From a8f07310e3a08910dde2b7e9550848ec400753ad Mon Sep 17 00:00:00 2001
From: =?utf8?q?Martin=20M=C3=B6hrmann?= <moehrmann@google.com>
Date: Mon, 19 Dec 2016 00:06:46 +0100
Subject: [PATCH] cmd/compile: fix assignment order in string range loop
MIME-Version: 1.0
Content-Type: text/plain; charset=utf8
Content-Transfer-Encoding: 8bit

Fixes #18376.

Change-Id: I4fe24f479311cd4cd1bdad9a966b681e50e3d500
Reviewed-on: https://go-review.googlesource.com/35955
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
---
 src/cmd/compile/internal/gc/range.go | 31 ++++++++++++++++++++--------
 test/range.go                        | 20 ++++++++++++++++++
 2 files changed, 42 insertions(+), 9 deletions(-)

diff --git a/src/cmd/compile/internal/gc/range.go b/src/cmd/compile/internal/gc/range.go
index 99ecdd3cc5..d1ac5780a0 100644
--- a/src/cmd/compile/internal/gc/range.go
+++ b/src/cmd/compile/internal/gc/range.go
@@ -156,6 +156,10 @@ func walkrange(n *Node) {
 		v2 = n.List.Second()
 	}
 
+	if v1 == nil && v2 != nil {
+		Fatalf("walkrange: v2 != nil while v1 == nil")
+	}
+
 	// n.List has no meaning anymore, clear it
 	// to avoid erroneous processing by racewalk.
 	n.List.Set(nil)
@@ -290,14 +294,14 @@ func walkrange(n *Node) {
 		//
 		// ha := a
 		// for hv1 := 0; hv1 < len(ha); {
-		//   v1 = hv1
+		//   hv1t := hv1
 		//   hv2 := rune(ha[hv1])
 		//   if hv2 < utf8.RuneSelf {
 		//      hv1++
 		//   } else {
 		//      hv2, hv1 = decoderune(ha, hv1)
 		//   }
-		//   v2 = hv2
+		//   v1, v2 = hv1t, hv2
 		//   // original body
 		// }
 
@@ -305,6 +309,7 @@ func walkrange(n *Node) {
 		ha := a
 
 		hv1 := temp(Types[TINT])
+		hv1t := temp(Types[TINT])
 		hv2 := temp(runetype)
 
 		// hv1 := 0
@@ -314,18 +319,18 @@ func walkrange(n *Node) {
 		n.Left = nod(OLT, hv1, nod(OLEN, ha, nil))
 
 		if v1 != nil {
-			// v1 = hv1
-			body = append(body, nod(OAS, v1, hv1))
+			// hv1t = hv1
+			body = append(body, nod(OAS, hv1t, hv1))
 		}
 
-		// hv2 := ha[hv1]
+		// hv2 := rune(ha[hv1])
 		nind := nod(OINDEX, ha, hv1)
 		nind.Bounded = true
 		body = append(body, nod(OAS, hv2, conv(nind, runetype)))
 
 		// if hv2 < utf8.RuneSelf
 		nif := nod(OIF, nil, nil)
-		nif.Left = nod(OLT, nind, nodintconst(utf8.RuneSelf))
+		nif.Left = nod(OLT, hv2, nodintconst(utf8.RuneSelf))
 
 		// hv1++
 		nif.Nbody.Set1(nod(OAS, hv1, nod(OADD, hv1, nodintconst(1))))
@@ -341,9 +346,17 @@ func walkrange(n *Node) {
 
 		body = append(body, nif)
 
-		if v2 != nil {
-			// v2 = hv2
-			body = append(body, nod(OAS, v2, hv2))
+		if v1 != nil {
+			if v2 != nil {
+				// v1, v2 = hv1t, hv2
+				a := nod(OAS2, nil, nil)
+				a.List.Set2(v1, v2)
+				a.Rlist.Set2(hv1t, hv2)
+				body = append(body, a)
+			} else {
+				// v1 = hv1t
+				body = append(body, nod(OAS, v1, hv1t))
+			}
 		}
 	}
 
diff --git a/test/range.go b/test/range.go
index bae7a1c3c9..afdac57fa3 100644
--- a/test/range.go
+++ b/test/range.go
@@ -277,6 +277,26 @@ func teststring() {
 		println("wrong sum ranging over makestring", s)
 		panic("fail")
 	}
+
+	x := []rune{'a', 'b'}
+	i := 1
+	for i, x[i] = range "c" {
+		break
+	}
+	if i != 0 || x[0] != 'a' || x[1] != 'c' {
+		println("wrong parallel assignment", i, x[0], x[1])
+		panic("fail")
+	}
+
+	y := []int{1, 2, 3}
+	r := rune(1)
+	for y[r], r = range "\x02" {
+		break
+	}
+	if r != 2 || y[0] != 1 || y[1] != 0 || y[2] != 3 {
+		println("wrong parallel assignment", r, y[0], y[1], y[2])
+		panic("fail")
+	}
 }
 
 func teststring1() {
-- 
2.50.0