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//===--- LifetimeDependenceInsertion.swift - insert lifetime dependence ---===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2024 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
//
//===----------------------------------------------------------------------===//
///
/// Insert mark_dependence [nonescaping] markers on the owned returned
/// or yielded value of a call whose return type is non-escaping.
///
/// Pass dependencies: This must run as a SILGen cleanup pass before
/// any lifetime canonicalization or optimization can be performed.
///
//===----------------------------------------------------------------------===//
import SIL
private let verbose = false
private func log(prefix: Bool = true, _ message: @autoclosure () -> String) {
if verbose {
print((prefix ? "### " : "") + message())
}
}
let lifetimeDependenceInsertionPass = FunctionPass(
name: "lifetime-dependence-insertion")
{ (function: Function, context: FunctionPassContext) in
if !context.options.hasFeature(.NonescapableTypes) {
return
}
log(prefix: false, "\n--- Inserting lifetime dependence markers in \(function.name)")
for instruction in function.instructions {
if let dependentApply = LifetimeDependentApply(instruction) {
insertDependencies(for: dependentApply, context)
}
}
}
/// An apply that produces a non-escapable value, linking it to a parent value.
private struct LifetimeDependentApply {
let applySite: FullApplySite
init?(_ instruction: Instruction) {
guard let apply = instruction as? FullApplySite else {
return nil
}
if !apply.hasResultDependence {
return nil
}
self.applySite = apply
}
init?(withResult value: Value) {
switch value {
case let apply as ApplyInst:
if let dependentApply = LifetimeDependentApply(apply) {
self = dependentApply
}
case let arg as Argument:
guard let termResult = TerminatorResult(arg) else { return nil }
switch termResult.terminator {
case let ta as TryApplyInst:
if termResult.successor == ta.errorBlock {
if let dependentApply = LifetimeDependentApply(ta) {
self = dependentApply
}
}
default:
break
}
default:
break
}
return nil
}
}
extension LifetimeDependentApply {
/// A lifetime argument copies, borrows, or mutatably borrows the
/// lifetime of the argument value.
struct LifetimeArgument {
let convention: LifetimeDependenceConvention
let value: Value
}
func getLifetimeArguments() -> SingleInlineArray<LifetimeArgument> {
var args = SingleInlineArray<LifetimeArgument>()
for operand in applySite.parameterOperands {
guard let dep = applySite.resultDependence(on: operand) else {
continue
}
args.push(LifetimeArgument(convention: dep, value: operand.value))
}
return args
}
}
/// If the result of this apply depends on the scope of one or more
/// arguments, then insert a mark_dependence [unresolved] from the
/// result on each argument so that the result is recognized as a
/// dependent value within each scope.
private func insertDependencies(for apply: LifetimeDependentApply,
_ context: FunctionPassContext ) {
let bases = findDependenceBases(of: apply, context)
for dependentValue in apply.applySite.resultOrYields {
let builder = Builder(before: dependentValue.nextInstruction, context)
insertMarkDependencies(value: dependentValue, initializer: nil,
bases: bases, builder: builder, context)
}
let builder = Builder(after: apply.applySite, context)
for resultOper in apply.applySite.indirectResultOperands {
let accessBase = resultOper.value.accessBase
guard let (initialAddress, initializingStore) =
accessBase.findSingleInitializer(context) else {
continue
}
// TODO: This is currently too strict for a diagnostic pass. We
// should handle/cleanup projections and casts that occur before
// the initializingStore. Or check in the SIL verifier that all
// stores without an access scope follow this form. Then convert
// this bail-out to an assert.
guard initialAddress.usesOccurOnOrAfter(instruction: initializingStore,
context) else {
continue
}
assert(initializingStore == resultOper.instruction,
"an indirect result is a store")
insertMarkDependencies(value: initialAddress,
initializer: initializingStore, bases: bases,
builder: builder, context)
}
}
private func findDependenceBases(of apply: LifetimeDependentApply,
_ context: FunctionPassContext)
-> [Value] {
log("Creating dependencies for \(apply.applySite)")
var bases: [Value] = []
for lifetimeArg in apply.getLifetimeArguments() {
switch lifetimeArg.convention {
case .inherit:
continue
case .scope:
// Create a new dependence on the apply's access to the argument.
for varIntoducer in gatherVariableIntroducers(for: lifetimeArg.value,
context) {
if let scope =
LifetimeDependence.Scope(base: varIntoducer, context) {
log("Scoped lifetime from \(lifetimeArg.value)")
log(" scope: \(scope)")
bases.append(scope.parentValue)
}
}
}
}
return bases
}
private func insertMarkDependencies(value: Value, initializer: Instruction?,
bases: [Value], builder: Builder,
_ context: FunctionPassContext) {
var currentValue = value
for base in bases {
let markDep = builder.createMarkDependence(
value: currentValue, base: base, kind: .Unresolved)
let uses = currentValue.uses.lazy.filter {
let inst = $0.instruction
return inst != markDep && inst != initializer && !(inst is Deallocation)
}
uses.replaceAll(with: markDep, context)
currentValue = markDep
}
}
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