internal/cpu: enable support for GODEBUGCPU in non-experimental builds

Enabling GODEBUGCPU without the need to set GOEXPERIMENT=debugcpu  enables
trybots and builders to run tests for GODEBUGCPU features in upcoming CLs
that will implement the new syntax and features for non-experimental
GODEBUGCPU support from proposal golang.org/issue/27218.

Updates #27218

Change-Id: Icc69e51e736711a86b02b46bd441ffc28423beba
Reviewed-on: https://go-review.googlesource.com/c/141817
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/internal/objabi/util.go

@@ -105,7 +105,6 @@ var (
 	Fieldtrack_enabled       int
 	Preemptibleloops_enabled int
 	Clobberdead_enabled      int
-	DebugCPU_enabled         int
 )
 
 // Toolchain experiments.
@@ -120,7 +119,6 @@ var exper = []struct {
 	{"framepointer", &framepointer_enabled},
 	{"preemptibleloops", &Preemptibleloops_enabled},
 	{"clobberdead", &Clobberdead_enabled},
-	{"debugcpu", &DebugCPU_enabled},
 }
 
 var defaultExpstring = Expstring()

src/internal/cpu/cpu.go

@@ -6,8 +6,7 @@
 // used by the Go standard library.
 package cpu
 
-// DebugOptions is set to true by the runtime if go was compiled with GOEXPERIMENT=debugcpu
-// and GOOS is Linux or Darwin.
+// DebugOptions is set to true by the runtime if the OS supports GODEBUGCPU.
 // This should not be changed after it is initialized.
 var DebugOptions bool
 
@@ -139,8 +138,7 @@ type s390x struct {
 
 // Initialize examines the processor and sets the relevant variables above.
 // This is called by the runtime package early in program initialization,
-// before normal init functions are run. env is set by runtime on Linux and Darwin
-// if go was compiled with GOEXPERIMENT=debugcpu.
+// before normal init functions are run. env is set by runtime if the OS supports GODEBUGCPU.
 func Initialize(env string) {
 	doinit()
 	processOptions(env)

src/internal/cpu/cpu_test.go

@@ -13,14 +13,14 @@ import (
 	"testing"
 )
 
-func MustHaveDebugOptionsEnabled(t *testing.T) {
+func MustHaveDebugOptionsSupport(t *testing.T) {
 	if !DebugOptions {
-		t.Skipf("skipping test: cpu feature options not enabled")
+		t.Skipf("skipping test: cpu feature options not supported by OS")
 	}
 }
 
 func runDebugOptionsTest(t *testing.T, test string, options string) {
-	MustHaveDebugOptionsEnabled(t)
+	MustHaveDebugOptionsSupport(t)
 
 	testenv.MustHaveExec(t)
 
@@ -42,7 +42,7 @@ func TestDisableAllCapabilities(t *testing.T) {
 }
 
 func TestAllCapabilitiesDisabled(t *testing.T) {
-	MustHaveDebugOptionsEnabled(t)
+	MustHaveDebugOptionsSupport(t)
 
 	if os.Getenv("GODEBUGCPU") != "all=0" {
 		t.Skipf("skipping test: GODEBUGCPU=all=0 not set")

src/internal/cpu/cpu_x86_test.go

@@ -34,7 +34,7 @@ func TestDisableSSE2(t *testing.T) {
 }
 
 func TestSSE2DebugOption(t *testing.T) {
-	MustHaveDebugOptionsEnabled(t)
+	MustHaveDebugOptionsSupport(t)
 
 	if os.Getenv("GODEBUGCPU") != "sse2=0" {
 		t.Skipf("skipping test: GODEBUGCPU=sse2=0 not set")

src/runtime/proc.go

@@ -478,12 +478,12 @@ const (
 )
 
 // cpuinit extracts the environment variable GODEBUGCPU from the environment on
-// Linux and Darwin if the GOEXPERIMENT debugcpu was set and calls internal/cpu.Initialize.
+// Linux and Darwin and calls internal/cpu.Initialize.
 func cpuinit() {
 	const prefix = "GODEBUGCPU="
 	var env string
 
-	if haveexperiment("debugcpu") && (GOOS == "linux" || GOOS == "darwin") {
+	if GOOS == "linux" || GOOS == "darwin" {
 		cpu.DebugOptions = true
 
 		// Similar to goenv_unix but extracts the environment value for