TInstrType = uint64

TRegister = range[0 .. 65535'u64.int]

TDest = range[-1 .. 65535'u64.int]

TInstr = distinct TInstrType

TOpcode = enum
  opcEof, opcRet, opcYldYoid, opcYldVal, opcAsgnInt, opcAsgnFloat, opcAsgnRef,
  opcAsgnComplex, opcCastIntToFloat32, opcCastIntToFloat64, opcCastFloatToInt32,
  opcCastFloatToInt64, opcCastPtrToInt, opcCastIntToPtr, opcFastAsgnComplex,
  opcNodeToReg, opcLdArr, opcLdArrAddr, opcWrArr, opcLdObj, opcLdObjAddr,
  opcWrObj, opcAddrReg, opcAddrNode, opcLdDeref, opcWrDeref, opcWrStrIdx,
  opcLdStrIdx, opcAddInt, opcAddImmInt, opcSubInt, opcSubImmInt, opcLenSeq,
  opcLenStr, opcIncl, opcInclRange, opcExcl, opcCard, opcMulInt, opcDivInt,
  opcModInt, opcAddFloat, opcSubFloat, opcMulFloat, opcDivFloat, opcShrInt,
  opcShlInt, opcAshrInt, opcBitandInt, opcBitorInt, opcBitxorInt, opcAddu,
  opcSubu, opcMulu, opcDivu, opcModu, opcEqInt, opcLeInt, opcLtInt, opcEqFloat,
  opcLeFloat, opcLtFloat, opcLeu, opcLtu, opcEqRef, opcEqNimNode,
  opcSameNodeType, opcXor, opcNot, opcUnaryMinusInt, opcUnaryMinusFloat,
  opcBitnotInt, opcEqStr, opcLeStr, opcLtStr, opcEqSet, opcLeSet, opcLtSet,
  opcMulSet, opcPlusSet, opcMinusSet, opcConcatStr, opcContainsSet, opcRepr,
  opcSetLenStr, opcSetLenSeq, opcIsNil, opcOf, opcIs, opcSubStr, opcParseFloat,
  opcConv, opcCast, opcQuit, opcInvalidField, opcNarrowS, opcNarrowU,
  opcSignExtend, opcAddStrCh, opcAddStrStr, opcAddSeqElem, opcRangeChck,
  opcNAdd, opcNAddMultiple, opcNKind, opcNSymKind, opcNIntVal, opcNFloatVal,
  opcNSymbol, opcNIdent, opcNGetType, opcNStrVal, opcNSigHash, opcNGetSize,
  opcNSetIntVal, opcNSetFloatVal, opcNSetSymbol, opcNSetIdent, opcNSetType,
  opcNSetStrVal, opcNNewNimNode, opcNCopyNimNode, opcNCopyNimTree, opcNDel,
  opcGenSym, opcNccValue, opcNccInc, opcNcsAdd, opcNcsIncl, opcNcsLen, opcNcsAt,
  opcNctPut, opcNctLen, opcNctGet, opcNctHasNext, opcNctNext, opcNodeId,
  opcSlurp, opcGorge, opcParseExprToAst, opcParseStmtToAst, opcQueryErrorFlag,
  opcNError, opcNWarning, opcNHint, opcNGetLineInfo, opcNSetLineInfo,
  opcEqIdent, opcStrToIdent, opcGetImpl, opcGetImplTransf, opcEcho, opcIndCall,
  opcIndCallAsgn, opcRaise, opcNChild, opcNSetChild, opcCallSite, opcNewStr,
  opcTJmp, opcFJmp, opcJmp, opcJmpBack, opcBranch, opcTry, opcExcept,
  opcFinally, opcFinallyEnd, opcNew, opcNewSeq, opcLdNull, opcLdNullReg,
  opcLdConst, opcAsgnConst, opcLdGlobal, opcLdGlobalAddr, opcLdGlobalDerefFFI,
  opcLdGlobalAddrDerefFFI, opcLdImmInt, opcNBindSym, opcNDynBindSym, opcSetType,
  opcTypeTrait, opcMarshalLoad, opcMarshalStore, opcSymOwner,
  opcSymIsInstantiationOf

TBlock = object
  label*: PSym
  fixups*: seq[TPosition]

TEvalMode = enum
  emRepl,                   ## evaluate because in REPL mode
  emConst,                  ## evaluate for 'const' according to spec
  emOptimize,               ## evaluate for optimization purposes (same as
                             ## emConst?)
  emStaticExpr,             ## evaluate for enforced compile time eval
                             ## ('static' context)
  emStaticStmt               ## 'static' as an expression

TSandboxFlag = enum
  allowCast,                ## allow unsafe language feature: 'cast'
  allowInfiniteLoops         ## allow endless loops

TSandboxFlags = set[TSandboxFlag]

TSlotKind = enum
  slotEmpty, slotFixedVar, slotFixedLet, slotTempUnknown, slotTempInt,
  slotTempFloat, slotTempStr, slotTempComplex, slotTempPerm

TRegisterKind = enum
  rkNone, rkNode, rkInt, rkFloat, rkRegisterAddr, rkNodeAddr

TFullReg = object
  case kind*: TRegisterKind
  of rkNone:
    nil
  of rkInt:
    intVal*: BiggestInt
  of rkFloat:
    floatVal*: BiggestFloat
  of rkNode:
    node*: PNode
  of rkRegisterAddr:
    regAddr*: ptr TFullReg
  of rkNodeAddr:
    nodeAddr*: ptr PNode
  

PProc = ref object
  blocks*: seq[TBlock]
  sym*: PSym
  slots*: array[TRegister, tuple[inUse: bool, kind: TSlotKind]]
  maxSlots*: int

VmArgs = object
  ra*, rb*, rc*: Natural
  slots*: ptr UncheckedArray[TFullReg]
  currentException*: PNode
  currentLineInfo*: TLineInfo

VmCallback = proc (args: VmArgs) {...}{.closure.}

PCtx = ref TCtx

TCtx = object of TPassContext
  code*: seq[TInstr]
  debug*: seq[TLineInfo]
  globals*: PNode
  constants*: PNode
  types*: seq[PType]
  currentExceptionA*, currentExceptionB*: PNode
  exceptionInstr*: int
  prc*: PProc
  module*: PSym
  callsite*: PNode
  mode*: TEvalMode
  features*: TSandboxFlags
  traceActive*: bool
  loopIterations*: int
  comesFromHeuristic*: TLineInfo
  callbacks*: seq[tuple[key: string, value: VmCallback]]
  errorFlag*: string
  cache*: IdentCache
  config*: ConfigRef
  graph*: ModuleGraph
  oldErrorCount*: int
  profiler*: Profiler
  templInstCounter*: ref int

PStackFrame = ref TStackFrame

TStackFrame {...}{.acyclic.} = object
  prc*: PSym
  slots*: seq[TFullReg]
  next*: PStackFrame
  comesFrom*: int
  safePoints*: seq[int]

Profiler = object
  tEnter*: float
  tos*: PStackFrame

TPosition = distinct int

PEvalContext = PCtx

byteExcess = 128

regOShift = 0'u

regAShift = 8'u64

regBShift = 24'u64

regCShift = 40'u64

regBxShift = 24'u64

regOMask = 255'u64

regAMask = 65535'u64

regBMask = 65535'u64

regCMask = 65535'u64

regBxMask = 16777215'u64

wordExcess = 8388608

regBxMin = -8388607

regBxMax = 8388607

firstABxInstr = opcTJmp

largeInstrs = {opcSubStr, opcConv, opcCast, opcNewSeq, opcOf, opcMarshalLoad,
               opcMarshalStore}

slotSomeTemp = slotTempUnknown

relativeJumps = {opcTJmp, opcFJmp, opcJmp, opcJmpBack}

nimNodeFlag = 16

proc newCtx(module: PSym; cache: IdentCache; g: ModuleGraph): PCtx {...}{.raises: [],
    tags: [].}

proc refresh(c: PCtx; module: PSym) {...}{.raises: [], tags: [].}

proc registerCallback(c: PCtx; name: string; callback: VmCallback): int {...}{.
    discardable, raises: [], tags: [].}

template opcode(x: TInstr): TOpcode

template regA(x: TInstr): TRegister

template regB(x: TInstr): TRegister

template regC(x: TInstr): TRegister

template regBx(x: TInstr): int

template jmpDiff(x: TInstr): int