[dev.typeparams] cmd/compile/internal/types2: expand is only required for *Named types

Now that the pointer identity for a *Named type doesn't change
anymore when going from lazy instantiated to actually instantiated
(= expanded) state, expand() only needs to be called when we deal
with *Named types and only if we care about a *Named type's internals.

Remove the expand function and respective calls for all types and
replace with specific t.expand() method calls where t is a *Named.

Change-Id: If82299360d60108b00adc4013b29399aec90b940
Reviewed-on: https://go-review.googlesource.com/c/go/+/340749
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

1 files changed, 5 insertions, 6 deletions

diff --git a/src/cmd/compile/internal/types2/union.go b/src/cmd/compile/internal/types2/union.go
index 85aa3d9104..f61c37a6af 100644
--- a/src/cmd/compile/internal/types2/union.go
+++ b/src/cmd/compile/internal/types2/union.go
@@ -68,8 +68,7 @@ func parseUnion(check *Checker, tlist []syntax.Expr) Type {
 	// Note: This is a quadratic algorithm, but unions tend to be short.
 	check.later(func() {
 		for i, t := range terms {
-			typ := expand(t.typ)
-			if typ == Typ[Invalid] {
+			if t.typ == Typ[Invalid] {
 				continue
 			}
 
@@ -85,16 +84,16 @@ func parseUnion(check *Checker, tlist []syntax.Expr) Type {
 				}
 			}
 
-			u := under(typ)
+			u := under(t.typ)
 			f, _ := u.(*Interface)
 			if t.tilde {
 				if f != nil {
-					check.errorf(x, "invalid use of ~ (%s is an interface)", typ)
+					check.errorf(x, "invalid use of ~ (%s is an interface)", t.typ)
 					continue // don't report another error for t
 				}
 
-				if !Identical(u, typ) {
-					check.errorf(x, "invalid use of ~ (underlying type of %s is %s)", typ, u)
+				if !Identical(u, t.typ) {
+					check.errorf(x, "invalid use of ~ (underlying type of %s is %s)", t.typ, u)
 					continue // don't report another error for t
 				}
 			}