[dev.typeparams] cmd/compile: use old export format if not compiling with generics

Write out export data with the old export format (iexportVersionPosCol)
if not compiling with generics (-G=0, the default value). This helps
ensure we don't break tests involving x/tools/go/gcexportdata (since we
can't modify that tool yet to use the new format).

Change-Id: I5f9bce44ed1e0696fc65fead6bab9e30de88461d
Reviewed-on: https://go-review.googlesource.com/c/go/+/323189
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Trust: Robert Griesemer <gri@golang.org>

diff --git a/src/cmd/compile/internal/typecheck/iexport.go b/src/cmd/compile/internal/typecheck/iexport.go
index ea8e751852c61af80e11424ae42aa19a6287421d..9c24213176957d780758083b7d5868b1208e063c 100644 (file)
--- a/src/cmd/compile/internal/typecheck/iexport.go
+++ b/src/cmd/compile/internal/typecheck/iexport.go
@@ -306,7 +306,12 @@ func WriteExports(out *bufio.Writer) {
        // Assemble header.
        var hdr intWriter
        hdr.WriteByte('i')
-       hdr.uint64(iexportVersionCurrent)
+       if base.Flag.G > 0 {
+               hdr.uint64(iexportVersionCurrent)
+       } else {
+               // Use old export format if doing -G=0 (no generics)
+               hdr.uint64(iexportVersionPosCol)
+       }
        hdr.uint64(uint64(p.strings.Len()))
        hdr.uint64(dataLen)
 
@@ -478,7 +483,9 @@ func (p *iexporter) doDecl(n *ir.Name) {
                        // referenced via their type offset (via typOff) in all
                        // other places in the signature and function that they
                        // are used.
-                       w.tparamList(n.Type().TParams().FieldSlice())
+                       if base.Flag.G > 0 {
+                               w.tparamList(n.Type().TParams().FieldSlice())
+                       }
                        w.signature(n.Type())
                        w.funcExt(n)
 
@@ -511,8 +518,10 @@ func (p *iexporter) doDecl(n *ir.Name) {
                w.tag('T')
                w.pos(n.Pos())
 
-               // Export any new typeparams needed for this type
-               w.typeList(n.Type().RParams())
+               if base.Flag.G > 0 {
+                       // Export any new typeparams needed for this type
+                       w.typeList(n.Type().RParams())
+               }
                underlying := n.Type().Underlying()
                if underlying == types.ErrorType.Underlying() {
                        // For "type T error", use error as the
@@ -826,6 +835,7 @@ func (w *exportWriter) startType(k itag) {
 
 func (w *exportWriter) doTyp(t *types.Type) {
        if t.Kind() == types.TTYPEPARAM {
+               assert(base.Flag.G > 0)
                // A typeparam has a name, but doesn't have an underlying type.
                // Just write out the details of the type param here. All other
                // uses of this typeparam type will be written out as its unique
@@ -846,6 +856,7 @@ func (w *exportWriter) doTyp(t *types.Type) {
 
        s := t.Sym()
        if s != nil && t.OrigSym != nil {
+               assert(base.Flag.G > 0)
                // This is an instantiated type - could be a re-instantiation like
                // Value[T2] or a full instantiation like Value[int].
                if strings.Index(s.Name, "[") < 0 {
@@ -945,6 +956,7 @@ func (w *exportWriter) doTyp(t *types.Type) {
                }
 
        case types.TUNION:
+               assert(base.Flag.G > 0)
                // TODO(danscales): possibly put out the tilde bools in more
                // compact form.
                w.startType(unionType)