swift-mirror/SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyInitEnumDataAddr.swift

//===--- SimplifyInitEnumDataAddr.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

extension InitEnumDataAddrInst : OnoneSimplifyable {
  func simplify(_ context: SimplifyContext) {

    // Optimize the sequence
    // ```
    //   %1 = init_enum_data_addr %enum_addr, #someCaseWithPayload
    //   store %payload to %1
    //   inject_enum_addr %enum_addr, #someCaseWithPayload
    // ```
    // to
    // ```
    //   %1 = enum  $E, #someCaseWithPayload, %payload
    //   store %1 to %enum_addr
    // ```
    // This sequence of three instructions must appear in consecutive order.
    // But usually this is the case, because it's generated this way by SILGen.
    //
    if let nextInst = self.next,
       let store = nextInst as? StoreInst,
       store.destination == self,
       let singleUse = self.uses.singleUse,
       singleUse.instruction == store,
       let nextAfterStore = store.next,
       let inject = nextAfterStore as? InjectEnumAddrInst,
       inject.enum == self.enum,
       inject.enum.type.isLoadable(in: parentFunction) {

      assert(self.caseIndex == inject.caseIndex, "mismatching case indices when creating an enum")

      let builder = Builder(before: store, context)
      let enumInst = builder.createEnum(caseIndex: self.caseIndex, payload: store.source, enumType: self.enum.type.objectType)
      let storeOwnership = StoreInst.StoreOwnership(for: self.enum.type, in: parentFunction, initialize: true)
      builder.createStore(source: enumInst, destination: self.enum, ownership: storeOwnership)
      context.erase(instruction: store)
      context.erase(instruction: inject)
      context.erase(instruction: self)
    }
  }
}