[perf] Implement auto-possessification

Sources/_StringProcessing/ByteCodeGen+DSLList.swift

@@ -12,7 +12,7 @@
 internal import _RegexParser
 
 extension Compiler.ByteCodeGen {
-  mutating func emitRoot(_ root: DSLList) throws -> MEProgram {
+  mutating func emitRoot(_ root: inout DSLList) throws -> MEProgram {
     // If the whole regex is a matcher, then the whole-match value
     // is the constructed value. Denote that the current value
     // register is the processor's value output.
@@ -22,7 +22,11 @@ extension Compiler.ByteCodeGen {
     default:
       break
     }
-
+
+    if optimizationsEnabled {
+      root.autoPossessify()
+    }
+
     var list = root.nodes[...]
     try emitNode(&list)
 
@@ -352,15 +356,7 @@ fileprivate extension Compiler.ByteCodeGen {
     _ kind: DSLTree.QuantificationKind,
     _ list: inout ArraySlice<DSLTree.Node>
   ) throws {
-    let updatedKind: AST.Quantification.Kind
-    switch kind {
-    case .explicit(let kind):
-      updatedKind = kind.ast
-    case .syntax(let kind):
-      updatedKind = kind.ast.applying(options)
-    case .default:
-      updatedKind = options.defaultQuantificationKind
-    }
+    let updatedKind = kind.applying(options: options)
 
     let (low, high) = amount.bounds
     guard let low = low else {

Sources/_StringProcessing/ByteCodeGen.swift

@@ -506,15 +506,7 @@ extension Compiler.ByteCodeGen {
     _ kind: DSLTree.QuantificationKind,
     _ child: DSLTree.Node
   ) throws {
-    let updatedKind: AST.Quantification.Kind
-    switch kind {
-    case .explicit(let kind):
-      updatedKind = kind.ast
-    case .syntax(let kind):
-      updatedKind = kind.ast.applying(options)
-    case .default:
-      updatedKind = options.defaultQuantificationKind
-    }
+    let updatedKind = kind.applying(options: options)
 
     let (low, high) = amount.bounds
     guard let low = low else {

Sources/_StringProcessing/Compiler.swift

@@ -47,13 +47,13 @@ class Compiler {
 
   __consuming func emitViaList() throws -> MEProgram {
     // TODO: Handle global options
-    let dslList = DSLList(tree: tree)
+    var dslList = DSLList(tree: tree)
     var codegen = ByteCodeGen(
       options: options,
       compileOptions:
         compileOptions,
       captureList: tree.captureList)
-    return try codegen.emitRoot(dslList)
+    return try codegen.emitRoot(&dslList)
   }
 }
 

Sources/_StringProcessing/LiteralPrinter.swift

@@ -224,13 +224,16 @@ extension LiteralPrinter {
   }
 
   mutating func outputQuantificationKind(_ kind: DSLTree.QuantificationKind) {
-    switch kind {
-    case .`default`:
+    guard let astKind = kind.quantificationKind?.ast else {
       // We can treat this as if the current default had been given explicity.
       outputQuantificationKind(
         .explicit(.init(ast: options.defaultQuantificationKind)))
-    case let .explicit(kind):
-      switch kind.ast {
+      return
+    }
+
+    if kind.isExplicit {
+      // Explicitly provided modifiers need to match the current option state.
+      switch astKind {
       case .eager:
         output(options.isReluctantByDefault ? "?" : "")
       case .reluctant:
@@ -242,9 +245,9 @@ extension LiteralPrinter {
         fatalError()
       #endif
       }
-    case let .syntax(kind):
+    } else {
       // Syntactically-specified quantification modifiers can stay as-is.
-      switch kind.ast {
+      switch astKind {
       case .eager:
         output("")
       case .reluctant: