===============
Code generation
===============

Tests currently passing (flag --rust):

  features/action_lang/test_closure.xml
  features/action_lang/test_cond.xml
  features/action_lang/test_expressions.xml
  features/action_lang/test_functions2.xml
  features/action_lang/test_guard_action.xml
  features/history/test_composite_shallow.xml
  features/history/test_default.xml
  features/history/test_shallow.xml
  features/after/test_after.xml
  features/parallel/test_parallel.xml
  day_atlee/test_01_dialer_takemany.xml
  day_atlee/test_01_dialer_takeone.xml
  day_atlee/test_02_counter_takeone.xml
  day_atlee/test_03_trafficlight_single.xml
  day_atlee/test_04_counter_single.xml
  day_atlee/test_06_counter_lifeline.xml
  day_atlee/test_21_counter_combo.xml
  semantics/priority/test_explicit_flat.xml
  semantics/priority/test_explicit_ortho.xml
  semantics/priority/test_source_child.xml
  semantics/priority/test_source_parent.xml
  semantics/event_lifeline/test_flat_nextss_takemany.xml
  semantics/event_lifeline/test_flat_nextss_takeone.xml
  semantics/event_lifeline/test_flat_remainder.xml
  semantics/event_lifeline/test_ortho_nextcs_takemany.xml
  semantics/event_lifeline/test_ortho_nextcs_takeone.xml
  semantics/event_lifeline/test_ortho_nextss.xml
  semantics/big_step_maximality/test_cross_region1.xml
  semantics/big_step_maximality/test_cross_region2.xml
  semantics/big_step_maximality/test_flat_syntactic.xml
  semantics/big_step_maximality/test_flat_takemany.xml
  semantics/big_step_maximality/test_flat_takeone.xml
  semantics/big_step_maximality/test_ortho_syntactic.xml
  semantics/big_step_maximality/test_ortho_takemany.xml
  semantics/big_step_maximality/test_ortho_takeone.xml
  xml_syntax/stateref/test_flat_absolute.xml
  xml_syntax/stateref/test_flat_relative.xml
  xml_syntax/stateref/test_nested_absolute.xml
  xml_syntax/stateref/test_nested_relative.xml

Currently unimplemented:

    - event parameters
    - builtin functions: e.g. INSTATE (should be turned into a macro)
    - memory protocol semantics
    - 'queuing' internal event semantics
    - concurrency semantics

Roadmap
-------

  (DONE) Milestone 1: Initial compilation to Rust
  
    - (DONE) entering and exiting states correctly
    - (DONE) incoming event triggers the right transition
    - (DONE) a port of the Controller class to Rust
    - (DONE) one implemented action: raise output event

    - (DONE) fixed semantics (YAKINDU-like)
        - "Take One" big step maximality
        - parent-first 

    - (DONE) goal: subset of SCCD tests passes:
        semantics/big_step_maximality/test_flat_takeone.xml
        semantics/big_step_maximality/test_ortho_takeone.xml
        semantics/priority/test_source_parent.xml
        semantics/priority/test_explicit_flat.xml
        semantics/priority/test_explicit_ortho.xml

    - no history
    - no action language
      - guards evals and action stmts are just logged to console
      - guards always true, actions no effect
    - no event parameters


  (DONE) Milestone 2: Minimal support for semantic variability:

    - (DONE) Priority: Child-first
    - (DONE) Big-Step Maximality: Take Many

    - (DONE) goal: following tests should pass:
        semantics/priority/test_source_child.xml
        semantics/big_step_maximality/test_flat_takemany.xml
        semantics/big_step_maximality/test_ortho_takemany.xml


  (DONE) Milestone 3: Support history

  (DONE) Milestone 4: Timers (should be easy)

  (DONE) Milestone 5: Internal Events

  (DONE) Milestone 6: Action language


Insights
--------

- Rust compiler warnings are actually useful for the modeler:
  - e.g. An unexecutable transition is detected as an unreachable statement
  - e.g. An unused event is detected as an unused variable or never-constructed enum variant.



Performance over time
---------------------

for test semantics/big_step_maximality/test_ortho_takemany.xml


commit ec39dd73ea42a9ccee6f1edc8863b36625e0721a - Dec 20, 2020 - put reusable stuff in library

binary size, opt-level=3:                       422192 bytes
instruction count (perf stat) (opt-level=3):    571.641 instructions:u


commit 354576dd47587fd8e6277539a26a4743b2167565 - Dec 17, 2020 - action lang working

binary size, no opt:                            513760 bytes
binary size, opt-level=3:                       421056 bytes
binary size, opt-level=3 inline-threshold=1000: 421056 bytes
binary size, opt-level=z:                       429200 bytes
instruction count (perf stat) (opt-level=3):    575.539 instructions:u


commit aa6a734f7d900479de9be99a8cdf68af0d561481 - Dec 2, 2020 - implemented big-step maximality

binary size, no opt:                            478976 bytes
binary size, opt-level=3 inline-threshold=1000: 410880 bytes
binary size, opt-level=z:                       413576 bytes
instruction count (perf stat) (opt-level=3):    580.701 instructions:u


Performance insights

  - instruction count improved a little over time (but could be due to non-relevant changes such as debug output)
  - binary size slightly worse when optimizing for size (opt-level=z). this means that inlining is actually reducing the binaries' size, as we would expect (lots of dead code can be eliminated)