cmd/compile: simplify extendslice and isAppendOfMake

Change-Id: Ia66361812837dde23aac09e916f058ba509a323c
Reviewed-on: https://go-review.googlesource.com/111737
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

src/cmd/compile/internal/gc/walk.go

@@ -3054,11 +3054,7 @@ func isAppendOfMake(n *Node) bool {
 	}
 
 	second := n.List.Second()
-	if second.Op != OMAKESLICE {
-		return false
-	}
-
-	if n.List.Second().Right != nil {
+	if second.Op != OMAKESLICE || second.Right != nil {
 		return false
 	}
 
@@ -3135,10 +3131,8 @@ func extendslice(n *Node, init *Nodes) *Node {
 	nodes = append(nodes, nod(OAS, nn, nod(OADD, nod(OLEN, s, nil), l2)))
 
 	// if uint(n) > uint(cap(s))
-	nuint := nod(OCONV, nn, nil)
-	nuint.Type = types.Types[TUINT]
-	capuint := nod(OCONV, nod(OCAP, s, nil), nil)
-	capuint.Type = types.Types[TUINT]
+	nuint := conv(nn, types.Types[TUINT])
+	capuint := conv(nod(OCAP, s, nil), types.Types[TUINT])
 	nif := nod(OIF, nod(OGT, nuint, capuint), nil)
 
 	// instantiate growslice(typ *type, old []any, newcap int) []any