//===- llvm/BasicBlock.h - Represent a basic block in the VM ----*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file contains the declaration of the BasicBlock class.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_IR_BASICBLOCK_H
#define LLVM_IR_BASICBLOCK_H
#include "llvm-c/Types.h"
#include "llvm/ADT/Twine.h"
#include "llvm/ADT/ilist.h"
#include "llvm/ADT/ilist_node.h"
#include "llvm/ADT/iterator.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/SymbolTableListTraits.h"
#include "llvm/IR/Value.h"
#include <cassert>
#include <cstddef>
#include <iterator>
namespace llvm {
class AssemblyAnnotationWriter;
class CallInst;
class Function;
class LandingPadInst;
class LLVMContext;
class Module;
class PHINode;
class ValueSymbolTable;
/// 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 terminator instruction. Terminator
/// instructions 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 final : public Value, // Basic blocks are data objects also
public ilist_node_with_parent<BasicBlock, Function> {
public:
using InstListType = SymbolTableList<Instruction>;
private:
friend class BlockAddress;
friend class SymbolTableListTraits<BasicBlock>;
InstListType InstList;
Function *Parent;
void setParent(Function *parent);
/// 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);
public:
BasicBlock(const BasicBlock &) = delete;
BasicBlock &operator=(const BasicBlock &) = delete;
~BasicBlock();
/// Get the context in which this basic block lives.
LLVMContext &getContext() const;
/// Instruction iterators...
using iterator = InstListType::iterator;
using const_iterator = InstListType::const_iterator;
using reverse_iterator = InstListType::reverse_iterator;
using const_reverse_iterator = InstListType::const_reverse_iterator;
// These functions and classes need access to the instruction list.
friend void Instruction::removeFromParent();
friend iplist<Instruction>::iterator Instruction::eraseFromParent();
friend BasicBlock::iterator Instruction::insertInto(BasicBlock *BB,
BasicBlock::iterator It);
friend class llvm::SymbolTableListTraits<llvm::Instruction>;
friend class llvm::ilist_node_with_parent<llvm::Instruction, llvm::BasicBlock>;
/// 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);
}
/// Return the enclosing method, or null if none.
const Function *getParent() const { return Parent; }
Function *getParent() { return Parent; }
/// Return the module owning the function this basic block belongs to, or
/// nullptr if the function does not have a module.
///
/// Note: this is undefined behavior if the block does not have a parent.
const Module *getModule() const;
Module *getModule() {
return const_cast<Module *>(
static_cast<const BasicBlock *>(this)->getModule());
}
/// Returns the terminator instruction if the block is well formed or null
/// if the block is not well formed.
const Instruction *getTerminator() const LLVM_READONLY {
if (InstList.empty() || !InstList.back().isTerminator())
return nullptr;
return &InstList.back();
}
Instruction *getTerminator() {
return const_cast<Instruction *>(
static_cast<const BasicBlock *>(this)->getTerminator());
}
/// Returns the call instruction calling \@llvm.experimental.deoptimize
/// prior to the terminating return instruction of this basic block, if such
/// a call is present. Otherwise, returns null.
const CallInst *getTerminatingDeoptimizeCall() const;
CallInst *getTerminatingDeoptimizeCall() {
return const_cast<CallInst *>(
static_cast<const BasicBlock *>(this)->getTerminatingDeoptimizeCall());
}
/// Returns the call instruction calling \@llvm.experimental.deoptimize
/// that is present either in current basic block or in block that is a unique
/// successor to current block, if such call is present. Otherwise, returns null.
const CallInst *getPostdominatingDeoptimizeCall() const;
CallInst *getPostdominatingDeoptimizeCall() {
return const_cast<CallInst *>(
static_cast<const BasicBlock *>(this)->getPostdominatingDeoptimizeCall());
}
/// Returns the call instruction marked 'musttail' prior to the terminating
/// return instruction of this basic block, if such a call is present.
/// Otherwise, returns null.
const CallInst *getTerminatingMustTailCall() const;
CallInst *getTerminatingMustTailCall() {
return const_cast<CallInst *>(
static_cast<const BasicBlock *>(this)->getTerminatingMustTailCall());
}
/// 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.
const Instruction* getFirstNonPHI() const;
Instruction* getFirstNonPHI() {
return const_cast<Instruction *>(
static_cast<const BasicBlock *>(this)->getFirstNonPHI());
}
/// Returns a pointer to the first instruction in this block that is not a
/// PHINode or a debug intrinsic, or any pseudo operation if \c SkipPseudoOp
/// is true.
const Instruction *getFirstNonPHIOrDbg(bool SkipPseudoOp = true) const;
Instruction *getFirstNonPHIOrDbg(bool SkipPseudoOp = true) {
return const_cast<Instruction *>(
static_cast<const BasicBlock *>(this)->getFirstNonPHIOrDbg(
SkipPseudoOp));
}
/// Returns a pointer to the first instruction in this block that is not a
/// PHINode, a debug intrinsic, or a lifetime intrinsic, or any pseudo
/// operation if \c SkipPseudoOp is true.
const Instruction *
getFirstNonPHIOrDbgOrLifetime(bool SkipPseudoOp = true) const;
Instruction *getFirstNonPHIOrDbgOrLifetime(bool SkipPseudoOp = true) {
return const_cast<Instruction *>(
static_cast<const BasicBlock *>(this)->getFirstNonPHIOrDbgOrLifetime(
SkipPseudoOp));
}
/// 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.
const_iterator getFirstInsertionPt() const;
iterator getFirstInsertionPt() {
return static_cast<const BasicBlock *>(this)
->getFirstInsertionPt().getNonConst();
}
/// Returns an iterator to the first instruction in this block that is
/// not a PHINode, a debug intrinsic, a static alloca or any pseudo operation.
const_iterator getFirstNonPHIOrDbgOrAlloca() const;
iterator getFirstNonPHIOrDbgOrAlloca() {
return static_cast<const BasicBlock *>(this)
->getFirstNonPHIOrDbgOrAlloca()
.getNonConst();
}
/// Return a const iterator range over the instructions in the block, skipping
/// any debug instructions. Skip any pseudo operations as well if \c
/// SkipPseudoOp is true.
iterator_range<filter_iterator<BasicBlock::const_iterator,
std::function<bool(const Instruction &)>>>
instructionsWithoutDebug(bool SkipPseudoOp = true) const;
/// Return an iterator range over the instructions in the block, skipping any
/// debug instructions. Skip and any pseudo operations as well if \c
/// SkipPseudoOp is true.
iterator_range<
filter_iterator<BasicBlock::iterator, std::function<bool(Instruction &)>>>
instructionsWithoutDebug(bool SkipPseudoOp = true);
/// Return the size of the basic block ignoring debug instructions
filter_iterator<BasicBlock::const_iterator,
std::function<bool(const Instruction &)>>::difference_type
sizeWithoutDebug() const;
/// Unlink 'this' from the containing function, but do not delete it.
void removeFromParent();
/// Unlink 'this' from the containing function and delete it.
///
// \returns an iterator pointing to the element after the erased one.
SymbolTableList<BasicBlock>::iterator eraseFromParent();
/// 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);
/// 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);
/// Insert unlinked basic block into a function.
///
/// Inserts an unlinked basic block into \c Parent. If \c InsertBefore is
/// provided, inserts before that basic block, otherwise inserts at the end.
///
/// \pre \a getParent() is \c nullptr.
void insertInto(Function *Parent, BasicBlock *InsertBefore = nullptr);
/// Return the predecessor of this block if it has a single predecessor
/// block. Otherwise return a null pointer.
const BasicBlock *getSinglePredecessor() const;
BasicBlock *getSinglePredecessor() {
return const_cast<BasicBlock *>(
static_cast<const BasicBlock *>(this)->getSinglePredecessor());
}
/// 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).
const BasicBlock *getUniquePredecessor() const;
BasicBlock *getUniquePredecessor() {
return const_cast<BasicBlock *>(
static_cast<const BasicBlock *>(this)->getUniquePredecessor());
}
/// Return true if this block has exactly N predecessors.
bool hasNPredecessors(unsigned N) const;
/// Return true if this block has N predecessors or more.
bool hasNPredecessorsOrMore(unsigned N) const;
/// Return the successor of this block if it has a single successor.
/// Otherwise return a null pointer.
///
/// This method is analogous to getSinglePredecessor above.
const BasicBlock *getSingleSuccessor() const;
BasicBlock *getSingleSuccessor() {
return const_cast<BasicBlock *>(
static_cast<const BasicBlock *>(this)->getSingleSuccessor());
}
/// Return the successor of this block if it has a unique successor.
/// Otherwise return a null pointer.
///
/// This method is analogous to getUniquePredecessor above.
const BasicBlock *getUniqueSuccessor() const;
BasicBlock *getUniqueSuccessor() {
return const_cast<BasicBlock *>(
static_cast<const BasicBlock *>(this)->getUniqueSuccessor());
}
/// Print the basic block to an output stream with an optional
/// AssemblyAnnotationWriter.
void print(raw_ostream &OS, AssemblyAnnotationWriter *AAW = nullptr,
bool ShouldPreserveUseListOrder = false,
bool IsForDebug = false) const;
//===--------------------------------------------------------------------===//
/// 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(); }
/// Iterator to walk just the phi nodes in the basic block.
template <typename PHINodeT = PHINode, typename BBIteratorT = iterator>
class phi_iterator_impl
: public iterator_facade_base<phi_iterator_impl<PHINodeT, BBIteratorT>,
std::forward_iterator_tag, PHINodeT> {
friend BasicBlock;
PHINodeT *PN;
phi_iterator_impl(PHINodeT *PN) : PN(PN) {}
public:
// Allow default construction to build variables, but this doesn't build
// a useful iterator.
phi_iterator_impl() = default;
// Allow conversion between instantiations where valid.
template <typename PHINodeU, typename BBIteratorU,
typename = std::enable_if_t<
std::is_convertible<PHINodeU *, PHINodeT *>::value>>
phi_iterator_impl(const phi_iterator_impl<PHINodeU, BBIteratorU> &Arg)
: PN(Arg.PN) {}
bool operator==(const phi_iterator_impl &Arg) const { return PN == Arg.PN; }
PHINodeT &operator*() const { return *PN; }
using phi_iterator_impl::iterator_facade_base::operator++;
phi_iterator_impl &operator++() {
assert(PN && "Cannot increment the end iterator!");
PN = dyn_cast<PHINodeT>(std::next(BBIteratorT(PN)));
return *this;
}
};
using phi_iterator = phi_iterator_impl<>;
using const_phi_iterator =
phi_iterator_impl<const PHINode, BasicBlock::const_iterator>;
/// Returns a range that iterates over the phis in the basic block.
///
/// Note that this cannot be used with basic blocks that have no terminator.
iterator_range<const_phi_iterator> phis() const {
return const_cast<BasicBlock *>(this)->phis();
}
iterator_range<phi_iterator> phis();
private:
/// Return the underlying instruction list container.
/// This is deliberately private because we have implemented an adequate set
/// of functions to modify the list, including BasicBlock::splice(),
/// BasicBlock::erase(), Instruction::insertInto() etc.
const InstListType &getInstList() const { return InstList; }
InstListType &getInstList() { return InstList; }
/// Returns a pointer to a member of the instruction list.
/// This is private on purpose, just like `getInstList()`.
static InstListType BasicBlock::*getSublistAccess(Instruction *) {
return &BasicBlock::InstList;
}
public:
/// Returns a pointer to the symbol table if one exists.
ValueSymbolTable *getValueSymbolTable();
/// Methods for support type inquiry through isa, cast, and dyn_cast.
static bool classof(const Value *V) {
return V->getValueID() == Value::BasicBlockVal;
}
/// 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();
/// Update PHI nodes in this BasicBlock before removal of predecessor \p Pred.
/// Note that this function does not actually remove the predecessor.
///
/// If \p KeepOneInputPHIs is true then don't remove PHIs that are left with
/// zero or one incoming values, and don't simplify PHIs with all incoming
/// values the same.
void removePredecessor(BasicBlock *Pred, bool KeepOneInputPHIs = false);
bool canSplitPredecessors() const;
/// Split the basic block into two basic blocks at the specified instruction.
///
/// If \p Before is true, splitBasicBlockBefore handles the
/// block splitting. Otherwise, execution proceeds as described below.
///
/// 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 basic block
/// is returned. This function invalidates the specified iterator.
///
/// Note that this only works on well formed basic blocks (must have a
/// terminator), and \p '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 = "",
bool Before = false);
BasicBlock *splitBasicBlock(Instruction *I, const Twine &BBName = "",
bool Before = false) {
return splitBasicBlock(I->getIterator(), BBName, Before);
}
/// Split the basic block into two basic blocks at the specified instruction
/// and insert the new basic blocks as the predecessor of the current block.
///
/// This function ensures all instructions AFTER and including the specified
/// iterator \p I are part of the original basic block. All Instructions
/// BEFORE the iterator \p I are moved to the new BB and an unconditional
/// branch is added to the new BB. The new basic block is returned.
///
/// Note that this only works on well formed basic blocks (must have a
/// terminator), and \p '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). \p 'I' cannot be a iterator for a PHINode
/// with multiple incoming blocks.
///
/// Also note that this doesn't preserve any passes. To split blocks while
/// keeping loop information consistent, use the SplitBlockBefore utility
/// function.
BasicBlock *splitBasicBlockBefore(iterator I, const Twine &BBName = "");
BasicBlock *splitBasicBlockBefore(Instruction *I, const Twine &BBName = "") {
return splitBasicBlockBefore(I->getIterator(), BBName);
}
/// Transfer all instructions from \p FromBB to this basic block at \p ToIt.
void splice(BasicBlock::iterator ToIt, BasicBlock *FromBB) {
splice(ToIt, FromBB, FromBB->begin(), FromBB->end());
}
/// Transfer one instruction from \p FromBB at \p FromIt to this basic block
/// at \p ToIt.
void splice(BasicBlock::iterator ToIt, BasicBlock *FromBB,
BasicBlock::iterator FromIt) {
auto FromItNext = std::next(FromIt);
// Single-element splice is a noop if destination == source.
if (ToIt == FromIt || ToIt == FromItNext)
return;
splice(ToIt, FromBB, FromIt, FromItNext);
}
/// Transfer a range of instructions that belong to \p FromBB from \p
/// FromBeginIt to \p FromEndIt, to this basic block at \p ToIt.
void splice(BasicBlock::iterator ToIt, BasicBlock *FromBB,
BasicBlock::iterator FromBeginIt,
BasicBlock::iterator FromEndIt);
/// Erases a range of instructions from \p FromIt to (not including) \p ToIt.
/// \Returns \p ToIt.
BasicBlock::iterator erase(BasicBlock::iterator FromIt, BasicBlock::iterator ToIt);
/// Returns true if there are any uses of this basic block other than
/// direct branches, switches, etc. to it.
bool hasAddressTaken() const {
return getBasicBlockBits().BlockAddressRefCount != 0;
}
/// Update all phi nodes in this basic block to refer to basic block \p New
/// instead of basic block \p Old.
void replacePhiUsesWith(BasicBlock *Old, BasicBlock *New);
/// Update all phi nodes in this basic block's successors to refer to basic
/// block \p New instead of basic block \p Old.
void replaceSuccessorsPhiUsesWith(BasicBlock *Old, BasicBlock *New);
/// 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);
/// Return true if this basic block is an exception handling block.
bool isEHPad() const { return getFirstNonPHI()->isEHPad(); }
/// 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;
/// Return the landingpad instruction associated with the landing pad.
const LandingPadInst *getLandingPadInst() const;
LandingPadInst *getLandingPadInst() {
return const_cast<LandingPadInst *>(
static_cast<const BasicBlock *>(this)->getLandingPadInst());
}
/// Return true if it is legal to hoist instructions into this block.
bool isLegalToHoistInto() const;
/// Return true if this is the entry block of the containing function.
/// This method can only be used on blocks that have a parent function.
bool isEntryBlock() const;
std::optional<uint64_t> getIrrLoopHeaderWeight() const;
/// Returns true if the Order field of child Instructions is valid.
bool isInstrOrderValid() const {
return getBasicBlockBits().InstrOrderValid;
}
/// Mark instruction ordering invalid. Done on every instruction insert.
void invalidateOrders() {
validateInstrOrdering();
BasicBlockBits Bits = getBasicBlockBits();
Bits.InstrOrderValid = false;
setBasicBlockBits(Bits);
}
/// Renumber instructions and mark the ordering as valid.
void renumberInstructions();
/// Asserts that instruction order numbers are marked invalid, or that they
/// are in ascending order. This is constant time if the ordering is invalid,
/// and linear in the number of instructions if the ordering is valid. Callers
/// should be careful not to call this in ways that make common operations
/// O(n^2). For example, it takes O(n) time to assign order numbers to
/// instructions, so the order should be validated no more than once after
/// each ordering to ensure that transforms have the same algorithmic
/// complexity when asserts are enabled as when they are disabled.
void validateInstrOrdering() const;
private:
#if defined(_AIX) && (!defined(__GNUC__) || defined(__clang__))
// Except for GCC; by default, AIX compilers store bit-fields in 4-byte words
// and give the `pack` pragma push semantics.
#define BEGIN_TWO_BYTE_PACK() _Pragma("pack(2)")
#define END_TWO_BYTE_PACK() _Pragma("pack(pop)")
#else
#define BEGIN_TWO_BYTE_PACK()
#define END_TWO_BYTE_PACK()
#endif
BEGIN_TWO_BYTE_PACK()
/// Bitfield to help interpret the bits in Value::SubclassData.
struct BasicBlockBits {
unsigned short BlockAddressRefCount : 15;
unsigned short InstrOrderValid : 1;
};
END_TWO_BYTE_PACK()
#undef BEGIN_TWO_BYTE_PACK
#undef END_TWO_BYTE_PACK
/// Safely reinterpret the subclass data bits to a more useful form.
BasicBlockBits getBasicBlockBits() const {
static_assert(sizeof(BasicBlockBits) == sizeof(unsigned short),
"too many bits for Value::SubclassData");
unsigned short ValueData = getSubclassDataFromValue();
BasicBlockBits AsBits;
memcpy(&AsBits, &ValueData, sizeof(AsBits));
return AsBits;
}
/// Reinterpret our subclass bits and store them back into Value.
void setBasicBlockBits(BasicBlockBits AsBits) {
unsigned short D;
memcpy(&D, &AsBits, sizeof(D));
Value::setValueSubclassData(D);
}
/// 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) {
BasicBlockBits Bits = getBasicBlockBits();
Bits.BlockAddressRefCount += Amt;
setBasicBlockBits(Bits);
assert(Bits.BlockAddressRefCount < 255 && "Refcount wrap-around");
}
/// Shadow Value::setValueSubclassData with a private forwarding method so
/// that any future subclasses cannot accidentally use it.
void setValueSubclassData(unsigned short D) {
Value::setValueSubclassData(D);
}
};
// Create wrappers for C Binding types (see CBindingWrapping.h).
DEFINE_SIMPLE_CONVERSION_FUNCTIONS(BasicBlock, LLVMBasicBlockRef)
/// Advance \p It while it points to a debug instruction and return the result.
/// This assumes that \p It is not at the end of a block.
BasicBlock::iterator skipDebugIntrinsics(BasicBlock::iterator It);
#ifdef NDEBUG
/// In release builds, this is a no-op. For !NDEBUG builds, the checks are
/// implemented in the .cpp file to avoid circular header deps.
inline void BasicBlock::validateInstrOrdering() const {}
#endif
} // end namespace llvm
#endif // LLVM_IR_BASICBLOCK_H