From: Robert Findley <rfindley@google.com>
Date: Thu, 18 Nov 2021 00:22:22 +0000 (-0500)
Subject: go/types: optimize common case in structuralType
X-Git-Tag: go1.18beta1~256
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=353cb71ea29e02a41f77b7576d658de4515e264d;p=gostls13.git

go/types: optimize common case in structuralType

This is a port of CL 363668 from types2 to go/types.

Change-Id: Ic55acb2e27f57c33467cef2f687cd695e092ba6d
Reviewed-on: https://go-review.googlesource.com/c/go/+/364898
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
---

diff --git a/src/go/types/type.go b/src/go/types/type.go
index 6611c25f25..e283c65289 100644
--- a/src/go/types/type.go
+++ b/src/go/types/type.go
@@ -56,15 +56,20 @@ func match(x, y Type) Type {
 	return nil
 }
 
-// If typ is a type parameter, structuralType returns the single underlying
-// type of all types in the corresponding type constraint if it exists, or
-// nil otherwise. If the type set contains only unrestricted and restricted
-// channel types (with identical element types), the single underlying type
-// is the restricted channel type if the restrictions are always the same.
-// If typ is not a type parameter, structuralType returns the underlying type.
-func structuralType(typ Type) Type {
+// If t is not a type parameter, structuralType returns the underlying type.
+// If t is a type parameter, structuralType returns the single underlying
+// type of all types in its type set if it exists, or nil otherwise. If the
+// type set contains only unrestricted and restricted channel types (with
+// identical element types), the single underlying type is the restricted
+// channel type if the restrictions are always the same, or nil otherwise.
+func structuralType(t Type) Type {
+	tpar, _ := t.(*TypeParam)
+	if tpar == nil {
+		return under(t)
+	}
+
 	var su Type
-	if underIs(typ, func(u Type) bool {
+	if tpar.underIs(func(u Type) bool {
 		if u == nil {
 			return false
 		}