//===--- GlobalVariable.swift - Defines the GlobalVariable class ----------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2021 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 Basic
import SILBridging

final public class GlobalVariable : CustomStringConvertible, HasShortDescription, Hashable {
  public var name: StringRef {
    return StringRef(bridged: bridged.getName())
  }

  public var description: String {
    return String(taking: bridged.getDebugDescription())
  }

  public var shortDescription: String { name.string }

  public var isLet: Bool { bridged.isLet() }

  /// True, if the linkage of the global variable indicates that it is visible outside the current
  /// compilation unit and therefore not all of its uses are known.
  ///
  /// For example, `public` linkage.
  public var isPossiblyUsedExternally: Bool {
    return bridged.isPossiblyUsedExternally()
  }

  /// True, if the linkage of the global indicates that it has a definition outside the
  /// current compilation unit.
  ///
  /// For example, `public_external` linkage.
  public var isAvailableExternally: Bool {
    return bridged.isAvailableExternally()
  }

  public var staticInitializerInstructions: InstructionList? {
    if let firstStaticInitInst = bridged.getFirstStaticInitInst().instruction {
      return InstructionList(first: firstStaticInitInst)
    }
    return nil
  }

  public var staticInitValue: SingleValueInstruction? {
    if let staticInitInsts = staticInitializerInstructions {
      return staticInitInsts.reversed().first! as? SingleValueInstruction
    }
    return nil
  }

  /// True if the global's linkage and resilience expansion allow the global
  /// to be initialized statically.
  public var canBeInitializedStatically: Bool {
    return bridged.canBeInitializedStatically()
  }

  public var mustBeInitializedStatically: Bool {
    return bridged.mustBeInitializedStatically()
  }

  public static func ==(lhs: GlobalVariable, rhs: GlobalVariable) -> Bool {
    lhs === rhs
  }

  public func hash(into hasher: inout Hasher) {
    hasher.combine(ObjectIdentifier(self))
  }

  public var bridged: BridgedGlobalVar { BridgedGlobalVar(SwiftObject(self)) }
}

extension Instruction {
  public var isValidInStaticInitializerOfGlobal: Bool {
    // Rule out SILUndef and SILArgument.
    if operands.contains(where: { $0.value.definingInstruction == nil }) {
      return false
    }
    switch self {
    case let bi as BuiltinInst:
      switch bi.id {
      case .ZeroInitializer:
        let type = bi.type.isBuiltinVector ? bi.type.builtinVectorElementType : bi.type
        return type.isBuiltinInteger || type.isBuiltinFloat
      case .PtrToInt:
        return bi.operands[0].value is StringLiteralInst
      case .IntToPtr:
        return bi.operands[0].value is IntegerLiteralInst
      case .StringObjectOr:
        // The first operand can be a string literal (i.e. a pointer), but the
        // second operand must be a constant. This enables creating a
        // a pointer+offset relocation.
        // Note that StringObjectOr requires the or'd bits in the first
        // operand to be 0, so the operation is equivalent to an addition.
        return bi.operands[1].value is IntegerLiteralInst
      case .ZExtOrBitCast:
        return true;
      case .USubOver:
        // Handle StringObjectOr(tuple_extract(usub_with_overflow(x, offset)), bits)
        // This pattern appears in UTF8 String literal construction.
        if let tei = bi.uses.getSingleUser(ofType: TupleExtractInst.self),
           tei.isResultOfOffsetSubtract {
          return true
        }
        return false
      case .OnFastPath:
        return true
      default:
        return false
      }
    case let tei as TupleExtractInst:
      // Handle StringObjectOr(tuple_extract(usub_with_overflow(x, offset)), bits)
      // This pattern appears in UTF8 String literal construction.
      if tei.isResultOfOffsetSubtract,
         let bi = tei.uses.getSingleUser(ofType: BuiltinInst.self),
         bi.id == .StringObjectOr {
        return true
      }
      return false
    case let sli as StringLiteralInst:
      switch sli.encoding {
      case .Bytes, .UTF8:
        return true
      case .ObjCSelector:
        // Objective-C selector string literals cannot be used in static
        // initializers.
        return false
      }
    case let fri as FunctionRefInst:
      // TODO: support async function pointers in static globals.
      return !fri.referencedFunction.isAsync
    case is StructInst,
         is TupleInst,
         is EnumInst,
         is IntegerLiteralInst,
         is FloatLiteralInst,
         is ObjectInst,
         is VectorInst,
         is AllocVectorInst,
         is ValueToBridgeObjectInst,
         is ConvertFunctionInst,
         is ThinToThickFunctionInst,
         is AddressToPointerInst,
         is GlobalAddrInst:
      return true
    default:
      return false
    }
  }
}

// Match the pattern:
// tuple_extract(usub_with_overflow(x, integer_literal, integer_literal 0), 0)
private extension TupleExtractInst {
  var isResultOfOffsetSubtract: Bool {
    if fieldIndex == 0,
       let bi = tuple as? BuiltinInst,
       bi.id == .USubOver,
       bi.operands[1].value is IntegerLiteralInst,
       let overflowLiteral = bi.operands[2].value as? IntegerLiteralInst,
       let overflowValue = overflowLiteral.value,
       overflowValue == 0
    {
      return true
    }
    return false
  }
}

// Bridging utilities

extension BridgedGlobalVar {
  public var globalVar: GlobalVariable { obj.getAs(GlobalVariable.self) }

  public var optional: OptionalBridgedGlobalVar {
    OptionalBridgedGlobalVar(obj: self.obj)
  }
}

extension OptionalBridgedGlobalVar {
  public var globalVar: GlobalVariable? { obj.getAs(GlobalVariable.self) }

  public static var none: OptionalBridgedGlobalVar {
    OptionalBridgedGlobalVar(obj: nil)
  }
}