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

This CL optimizes the compilation of string-to-bytes conversion in the
case of string additions.

Fixes #62407

Change-Id: Ic47df758478e5d061880620025c4ec7dbbff8a64
Reviewed-on: https://go-review.googlesource.com/c/go/+/527935
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Tim King <taking@google.com>

7 files changed, 432 insertions, 286 deletions

diff --git a/src/cmd/compile/internal/test/issue62407_test.go b/src/cmd/compile/internal/test/issue62407_test.go
new file mode 100644
index 0000000000..d065673627
--- /dev/null
+++ b/src/cmd/compile/internal/test/issue62407_test.go
@@ -0,0 +1,62 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package test
+
+import (
+	"reflect"
+	"testing"
+)
+
+//go:noinline
+func foo() string { return "foo" }
+
+//go:noinline
+func empty() string { return "" }
+
+func TestConcatBytes(t *testing.T) {
+	empty := empty()
+	s := foo()
+	tests := map[string]struct {
+		got  []byte
+		want []byte
+	}{
+		"two empty elements":                 {got: []byte(empty + empty), want: []byte{}},
+		"two nonempty elements":              {got: []byte(s + s), want: []byte("foofoo")},
+		"one empty and one nonempty element": {got: []byte(s + empty), want: []byte("foo")},
+		"multiple empty elements":            {got: []byte(empty + empty + empty + empty + empty + empty), want: []byte{}},
+		"multiple nonempty elements":         {got: []byte("1" + "2" + "3" + "4" + "5" + "6"), want: []byte("123456")},
+	}
+
+	for name, test := range tests {
+		if !reflect.DeepEqual(test.got, test.want) {
+			t.Errorf("[%s] got: %s, want: %s", name, test.got, test.want)
+		}
+	}
+}
+
+func TestConcatBytesAllocations(t *testing.T) {
+	empty := empty()
+	s := foo()
+	tests := map[string]struct {
+		f      func() []byte
+		allocs float64
+	}{
+		"two empty elements":      {f: func() []byte { return []byte(empty + empty) }, allocs: 0},
+		"multiple empty elements": {f: func() []byte { return []byte(empty + empty + empty + empty + empty + empty) }, allocs: 0},
+
+		"two elements":                       {f: func() []byte { return []byte(s + s) }, allocs: 1},
+		"three elements":                     {f: func() []byte { return []byte(s + s + s) }, allocs: 1},
+		"four elements":                      {f: func() []byte { return []byte(s + s + s + s) }, allocs: 1},
+		"five elements":                      {f: func() []byte { return []byte(s + s + s + s + s) }, allocs: 1},
+		"one empty and one nonempty element": {f: func() []byte { return []byte(s + empty) }, allocs: 1},
+		"two empty and two nonempty element": {f: func() []byte { return []byte(s + empty + s + empty) }, allocs: 1},
+	}
+	for name, test := range tests {
+		allocs := testing.AllocsPerRun(100, func() { test.f() })
+		if allocs != test.allocs {
+			t.Errorf("concatbytes [%s]: %v allocs, want %v", name, allocs, test.allocs)
+		}
+	}
+}
diff --git a/src/cmd/compile/internal/typecheck/_builtin/runtime.go b/src/cmd/compile/internal/typecheck/_builtin/runtime.go
index 3a5d3576be..bf6b586725 100644
--- a/src/cmd/compile/internal/typecheck/_builtin/runtime.go
+++ b/src/cmd/compile/internal/typecheck/_builtin/runtime.go
@@ -71,6 +71,12 @@ func concatstring4(*[32]byte, string, string, string, string) string
 func concatstring5(*[32]byte, string, string, string, string, string) string
 func concatstrings(*[32]byte, []string) string
 
+func concatbyte2(string, string) []byte
+func concatbyte3(string, string, string) []byte
+func concatbyte4(string, string, string, string) []byte
+func concatbyte5(string, string, string, string, string) []byte
+func concatbytes([]string) []byte
+
 func cmpstring(string, string) int
 func intstring(*[4]byte, int64) string
 func slicebytetostring(buf *[32]byte, ptr *byte, n int) string
diff --git a/src/cmd/compile/internal/typecheck/builtin.go b/src/cmd/compile/internal/typecheck/builtin.go
index 2f43b1d01c..b4d2ff73ec 100644
--- a/src/cmd/compile/internal/typecheck/builtin.go
+++ b/src/cmd/compile/internal/typecheck/builtin.go
@@ -76,168 +76,173 @@ var runtimeDecls = [...]struct {
 	{"concatstring4", funcTag, 36},
 	{"concatstring5", funcTag, 37},
 	{"concatstrings", funcTag, 39},
-	{"cmpstring", funcTag, 40},
-	{"intstring", funcTag, 43},
-	{"slicebytetostring", funcTag, 44},
-	{"slicebytetostringtmp", funcTag, 45},
-	{"slicerunetostring", funcTag, 48},
-	{"stringtoslicebyte", funcTag, 50},
-	{"stringtoslicerune", funcTag, 53},
-	{"slicecopy", funcTag, 54},
-	{"decoderune", funcTag, 55},
-	{"countrunes", funcTag, 56},
-	{"convT", funcTag, 57},
-	{"convTnoptr", funcTag, 57},
-	{"convT16", funcTag, 59},
-	{"convT32", funcTag, 61},
-	{"convT64", funcTag, 62},
-	{"convTstring", funcTag, 63},
-	{"convTslice", funcTag, 66},
-	{"assertE2I", funcTag, 67},
-	{"assertE2I2", funcTag, 67},
-	{"panicdottypeE", funcTag, 68},
-	{"panicdottypeI", funcTag, 68},
-	{"panicnildottype", funcTag, 69},
-	{"typeAssert", funcTag, 67},
-	{"interfaceSwitch", funcTag, 70},
-	{"ifaceeq", funcTag, 72},
-	{"efaceeq", funcTag, 72},
-	{"panicrangestate", funcTag, 73},
-	{"deferrangefunc", funcTag, 74},
-	{"rand32", funcTag, 75},
-	{"makemap64", funcTag, 77},
-	{"makemap", funcTag, 78},
-	{"makemap_small", funcTag, 79},
-	{"mapaccess1", funcTag, 80},
-	{"mapaccess1_fast32", funcTag, 81},
-	{"mapaccess1_fast64", funcTag, 82},
-	{"mapaccess1_faststr", funcTag, 83},
-	{"mapaccess1_fat", funcTag, 84},
-	{"mapaccess2", funcTag, 85},
-	{"mapaccess2_fast32", funcTag, 86},
-	{"mapaccess2_fast64", funcTag, 87},
-	{"mapaccess2_faststr", funcTag, 88},
-	{"mapaccess2_fat", funcTag, 89},
-	{"mapassign", funcTag, 80},
-	{"mapassign_fast32", funcTag, 81},
-	{"mapassign_fast32ptr", funcTag, 90},
-	{"mapassign_fast64", funcTag, 82},
-	{"mapassign_fast64ptr", funcTag, 90},
-	{"mapassign_faststr", funcTag, 83},
-	{"mapiterinit", funcTag, 91},
-	{"mapdelete", funcTag, 91},
-	{"mapdelete_fast32", funcTag, 92},
-	{"mapdelete_fast64", funcTag, 93},
-	{"mapdelete_faststr", funcTag, 94},
-	{"mapiternext", funcTag, 95},
-	{"mapclear", funcTag, 96},
-	{"makechan64", funcTag, 98},
-	{"makechan", funcTag, 99},
-	{"chanrecv1", funcTag, 101},
-	{"chanrecv2", funcTag, 102},
-	{"chansend1", funcTag, 104},
-	{"closechan", funcTag, 105},
-	{"chanlen", funcTag, 106},
-	{"chancap", funcTag, 106},
-	{"writeBarrier", varTag, 108},
-	{"typedmemmove", funcTag, 109},
-	{"typedmemclr", funcTag, 110},
-	{"typedslicecopy", funcTag, 111},
-	{"selectnbsend", funcTag, 112},
-	{"selectnbrecv", funcTag, 113},
-	{"selectsetpc", funcTag, 114},
-	{"selectgo", funcTag, 115},
+	{"concatbyte2", funcTag, 41},
+	{"concatbyte3", funcTag, 42},
+	{"concatbyte4", funcTag, 43},
+	{"concatbyte5", funcTag, 44},
+	{"concatbytes", funcTag, 45},
+	{"cmpstring", funcTag, 46},
+	{"intstring", funcTag, 49},
+	{"slicebytetostring", funcTag, 50},
+	{"slicebytetostringtmp", funcTag, 51},
+	{"slicerunetostring", funcTag, 54},
+	{"stringtoslicebyte", funcTag, 55},
+	{"stringtoslicerune", funcTag, 58},
+	{"slicecopy", funcTag, 59},
+	{"decoderune", funcTag, 60},
+	{"countrunes", funcTag, 61},
+	{"convT", funcTag, 62},
+	{"convTnoptr", funcTag, 62},
+	{"convT16", funcTag, 64},
+	{"convT32", funcTag, 66},
+	{"convT64", funcTag, 67},
+	{"convTstring", funcTag, 68},
+	{"convTslice", funcTag, 71},
+	{"assertE2I", funcTag, 72},
+	{"assertE2I2", funcTag, 72},
+	{"panicdottypeE", funcTag, 73},
+	{"panicdottypeI", funcTag, 73},
+	{"panicnildottype", funcTag, 74},
+	{"typeAssert", funcTag, 72},
+	{"interfaceSwitch", funcTag, 75},
+	{"ifaceeq", funcTag, 77},
+	{"efaceeq", funcTag, 77},
+	{"panicrangestate", funcTag, 78},
+	{"deferrangefunc", funcTag, 79},
+	{"rand32", funcTag, 80},
+	{"makemap64", funcTag, 82},
+	{"makemap", funcTag, 83},
+	{"makemap_small", funcTag, 84},
+	{"mapaccess1", funcTag, 85},
+	{"mapaccess1_fast32", funcTag, 86},
+	{"mapaccess1_fast64", funcTag, 87},
+	{"mapaccess1_faststr", funcTag, 88},
+	{"mapaccess1_fat", funcTag, 89},
+	{"mapaccess2", funcTag, 90},
+	{"mapaccess2_fast32", funcTag, 91},
+	{"mapaccess2_fast64", funcTag, 92},
+	{"mapaccess2_faststr", funcTag, 93},
+	{"mapaccess2_fat", funcTag, 94},
+	{"mapassign", funcTag, 85},
+	{"mapassign_fast32", funcTag, 86},
+	{"mapassign_fast32ptr", funcTag, 95},
+	{"mapassign_fast64", funcTag, 87},
+	{"mapassign_fast64ptr", funcTag, 95},
+	{"mapassign_faststr", funcTag, 88},
+	{"mapiterinit", funcTag, 96},
+	{"mapdelete", funcTag, 96},
+	{"mapdelete_fast32", funcTag, 97},
+	{"mapdelete_fast64", funcTag, 98},
+	{"mapdelete_faststr", funcTag, 99},
+	{"mapiternext", funcTag, 100},
+	{"mapclear", funcTag, 101},
+	{"makechan64", funcTag, 103},
+	{"makechan", funcTag, 104},
+	{"chanrecv1", funcTag, 106},
+	{"chanrecv2", funcTag, 107},
+	{"chansend1", funcTag, 109},
+	{"closechan", funcTag, 110},
+	{"chanlen", funcTag, 111},
+	{"chancap", funcTag, 111},
+	{"writeBarrier", varTag, 113},
+	{"typedmemmove", funcTag, 114},
+	{"typedmemclr", funcTag, 115},
+	{"typedslicecopy", funcTag, 116},
+	{"selectnbsend", funcTag, 117},
+	{"selectnbrecv", funcTag, 118},
+	{"selectsetpc", funcTag, 119},
+	{"selectgo", funcTag, 120},
 	{"block", funcTag, 9},
-	{"makeslice", funcTag, 116},
-	{"makeslice64", funcTag, 117},
-	{"makeslicecopy", funcTag, 118},
-	{"growslice", funcTag, 120},
-	{"unsafeslicecheckptr", funcTag, 121},
+	{"makeslice", funcTag, 121},
+	{"makeslice64", funcTag, 122},
+	{"makeslicecopy", funcTag, 123},
+	{"growslice", funcTag, 125},
+	{"unsafeslicecheckptr", funcTag, 126},
 	{"panicunsafeslicelen", funcTag, 9},
 	{"panicunsafeslicenilptr", funcTag, 9},
-	{"unsafestringcheckptr", funcTag, 122},
+	{"unsafestringcheckptr", funcTag, 127},
 	{"panicunsafestringlen", funcTag, 9},
 	{"panicunsafestringnilptr", funcTag, 9},
-	{"memmove", funcTag, 123},
-	{"memclrNoHeapPointers", funcTag, 124},
-	{"memclrHasPointers", funcTag, 124},
-	{"memequal", funcTag, 125},
-	{"memequal0", funcTag, 126},
-	{"memequal8", funcTag, 126},
-	{"memequal16", funcTag, 126},
-	{"memequal32", funcTag, 126},
-	{"memequal64", funcTag, 126},
-	{"memequal128", funcTag, 126},
-	{"f32equal", funcTag, 127},
-	{"f64equal", funcTag, 127},
-	{"c64equal", funcTag, 127},
-	{"c128equal", funcTag, 127},
-	{"strequal", funcTag, 127},
-	{"interequal", funcTag, 127},
-	{"nilinterequal", funcTag, 127},
-	{"memhash", funcTag, 128},
-	{"memhash0", funcTag, 129},
-	{"memhash8", funcTag, 129},
-	{"memhash16", funcTag, 129},
-	{"memhash32", funcTag, 129},
-	{"memhash64", funcTag, 129},
-	{"memhash128", funcTag, 129},
-	{"f32hash", funcTag, 130},
-	{"f64hash", funcTag, 130},
-	{"c64hash", funcTag, 130},
-	{"c128hash", funcTag, 130},
-	{"strhash", funcTag, 130},
-	{"interhash", funcTag, 130},
-	{"nilinterhash", funcTag, 130},
-	{"int64div", funcTag, 131},
-	{"uint64div", funcTag, 132},
-	{"int64mod", funcTag, 131},
-	{"uint64mod", funcTag, 132},
-	{"float64toint64", funcTag, 133},
-	{"float64touint64", funcTag, 134},
-	{"float64touint32", funcTag, 135},
-	{"int64tofloat64", funcTag, 136},
-	{"int64tofloat32", funcTag, 138},
-	{"uint64tofloat64", funcTag, 139},
-	{"uint64tofloat32", funcTag, 140},
-	{"uint32tofloat64", funcTag, 141},
-	{"complex128div", funcTag, 142},
-	{"getcallerpc", funcTag, 143},
-	{"getcallersp", funcTag, 143},
+	{"memmove", funcTag, 128},
+	{"memclrNoHeapPointers", funcTag, 129},
+	{"memclrHasPointers", funcTag, 129},
+	{"memequal", funcTag, 130},
+	{"memequal0", funcTag, 131},
+	{"memequal8", funcTag, 131},
+	{"memequal16", funcTag, 131},
+	{"memequal32", funcTag, 131},
+	{"memequal64", funcTag, 131},
+	{"memequal128", funcTag, 131},
+	{"f32equal", funcTag, 132},
+	{"f64equal", funcTag, 132},
+	{"c64equal", funcTag, 132},
+	{"c128equal", funcTag, 132},
+	{"strequal", funcTag, 132},
+	{"interequal", funcTag, 132},
+	{"nilinterequal", funcTag, 132},
+	{"memhash", funcTag, 133},
+	{"memhash0", funcTag, 134},
+	{"memhash8", funcTag, 134},
+	{"memhash16", funcTag, 134},
+	{"memhash32", funcTag, 134},
+	{"memhash64", funcTag, 134},
+	{"memhash128", funcTag, 134},
+	{"f32hash", funcTag, 135},
+	{"f64hash", funcTag, 135},
+	{"c64hash", funcTag, 135},
+	{"c128hash", funcTag, 135},
+	{"strhash", funcTag, 135},
+	{"interhash", funcTag, 135},
+	{"nilinterhash", funcTag, 135},
+	{"int64div", funcTag, 136},
+	{"uint64div", funcTag, 137},
+	{"int64mod", funcTag, 136},
+	{"uint64mod", funcTag, 137},
+	{"float64toint64", funcTag, 138},
+	{"float64touint64", funcTag, 139},
+	{"float64touint32", funcTag, 140},
+	{"int64tofloat64", funcTag, 141},
+	{"int64tofloat32", funcTag, 143},
+	{"uint64tofloat64", funcTag, 144},
+	{"uint64tofloat32", funcTag, 145},
+	{"uint32tofloat64", funcTag, 146},
+	{"complex128div", funcTag, 147},
+	{"getcallerpc", funcTag, 148},
+	{"getcallersp", funcTag, 148},
 	{"racefuncenter", funcTag, 31},
 	{"racefuncexit", funcTag, 9},
 	{"raceread", funcTag, 31},
 	{"racewrite", funcTag, 31},
-	{"racereadrange", funcTag, 144},
-	{"racewriterange", funcTag, 144},
-	{"msanread", funcTag, 144},
-	{"msanwrite", funcTag, 144},
-	{"msanmove", funcTag, 145},
-	{"asanread", funcTag, 144},
-	{"asanwrite", funcTag, 144},
-	{"checkptrAlignment", funcTag, 146},
-	{"checkptrArithmetic", funcTag, 148},
-	{"libfuzzerTraceCmp1", funcTag, 149},
-	{"libfuzzerTraceCmp2", funcTag, 150},
-	{"libfuzzerTraceCmp4", funcTag, 151},
-	{"libfuzzerTraceCmp8", funcTag, 152},
-	{"libfuzzerTraceConstCmp1", funcTag, 149},
-	{"libfuzzerTraceConstCmp2", funcTag, 150},
-	{"libfuzzerTraceConstCmp4", funcTag, 151},
-	{"libfuzzerTraceConstCmp8", funcTag, 152},
-	{"libfuzzerHookStrCmp", funcTag, 153},
-	{"libfuzzerHookEqualFold", funcTag, 153},
-	{"addCovMeta", funcTag, 155},
+	{"racereadrange", funcTag, 149},
+	{"racewriterange", funcTag, 149},
+	{"msanread", funcTag, 149},
+	{"msanwrite", funcTag, 149},
+	{"msanmove", funcTag, 150},
+	{"asanread", funcTag, 149},
+	{"asanwrite", funcTag, 149},
+	{"checkptrAlignment", funcTag, 151},
+	{"checkptrArithmetic", funcTag, 153},
+	{"libfuzzerTraceCmp1", funcTag, 154},
+	{"libfuzzerTraceCmp2", funcTag, 155},
+	{"libfuzzerTraceCmp4", funcTag, 156},
+	{"libfuzzerTraceCmp8", funcTag, 157},
+	{"libfuzzerTraceConstCmp1", funcTag, 154},
+	{"libfuzzerTraceConstCmp2", funcTag, 155},
+	{"libfuzzerTraceConstCmp4", funcTag, 156},
+	{"libfuzzerTraceConstCmp8", funcTag, 157},
+	{"libfuzzerHookStrCmp", funcTag, 158},
+	{"libfuzzerHookEqualFold", funcTag, 158},
+	{"addCovMeta", funcTag, 160},
 	{"x86HasPOPCNT", varTag, 6},
 	{"x86HasSSE41", varTag, 6},
 	{"x86HasFMA", varTag, 6},
 	{"armHasVFPv4", varTag, 6},
 	{"arm64HasATOMICS", varTag, 6},
-	{"asanregisterglobals", funcTag, 124},
+	{"asanregisterglobals", funcTag, 129},
 }
 
 func runtimeTypes() []*types.Type {
-	var typs [156]*types.Type
+	var typs [161]*types.Type
 	typs[0] = types.ByteType
 	typs[1] = types.NewPtr(typs[0])
 	typs[2] = types.Types[types.TANY]
@@ -278,122 +283,127 @@ func runtimeTypes() []*types.Type {
 	typs[37] = newSig(params(typs[33], typs[28], typs[28], typs[28], typs[28], typs[28]), params(typs[28]))
 	typs[38] = types.NewSlice(typs[28])
 	typs[39] = newSig(params(typs[33], typs[38]), params(typs[28]))
-	typs[40] = newSig(params(typs[28], typs[28]), params(typs[15]))
-	typs[41] = types.NewArray(typs[0], 4)
-	typs[42] = types.NewPtr(typs[41])
-	typs[43] = newSig(params(typs[42], typs[22]), params(typs[28]))
-	typs[44] = newSig(params(typs[33], typs[1], typs[15]), params(typs[28]))
-	typs[45] = newSig(params(typs[1], typs[15]), params(typs[28]))
-	typs[46] = types.RuneType
-	typs[47] = types.NewSlice(typs[46])
-	typs[48] = newSig(params(typs[33], typs[47]), params(typs[28]))
-	typs[49] = types.NewSlice(typs[0])
-	typs[50] = newSig(params(typs[33], typs[28]), params(typs[49]))
-	typs[51] = types.NewArray(typs[46], 32)
-	typs[52] = types.NewPtr(typs[51])
-	typs[53] = newSig(params(typs[52], typs[28]), params(typs[47]))
-	typs[54] = newSig(params(typs[3], typs[15], typs[3], typs[15], typs[5]), params(typs[15]))
-	typs[55] = newSig(params(typs[28], typs[15]), params(typs[46], typs[15]))
-	typs[56] = newSig(params(typs[28]), params(typs[15]))
-	typs[57] = newSig(params(typs[1], typs[3]), params(typs[7]))
-	typs[58] = types.Types[types.TUINT16]
-	typs[59] = newSig(params(typs[58]), params(typs[7]))
-	typs[60] = types.Types[types.TUINT32]
-	typs[61] = newSig(params(typs[60]), params(typs[7]))
-	typs[62] = newSig(params(typs[24]), params(typs[7]))
-	typs[63] = newSig(params(typs[28]), params(typs[7]))
-	typs[64] = types.Types[types.TUINT8]
-	typs[65] = types.NewSlice(typs[64])
+	typs[40] = types.NewSlice(typs[0])
+	typs[41] = newSig(params(typs[28], typs[28]), params(typs[40]))
+	typs[42] = newSig(params(typs[28], typs[28], typs[28]), params(typs[40]))
+	typs[43] = newSig(params(typs[28], typs[28], typs[28], typs[28]), params(typs[40]))
+	typs[44] = newSig(params(typs[28], typs[28], typs[28], typs[28], typs[28]), params(typs[40]))
+	typs[45] = newSig(params(typs[38]), params(typs[40]))
+	typs[46] = newSig(params(typs[28], typs[28]), params(typs[15]))
+	typs[47] = types.NewArray(typs[0], 4)
+	typs[48] = types.NewPtr(typs[47])
+	typs[49] = newSig(params(typs[48], typs[22]), params(typs[28]))
+	typs[50] = newSig(params(typs[33], typs[1], typs[15]), params(typs[28]))
+	typs[51] = newSig(params(typs[1], typs[15]), params(typs[28]))
+	typs[52] = types.RuneType
+	typs[53] = types.NewSlice(typs[52])
+	typs[54] = newSig(params(typs[33], typs[53]), params(typs[28]))
+	typs[55] = newSig(params(typs[33], typs[28]), params(typs[40]))
+	typs[56] = types.NewArray(typs[52], 32)
+	typs[57] = types.NewPtr(typs[56])
+	typs[58] = newSig(params(typs[57], typs[28]), params(typs[53]))
+	typs[59] = newSig(params(typs[3], typs[15], typs[3], typs[15], typs[5]), params(typs[15]))
+	typs[60] = newSig(params(typs[28], typs[15]), params(typs[52], typs[15]))
+	typs[61] = newSig(params(typs[28]), params(typs[15]))
+	typs[62] = newSig(params(typs[1], typs[3]), params(typs[7]))
+	typs[63] = types.Types[types.TUINT16]
+	typs[64] = newSig(params(typs[63]), params(typs[7]))
+	typs[65] = types.Types[types.TUINT32]
 	typs[66] = newSig(params(typs[65]), params(typs[7]))
-	typs[67] = newSig(params(typs[1], typs[1]), params(typs[1]))
-	typs[68] = newSig(params(typs[1], typs[1], typs[1]), nil)
-	typs[69] = newSig(params(typs[1]), nil)
-	typs[70] = newSig(params(typs[1], typs[1]), params(typs[15], typs[1]))
-	typs[71] = types.NewPtr(typs[5])
-	typs[72] = newSig(params(typs[71], typs[7], typs[7]), params(typs[6]))
-	typs[73] = newSig(params(typs[15]), nil)
-	typs[74] = newSig(nil, params(typs[10]))
-	typs[75] = newSig(nil, params(typs[60]))
-	typs[76] = types.NewMap(typs[2], typs[2])
-	typs[77] = newSig(params(typs[1], typs[22], typs[3]), params(typs[76]))
-	typs[78] = newSig(params(typs[1], typs[15], typs[3]), params(typs[76]))
-	typs[79] = newSig(nil, params(typs[76]))
-	typs[80] = newSig(params(typs[1], typs[76], typs[3]), params(typs[3]))
-	typs[81] = newSig(params(typs[1], typs[76], typs[60]), params(typs[3]))
-	typs[82] = newSig(params(typs[1], typs[76], typs[24]), params(typs[3]))
-	typs[83] = newSig(params(typs[1], typs[76], typs[28]), params(typs[3]))
-	typs[84] = newSig(params(typs[1], typs[76], typs[3], typs[1]), params(typs[3]))
-	typs[85] = newSig(params(typs[1], typs[76], typs[3]), params(typs[3], typs[6]))
-	typs[86] = newSig(params(typs[1], typs[76], typs[60]), params(typs[3], typs[6]))
-	typs[87] = newSig(params(typs[1], typs[76], typs[24]), params(typs[3], typs[6]))
-	typs[88] = newSig(params(typs[1], typs[76], typs[28]), params(typs[3], typs[6]))
-	typs[89] = newSig(params(typs[1], typs[76], typs[3], typs[1]), params(typs[3], typs[6]))
-	typs[90] = newSig(params(typs[1], typs[76], typs[7]), params(typs[3]))
-	typs[91] = newSig(params(typs[1], typs[76], typs[3]), nil)
-	typs[92] = newSig(params(typs[1], typs[76], typs[60]), nil)
-	typs[93] = newSig(params(typs[1], typs[76], typs[24]), nil)
-	typs[94] = newSig(params(typs[1], typs[76], typs[28]), nil)
-	typs[95] = newSig(params(typs[3]), nil)
-	typs[96] = newSig(params(typs[1], typs[76]), nil)
-	typs[97] = types.NewChan(typs[2], types.Cboth)
-	typs[98] = newSig(params(typs[1], typs[22]), params(typs[97]))
-	typs[99] = newSig(params(typs[1], typs[15]), params(typs[97]))
-	typs[100] = types.NewChan(typs[2], types.Crecv)
-	typs[101] = newSig(params(typs[100], typs[3]), nil)
-	typs[102] = newSig(params(typs[100], typs[3]), params(typs[6]))
-	typs[103] = types.NewChan(typs[2], types.Csend)
-	typs[104] = newSig(params(typs[103], typs[3]), nil)
-	typs[105] = newSig(params(typs[103]), nil)
-	typs[106] = newSig(params(typs[2]), params(typs[15]))
-	typs[107] = types.NewArray(typs[0], 3)
-	typs[108] = types.NewStruct([]*types.Field{types.NewField(src.NoXPos, Lookup("enabled"), typs[6]), types.NewField(src.NoXPos, Lookup("pad"), typs[107]), types.NewField(src.NoXPos, Lookup("cgo"), typs[6]), types.NewField(src.NoXPos, Lookup("alignme"), typs[24])})
-	typs[109] = newSig(params(typs[1], typs[3], typs[3]), nil)
-	typs[110] = newSig(params(typs[1], typs[3]), nil)
-	typs[111] = newSig(params(typs[1], typs[3], typs[15], typs[3], typs[15]), params(typs[15]))
-	typs[112] = newSig(params(typs[103], typs[3]), params(typs[6]))
-	typs[113] = newSig(params(typs[3], typs[100]), params(typs[6], typs[6]))
-	typs[114] = newSig(params(typs[71]), nil)
-	typs[115] = newSig(params(typs[1], typs[1], typs[71], typs[15], typs[15], typs[6]), params(typs[15], typs[6]))
-	typs[116] = newSig(params(typs[1], typs[15], typs[15]), params(typs[7]))
-	typs[117] = newSig(params(typs[1], typs[22], typs[22]), params(typs[7]))
-	typs[118] = newSig(params(typs[1], typs[15], typs[15], typs[7]), params(typs[7]))
-	typs[119] = types.NewSlice(typs[2])
-	typs[120] = newSig(params(typs[3], typs[15], typs[15], typs[15], typs[1]), params(typs[119]))
-	typs[121] = newSig(params(typs[1], typs[7], typs[22]), nil)
-	typs[122] = newSig(params(typs[7], typs[22]), nil)
-	typs[123] = newSig(params(typs[3], typs[3], typs[5]), nil)
-	typs[124] = newSig(params(typs[7], typs[5]), nil)
-	typs[125] = newSig(params(typs[3], typs[3], typs[5]), params(typs[6]))
-	typs[126] = newSig(params(typs[3], typs[3]), params(typs[6]))
-	typs[127] = newSig(params(typs[7], typs[7]), params(typs[6]))
-	typs[128] = newSig(params(typs[3], typs[5], typs[5]), params(typs[5]))
-	typs[129] = newSig(params(typs[7], typs[5]), params(typs[5]))
-	typs[130] = newSig(params(typs[3], typs[5]), params(typs[5]))
-	typs[131] = newSig(params(typs[22], typs[22]), params(typs[22]))
-	typs[132] = newSig(params(typs[24], typs[24]), params(typs[24]))
-	typs[133] = newSig(params(typs[20]), params(typs[22]))
-	typs[134] = newSig(params(typs[20]), params(typs[24]))
-	typs[135] = newSig(params(typs[20]), params(typs[60]))
-	typs[136] = newSig(params(typs[22]), params(typs[20]))
-	typs[137] = types.Types[types.TFLOAT32]
-	typs[138] = newSig(params(typs[22]), params(typs[137]))
-	typs[139] = newSig(params(typs[24]), params(typs[20]))
-	typs[140] = newSig(params(typs[24]), params(typs[137]))
-	typs[141] = newSig(params(typs[60]), params(typs[20]))
-	typs[142] = newSig(params(typs[26], typs[26]), params(typs[26]))
-	typs[143] = newSig(nil, params(typs[5]))
-	typs[144] = newSig(params(typs[5], typs[5]), nil)
-	typs[145] = newSig(params(typs[5], typs[5], typs[5]), nil)
-	typs[146] = newSig(params(typs[7], typs[1], typs[5]), nil)
-	typs[147] = types.NewSlice(typs[7])
-	typs[148] = newSig(params(typs[7], typs[147]), nil)
-	typs[149] = newSig(params(typs[64], typs[64], typs[17]), nil)
-	typs[150] = newSig(params(typs[58], typs[58], typs[17]), nil)
-	typs[151] = newSig(params(typs[60], typs[60], typs[17]), nil)
-	typs[152] = newSig(params(typs[24], typs[24], typs[17]), nil)
-	typs[153] = newSig(params(typs[28], typs[28], typs[17]), nil)
-	typs[154] = types.NewArray(typs[0], 16)
-	typs[155] = newSig(params(typs[7], typs[60], typs[154], typs[28], typs[15], typs[64], typs[64]), params(typs[60]))
+	typs[67] = newSig(params(typs[24]), params(typs[7]))
+	typs[68] = newSig(params(typs[28]), params(typs[7]))
+	typs[69] = types.Types[types.TUINT8]
+	typs[70] = types.NewSlice(typs[69])
+	typs[71] = newSig(params(typs[70]), params(typs[7]))
+	typs[72] = newSig(params(typs[1], typs[1]), params(typs[1]))
+	typs[73] = newSig(params(typs[1], typs[1], typs[1]), nil)
+	typs[74] = newSig(params(typs[1]), nil)
+	typs[75] = newSig(params(typs[1], typs[1]), params(typs[15], typs[1]))
+	typs[76] = types.NewPtr(typs[5])
+	typs[77] = newSig(params(typs[76], typs[7], typs[7]), params(typs[6]))
+	typs[78] = newSig(params(typs[15]), nil)
+	typs[79] = newSig(nil, params(typs[10]))
+	typs[80] = newSig(nil, params(typs[65]))
+	typs[81] = types.NewMap(typs[2], typs[2])
+	typs[82] = newSig(params(typs[1], typs[22], typs[3]), params(typs[81]))
+	typs[83] = newSig(params(typs[1], typs[15], typs[3]), params(typs[81]))
+	typs[84] = newSig(nil, params(typs[81]))
+	typs[85] = newSig(params(typs[1], typs[81], typs[3]), params(typs[3]))
+	typs[86] = newSig(params(typs[1], typs[81], typs[65]), params(typs[3]))
+	typs[87] = newSig(params(typs[1], typs[81], typs[24]), params(typs[3]))
+	typs[88] = newSig(params(typs[1], typs[81], typs[28]), params(typs[3]))
+	typs[89] = newSig(params(typs[1], typs[81], typs[3], typs[1]), params(typs[3]))
+	typs[90] = newSig(params(typs[1], typs[81], typs[3]), params(typs[3], typs[6]))
+	typs[91] = newSig(params(typs[1], typs[81], typs[65]), params(typs[3], typs[6]))
+	typs[92] = newSig(params(typs[1], typs[81], typs[24]), params(typs[3], typs[6]))
+	typs[93] = newSig(params(typs[1], typs[81], typs[28]), params(typs[3], typs[6]))
+	typs[94] = newSig(params(typs[1], typs[81], typs[3], typs[1]), params(typs[3], typs[6]))
+	typs[95] = newSig(params(typs[1], typs[81], typs[7]), params(typs[3]))
+	typs[96] = newSig(params(typs[1], typs[81], typs[3]), nil)
+	typs[97] = newSig(params(typs[1], typs[81], typs[65]), nil)
+	typs[98] = newSig(params(typs[1], typs[81], typs[24]), nil)
+	typs[99] = newSig(params(typs[1], typs[81], typs[28]), nil)
+	typs[100] = newSig(params(typs[3]), nil)
+	typs[101] = newSig(params(typs[1], typs[81]), nil)
+	typs[102] = types.NewChan(typs[2], types.Cboth)
+	typs[103] = newSig(params(typs[1], typs[22]), params(typs[102]))
+	typs[104] = newSig(params(typs[1], typs[15]), params(typs[102]))
+	typs[105] = types.NewChan(typs[2], types.Crecv)
+	typs[106] = newSig(params(typs[105], typs[3]), nil)
+	typs[107] = newSig(params(typs[105], typs[3]), params(typs[6]))
+	typs[108] = types.NewChan(typs[2], types.Csend)
+	typs[109] = newSig(params(typs[108], typs[3]), nil)
+	typs[110] = newSig(params(typs[108]), nil)
+	typs[111] = newSig(params(typs[2]), params(typs[15]))
+	typs[112] = types.NewArray(typs[0], 3)
+	typs[113] = types.NewStruct([]*types.Field{types.NewField(src.NoXPos, Lookup("enabled"), typs[6]), types.NewField(src.NoXPos, Lookup("pad"), typs[112]), types.NewField(src.NoXPos, Lookup("cgo"), typs[6]), types.NewField(src.NoXPos, Lookup("alignme"), typs[24])})
+	typs[114] = newSig(params(typs[1], typs[3], typs[3]), nil)
+	typs[115] = newSig(params(typs[1], typs[3]), nil)
+	typs[116] = newSig(params(typs[1], typs[3], typs[15], typs[3], typs[15]), params(typs[15]))
+	typs[117] = newSig(params(typs[108], typs[3]), params(typs[6]))
+	typs[118] = newSig(params(typs[3], typs[105]), params(typs[6], typs[6]))
+	typs[119] = newSig(params(typs[76]), nil)
+	typs[120] = newSig(params(typs[1], typs[1], typs[76], typs[15], typs[15], typs[6]), params(typs[15], typs[6]))
+	typs[121] = newSig(params(typs[1], typs[15], typs[15]), params(typs[7]))
+	typs[122] = newSig(params(typs[1], typs[22], typs[22]), params(typs[7]))
+	typs[123] = newSig(params(typs[1], typs[15], typs[15], typs[7]), params(typs[7]))
+	typs[124] = types.NewSlice(typs[2])
+	typs[125] = newSig(params(typs[3], typs[15], typs[15], typs[15], typs[1]), params(typs[124]))
+	typs[126] = newSig(params(typs[1], typs[7], typs[22]), nil)
+	typs[127] = newSig(params(typs[7], typs[22]), nil)
+	typs[128] = newSig(params(typs[3], typs[3], typs[5]), nil)
+	typs[129] = newSig(params(typs[7], typs[5]), nil)
+	typs[130] = newSig(params(typs[3], typs[3], typs[5]), params(typs[6]))
+	typs[131] = newSig(params(typs[3], typs[3]), params(typs[6]))
+	typs[132] = newSig(params(typs[7], typs[7]), params(typs[6]))
+	typs[133] = newSig(params(typs[3], typs[5], typs[5]), params(typs[5]))
+	typs[134] = newSig(params(typs[7], typs[5]), params(typs[5]))
+	typs[135] = newSig(params(typs[3], typs[5]), params(typs[5]))
+	typs[136] = newSig(params(typs[22], typs[22]), params(typs[22]))
+	typs[137] = newSig(params(typs[24], typs[24]), params(typs[24]))
+	typs[138] = newSig(params(typs[20]), params(typs[22]))
+	typs[139] = newSig(params(typs[20]), params(typs[24]))
+	typs[140] = newSig(params(typs[20]), params(typs[65]))
+	typs[141] = newSig(params(typs[22]), params(typs[20]))
+	typs[142] = types.Types[types.TFLOAT32]
+	typs[143] = newSig(params(typs[22]), params(typs[142]))
+	typs[144] = newSig(params(typs[24]), params(typs[20]))
+	typs[145] = newSig(params(typs[24]), params(typs[142]))
+	typs[146] = newSig(params(typs[65]), params(typs[20]))
+	typs[147] = newSig(params(typs[26], typs[26]), params(typs[26]))
+	typs[148] = newSig(nil, params(typs[5]))
+	typs[149] = newSig(params(typs[5], typs[5]), nil)
+	typs[150] = newSig(params(typs[5], typs[5], typs[5]), nil)
+	typs[151] = newSig(params(typs[7], typs[1], typs[5]), nil)
+	typs[152] = types.NewSlice(typs[7])
+	typs[153] = newSig(params(typs[7], typs[152]), nil)
+	typs[154] = newSig(params(typs[69], typs[69], typs[17]), nil)
+	typs[155] = newSig(params(typs[63], typs[63], typs[17]), nil)
+	typs[156] = newSig(params(typs[65], typs[65], typs[17]), nil)
+	typs[157] = newSig(params(typs[24], typs[24], typs[17]), nil)
+	typs[158] = newSig(params(typs[28], typs[28], typs[17]), nil)
+	typs[159] = types.NewArray(typs[0], 16)
+	typs[160] = newSig(params(typs[7], typs[65], typs[159], typs[28], typs[15], typs[69], typs[69]), params(typs[65]))
 	return typs[:]
 }
 
diff --git a/src/cmd/compile/internal/walk/convert.go b/src/cmd/compile/internal/walk/convert.go
index 280b3b65e8..3118233697 100644
--- a/src/cmd/compile/internal/walk/convert.go
+++ b/src/cmd/compile/internal/walk/convert.go
@@ -270,6 +270,11 @@ func walkRuneToString(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
 // walkStringToBytes walks an OSTR2BYTES node.
 func walkStringToBytes(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
 	s := n.X
+
+	if expr, ok := s.(*ir.AddStringExpr); ok {
+		return walkAddString(n.Type(), expr, init)
+	}
+
 	if ir.IsConst(s, constant.String) {
 		sc := ir.StringVal(s)
 
diff --git a/src/cmd/compile/internal/walk/expr.go b/src/cmd/compile/internal/walk/expr.go
index f73b5d9503..8c36e03aa0 100644
--- a/src/cmd/compile/internal/walk/expr.go
+++ b/src/cmd/compile/internal/walk/expr.go
@@ -273,7 +273,7 @@ func walkExpr1(n ir.Node, init *ir.Nodes) ir.Node {
 		return walkNew(n, init)
 
 	case ir.OADDSTR:
-		return walkAddString(n.(*ir.AddStringExpr), init)
+		return walkAddString(n.Type(), n.(*ir.AddStringExpr), init)
 
 	case ir.OAPPEND:
 		// order should make sure we only see OAS(node, OAPPEND), which we handle above.
@@ -464,49 +464,64 @@ func copyExpr(n ir.Node, t *types.Type, init *ir.Nodes) ir.Node {
 	return l
 }
 
-func walkAddString(n *ir.AddStringExpr, init *ir.Nodes) ir.Node {
+func walkAddString(typ *types.Type, n *ir.AddStringExpr, init *ir.Nodes) ir.Node {
 	c := len(n.List)
 
 	if c < 2 {
 		base.Fatalf("walkAddString count %d too small", c)
 	}
 
-	buf := typecheck.NodNil()
-	if n.Esc() == ir.EscNone {
-		sz := int64(0)
-		for _, n1 := range n.List {
-			if n1.Op() == ir.OLITERAL {
-				sz += int64(len(ir.StringVal(n1)))
+	// list of string arguments
+	var args []ir.Node
+
+	var fn, fnsmall, fnbig string
+
+	switch {
+	default:
+		base.FatalfAt(n.Pos(), "unexpected type: %v", typ)
+	case typ.IsString():
+		buf := typecheck.NodNil()
+		if n.Esc() == ir.EscNone {
+			sz := int64(0)
+			for _, n1 := range n.List {
+				if n1.Op() == ir.OLITERAL {
+					sz += int64(len(ir.StringVal(n1)))
+				}
 			}
-		}
 
-		// Don't allocate the buffer if the result won't fit.
-		if sz < tmpstringbufsize {
-			// Create temporary buffer for result string on stack.
-			buf = stackBufAddr(tmpstringbufsize, types.Types[types.TUINT8])
+			// Don't allocate the buffer if the result won't fit.
+			if sz < tmpstringbufsize {
+				// Create temporary buffer for result string on stack.
+				buf = stackBufAddr(tmpstringbufsize, types.Types[types.TUINT8])
+			}
 		}
-	}
 
-	// build list of string arguments
-	args := []ir.Node{buf}
-	for _, n2 := range n.List {
-		args = append(args, typecheck.Conv(n2, types.Types[types.TSTRING]))
+		args = []ir.Node{buf}
+		fnsmall, fnbig = "concatstring%d", "concatstrings"
+	case typ.IsSlice() && typ.Elem().IsKind(types.TUINT8): // Optimize []byte(str1+str2+...)
+		fnsmall, fnbig = "concatbyte%d", "concatbytes"
 	}
 
-	var fn string
 	if c <= 5 {
 		// small numbers of strings use direct runtime helpers.
 		// note: order.expr knows this cutoff too.
-		fn = fmt.Sprintf("concatstring%d", c)
+		fn = fmt.Sprintf(fnsmall, c)
+
+		for _, n2 := range n.List {
+			args = append(args, typecheck.Conv(n2, types.Types[types.TSTRING]))
+		}
 	} else {
 		// large numbers of strings are passed to the runtime as a slice.
-		fn = "concatstrings"
-
+		fn = fnbig
 		t := types.NewSlice(types.Types[types.TSTRING])
-		// args[1:] to skip buf arg
-		slice := ir.NewCompLitExpr(base.Pos, ir.OCOMPLIT, t, args[1:])
+
+		slargs := make([]ir.Node, len(n.List))
+		for i, n2 := range n.List {
+			slargs[i] = typecheck.Conv(n2, types.Types[types.TSTRING])
+		}
+		slice := ir.NewCompLitExpr(base.Pos, ir.OCOMPLIT, t, slargs)
 		slice.Prealloc = n.Prealloc
-		args = []ir.Node{buf, slice}
+		args = append(args, slice)
 		slice.SetEsc(ir.EscNone)
 	}
 
@@ -515,7 +530,7 @@ func walkAddString(n *ir.AddStringExpr, init *ir.Nodes) ir.Node {
 	r.Args = args
 	r1 := typecheck.Expr(r)
 	r1 = walkExpr(r1, init)
-	r1.SetType(n.Type())
+	r1.SetType(typ)
 
 	return r1
 }
diff --git a/src/cmd/internal/goobj/builtinlist.go b/src/cmd/internal/goobj/builtinlist.go
index e2aae748a0..98a7fd0411 100644
--- a/src/cmd/internal/goobj/builtinlist.go
+++ b/src/cmd/internal/goobj/builtinlist.go
@@ -55,6 +55,11 @@ var builtins = [...]struct {
 	{"runtime.concatstring4", 1},
 	{"runtime.concatstring5", 1},
 	{"runtime.concatstrings", 1},
+	{"runtime.concatbyte2", 1},
+	{"runtime.concatbyte3", 1},
+	{"runtime.concatbyte4", 1},
+	{"runtime.concatbyte5", 1},
+	{"runtime.concatbytes", 1},
 	{"runtime.cmpstring", 1},
 	{"runtime.intstring", 1},
 	{"runtime.slicebytetostring", 1},
diff --git a/src/runtime/string.go b/src/runtime/string.go
index d45888b7a8..3c34541ee8 100644
--- a/src/runtime/string.go
+++ b/src/runtime/string.go
@@ -72,6 +72,49 @@ func concatstring5(buf *tmpBuf, a0, a1, a2, a3, a4 string) string {
 	return concatstrings(buf, []string{a0, a1, a2, a3, a4})
 }
 
+// concatbytes implements a Go string concatenation x+y+z+... returning a slice
+// of bytes.
+// The operands are passed in the slice a.
+func concatbytes(a []string) []byte {
+	l := 0
+	for _, x := range a {
+		n := len(x)
+		if l+n < l {
+			throw("string concatenation too long")
+		}
+		l += n
+	}
+	if l == 0 {
+		// This is to match the return type of the non-optimized concatenation.
+		return []byte{}
+	}
+
+	b := rawbyteslice(l)
+	offset := 0
+	for _, x := range a {
+		copy(b[offset:], x)
+		offset += len(x)
+	}
+
+	return b
+}
+
+func concatbyte2(a0, a1 string) []byte {
+	return concatbytes([]string{a0, a1})
+}
+
+func concatbyte3(a0, a1, a2 string) []byte {
+	return concatbytes([]string{a0, a1, a2})
+}
+
+func concatbyte4(a0, a1, a2, a3 string) []byte {
+	return concatbytes([]string{a0, a1, a2, a3})
+}
+
+func concatbyte5(a0, a1, a2, a3, a4 string) []byte {
+	return concatbytes([]string{a0, a1, a2, a3, a4})
+}
+
 // slicebytetostring converts a byte slice to a string.
 // It is inserted by the compiler into generated code.
 // ptr is a pointer to the first element of the slice;