TODO
====

For next release
^^^^^^^^^^^^^^^^
- vm: get rid of all the conditional set instructions
- vm: add more instructions operating directly on memory instead of only registers?
- vm: check array type in PtAssignTarget
- in-place modifiying functions (rol, ror, ..) don't accept a memory address but require a memory-read expression. that is weird.
- complete the Inliner
- add McCarthy evaluation to shortcircuit and/or expressions. First do ifs by splitting them up? Then do expressions that compute a value?

...


Need help with
^^^^^^^^^^^^^^
- c128 target: various machine specific things (free zp locations, how banking works, getting the floating point routines working, ...)
- 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:

- vm: codeGen: various TODOs to tweak code
- vm: somehow deal with asmsubs otherwise the vm IR can't fully encode all of prog8
- vm: make registers typed? so that it's immediately obvious what type they represent. Much like regular variables in memory.
  so we have a set of byte registers, a set of word registers, and other sets if we introduce other types.
- vm: don't store symbol names in instructions to make optimizing the IR easier? but what about jumps to labels. And it's no longer readable by humans.
- vm: how to remove all unused subroutines? (in the assembly codegen, we let 64tass solve this for us)
- vm: rather than being able to jump to any 'address' (IPTR), use 'blocks' that have entry and exit points -> even better dead code elimination possible too
- when the vm is stable and *if* its language can get promoted to prog8 IL, the variable allocation should be changed.
  It's now done before the vm code generation, but the IL should probably not depend on the allocations already performed.
  So the CodeGen doesn't do VariableAlloc *before* the codegen, but as a last step.
- createAssemblyAndAssemble(): make it possible to actually get rid of the VarDecl nodes by fixing the rest of the code mentioned there.
  but probably better to rewrite the 6502 codegen on top of the new Ast.
- make everything an expression? (get rid of Statements. Statements are expressions with void return types?).
- simplifyConditionalExpression() should not split expression if it still results in stack-based evaluation, but how does it know?
- simplifyConditionalExpression() sometimes introduces needless assignment to r9 tempvar (what scenarios?)
- make it possible to use cpu opcodes such as 'nop' as variable names by prefixing all asm vars with something such as ``p8v_``? Or not worth it (most 3 letter opcodes as variables are nonsensical anyway)
  then we can get rid of the instruction lists in the machinedefinitions as well?
- [problematic due to using 64tass:] add a compiler option to not remove unused subroutines. this allows for building library programs. But this won't work with 64tass's .proc ...
  Perhaps replace all uses of .proc/.pend by .block/.bend will fix that?
  (but we lose the optimizing aspect of the assembler where it strips out unused code.
  There's not really a dynamic switch possible as all assembly lib code is static and uses one or the other)
- 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)
- add special (u)word array type (or modifier?) that puts the array into memory as 2 separate byte-arrays 1 for LSB 1 for MSB -> allows for word arrays of length 256

Libraries:

- fix the problems in c128 target, and flesh out its libraries.
- fix the problems in atari target, and flesh out its libraries.
- c64: make the graphics.BITMAP_ADDRESS configurable (VIC banking)
- optimize several inner loops in gfx2 even further?
- add modes 2 and 3 to gfx2 (lowres 4 color and 16 color)?
- add a flood fill routine to gfx2?
- diskio: use cx16 MACPTR() to load stuff faster? (see its use in X16edit to fast load blocks)
  note that it might fail on non sdcard files so have to make graceful degradation

Expressions:

- pipe operator: (targets other than 'Virtual'): allow non-unary function calls in the pipe that specify the other argument(s) in the calls.
- rethink the whole "isAugmentable" business.  Because the way this is determined, should always also be exactly mirrorred in the AugmentableAssignmentAsmGen or you'll get a crash at code gen time.
  note: new ast PtAssignment already has no knowledge about this anymore.
- can we get rid of pieces of asmgen.AssignmentAsmGen by just reusing the AugmentableAssignment ? generated code should not suffer
- rewrite expression tree evaluation suchthat it doesn't use an eval stack but flatten the tree into linear code that uses a fixed number of predetermined value 'variables'?
  "Three address code" was mentioned.  https://en.wikipedia.org/wiki/Three-address_code
  these variables have to be unique for each subroutine because they could otherwise be interfered with from irq routines etc.
- this removes the need for the BinExprSplitter? (which is problematic and very limited now)
  and perhaps as well the assignment splitting in  BeforeAsmAstChanger too

Optimizations:

- various optimizers skip stuff if compTarget.name==VMTarget.NAME.  Once (if?) 6502-codegen is no longer done from
  the old CompilerAst, those checks should probably be removed, or be made permanent
- VariableAllocator: can we think of a smarter strategy for allocating variables into zeropage, rather than first-come-first-served
- translateUnaryFunctioncall() in BuiltinFunctionsAsmGen: should be able to assign parameters to a builtin function directly from register(s), this will make the use of a builtin function in a pipe expression more efficient without using a temporary variable
   compare ``aa = startvalue(1) |> sin8u() |> cos8u() |> sin8u() |> cos8u()``
   versus: ``aa = cos8u(sin8u(cos8u(sin8u(startvalue(1)))))``  the second one contains no sta cx16.r9L in between.
- AssignmentAsmGen.assignExpression() -> better code gen for assigning boolean comparison expressions
- when a for loop's loopvariable isn't referenced in the body, and the iterations are known, replace the loop by a repeatloop
  but we have no efficient way right now to see if the body references a variable.
- introduce byte-index operator to avoid index multiplications in loops over arrays? see github issue #4