runtime: test a frameless function for async preemption

Frameless function is an interesting case for call injection
espcially for LR architectures. Extend the test for this case.

Change-Id: I074090d09eeaf642e71e3f44fea216f66d39b817
Reviewed-on: https://go-review.googlesource.com/c/go/+/202339
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

src/runtime/testdata/testprog/preempt.go

@@ -22,16 +22,23 @@ func AsyncPreempt() {
 	debug.SetGCPercent(-1)
 
 	// Start a goroutine with no sync safe-points.
-	var ready uint32
+	var ready, ready2 uint32
 	go func() {
 		for {
 			atomic.StoreUint32(&ready, 1)
 		}
 	}()
+	// Also start one with a frameless function.
+	// This is an especially interesting case for
+	// LR machines.
+	go func() {
+		atomic.StoreUint32(&ready2, 1)
+		frameless()
+	}()
 
 	// Wait for the goroutine to stop passing through sync
 	// safe-points.
-	for atomic.LoadUint32(&ready) == 0 {
+	for atomic.LoadUint32(&ready) == 0 || atomic.LoadUint32(&ready2) == 0 {
 		runtime.Gosched()
 	}
 
@@ -42,3 +49,12 @@ func AsyncPreempt() {
 
 	println("OK")
 }
+
+//go:noinline
+func frameless() {
+	for i := int64(0); i < 1<<62; i++ {
+		out += i
+	}
+}
+
+var out int64