internal/abi, internal/buildcfg: always enable register ABI on ARM64

In last cycle we developed register ABI for ARM64, enabled by
default as a GOEXPERIMENT. This cycle we turn it on all the time.
Later CLs will clean up fallback code.

To support in-development platforms (e.g. RISC-V), separate the
boolean variables for in-development platforms and always-on
platforms.

Change-Id: I97c27f6aeccc85ccc57eed2abd783b176da3ad80
Reviewed-on: https://go-review.googlesource.com/c/go/+/393364
Trust: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

3 files changed, 11 insertions, 7 deletions

diff --git a/src/internal/abi/abi_arm64.go b/src/internal/abi/abi_arm64.go
index 8f85901c47..4dc51431bf 100644
--- a/src/internal/abi/abi_arm64.go
+++ b/src/internal/abi/abi_arm64.go
@@ -2,8 +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.regabiargs
-
 package abi
 
 const (
diff --git a/src/internal/abi/abi_generic.go b/src/internal/abi/abi_generic.go
index d7d2f3749b..bc8483b4f9 100644
--- a/src/internal/abi/abi_generic.go
+++ b/src/internal/abi/abi_generic.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build !goexperiment.regabiargs && !amd64
+//go:build !goexperiment.regabiargs && !amd64 && !arm64
 
 package abi
 
diff --git a/src/internal/buildcfg/exp.go b/src/internal/buildcfg/exp.go
index a56b36efdf..b2bf9b2c83 100644
--- a/src/internal/buildcfg/exp.go
+++ b/src/internal/buildcfg/exp.go
@@ -56,9 +56,16 @@ var FramePointerEnabled = GOARCH == "amd64" || GOARCH == "arm64"
 //
 // TODO(mdempsky): Move to internal/goexperiment.
 func ParseGOEXPERIMENT(goos, goarch, goexp string) (*ExperimentFlags, error) {
-	regabiSupported := false
+	// regabiSupported is set to true on platforms where register ABI is
+	// supported and enabled by default.
+	// regabiAlwaysOn is set to true on platforms where register ABI is
+	// always on.
+	var regabiSupported, regabiAlwaysOn bool
 	switch goarch {
-	case "amd64", "arm64", "ppc64le", "ppc64":
+	case "amd64", "arm64":
+		regabiAlwaysOn = true
+		fallthrough
+	case "ppc64le", "ppc64":
 		regabiSupported = true
 	}
 
@@ -120,8 +127,7 @@ func ParseGOEXPERIMENT(goos, goarch, goexp string) (*ExperimentFlags, error) {
 		}
 	}
 
-	// regabi is always enabled on amd64.
-	if goarch == "amd64" {
+	if regabiAlwaysOn {
 		flags.RegabiWrappers = true
 		flags.RegabiArgs = true
 	}