cmd/compile: optimize []byte(string1 + string2)

[mdempsky]

A somewhat common code pattern is []byte(string1 + string2).

Today this gets compiled as two separate steps: concatenating the two strings into a new string, and then copying that string result into a new []byte slice.

But it shouldn't be too much trouble to have the compiler instead recognize these patterns (e.g., recognize an OSTR2BYTES whose operand is an OADDSTR), and optimize accordingly.

[robpike]

What is your evidence that it's common code? It doesn't sound familiar to me.

[mdempsky]

Searching kubernetes, it happens a lot in test files, but not exclusively there.

string concatenations converted to bytes

go/src/bufio/bufio_test.go:1003:33: string concatenation converted to bytes
go/src/bytes/bytes_test.go:1846:9: string concatenation converted to bytes
go/src/crypto/tls/tls_test.go:106:15: string concatenation converted to bytes
go/src/crypto/tls/tls_test.go:110:15: string concatenation converted to bytes
go/src/encoding/base64/base64_test.go:571:52: string concatenation converted to bytes
go/src/encoding/json/decode_test.go:106:15: string concatenation converted to bytes
go/src/encoding/json/encode_test.go:584:15: string concatenation converted to bytes
go/src/encoding/pem/pem.go:235:28: string concatenation converted to bytes
go/src/encoding/pem/pem.go:254:31: string concatenation converted to bytes
go/src/encoding/pem/pem.go:301:28: string concatenation converted to bytes
go/src/mime/multipart/multipart.go:120:13: string concatenation converted to bytes
go/src/net/http/readrequest_test.go:440:15: string concatenation converted to bytes
go/src/net/http/serve_test.go:1212:17: string concatenation converted to bytes
go/src/net/http/serve_test.go:135:15: string concatenation converted to bytes
go/src/net/netip/netip_test.go:296:16: string concatenation converted to bytes
go/src/regexp/all_test.go:591:13: string concatenation converted to bytes
go/src/regexp/all_test.go:634:13: string concatenation converted to bytes
kubernetes/cmd/kubeadm/app/cmd/upgrade/common_test.go:180:25: string concatenation converted to bytes
kubernetes/cmd/kubeadm/app/preflight/checks_test.go:799:52: string concatenation converted to bytes
kubernetes/pkg/api/testing/serialization_test.go:191:70: string concatenation converted to bytes
kubernetes/pkg/api/testing/serialization_test.go:199:35: string concatenation converted to bytes
kubernetes/pkg/api/testing/serialization_test.go:205:36: string concatenation converted to bytes
kubernetes/pkg/proxy/iptables/proxier.go:671:30: string concatenation converted to bytes
kubernetes/pkg/proxy/iptables/proxier.go:715:30: string concatenation converted to bytes
kubernetes/pkg/proxy/ipvs/ipset/ipset_test.go:468:18: string concatenation converted to bytes
kubernetes/pkg/proxy/ipvs/ipset/ipset_test.go:472:18: string concatenation converted to bytes
kubernetes/pkg/proxy/ipvs/ipset/ipset_test.go:516:18: string concatenation converted to bytes
kubernetes/pkg/util/iptables/iptables_test.go:53:50: string concatenation converted to bytes
kubernetes/pkg/util/iptables/iptables_test.go:55:50: string concatenation converted to bytes
kubernetes/pkg/util/iptables/iptables_test.go:778:50: string concatenation converted to bytes
kubernetes/pkg/util/iptables/iptables_test.go:842:50: string concatenation converted to bytes
kubernetes/pkg/util/tail/tail_test.go:34:21: string concatenation converted to bytes
kubernetes/pkg/util/tail/tail_test.go:95:21: string concatenation converted to bytes
kubernetes/test/e2e/apimachinery/apply.go:1022:17: string concatenation converted to bytes
kubernetes/test/e2e/apimachinery/apply.go:274:16: string concatenation converted to bytes
kubernetes/test/e2e/apimachinery/apply.go:319:15: string concatenation converted to bytes
kubernetes/test/e2e/apimachinery/apply.go:379:18: string concatenation converted to bytes
kubernetes/test/e2e/apimachinery/apply.go:426:17: string concatenation converted to bytes
kubernetes/test/e2e/apimachinery/apply.go:486:16: string concatenation converted to bytes
kubernetes/test/e2e/apimachinery/apply.go:972:18: string concatenation converted to bytes
kubernetes/test/e2e/apimachinery/namespace.go:332:10: string concatenation converted to bytes
kubernetes/test/e2e/apimachinery/resource_quota.go:1109:10: string concatenation converted to bytes
kubernetes/test/e2e/apimachinery/resource_quota.go:1161:10: string concatenation converted to bytes
kubernetes/test/e2e/apps/cronjob.go:424:10: string concatenation converted to bytes
kubernetes/test/e2e/apps/job.go:667:10: string concatenation converted to bytes
kubernetes/test/e2e/auth/certificates.go:396:10: string concatenation converted to bytes
kubernetes/test/e2e/common/node/pods.go:1119:10: string concatenation converted to bytes
kubernetes/test/e2e/network/ingress.go:755:10: string concatenation converted to bytes
kubernetes/test/e2e/network/service.go:3405:10: string concatenation converted to bytes
kubernetes/test/integration/apiserver/admissionwebhook/client_auth_test.go:120:59: string concatenation converted to bytes
kubernetes/test/integration/apiserver/admissionwebhook/client_auth_test.go:94:54: string concatenation converted to bytes
kubernetes/test/integration/apiserver/apply/apply_test.go:153:20: string concatenation converted to bytes
kubernetes/test/integration/apiserver/apply/apply_test.go:619:15: string concatenation converted to bytes
kubernetes/test/integration/apiserver/apply/apply_test.go:885:20: string concatenation converted to bytes
kubernetes/test/integration/apiserver/max_json_patch_operations_test.go:49:21: string concatenation converted to bytes
kubernetes/test/integration/apiserver/max_request_body_bytes_test.go:106:22: string concatenation converted to bytes
kubernetes/test/integration/apiserver/max_request_body_bytes_test.go:117:22: string concatenation converted to bytes
kubernetes/test/integration/apiserver/max_request_body_bytes_test.go:128:22: string concatenation converted to bytes
kubernetes/test/integration/apiserver/max_request_body_bytes_test.go:139:22: string concatenation converted to bytes
kubernetes/test/integration/apiserver/max_request_body_bytes_test.go:150:22: string concatenation converted to bytes
kubernetes/test/integration/apiserver/max_request_body_bytes_test.go:161:22: string concatenation converted to bytes
kubernetes/test/integration/apiserver/max_request_body_bytes_test.go:172:22: string concatenation converted to bytes
kubernetes/test/integration/apiserver/max_request_body_bytes_test.go:193:21: string concatenation converted to bytes
kubernetes/test/integration/apiserver/max_request_body_bytes_test.go:216:21: string concatenation converted to bytes
kubernetes/test/integration/apiserver/max_request_body_bytes_test.go:239:21: string concatenation converted to bytes
kubernetes/test/integration/apiserver/max_request_body_bytes_test.go:259:21: string concatenation converted to bytes
kubernetes/test/integration/apiserver/max_request_body_bytes_test.go:283:21: string concatenation converted to bytes
kubernetes/test/integration/apiserver/max_request_body_bytes_test.go:308:21: string concatenation converted to bytes
kubernetes/test/integration/apiserver/max_request_body_bytes_test.go:95:22: string concatenation converted to bytes
kubernetes/vendor/github.com/coreos/go-semver/semver/semver.go:131:15: string concatenation converted to bytes
kubernetes/vendor/github.com/google/go-cmp/cmp/report_reflect.go:337:70: string concatenation converted to bytes
kubernetes/vendor/github.com/google/go-cmp/cmp/report_reflect.go:346:70: string concatenation converted to bytes
kubernetes/vendor/github.com/google/go-cmp/cmp/report_reflect.go:352:18: string concatenation converted to bytes
kubernetes/vendor/github.com/google/go-cmp/cmp/report_reflect.go:354:17: string concatenation converted to bytes
kubernetes/vendor/github.com/gorilla/websocket/proxy.go:45:58: string concatenation converted to bytes
kubernetes/vendor/github.com/opencontainers/runc/libcontainer/intelrdt/intelrdt.go:317:57: string concatenation converted to bytes
kubernetes/vendor/github.com/russross/blackfriday/v2/block.go:493:20: string concatenation converted to bytes
kubernetes/vendor/github.com/vmware/govmomi/toolbox/vix/protocol.go:838:22: string concatenation converted to bytes
kubernetes/vendor/github.com/vmware/govmomi/toolbox/vix/protocol.go:838:45: string concatenation converted to bytes
kubernetes/vendor/go.etcd.io/etcd/server/v3/etcdserver/api/v2error/error.go:163:26: string concatenation converted to bytes
kubernetes/vendor/golang.org/x/oauth2/google/internal/externalaccount/aws.go:240:22: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apiextensions-apiserver/test/integration/limit_test.go:208:22: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apiextensions-apiserver/test/integration/limit_test.go:219:22: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apiextensions-apiserver/test/integration/limit_test.go:230:22: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/embedded_test.go:45:38: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/embedded_test.go:57:37: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/json/json_limit_test.go:102:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/json/json_limit_test.go:107:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/json/json_limit_test.go:112:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/json/json_limit_test.go:117:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/json/json_limit_test.go:53:20: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/json/json_limit_test.go:58:20: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/json/json_limit_test.go:63:20: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/json/json_limit_test.go:72:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/json/json_limit_test.go:77:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/json/json_limit_test.go:82:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/json/json_limit_test.go:87:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/json/json_limit_test.go:92:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/json/json_limit_test.go:97:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/yaml/yaml_test.go:280:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/yaml/yaml_test.go:286:16: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/yaml/yaml_test.go:299:17: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/yaml/yaml_test.go:313:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/yaml/yaml_test.go:318:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/yaml/yaml_test.go:323:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/yaml/yaml_test.go:328:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/yaml/yaml_test.go:333:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/yaml/yaml_test.go:338:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/yaml/yaml_test.go:343:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/yaml/yaml_test.go:348:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/yaml/yaml_test.go:353:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/runtime/serializer/yaml/yaml_test.go:358:21: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/util/managedfields/internal/lastappliedupdater_test.go:43:29: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apimachinery/pkg/util/proxy/upgradeaware_test.go:517:20: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apiserver/pkg/endpoints/handlers/responsewriters/writers_test.go:346:32: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apiserver/pkg/server/options/encryptionconfig/config.go:591:24: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apiserver/pkg/server/options/encryptionconfig/config.go:643:24: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apiserver/pkg/server/options/encryptionconfig/config.go:739:23: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apiserver/pkg/server/options/encryptionconfig/config.go:818:22: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apiserver/pkg/storage/testing/store_tests.go:2137:31: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apiserver/pkg/storage/value/encrypt/envelope/envelope_test.go:63:15: string concatenation converted to bytes
kubernetes/vendor/k8s.io/apiserver/plugin/pkg/audit/truncate/truncate_test.go:56:17: string concatenation converted to bytes
kubernetes/vendor/k8s.io/kube-aggregator/pkg/apiserver/handler_proxy_test.go:533:20: string concatenation converted to bytes

The opposite scenario happens about as frequently too, which we could also optimize:

bytes converted to concatenated strings

go/src/archive/tar/reader_test.go:1151:20: bytes converted to concatenated string
go/src/archive/tar/reader_test.go:1286:20: bytes converted to concatenated string
go/src/bytes/bytes_test.go:1194:30: bytes converted to concatenated string
go/src/bytes/example_test.go:506:36: bytes converted to concatenated string
go/src/bytes/example_test.go:507:35: bytes converted to concatenated string
go/src/bytes/example_test.go:602:36: bytes converted to concatenated string
go/src/bytes/example_test.go:603:35: bytes converted to concatenated string
go/src/bytes/example_test.go:617:36: bytes converted to concatenated string
go/src/bytes/example_test.go:618:35: bytes converted to concatenated string
go/src/encoding/binary/varint_test.go:41:36: bytes converted to concatenated string
go/src/encoding/binary/varint_test.go:42:73: bytes converted to concatenated string
go/src/encoding/binary/varint_test.go:67:36: bytes converted to concatenated string
go/src/encoding/binary/varint_test.go:68:74: bytes converted to concatenated string
go/src/encoding/hex/hex_test.go:64:41: bytes converted to concatenated string
go/src/encoding/hex/hex_test.go:65:61: bytes converted to concatenated string
go/src/encoding/json/decode.go:1000:62: bytes converted to concatenated string
go/src/encoding/json/decode.go:1008:62: bytes converted to concatenated string
go/src/encoding/json/decode.go:992:62: bytes converted to concatenated string
go/src/encoding/json/encode.go:1164:38: bytes converted to concatenated string
go/src/encoding/xml/xml.go:1191:54: bytes converted to concatenated string
go/src/go/doc/comment/html.go:105:21: bytes converted to concatenated string
go/src/go/scanner/scanner.go:252:49: bytes converted to concatenated string
go/src/go/scanner/scanner.go:267:53: bytes converted to concatenated string
go/src/go/scanner/scanner.go:277:49: bytes converted to concatenated string
go/src/math/big/ftoa.go:391:40: bytes converted to concatenated string
go/src/math/big/nat.go:44:22: bytes converted to concatenated string
go/src/net/http/clientserver_test.go:663:15: bytes converted to concatenated string
go/src/net/http/clientserver_test.go:663:35: bytes converted to concatenated string
go/src/net/mail/message_test.go:374:14: bytes converted to concatenated string
go/src/net/mail/message_test.go:375:21: bytes converted to concatenated string
go/src/net/mail/message_test.go:376:23: bytes converted to concatenated string
go/src/net/textproto/reader.go:514:74: bytes converted to concatenated string
go/src/net/textproto/reader.go:526:67: bytes converted to concatenated string
go/src/net/textproto/reader.go:530:67: bytes converted to concatenated string
go/src/net/textproto/reader.go:534:68: bytes converted to concatenated string
go/src/os/dir_unix.go:132:44: bytes converted to concatenated string
go/src/os/env.go:44:15: bytes converted to concatenated string
go/src/path/filepath/path.go:65:41: bytes converted to concatenated string
go/src/runtime/export_test.go:1961:46: bytes converted to concatenated string
go/src/runtime/malloc_test.go:145:22: bytes converted to concatenated string
go/src/runtime/string_test.go:230:22: bytes converted to concatenated string
go/src/runtime/string_test.go:231:69: bytes converted to concatenated string
go/src/runtime/string_test.go:64:41: bytes converted to concatenated string
go/src/runtime/string_test.go:90:24: bytes converted to concatenated string
go/src/strings/export_test.go:32:37: bytes converted to concatenated string
go/src/strings/strings_test.go:1113:30: bytes converted to concatenated string
go/src/syscall/exec_linux_test.go:414:46: bytes converted to concatenated string
go/src/time/time.go:335:28: bytes converted to concatenated string
go/src/time/time.go:358:30: bytes converted to concatenated string
kubernetes/pkg/controlplane/controller/clusterauthenticationtrust/cluster_authentication_trust_controller_test.go:195:31: bytes converted to concatenated string
kubernetes/pkg/controlplane/controller/clusterauthenticationtrust/cluster_authentication_trust_controller_test.go:195:57: bytes converted to concatenated string
kubernetes/pkg/controlplane/controller/clusterauthenticationtrust/cluster_authentication_trust_controller_test.go:228:51: bytes converted to concatenated string
kubernetes/pkg/controlplane/controller/clusterauthenticationtrust/cluster_authentication_trust_controller_test.go:228:74: bytes converted to concatenated string
kubernetes/test/e2e/apimachinery/namespace.go:332:107: bytes converted to concatenated string
kubernetes/test/e2e/apimachinery/resource_quota.go:1109:40: bytes converted to concatenated string
kubernetes/test/e2e/apimachinery/resource_quota.go:1161:40: bytes converted to concatenated string
kubernetes/test/e2e/apps/cronjob.go:424:82: bytes converted to concatenated string
kubernetes/test/e2e/apps/job.go:667:82: bytes converted to concatenated string
kubernetes/test/e2e/auth/certificates.go:396:97: bytes converted to concatenated string
kubernetes/test/e2e/common/node/pods.go:1119:82: bytes converted to concatenated string
kubernetes/test/e2e/network/ingress.go:755:98: bytes converted to concatenated string
kubernetes/test/e2e/network/service.go:3405:98: bytes converted to concatenated string
kubernetes/test/e2e/network/util_iperf.go:75:36: bytes converted to concatenated string
kubernetes/vendor/github.com/Azure/go-autorest/autorest/preparer.go:434:39: bytes converted to concatenated string
kubernetes/vendor/github.com/cilium/ebpf/internal/output.go:79:27: bytes converted to concatenated string
kubernetes/vendor/github.com/cpuguy83/go-md2man/v2/md2man/roff.go:113:25: bytes converted to concatenated string
kubernetes/vendor/github.com/godbus/dbus/v5/auth_sha1.go:66:59: bytes converted to concatenated string
kubernetes/vendor/github.com/go-errors/errors/error.go:181:59: bytes converted to concatenated string
kubernetes/vendor/github.com/google/go-cmp/cmp/report_reflect.go:352:61: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_array.go:22:77: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_array.go:50:77: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_array.go:62:68: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter.go:177:85: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_int.go:129:65: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_int.go:251:65: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:124:84: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:135:85: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:153:73: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:161:69: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:177:83: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:189:84: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:209:70: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:217:66: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:234:72: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:24:84: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:250:94: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:31:71: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:37:83: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:53:66: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:71:69: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_object.go:80:69: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_skip.go:28:65: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_str.go:142:75: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_str.go:159:70: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/iter_str.go:31:68: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/reflect_array.go:101:65: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/reflect_array.go:79:70: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/reflect_map.go:163:67: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/reflect_map.go:175:81: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/reflect_map.go:186:82: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/reflect_map.go:194:62: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/reflect_map.go:205:62: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/reflect_map.go:211:62: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/reflect_slice.go:75:70: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/reflect_slice.go:96:65: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/reflect_struct_decoder.go:1085:76: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/reflect_struct_decoder.go:1094:76: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/reflect_struct_decoder.go:514:66: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/reflect_struct_decoder.go:543:83: bytes converted to concatenated string
kubernetes/vendor/github.com/json-iterator/go/reflect_struct_decoder.go:550:82: bytes converted to concatenated string
kubernetes/vendor/github.com/mailru/easyjson/jlexer/lexer.go:421:16: bytes converted to concatenated string
kubernetes/vendor/github.com/mailru/easyjson/jlexer/lexer.go:463:15: bytes converted to concatenated string
kubernetes/vendor/github.com/onsi/ginkgo/v2/internal/suite.go:354:73: bytes converted to concatenated string
kubernetes/vendor/github.com/opencontainers/runc/libcontainer/container_linux.go:592:37: bytes converted to concatenated string
kubernetes/vendor/github.com/robfig/cron/v3/chain.go:50:56: bytes converted to concatenated string
kubernetes/vendor/github.com/russross/blackfriday/v2/html.go:344:28: bytes converted to concatenated string
kubernetes/vendor/github.com/vmware/govmomi/vim25/xml/xml.go:1184:54: bytes converted to concatenated string
kubernetes/vendor/go.etcd.io/etcd/server/v3/etcdserver/api/membership/confstate.go:52:39: bytes converted to concatenated string
kubernetes/vendor/golang.org/x/net/websocket/hybi.go:418:47: bytes converted to concatenated string
kubernetes/vendor/golang.org/x/net/websocket/hybi.go:561:51: bytes converted to concatenated string
kubernetes/vendor/google.golang.org/protobuf/internal/encoding/json/decode_number.go:251:22: bytes converted to concatenated string
kubernetes/vendor/k8s.io/apimachinery/pkg/util/managedfields/internal/pathelement.go:128:28: bytes converted to concatenated string
kubernetes/vendor/k8s.io/apimachinery/pkg/util/managedfields/internal/pathelement.go:134:30: bytes converted to concatenated string
kubernetes/vendor/k8s.io/apimachinery/pkg/util/proxy/upgradeaware_test.go:517:38: bytes converted to concatenated string
kubernetes/vendor/k8s.io/apiserver/pkg/endpoints/apiserver_test.go:1640:19: bytes converted to concatenated string
kubernetes/vendor/k8s.io/apiserver/pkg/endpoints/discovery/aggregated/handler_test.go:140:24: bytes converted to concatenated string
kubernetes/vendor/k8s.io/apiserver/pkg/endpoints/handlers/responsewriters/writers_test.go:346:44: bytes converted to concatenated string
kubernetes/vendor/k8s.io/apiserver/pkg/endpoints/handlers/rest.go:362:17: bytes converted to concatenated string
kubernetes/vendor/k8s.io/apiserver/pkg/server/httplog/httplog.go:320:33: bytes converted to concatenated string
kubernetes/vendor/k8s.io/apiserver/pkg/storage/etcd3/store.go:787:23: bytes converted to concatenated string
kubernetes/vendor/k8s.io/apiserver/pkg/storage/etcd3/store.go:807:45: bytes converted to concatenated string
kubernetes/vendor/k8s.io/apiserver/pkg/storage/etcd3/watcher.go:264:23: bytes converted to concatenated string
kubernetes/vendor/k8s.io/apiserver/pkg/storage/testing/store_tests.go:2137:38: bytes converted to concatenated string
kubernetes/vendor/k8s.io/client-go/plugin/pkg/client/auth/exec/exec_test.go:1051:42: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-aggregator/pkg/apiserver/handler_proxy_test.go:533:38: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kubectl/pkg/cmd/get/get_test.go:2812:42: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kubectl/pkg/cmd/get/get_test.go:2836:37: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-openapi/pkg/builder3/openapi.go:355:15: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-openapi/pkg/builder/openapi.go:370:15: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json/arshal_any.go:161:59: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json/arshal_default.go:1032:62: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json/arshal_default.go:1052:60: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json/arshal_default.go:781:61: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json/arshal_inlined.go:109:60: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json/arshal_inlined.go:69:60: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json/decode.go:495:58: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json/decode.go:665:58: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json/decode.go:904:67: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json/encode.go:451:58: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json/encode.go:546:59: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json/encode.go:619:58: bytes converted to concatenated string
kubernetes/vendor/k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json/encode.go:776:68: bytes converted to concatenated string
kubernetes/vendor/sigs.k8s.io/kustomize/api/internal/plugins/execplugin/execplugin.go:188:43: bytes converted to concatenated string

[zigo101]

This is just another evidence that a builtin concat function is needed.

With the builtin concat supported, this pattern can be rewritten as concat([]byte{}, string1, string2).

[zigo101]

BTW, currently, without the builtin concat, this pattern should not be encouraged.
Using bytes.Buffer or make([]byte,...)+copy/append is more efficient (though the
two are still less efficient than the builtin concat way).

[mateusz834]

But turning the conversions around causes only one allocation.

slices.Concat([]byte(str), []byte(str[:32]))

BenchmarkConcat-4       19893025                59.09 ns/op           96 B/op          1 allocs/op

[zigo101]

@mateusz834 Please read this comment. Generally, it makes 3 allocations.

[mateusz834]

@go101 I belive that is not true on gotip, []byte(str) doesn't cause allocations when the function does not mutate the slice.

#2205

[zigo101]

Aha, that is a cool improvement.

In Go programming, there are many string and byte slice manipulation patterns which are needed to be specially optimized.
The long-tail effect of these patterns are hard to neglect. But it is also tedious (and error-prone) to optimize them one by one.
So I think it would be a good idea to find a universal way to rewrite these patterns. The builtin concat is such an attempt.

[edit] BTW: the optimizations doesn't work for arguments of builtin functions.