go/types, types2: store Named instance information separately

Separate instance information into an instance struct, to reduce memory
footprint for non-instance Named types. This may induce a sense of
deja-vu: we had a similar construct in the past that was removed as
unnecessary. With additional new fields being added that only apply to
instances, having a separate struct makes sense again.

Updates #52728

Change-Id: I0bb5982d71c27e6b574bfb4f7b886a6aeb9c5390
Reviewed-on: https://go-review.googlesource.com/c/go/+/404884
Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/cmd/compile/internal/types2/predicates.go b/src/cmd/compile/internal/types2/predicates.go
index 6bce26137e..6b6c21c780 100644
--- a/src/cmd/compile/internal/types2/predicates.go
+++ b/src/cmd/compile/internal/types2/predicates.go
@@ -102,7 +102,7 @@ func isTypeParam(t Type) bool {
 func isGeneric(t Type) bool {
 	// A parameterized type is only generic if it doesn't have an instantiation already.
 	named, _ := t.(*Named)
-	return named != nil && named.obj != nil && named.targs == nil && named.TypeParams() != nil
+	return named != nil && named.obj != nil && named.inst == nil && named.TypeParams().Len() > 0
 }
 
 // Comparable reports whether values of type T are comparable.
@@ -401,7 +401,7 @@ func identical(x, y Type, cmpTags bool, p *ifacePair) bool {
 			if len(xargs) > 0 {
 				// Instances are identical if their original type and type arguments
 				// are identical.
-				if !Identical(x.orig, y.orig) {
+				if !Identical(x.Origin(), y.Origin()) {
 					return false
 				}
 				for i, xa := range xargs {