[dev.typeparams] internal/buildcfg: always enable regabi on AMD64

In Go 1.17 we added register ABI on AMD64 on Linux/macOS/Windows
as a GOEXPERIMENT, on by default. In Go 1.18, we commit to always
enabling register ABI on AMD64.

Now "go build" for AMD64 always have goexperiment.regabi* tags
set. However, at bootstrapping cmd/dist does not set the tags
when building go_bootstrap. For this to work, unfortunately, we
need to hard-code AMD64 to use register ABI in runtime code.

Change-Id: I0b31e678e186b9cdeeb8502cd9e38ed0d7e72d4f
Reviewed-on: https://go-review.googlesource.com/c/go/+/341151
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Austin Clements <austin@google.com>

abi/abi_amd64.go

@@ -2,9 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build goexperiment.regabireflect
-// +build goexperiment.regabireflect
-
 package abi
 
 const (

abi/abi_generic.go

@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build !goexperiment.regabireflect
-// +build !goexperiment.regabireflect
+//go:build !goexperiment.regabireflect && !amd64
+// +build !goexperiment.regabireflect,!amd64
 
 package abi
 

buildcfg/exp.go

@@ -105,9 +105,11 @@ func ParseGOEXPERIMENT(goos, goarch, goexp string) (flags, baseline goexperiment
 		}
 	}
 
-	// regabiwrappers is always enabled on amd64.
+	// regabi is always enabled on amd64.
 	if goarch == "amd64" {
 		flags.RegabiWrappers = true
+		flags.RegabiReflect = true
+		flags.RegabiArgs = true
 	}
 	// regabi is only supported on amd64 and arm64.
 	if goarch != "amd64" && goarch != "arm64" {