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//===--- DeadEndBlocks.swift ----------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 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
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
import SIL
/// A utility for finding dead-end blocks.
///
/// Dead-end blocks are blocks from which there is no path to the function exit
/// (`return`, `throw` or unwind). These are blocks which end with an unreachable
/// instruction and blocks from which all paths end in "unreachable" blocks.
struct DeadEndBlocks : CustomStringConvertible, NoReflectionChildren {
private var worklist: BasicBlockWorklist
private var function: Function
init(function: Function, _ context: FunctionPassContext) {
self.function = function
self.worklist = BasicBlockWorklist(context)
// Initialize the worklist with all function-exiting blocks.
for block in function.blocks where block.terminator.isFunctionExiting {
worklist.pushIfNotVisited(block)
}
// Propagate lifeness up the control flow.
while let block = worklist.pop() {
worklist.pushIfNotVisited(contentsOf: block.predecessors)
}
}
/// Returns true if `block` is a dead-end block.
func isDeadEnd(block: BasicBlock) -> Bool {
return !worklist.hasBeenPushed(block)
}
var description: String {
let blockNames = function.blocks.filter(isDeadEnd).map(\.name)
return "[" + blockNames.joined(separator: ",") + "]"
}
/// TODO: once we have move-only types, make this a real deinit.
mutating func deinitialize() {
worklist.deinitialize()
}
}
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