Eliminating the call stack to save RAM

Most programming languages support a call stack in the programming model and also in the runtime system. We show that for applications targeting low-power embedded microcontrollers (MCUs), RAM usage can be significantly decreased by partially or completely eliminating the runtime callstack. We present flattening, a transformation that absorbs a function into its caller, replacing function invocations and returns with jumps. Unlike inlining, flattening does not duplicate the bodies of functions that have multiple callsites. Applied aggressively, flattening results in stack elimination. Flattening is most useful in conjunction with a lifting transformation that moves global variables into a local scope. Flattening and lifting can save RAM. However, even more benefit can be obtained by adapting the compiler to cope with properties of flattened code. First, we show that flattening adds false paths that confuse a standard live variables analysis. The resulting problems can be mitiga...

• Type: Conference
• Year: 2009
• Where: LCTRTS
• Authors: Xuejun Yang, Nathan Cooprider, John Regehr
• Keywords: LCTRTS 2009, Low-power Embedded Microcontrollers, Programming Languages, RAM Usage, Software Engineering