+/// Byval parameters are handled separately because they don't use alloca's,
+/// which busts the normal mechanism. There is good reason for handling all
+/// parameters separately: they may not have code generated for them, they
+/// should always go at the beginning of the function regardless of other code
+/// motion, and debug info for them is potentially useful even if the parameter
+/// is unused. Right now only byval parameters are handled separately.