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This instructions marks the point where all let-fields of a class are initialized. This is important to ensure the correctness of ``ref_element_addr [immutable]`` for let-fields, because in the initializer of a class, its let-fields are not immutable, yet.
78 lines
2.6 KiB
Swift
78 lines
2.6 KiB
Swift
//===--- StripObjectHeaders.swift ------------------------------------------==//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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import SIL
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/// Sets the `[bare]` attribute for `alloc_ref` and `global_value` instructions
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/// if their header (reference count and metatype) is not used throughout the
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/// lifetime of the object.
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///
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let stripObjectHeadersPass = FunctionPass(name: "strip-object-headers") {
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(function: Function, context: FunctionPassContext) in
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for inst in function.instructions {
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switch inst {
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case let gv as GlobalValueInst:
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if !gv.isBare && !gv.needObjectHeader() {
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gv.setIsBare(context)
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}
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case let ar as AllocRefInst:
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if !ar.isBare && !ar.needObjectHeader() {
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ar.setIsBare(context)
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}
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default:
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break
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}
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}
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}
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private extension Value {
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func needObjectHeader() -> Bool {
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var walker = IsBareObjectWalker()
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return walker.walkDownUses(ofValue: self, path: SmallProjectionPath()) == .abortWalk
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}
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}
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private struct IsBareObjectWalker : ValueDefUseWalker {
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var walkDownCache = WalkerCache<SmallProjectionPath>()
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mutating func walkDown(value operand: Operand, path: Path) -> WalkResult {
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switch operand.instruction {
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// White-list all instructions which don't use the object header.
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case is StructInst, is TupleInst, is EnumInst,
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is StructExtractInst, is TupleExtractInst, is UncheckedEnumDataInst,
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is DestructureStructInst, is DestructureTupleInst,
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is BeginBorrowInst, is MarkDependenceInst,
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is BranchInst, is CondBranchInst, is SwitchEnumInst,
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is UpcastInst, is UncheckedRefCastInst,
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is BeginDeallocRefInst,
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is EndInitLetRefInst,
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is EndCOWMutationInst:
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return walkDownDefault(value: operand, path: path)
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default:
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return leafUse(value: operand, path: path)
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}
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}
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mutating func leafUse(value operand: Operand, path: SmallProjectionPath) -> WalkResult {
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switch operand.instruction {
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// White-list all instructions which don't use the object header.
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case is RefElementAddrInst, is RefTailAddrInst,
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is DeallocRefInst, is DeallocStackRefInst,
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is DebugValueInst, is FixLifetimeInst:
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return .continueWalk
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default:
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return .abortWalk
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}
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}
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}
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