runtime: make TestGcSys actually test something

ianlancetaylor · bradfitz · commit 0a519401651f · 2018-08-22T19:47:55.000Z
The workthegc function was being inlined, and the slice did not escape, so there was no memory allocation. Use a sink variable to force memory allocation, at least for now. Fixes #23343 Change-Id: I02f4618e343c8b6cb552cb4e9f272e112785f7cf Reviewed-on: https://go-review.googlesource.com/122576 Run-TryBot: Ian Lance Taylor <iant@golang.org> Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/runtime/testdata/testprog/gc.go b/src/runtime/testdata/testprog/gc.go
@@ -48,8 +48,11 @@ func GCSys() {
 	fmt.Printf("OK\n")
 }
 
+var sink []byte
+
 func workthegc() []byte {
-	return make([]byte, 1029)
+	sink = make([]byte, 1029)
+	return sink
 }
 
 func GCFairness() {

Original file line number	Diff line number	Diff line change
`@@ -48,8 +48,11 @@ func GCSys() {`
`48`	`48`	`fmt.Printf("OK\n")`
`49`	`49`	`}`
`50`	`50`
	`51`	`+var sink []byte`
	`52`	`+`
`51`	`53`	`func workthegc() []byte {`
`52`		`- return make([]byte, 1029)`
	`54`	`+ sink = make([]byte, 1029)`
	`55`	`+ return sink`
`53`	`56`	`}`
`54`	`57`
`55`	`58`	`func GCFairness() {`