cmd/gc: implement 'for range x {'

Fixes issue 6102.

LGTM=gri
R=ken, r, gri
CC=golang-codereviews
https://codereview.appspot.com/113120043

6 files changed, 102 insertions, 1 deletions

diff --git a/test/bench/shootout/chameneosredux.go b/test/bench/shootout/chameneosredux.go
index 339579862..72ce7dd13 100644
--- a/test/bench/shootout/chameneosredux.go
+++ b/test/bench/shootout/chameneosredux.go
@@ -123,7 +123,7 @@ func pallmall(cols []int) {
 	fmt.Println(msg)
 	tot := 0
 	// wait for all results
-	for _ = range cols {
+	for range cols {
 		result := <-ended
 		tot += result.met
 		fmt.Printf("%v%v\n", result.met, spell(result.same, true))
diff --git a/test/chan/perm.go b/test/chan/perm.go
index 7e152c5eb..919fa30fb 100644
--- a/test/chan/perm.go
+++ b/test/chan/perm.go
@@ -56,6 +56,9 @@ func main() {
 	for _ = range cs {// ERROR "receive"
 	}
 
+	for range cs {// ERROR "receive"
+	}
+
 	close(c)
 	close(cs)
 	close(cr)  // ERROR "receive"
diff --git a/test/fixedbugs/bug173.go b/test/fixedbugs/bug173.go
index 6479bb253..3515c649b 100644
--- a/test/fixedbugs/bug173.go
+++ b/test/fixedbugs/bug173.go
@@ -18,4 +18,6 @@ func main() {
 	}
 	for _ = range t {
 	}
+	for range t {
+	}
 }
diff --git a/test/fixedbugs/bug406.go b/test/fixedbugs/bug406.go
index c6f8534c9..6df3c5cae 100644
--- a/test/fixedbugs/bug406.go
+++ b/test/fixedbugs/bug406.go
@@ -14,6 +14,8 @@ type matrix struct {
 func (a matrix) equal() bool {
 	for _ = range a.e {
 	}
+	for range a.e {
+	}
 	return true
 }
 
diff --git a/test/range.go b/test/range.go
index 8effbe9c5..af89edac5 100644
--- a/test/range.go
+++ b/test/range.go
@@ -32,6 +32,13 @@ func testchan() {
 		println("Wanted lowercase alphabet; got", s)
 		panic("fail")
 	}
+	n := 0
+	for range seq('a', 'z') {
+		n++
+	}
+	if n != 26 {
+		println("testchan wrong count", n, "want 26")
+	}
 }
 
 // test that range over slice only evaluates
@@ -87,6 +94,22 @@ func testslice1() {
 	}
 }
 
+func testslice2() {
+	n := 0
+	nmake = 0
+	for range makeslice() {
+		n++
+	}
+	if nmake != 1 {
+		println("range called makeslice", nmake, "times")
+		panic("fail")
+	}
+	if n != 5 {
+		println("wrong count ranging over makeslice", n)
+		panic("fail")
+	}
+}
+
 // test that range over array only evaluates
 // the expression after "range" once.
 
@@ -127,6 +150,22 @@ func testarray1() {
 	}
 }
 
+func testarray2() {
+	n := 0
+	nmake = 0
+	for range makearray() {
+		n++
+	}
+	if nmake != 1 {
+		println("range called makearray", nmake, "times")
+		panic("fail")
+	}
+	if n != 5 {
+		println("wrong count ranging over makearray", n)
+		panic("fail")
+	}
+}
+
 func makearrayptr() *[5]int {
 	nmake++
 	return &[5]int{1, 2, 3, 4, 5}
@@ -176,6 +215,22 @@ func testarrayptr1() {
 	}
 }
 
+func testarrayptr2() {
+	n := 0
+	nmake = 0
+	for range makearrayptr() {
+		n++
+	}
+	if nmake != 1 {
+		println("range called makearrayptr", nmake, "times")
+		panic("fail")
+	}
+	if n != 5 {
+		println("wrong count ranging over makearrayptr", n)
+		panic("fail")
+	}
+}
+
 // test that range over string only evaluates
 // the expression after "range" once.
 
@@ -216,6 +271,22 @@ func teststring1() {
 	}
 }
 
+func teststring2() {
+	n := 0
+	nmake = 0
+	for range makestring() {
+		n++
+	}
+	if nmake != 1 {
+		println("range called makestring", nmake, "times")
+		panic("fail")
+	}
+	if n != 5 {
+		println("wrong count ranging over makestring", n)
+		panic("fail")
+	}
+}
+
 // test that range over map only evaluates
 // the expression after "range" once.
 
@@ -256,6 +327,22 @@ func testmap1() {
 	}
 }
 
+func testmap2() {
+	n := 0
+	nmake = 0
+	for range makemap() {
+		n++
+	}
+	if nmake != 1 {
+		println("range called makemap", nmake, "times")
+		panic("fail")
+	}
+	if n != 5 {
+		println("wrong count ranging over makemap", n)
+		panic("fail")
+	}
+}
+
 // test that range evaluates the index and value expressions
 // exactly once per iteration.
 
@@ -298,13 +385,18 @@ func main() {
 	testchan()
 	testarray()
 	testarray1()
+	testarray2()
 	testarrayptr()
 	testarrayptr1()
+	testarrayptr2()
 	testslice()
 	testslice1()
+	testslice2()
 	teststring()
 	teststring1()
+	teststring2()
 	testmap()
 	testmap1()
+	testmap2()
 	testcalls()
 }
diff --git a/test/stress/maps.go b/test/stress/maps.go
index d022e19ad..fc5ab05a2 100644
--- a/test/stress/maps.go
+++ b/test/stress/maps.go
@@ -97,6 +97,8 @@ func (m intMap) Len() int { return len(m) }
 func (m intMap) RangeAll() {
 	for _ = range m {
 	}
+	for range m {
+	}
 }
 
 func stressMaps() {