[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, 2 insertions, 4 deletions

diff --git a/src/cmd/compile/internal/types2/predicates.go b/src/cmd/compile/internal/types2/predicates.go
index afef488b96..1541b3f416 100644
--- a/src/cmd/compile/internal/types2/predicates.go
+++ b/src/cmd/compile/internal/types2/predicates.go
@@ -140,10 +140,6 @@ func (p *ifacePair) identical(q *ifacePair) bool {
 
 // For changes to this code the corresponding changes should be made to unifier.nify.
 func identical(x, y Type, cmpTags bool, p *ifacePair) bool {
-	// types must be expanded for comparison
-	x = expand(x)
-	y = expand(y)
-
 	if x == y {
 		return true
 	}
@@ -306,6 +302,8 @@ func identical(x, y Type, cmpTags bool, p *ifacePair) bool {
 		// Two named types are identical if their type names originate
 		// in the same type declaration.
 		if y, ok := y.(*Named); ok {
+			x.expand()
+			y.expand()
 			// TODO(gri) Why is x == y not sufficient? And if it is,
 			//           we can just return false here because x == y
 			//           is caught in the very beginning of this function.