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+//===- DependencyAnalysis.cpp - ObjC ARC Optimization ---------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file
+///
+/// This file defines special dependency analysis routines used in Objective C
+/// ARC Optimizations.
+///
+/// WARNING: This file knows about certain library functions. It recognizes them
+/// by name, and hardwires knowledge of their semantics.
+///
+/// WARNING: This file knows about how certain Objective-C library functions are
+/// used. Naive LLVM IR transformations which would otherwise be
+/// behavior-preserving may break these assumptions.
+///
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "objc-arc-dependency"
+#include "ObjCARC.h"
+#include "DependencyAnalysis.h"
+#include "ProvenanceAnalysis.h"
+#include "llvm/Support/CFG.h"
+
+using namespace llvm;
+using namespace llvm::objcarc;
+
+/// Test whether the given instruction can result in a reference count
+/// modification (positive or negative) for the pointer's object.
+bool
+llvm::objcarc::CanAlterRefCount(const Instruction *Inst, const Value *Ptr,
+ ProvenanceAnalysis &PA,
+ InstructionClass Class) {
+ switch (Class) {
+ case IC_Autorelease:
+ case IC_AutoreleaseRV:
+ case IC_User:
+ // These operations never directly modify a reference count.
+ return false;
+ default: break;
+ }
+
+ ImmutableCallSite CS = static_cast<const Value *>(Inst);
+ assert(CS && "Only calls can alter reference counts!");
+
+ // See if AliasAnalysis can help us with the call.
+ AliasAnalysis::ModRefBehavior MRB = PA.getAA()->getModRefBehavior(CS);
+ if (AliasAnalysis::onlyReadsMemory(MRB))
+ return false;
+ if (AliasAnalysis::onlyAccessesArgPointees(MRB)) {
+ for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
+ I != E; ++I) {
+ const Value *Op = *I;
+ if (IsPotentialRetainableObjPtr(Op, *PA.getAA()) && PA.related(Ptr, Op))
+ return true;
+ }
+ return false;
+ }
+
+ // Assume the worst.
+ return true;
+}
+
+/// Test whether the given instruction can "use" the given pointer's object in a
+/// way that requires the reference count to be positive.
+bool
+llvm::objcarc::CanUse(const Instruction *Inst, const Value *Ptr,
+ ProvenanceAnalysis &PA, InstructionClass Class) {
+ // IC_Call operations (as opposed to IC_CallOrUser) never "use" objc pointers.
+ if (Class == IC_Call)
+ return false;
+
+ // Consider various instructions which may have pointer arguments which are
+ // not "uses".
+ if (const ICmpInst *ICI = dyn_cast<ICmpInst>(Inst)) {
+ // Comparing a pointer with null, or any other constant, isn't really a use,
+ // because we don't care what the pointer points to, or about the values
+ // of any other dynamic reference-counted pointers.
+ if (!IsPotentialRetainableObjPtr(ICI->getOperand(1), *PA.getAA()))
+ return false;
+ } else if (ImmutableCallSite CS = static_cast<const Value *>(Inst)) {
+ // For calls, just check the arguments (and not the callee operand).
+ for (ImmutableCallSite::arg_iterator OI = CS.arg_begin(),
+ OE = CS.arg_end(); OI != OE; ++OI) {
+ const Value *Op = *OI;
+ if (IsPotentialRetainableObjPtr(Op, *PA.getAA()) && PA.related(Ptr, Op))
+ return true;
+ }
+ return false;
+ } else if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
+ // Special-case stores, because we don't care about the stored value, just
+ // the store address.
+ const Value *Op = GetUnderlyingObjCPtr(SI->getPointerOperand());
+ // If we can't tell what the underlying object was, assume there is a
+ // dependence.
+ return IsPotentialRetainableObjPtr(Op, *PA.getAA()) && PA.related(Op, Ptr);
+ }
+
+ // Check each operand for a match.
+ for (User::const_op_iterator OI = Inst->op_begin(), OE = Inst->op_end();
+ OI != OE; ++OI) {
+ const Value *Op = *OI;
+ if (IsPotentialRetainableObjPtr(Op, *PA.getAA()) && PA.related(Ptr, Op))
+ return true;
+ }
+ return false;
+}
+
+/// Test if there can be dependencies on Inst through Arg. This function only
+/// tests dependencies relevant for removing pairs of calls.
+bool
+llvm::objcarc::Depends(DependenceKind Flavor, Instruction *Inst,
+ const Value *Arg, ProvenanceAnalysis &PA) {
+ // If we've reached the definition of Arg, stop.
+ if (Inst == Arg)
+ return true;
+
+ switch (Flavor) {
+ case NeedsPositiveRetainCount: {
+ InstructionClass Class = GetInstructionClass(Inst);
+ switch (Class) {
+ case IC_AutoreleasepoolPop:
+ case IC_AutoreleasepoolPush:
+ case IC_None:
+ return false;
+ default:
+ return CanUse(Inst, Arg, PA, Class);
+ }
+ }
+
+ case AutoreleasePoolBoundary: {
+ InstructionClass Class = GetInstructionClass(Inst);
+ switch (Class) {
+ case IC_AutoreleasepoolPop:
+ case IC_AutoreleasepoolPush:
+ // These mark the end and begin of an autorelease pool scope.
+ return true;
+ default:
+ // Nothing else does this.
+ return false;
+ }
+ }
+
+ case CanChangeRetainCount: {
+ InstructionClass Class = GetInstructionClass(Inst);
+ switch (Class) {
+ case IC_AutoreleasepoolPop:
+ // Conservatively assume this can decrement any count.
+ return true;
+ case IC_AutoreleasepoolPush:
+ case IC_None:
+ return false;
+ default:
+ return CanAlterRefCount(Inst, Arg, PA, Class);
+ }
+ }
+
+ case RetainAutoreleaseDep:
+ switch (GetBasicInstructionClass(Inst)) {
+ case IC_AutoreleasepoolPop:
+ case IC_AutoreleasepoolPush:
+ // Don't merge an objc_autorelease with an objc_retain inside a different
+ // autoreleasepool scope.
+ return true;
+ case IC_Retain:
+ case IC_RetainRV:
+ // Check for a retain of the same pointer for merging.
+ return GetObjCArg(Inst) == Arg;
+ default:
+ // Nothing else matters for objc_retainAutorelease formation.
+ return false;
+ }
+
+ case RetainAutoreleaseRVDep: {
+ InstructionClass Class = GetBasicInstructionClass(Inst);
+ switch (Class) {
+ case IC_Retain:
+ case IC_RetainRV:
+ // Check for a retain of the same pointer for merging.
+ return GetObjCArg(Inst) == Arg;
+ default:
+ // Anything that can autorelease interrupts
+ // retainAutoreleaseReturnValue formation.
+ return CanInterruptRV(Class);
+ }
+ }
+
+ case RetainRVDep:
+ return CanInterruptRV(GetBasicInstructionClass(Inst));
+ }
+
+ llvm_unreachable("Invalid dependence flavor");
+}
+
+/// Walk up the CFG from StartPos (which is in StartBB) and find local and
+/// non-local dependencies on Arg.
+///
+/// TODO: Cache results?
+void
+llvm::objcarc::FindDependencies(DependenceKind Flavor,
+ const Value *Arg,
+ BasicBlock *StartBB, Instruction *StartInst,
+ SmallPtrSet<Instruction *, 4> &DependingInsts,
+ SmallPtrSet<const BasicBlock *, 4> &Visited,
+ ProvenanceAnalysis &PA) {
+ BasicBlock::iterator StartPos = StartInst;
+
+ SmallVector<std::pair<BasicBlock *, BasicBlock::iterator>, 4> Worklist;
+ Worklist.push_back(std::make_pair(StartBB, StartPos));
+ do {
+ std::pair<BasicBlock *, BasicBlock::iterator> Pair =
+ Worklist.pop_back_val();
+ BasicBlock *LocalStartBB = Pair.first;
+ BasicBlock::iterator LocalStartPos = Pair.second;
+ BasicBlock::iterator StartBBBegin = LocalStartBB->begin();
+ for (;;) {
+ if (LocalStartPos == StartBBBegin) {
+ pred_iterator PI(LocalStartBB), PE(LocalStartBB, false);
+ if (PI == PE)
+ // If we've reached the function entry, produce a null dependence.
+ DependingInsts.insert(0);
+ else
+ // Add the predecessors to the worklist.
+ do {
+ BasicBlock *PredBB = *PI;
+ if (Visited.insert(PredBB))
+ Worklist.push_back(std::make_pair(PredBB, PredBB->end()));
+ } while (++PI != PE);
+ break;
+ }
+
+ Instruction *Inst = --LocalStartPos;
+ if (Depends(Flavor, Inst, Arg, PA)) {
+ DependingInsts.insert(Inst);
+ break;
+ }
+ }
+ } while (!Worklist.empty());
+
+ // Determine whether the original StartBB post-dominates all of the blocks we
+ // visited. If not, insert a sentinal indicating that most optimizations are
+ // not safe.
+ for (SmallPtrSet<const BasicBlock *, 4>::const_iterator I = Visited.begin(),
+ E = Visited.end(); I != E; ++I) {
+ const BasicBlock *BB = *I;
+ if (BB == StartBB)
+ continue;
+ const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
+ for (succ_const_iterator SI(TI), SE(TI, false); SI != SE; ++SI) {
+ const BasicBlock *Succ = *SI;
+ if (Succ != StartBB && !Visited.count(Succ)) {
+ DependingInsts.insert(reinterpret_cast<Instruction *>(-1));
+ return;
+ }
+ }
+ }
+}
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