32Type, protowire.Fixed64Type:
+		fn, ok := predefiniedDecoders[dst.Type()]
+		if !ok {
+			return false, nil
+		}
+
+		return fn(buf, dst)
+	default:
+		return false, nil
+	}
+}
+
+type integer interface {
+	int32 | int64 | uint32 | uint64 | int | uint
+}
+
+func decodeIntSlice[I integer](buf []byte, dst reflect.Value) (bool, error) {
+	var result []I
+
+	for len(buf) > 0 {
+		v, n := protowire.ConsumeVarint(buf)
+		if n < 0 {
+			return false, errors.New("bad protobuf varint value")
+		}
+
+		buf = buf[n:]
+
+		result = append(result, I(v))
+	}
+
+	*(*[]I)(unsafe.Pointer(dst.UnsafeAddr())) = result
+
+	return true, nil
+}
+
+func decodeFixed32[F FixedU32 | FixedS32](buf []byte, dst reflect.Value) (bool, error) {
+	var result []F
+
+	for len(buf) > 0 {
+		v, n := protowire.ConsumeFixed32(buf)
+		if n < 0 {
+			return false, errors.New("bad protobuf 32-bit value")
+		}
+
+		buf = buf[n:]
+
+		result = append(result, F(v))
+	}
+
+	*(*[]F)(unsafe.Pointer(dst.UnsafeAddr())) = result
+
+	return true, nil
+}
+
+func decodeFixed64[F FixedU64 | FixedS64](buf []byte, dst reflect.Value) (bool, error) {
+	var result []F
+
+	for len(buf) > 0 {
+		v, n := protowire.ConsumeFixed64(buf)
+		if n < 0 {
+			return false, errors.New("bad protobuf 64-bit value")
+		}
+
+		buf = buf[n:]
+
+		result = append(result, F(v))
+	}
+
+	*(*[]F)(unsafe.Pointer(dst.UnsafeAddr())) = result
+
+	return true, nil
+}
+
+func decodeFloat32(buf []byte, dst reflect.Value) (bool, error) {
+	var result []float32
+
+	for len(buf) > 0 {
+		v, n := protowire.ConsumeFixed32(buf)
+		if n < 0 {
+			return false, errors.New("bad protobuf 32-bit value")
+		}
+
+		buf = buf[n:]
+
+		result = append(result, math.Float32frombits(v))
+	}
+
+	*(*[]float32)(unsafe.Pointer(dst.UnsafeAddr())) = result
+
+	return true, nil
+}
+
+func decodeFloat64(buf []byte, dst reflect.Value) (bool, error) {
+	var result []float64
+
+	for len(buf) > 0 {
+		v, n := protowire.ConsumeFixed64(buf)
+		if n < 0 {
+			return false, errors.New("bad protobuf 64-bit value")
+		}
+
+		buf = buf[n:]
+
+		result = append(result, math.Float64frombits(v))
+	}
+
+	*(*[]float64)(unsafe.Pointer(dst.UnsafeAddr())) = result
+
+	return true, nil
+}