cmd/compile: fix error when revcType is ptr in selectorExpr

Fixes #48056

Change-Id: I13ca4caadbabf02084f66ab28b4cf0c4a3705370
Reviewed-on: https://go-review.googlesource.com/c/go/+/346049
Reviewed-by: Dan Scales <[email protected]>
Trust: Dan Scales <[email protected]>
Trust: Keith Randall <[email protected]>
Run-TryBot: Dan Scales <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: korzhao

src/cmd/compile/internal/noder/expr.go

@@ -270,7 +270,7 @@ func (g *irgen) selectorExpr(pos src.XPos, typ types2.Type, expr *syntax.Selecto
 		if types2.AsInterface(recvType.Underlying()) != nil {
 			fieldType := n.X.Type()
 			for _, ix := range index[:len(index)-1] {
-				fieldType = fieldType.Field(ix).Type
+				fieldType = deref(fieldType).Field(ix).Type
 			}
 			if fieldType.Kind() == types.TTYPEPARAM {
 				n.Selection = fieldType.Bound().AllMethods().Index(last)

test/typeparam/issue48056.go

@@ -0,0 +1,27 @@
+// compile -G=3
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+type B[T any] interface {
+	Work()
+}
+type BImpl[T any] struct{}
+
+func (b *BImpl[T]) Work() {
+}
+
+type A[T any] struct {
+	B[T]
+}
+
+func f[T any]() {
+	s := &A[T]{
+		&BImpl[T]{},
+	}
+	// golang.org/issue/48056
+	s.Work()
+}