internal/goexperiment: consolidate experiment-enabled constants

Currently, we have boolean and integral constants for GOEXPERIMENTs in
various places. Consolidate these into automatically generated
constants in the internal/goexperiment package.

Change-Id: I42a49aba2a3b4c722fedea23a613162cd8a67bee
Reviewed-on: https://go-review.googlesource.com/c/go/+/307818
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/go/build/deps_test.go

@@ -71,7 +71,7 @@ var depsRules = `
 	# No dependencies allowed for any of these packages.
 	NONE
 	< container/list, container/ring,
-	  internal/cfg, internal/cpu,
+	  internal/cfg, internal/cpu, internal/goexperiment,
 	  internal/goversion, internal/nettrace,
 	  unicode/utf8, unicode/utf16, unicode,
 	  unsafe;
@@ -81,7 +81,7 @@ var depsRules = `
 	< internal/abi;
 
 	# RUNTIME is the core runtime group of packages, all of them very light-weight.
-	internal/abi, internal/cpu, unsafe
+	internal/abi, internal/cpu, internal/goexperiment, unsafe
 	< internal/bytealg
 	< internal/itoa
 	< internal/unsafeheader

src/internal/goexperiment/exp_fieldtrack_off.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.fieldtrack
+// +build !goexperiment.fieldtrack
+
+package goexperiment
+
+const FieldTrack = false
+const FieldTrackInt = 0

src/internal/goexperiment/exp_fieldtrack_on.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.fieldtrack
+// +build goexperiment.fieldtrack
+
+package goexperiment
+
+const FieldTrack = true
+const FieldTrackInt = 1

src/internal/goexperiment/exp_preemptibleloops_off.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.preemptibleloops
+// +build !goexperiment.preemptibleloops
+
+package goexperiment
+
+const PreemptibleLoops = false
+const PreemptibleLoopsInt = 0

src/internal/goexperiment/exp_preemptibleloops_on.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.preemptibleloops
+// +build goexperiment.preemptibleloops
+
+package goexperiment
+
+const PreemptibleLoops = true
+const PreemptibleLoopsInt = 1

src/internal/goexperiment/exp_regabi_off.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.regabi
+// +build !goexperiment.regabi
+
+package goexperiment
+
+const Regabi = false
+const RegabiInt = 0

src/internal/goexperiment/exp_regabi_on.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.regabi
+// +build goexperiment.regabi
+
+package goexperiment
+
+const Regabi = true
+const RegabiInt = 1

src/internal/goexperiment/exp_regabiargs_off.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.regabiargs
+// +build !goexperiment.regabiargs
+
+package goexperiment
+
+const RegabiArgs = false
+const RegabiArgsInt = 0

src/internal/goexperiment/exp_regabiargs_on.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.regabiargs
+// +build goexperiment.regabiargs
+
+package goexperiment
+
+const RegabiArgs = true
+const RegabiArgsInt = 1

src/internal/goexperiment/exp_regabidefer_off.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.regabidefer
+// +build !goexperiment.regabidefer
+
+package goexperiment
+
+const RegabiDefer = false
+const RegabiDeferInt = 0

src/internal/goexperiment/exp_regabidefer_on.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.regabidefer
+// +build goexperiment.regabidefer
+
+package goexperiment
+
+const RegabiDefer = true
+const RegabiDeferInt = 1

src/internal/goexperiment/exp_regabig_off.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.regabig
+// +build !goexperiment.regabig
+
+package goexperiment
+
+const RegabiG = false
+const RegabiGInt = 0

src/internal/goexperiment/exp_regabig_on.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.regabig
+// +build goexperiment.regabig
+
+package goexperiment
+
+const RegabiG = true
+const RegabiGInt = 1

src/internal/goexperiment/exp_regabireflect_off.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.regabireflect
+// +build !goexperiment.regabireflect
+
+package goexperiment
+
+const RegabiReflect = false
+const RegabiReflectInt = 0

src/internal/goexperiment/exp_regabireflect_on.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.regabireflect
+// +build goexperiment.regabireflect
+
+package goexperiment
+
+const RegabiReflect = true
+const RegabiReflectInt = 1

src/internal/goexperiment/exp_regabiwrappers_off.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.regabiwrappers
+// +build !goexperiment.regabiwrappers
+
+package goexperiment
+
+const RegabiWrappers = false
+const RegabiWrappersInt = 0

src/internal/goexperiment/exp_regabiwrappers_on.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.regabiwrappers
+// +build goexperiment.regabiwrappers
+
+package goexperiment
+
+const RegabiWrappers = true
+const RegabiWrappersInt = 1

src/internal/goexperiment/exp_staticlockranking_off.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.staticlockranking
+// +build !goexperiment.staticlockranking
+
+package goexperiment
+
+const StaticLockRanking = false
+const StaticLockRankingInt = 0

src/internal/goexperiment/exp_staticlockranking_on.go

@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.staticlockranking
+// +build goexperiment.staticlockranking
+
+package goexperiment
+
+const StaticLockRanking = true
+const StaticLockRankingInt = 1

src/internal/goexperiment/flags.go

@@ -17,11 +17,12 @@
 // - Build tag goexperiment.x is set if experiment x (lower case) is
 // enabled.
 //
+// - For each experiment x (in camel case), this package contains a
+// boolean constant x and an integer constant xInt.
+//
 // - In runtime assembly, the macro GOEXPERIMENT_x is defined if
 // experiment x (lower case) is enabled.
 //
-// - TODO(austin): More to come.
-//
 // In the toolchain, the set of experiments enabled for the current
 // build should be accessed via objabi.Experiment.
 //
@@ -29,11 +30,15 @@
 // go doc internal/experiment.Flags.
 package goexperiment
 
+//go:generate go run mkconsts.go
+
 // Flags is the set of experiments that can be enabled or disabled in
 // the current toolchain.
 //
 // When specified in the GOEXPERIMENT environment variable or as build
 // tags, experiments use the strings.ToLower of their field name.
+//
+// If you change this struct definition, run "go generate".
 type Flags struct {
 	FieldTrack        bool
 	PreemptibleLoops  bool

src/internal/goexperiment/mkconsts.go

@@ -0,0 +1,74 @@
+// Copyright 2021 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.
+
+//go:build ignore
+// +build ignore
+
+// mkconsts generates const definition files for each GOEXPERIMENT.
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"internal/goexperiment"
+	"log"
+	"os"
+	"reflect"
+	"strings"
+)
+
+func main() {
+	// Delete existing experiment constant files.
+	ents, err := os.ReadDir(".")
+	if err != nil {
+		log.Fatal(err)
+	}
+	for _, ent := range ents {
+		name := ent.Name()
+		if !strings.HasPrefix(name, "exp_") {
+			continue
+		}
+		// Check that this is definitely a generated file.
+		data, err := os.ReadFile(name)
+		if err != nil {
+			log.Fatalf("reading %s: %v", name, err)
+		}
+		if !bytes.Contains(data, []byte("Code generated by mkconsts")) {
+			log.Fatalf("%s: expected generated file", name)
+		}
+		if err := os.Remove(name); err != nil {
+			log.Fatal(err)
+		}
+	}
+
+	// Generate new experiment constant files.
+	rt := reflect.TypeOf(&goexperiment.Flags{}).Elem()
+	for i := 0; i < rt.NumField(); i++ {
+		f := rt.Field(i).Name
+		buildTag := "goexperiment." + strings.ToLower(f)
+		for _, val := range []bool{false, true} {
+			name := fmt.Sprintf("exp_%s_%s.go", strings.ToLower(f), pick(val, "off", "on"))
+			data := fmt.Sprintf(`// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build %s%s
+// +build %s%s
+
+package goexperiment
+
+const %s = %v
+const %sInt = %s
+`, pick(val, "!", ""), buildTag, pick(val, "!", ""), buildTag, f, val, f, pick(val, "0", "1"))
+			if err := os.WriteFile(name, []byte(data), 0666); err != nil {
+				log.Fatalf("writing %s: %v", name, err)
+			}
+		}
+	}
+}
+
+func pick(v bool, f, t string) string {
+	if v {
+		return t
+	}
+	return f
+}

src/reflect/abi.go

@@ -6,6 +6,7 @@ package reflect
 
 import (
 	"internal/abi"
+	"internal/goexperiment"
 	"unsafe"
 )
 
@@ -28,9 +29,9 @@ import (
 // commented out there should be the actual values once
 // we're ready to use the register ABI everywhere.
 var (
-	intArgRegs   = abi.IntArgRegs * experimentRegabiArgs
+	intArgRegs   = abi.IntArgRegs * goexperiment.RegabiArgsInt
-	floatArgRegs = abi.FloatArgRegs * experimentRegabiArgs
+	floatArgRegs = abi.FloatArgRegs * goexperiment.RegabiArgsInt
-	floatRegSize = uintptr(abi.EffectiveFloatRegSize * experimentRegabiArgs)
+	floatRegSize = uintptr(abi.EffectiveFloatRegSize * goexperiment.RegabiArgsInt)
 )
 
 // abiStep represents an ABI "instruction." Each instruction

src/reflect/regabiargs_off.go

@@ -1,10 +0,0 @@
-// Copyright 2021 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.
-
-//go:build !goexperiment.regabiargs
-// +build !goexperiment.regabiargs
-
-package reflect
-
-const experimentRegabiArgs = 0

src/reflect/regabiargs_on.go

@@ -1,10 +0,0 @@
-// Copyright 2021 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.
-
-//go:build goexperiment.regabiargs
-// +build goexperiment.regabiargs
-
-package reflect
-
-const experimentRegabiArgs = 1

src/runtime/panic.go

@@ -6,6 +6,7 @@ package runtime
 
 import (
 	"internal/abi"
+	"internal/goexperiment"
 	"runtime/internal/atomic"
 	"runtime/internal/sys"
 	"unsafe"
@@ -228,7 +229,7 @@ func deferproc(siz int32, fn *funcval) { // arguments of fn follow fn
 		throw("defer on system stack")
 	}
 
-	if experimentRegabiDefer && siz != 0 {
+	if goexperiment.RegabiDefer && siz != 0 {
 		// TODO: Make deferproc just take a func().
 		throw("defer with non-empty frame")
 	}
@@ -285,7 +286,7 @@ func deferprocStack(d *_defer) {
 		// go code on the system stack can't defer
 		throw("defer on system stack")
 	}
-	if experimentRegabiDefer && d.siz != 0 {
+	if goexperiment.RegabiDefer && d.siz != 0 {
 		throw("defer with non-empty frame")
 	}
 	// siz and fn are already set.
@@ -387,8 +388,8 @@ func deferArgs(d *_defer) unsafe.Pointer {
 // that experiment, we should change the type of d.fn.
 //go:nosplit
 func deferFunc(d *_defer) func() {
-	if !experimentRegabiDefer {
+	if !goexperiment.RegabiDefer {
-		throw("requires experimentRegabiDefer")
+		throw("requires GOEXPERIMENT=regabidefer")
 	}
 	var fn func()
 	*(**funcval)(unsafe.Pointer(&fn)) = d.fn
@@ -648,7 +649,7 @@ func Goexit() {
 				addOneOpenDeferFrame(gp, 0, nil)
 			}
 		} else {
-			if experimentRegabiDefer {
+			if goexperiment.RegabiDefer {
 				// Save the pc/sp in deferCallSave(), so we can "recover" back to this
 				// loop if necessary.
 				deferCallSave(&p, deferFunc(d))
@@ -850,7 +851,7 @@ func runOpenDeferFrame(gp *g, d *_defer) bool {
 		argWidth, fd = readvarintUnsafe(fd)
 		closureOffset, fd = readvarintUnsafe(fd)
 		nArgs, fd = readvarintUnsafe(fd)
-		if experimentRegabiDefer && argWidth != 0 {
+		if goexperiment.RegabiDefer && argWidth != 0 {
 			throw("defer with non-empty frame")
 		}
 		if deferBits&(1<<i) == 0 {
@@ -878,7 +879,7 @@ func runOpenDeferFrame(gp *g, d *_defer) bool {
 		deferBits = deferBits &^ (1 << i)
 		*(*uint8)(unsafe.Pointer(d.varp - uintptr(deferBitsOffset))) = deferBits
 		p := d._panic
-		if experimentRegabiDefer {
+		if goexperiment.RegabiDefer {
 			deferCallSave(p, deferFunc(d))
 		} else {
 			reflectcallSave(p, unsafe.Pointer(closure), deferArgs, argWidth)
@@ -906,8 +907,8 @@ func runOpenDeferFrame(gp *g, d *_defer) bool {
 // This is marked as a wrapper by the compiler so it doesn't appear in
 // tracebacks.
 func reflectcallSave(p *_panic, fn, arg unsafe.Pointer, argsize uint32) {
-	if experimentRegabiDefer {
+	if goexperiment.RegabiDefer {
-		throw("not allowed with experimentRegabiDefer")
+		throw("not allowed with GOEXPERIMENT=regabidefer")
 	}
 	if p != nil {
 		p.argp = unsafe.Pointer(getargp(0))
@@ -932,8 +933,8 @@ func reflectcallSave(p *_panic, fn, arg unsafe.Pointer, argsize uint32) {
 // This is marked as a wrapper by the compiler so it doesn't appear in
 // tracebacks.
 func deferCallSave(p *_panic, fn func()) {
-	if !experimentRegabiDefer {
+	if !goexperiment.RegabiDefer {
-		throw("only allowed with experimentRegabiDefer")
+		throw("only allowed with GOEXPERIMENT=regabidefer")
 	}
 	if p != nil {
 		p.argp = unsafe.Pointer(getargp(0))
@@ -1035,7 +1036,7 @@ func gopanic(e interface{}) {
 		} else {
 			p.argp = unsafe.Pointer(getargp(0))
 
-			if experimentRegabiDefer {
+			if goexperiment.RegabiDefer {
 				fn := deferFunc(d)
 				fn()
 			} else {

src/runtime/proc.go

@@ -6,6 +6,7 @@ package runtime
 
 import (
 	"internal/cpu"
+	"internal/goexperiment"
 	"runtime/internal/atomic"
 	"runtime/internal/sys"
 	"unsafe"
@@ -4021,8 +4022,8 @@ func malg(stacksize int32) *g {
 //
 //go:nosplit
 func newproc(siz int32, fn *funcval) {
-	if experimentRegabiDefer && siz != 0 {
+	if goexperiment.RegabiDefer && siz != 0 {
-		// TODO: When we commit to experimentRegabiDefer,
+		// TODO: When we commit to GOEXPERIMENT=regabidefer,
 		// rewrite newproc's comment, since it will no longer
 		// have a funny stack layout or need to be nosplit.
 		throw("go with non-empty frame")

src/runtime/regabiargs_off.go

@@ -1,10 +0,0 @@
-// Copyright 2021 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.
-
-//go:build !goexperiment.regabiargs
-// +build !goexperiment.regabiargs
-
-package runtime
-
-const experimentRegabiArgs = 0

src/runtime/regabiargs_on.go

@@ -1,10 +0,0 @@
-// Copyright 2021 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.
-
-//go:build goexperiment.regabiargs
-// +build goexperiment.regabiargs
-
-package runtime
-
-const experimentRegabiArgs = 1

src/runtime/regabidefer_off.go

@@ -1,10 +0,0 @@
-// Copyright 2021 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.
-
-//go:build !goexperiment.regabidefer
-// +build !goexperiment.regabidefer
-
-package runtime
-
-const experimentRegabiDefer = false

src/runtime/regabidefer_on.go

@@ -1,10 +0,0 @@
-// Copyright 2021 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.
-
-//go:build goexperiment.regabidefer
-// +build goexperiment.regabidefer
-
-package runtime
-
-const experimentRegabiDefer = true

src/runtime/stubs.go

@@ -6,6 +6,7 @@ package runtime
 
 import (
 	"internal/abi"
+	"internal/goexperiment"
 	"unsafe"
 )
 
@@ -423,4 +424,4 @@ func sigpanic0()
 // everywhere.
 //
 // Protected by finlock.
-var intArgRegs = abi.IntArgRegs * experimentRegabiArgs
+var intArgRegs = abi.IntArgRegs * goexperiment.RegabiArgsInt