Documentation/TODO.md

TODO
====

Essential
---------
* SSA is broken by simplify_loads() & branches rewriting/simplification
* add support for bitwise enums (wip)

Documentation
-------------
* document the API
* document the limitations of modifying ptrlists during list walking
* document the data structures
* document flow of data / architecture / code structure

Core
----
* if a variable has its address taken but in an unreachable BB then
  its MOD_ADDRESSABLE may be wrong and it won't be SSA converted.
  - let kill_insn() check killing of SYMADDR,
  - add the sym into a list and
  - recalculate the addressability before memops's SSA conversion
* bool_ctype should be split into internal 1-bit / external 8-bit

Testsuite
---------
* there are 60 failing tests. They should be fixed
  (but most are non-trivial to fix).

Misc
----
* GCC's -Wenum-compare / clangs's -Wenum-conversion -Wassign-enum
* parse __attribute_((fallthrough))
* add support for format(printf())  (WIP by Ben Dooks)
* make use of UNDEFs (issues warnings, simplification, ... ?)
* make memory accesses more explicit: add EXPR_ACCESS (wip)
* it would be nice to do our own parsing of floating point (wip)
* some header files needed for crypto/ need __vector or __fp16
* some even need __complex

Optimization
------------
* a lot of small simplifications are waiting to be upstreamed
* the domtree need to be rebuilt (or updated)
* critical edges need to be split
* the current way of doing CSE uses a lot of time
* add SSA based DCE
* add SSA based PRE
* Add SSA based SCCP
* add a pass to inline small functions during simplification.
* use better/more systematic use of internal verification framework
* tracking of operands size should be improved (WIP)
* OP_INLINE is sometimes in the way
* would be nice to strictly separate phases that don't changes the
  CFG and thus the dominance tree.

IR
--
* pseudos are untyped, it's usually OK but often it complicates things:

  - PSEUDO_REGs are defined by instructions and their type is normally
    retrievable via this defining instruction but in some cases they're not:
    for example, pseudos defined by ASM output.
  - PSEUDO_ARGs are considered as defined by OP_ENTRY and are used like
    this for liveness trackability but their type can't simply be
    retrieved via this instruction like PSEUDO_REGs are (with ->def->type).
  - PSEUDO_VALs are completely typeless.

  Maybe a few bits should be used to store some kind of low-level type.
* OP_SET should return a bool, always
* add IR instructions for va_arg() & friends
* add a possibility to import of file in "IR assembly"
* dump the symtable
* dump the CFG

LLVM
----
* fix ...

Internal backends
-----------------
* it would be nice the upstream the code generator
* add a pass to transform 3-addresses code to 2-addresses
* add some basic register allocation
* add a pass to order the BBs and changes 2-ways CBR into one-way branches
* what can be done for x86?
* add support to add constraints in the MD rules

Longer term/to investigate
--------------------------
* attributes are represented as ctypes's alignment, modifiers & contexts
  but plenty of attributes doesn't fit, for example they need arguments.
  * format(printf, ...),
  * section("...")
  * assume_aligned(alignment[, offsert])
  * error("message"), warning("message")
  * ...
* should support "-Werror=..." ?
* All warning messages should include the option how to disable it.
  For example:

  	"warning: Variable length array is used."

  should be something like:

	"warning: Variable length array is used. (-Wno-vla)"

* ptrlists must not have elements removed while being iterated;
  this should somehow be enforced.
* having 'struct symbol' used to represent symbols *and* types is
  quite handy but it also creates lots of problems and complications
* Possible mixup of symbol for a function designator being not a pointer?
  This seems to make evaluation of function pointers much more complex
  than needed.
* extend test-inspect to inspect more AST fields.
* extend test-inspect to inspect instructions.