cmd/go: add GOAMD64 environment variable

The variable represents the microarchitecture levels for which to compile.
Valid values are v1 (default), v2, v3, v4.

Updates #45453

src/cmd/dist/build.go

@@ -32,6 +32,7 @@ var (
 	goos             string
 	goarm            string
 	go386            string
+	goamd64          string
 	gomips           string
 	gomips64         string
 	goppc64          string
@@ -145,6 +146,12 @@ func xinit() {
 	}
 	go386 = b
 
+	b = os.Getenv("GOAMD64")
+	if b == "" {
+		b = "v1"
+	}
+	goamd64 = b
+
 	b = os.Getenv("GOMIPS")
 	if b == "" {
 		b = "hardfloat"
@@ -217,6 +224,7 @@ func xinit() {
 
 	// For tools being invoked but also for os.ExpandEnv.
 	os.Setenv("GO386", go386)
+	os.Setenv("GOAMD64", goamd64)
 	os.Setenv("GOARCH", goarch)
 	os.Setenv("GOARM", goarm)
 	os.Setenv("GOHOSTARCH", gohostarch)
@@ -1181,6 +1189,9 @@ func cmdenv() {
 	if goarch == "386" {
 		xprintf(format, "GO386", go386)
 	}
+	if goarch == "amd64" {
+		xprintf(format, "GOAMD64", goamd64)
+	}
 	if goarch == "mips" || goarch == "mipsle" {
 		xprintf(format, "GOMIPS", gomips)
 	}

src/cmd/dist/buildruntime.go

@@ -60,6 +60,7 @@ func mkbuildcfg(file string) {
 	fmt.Fprintf(&buf, "import \"runtime\"\n")
 	fmt.Fprintln(&buf)
 	fmt.Fprintf(&buf, "const defaultGO386 = `%s`\n", go386)
+	fmt.Fprintf(&buf, "const defaultGOAMD64 = `%s`\n", goamd64)
 	fmt.Fprintf(&buf, "const defaultGOARM = `%s`\n", goarm)
 	fmt.Fprintf(&buf, "const defaultGOMIPS = `%s`\n", gomips)
 	fmt.Fprintf(&buf, "const defaultGOMIPS64 = `%s`\n", gomips64)

src/cmd/go/internal/cfg/cfg.go

@@ -263,6 +263,7 @@ var (
 	// Used in envcmd.MkEnv and build ID computations.
 	GOARM    = envOr("GOARM", fmt.Sprint(buildcfg.GOARM))
 	GO386    = envOr("GO386", buildcfg.GO386)
+	GOAMD64  = envOr("GOAMD64", fmt.Sprintf("%s%d", "v", buildcfg.GOAMD64))
 	GOMIPS   = envOr("GOMIPS", buildcfg.GOMIPS)
 	GOMIPS64 = envOr("GOMIPS64", buildcfg.GOMIPS64)
 	GOPPC64  = envOr("GOPPC64", fmt.Sprintf("%s%d", "power", buildcfg.GOPPC64))
@@ -289,6 +290,8 @@ func GetArchEnv() (key, val string) {
 		return "GOARM", GOARM
 	case "386":
 		return "GO386", GO386
+	case "amd64":
+		return "GOAMD64", GOAMD64
 	case "mips", "mipsle":
 		return "GOMIPS", GOMIPS
 	case "mips64", "mips64le":

src/cmd/go/internal/help/helpdoc.go

@@ -592,6 +592,9 @@ Architecture-specific environment variables:
 	GO386
 		For GOARCH=386, how to implement floating point instructions.
 		Valid values are sse2 (default), softfloat.
+	GOAMD64
+		For GOARCH=GOAMD64, the microarchitecture levels for which to compile.
+		Valid values are v1 (default), v2, v3, v4.
 	GOMIPS
 		For GOARCH=mips{,le}, whether to use floating point instructions.
 		Valid values are hardfloat (default), softfloat.

src/cmd/go/internal/work/gc.go

@@ -379,6 +379,11 @@ func asmArgs(a *Action, p *load.Package) []interface{} {
 		args = append(args, "-D", "GO386_"+cfg.GO386)
 	}
 
+	if cfg.Goarch == "amd64" {
+		// Define GOAMD64_value from cfg.GOAMD64.
+		args = append(args, "-D", "GOAMD64_"+cfg.GOAMD64)
+	}
+
 	if cfg.Goarch == "mips" || cfg.Goarch == "mipsle" {
 		// Define GOMIPS_value from cfg.GOMIPS.
 		args = append(args, "-D", "GOMIPS_"+cfg.GOMIPS)

src/internal/buildcfg/cfg.go

@@ -25,6 +25,7 @@ var (
 	GOARCH   = envOr("GOARCH", defaultGOARCH)
 	GOOS     = envOr("GOOS", defaultGOOS)
 	GO386    = envOr("GO386", defaultGO386)
+	GOAMD64  = goamd64()
 	GOARM    = goarm()
 	GOMIPS   = gomips()
 	GOMIPS64 = gomips64()
@@ -52,6 +53,22 @@ func envOr(key, value string) string {
 	return value
 }
 
+func goamd64() int {
+	def := defaultGOAMD64
+	switch v := envOr("GOAMD64", def); v {
+	case "v1":
+		return 1
+	case "v2":
+		return 2
+	case "v3":
+		return 3
+	case "v4":
+		return 4
+	}
+	Error = fmt.Errorf("invalid GOAMD64: must be v1, v2, v3 or v4")
+	return int(def[len("v")] - '0')
+}
+
 func goarm() int {
 	def := defaultGOARM
 	if GOOS == "android" && GOARCH == "arm" {

src/internal/cfg/cfg.go

@@ -33,6 +33,7 @@ const KnownEnv = `
 	GCCGO
 	GO111MODULE
 	GO386
+	GOAMD64
 	GOARCH
 	GOARM
 	GOBIN

test/run.go

@@ -1753,7 +1753,7 @@ var (
 	// are the supported variants.
 	archVariants = map[string][]string{
 		"386":     {"GO386", "sse2", "softfloat"},
-		"amd64":   {},
+		"amd64":   {"GOAMD64", "v1", "v2", "v3", "v4"},
 		"arm":     {"GOARM", "5", "6", "7"},
 		"arm64":   {},
 		"mips":    {"GOMIPS", "hardfloat", "softfloat"},