Processor cleanup (#655)

Clean up and refactor the processor

* Simplify instruction fetching

* Refactor metrics out, and void their storage in release builds

*Put operations onto String

Author: milseman

Sources/_StringProcessing/Engine/MEBuiltins.swift

@@ -30,6 +30,7 @@ extension Processor {
   }
 
   func isAtStartOfLine(_ payload: AssertionPayload) -> Bool {
+    // TODO: needs benchmark coverage
     if currentPosition == subjectBounds.lowerBound { return true }
     switch payload.semanticLevel {
     case .graphemeCluster:
@@ -40,6 +41,7 @@ extension Processor {
   }
 
   func isAtEndOfLine(_ payload: AssertionPayload) -> Bool {
+    // TODO: needs benchmark coverage
     if currentPosition == subjectBounds.upperBound { return true }
     switch payload.semanticLevel {
     case .graphemeCluster:
@@ -50,6 +52,8 @@ extension Processor {
   }
 
   mutating func builtinAssert(by payload: AssertionPayload) throws -> Bool {
+    // TODO: needs benchmark coverage
+
     // Future work: Optimize layout and dispatch
     switch payload.kind {
     case .startOfSubject: return currentPosition == subjectBounds.lowerBound

Sources/_StringProcessing/Engine/MEQuantify.swift

@@ -3,10 +3,14 @@ extension Processor {
     var next: Input.Index?
     switch payload.type {
     case .bitset:
-      next = _doMatchBitset(registers[payload.bitset])
+      next = input.matchBitset(
+        registers[payload.bitset], at: currentPosition, limitedBy: end)
     case .asciiChar:
-      next = _doMatchScalar(
-        UnicodeScalar.init(_value: UInt32(payload.asciiChar)), true)
+      next = input.matchScalar(
+        UnicodeScalar.init(_value: UInt32(payload.asciiChar)),
+        at: currentPosition,
+        limitedBy: end,
+        boundaryCheck: true)
     case .builtin:
       // We only emit .quantify if it consumes a single character
       next = input._matchBuiltinCC(
@@ -16,6 +20,7 @@ extension Processor {
         isStrictASCII: payload.builtinIsStrict,
         isScalarSemantics: false)
     case .any:
+      // TODO: call out to existing code with quick check
       let matched = currentPosition != input.endIndex
         && (!input[currentPosition].isNewline || payload.anyMatchesNewline)
       next = matched ? input.index(after: currentPosition) : nil

Sources/_StringProcessing/Engine/Metrics.swift

@@ -1,13 +1,71 @@
 extension Processor {
+#if PROCESSOR_MEASUREMENTS_ENABLED
   struct ProcessorMetrics {
     var instructionCounts: [Instruction.OpCode: Int] = [:]
     var backtracks: Int = 0
     var resets: Int = 0
+    var cycleCount: Int = 0
+
+    var isTracingEnabled: Bool = false
+    var shouldMeasureMetrics: Bool = false
+
+    init(isTracingEnabled: Bool, shouldMeasureMetrics: Bool) {
+      self.isTracingEnabled = isTracingEnabled
+      self.shouldMeasureMetrics = shouldMeasureMetrics
+    }
   }
-  
+#else
+  struct ProcessorMetrics {
+    var isTracingEnabled: Bool { false }
+    var shouldMeasureMetrics: Bool { false }
+    var cycleCount: Int { 0 }
+
+    init(isTracingEnabled: Bool, shouldMeasureMetrics: Bool) { }
+  }
+#endif
+}
+
+extension Processor {
+
+  mutating func startCycleMetrics() {
+#if PROCESSOR_MEASUREMENTS_ENABLED
+    if metrics.cycleCount == 0 {
+      trace()
+      measureMetrics()
+    }
+#endif
+  }
+
+  mutating func endCycleMetrics() {
+#if PROCESSOR_MEASUREMENTS_ENABLED
+    metrics.cycleCount += 1
+    trace()
+    measureMetrics()
+    _checkInvariants()
+#endif
+  }
+}
+
+extension Processor.ProcessorMetrics {
+
+  mutating func addReset() {
+#if PROCESSOR_MEASUREMENTS_ENABLED
+    self.resets += 1
+#endif
+  }
+
+  mutating func addBacktrack() {
+#if PROCESSOR_MEASUREMENTS_ENABLED
+    self.backtracks += 1
+#endif
+  }
+}
+
+extension Processor {
+#if PROCESSOR_MEASUREMENTS_ENABLED
   func printMetrics() {
     print("===")
-    print("Total cycle count: \(cycleCount)")
+    print("Total cycle count: \(metrics.cycleCount)")
     print("Backtracks: \(metrics.backtracks)")
     print("Resets: \(metrics.resets)")
     print("Instructions:")
@@ -21,7 +79,7 @@ extension Processor {
   }
 
   mutating func measure() {
-    let (opcode, _) = fetch().destructure
+    let (opcode, _) = fetch()
     if metrics.instructionCounts.keys.contains(opcode) {
       metrics.instructionCounts[opcode]! += 1
     } else {
@@ -30,8 +88,9 @@ extension Processor {
   }
 
   mutating func measureMetrics() {
-    if shouldMeasureMetrics {
+    if metrics.shouldMeasureMetrics {
       measure()
     }
   }
+#endif
 }