cmd/compile: fix export/import of range loop.

As with other recent issues, the Init field of a range loop was not
being handled properly. Generally, it is much better to explicitly
import/export the Init statements, else they are incorrectly added
before the associated node, rather than as the Init value of the node.
This was causing labels to not be correctly added to the range loop that
it is immediately preceding.

Made the ORANGE handling completely similar to the OFOR handling.

Fixes #48462

Change-Id: I999530e84f9357f81deaa3dda50660061f710e7c
Reviewed-on: https://go-review.googlesource.com/c/go/+/350911
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Trust: Dan Scales <danscales@google.com>

src/cmd/compile/internal/typecheck/iexport.go

@@ -1472,7 +1472,7 @@ func isNonEmptyAssign(n ir.Node) bool {
 // non-empty n.Ninit and where n is not a non-empty assignment or a node with a natural init
 // section (such as in "if", "for", etc.).
 func (w *exportWriter) stmt(n ir.Node) {
-	if len(n.Init()) > 0 && !ir.StmtWithInit(n.Op()) && !isNonEmptyAssign(n) {
+	if len(n.Init()) > 0 && !ir.StmtWithInit(n.Op()) && !isNonEmptyAssign(n) && n.Op() != ir.ORANGE {
 		// can't use stmtList here since we don't want the final OEND
 		for _, n := range n.Init() {
 			w.stmt(n)
@@ -1573,6 +1573,7 @@ func (w *exportWriter) stmt(n ir.Node) {
 		n := n.(*ir.RangeStmt)
 		w.op(ir.ORANGE)
 		w.pos(n.Pos())
+		w.stmtList(n.Init())
 		w.exprsOrNil(n.Key, n.Value)
 		w.expr(n.X)
 		w.stmtList(n.Body)

src/cmd/compile/internal/typecheck/iimport.go

@@ -1515,7 +1515,7 @@ func (r *importReader) node() ir.Node {
 		if go117ExportTypes {
 			n.SetOp(op)
 		}
-		*n.PtrInit() = init
+		n.SetInit(init)
 		n.IsDDD = r.bool()
 		if go117ExportTypes {
 			n.SetType(r.exoticType())
@@ -1660,26 +1660,28 @@ func (r *importReader) node() ir.Node {
 	case ir.OIF:
 		pos, init := r.pos(), r.stmtList()
 		n := ir.NewIfStmt(pos, r.expr(), r.stmtList(), r.stmtList())
-		*n.PtrInit() = init
+		n.SetInit(init)
 		return n
 
 	case ir.OFOR:
 		pos, init := r.pos(), r.stmtList()
 		cond, post := r.exprsOrNil()
 		n := ir.NewForStmt(pos, nil, cond, post, r.stmtList())
-		*n.PtrInit() = init
+		n.SetInit(init)
 		return n
 
 	case ir.ORANGE:
-		pos := r.pos()
+		pos, init := r.pos(), r.stmtList()
 		k, v := r.exprsOrNil()
-		return ir.NewRangeStmt(pos, k, v, r.expr(), r.stmtList())
+		n := ir.NewRangeStmt(pos, k, v, r.expr(), r.stmtList())
+		n.SetInit(init)
+		return n
 
 	case ir.OSELECT:
 		pos := r.pos()
 		init := r.stmtList()
 		n := ir.NewSelectStmt(pos, r.commList())
-		*n.PtrInit() = init
+		n.SetInit(init)
 		return n
 
 	case ir.OSWITCH:
@@ -1687,7 +1689,7 @@ func (r *importReader) node() ir.Node {
 		init := r.stmtList()
 		x, _ := r.exprsOrNil()
 		n := ir.NewSwitchStmt(pos, x, r.caseList(x))
-		*n.PtrInit() = init
+		n.SetInit(init)
 		return n
 
 	// case OCASE:

test/typeparam/issue48462.dir/a.go

@@ -0,0 +1,22 @@
+// 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 a
+
+func Unique[T comparable](set []T) []T {
+	nset := make([]T, 0, 8)
+
+loop:
+	for _, s := range set {
+		for _, e := range nset {
+			if s == e {
+				continue loop
+			}
+		}
+
+		nset = append(nset, s)
+	}
+
+	return nset
+}

test/typeparam/issue48462.dir/main.go

@@ -0,0 +1,23 @@
+// 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 main
+
+import (
+	"fmt"
+	"reflect"
+
+	"a"
+)
+
+func main() {
+	e := []int{1, 2, 2, 3, 1, 6}
+
+	got := a.Unique(e)
+	want := []int{1, 2, 3, 6}
+	if !reflect.DeepEqual(got, want) {
+		panic(fmt.Sprintf("got %d, want %d", got, want))
+	}
+
+}

test/typeparam/issue48462.go

@@ -0,0 +1,7 @@
+// rundir -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 ignored