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//===-- BasicBlock.cpp - Implement BasicBlock related methods -------------===//
// The LLVM Compiler Infrastructure
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
// This file implements the BasicBlock class for the VMCore library.
#include "llvm/BasicBlock.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Type.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/LeakDetector.h"
#include "llvm/Support/Compiler.h"
#include "SymbolTableListTraitsImpl.h"
#include <algorithm>
using namespace llvm;
inline ValueSymbolTable *
ilist_traits<Instruction>::getSymTab(BasicBlock *BB) {
if (BB)
if (Function *F = BB->getParent())
return &F->getValueSymbolTable();
return 0;
namespace {
/// DummyInst - An instance of this class is used to mark the end of the
/// instruction list. This is not a real instruction.
struct VISIBILITY_HIDDEN DummyInst : public Instruction {
DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd, 0, 0) {
// This should not be garbage monitored.
Instruction *clone() const {
assert(0 && "Cannot clone EOL");abort();
return 0;
const char *getOpcodeName() const { return "*end-of-list-inst*"; }
// Methods for support type inquiry through isa, cast, and dyn_cast...
static inline bool classof(const DummyInst *) { return true; }
static inline bool classof(const Instruction *I) {
return I->getOpcode() == OtherOpsEnd;
static inline bool classof(const Value *V) {
return isa<Instruction>(V) && classof(cast<Instruction>(V));
Instruction *ilist_traits<Instruction>::createSentinel() {
return new DummyInst();
iplist<Instruction> &ilist_traits<Instruction>::getList(BasicBlock *BB) {
return BB->getInstList();
// Explicit instantiation of SymbolTableListTraits since some of the methods
// are not in the public header file...
template class SymbolTableListTraits<Instruction, BasicBlock>;
BasicBlock::BasicBlock(const std::string &Name, Function *NewParent,
BasicBlock *InsertBefore)
: Value(Type::LabelTy, Value::BasicBlockVal), Parent(0) {
// Make sure that we get added to a function
if (InsertBefore) {
assert(NewParent &&
"Cannot insert block before another block with no function!");
NewParent->getBasicBlockList().insert(InsertBefore, this);
} else if (NewParent) {
BasicBlock::~BasicBlock() {
assert(getParent() == 0 && "BasicBlock still linked into the program!");
void BasicBlock::setParent(Function *parent) {
if (getParent())
// Set Parent=parent, updating instruction symtab entries as appropriate.
InstList.setSymTabObject(&Parent, parent);
if (getParent())
void BasicBlock::removeFromParent() {
void BasicBlock::eraseFromParent() {
/// moveBefore - Unlink this basic block from its current function and
/// insert it into the function that MovePos lives in, right before MovePos.
void BasicBlock::moveBefore(BasicBlock *MovePos) {
getParent()->getBasicBlockList(), this);
/// moveAfter - Unlink this basic block from its current function and
/// insert it into the function that MovePos lives in, right after MovePos.
void BasicBlock::moveAfter(BasicBlock *MovePos) {
Function::iterator I = MovePos;
getParent()->getBasicBlockList(), this);
TerminatorInst *BasicBlock::getTerminator() {
if (InstList.empty()) return 0;
return dyn_cast<TerminatorInst>(&InstList.back());
const TerminatorInst *const BasicBlock::getTerminator() const {
if (InstList.empty()) return 0;
return dyn_cast<TerminatorInst>(&InstList.back());
Instruction* BasicBlock::getFirstNonPHI()
BasicBlock::iterator i = begin();
// All valid basic blocks should have a terminator,
// which is not a PHINode. If we have invalid basic
// block we'll get assert when dereferencing past-the-end
// iterator.
while (isa<PHINode>(i)) ++i;
return &*i;
void BasicBlock::dropAllReferences() {
for(iterator I = begin(), E = end(); I != E; ++I)
/// getSinglePredecessor - If this basic block has a single predecessor block,
/// return the block, otherwise return a null pointer.
BasicBlock *BasicBlock::getSinglePredecessor() {
pred_iterator PI = pred_begin(this), E = pred_end(this);
if (PI == E) return 0; // No preds.
BasicBlock *ThePred = *PI;
return (PI == E) ? ThePred : 0 /*multiple preds*/;
/// removePredecessor - This method is used to notify a BasicBlock that the
/// specified Predecessor of the block 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 BasicBlock::removePredecessor(BasicBlock *Pred,
bool DontDeleteUselessPHIs) {
assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
"removePredecessor: BB is not a predecessor!");
if (InstList.empty()) return;
PHINode *APN = dyn_cast<PHINode>(&front());
if (!APN) return; // Quick exit.
// If there are exactly two predecessors, then we want to nuke the PHI nodes
// altogether. However, we cannot do this, if this in this case:
// Loop:
// %x = phi [X, Loop]
// %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
// br Loop ;; %x2 does not dominate all uses
// This is because the PHI node input is actually taken from the predecessor
// basic block. The only case this can happen is with a self loop, so we
// check for this case explicitly now.
unsigned max_idx = APN->getNumIncomingValues();
assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
if (max_idx == 2) {
BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
// Disable PHI elimination!
if (this == Other) max_idx = 3;
// <= Two predecessors BEFORE I remove one?
if (max_idx <= 2 && !DontDeleteUselessPHIs) {
// Yup, loop through and nuke the PHI nodes
while (PHINode *PN = dyn_cast<PHINode>(&front())) {
// Remove the predecessor first.
PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
// If the PHI _HAD_ two uses, replace PHI node with its now *single* value
if (max_idx == 2) {
if (PN->getOperand(0) != PN)
// We are left with an infinite loop with no entries: kill the PHI.
getInstList().pop_front(); // Remove the PHI node
// If the PHI node already only had one entry, it got deleted by
// removeIncomingValue.
} else {
// Okay, now we know that we need to remove predecessor #pred_idx from all
// PHI nodes. Iterate over each PHI node fixing them up
PHINode *PN;
for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
PN->removeIncomingValue(Pred, false);
// If all incoming values to the Phi are the same, we can replace the Phi
// with that value.
Value* PNV = 0;
if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue())) {
/// splitBasicBlock - This splits a basic block into two 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 new BB, and the rest of the instructions in the BB are moved to the new
/// BB, including the old terminator. This invalidates the 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).
BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) {
assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
assert(I != InstList.end() &&
"Trying to get me to create degenerate basic block!");
BasicBlock *New = new BasicBlock(BBName, getParent(), getNext());
// Move all of the specified instructions from the original basic block into
// the new basic block.
New->getInstList().splice(New->end(), this->getInstList(), I, end());
// Add a branch instruction to the newly formed basic block.
new BranchInst(New, this);
// Now we must loop through all of the successors of the New block (which
// _were_ the successors of the 'this' block), and update any PHI nodes in
// successors. If there were PHI nodes in the successors, then they need to
// know that incoming branches will be from New, not from Old.
for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
// Loop over any phi nodes in the basic block, updating the BB field of
// incoming values...
BasicBlock *Successor = *I;
PHINode *PN;
for (BasicBlock::iterator II = Successor->begin();
(PN = dyn_cast<PHINode>(II)); ++II) {
int IDX = PN->getBasicBlockIndex(this);
while (IDX != -1) {
PN->setIncomingBlock((unsigned)IDX, New);
IDX = PN->getBasicBlockIndex(this);
return New;