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//===-- llvm/BasicBlock.h - Represent a basic block in the VM ---*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This file contains the declaration of the BasicBlock class.
#include "llvm/ADT/Twine.h"
#include "llvm/ADT/ilist.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/SymbolTableListTraits.h"
#include "llvm/Support/CBindingWrapping.h"
#include "llvm/Support/DataTypes.h"
namespace llvm {
class LandingPadInst;
class TerminatorInst;
class LLVMContext;
class BlockAddress;
template<> struct ilist_traits<Instruction>
: public SymbolTableListTraits<Instruction, BasicBlock> {
/// \brief Return a node that marks the end of a list.
/// The sentinel is relative to this instance, so we use a non-static
/// method.
Instruction *createSentinel() const {
// Since i(p)lists always publicly derive from their corresponding traits,
// placing a data member in this class will augment the i(p)list. But since
// the NodeTy is expected to be publicly derive from ilist_node<NodeTy>,
// there is a legal viable downcast from it to NodeTy. We use this trick to
// superimpose an i(p)list with a "ghostly" NodeTy, which becomes the
// sentinel. Dereferencing the sentinel is forbidden (save the
// ilist_node<NodeTy>), so no one will ever notice the superposition.
return static_cast<Instruction*>(&Sentinel);
static void destroySentinel(Instruction*) {}
Instruction *provideInitialHead() const { return createSentinel(); }
Instruction *ensureHead(Instruction*) const { return createSentinel(); }
static void noteHead(Instruction*, Instruction*) {}
mutable ilist_half_node<Instruction> Sentinel;
/// \brief LLVM Basic Block Representation
/// This represents a single basic block in LLVM. A basic block is simply a
/// container of instructions that execute sequentially. Basic blocks are Values
/// because they are referenced by instructions such as branches and switch
/// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
/// represents a label to which a branch can jump.
/// A well formed basic block is formed of a list of non-terminating
/// instructions followed by a single TerminatorInst instruction.
/// TerminatorInst's may not occur in the middle of basic blocks, and must
/// terminate the blocks. The BasicBlock class allows malformed basic blocks to
/// occur because it may be useful in the intermediate stage of constructing or
/// modifying a program. However, the verifier will ensure that basic blocks
/// are "well formed".
class BasicBlock : public Value, // Basic blocks are data objects also
public ilist_node<BasicBlock> {
friend class BlockAddress;
typedef iplist<Instruction> InstListType;
InstListType InstList;
Function *Parent;
void setParent(Function *parent);
friend class SymbolTableListTraits<BasicBlock, Function>;
BasicBlock(const BasicBlock &) LLVM_DELETED_FUNCTION;
void operator=(const BasicBlock &) LLVM_DELETED_FUNCTION;
/// \brief Constructor.
/// If the function parameter is specified, the basic block is automatically
/// inserted at either the end of the function (if InsertBefore is null), or
/// before the specified basic block.
explicit BasicBlock(LLVMContext &C, const Twine &Name = "",
Function *Parent = nullptr,
BasicBlock *InsertBefore = nullptr);
/// \brief Get the context in which this basic block lives.
LLVMContext &getContext() const;
/// Instruction iterators...
typedef InstListType::iterator iterator;
typedef InstListType::const_iterator const_iterator;
typedef InstListType::reverse_iterator reverse_iterator;
typedef InstListType::const_reverse_iterator const_reverse_iterator;
/// \brief Creates a new BasicBlock.
/// If the Parent parameter is specified, the basic block is automatically
/// inserted at either the end of the function (if InsertBefore is 0), or
/// before the specified basic block.
static BasicBlock *Create(LLVMContext &Context, const Twine &Name = "",
Function *Parent = nullptr,
BasicBlock *InsertBefore = nullptr) {
return new BasicBlock(Context, Name, Parent, InsertBefore);
/// \brief Return the enclosing method, or null if none.
const Function *getParent() const { return Parent; }
Function *getParent() { return Parent; }
const DataLayout *getDataLayout() const;
/// \brief Returns the terminator instruction if the block is well formed or
/// null if the block is not well formed.
TerminatorInst *getTerminator();
const TerminatorInst *getTerminator() const;
/// \brief Returns a pointer to the first instruction in this block that is
/// not a PHINode instruction.
/// When adding instructions to the beginning of the basic block, they should
/// be added before the returned value, not before the first instruction,
/// which might be PHI. Returns 0 is there's no non-PHI instruction.
Instruction* getFirstNonPHI();
const Instruction* getFirstNonPHI() const {
return const_cast<BasicBlock*>(this)->getFirstNonPHI();
/// \brief Returns a pointer to the first instruction in this block that is not
/// a PHINode or a debug intrinsic.
Instruction* getFirstNonPHIOrDbg();
const Instruction* getFirstNonPHIOrDbg() const {
return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbg();
/// \brief Returns a pointer to the first instruction in this block that is not
/// a PHINode, a debug intrinsic, or a lifetime intrinsic.
Instruction* getFirstNonPHIOrDbgOrLifetime();
const Instruction* getFirstNonPHIOrDbgOrLifetime() const {
return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbgOrLifetime();
/// \brief Returns an iterator to the first instruction in this block that is
/// suitable for inserting a non-PHI instruction.
/// In particular, it skips all PHIs and LandingPad instructions.
iterator getFirstInsertionPt();
const_iterator getFirstInsertionPt() const {
return const_cast<BasicBlock*>(this)->getFirstInsertionPt();
/// \brief Unlink 'this' from the containing function, but do not delete it.
void removeFromParent();
/// \brief Unlink 'this' from the containing function and delete it.
void eraseFromParent();
/// \brief Unlink this basic block from its current function and insert it
/// into the function that \p MovePos lives in, right before \p MovePos.
void moveBefore(BasicBlock *MovePos);
/// \brief Unlink this basic block from its current function and insert it
/// right after \p MovePos in the function \p MovePos lives in.
void moveAfter(BasicBlock *MovePos);
/// \brief Return the predecessor of this block if it has a single predecessor
/// block. Otherwise return a null pointer.
BasicBlock *getSinglePredecessor();
const BasicBlock *getSinglePredecessor() const {
return const_cast<BasicBlock*>(this)->getSinglePredecessor();
/// \brief Return the predecessor of this block if it has a unique predecessor
/// block. Otherwise return a null pointer.
/// Note that unique predecessor doesn't mean single edge, there can be
/// multiple edges from the unique predecessor to this block (for example a
/// switch statement with multiple cases having the same destination).
BasicBlock *getUniquePredecessor();
const BasicBlock *getUniquePredecessor() const {
return const_cast<BasicBlock*>(this)->getUniquePredecessor();
/// Instruction iterator methods
inline iterator begin() { return InstList.begin(); }
inline const_iterator begin() const { return InstList.begin(); }
inline iterator end () { return InstList.end(); }
inline const_iterator end () const { return InstList.end(); }
inline reverse_iterator rbegin() { return InstList.rbegin(); }
inline const_reverse_iterator rbegin() const { return InstList.rbegin(); }
inline reverse_iterator rend () { return InstList.rend(); }
inline const_reverse_iterator rend () const { return InstList.rend(); }
inline size_t size() const { return InstList.size(); }
inline bool empty() const { return InstList.empty(); }
inline const Instruction &front() const { return InstList.front(); }
inline Instruction &front() { return InstList.front(); }
inline const Instruction &back() const { return InstList.back(); }
inline Instruction &back() { return InstList.back(); }
/// \brief Return the underlying instruction list container.
/// Currently you need to access the underlying instruction list container
/// directly if you want to modify it.
const InstListType &getInstList() const { return InstList; }
InstListType &getInstList() { return InstList; }
/// \brief Returns a pointer to a member of the instruction list.
static iplist<Instruction> BasicBlock::*getSublistAccess(Instruction*) {
return &BasicBlock::InstList;
/// \brief Returns a pointer to the symbol table if one exists.
ValueSymbolTable *getValueSymbolTable();
/// \brief Methods for support type inquiry through isa, cast, and dyn_cast.
static inline bool classof(const Value *V) {
return V->getValueID() == Value::BasicBlockVal;
/// \brief Cause all subinstructions to "let go" of all the references that
/// said subinstructions are maintaining.
/// This allows one to 'delete' a whole class at a time, even though there may
/// be circular references... first all references are dropped, and all use
/// counts go to zero. Then everything is delete'd for real. Note that no
/// operations are valid on an object that has "dropped all references",
/// except operator delete.
void dropAllReferences();
/// \brief Notify the BasicBlock that the predecessor \p Pred is no longer
/// able to reach it.
/// This is actually not used to update the Predecessor list, but is actually
/// used to update the PHI nodes that reside in the block. Note that this
/// should be called while the predecessor still refers to this block.
void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
/// \brief Split the basic block into two basic blocks at the specified
/// instruction.
/// Note that all instructions BEFORE the specified iterator stay as part of
/// the original basic block, an unconditional branch is added to the original
/// BB, and the rest of the instructions in the BB are moved to the new BB,
/// including the old terminator. The newly formed BasicBlock is returned.
/// This function invalidates the specified iterator.
/// Note that this only works on well formed basic blocks (must have a
/// terminator), and 'I' must not be the end of instruction list (which would
/// cause a degenerate basic block to be formed, having a terminator inside of
/// the basic block).
/// Also note that this doesn't preserve any passes. To split blocks while
/// keeping loop information consistent, use the SplitBlock utility function.
BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = "");
/// \brief Returns true if there are any uses of this basic block other than
/// direct branches, switches, etc. to it.
bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; }
/// \brief Update all phi nodes in this basic block's successors to refer to
/// basic block \p New instead of to it.
void replaceSuccessorsPhiUsesWith(BasicBlock *New);
/// \brief Return true if this basic block is a landing pad.
/// Being a ``landing pad'' means that the basic block is the destination of
/// the 'unwind' edge of an invoke instruction.
bool isLandingPad() const;
/// \brief Return the landingpad instruction associated with the landing pad.
LandingPadInst *getLandingPadInst();
const LandingPadInst *getLandingPadInst() const;
/// \brief Increment the internal refcount of the number of BlockAddresses
/// referencing this BasicBlock by \p Amt.
/// This is almost always 0, sometimes one possibly, but almost never 2, and
/// inconceivably 3 or more.
void AdjustBlockAddressRefCount(int Amt) {
assert((int)(signed char)getSubclassDataFromValue() >= 0 &&
"Refcount wrap-around");
/// \brief Shadow Value::setValueSubclassData with a private forwarding method
/// so that any future subclasses cannot accidentally use it.
void setValueSubclassData(unsigned short D) {
// Create wrappers for C Binding types (see CBindingWrapping.h).
} // End llvm namespace