RE: [avr-gcc-list] Stack usage under heavy inlining

[John Regehr]

Couple responses:

I have a student who has hacked gcc so that stack slots are reused, when 
possible, eliminating the "stack bloat under inlining" problem.  He has 
also increased the precision of the live range analysis.  All of this is 
towards the goal of greatly reducing stack memory usage (we can already 
substantially reduce stack usage vs. default avr-gcc, at least for some 
applications).  He's integrating with IRA now, not sure when this'll all 
be ready to share.  We hope to publish something in the Fall but there's a 
big gap between publishability and usability.

My original stack analysis tool for AVR was too complicated and had to be 
abandoned.  I have a newer, simpler one that needs a bit more work before 
it can be deployed.  It is (in most cases) not hard to compute a stack 
bound for a single C function.  It is also (in most cases) not hard to 
compute a callgraph for an embedded application.  The hard part, which 
cannot be automated, is turning these parts into a sound and precise 
global stack bound.  To see why this is hard, consider that there may be 
threads, there may be coroutines, there may be reentrant and/or nested 
interrupts, etc.

John Regehr