cmd/compile/internal/noder: write V2 bitstream aliastypeparams=1

Enables V2 unified IR bitstreams when GOEXPERIMENT aliastypeparams
are enabled.

Allows pkgbits.NewPkgEncoder to set the output version.
Reenables support for writing V0 streams.

Updates #68778
Updates #68526

Change-Id: I590c494d81ab7db148232ceaba52229068d1e986
Reviewed-on: https://go-review.googlesource.com/c/go/+/608595
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

2 files changed, 14 insertions, 4 deletions

diff --git a/src/cmd/compile/internal/noder/unified.go b/src/cmd/compile/internal/noder/unified.go
index ead348f0c1..c8dbc43e67 100644
--- a/src/cmd/compile/internal/noder/unified.go
+++ b/src/cmd/compile/internal/noder/unified.go
@@ -6,6 +6,7 @@ package noder
 
 import (
 	"fmt"
+	"internal/buildcfg"
 	"internal/pkgbits"
 	"internal/types/errors"
 	"io"
@@ -462,8 +463,13 @@ func readPackage(pr *pkgReader, importpkg *types.Pkg, localStub bool) {
 // writeUnifiedExport writes to `out` the finalized, self-contained
 // Unified IR export data file for the current compilation unit.
 func writeUnifiedExport(out io.Writer) {
+	// Use V2 as the encoded version aliastypeparams GOEXPERIMENT is enabled.
+	version := pkgbits.V1
+	if buildcfg.Experiment.AliasTypeParams {
+		version = pkgbits.V2
+	}
 	l := linker{
-		pw: pkgbits.NewPkgEncoder(base.Debug.SyncFrames),
+		pw: pkgbits.NewPkgEncoder(version, base.Debug.SyncFrames),
 
 		pkgs:   make(map[string]index),
 		decls:  make(map[*types.Sym]index),
diff --git a/src/cmd/compile/internal/noder/writer.go b/src/cmd/compile/internal/noder/writer.go
index 695fdcceea..564087d912 100644
--- a/src/cmd/compile/internal/noder/writer.go
+++ b/src/cmd/compile/internal/noder/writer.go
@@ -96,8 +96,13 @@ type pkgWriter struct {
 // newPkgWriter returns an initialized pkgWriter for the specified
 // package.
 func newPkgWriter(m posMap, pkg *types2.Package, info *types2.Info, otherInfo map[*syntax.FuncLit]bool) *pkgWriter {
+	// Use V2 as the encoded version aliastypeparams GOEXPERIMENT is enabled.
+	version := pkgbits.V1
+	if buildcfg.Experiment.AliasTypeParams {
+		version = pkgbits.V2
+	}
 	return &pkgWriter{
-		PkgEncoder: pkgbits.NewPkgEncoder(base.Debug.SyncFrames),
+		PkgEncoder: pkgbits.NewPkgEncoder(version, base.Debug.SyncFrames),
 
 		m:                     m,
 		curpkg:                pkg,
@@ -864,8 +869,7 @@ func (w *writer) doObj(wext *writer, obj types2.Object) pkgbits.CodeObj {
 			if w.Version().Has(pkgbits.AliasTypeParamNames) {
 				w.typeParamNames(tparams)
 			}
-			// TODO(taking): enable this assertion once this is not intended to be a nop.
-			// assert(w.Version().Has(pkgbits.AliasTypeParamNames) || tparams.Len() == 0)
+			assert(w.Version().Has(pkgbits.AliasTypeParamNames) || tparams.Len() == 0)
 			w.typ(rhs)
 			return pkgbits.ObjAlias
 		}