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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231436 91177308-0d34-0410-b5e6-96231b3b80d8
276 lines
9.6 KiB
C++
276 lines
9.6 KiB
C++
//===- ObjCARC.h - ObjC ARC Optimization --------------*- C++ -*-----------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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/// \file
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/// This file defines common definitions/declarations used by the ObjC ARC
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/// Optimizer. ARC stands for Automatic Reference Counting and is a system for
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/// managing reference counts for objects in Objective C.
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///
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/// WARNING: This file knows about certain library functions. It recognizes them
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/// by name, and hardwires knowledge of their semantics.
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///
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/// WARNING: This file knows about how certain Objective-C library functions are
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/// used. Naive LLVM IR transformations which would otherwise be
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/// behavior-preserving may break these assumptions.
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///
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_LIB_TRANSFORMS_OBJCARC_OBJCARC_H
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#define LLVM_LIB_TRANSFORMS_OBJCARC_OBJCARC_H
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#include "llvm/ADT/StringSwitch.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/Passes.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/CallSite.h"
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#include "llvm/IR/InstIterator.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Transforms/ObjCARC.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "ARCInstKind.h"
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namespace llvm {
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class raw_ostream;
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}
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namespace llvm {
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namespace objcarc {
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/// \brief A handy option to enable/disable all ARC Optimizations.
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extern bool EnableARCOpts;
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/// \brief Test if the given module looks interesting to run ARC optimization
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/// on.
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static inline bool ModuleHasARC(const Module &M) {
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return
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M.getNamedValue("objc_retain") ||
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M.getNamedValue("objc_release") ||
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M.getNamedValue("objc_autorelease") ||
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M.getNamedValue("objc_retainAutoreleasedReturnValue") ||
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M.getNamedValue("objc_retainBlock") ||
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M.getNamedValue("objc_autoreleaseReturnValue") ||
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M.getNamedValue("objc_autoreleasePoolPush") ||
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M.getNamedValue("objc_loadWeakRetained") ||
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M.getNamedValue("objc_loadWeak") ||
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M.getNamedValue("objc_destroyWeak") ||
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M.getNamedValue("objc_storeWeak") ||
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M.getNamedValue("objc_initWeak") ||
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M.getNamedValue("objc_moveWeak") ||
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M.getNamedValue("objc_copyWeak") ||
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M.getNamedValue("objc_retainedObject") ||
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M.getNamedValue("objc_unretainedObject") ||
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M.getNamedValue("objc_unretainedPointer") ||
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M.getNamedValue("clang.arc.use");
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}
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/// \brief This is a wrapper around getUnderlyingObject which also knows how to
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/// look through objc_retain and objc_autorelease calls, which we know to return
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/// their argument verbatim.
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static inline const Value *GetUnderlyingObjCPtr(const Value *V) {
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for (;;) {
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V = GetUnderlyingObject(V);
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if (!IsForwarding(GetBasicARCInstKind(V)))
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break;
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V = cast<CallInst>(V)->getArgOperand(0);
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}
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return V;
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}
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/// The RCIdentity root of a value \p V is a dominating value U for which
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/// retaining or releasing U is equivalent to retaining or releasing V. In other
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/// words, ARC operations on \p V are equivalent to ARC operations on \p U.
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///
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/// We use this in the ARC optimizer to make it easier to match up ARC
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/// operations by always mapping ARC operations to RCIdentityRoots instead of
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/// pointers themselves.
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///
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/// The two ways that we see RCIdentical values in ObjC are via:
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///
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/// 1. PointerCasts
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/// 2. Forwarding Calls that return their argument verbatim.
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///
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/// Thus this function strips off pointer casts and forwarding calls. *NOTE*
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/// This implies that two RCIdentical values must alias.
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static inline const Value *GetRCIdentityRoot(const Value *V) {
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for (;;) {
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V = V->stripPointerCasts();
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if (!IsForwarding(GetBasicARCInstKind(V)))
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break;
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V = cast<CallInst>(V)->getArgOperand(0);
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}
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return V;
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}
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/// Helper which calls const Value *GetRCIdentityRoot(const Value *V) and just
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/// casts away the const of the result. For documentation about what an
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/// RCIdentityRoot (and by extension GetRCIdentityRoot is) look at that
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/// function.
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static inline Value *GetRCIdentityRoot(Value *V) {
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return const_cast<Value *>(GetRCIdentityRoot((const Value *)V));
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}
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/// \brief Assuming the given instruction is one of the special calls such as
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/// objc_retain or objc_release, return the RCIdentity root of the argument of
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/// the call.
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static inline Value *GetArgRCIdentityRoot(Value *Inst) {
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return GetRCIdentityRoot(cast<CallInst>(Inst)->getArgOperand(0));
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}
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static inline bool IsNullOrUndef(const Value *V) {
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return isa<ConstantPointerNull>(V) || isa<UndefValue>(V);
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}
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static inline bool IsNoopInstruction(const Instruction *I) {
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return isa<BitCastInst>(I) ||
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(isa<GetElementPtrInst>(I) &&
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cast<GetElementPtrInst>(I)->hasAllZeroIndices());
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}
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/// \brief Erase the given instruction.
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///
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/// Many ObjC calls return their argument verbatim,
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/// so if it's such a call and the return value has users, replace them with the
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/// argument value.
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///
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static inline void EraseInstruction(Instruction *CI) {
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Value *OldArg = cast<CallInst>(CI)->getArgOperand(0);
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bool Unused = CI->use_empty();
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if (!Unused) {
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// Replace the return value with the argument.
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assert((IsForwarding(GetBasicARCInstKind(CI)) ||
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(IsNoopOnNull(GetBasicARCInstKind(CI)) &&
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isa<ConstantPointerNull>(OldArg))) &&
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"Can't delete non-forwarding instruction with users!");
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CI->replaceAllUsesWith(OldArg);
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}
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CI->eraseFromParent();
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if (Unused)
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RecursivelyDeleteTriviallyDeadInstructions(OldArg);
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}
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/// \brief Test whether the given value is possible a retainable object pointer.
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static inline bool IsPotentialRetainableObjPtr(const Value *Op) {
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// Pointers to static or stack storage are not valid retainable object
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// pointers.
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if (isa<Constant>(Op) || isa<AllocaInst>(Op))
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return false;
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// Special arguments can not be a valid retainable object pointer.
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if (const Argument *Arg = dyn_cast<Argument>(Op))
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if (Arg->hasByValAttr() ||
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Arg->hasInAllocaAttr() ||
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Arg->hasNestAttr() ||
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Arg->hasStructRetAttr())
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return false;
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// Only consider values with pointer types.
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//
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// It seemes intuitive to exclude function pointer types as well, since
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// functions are never retainable object pointers, however clang occasionally
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// bitcasts retainable object pointers to function-pointer type temporarily.
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PointerType *Ty = dyn_cast<PointerType>(Op->getType());
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if (!Ty)
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return false;
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// Conservatively assume anything else is a potential retainable object
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// pointer.
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return true;
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}
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static inline bool IsPotentialRetainableObjPtr(const Value *Op,
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AliasAnalysis &AA) {
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// First make the rudimentary check.
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if (!IsPotentialRetainableObjPtr(Op))
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return false;
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// Objects in constant memory are not reference-counted.
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if (AA.pointsToConstantMemory(Op))
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return false;
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// Pointers in constant memory are not pointing to reference-counted objects.
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if (const LoadInst *LI = dyn_cast<LoadInst>(Op))
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if (AA.pointsToConstantMemory(LI->getPointerOperand()))
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return false;
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// Otherwise assume the worst.
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return true;
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}
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/// \brief Helper for GetARCInstKind. Determines what kind of construct CS
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/// is.
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static inline ARCInstKind GetCallSiteClass(ImmutableCallSite CS) {
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for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
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I != E; ++I)
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if (IsPotentialRetainableObjPtr(*I))
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return CS.onlyReadsMemory() ? ARCInstKind::User : ARCInstKind::CallOrUser;
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return CS.onlyReadsMemory() ? ARCInstKind::None : ARCInstKind::Call;
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}
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/// \brief Return true if this value refers to a distinct and identifiable
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/// object.
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///
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/// This is similar to AliasAnalysis's isIdentifiedObject, except that it uses
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/// special knowledge of ObjC conventions.
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static inline bool IsObjCIdentifiedObject(const Value *V) {
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// Assume that call results and arguments have their own "provenance".
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// Constants (including GlobalVariables) and Allocas are never
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// reference-counted.
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if (isa<CallInst>(V) || isa<InvokeInst>(V) ||
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isa<Argument>(V) || isa<Constant>(V) ||
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isa<AllocaInst>(V))
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return true;
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if (const LoadInst *LI = dyn_cast<LoadInst>(V)) {
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const Value *Pointer =
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GetRCIdentityRoot(LI->getPointerOperand());
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if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) {
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// A constant pointer can't be pointing to an object on the heap. It may
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// be reference-counted, but it won't be deleted.
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if (GV->isConstant())
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return true;
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StringRef Name = GV->getName();
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// These special variables are known to hold values which are not
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// reference-counted pointers.
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if (Name.startswith("\01l_objc_msgSend_fixup_"))
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return true;
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StringRef Section = GV->getSection();
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if (Section.find("__message_refs") != StringRef::npos ||
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Section.find("__objc_classrefs") != StringRef::npos ||
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Section.find("__objc_superrefs") != StringRef::npos ||
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Section.find("__objc_methname") != StringRef::npos ||
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Section.find("__cstring") != StringRef::npos)
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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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/// A cache of MDKinds used by various ARC optimizations.
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struct ARCMDKindCache {
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/// The Metadata Kind for clang.imprecise_release metadata.
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unsigned ImpreciseReleaseMDKind;
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/// The Metadata Kind for clang.arc.copy_on_escape metadata.
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unsigned CopyOnEscapeMDKind;
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/// The Metadata Kind for clang.arc.no_objc_arc_exceptions metadata.
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unsigned NoObjCARCExceptionsMDKind;
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};
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} // end namespace objcarc
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} // end namespace llvm
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#endif
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