prog8/docs/source/todo.rst

TODO
====

- (branch): remove ExpressionsAsmGen.kt altogether
- (branch): clean up all X register special handling
- (branch): fix optimizeCmpSequence in AsmOptimizer
- (branch): fix inplaceModification TODO in AugmentableAssignmentAsmGen
- (branch): fix up cx16/keyboardhandler.p8 X register shenanigans
- (branch): clean up docs about eval stack and X register

- IR: instructions that do type conversion (SZ etc, CONCAT, SGN) should put the result in a DIFFERENT register.
- IR: reduce the number of branch instructions (gradually), replace with CMP(I) + status branch instruction

...


Need help with
^^^^^^^^^^^^^^
- getting the IR in shape for code generation
- atari target: more details details about the machine, fixing library routines. I have no clue whatsoever.
- see the :ref:`portingguide` for details on what information is needed.


Future Things and Ideas
^^^^^^^^^^^^^^^^^^^^^^^
Compiler:
- [much work:] more support for (64tass) SEGMENTS ?
    - (What, how, isn't current BSS support enough?)
    - Add a mechanism to allocate variables into golden ram (or segments really) (see GoldenRam class)
    - maybe treat block "golden" in a special way: can only contain vars, every var will be allocated in the Golden ram area?
    - maybe or may not needed: the variables can NOT have initialization values, they will all be set to zero on startup (simple memset)
      just initialize them yourself in start() if you need a non-zero value .
    - OR.... do all this automatically if 'golden' is enabled as a compiler option? So compiler allocates in ZP first, then Golden Ram, then regular ram
    - OR.... make all this more generic and use some %segment option to create real segments for 64tass?
    - (need separate step in codegen and IR to write the "golden" variables)
- ir: idea: (but LLVM IR simply keeps the variables, so not a good idea then?...): replace all scalar variables by an allocated register. Keep a table of the variable to register mapping (including the datatype)
  global initialization values are simply a list of LOAD instructions.
  Variables replaced include all subroutine parameters!  So the only variables that remain as variables are arrays and strings.
- ir: add more optimizations in IRPeepholeOptimizer
- ir: the @split arrays are currently also split in _lsb/_msb arrays in the IR, and operations take multiple (byte) instructions that may lead to verbose and slow operation and machine code generation down the line.
- ir: for expressions with array indexes that occur multiple times, can we avoid loading them into new virtualregs everytime and just reuse a single virtualreg as indexer? (simple form of common subexpression elimination)
- PtAst/IR: more complex common subexpression eliminations
- can we get rid of pieces of asmgen.AssignmentAsmGen by just reusing the AugmentableAssignment ? generated code should not suffer
- [problematic due to using 64tass:] better support for building library programs, where unused .proc shouldn't be deleted from the assembly?
  Perhaps replace all uses of .proc/.pend/.endproc by .block/.bend will fix that with a compiler flag?
  But all library code written in asm uses .proc already..... (textual search/replace when writing the actual asm?)
  Once new codegen is written that is based on the IR, this point is mostly moot anyway as that will have its own dead code removal on the IR level.
- Zig-like try-based error handling where the V flag could indicate error condition? and/or BRK to jump into monitor on failure? (has to set BRK vector for that) But the V flag is also set on certain normal instructions
- generate WASM to eventually run prog8 on a browser canvas? Use binaryen toolkit or my binaryen kotlin library?


Libraries:

- fix the problems in atari target, and flesh out its libraries.
- c128 target: make syslib more complete (missing kernal routines)?
- c64: make the graphics.BITMAP_ADDRESS configurable (VIC banking)
- optimize several inner loops in gfx2 even further?
- actually implement modes 3 and perhaps even 2 to gfx2 (lores 16 color and 4 color)


Expressions:

- Once the evalstack-free expression codegen is in place, the Eval Stack can be removed from the compiler.
    Machinedefinition, .p8 and .asm library files, all routines operationg on estack, and everything saving/restoring the X register related to this stack.
- Or rewrite expression tree evaluation such that it doesn't use an eval stack but flatten the tree into linear code
  that, for instance, uses a fixed number of predetermined value 'variables'?
  The VM IL solves this already (by using unlimited registers) but that still lacks a translation to 6502.
- this removes the need for the BinExprSplitter? (which is problematic and very limited now)
  and perhaps the assignment splitting in  BeforeAsmAstChanger  too

Optimizations:

- VariableAllocator: can we think of a smarter strategy for allocating variables into zeropage, rather than first-come-first-served?
  for instance, vars used inside loops first, then loopvars, then uwords used as pointers, then the rest
- various optimizers skip stuff if compTarget.name==VMTarget.NAME.  Once 6502-codegen is done from IR code,
  those checks should probably be removed, or be made permanent


STRUCTS again?
--------------

What if we were to re-introduce Structs in prog8? Some thoughts:

- can contain only numeric types (byte,word,float) - no nested structs, no reference types (strings, arrays) inside structs
- is just some syntactic sugar for a scoped set of variables -> ast transform to do exactly this before codegen. Codegen doesn't know about struct.
- no arrays of struct -- because too slow on 6502 to access those, rather use struct of arrays instead.
  can we make this a compiler/codegen only issue? i.e. syntax is just as if it was an array of structs?
  or make it explicit in the syntax so that it is clear what the memory layout of it is.
- ability to assign struct variable to another?   this is slow but can be quite handy sometimes.
  however how to handle this in a function that gets the struct passed as reference? Don't allow it there? (there's no pointer dereferencing concept in prog8)
- ability to be passed as argument to a function (by reference)?
  however there is no typed pointer in prog8 at the moment so this can't be implemented in a meaningful way yet,
  because there is no way to reference it as the struct type again. (current ast gets the by-reference parameter
  type replaced by uword)
  So-- maybe don't replace the parameter type in the ast?  Should fix that for str and array types as well then