[Vm-dev] Small refactoring and Lowcode

[Eliot Miranda]

Hi Ronie, (Hi Clément),

   for a while now Clément and I have been unhappy about optStatus
(CogSSOptStatus).  Now that the RegisterAllocatingCogit is nearly working
it's clear that a much nicer approach is to give CogSimStackEntry a
liveRegister instance variable and have simSelf take the place of
optStatus, so that what were

    optStatus isReceiverResultRegLive
    optStatus isReceiverResultRegLive: true
    optStatus isReceiverResultRegLive: false

are replaced by

    simSelf liveRegister = ReceiverResultReg
    simSelf liveRegister: ReceiverResultReg
    simSelf liveRegister: NoReg

To this end can you rewrite the Lowcode code generator so that e.g. the
following

genLowcodeAlloca32
<option: #LowcodeVM> "Lowcode instruction generator"
| size |

(size := backEnd availableRegisterOrNoneFor: self liveRegisters) = NoReg
ifTrue:
[self ssAllocateRequiredReg:
(size := optStatus isReceiverResultRegLive
ifTrue: [Arg0Reg]
ifFalse: [ReceiverResultReg])].
size = ReceiverResultReg ifTrue:
[ optStatus isReceiverResultRegLive: false ].
self ssNativeTop nativePopToReg: size.
self ssNativePop: 1.

self MoveAw: coInterpreter nativeStackPointerAddress R: TempReg.
self SubR: size R: TempReg.
self AndCq: -16 R: TempReg.
self MoveR: TempReg R: size.
self MoveR: size Aw: coInterpreter nativeStackPointerAddress.
self ssPushNativeRegister: size.

^ 0

reads something more like

genLowcodeAlloca32
<option: #LowcodeVM> "Lowcode instruction generator"
| size |

self allocateOneRegisterForLowcodeInto: [:reg| size := reg].
self ssNativeTop nativePopToReg: size.
self ssNativePop: 1.

self MoveAw: coInterpreter nativeStackPointerAddress R: TempReg.
self SubR: size R: TempReg.
self AndCq: -16 R: TempReg.
self MoveR: TempReg R: size.
self MoveR: size Aw: coInterpreter nativeStackPointerAddress.
self ssPushNativeRegister: size.

^ 0

etc?  So there are allocateOneRegisterForLowcodeInto: through
allocateThreeRegistersForLowcodeInto:. This way it'll be much easier to
make the above change which I'm making now.

_,,,^..^,,,_
best, Eliot
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