C++ SCCNodeSet类代码示例

static bool addNoRecurseAttrs(const SCCNodeSet &SCCNodes) {
  // Try and identify functions that do not recurse.

  // If the SCC contains multiple nodes we know for sure there is recursion.
  if (SCCNodes.size() != 1)
    return false;

  Function *F = *SCCNodes.begin();
  if (!F || F->isDeclaration() || F->doesNotRecurse())
    return false;

  // If all of the calls in F are identifiable and are to norecurse functions, F
  // is norecurse. This check also detects self-recursion as F is not currently
  // marked norecurse, so any called from F to F will not be marked norecurse.
  for (Instruction &I : instructions(*F))
    if (auto CS = CallSite(&I)) {
      Function *Callee = CS.getCalledFunction();
      if (!Callee || Callee == F || !Callee->doesNotRecurse())
        // Function calls a potentially recursive function.
        return false;
    }

  // Every call was to a non-recursive function other than this function, and
  // we have no indirect recursion as the SCC size is one. This function cannot
  // recurse.
  return setDoesNotRecurse(*F);
}

PreservedAnalyses PostOrderFunctionAttrsPass::run(LazyCallGraph::SCC &C,
                                                  CGSCCAnalysisManager &AM,
                                                  LazyCallGraph &CG,
                                                  CGSCCUpdateResult &) {
  FunctionAnalysisManager &FAM =
      AM.getResult<FunctionAnalysisManagerCGSCCProxy>(C, CG).getManager();

  // We pass a lambda into functions to wire them up to the analysis manager
  // for getting function analyses.
  auto AARGetter = [&](Function &F) -> AAResults & {
    return FAM.getResult<AAManager>(F);
  };

  // Fill SCCNodes with the elements of the SCC. Also track whether there are
  // any external or opt-none nodes that will prevent us from optimizing any
  // part of the SCC.
  SCCNodeSet SCCNodes;
  bool HasUnknownCall = false;
  for (LazyCallGraph::Node &N : C) {
    Function &F = N.getFunction();
    if (F.hasFnAttribute(Attribute::OptimizeNone)) {
      // Treat any function we're trying not to optimize as if it were an
      // indirect call and omit it from the node set used below.
      HasUnknownCall = true;
      continue;
    }
    // Track whether any functions in this SCC have an unknown call edge.
    // Note: if this is ever a performance hit, we can common it with
    // subsequent routines which also do scans over the instructions of the
    // function.
    if (!HasUnknownCall)
      for (Instruction &I : instructions(F))
        if (auto CS = CallSite(&I))
          if (!CS.getCalledFunction()) {
            HasUnknownCall = true;
            break;
          }

    SCCNodes.insert(&F);
  }

  bool Changed = false;
  Changed |= addArgumentReturnedAttrs(SCCNodes);
  Changed |= addReadAttrs(SCCNodes, AARGetter);
  Changed |= addArgumentAttrs(SCCNodes);

  // If we have no external nodes participating in the SCC, we can deduce some
  // more precise attributes as well.
  if (!HasUnknownCall) {
    Changed |= addNoAliasAttrs(SCCNodes);
    Changed |= addNonNullAttrs(SCCNodes);
    Changed |= removeConvergentAttrs(SCCNodes);
    Changed |= addNoRecurseAttrs(SCCNodes);
  }

  return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
}

bool PostOrderFunctionAttrsLegacyPass::runOnSCC(CallGraphSCC &SCC) {
  TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
  bool Changed = false;

  // We compute dedicated AA results for each function in the SCC as needed. We
  // use a lambda referencing external objects so that they live long enough to
  // be queried, but we re-use them each time.
  Optional<BasicAAResult> BAR;
  Optional<AAResults> AAR;
  auto AARGetter = [&](Function &F) -> AAResults & {
    BAR.emplace(createLegacyPMBasicAAResult(*this, F));
    AAR.emplace(createLegacyPMAAResults(*this, F, *BAR));
    return *AAR;
  };

  // Fill SCCNodes with the elements of the SCC. Used for quickly looking up
  // whether a given CallGraphNode is in this SCC. Also track whether there are
  // any external or opt-none nodes that will prevent us from optimizing any
  // part of the SCC.
  SCCNodeSet SCCNodes;
  bool ExternalNode = false;
  for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
    Function *F = (*I)->getFunction();
    if (!F || F->hasFnAttribute(Attribute::OptimizeNone)) {
      // External node or function we're trying not to optimize - we both avoid
      // transform them and avoid leveraging information they provide.
      ExternalNode = true;
      continue;
    }

    SCCNodes.insert(F);
  }

  Changed |= addReadAttrs(SCCNodes, AARGetter);
  Changed |= addArgumentAttrs(SCCNodes);

  // If we have no external nodes participating in the SCC, we can deduce some
  // more precise attributes as well.
  if (!ExternalNode) {
    Changed |= addNoAliasAttrs(SCCNodes);
    Changed |= addNonNullAttrs(SCCNodes, *TLI);
    Changed |= removeConvergentAttrs(SCCNodes);
    Changed |= addNoRecurseAttrs(SCCNodes);
  }

  return Changed;
}

/// Removes convergent attributes where we can prove that none of the SCC's
/// callees are themselves convergent.  Returns true if successful at removing
/// the attribute.
static bool removeConvergentAttrs(const CallGraphSCC &SCC,
                                  const SCCNodeSet &SCCNodes) {
  // Determines whether a function can be made non-convergent, ignoring all
  // other functions in SCC.  (A function can *actually* be made non-convergent
  // only if all functions in its SCC can be made convergent.)
  auto CanRemoveConvergent = [&] (CallGraphNode *CGN) {
    Function *F = CGN->getFunction();
    if (!F) return false;

    if (!F->isConvergent()) return true;

    // Can't remove convergent from declarations.
    if (F->isDeclaration()) return false;

    // Don't remove convergent from optnone functions.
    if (F->hasFnAttribute(Attribute::OptimizeNone))
      return false;

    // Can't remove convergent if any of F's callees -- ignoring functions in the
    // SCC itself -- are convergent.
    if (llvm::any_of(*CGN, [&](const CallGraphNode::CallRecord &CR) {
          Function *F = CR.second->getFunction();
          return SCCNodes.count(F) == 0 && (!F || F->isConvergent());
        }))
      return false;

    // CGN doesn't contain calls to intrinsics, so iterate over all of F's
    // callsites, looking for any calls to convergent intrinsics.  If we find one,
    // F must remain marked as convergent.
    auto IsConvergentIntrinsicCall = [](Instruction &I) {
      CallSite CS(cast<Value>(&I));
      if (!CS)
        return false;
      Function *Callee = CS.getCalledFunction();
      return Callee && Callee->isIntrinsic() && Callee->isConvergent();
    };
    return !llvm::any_of(*F, [=](BasicBlock &BB) {
      return llvm::any_of(BB, IsConvergentIntrinsicCall);
    });
  };

  // We can remove the convergent attr from functions in the SCC if they all can
  // be made non-convergent (because they call only non-convergent functions,
  // other than each other).
  if (!llvm::all_of(SCC, CanRemoveConvergent)) return false;

  // If we got here, all of the SCC's callees are non-convergent, and none of
  // the optnone functions in the SCC are marked as convergent.  Therefore all
  // of the SCC's functions can be marked as non-convergent.
  for (CallGraphNode *CGN : SCC)
    if (Function *F = CGN->getFunction()) {
      if (F->isConvergent())
        DEBUG(dbgs() << "Removing convergent attr from " << F->getName()
                     << "\n");
      F->setNotConvergent();
    }
  return true;
}

static bool runImpl(CallGraphSCC &SCC, AARGetterT AARGetter) {
  bool Changed = false;

  // Fill SCCNodes with the elements of the SCC. Used for quickly looking up
  // whether a given CallGraphNode is in this SCC. Also track whether there are
  // any external or opt-none nodes that will prevent us from optimizing any
  // part of the SCC.
  SCCNodeSet SCCNodes;
  bool ExternalNode = false;
  for (CallGraphNode *I : SCC) {
    Function *F = I->getFunction();
    if (!F || F->hasFnAttribute(Attribute::OptimizeNone)) {
      // External node or function we're trying not to optimize - we both avoid
      // transform them and avoid leveraging information they provide.
      ExternalNode = true;
      continue;
    }

    SCCNodes.insert(F);
  }

  Changed |= addArgumentReturnedAttrs(SCCNodes);
  Changed |= addReadAttrs(SCCNodes, AARGetter);
  Changed |= addArgumentAttrs(SCCNodes);

  // If we have no external nodes participating in the SCC, we can deduce some
  // more precise attributes as well.
  if (!ExternalNode) {
    Changed |= addNoAliasAttrs(SCCNodes);
    Changed |= addNonNullAttrs(SCCNodes);
    Changed |= removeConvergentAttrs(SCCNodes);
    Changed |= addNoRecurseAttrs(SCCNodes);
  }

  return Changed;
}

/// Removes convergent attributes where we can prove that none of the SCC's
/// callees are themselves convergent.  Returns true if successful at removing
/// the attribute.
static bool removeConvergentAttrs(const SCCNodeSet &SCCNodes) {
  // Determines whether a function can be made non-convergent, ignoring all
  // other functions in SCC.  (A function can *actually* be made non-convergent
  // only if all functions in its SCC can be made convergent.)
  auto CanRemoveConvergent = [&](Function *F) {
    if (!F->isConvergent())
      return true;

    // Can't remove convergent from declarations.
    if (F->isDeclaration())
      return false;

    for (Instruction &I : instructions(*F))
      if (auto CS = CallSite(&I)) {
        // Can't remove convergent if any of F's callees -- ignoring functions
        // in the SCC itself -- are convergent. This needs to consider both
        // function calls and intrinsic calls. We also assume indirect calls
        // might call a convergent function.
        // FIXME: We should revisit this when we put convergent onto calls
        // instead of functions so that indirect calls which should be
        // convergent are required to be marked as such.
        Function *Callee = CS.getCalledFunction();
        if (!Callee || (SCCNodes.count(Callee) == 0 && Callee->isConvergent()))
          return false;
      }

    return true;
  };

  // We can remove the convergent attr from functions in the SCC if they all
  // can be made non-convergent (because they call only non-convergent
  // functions, other than each other).
  if (!llvm::all_of(SCCNodes, CanRemoveConvergent))
    return false;

  // If we got here, all of the SCC's callees are non-convergent. Therefore all
  // of the SCC's functions can be marked as non-convergent.
  for (Function *F : SCCNodes) {
    if (F->isConvergent())
      DEBUG(dbgs() << "Removing convergent attr from " << F->getName() << "\n");
    F->setNotConvergent();
  }
  return true;
}

/// Remove the convergent attribute from all functions in the SCC if every
/// callsite within the SCC is not convergent (except for calls to functions
/// within the SCC).  Returns true if changes were made.
static bool removeConvergentAttrs(const SCCNodeSet &SCCNodes) {
  // For every function in SCC, ensure that either
  //  * it is not convergent, or
  //  * we can remove its convergent attribute.
  bool HasConvergentFn = false;
  for (Function *F : SCCNodes) {
    if (!F->isConvergent()) continue;
    HasConvergentFn = true;

    // Can't remove convergent from function declarations.
    if (F->isDeclaration()) return false;

    // Can't remove convergent if any of our functions has a convergent call to a
    // function not in the SCC.
    for (Instruction &I : instructions(*F)) {
      CallSite CS(&I);
      // Bail if CS is a convergent call to a function not in the SCC.
      if (CS && CS.isConvergent() &&
          SCCNodes.count(CS.getCalledFunction()) == 0)
        return false;
    }
  }

  // If the SCC doesn't have any convergent functions, we have nothing to do.
  if (!HasConvergentFn) return false;

  // If we got here, all of the calls the SCC makes to functions not in the SCC
  // are non-convergent.  Therefore all of the SCC's functions can also be made
  // non-convergent.  We'll remove the attr from the callsites in
  // InstCombineCalls.
  for (Function *F : SCCNodes) {
    if (!F->isConvergent()) continue;

    DEBUG(dbgs() << "Removing convergent attr from fn " << F->getName()
                 << "\n");
    F->setNotConvergent();
  }
  return true;
}

/// Tests whether this function is known to not return null.
///
/// Requires that the function returns a pointer.
///
/// Returns true if it believes the function will not return a null, and sets
/// \p Speculative based on whether the returned conclusion is a speculative
/// conclusion due to SCC calls.
static bool isReturnNonNull(Function *F, const SCCNodeSet &SCCNodes,
                            bool &Speculative) {
  assert(F->getReturnType()->isPointerTy() &&
         "nonnull only meaningful on pointer types");
  Speculative = false;

  SmallSetVector<Value *, 8> FlowsToReturn;
  for (BasicBlock &BB : *F)
    if (auto *Ret = dyn_cast<ReturnInst>(BB.getTerminator()))
      FlowsToReturn.insert(Ret->getReturnValue());

  for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {
    Value *RetVal = FlowsToReturn[i];

    // If this value is locally known to be non-null, we're good
    if (isKnownNonNull(RetVal))
      continue;

    // Otherwise, we need to look upwards since we can't make any local
    // conclusions.
    Instruction *RVI = dyn_cast<Instruction>(RetVal);
    if (!RVI)
      return false;
    switch (RVI->getOpcode()) {
    // Extend the analysis by looking upwards.
    case Instruction::BitCast:
    case Instruction::GetElementPtr:
    case Instruction::AddrSpaceCast:
      FlowsToReturn.insert(RVI->getOperand(0));
      continue;
    case Instruction::Select: {
      SelectInst *SI = cast<SelectInst>(RVI);
      FlowsToReturn.insert(SI->getTrueValue());
      FlowsToReturn.insert(SI->getFalseValue());
      continue;
    }
    case Instruction::PHI: {
      PHINode *PN = cast<PHINode>(RVI);
      for (int i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
        FlowsToReturn.insert(PN->getIncomingValue(i));
      continue;
    }
    case Instruction::Call:
    case Instruction::Invoke: {
      CallSite CS(RVI);
      Function *Callee = CS.getCalledFunction();
      // A call to a node within the SCC is assumed to return null until
      // proven otherwise
      if (Callee && SCCNodes.count(Callee)) {
        Speculative = true;
        continue;
      }
      return false;
    }
    default:
      return false; // Unknown source, may be null
    };
    llvm_unreachable("should have either continued or returned");
  }

  return true;
}

/// Tests whether a function is "malloc-like".
///
/// A function is "malloc-like" if it returns either null or a pointer that
/// doesn't alias any other pointer visible to the caller.
static bool isFunctionMallocLike(Function *F, const SCCNodeSet &SCCNodes) {
  SmallSetVector<Value *, 8> FlowsToReturn;
  for (BasicBlock &BB : *F)
    if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB.getTerminator()))
      FlowsToReturn.insert(Ret->getReturnValue());

  for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {
    Value *RetVal = FlowsToReturn[i];

    if (Constant *C = dyn_cast<Constant>(RetVal)) {
      if (!C->isNullValue() && !isa<UndefValue>(C))
        return false;

      continue;
    }

    if (isa<Argument>(RetVal))
      return false;

    if (Instruction *RVI = dyn_cast<Instruction>(RetVal))
      switch (RVI->getOpcode()) {
      // Extend the analysis by looking upwards.
      case Instruction::BitCast:
      case Instruction::GetElementPtr:
      case Instruction::AddrSpaceCast:
        FlowsToReturn.insert(RVI->getOperand(0));
        continue;
      case Instruction::Select: {
        SelectInst *SI = cast<SelectInst>(RVI);
        FlowsToReturn.insert(SI->getTrueValue());
        FlowsToReturn.insert(SI->getFalseValue());
        continue;
      }
      case Instruction::PHI: {
        PHINode *PN = cast<PHINode>(RVI);
        for (Value *IncValue : PN->incoming_values())
          FlowsToReturn.insert(IncValue);
        continue;
      }

      // Check whether the pointer came from an allocation.
      case Instruction::Alloca:
        break;
      case Instruction::Call:
      case Instruction::Invoke: {
        CallSite CS(RVI);
        if (CS.hasRetAttr(Attribute::NoAlias))
          break;
        if (CS.getCalledFunction() && SCCNodes.count(CS.getCalledFunction()))
          break;
        LLVM_FALLTHROUGH;
      }
      default:
        return false; // Did not come from an allocation.
      }

    if (PointerMayBeCaptured(RetVal, false, /*StoreCaptures=*/false))
      return false;
  }

  return true;
}

/// Returns the memory access attribute for function F using AAR for AA results,
/// where SCCNodes is the current SCC.
///
/// If ThisBody is true, this function may examine the function body and will
/// return a result pertaining to this copy of the function. If it is false, the
/// result will be based only on AA results for the function declaration; it
/// will be assumed that some other (perhaps less optimized) version of the
/// function may be selected at link time.
static MemoryAccessKind checkFunctionMemoryAccess(Function &F, bool ThisBody,
                                                  AAResults &AAR,
                                                  const SCCNodeSet &SCCNodes) {
  FunctionModRefBehavior MRB = AAR.getModRefBehavior(&F);
  if (MRB == FMRB_DoesNotAccessMemory)
    // Already perfect!
    return MAK_ReadNone;

  if (!ThisBody) {
    if (AliasAnalysis::onlyReadsMemory(MRB))
      return MAK_ReadOnly;

    // Conservatively assume it writes to memory.
    return MAK_MayWrite;
  }

  // Scan the function body for instructions that may read or write memory.
  bool ReadsMemory = false;
  for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
    Instruction *I = &*II;

    // Some instructions can be ignored even if they read or write memory.
    // Detect these now, skipping to the next instruction if one is found.
    CallSite CS(cast<Value>(I));
    if (CS) {
      // Ignore calls to functions in the same SCC, as long as the call sites
      // don't have operand bundles.  Calls with operand bundles are allowed to
      // have memory effects not described by the memory effects of the call
      // target.
      if (!CS.hasOperandBundles() && CS.getCalledFunction() &&
          SCCNodes.count(CS.getCalledFunction()))
        continue;
      FunctionModRefBehavior MRB = AAR.getModRefBehavior(CS);

      // If the call doesn't access memory, we're done.
      if (!(MRB & MRI_ModRef))
        continue;

      if (!AliasAnalysis::onlyAccessesArgPointees(MRB)) {
        // The call could access any memory. If that includes writes, give up.
        if (MRB & MRI_Mod)
          return MAK_MayWrite;
        // If it reads, note it.
        if (MRB & MRI_Ref)
          ReadsMemory = true;
        continue;
      }

      // Check whether all pointer arguments point to local memory, and
      // ignore calls that only access local memory.
      for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
           CI != CE; ++CI) {
        Value *Arg = *CI;
        if (!Arg->getType()->isPtrOrPtrVectorTy())
          continue;

        AAMDNodes AAInfo;
        I->getAAMetadata(AAInfo);
        MemoryLocation Loc(Arg, MemoryLocation::UnknownSize, AAInfo);

        // Skip accesses to local or constant memory as they don't impact the
        // externally visible mod/ref behavior.
        if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
          continue;

        if (MRB & MRI_Mod)
          // Writes non-local memory.  Give up.
          return MAK_MayWrite;
        if (MRB & MRI_Ref)
          // Ok, it reads non-local memory.
          ReadsMemory = true;
      }
      continue;
    } else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
      // Ignore non-volatile loads from local memory. (Atomic is okay here.)
      if (!LI->isVolatile()) {
        MemoryLocation Loc = MemoryLocation::get(LI);
        if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
          continue;
      }
    } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
      // Ignore non-volatile stores to local memory. (Atomic is okay here.)
      if (!SI->isVolatile()) {
        MemoryLocation Loc = MemoryLocation::get(SI);
        if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
          continue;
      }
    } else if (VAArgInst *VI = dyn_cast<VAArgInst>(I)) {
      // Ignore vaargs on local memory.
      MemoryLocation Loc = MemoryLocation::get(VI);
      if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
        continue;
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