[dev.typeparams] all: always enable regabig on AMD64

Always enable regabig on AMD64, which enables the G register and
the X15 zero register. Remove the fallback path.

Also remove the regabig GOEXPERIMENT. On AMD64 it is always
enabled (this CL). Other architectures already have a G register,
except for 386, where there are too few registers and it is
unlikely that we will reserve one. (If we really do, we can just
add a new experiment).

Change-Id: I229cac0060f48fe58c9fdaabd38d6fa16b8a0855
Reviewed-on: https://go-review.googlesource.com/c/go/+/327272
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

4 files changed, 2 insertions, 31 deletions

diff --git a/src/internal/buildcfg/exp.go b/src/internal/buildcfg/exp.go
index b3f3de62a8..e78f987999 100644
--- a/src/internal/buildcfg/exp.go
+++ b/src/internal/buildcfg/exp.go
@@ -28,7 +28,6 @@ var regabiDeveloping = false
 // configuration and any variation from this is an experiment.
 var experimentBaseline = goexperiment.Flags{
 	RegabiWrappers: regabiSupported,
-	RegabiG:        regabiSupported,
 	RegabiReflect:  regabiSupported,
 	RegabiArgs:     regabiSupported,
 }
@@ -67,7 +66,6 @@ func parseExperiments() goexperiment.Flags {
 		// do the right thing.
 		names["regabi"] = func(v bool) {
 			flags.RegabiWrappers = v
-			flags.RegabiG = v
 			flags.RegabiReflect = v
 			flags.RegabiArgs = v
 		}
@@ -104,16 +102,12 @@ func parseExperiments() goexperiment.Flags {
 	// regabi is only supported on amd64 and arm64.
 	if GOARCH != "amd64" && GOARCH != "arm64" {
 		flags.RegabiWrappers = false
-		flags.RegabiG = false
 		flags.RegabiReflect = false
 		flags.RegabiArgs = false
 	}
 	// Check regabi dependencies.
-	if flags.RegabiG && !flags.RegabiWrappers {
-		Error = fmt.Errorf("GOEXPERIMENT regabig requires regabiwrappers")
-	}
-	if flags.RegabiArgs && !(flags.RegabiWrappers && flags.RegabiG && flags.RegabiReflect) {
-		Error = fmt.Errorf("GOEXPERIMENT regabiargs requires regabiwrappers,regabig,regabireflect")
+	if flags.RegabiArgs && !(flags.RegabiWrappers && flags.RegabiReflect) {
+		Error = fmt.Errorf("GOEXPERIMENT regabiargs requires regabiwrappers,regabireflect")
 	}
 	return flags
 }
diff --git a/src/internal/goexperiment/exp_regabig_off.go b/src/internal/goexperiment/exp_regabig_off.go
deleted file mode 100644
index 1b37d45186..0000000000
--- a/src/internal/goexperiment/exp_regabig_off.go
+++ /dev/null
@@ -1,9 +0,0 @@
-// Code generated by mkconsts.go. DO NOT EDIT.
-
-//go:build !goexperiment.regabig
-// +build !goexperiment.regabig
-
-package goexperiment
-
-const RegabiG = false
-const RegabiGInt = 0
diff --git a/src/internal/goexperiment/exp_regabig_on.go b/src/internal/goexperiment/exp_regabig_on.go
deleted file mode 100644
index 7e5b162e0b..0000000000
--- a/src/internal/goexperiment/exp_regabig_on.go
+++ /dev/null
@@ -1,9 +0,0 @@
-// Code generated by mkconsts.go. DO NOT EDIT.
-
-//go:build goexperiment.regabig
-// +build goexperiment.regabig
-
-package goexperiment
-
-const RegabiG = true
-const RegabiGInt = 1
diff --git a/src/internal/goexperiment/flags.go b/src/internal/goexperiment/flags.go
index c20dbcd9f5..71e38cd047 100644
--- a/src/internal/goexperiment/flags.go
+++ b/src/internal/goexperiment/flags.go
@@ -68,11 +68,6 @@ type Flags struct {
 	// ABI0 and ABIInternal functions. Without this, the ABIs are
 	// assumed to be identical so cross-ABI calls are direct.
 	RegabiWrappers bool
-	// RegabiG enables dedicated G and zero registers in
-	// ABIInternal.
-	//
-	// Requires wrappers because it makes the ABIs incompatible.
-	RegabiG bool
 	// RegabiReflect enables the register-passing paths in
 	// reflection calls. This is also gated by intArgRegs in
 	// reflect and runtime (which are disabled by default) so it