Remove the unused callstack

Sources/_StringProcessing/Engine/Backtracking.swift

@@ -21,13 +21,6 @@ extension Processor {
     //        points. We should try to separate out the concerns better.
     var isScalarSemantics: Bool
 
-    // The end of the call stack, so we can slice it off
-    // when failing inside a call.
-    //
-    // NOTE: Alternatively, also place return addresses on the
-    // save point stack
-    var stackEnd: CallStackAddress
-
     // FIXME: Save minimal info (e.g. stack position and
     // perhaps current start)
     var captureEnds: [_StoredCapture]
@@ -41,12 +34,11 @@ extension Processor {
     var destructure: (
       pc: InstructionAddress,
       pos: Position?,
-      stackEnd: CallStackAddress,
       captureEnds: [_StoredCapture],
       intRegisters: [Int],
       PositionRegister: [Input.Index]
     ) {
-      return (pc, pos, stackEnd, captureEnds, intRegisters, posRegisters)
+      return (pc, pos, captureEnds, intRegisters, posRegisters)
     }
 
     // Whether this save point is quantified, meaning it has a range of
@@ -85,7 +77,6 @@ extension Processor {
       pos: currentPosition,
       quantifiedRange: nil,
       isScalarSemantics: false,
-      stackEnd: .init(callStack.count),
       captureEnds: storedCaptures,
       intRegisters: registers.ints,
       posRegisters: registers.positions)
@@ -99,7 +90,6 @@ extension Processor {
       pos: nil,
       quantifiedRange: nil,
       isScalarSemantics: false,
-      stackEnd: .init(callStack.count),
       captureEnds: storedCaptures,
       intRegisters: registers.ints,
       posRegisters: registers.positions)
@@ -114,7 +104,6 @@ extension Processor {
       pos: nil,
       quantifiedRange: range,
       isScalarSemantics: isScalarSemantics,
-      stackEnd: .init(callStack.count),
       captureEnds: storedCaptures,
       intRegisters: registers.ints,
       posRegisters: registers.positions)

Sources/_StringProcessing/Engine/Processor.swift

@@ -81,8 +81,6 @@ struct Processor {
 
   var savePoints: [SavePoint] = []
 
-  var callStack: [InstructionAddress] = []
-
   var storedCaptures: Array<_StoredCapture>
 
   var state: State = .inProgress
@@ -142,9 +140,6 @@ extension Processor {
     if !self.savePoints.isEmpty {
       self.savePoints.removeAll(keepingCapacity: true)
     }
-    if !self.callStack.isEmpty {
-      self.callStack.removeAll(keepingCapacity: true)
-    }
 
     for idx in storedCaptures.indices {
       storedCaptures[idx] = .init()
@@ -163,7 +158,6 @@ extension Processor {
     _checkInvariants()
     guard self.controller == Controller(pc: 0),
           self.savePoints.isEmpty,
-          self.callStack.isEmpty,
           self.storedCaptures.allSatisfy({ $0.range == nil }),
           self.state == .inProgress,
           self.failureReason == nil
@@ -361,10 +355,9 @@ extension Processor {
       state = .fail
       return
     }
-    let (pc, pos, stackEnd, capEnds, intRegisters, posRegisters): (
+    let (pc, pos, capEnds, intRegisters, posRegisters): (
       pc: InstructionAddress,
       pos: Position?,
-      stackEnd: CallStackAddress,
       captureEnds: [_StoredCapture],
       intRegisters: [Int],
       PositionRegister: [Input.Index]
@@ -376,17 +369,15 @@ extension Processor {
     // pos instead of removing it
     if savePoints[idx].isQuantified {
       savePoints[idx].takePositionFromQuantifiedRange(input)
-      (pc, pos, stackEnd, capEnds, intRegisters, posRegisters) = savePoints[idx].destructure
+      (pc, pos, capEnds, intRegisters, posRegisters) = savePoints[idx].destructure
     } else {
-      (pc, pos, stackEnd, capEnds, intRegisters, posRegisters) = savePoints.removeLast().destructure
+      (pc, pos, capEnds, intRegisters, posRegisters) = savePoints.removeLast().destructure
     }
 
-    assert(stackEnd.rawValue <= callStack.count)
     assert(capEnds.count == storedCaptures.count)
 
     controller.pc = pc
     currentPosition = pos ?? currentPosition
-    callStack.removeLast(callStack.count - stackEnd.rawValue)
     registers.ints = intRegisters
     registers.positions = posRegisters
 

Sources/_StringProcessing/Engine/Tracing.swift

@@ -128,7 +128,7 @@ extension Processor.SavePoint {
       }
     }
     return """
-      pc: \(self.pc), pos: \(posStr), stackEnd: \(stackEnd)
+      pc: \(self.pc), pos: \(posStr)
       """
   }
 }

Sources/_StringProcessing/Utility/Protocols.swift

@@ -34,9 +34,6 @@ protocol ProcessorProtocol {
   var isAcceptState: Bool { get }
   var isFailState: Bool { get }
 
-  // Provide to get call stack formatting, default empty
-  var callStack: Array<InstructionAddress> { get }
-
   // Provide to get save point formatting, default empty
   var savePoints: Array<SavePoint> { get }
 

Sources/_StringProcessing/Utility/Traced.swift

@@ -18,7 +18,6 @@ protocol Traced {
 
 protocol TracedProcessor: ProcessorProtocol, Traced {
   // Empty defaulted
-  func formatCallStack() -> String // empty default
   func formatSavePoints() -> String // empty default
   func formatRegisters() -> String // empty default
 
@@ -52,14 +51,6 @@ extension TracedProcessor {
     if isTracingEnabled { printTrace() }
   }
 
-  // Helpers for the conformers
-  func formatCallStack() -> String {
-    if !callStack.isEmpty {
-      return "call stack: \(callStack)\n"
-    }
-    return ""
-  }
-
   func formatSavePoints() -> String {
     if !savePoints.isEmpty {
       var result = "save points:\n"
@@ -158,7 +149,6 @@ extension TracedProcessor {
 
   func formatTrace() -> String {
     var result = "\n--- cycle \(cycleCount) ---\n"
-    result += formatCallStack()
     result += formatSavePoints()
     result += formatRegisters()
     result += formatInput()

Sources/_StringProcessing/Utility/TypedInt.swift

@@ -99,10 +99,6 @@ enum _Distance {}
 typealias InstructionAddress = TypedInt<_InstructionAddress>
 enum _InstructionAddress {}
 
-/// A position in the call stack, i.e. for save point restores
-typealias CallStackAddress = TypedInt<_CallStackAddress>
-enum _CallStackAddress {}
-
 /// A position in a position stack, i.e. for NFA simulation
 typealias PositionStackAddress = TypedInt<_PositionStackAddress>
 enum _PositionStackAddress {}
@@ -111,7 +107,6 @@ enum _PositionStackAddress {}
 typealias SavePointStackAddress = TypedInt<_SavePointAddress>
 enum _SavePointAddress {}
 
-
 // MARK: - Registers
 
 /// The register number for a stored element