From 381b72a7a3cc4c7182319f84297d40bb7b459dc4 Mon Sep 17 00:00:00 2001
From: =?utf8?q?R=C3=A9my=20Oudompheng?= <oudomphe@phare.normalesup.org>
Date: Thu, 19 Sep 2013 09:23:04 +0200
Subject: [PATCH] cmd/gc: cleanup SWITCH nodes after walk.

Keeping pointers from the pre-walk phase confuses
the race detection instrumentation.

Fixes #6418.

R=golang-dev, dvyukov, r
CC=golang-dev
https://golang.org/cl/13368057
---
 src/cmd/gc/swt.c                          |  3 +++
 src/pkg/runtime/race/testdata/mop_test.go | 16 ++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/src/cmd/gc/swt.c b/src/cmd/gc/swt.c
index c5cb49170d..ced07790ac 100644
--- a/src/cmd/gc/swt.c
+++ b/src/cmd/gc/swt.c
@@ -820,6 +820,9 @@ walkswitch(Node *sw)
 		return;
 	}
 	exprswitch(sw);
+	// Discard old AST elements after a walk. They can confuse racewealk.
+	sw->ntest = nil;
+	sw->list = nil;
 }
 
 /*
diff --git a/src/pkg/runtime/race/testdata/mop_test.go b/src/pkg/runtime/race/testdata/mop_test.go
index fe62bb07e1..b0b66562cc 100644
--- a/src/pkg/runtime/race/testdata/mop_test.go
+++ b/src/pkg/runtime/race/testdata/mop_test.go
@@ -231,6 +231,22 @@ func TestRaceCaseFallthrough(t *testing.T) {
 	<-ch
 }
 
+func TestRaceCaseIssue6418(t *testing.T) {
+	m := map[string]map[string]string{
+		"a": map[string]string{
+			"b": "c",
+		},
+	}
+	ch := make(chan int)
+	go func() {
+		m["a"]["x"] = "y"
+		ch <- 1
+	}()
+	switch m["a"]["b"] {
+	}
+	<-ch
+}
+
 func TestRaceCaseType(t *testing.T) {
 	var x, y int
 	var i interface{} = x
-- 
2.50.0