C++ SILBasicBlock类代码示例

bool SILArgument::getIncomingValues(llvm::SmallVectorImpl<SILValue> &OutArray) {
  SILBasicBlock *Parent = getParent();

  if (Parent->pred_empty())
    return false;

  unsigned Index = getIndex();
  for (SILBasicBlock *Pred : getParent()->getPreds()) {
    TermInst *TI = Pred->getTerminator();

    if (auto *BI = dyn_cast<BranchInst>(TI)) {
      OutArray.push_back(BI->getArg(Index));
      continue;
    }

    if (auto *CBI = dyn_cast<CondBranchInst>(TI)) {
      OutArray.push_back(CBI->getArgForDestBB(getParent(), this));
      continue;
    }

    if (auto *CCBI = dyn_cast<CheckedCastBranchInst>(TI)) {
      OutArray.push_back(CCBI->getOperand());
      continue;
    }

    if (auto *SWEI = dyn_cast<SwitchEnumInst>(TI)) {
      OutArray.push_back(SWEI->getOperand());
      continue;
    }
    
    return false;
  }

  return true;
}

void ReleaseCodeMotionContext::convergeCodeMotionDataFlow() {
  // Process each basic block with the gen and kill set. Every time the
  // BBSetIn of a basic block changes, the optimization is rerun on its
  // predecessors.
  llvm::SmallVector<SILBasicBlock *, 16> WorkList;
  llvm::SmallPtrSet<SILBasicBlock *, 8> HandledBBs;
  // Push into reverse post order so that we can pop from the back and get
  // post order.
  for (SILBasicBlock *B : PO->getPostOrder()) {
    WorkList.push_back(B);
    HandledBBs.insert(B);
  }
  while (!WorkList.empty()) {
    SILBasicBlock *BB = WorkList.pop_back_val();
    HandledBBs.erase(BB);
    if (processBBWithGenKillSet(BB)) {
      for (auto X : BB->getPredecessorBlocks()) {
        // We do not push basic block into the worklist if its already 
        // in the worklist.
        if (HandledBBs.count(X))
          continue;
        WorkList.push_back(X);
      }
    }
  }
}

Condition SILGenFunction::emitCondition(SILValue V, SILLocation Loc,
                                        bool hasFalseCode, bool invertValue,
                                        ArrayRef<SILType> contArgs) {
  assert(B.hasValidInsertionPoint() &&
         "emitting condition at unreachable point");

  SILBasicBlock *ContBB = createBasicBlock();

  for (SILType argTy : contArgs) {
    ContBB->createPHIArgument(argTy, ValueOwnershipKind::Owned);
  }
  
  SILBasicBlock *FalseBB, *FalseDestBB;
  if (hasFalseCode) {
    FalseBB = FalseDestBB = createBasicBlock();
  } else {
    FalseBB = nullptr;
    FalseDestBB = ContBB;
  }

  SILBasicBlock *TrueBB = createBasicBlock();

  if (invertValue)
    B.createCondBranch(Loc, V, FalseDestBB, TrueBB);
  else
    B.createCondBranch(Loc, V, TrueBB, FalseDestBB);
  
  return Condition(TrueBB, FalseBB, ContBB, Loc);
}

/// Return true if this copy can be eliminated through Named Return Value
/// Optimization (NRVO).
///
/// Simple NRVO cases are handled naturally via backwardPropagateCopy. However,
/// general NRVO is not handled via local propagation without global data
/// flow. Nonetheless, NRVO is a simple pattern that can be detected using a
/// different technique from propagation.
///
/// Example:
/// func nrvo<T : P>(z : Bool) -> T {
///   var rvo : T
///   if (z) {
///     rvo = T(10)
///   }
///   else {
///     rvo = T(1)
///   }
///   return rvo
/// }
///
/// Because of the control flow, backward propagation with a block will fail to
/// find the initializer for the copy at "return rvo". Instead, we directly
/// check for an NRVO pattern by observing a copy in a return block that is the
/// only use of the copy's dest, which must be an @out arg. If there are no
/// instructions between the copy and the return that may write to the copy's
/// source, we simply replace the source's local stack address with the @out
/// address.
///
/// The following SIL pattern will be detected:
///
/// sil @foo : [email protected](thin) <T> (@out T) -> () {
/// bb0(%0 : $*T):
///   %2 = alloc_stack $T
/// ... // arbitrary control flow, but no other uses of %0
/// bbN:
///   copy_addr [take] %2 to [initialization] %0 : $*T
///   ... // no writes
///   return
static bool canNRVO(CopyAddrInst *CopyInst) {
  if (!isa<AllocStackInst>(CopyInst->getSrc()))
    return false;

  // The copy's dest must be an indirect SIL argument. Otherwise, it may not
  // dominate all uses of the source. Worse, it may be aliased. This
  // optimization will early-initialize the copy dest, so we can't allow aliases
  // to be accessed between the initialization and the return.
  auto OutArg = dyn_cast<SILArgument>(CopyInst->getDest());
  if (!OutArg)
    return false;

  auto ArgConv = OutArg->getParameterInfo().getConvention();
  if (ArgConv != ParameterConvention::Indirect_Out)
    return false;

  SILBasicBlock *BB = CopyInst->getParent();
  if (!isa<ReturnInst>(BB->getTerminator()))
    return false;

  SILValue CopyDest = CopyInst->getDest();
  if (!hasOneNonDebugUse(CopyDest))
    return false;

  auto SI = CopyInst->getIterator(), SE = BB->end();
  for (++SI; SI != SE; ++SI) {
    if (SI->mayWriteToMemory() && !isa<DeallocationInst>(SI))
      return false;
  }
  return true;
}

SILValue
StackAllocationPromoter::getLiveOutValue(BlockSet &PhiBlocks,
                                         SILBasicBlock *StartBB) {
  LLVM_DEBUG(llvm::dbgs() << "*** Searching for a value definition.\n");
  // Walk the Dom tree in search of a defining value:
  for (DomTreeNode *Node = DT->getNode(StartBB); Node; Node = Node->getIDom()) {
    SILBasicBlock *BB = Node->getBlock();

    // If there is a store (that must come after the phi), use its value.
    BlockToInstMap::iterator it = LastStoreInBlock.find(BB);
    if (it != LastStoreInBlock.end())
      if (auto *St = dyn_cast_or_null<StoreInst>(it->second)) {
        LLVM_DEBUG(llvm::dbgs() << "*** Found Store def " << *St->getSrc());
        return St->getSrc();
      }

    // If there is a Phi definition in this block:
    if (PhiBlocks.count(BB)) {
      // Return the dummy instruction that represents the new value that we will
      // add to the basic block.
      SILValue Phi = BB->getArgument(BB->getNumArguments() - 1);
      LLVM_DEBUG(llvm::dbgs() << "*** Found a dummy Phi def " << *Phi);
      return Phi;
    }

    // Move to the next dominating block.
    LLVM_DEBUG(llvm::dbgs() << "*** Walking up the iDOM.\n");
  }
  LLVM_DEBUG(llvm::dbgs() << "*** Could not find a Def. Using Undef.\n");
  return SILUndef::get(ASI->getElementType(), ASI->getModule());
}

/// Set up epilogue work for the thunk arguments based in the given argument.
/// Default implementation simply passes it through.
void
FunctionSignatureTransform::
OwnedToGuaranteedAddArgumentRelease(ArgumentDescriptor &AD, SILBuilder &Builder,
                                    SILFunction *F) {
  // If we have any arguments that were consumed but are now guaranteed,
  // insert a release_value.
  if (!AD.OwnedToGuaranteed) {
    return;
  }

  SILInstruction *Call = findOnlyApply(F);
  if (isa<ApplyInst>(Call)) {
    Builder.setInsertionPoint(&*std::next(SILBasicBlock::iterator(Call)));
    Builder.createReleaseValue(RegularLocation(SourceLoc()),
                               F->getArguments()[AD.Index],
                               Builder.getDefaultAtomicity());
  } else {
    SILBasicBlock *NormalBB = dyn_cast<TryApplyInst>(Call)->getNormalBB();
    Builder.setInsertionPoint(&*NormalBB->begin());
    Builder.createReleaseValue(RegularLocation(SourceLoc()),
                               F->getArguments()[AD.Index],
                               Builder.getDefaultAtomicity());

    SILBasicBlock *ErrorBB = dyn_cast<TryApplyInst>(Call)->getErrorBB();
    Builder.setInsertionPoint(&*ErrorBB->begin());
    Builder.createReleaseValue(RegularLocation(SourceLoc()),
                               F->getArguments()[AD.Index],
                               Builder.getDefaultAtomicity());
  }
}

SILValue BBState::computeForwardingValues(RLEContext &Ctx, MemLocation &L,
                                          SILInstruction *InsertPt,
                                          bool UseForwardValOut) {
  SILBasicBlock *ParentBB = InsertPt->getParent();
  bool IsTerminator = (InsertPt == ParentBB->getTerminator());
  // We do not have a SILValue for the current MemLocation, try to construct
  // one.
  //
  // Collect the locations and their corresponding values into a map.
  // First, collect current available locations and their corresponding values
  // into a map.
  MemLocationValueMap Values;
  if (!Ctx.gatherValues(ParentBB, L, Values, UseForwardValOut))
    return SILValue();

  // If the InsertPt is the terminator instruction of the basic block, we
  // *refresh* it as terminator instruction could be deleted as a result
  // of adding new edge values to the terminator instruction.
  if (IsTerminator)
    InsertPt = ParentBB->getTerminator();

  // Second, reduce the available values into a single SILValue we can use to
  // forward.
  SILValue TheForwardingValue;
  TheForwardingValue = MemLocation::reduceWithValues(L, &ParentBB->getModule(),
                                                     Values, InsertPt);
  /// Return the forwarding value.
  return TheForwardingValue;
}

void State::initializeAllConsumingUses(
    ArrayRef<BranchPropagatedUser> consumingUses,
    SmallVectorImpl<BrPropUserAndBlockPair> &predsToAddToWorklist) {
  for (BranchPropagatedUser user : consumingUses) {
    SILBasicBlock *userBlock = user.getParent();

    // First initialize our state for the consuming user.
    //
    // If we find another consuming instruction associated with userBlock this
    // will emit a checker error.
    initializeConsumingUse(user, userBlock);

    // Then check if the given block has a use after free and emit an error if
    // we find one.
    checkForSameBlockUseAfterFree(user, userBlock);

    // If this user is in the same block as the value, do not visit
    // predecessors. We must be extra tolerant here since we allow for
    // unreachable code.
    if (userBlock == value->getParentBlock())
      continue;

    // Then for each predecessor of this block...
    for (auto *pred : userBlock->getPredecessorBlocks()) {
      // If this block is not a block that we have already put on the list, add
      // it to the worklist.
      predsToAddToWorklist.push_back({user, pred});
    }
  }
}

void RLEContext::processBasicBlocksWithGenKillSet() {
  // Process each basic block with the gen and kill set. Every time the
  // ForwardSetOut of a basic block changes, the optimization is rerun on its
  // successors.
  llvm::SmallVector<SILBasicBlock *, 16> WorkList;
  llvm::DenseSet<SILBasicBlock *> HandledBBs;

  // Push into the worklist in post order so that we can pop from the back and
  // get reverse post order.
  for (SILBasicBlock *BB : PO->getPostOrder()) {
    WorkList.push_back(BB);
    HandledBBs.insert(BB);
  }
  while (!WorkList.empty()) {
    SILBasicBlock *BB = WorkList.pop_back_val();
    HandledBBs.erase(BB);

    // Intersection.
    BlockState &Forwarder = getBlockState(BB);
    // Compute the ForwardSetIn at the beginning of the basic block.
    Forwarder.mergePredecessorAvailSet(*this);

    if (Forwarder.processBasicBlockWithGenKillSet()) {
      for (auto &X : BB->getSuccessors()) {
        // We do not push basic block into the worklist if its already
        // in the worklist.
        if (HandledBBs.find(X) != HandledBBs.end())
          continue;
        WorkList.push_back(X);
      }
    }
  }
}

/// Perform a foreign error check by testing whether the error was nil.
static void
emitErrorIsNonNilErrorCheck(SILGenFunction &gen, SILLocation loc,
                            ManagedValue errorSlot, bool suppressErrorCheck) {
  // If we're suppressing the check, just don't check.
  if (suppressErrorCheck) return;

  SILValue optionalError = gen.B.emitLoadValueOperation(
      loc, errorSlot.forward(gen), LoadOwnershipQualifier::Take);

  ASTContext &ctx = gen.getASTContext();

  // Switch on the optional error.
  SILBasicBlock *errorBB = gen.createBasicBlock(FunctionSection::Postmatter);
  errorBB->createArgument(optionalError->getType().unwrapAnyOptionalType());
  SILBasicBlock *contBB = gen.createBasicBlock();
  gen.B.createSwitchEnum(loc, optionalError, /*default*/ nullptr,
                         { { ctx.getOptionalSomeDecl(), errorBB },
                           { ctx.getOptionalNoneDecl(), contBB } });

  // Emit the error block. Pass in none for the errorSlot since we have passed
  // in the errorSlot as our BB argument so we can pass ownership correctly. In
  // emitForeignErrorBlock, we will create the appropriate cleanup for the
  // argument.
  gen.emitForeignErrorBlock(loc, errorBB, None);

  // Return the result.
  gen.B.emitBlock(contBB);
  return;
}

SILValue SILArgument::getIncomingValue(unsigned BBIndex) {
  SILBasicBlock *Parent = getParent();

  if (Parent->pred_empty())
    return SILValue();

  unsigned Index = getIndex();

  // We could do an early check if the size of the pred list is <= BBIndex, but
  // that would involve walking the linked list anyways, so we just iterate once
  // over the loop.

  // We use this funky loop since predecessors are stored in a linked list but
  // we want array like semantics.
  unsigned BBCount = 0;
  for (SILBasicBlock *Pred : Parent->getPreds()) {
    // If BBCount is not BBIndex, continue.
    if (BBCount < BBIndex) {
      BBCount++;
      continue;
    }

    // This will return an empty SILValue if we found something we do not
    // understand.
    return getIncomingValueForPred(Parent, Pred, Index);
  }

  return SILValue();
}

// Given a block argument address base, check if it is actually a box projected
// from a switch_enum. This is a valid pattern at any SIL stage resulting in a
// block-type phi. In later SIL stages, the optimizer may form address-type
// phis, causing this assert if called on those cases.
static void checkSwitchEnumBlockArg(SILPhiArgument *arg) {
  assert(!arg->getType().isAddress());
  SILBasicBlock *Pred = arg->getParent()->getSinglePredecessorBlock();
  if (!Pred || !isa<SwitchEnumInst>(Pred->getTerminator())) {
    arg->dump();
    llvm_unreachable("unexpected box source.");
  }
}

/// \brief Splits a basic block into two at the specified instruction.
///
/// Note that all the instructions BEFORE the specified iterator
/// stay as part of the original basic block. The old basic block is left
/// without a terminator.
SILBasicBlock *SILBasicBlock::split(iterator I) {
  SILBasicBlock *New =
    new (Parent->getModule()) SILBasicBlock(Parent, this, /*after*/true);
  // Move all of the specified instructions from the original basic block into
  // the new basic block.
  New->InstList.splice(New->end(), InstList, I, end());
  return New;
}

void FunctionSignatureTransform::DeadArgumentTransformFunction() {
  SILBasicBlock *BB = &*F->begin();
  for (const ArgumentDescriptor &AD : ArgumentDescList) {
    if (!AD.IsEntirelyDead)
      continue;
    eraseUsesOfValue(BB->getArgument(AD.Index));
  }
}

/// getOrEraseBlock - If there are branches to the specified JumpDest,
/// return the block, otherwise return NULL. The JumpDest must be valid.
static SILBasicBlock *getOrEraseBlock(SILGenFunction &SGF, JumpDest &dest) {
  SILBasicBlock *BB = dest.takeBlock();
  if (BB->pred_empty()) {
    // If the block is unused, we don't need it; just delete it.
    SGF.eraseBasicBlock(BB);
    return nullptr;
  }
  return BB;
}