mirror of
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def3b6fab0
Makes e.g. alias analysis more precise in the early stage of the pass pipeline where addressor calls are not inlined, yet.
657 lines
25 KiB
Swift
657 lines
25 KiB
Swift
//===--- AccessUtils.swift - Utilities for analyzing memory accesses ------===//
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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 - 2022 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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// This file provides a set of utilities for analyzing memory accesses.
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// It defines the following concepts
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// - `AccessBase`: represents the base address of a memory access.
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// - `AccessPath`: a pair of an `AccessBase` and `SmallProjectionPath` with the
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// the path describing the specific address (in terms of projections) of the
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// access.
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// - Access storage path (which is of type `ProjectedValue`): identifies the
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// reference (or a value which contains a reference) an address originates from.
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//
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// The snippet below shows the relationship between the access concepts.
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// ```
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// %ref = struct_extract %value, #f1 access storage path
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// %base = ref_element_addr %ref, #f2 AccessBase AccessPath |
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// %scope = begin_access %base AccessScope | |
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// %t = tuple_element_addr %scope, 0 | |
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// %s = struct_element_addr %t, #f3 v v
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// %l = load %s the access
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// ```
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//===----------------------------------------------------------------------===//
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/// AccessBase describes the base address of a memory access (e.g. of a `load` or `store``).
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/// The "base address" is defined as the address which is obtained from the access address by
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/// looking through all address projections.
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/// This means that the base address is either the same as the access address or:
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/// the access address is a chain of address projections of the base address.
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/// The following snippets show examples of memory accesses and their respective bases.
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///
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/// ```
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/// %base1 = ref_element_addr %ref, #Obj.field // A `class` base
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/// %base2 = alloc_stack $S // A `stack` base
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/// %base3 = global_addr @gaddr // A `global` base
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/// %addr1 = struct_element_addr %base1
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/// %access1 = store %v1 to [trivial] %addr1 // accessed address is offset from base
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/// %access2 = store %v2 to [trivial] %base2 // accessed address is base itself
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/// ```
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///
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/// The base address is never inside an access scope.
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public enum AccessBase : CustomStringConvertible, Hashable {
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/// The address of a boxed variable, i.e. a field of an `alloc_box`.
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case box(ProjectBoxInst)
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/// The address of a stack-allocated value, i.e. an `alloc_stack`
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case stack(AllocStackInst)
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/// The address of a global variable.
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case global(GlobalVariable)
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/// The address of a stored property of a class instance.
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case `class`(RefElementAddrInst)
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/// The base address of the tail allocated elements of a class instance.
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case tail(RefTailAddrInst)
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/// An indirect function argument, like `@inout`.
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case argument(FunctionArgument)
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/// An indirect result of a `begin_apply`.
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case yield(MultipleValueInstructionResult)
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/// store_borrow is never the base of a formal access, but calling Value.enclosingScope on an arbitrary address will
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/// return it as the accessBase. A store_borrow always stores into an alloc_stack, but it is handled separately
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/// because it may be useful for clients to know which value was stored in the temporary stack location for the
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/// duration of this borrow scope.
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case storeBorrow(StoreBorrowInst)
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/// An address which is derived from a `Builtin.RawPointer`.
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case pointer(PointerToAddressInst)
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/// The access base is some SIL pattern which does not fit into any other case.
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/// This should be a very rare situation.
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case unidentified
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public init(baseAddress: Value) {
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switch baseAddress {
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case let rea as RefElementAddrInst : self = .class(rea)
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case let rta as RefTailAddrInst : self = .tail(rta)
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case let pbi as ProjectBoxInst : self = .box(pbi)
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case let asi as AllocStackInst : self = .stack(asi)
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case let arg as FunctionArgument : self = .argument(arg)
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case let ga as GlobalAddrInst : self = .global(ga.global)
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case let mvr as MultipleValueInstructionResult:
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if mvr.parentInstruction is BeginApplyInst && baseAddress.type.isAddress {
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self = .yield(mvr)
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} else {
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self = .unidentified
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}
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case let sb as StoreBorrowInst:
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self = .storeBorrow(sb)
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default:
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self = .unidentified
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}
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}
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public var description: String {
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switch self {
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case .unidentified: return "?"
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case .box(let pbi): return "box - \(pbi)"
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case .stack(let asi): return "stack - \(asi)"
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case .global(let gl): return "global - @\(gl.name)"
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case .class(let rea): return "class - \(rea)"
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case .tail(let rta): return "tail - \(rta.instance)"
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case .argument(let arg): return "argument - \(arg)"
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case .yield(let result): return "yield - \(result)"
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case .storeBorrow(let sb): return "storeBorrow - \(sb)"
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case .pointer(let p): return "pointer - \(p)"
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}
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}
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/// True, if this is an access to a class instance.
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public var isObjectAccess: Bool {
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switch self {
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case .class, .tail:
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return true
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case .box, .stack, .global, .argument, .yield, .storeBorrow, .pointer, .unidentified:
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return false
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}
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}
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/// The reference value if this is an access to a referenced object (class, box, tail).
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public var reference: Value? {
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switch self {
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case .box(let pbi): return pbi.box
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case .class(let rea): return rea.instance
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case .tail(let rta): return rta.instance
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case .stack, .global, .argument, .yield, .storeBorrow, .pointer, .unidentified:
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return nil
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}
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}
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/// True if this access base may be derived from a reference that is only valid within a locally
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/// scoped OSSA lifetime. For example:
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///
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/// %reference = begin_borrow %1
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/// %base = ref_tail_addr %reference <- %base must not be used outside the borrow scope
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/// end_borrow %reference
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///
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/// This is not true for scoped storage such as alloc_stack and @in arguments.
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///
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public var hasLocalOwnershipLifetime: Bool {
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if let reference = reference {
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// Conservatively assume that everything which is a ref-counted object is within an ownership scope.
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// TODO: we could e.g. exclude guaranteed function arguments.
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return reference.ownership != .none
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}
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return false
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}
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/// True, if the baseAddress is of an immutable property or global variable
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public var isLet: Bool {
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switch self {
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case .class(let rea): return rea.fieldIsLet
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case .global(let g): return g.isLet
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case .box, .stack, .tail, .argument, .yield, .storeBorrow, .pointer, .unidentified:
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return false
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}
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}
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/// True, if the address is produced by an allocation in its function.
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public var isLocal: Bool {
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switch self {
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case .box(let pbi): return pbi.box.referenceRoot is AllocBoxInst
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case .class(let rea): return rea.instance.referenceRoot is AllocRefInstBase
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case .tail(let rta): return rta.instance.referenceRoot is AllocRefInstBase
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case .stack, .storeBorrow: return true
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case .global, .argument, .yield, .pointer, .unidentified:
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return false
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}
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}
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/// True, if the kind of storage of the access is known (e.g. a class property, or global variable).
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public var hasKnownStorageKind: Bool {
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switch self {
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case .box, .class, .tail, .stack, .storeBorrow, .global:
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return true
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case .argument, .yield, .pointer, .unidentified:
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return false
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}
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}
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/// Returns true if it's guaranteed that this access has the same base address as the `other` access.
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///
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/// `isEqual` abstracts away the projection instructions that are included as part of the AccessBase:
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/// multiple `project_box` and `ref_element_addr` instructions are equivalent bases as long as they
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/// refer to the same variable or class property.
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public func isEqual(to other: AccessBase) -> Bool {
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switch (self, other) {
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case (.box(let pb1), .box(let pb2)):
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return pb1.box.referenceRoot == pb2.box.referenceRoot
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case (.class(let rea1), .class(let rea2)):
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return rea1.fieldIndex == rea2.fieldIndex &&
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rea1.instance.referenceRoot == rea2.instance.referenceRoot
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case (.tail(let rta1), .tail(let rta2)):
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return rta1.instance.referenceRoot == rta2.instance.referenceRoot &&
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rta1.type == rta2.type
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case (.stack(let as1), .stack(let as2)):
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return as1 == as2
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case (.global(let gl1), .global(let gl2)):
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return gl1 == gl2
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case (.argument(let arg1), .argument(let arg2)):
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return arg1 == arg2
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case (.yield(let baResult1), .yield(let baResult2)):
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return baResult1 == baResult2
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case (.storeBorrow(let sb1), .storeBorrow(let sb2)):
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return sb1 == sb2
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case (.pointer(let p1), .pointer(let p2)):
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return p1 == p2
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default:
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return false
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}
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}
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/// Returns `true` if the two access bases do not alias.
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public func isDistinct(from other: AccessBase) -> Bool {
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func isDifferentAllocation(_ lhs: Value, _ rhs: Value) -> Bool {
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switch (lhs, rhs) {
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case (is Allocation, is Allocation):
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return lhs != rhs
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case (is Allocation, is FunctionArgument),
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(is FunctionArgument, is Allocation):
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// A local allocation cannot alias with something passed to the function.
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return true
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default:
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return false
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}
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}
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func hasDifferentType(_ lhs: Value, _ rhs: Value) -> Bool {
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return lhs.type != rhs.type &&
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// If the types have unbound generic arguments then we don't know
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// the possible range of the type. A type such as $Array<Int> may
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// alias $Array<T>. Right now we are conservative and we assume
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// that $UnsafeMutablePointer<T> and $Int may alias.
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!lhs.type.hasArchetype && !rhs.type.hasArchetype
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}
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func argIsDistinct(_ arg: FunctionArgument, from other: AccessBase) -> Bool {
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if arg.convention.isExclusiveIndirect {
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// Exclusive indirect arguments cannot alias with an address for which we know that it
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// is not derived from that argument (which might be the case for `pointer` and `yield`).
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return other.hasKnownStorageKind
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}
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// Non-exclusive argument still cannot alias with anything allocated locally in the function.
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return other.isLocal
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}
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switch (self, other) {
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// First handle all pairs of the same kind (except `yield` and `pointer`).
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case (.box(let pb), .box(let otherPb)):
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return pb.fieldIndex != otherPb.fieldIndex ||
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isDifferentAllocation(pb.box.referenceRoot, otherPb.box.referenceRoot) ||
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hasDifferentType(pb.box, otherPb.box)
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case (.stack(let asi), .stack(let otherAsi)):
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return asi != otherAsi
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case (.global(let global), .global(let otherGlobal)):
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return global != otherGlobal
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case (.class(let rea), .class(let otherRea)):
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return rea.fieldIndex != otherRea.fieldIndex ||
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isDifferentAllocation(rea.instance, otherRea.instance) ||
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hasDifferentType(rea.instance, otherRea.instance)
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case (.tail(let rta), .tail(let otherRta)):
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return isDifferentAllocation(rta.instance, otherRta.instance) ||
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hasDifferentType(rta.instance, otherRta.instance)
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case (.argument(let arg), .argument(let otherArg)):
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return (arg.convention.isExclusiveIndirect || otherArg.convention.isExclusiveIndirect) && arg != otherArg
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// Handle arguments vs non-arguments
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case (.argument(let arg), _):
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return argIsDistinct(arg, from: other)
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case (_, .argument(let otherArg)):
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return argIsDistinct(otherArg, from: self)
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case (.storeBorrow(let arg), .storeBorrow(let otherArg)):
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return arg.allocStack != otherArg.allocStack
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// Handle the special case of store_borrow - alloc_stack, because that would give a false result in the default case.
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case (.storeBorrow(let sbi), .stack(let asi)):
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return sbi.allocStack != asi
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case (.stack(let asi), .storeBorrow(let sbi)):
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return sbi.allocStack != asi
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default:
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// As we already handled pairs of the same kind, here we handle pairs with different kinds.
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// Different storage kinds cannot alias, regardless where the storage comes from.
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// E.g. a class property address cannot alias with a global variable address.
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return hasKnownStorageKind && other.hasKnownStorageKind
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}
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}
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}
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/// An `AccessPath` is a pair of a `base: AccessBase` and a `projectionPath: Path`
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/// which denotes the offset of the access from the base in terms of projections.
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public struct AccessPath : CustomStringConvertible {
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public let base: AccessBase
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/// address projections only
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public let projectionPath: SmallProjectionPath
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public static func unidentified() -> AccessPath {
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return AccessPath(base: .unidentified, projectionPath: SmallProjectionPath())
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}
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public var description: String {
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"\(projectionPath): \(base)"
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}
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public func isDistinct(from other: AccessPath) -> Bool {
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if base.isDistinct(from: other.base) {
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// We can already derived from the bases that there is no alias.
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// No need to look at the projection paths.
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return true
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}
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if base == other.base ||
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(base.hasKnownStorageKind && other.base.hasKnownStorageKind) {
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if !projectionPath.mayOverlap(with: other.projectionPath) {
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return true
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}
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}
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return false
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}
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/// Returns true if this access addresses the same memory location as `other` or if `other`
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/// is a sub-field of this access.
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/// Note that this access _contains_ `other` if `other` has a _larger_ projection path than this acccess.
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/// For example:
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/// `%value.s0` contains `%value.s0.s1`
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public func isEqualOrContains(_ other: AccessPath) -> Bool {
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return getProjection(to: other) != nil
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}
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public var materializableProjectionPath: SmallProjectionPath? {
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if projectionPath.isMaterializable {
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return projectionPath
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}
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return nil
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}
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/// Returns the projection path to `other` if this access path is equal or contains `other`.
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///
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/// For example,
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/// `%value.s0`.getProjection(to: `%value.s0.s1`)
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/// yields
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/// `s1`
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public func getProjection(to other: AccessPath) -> SmallProjectionPath? {
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if !base.isEqual(to: other.base) {
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return nil
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}
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if let resultPath = projectionPath.subtract(from: other.projectionPath),
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// Indexing is not a projection where the base overlaps the projected address.
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!resultPath.pop().kind.isIndexedElement
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{
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return resultPath
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}
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return nil
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}
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/// Like `getProjection`, but also requires that the resulting projection path is materializable.
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public func getMaterializableProjection(to other: AccessPath) -> SmallProjectionPath? {
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if let projectionPath = getProjection(to: other),
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projectionPath.isMaterializable {
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return projectionPath
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}
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return nil
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}
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}
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private func canBeOperandOfIndexAddr(_ value: Value) -> Bool {
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switch value {
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case is IndexAddrInst, is RefTailAddrInst, is PointerToAddressInst:
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return true
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default:
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return false
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}
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}
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/// Tries to identify from which address the pointer operand originates from.
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/// This is useful to identify patterns like
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/// ```
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/// %orig_addr = global_addr @...
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/// %ptr = address_to_pointer %orig_addr
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/// %addr = pointer_to_address %ptr
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/// ```
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private extension PointerToAddressInst {
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var originatingAddress: Value? {
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struct Walker : ValueUseDefWalker {
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let addrType: Type
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var result: Value?
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var walkUpCache = WalkerCache<Path>()
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mutating func rootDef(value: Value, path: SmallProjectionPath) -> WalkResult {
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if let atp = value as? AddressToPointerInst {
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if let res = result, atp.address != res {
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return .abortWalk
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}
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if addrType != atp.address.type { return .abortWalk }
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if !path.isEmpty { return .abortWalk }
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self.result = atp.address
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return .continueWalk
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}
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return .abortWalk
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}
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mutating func walkUp(value: Value, path: SmallProjectionPath) -> WalkResult {
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switch value {
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case is Argument, is MarkDependenceInst, is CopyValueInst,
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is StructExtractInst, is TupleExtractInst, is StructInst, is TupleInst, is AddressToPointerInst:
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return walkUpDefault(value: value, path: path)
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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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var walker = Walker(addrType: type)
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if walker.walkUp(value: pointer, path: SmallProjectionPath()) == .abortWalk {
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return nil
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}
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return walker.result
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}
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var resultOfGlobalAddressorCall: GlobalVariable? {
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if isStrict,
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let apply = pointer as? ApplyInst,
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let callee = apply.referencedFunction,
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let global = callee.globalOfGlobalInitFunction
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{
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return global
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}
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return nil
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}
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}
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/// The `EnclosingScope` of an access is the innermost `begin_access`
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/// instruction that checks for exclusivity of the access.
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/// If there is no `begin_access` instruction found, then the scope is
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/// the base itself.
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///
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/// The access scopes for the snippet below are:
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/// (l1, .base(%addr)), (l2, .scope(%a2)), (l3, .scope(%a3))
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///
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/// ````
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/// %addr = ... : $*Int64
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/// %l1 = load %addr : $*Int64
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/// %a1 = begin_access [read] [dynamic] %addr : $*Int64
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/// %a2 = begin_access [read] [dynamic] %addr : $*Int64
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/// %l2 = load %a2 : $*Int64
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/// end_access %a2 : $*Int64
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/// end_access %a1 : $*Int64
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/// %a3 = begin_access [read] [dynamic] [no_nested_conflict] %addr : $*Int64
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/// %l3 = load %a3 : $*Int64
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/// end_access %a3 : $*Int64
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/// ```
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public enum EnclosingScope {
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case scope(BeginAccessInst)
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case base(AccessBase)
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}
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private struct AccessPathWalker : AddressUseDefWalker {
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var result = AccessPath.unidentified()
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var foundBeginAccess: BeginAccessInst?
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mutating func walk(startAt address: Value, initialPath: SmallProjectionPath = SmallProjectionPath()) {
|
|
if walkUp(address: address, path: Path(projectionPath: initialPath)) == .abortWalk {
|
|
assert(result.base == .unidentified,
|
|
"shouldn't have set an access base in an aborted walk")
|
|
}
|
|
}
|
|
|
|
struct Path : SmallProjectionWalkingPath {
|
|
let projectionPath: SmallProjectionPath
|
|
|
|
// Tracks whether an `index_addr` instruction was crossed.
|
|
// It should be (FIXME: check if it's enforced) that operands
|
|
// of `index_addr` must be `tail_addr` or other `index_addr` results.
|
|
let indexAddr: Bool
|
|
|
|
init(projectionPath: SmallProjectionPath = SmallProjectionPath(), indexAddr: Bool = false) {
|
|
self.projectionPath = projectionPath
|
|
self.indexAddr = indexAddr
|
|
}
|
|
|
|
func with(projectionPath: SmallProjectionPath) -> Self {
|
|
return Self(projectionPath: projectionPath, indexAddr: indexAddr)
|
|
}
|
|
|
|
func with(indexAddr: Bool) -> Self {
|
|
return Self(projectionPath: projectionPath, indexAddr: indexAddr)
|
|
}
|
|
|
|
func merge(with other: Self) -> Self {
|
|
return Self(
|
|
projectionPath: projectionPath.merge(with: other.projectionPath),
|
|
indexAddr: indexAddr || other.indexAddr
|
|
)
|
|
}
|
|
}
|
|
|
|
mutating func rootDef(address: Value, path: Path) -> WalkResult {
|
|
assert(result.base == .unidentified, "rootDef should only called once")
|
|
// Try identifying the address a pointer originates from
|
|
if let p2ai = address as? PointerToAddressInst {
|
|
if let originatingAddr = p2ai.originatingAddress {
|
|
return walkUp(address: originatingAddr, path: path)
|
|
} else if let global = p2ai.resultOfGlobalAddressorCall {
|
|
self.result = AccessPath(base: .global(global), projectionPath: path.projectionPath)
|
|
return .continueWalk
|
|
} else {
|
|
self.result = AccessPath(base: .pointer(p2ai), projectionPath: path.projectionPath)
|
|
return .continueWalk
|
|
}
|
|
}
|
|
|
|
let base = AccessBase(baseAddress: address)
|
|
self.result = AccessPath(base: base, projectionPath: path.projectionPath)
|
|
return .continueWalk
|
|
}
|
|
|
|
mutating func walkUp(address: Value, path: Path) -> WalkResult {
|
|
if address is IndexAddrInst {
|
|
// Track that we crossed an `index_addr` during the walk-up
|
|
return walkUpDefault(address: address, path: path.with(indexAddr: true))
|
|
} else if path.indexAddr && !canBeOperandOfIndexAddr(address) {
|
|
// An `index_addr` instruction cannot be derived from an address
|
|
// projection. Bail out
|
|
return .abortWalk
|
|
} else if let ba = address as? BeginAccessInst, foundBeginAccess == nil {
|
|
foundBeginAccess = ba
|
|
}
|
|
return walkUpDefault(address: address, path: path.with(indexAddr: false))
|
|
}
|
|
}
|
|
|
|
extension Value {
|
|
// Convenient properties to avoid instantiating an explicit AccessPathWalker.
|
|
//
|
|
// Although an AccessPathWalker is created for each call of these properties,
|
|
// it's very unlikely that this will end up in memory allocations.
|
|
// Only in the rare case of `pointer_to_address` -> `address_to_pointer` pairs, which
|
|
// go through phi-arguments, the AccessPathWalker will allocate memnory in its cache.
|
|
|
|
/// Computes the access base of this address value.
|
|
public var accessBase: AccessBase { accessPath.base }
|
|
|
|
/// Computes the access path of this address value.
|
|
public var accessPath: AccessPath {
|
|
var walker = AccessPathWalker()
|
|
walker.walk(startAt: self)
|
|
return walker.result
|
|
}
|
|
|
|
public func getAccessPath(fromInitialPath: SmallProjectionPath) -> AccessPath {
|
|
var walker = AccessPathWalker()
|
|
walker.walk(startAt: self, initialPath: fromInitialPath)
|
|
return walker.result
|
|
}
|
|
|
|
/// Computes the access path of this address value and also returns the scope.
|
|
public var accessPathWithScope: (AccessPath, scope: BeginAccessInst?) {
|
|
var walker = AccessPathWalker()
|
|
walker.walk(startAt: self)
|
|
return (walker.result, walker.foundBeginAccess)
|
|
}
|
|
|
|
/// Computes the enclosing access scope of this address value.
|
|
public var enclosingAccessScope: EnclosingScope {
|
|
var walker = AccessPathWalker()
|
|
walker.walk(startAt: self)
|
|
if let ba = walker.foundBeginAccess {
|
|
return .scope(ba)
|
|
}
|
|
return .base(walker.result.base)
|
|
}
|
|
|
|
/// The root definition of a reference, obtained by skipping ownership forwarding and ownership transition.
|
|
public var referenceRoot: Value {
|
|
var value: Value = self
|
|
while true {
|
|
if let forward = value.forwardingInstruction, forward.preservesIdentity,
|
|
let operand = forward.singleForwardedOperand {
|
|
value = operand.value
|
|
continue
|
|
}
|
|
if let transition = value.definingInstruction as? OwnershipTransitionInstruction {
|
|
value = transition.operand.value
|
|
continue
|
|
}
|
|
return value
|
|
}
|
|
}
|
|
}
|
|
|
|
/// A ValueUseDef walker that that visits access storage paths of an address.
|
|
///
|
|
/// An access storage path is the reference (or a value which contains a reference)
|
|
/// an address originates from.
|
|
/// In the following example the `storage` is `contains_ref` with `path` `"s0.c0.s0"`
|
|
/// ```
|
|
/// %ref = struct_extract %contains_ref : $S, #S.l
|
|
/// %base = ref_element_addr %ref : $List, #List.x
|
|
/// %addr = struct_element_addr %base : $X, #X.e
|
|
/// store %v to [trivial] %addr : $*Int
|
|
/// ```
|
|
///
|
|
/// Warning: This does not find the correct storage root of the
|
|
/// lifetime of an object projection, such as .box or .class because
|
|
/// ValueUseDefWalker ignores ownership and, for example, walks past copies.
|
|
extension ValueUseDefWalker where Path == SmallProjectionPath {
|
|
/// The main entry point.
|
|
/// Given an `accessPath` where the access base is a reference (class, tail, box), call
|
|
/// the `visit` function for all storage roots with a the corresponding path.
|
|
/// Returns true on success.
|
|
/// Returns false if not all storage roots could be identified or if `accessPath` has not a "reference" base.
|
|
public mutating func visitAccessStorageRoots(of accessPath: AccessPath) -> Bool {
|
|
walkUpCache.clear()
|
|
let path = accessPath.projectionPath
|
|
switch accessPath.base {
|
|
case .box(let pbi):
|
|
return walkUp(value: pbi.box, path: path.push(.classField, index: pbi.fieldIndex)) != .abortWalk
|
|
case .class(let rea):
|
|
return walkUp(value: rea.instance, path: path.push(.classField, index: rea.fieldIndex)) != .abortWalk
|
|
case .tail(let rta):
|
|
return walkUp(value: rta.instance, path: path.push(.tailElements, index: 0)) != .abortWalk
|
|
case .stack, .global, .argument, .yield, .storeBorrow, .pointer, .unidentified:
|
|
return false
|
|
}
|
|
}
|
|
}
|
|
|
|
extension Function {
|
|
public var globalOfGlobalInitFunction: GlobalVariable? {
|
|
if isGlobalInitFunction,
|
|
let ret = returnInstruction,
|
|
let atp = ret.returnedValue as? AddressToPointerInst,
|
|
let ga = atp.address as? GlobalAddrInst {
|
|
return ga.global
|
|
}
|
|
return nil
|
|
}
|
|
}
|