cmd: move GOEXPERIMENT knob from make.bash to cmd/go

This CL changes GOEXPERIMENT to act like other GO[CONFIG] environment
variables. Namely, that it can be set at make.bash time to provide a
default value used by the toolchain, but then can be manually set when
running either cmd/go or the individual tools (compiler, assembler,
linker).

For example, it's now possible to test rsc.io/tmp/fieldtrack by simply
running:

GOEXPERIMENT=fieldtrack go test -gcflags=-l rsc.io/tmp/fieldtrack \
  -ldflags=-k=rsc.io/tmp/fieldtrack.tracked

without needing to re-run make.bash. (-gcflags=-l is needed because
the compiler's inlining abilities have improved, so calling a function
with a for loop is no longer sufficient to suppress inlining.)

Fixes #42681.

Change-Id: I2cf8995d5d0d05f6785a2ee1d3b54b2cfb3331ca
Reviewed-on: https://go-review.googlesource.com/c/go/+/300991
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

2 files changed, 6 insertions, 16 deletions

diff --git a/src/cmd/dist/build.go b/src/cmd/dist/build.go
index 158cedbadc..b2d13e7db4 100644
--- a/src/cmd/dist/build.go
+++ b/src/cmd/dist/build.go
@@ -39,6 +39,7 @@ var (
 	goextlinkenabled string
 	gogcflags        string // For running built compiler
 	goldflags        string
+	goexperiment     string
 	workdir          string
 	tooldir          string
 	oldgoos          string
@@ -194,6 +195,9 @@ func xinit() {
 		goextlinkenabled = b
 	}
 
+	goexperiment = os.Getenv("GOEXPERIMENT")
+	// TODO(mdempsky): Validate known experiments?
+
 	gogcflags = os.Getenv("BOOT_GO_GCFLAGS")
 	goldflags = os.Getenv("BOOT_GO_LDFLAGS")
 
@@ -834,18 +838,6 @@ func runInstall(pkg string, ch chan struct{}) {
 	goasmh := pathf("%s/go_asm.h", workdir)
 	if IsRuntimePackagePath(pkg) {
 		asmArgs = append(asmArgs, "-compiling-runtime")
-		if os.Getenv("GOEXPERIMENT") == "regabi" {
-			// In order to make it easier to port runtime assembly
-			// to the register ABI, we introduce a macro
-			// indicating the experiment is enabled.
-			//
-			// Note: a similar change also appears in
-			// cmd/go/internal/work/gc.go.
-			//
-			// TODO(austin): Remove this once we commit to the
-			// register ABI (#40724).
-			asmArgs = append(asmArgs, "-D=GOEXPERIMENT_REGABI=1")
-		}
 	}
 
 	// Collect symabis from assembly code.
diff --git a/src/cmd/dist/buildruntime.go b/src/cmd/dist/buildruntime.go
index 2744951597..e0a101a353 100644
--- a/src/cmd/dist/buildruntime.go
+++ b/src/cmd/dist/buildruntime.go
@@ -20,7 +20,6 @@ import (
 //	package sys
 //
 //	const TheVersion = <version>
-//	const Goexperiment = <goexperiment>
 //	const StackGuardMultiplier = <multiplier value>
 //
 func mkzversion(dir, file string) {
@@ -30,7 +29,6 @@ func mkzversion(dir, file string) {
 	fmt.Fprintf(&buf, "package sys\n")
 	fmt.Fprintln(&buf)
 	fmt.Fprintf(&buf, "const TheVersion = `%s`\n", findgoversion())
-	fmt.Fprintf(&buf, "const Goexperiment = `%s`\n", os.Getenv("GOEXPERIMENT"))
 	fmt.Fprintf(&buf, "const StackGuardMultiplierDefault = %d\n", stackGuardMultiplierDefault())
 
 	writefile(buf.String(), file, writeSkipSame)
@@ -48,10 +46,10 @@ func mkzversion(dir, file string) {
 //	const defaultGOPPC64 = <goppc64>
 //	const defaultGOOS = runtime.GOOS
 //	const defaultGOARCH = runtime.GOARCH
+//	const defaultGOEXPERIMENT = <goexperiment>
 //	const defaultGO_EXTLINK_ENABLED = <goextlinkenabled>
 //	const version = <version>
 //	const stackGuardMultiplierDefault = <multiplier value>
-//	const goexperiment = <goexperiment>
 //
 // The use of runtime.GOOS and runtime.GOARCH makes sure that
 // a cross-compiled compiler expects to compile for its own target
@@ -77,11 +75,11 @@ func mkzbootstrap(file string) {
 	fmt.Fprintf(&buf, "const defaultGOPPC64 = `%s`\n", goppc64)
 	fmt.Fprintf(&buf, "const defaultGOOS = runtime.GOOS\n")
 	fmt.Fprintf(&buf, "const defaultGOARCH = runtime.GOARCH\n")
+	fmt.Fprintf(&buf, "const defaultGOEXPERIMENT = `%s`\n", goexperiment)
 	fmt.Fprintf(&buf, "const defaultGO_EXTLINK_ENABLED = `%s`\n", goextlinkenabled)
 	fmt.Fprintf(&buf, "const defaultGO_LDSO = `%s`\n", defaultldso)
 	fmt.Fprintf(&buf, "const version = `%s`\n", findgoversion())
 	fmt.Fprintf(&buf, "const stackGuardMultiplierDefault = %d\n", stackGuardMultiplierDefault())
-	fmt.Fprintf(&buf, "const goexperiment = `%s`\n", os.Getenv("GOEXPERIMENT"))
 
 	writefile(buf.String(), file, writeSkipSame)
 }