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201 lines
7.3 KiB
C++
201 lines
7.3 KiB
C++
//===-------------- ARCAnalysis.cpp - SIL ARC Analysis --------------------===//
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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 - 2015 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 http://swift.org/LICENSE.txt for license information
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// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "sil-arc-analysis"
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#include "swift/SILAnalysis/ARCAnalysis.h"
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#include "swift/Basic/Fallthrough.h"
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#include "swift/SIL/SILInstruction.h"
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#include "swift/SILAnalysis/AliasAnalysis.h"
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#include "swift/SILAnalysis/ValueTracking.h"
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#include "swift/SILPasses/Utils/Local.h"
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#include "llvm/Support/Debug.h"
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using namespace swift;
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//===----------------------------------------------------------------------===//
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// Decrement Analysis
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//===----------------------------------------------------------------------===//
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static bool canApplyDecrementRefCount(ApplyInst *AI, SILValue Ptr,
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AliasAnalysis *AA) {
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// Ignore any thick functions for now due to us not handling the ref-counted
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// nature of its context.
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if (auto FTy = AI->getCallee().getType().getAs<SILFunctionType>())
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if (FTy->getExtInfo().hasContext())
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return true;
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// If we have a builtin that is side effect free, we can commute the
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// ApplyInst and the retain.
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if (auto *BI = dyn_cast<BuiltinFunctionRefInst>(AI->getCallee()))
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if (isSideEffectFree(BI))
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return false;
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// Ok, this apply *MAY* decrement ref counts. Now our strategy is to attempt
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// to use properties of the pointer, the function's arguments, and the
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// function itself to prove that the pointer can not have its ref count be
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// effected by function.
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// TODO: Put in function property check section here when we get access to
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// such information.
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// First make sure that the underlying object of ptr is a local object which
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// does not escape. This prevents the apply from indirectly via the global
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// affecting the reference count of the pointer.
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if (!isNonEscapingLocalObject(getUnderlyingObject(Ptr)))
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return true;
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// Now that we know that the function can not affect the pointer indirectly,
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// make sure that the apply can not affect the pointer directly via the
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// applies arguments by proving that the pointer can not alias any of the
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// functions arguments.
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for (auto Op : AI->getArgumentsWithoutIndirectResult()) {
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for (int i = 0, e = Ptr->getNumTypes(); i < e; i++) {
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if (!AA->isNoAlias(Op, SILValue(Ptr.getDef(), i)))
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return true;
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}
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}
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// Success! The apply inst can not affect the reference count of ptr!
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return false;
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}
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/// Is the may have side effects user by the definition of its value kind unable
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/// to decrement ref counts.
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static bool canDecrementRefCountsByValueKind(SILInstruction *User) {
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assert(User->getMemoryBehavior()
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== SILInstruction::MemoryBehavior::MayHaveSideEffects &&
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"Invalid argument. Function is only applicable to isntructions with "
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"side effects.");
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switch (User->getKind()) {
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case ValueKind::DeallocStackInst:
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case ValueKind::StrongRetainInst:
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case ValueKind::StrongRetainAutoreleasedInst:
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case ValueKind::StrongRetainUnownedInst:
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case ValueKind::UnownedRetainInst:
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case ValueKind::PartialApplyInst:
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case ValueKind::FixLifetimeInst:
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case ValueKind::CopyBlockInst:
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case ValueKind::RetainValueInst:
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case ValueKind::CondFailInst:
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return false;
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case ValueKind::CopyAddrInst: {
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auto *CA = cast<CopyAddrInst>(User);
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if (CA->isInitializationOfDest() == IsInitialization_t::IsInitialization)
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return false;
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}
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SWIFT_FALLTHROUGH;
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default:
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return true;
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}
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}
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bool swift::arc::canDecrementRefCount(SILInstruction *User,
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SILValue Ptr, AliasAnalysis *AA) {
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// If we have an instruction that does not have *pure* side effects, it can
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// not affect ref counts.
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//
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// This distinguishes in between a "write" side effect and ref count side
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// effects.
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if (User->getMemoryBehavior() !=
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SILInstruction::MemoryBehavior::MayHaveSideEffects)
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return false;
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// Ok, we know that this instruction's generic behavior is
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// "MayHaveSideEffects". That is a criterion (it has effects not represented
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// by use-def chains) that is broader than ours (does it effect a particular
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// pointers ref counts). Thus begin by attempting to prove that the type of
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// instruction that the user is by definition can not decrement ref counts.
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if (!canDecrementRefCountsByValueKind(User))
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return false;
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// Ok, this instruction may have ref counts. If it is an apply, attempt to
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// prove that the callee is unable to affect Ptr.
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if (auto *AI = dyn_cast<ApplyInst>(User))
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return canApplyDecrementRefCount(AI, Ptr, AA);
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// We can not conservatively prove that this instruction can not decrement the
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// ref count of Ptr. So assume that it does.
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return true;
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}
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//===----------------------------------------------------------------------===//
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// Use Analysis
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//===----------------------------------------------------------------------===//
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/// Returns true if Inst is a function that we know never uses ref count values.
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static bool canInstUseRefCountValues(SILInstruction *Inst) {
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switch (Inst->getKind()) {
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// These instructions do not use other values.
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case ValueKind::FunctionRefInst:
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case ValueKind::BuiltinFunctionRefInst:
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case ValueKind::IntegerLiteralInst:
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case ValueKind::FloatLiteralInst:
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case ValueKind::StringLiteralInst:
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case ValueKind::AllocStackInst:
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case ValueKind::AllocRefInst:
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case ValueKind::AllocRefDynamicInst:
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case ValueKind::AllocBoxInst:
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case ValueKind::AllocArrayInst:
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case ValueKind::MetatypeInst:
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case ValueKind::WitnessMethodInst:
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return true;
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// DeallocStackInst do not use reference counted values, only local storage
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// handles.
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case ValueKind::DeallocStackInst:
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return true;
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// Debug values do not use referenced counted values in a manner we care
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// about.
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case ValueKind::DebugValueInst:
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case ValueKind::DebugValueAddrInst:
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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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bool swift::arc::canUseValue(SILInstruction *User, SILValue Ptr,
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AliasAnalysis *AA) {
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// If Inst is an instruction that we know can never use values with reference
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// semantics, return true.
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if (canInstUseRefCountValues(User))
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return false;
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// If the user is a load or a store and we can prove that it does not access
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// the object then return true.
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// Notice that we need to check all of the values of the object.
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if (isa<StoreInst>(User)) {
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for (int i = 0, e = Ptr->getNumTypes(); i < e; i++) {
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if (AA->mayWriteToMemory(User, SILValue(Ptr.getDef(), i)))
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return true;
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}
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return false;
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}
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if (isa<LoadInst>(User) ) {
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for (int i = 0, e = Ptr->getNumTypes(); i < e; i++) {
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if (AA->mayReadFromMemory(User, SILValue(Ptr.getDef(), i)))
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return true;
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}
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return false;
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}
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// TODO: If we add in alias analysis support here for apply inst, we will need
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// to check that the pointer does not escape.
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// Otherwise, assume that Inst can use Target.
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return true;
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}
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