Imported Upstream version 5.18.0.225

Former-commit-id: 10196d987d5fc5564b9d3b33b1fdf13190f4d0b5

external/llvm/lib/Transforms/ObjCARC/DependencyAnalysis.cpp

@@ -0,0 +1,278 @@
+//===- 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.
+///
+//===----------------------------------------------------------------------===//
+
+#include "DependencyAnalysis.h"
+#include "ObjCARC.h"
+#include "ProvenanceAnalysis.h"
+#include "llvm/IR/CFG.h"
+
+using namespace llvm;
+using namespace llvm::objcarc;
+
+#define DEBUG_TYPE "objc-arc-dependency"
+
+/// 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,
+                                     ARCInstKind Class) {
+  switch (Class) {
+  case ARCInstKind::Autorelease:
+  case ARCInstKind::AutoreleaseRV:
+  case ARCInstKind::IntrinsicUser:
+  case ARCInstKind::User:
+    // These operations never directly modify a reference count.
+    return false;
+  default: break;
+  }
+
+  ImmutableCallSite CS(Inst);
+  assert(CS && "Only calls can alter reference counts!");
+
+  // See if AliasAnalysis can help us with the call.
+  FunctionModRefBehavior MRB = PA.getAA()->getModRefBehavior(CS);
+  if (AliasAnalysis::onlyReadsMemory(MRB))
+    return false;
+  if (AliasAnalysis::onlyAccessesArgPointees(MRB)) {
+    const DataLayout &DL = Inst->getModule()->getDataLayout();
+    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, DL))
+        return true;
+    }
+    return false;
+  }
+
+  // Assume the worst.
+  return true;
+}
+
+bool llvm::objcarc::CanDecrementRefCount(const Instruction *Inst,
+                                         const Value *Ptr,
+                                         ProvenanceAnalysis &PA,
+                                         ARCInstKind Class) {
+  // First perform a quick check if Class can not touch ref counts.
+  if (!CanDecrementRefCount(Class))
+    return false;
+
+  // Otherwise, just use CanAlterRefCount for now.
+  return CanAlterRefCount(Inst, Ptr, PA, Class);
+}
+
+/// 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, ARCInstKind Class) {
+  // ARCInstKind::Call operations (as opposed to
+  // ARCInstKind::CallOrUser) never "use" objc pointers.
+  if (Class == ARCInstKind::Call)
+    return false;
+
+  const DataLayout &DL = Inst->getModule()->getDataLayout();
+
+  // 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 (auto CS = ImmutableCallSite(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, DL))
+        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(), DL);
+    // If we can't tell what the underlying object was, assume there is a
+    // dependence.
+    return IsPotentialRetainableObjPtr(Op, *PA.getAA()) &&
+           PA.related(Op, Ptr, DL);
+  }
+
+  // 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, DL))
+      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: {
+    ARCInstKind Class = GetARCInstKind(Inst);
+    switch (Class) {
+    case ARCInstKind::AutoreleasepoolPop:
+    case ARCInstKind::AutoreleasepoolPush:
+    case ARCInstKind::None:
+      return false;
+    default:
+      return CanUse(Inst, Arg, PA, Class);
+    }
+  }
+
+  case AutoreleasePoolBoundary: {
+    ARCInstKind Class = GetARCInstKind(Inst);
+    switch (Class) {
+    case ARCInstKind::AutoreleasepoolPop:
+    case ARCInstKind::AutoreleasepoolPush:
+      // These mark the end and begin of an autorelease pool scope.
+      return true;
+    default:
+      // Nothing else does this.
+      return false;
+    }
+  }
+
+  case CanChangeRetainCount: {
+    ARCInstKind Class = GetARCInstKind(Inst);
+    switch (Class) {
+    case ARCInstKind::AutoreleasepoolPop:
+      // Conservatively assume this can decrement any count.
+      return true;
+    case ARCInstKind::AutoreleasepoolPush:
+    case ARCInstKind::None:
+      return false;
+    default:
+      return CanAlterRefCount(Inst, Arg, PA, Class);
+    }
+  }
+
+  case RetainAutoreleaseDep:
+    switch (GetBasicARCInstKind(Inst)) {
+    case ARCInstKind::AutoreleasepoolPop:
+    case ARCInstKind::AutoreleasepoolPush:
+      // Don't merge an objc_autorelease with an objc_retain inside a different
+      // autoreleasepool scope.
+      return true;
+    case ARCInstKind::Retain:
+    case ARCInstKind::RetainRV:
+      // Check for a retain of the same pointer for merging.
+      return GetArgRCIdentityRoot(Inst) == Arg;
+    default:
+      // Nothing else matters for objc_retainAutorelease formation.
+      return false;
+    }
+
+  case RetainAutoreleaseRVDep: {
+    ARCInstKind Class = GetBasicARCInstKind(Inst);
+    switch (Class) {
+    case ARCInstKind::Retain:
+    case ARCInstKind::RetainRV:
+      // Check for a retain of the same pointer for merging.
+      return GetArgRCIdentityRoot(Inst) == Arg;
+    default:
+      // Anything that can autorelease interrupts
+      // retainAutoreleaseReturnValue formation.
+      return CanInterruptRV(Class);
+    }
+  }
+
+  case RetainRVDep:
+    return CanInterruptRV(GetBasicARCInstKind(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,
+                                SmallPtrSetImpl<Instruction *> &DependingInsts,
+                                SmallPtrSetImpl<const BasicBlock *> &Visited,
+                                ProvenanceAnalysis &PA) {
+  BasicBlock::iterator StartPos = StartInst->getIterator();
+
+  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(nullptr);
+        else
+          // Add the predecessors to the worklist.
+          do {
+            BasicBlock *PredBB = *PI;
+            if (Visited.insert(PredBB).second)
+              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 (const BasicBlock *BB : Visited) {
+    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;
+      }
+    }
+  }
+}