Remove obsolete limit/mark comment
diff --git a/internal/cgen/cgen.go b/internal/cgen/cgen.go
index 88d23ff..8603fae 100644
--- a/internal/cgen/cgen.go
+++ b/internal/cgen/cgen.go
@@ -74,18 +74,14 @@
// pointer retreats, undoing a read or write, it cannot retreat past io0_etc.
//
// At the start of a function, these pointers are initialized from an
-// io_buffer's fields (ptr, ri, wi, len), or possibly a limit field. For an
-// io_reader:
+// io_buffer's fields (ptr, ri, wi, len). For an io_reader:
// - io0_etc = ptr + ri
// - iop_etc = ptr + ri
-// - io1_etc = ptr + wi or limit
+// - io1_etc = ptr + wi
// and for an io_writer:
// - io0_etc = ptr + wi
// - iop_etc = ptr + wi
-// - io1_etc = ptr + len or limit
-//
-// TODO: discuss marks and limits, and how (if at all) auxilliary pointers can
-// change over a function's lifetime.
+// - io1_etc = ptr + len
const (
io0Prefix = "io0_" // Lower bound.
io1Prefix = "io1_" // Upper bound.
