ssa:fit slice int size

cl/_testrt/slicelen/in.go

@@ -0,0 +1,16 @@
+package main
+
+import (
+	"unsafe"
+)
+
+func main() {
+	var s *int
+	var lens uint32
+	sl := unsafe.Slice(s, lens)
+	slen := len(sl)
+	println(slen)
+	if slen > 0 {
+		println("len > 0")
+	}
+}