remove eval stack from documentation

docs/source/targetsystem.rst

@@ -56,9 +56,7 @@ Both systems have ways to alter the memory map and/or to switch memory banks, bu
 Footnotes for the Commander X16
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 *Golden Ram $0400 - $07FF*
-    *reserved:* $0700 - $07FF (expression evaluation stack)
-
-    *free to use:* $0400 - $06FF
+    *free to use.*
 
 *Zero Page $0000 - $00FF*
     $00 and $01 are hardwired as Rom and Ram banking registers.
@@ -76,10 +74,8 @@ Footnotes for the Commodore 64
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 *RAM $C000-$CFFF*
-    *reserved:* $CF00 - $CFFF (expression evaluation stack)
-    *this includes:* $CF00 - $CF20 for the 16 virtual cx16 registers R0-R15
-
-    *free to use:* $C000 - $CEFF
+    *free to use:* $C000 - $CFDF
+    *reserved:* $CFE0 - $CFFF for the 16 virtual cx16 registers R0-R15
 
 *Zero Page $0000 - $00FF*
     Consider the full zero page to be reserved for use by the Kernal and Basic in normal operation.
@@ -127,8 +123,6 @@ Directly Usable Registers
 
 The hardware CPU registers are not directly accessible from regular Prog8 code.
 If you need to mess with them, you'll have to use inline assembly.
-Be extra wary of the ``X`` register because it is used as an evaluation stack pointer and
-changing its value you will destroy the evaluation stack and likely crash the program.
 
 The status register (P) carry flag and interrupt disable flag can be written via a couple of special
 builtin functions (``set_carry()``, ``clear_carry()``, ``set_irqd()``,  ``clear_irqd()``),

docs/source/technical.rst

@@ -44,28 +44,6 @@ All elements in scoped names such as ``main.routine.var1`` are prefixed so this
         }}
 
 
-Software stack for expression evaluation
-----------------------------------------
-
-Prog8 uses a software stack to evaluate complex expressions that it can't calculate in-place or
-directly into the target variable, register, or memory location.
-
-'software stack' means: seperated and not using the processor's hardware stack.
-
-The software stack is implemented as follows:
-
-- 2*128 bytes = 1 page of memory allocated for this, exact locations vary per machine target.
-  For the C64 this page is at $cf00-$cfff.
-  For the Commander X16 it is at $0700-$07ff (top of the "golden ram" area).
-  This default location can be overridden using the `-esa` command line option.
-- these are the high and low bytes of the values on the stack (it's a 'split 16 bit word stack')
-- for byte values just the lsb page is used, for word values both pages
-- float values (5 bytes) are chopped up into 2 words and 1 byte on this stack.
-- the X register is permanently allocated to be the stack pointer in the software stack.
-- you can use the X register as long as you're not using the software stack.
-  But you *must* make sure it is saved and restored after the code that modifies it,
-  otherwise the evaluation stack gets corrupted.
-
 Subroutine Calling Convention
 -----------------------------
 
@@ -94,8 +72,7 @@ regular subroutines
 ^^^^^^^^^^^^^^^^^^^
 
 - subroutine parameters are just variables scoped to the subroutine.
-- the arguments passed in a call are evaluated (using the eval-stack if needed) and then
-  copied into those variables.
+- the arguments passed in a call are evaluated and then copied into those variables.
   Using variables for this sometimes can seem inefficient but it's required to allow subroutines to work locally
   with their parameters and allow them to modify them as required, without changing the
   variables used in the call's arguments.  If you want to get rid of this overhead you'll

docs/source/todo.rst

@@ -1,7 +1,6 @@
 TODO
 ====
 
-- (branch): clean up docs about eval stack and X register
 - (branch): fix optimizeCmpSequence in AsmOptimizer
 - (branch): fix inplaceModification TODO in AugmentableAssignmentAsmGen
 - (branch): fix up cx16/keyboardhandler.p8 X register shenanigans
@@ -56,16 +55,6 @@ Libraries:
 - 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?