Swift Optimizer: add the SSAUpdater utility

SwiftCompilerSources/Sources/Optimizer/Utilities/CMakeLists.txt

@@ -11,5 +11,6 @@ swift_compiler_sources(Optimizer
   OptUtils.swift
   WalkUtils.swift
   AccessUtils.swift
+  SSAUpdater.swift
   StaticInitCloner.swift
 )

SwiftCompilerSources/Sources/Optimizer/Utilities/SSAUpdater.swift

@@ -0,0 +1,51 @@
+//===--- SSAUpdater.swift -------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SIL
+import OptimizerBridging
+
+/// Utility for updating SSA for a set of SIL instructions defined in multiple blocks.
+struct SSAUpdater<Context: MutatingContext> {
+  let context: Context
+
+  init(type: Type, ownership: Ownership, _ context: Context) {
+    self.context = context
+    context._bridged.SSAUpdater_initialize(type.bridged, ownership._bridged)
+  }
+
+  mutating func addAvailableValue(_ value: Value, in block: BasicBlock) {
+    context._bridged.SSAUpdater_addAvailableValue(block.bridged, value.bridged)
+  }
+
+  /// Construct SSA for a value that is live at the *end* of a basic block.
+  mutating func getValue(atEndOf block: BasicBlock) -> Value {
+    context.notifyInstructionsChanged()
+    return context._bridged.SSAUpdater_getValueAtEndOfBlock(block.bridged).value
+  }
+
+  /// Construct SSA for a value that is live in the *middle* of a block.
+  /// This handles the case where the use is before a definition of the value in the same block.
+  ///
+  ///   bb1:
+  ///     %1 = def
+  ///     br bb2
+  ///   bb2:
+  ///       = use(?)
+  ///    %2 = def
+  ///    cond_br bb2, bb3
+  ///
+  /// In this case we need to insert a phi argument in bb2, merging %1 and %2.
+  mutating func getValue(inMiddleOf block: BasicBlock) -> Value {
+    context.notifyInstructionsChanged()
+    return context._bridged.SSAUpdater_getValueInMiddleOfBlock(block.bridged).value
+  }
+}