go/build: add GO$GOARCH-based ToolTags

Implement proposal #45454, providing build tags based on the
sub-architecture information in the GO$GOARCH variable
(for example, GOARM for GOARCH=arm).

For example, when GOAMD64=v2, the additional build tags
amd64.v1 and amd64.v2 are defined to be true.

Fixes #45454.

Change-Id: I7be56060d47fc61843b97fd8a78498e8202c1ee7
Reviewed-on: https://go-review.googlesource.com/c/go/+/421434
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -93,9 +93,14 @@ func defaultContext() build.Context {
 	ctxt.GOOS = Goos
 	ctxt.GOARCH = Goarch
 
-	// ToolTags are based on GOEXPERIMENT, which we will parse and
-	// initialize later.
-	ctxt.ToolTags = nil
+	// Clear the GOEXPERIMENT-based tool tags, which we will recompute later.
+	var save []string
+	for _, tag := range ctxt.ToolTags {
+		if !strings.HasPrefix(tag, "goexperiment.") {
+			save = append(save, tag)
+		}
+	}
+	ctxt.ToolTags = save
 
 	// The go/build rule for whether cgo is enabled is:
 	//	1. If $CGO_ENABLED is set, respect it.

src/cmd/go/testdata/script/tooltags.txt

@@ -0,0 +1,45 @@
+env GOARCH=amd64
+env GOAMD64=v3
+go list -f '{{context.ToolTags}}'
+stdout 'amd64.v1 amd64.v2 amd64.v3'
+
+env GOARCH=arm
+env GOARM=6
+go list -f '{{context.ToolTags}}'
+stdout 'arm.5 arm.6'
+
+env GOARCH=mips
+env GOMIPS=hardfloat
+go list -f '{{context.ToolTags}}'
+stdout 'mips.hardfloat'
+
+env GOARCH=mips64
+env GOMIPS=hardfloat
+go list -f '{{context.ToolTags}}'
+stdout 'mips64.hardfloat'
+
+env GOARCH=ppc64
+env GOPPC64=power9
+go list -f '{{context.ToolTags}}'
+stdout 'ppc64.power8 ppc64.power9'
+
+env GOARCH=ppc64le
+env GOPPC64=power9
+go list -f '{{context.ToolTags}}'
+stdout 'ppc64le.power8 ppc64le.power9'
+
+env GOARCH=386
+env GO386=sse2
+go list -f '{{context.ToolTags}}'
+stdout '386.sse2'
+
+env GOARCH=wasm
+env GOWASM=satconv
+go list -f '{{context.ToolTags}}'
+stdout 'wasm.satconv'
+
+-- go.mod --
+module m
+
+-- p.go --
+package p

src/go/build/build.go

@@ -314,15 +314,8 @@ func defaultContext() Context {
 	}
 	c.GOPATH = envOr("GOPATH", defaultGOPATH())
 	c.Compiler = runtime.Compiler
+	c.ToolTags = append(c.ToolTags, buildcfg.ToolTags...)
 
-	// For each experiment that has been enabled in the toolchain, define a
-	// build tag with the same name but prefixed by "goexperiment." which can be
-	// used for compiling alternative files for the experiment. This allows
-	// changes for the experiment, like extra struct fields in the runtime,
-	// without affecting the base non-experiment code at all.
-	for _, exp := range buildcfg.Experiment.Enabled() {
-		c.ToolTags = append(c.ToolTags, "goexperiment."+exp)
-	}
 	defaultToolTags = append([]string{}, c.ToolTags...) // our own private copy
 
 	// Each major Go release in the Go 1.x series adds a new

src/internal/buildcfg/cfg.go

@@ -30,6 +30,7 @@ var (
 	GOMIPS64 = gomips64()
 	GOPPC64  = goppc64()
 	GOWASM   = gowasm()
+	ToolTags = toolTags()
 	GO_LDSO  = defaultGO_LDSO
 	Version  = version
 )
@@ -115,8 +116,8 @@ func goppc64() int {
 }
 
 type gowasmFeatures struct {
-	SignExt bool
 	SatConv bool
+	SignExt bool
 }
 
 func (f gowasmFeatures) String() string {
@@ -149,3 +150,61 @@ func gowasm() (f gowasmFeatures) {
 func Getgoextlinkenabled() string {
 	return envOr("GO_EXTLINK_ENABLED", defaultGO_EXTLINK_ENABLED)
 }
+
+func toolTags() []string {
+	tags := experimentTags()
+	tags = append(tags, gogoarchTags()...)
+	return tags
+}
+
+func experimentTags() []string {
+	var list []string
+	// For each experiment that has been enabled in the toolchain, define a
+	// build tag with the same name but prefixed by "goexperiment." which can be
+	// used for compiling alternative files for the experiment. This allows
+	// changes for the experiment, like extra struct fields in the runtime,
+	// without affecting the base non-experiment code at all.
+	for _, exp := range Experiment.Enabled() {
+		list = append(list, "goexperiment."+exp)
+	}
+	return list
+}
+
+func gogoarchTags() []string {
+	switch GOARCH {
+	case "386":
+		return []string{GOARCH + "." + GO386}
+	case "amd64":
+		var list []string
+		for i := 1; i <= GOAMD64; i++ {
+			list = append(list, fmt.Sprintf("%s.v%d", GOARCH, i))
+		}
+		return list
+	case "arm":
+		var list []string
+		for i := 5; i <= GOARM; i++ {
+			list = append(list, fmt.Sprintf("%s.%d", GOARCH, i))
+		}
+		return list
+	case "mips", "mipsle":
+		return []string{GOARCH + "." + GOMIPS}
+	case "mips64", "mips64le":
+		return []string{GOARCH + "." + GOMIPS64}
+	case "ppc64", "ppc64le":
+		var list []string
+		for i := 8; i <= GOPPC64; i++ {
+			list = append(list, fmt.Sprintf("%s.power%d", GOARCH, i))
+		}
+		return list
+	case "wasm":
+		var list []string
+		if GOWASM.SatConv {
+			list = append(list, GOARCH+".satconv")
+		}
+		if GOWASM.SignExt {
+			list = append(list, GOARCH+".signext")
+		}
+		return list
+	}
+	return nil
+}