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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2021-2022 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
//
//===----------------------------------------------------------------------===//
extension Processor {
struct SavePoint {
var pc: InstructionAddress
var pos: Position?
// Quantifiers may store a range of positions to restore to
var quantifiedRange: Range<Position>?
// FIXME: refactor, for now this field is only used for quantifier save
// points. We should try to separate out the concerns better.
var isScalarSemantics: Bool
// The end of the call stack, so we can slice it off
// when failing inside a call.
//
// NOTE: Alternatively, also place return addresses on the
// save point stack
var stackEnd: CallStackAddress
// FIXME: Save minimal info (e.g. stack position and
// perhaps current start)
var captureEnds: [_StoredCapture]
// The int registers store values that can be relevant to
// backtracking, such as the number of trips in a quantification.
var intRegisters: [Int]
// Same with position registers
var posRegisters: [Input.Index]
var destructure: (
pc: InstructionAddress,
pos: Position?,
stackEnd: CallStackAddress,
captureEnds: [_StoredCapture],
intRegisters: [Int],
PositionRegister: [Input.Index]
) {
return (pc, pos, stackEnd, captureEnds, intRegisters, posRegisters)
}
// Whether this save point is quantified, meaning it has a range of
// possible positions to explore.
var isQuantified: Bool {
quantifiedRange != nil
}
/// Move the next range position into pos, and removing it from the range
mutating func takePositionFromQuantifiedRange(_ input: Input) {
assert(isQuantified)
let range = quantifiedRange!
pos = range.upperBound
if range.isEmpty {
// Becomes a normal save point
quantifiedRange = nil
return
}
// Shrink the range
let newUpper: Position
if isScalarSemantics {
newUpper = input.unicodeScalars.index(before: range.upperBound)
} else {
newUpper = input.index(before: range.upperBound)
}
quantifiedRange = range.lowerBound..<newUpper
}
}
func makeSavePoint(
resumingAt pc: InstructionAddress
) -> SavePoint {
SavePoint(
pc: pc,
pos: currentPosition,
quantifiedRange: nil,
isScalarSemantics: false,
stackEnd: .init(callStack.count),
captureEnds: storedCaptures,
intRegisters: registers.ints,
posRegisters: registers.positions)
}
func makeAddressOnlySavePoint(
resumingAt pc: InstructionAddress
) -> SavePoint {
SavePoint(
pc: pc,
pos: nil,
quantifiedRange: nil,
isScalarSemantics: false,
stackEnd: .init(callStack.count),
captureEnds: storedCaptures,
intRegisters: registers.ints,
posRegisters: registers.positions)
}
func makeQuantifiedSavePoint(
_ range: Range<Position>,
isScalarSemantics: Bool
) -> SavePoint {
SavePoint(
pc: controller.pc + 1,
pos: nil,
quantifiedRange: range,
isScalarSemantics: isScalarSemantics,
stackEnd: .init(callStack.count),
captureEnds: storedCaptures,
intRegisters: registers.ints,
posRegisters: registers.positions)
}
}
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