//===-- BasicBlock.cpp - Implement BasicBlock related methods -------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the BasicBlock class for the IR library.
//
//===----------------------------------------------------------------------===//
#include "llvm/IR/BasicBlock.h"
#include "SymbolTableListTraitsImpl.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Type.h"
#include <algorithm>
using namespace llvm;
ValueSymbolTable *BasicBlock::getValueSymbolTable() {
if (Function *F = getParent())
return &F->getValueSymbolTable();
return nullptr;
}
LLVMContext &BasicBlock::getContext() const {
return getType()->getContext();
}
// Explicit instantiation of SymbolTableListTraits since some of the methods
// are not in the public header file...
template class llvm::SymbolTableListTraits<Instruction, BasicBlock>;
BasicBlock::BasicBlock(LLVMContext &C, const Twine &Name, Function *NewParent,
BasicBlock *InsertBefore)
: Value(Type::getLabelTy(C), Value::BasicBlockVal), Parent(nullptr) {
if (NewParent)
insertInto(NewParent, InsertBefore);
else
assert(!InsertBefore &&
"Cannot insert block before another block with no function!");
setName(Name);
}
void BasicBlock::insertInto(Function *NewParent, BasicBlock *InsertBefore) {
assert(NewParent && "Expected a parent");
assert(!Parent && "Already has a parent");
if (InsertBefore)
NewParent->getBasicBlockList().insert(InsertBefore, this);
else
NewParent->getBasicBlockList().push_back(this);
}
BasicBlock::~BasicBlock() {
// If the address of the block is taken and it is being deleted (e.g. because
// it is dead), this means that there is either a dangling constant expr
// hanging off the block, or an undefined use of the block (source code
// expecting the address of a label to keep the block alive even though there
// is no indirect branch). Handle these cases by zapping the BlockAddress
// nodes. There are no other possible uses at this point.
if (hasAddressTaken()) {
assert(!use_empty() && "There should be at least one blockaddress!");
Constant *Replacement =
ConstantInt::get(llvm::Type::getInt32Ty(getContext()), 1);
while (!use_empty()) {
BlockAddress *BA = cast<BlockAddress>(user_back());
BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
BA->getType()));
BA->destroyConstant();
}
}
assert(getParent() == nullptr && "BasicBlock still linked into the program!");
dropAllReferences();
InstList.clear();
}
void BasicBlock::setParent(Function *parent) {
// Set Parent=parent, updating instruction symtab entries as appropriate.
InstList.setSymTabObject(&Parent, parent);
}
void BasicBlock::removeFromParent() {
getParent()->getBasicBlockList().remove(this);
}
iplist<BasicBlock>::iterator BasicBlock::eraseFromParent() {
return getParent()->getBasicBlockList().erase(this);
}
/// 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) {
MovePos->getParent()->getBasicBlockList().splice(MovePos,
getParent()->getBasicBlockList(), this);
}
/// 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;
MovePos->getParent()->getBasicBlockList().splice(++I,
getParent()->getBasicBlockList(), this);
}
const Module *BasicBlock::getModule() const {
return getParent()->getParent();
}
TerminatorInst *BasicBlock::getTerminator() {
if (InstList.empty()) return nullptr;
return dyn_cast<TerminatorInst>(&InstList.back());
}
const TerminatorInst *BasicBlock::getTerminator() const {
if (InstList.empty()) return nullptr;
return dyn_cast<TerminatorInst>(&InstList.back());
}
CallInst *BasicBlock::getTerminatingMustTailCall() {
if (InstList.empty())
return nullptr;
ReturnInst *RI = dyn_cast<ReturnInst>(&InstList.back());
if (!RI || RI == &InstList.front())
return nullptr;
Instruction *Prev = RI->getPrevNode();
if (!Prev)
return nullptr;
if (Value *RV = RI->getReturnValue()) {
if (RV != Prev)
return nullptr;
// Look through the optional bitcast.
if (auto *BI = dyn_cast<BitCastInst>(Prev)) {
RV = BI->getOperand(0);
Prev = BI->getPrevNode();
if (!Prev || RV != Prev)
return nullptr;
}
}
if (auto *CI = dyn_cast<CallInst>(Prev)) {
if (CI->isMustTailCall())
return CI;
}
return nullptr;
}
Instruction* BasicBlock::getFirstNonPHI() {
BasicBlock::iterator i = begin();
// All valid basic blocks should have a terminator,
// which is not a PHINode. If we have an invalid basic
// block we'll get an assertion failure when dereferencing
// a past-the-end iterator.
while (isa<PHINode>(i)) ++i;
return &*i;
}
Instruction* BasicBlock::getFirstNonPHIOrDbg() {
BasicBlock::iterator i = begin();
// All valid basic blocks should have a terminator,
// which is not a PHINode. If we have an invalid basic
// block we'll get an assertion failure when dereferencing
// a past-the-end iterator.
while (isa<PHINode>(i) || isa<DbgInfoIntrinsic>(i)) ++i;
return &*i;
}
Instruction* BasicBlock::getFirstNonPHIOrDbgOrLifetime() {
// All valid basic blocks should have a terminator,
// which is not a PHINode. If we have an invalid basic
// block we'll get an assertion failure when dereferencing
// a past-the-end iterator.
BasicBlock::iterator i = begin();
for (;; ++i) {
if (isa<PHINode>(i) || isa<DbgInfoIntrinsic>(i))
continue;
const IntrinsicInst *II = dyn_cast<IntrinsicInst>(i);
if (!II)
break;
if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
II->getIntrinsicID() != Intrinsic::lifetime_end)
break;
}
return &*i;
}
BasicBlock::iterator BasicBlock::getFirstInsertionPt() {
iterator InsertPt = getFirstNonPHI();
if (isa<LandingPadInst>(InsertPt)) ++InsertPt;
return InsertPt;
}
void BasicBlock::dropAllReferences() {
for(iterator I = begin(), E = end(); I != E; ++I)
I->dropAllReferences();
}
/// 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 nullptr; // No preds.
BasicBlock *ThePred = *PI;
++PI;
return (PI == E) ? ThePred : nullptr /*multiple preds*/;
}
/// If this basic block has a unique predecessor block,
/// return the 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 *BasicBlock::getUniquePredecessor() {
pred_iterator PI = pred_begin(this), E = pred_end(this);
if (PI == E) return nullptr; // No preds.
BasicBlock *PredBB = *PI;
++PI;
for (;PI != E; ++PI) {
if (*PI != PredBB)
return nullptr;
// The same predecessor appears multiple times in the predecessor list.
// This is OK.
}
return PredBB;
}
BasicBlock *BasicBlock::getUniqueSuccessor() {
succ_iterator SI = succ_begin(this), E = succ_end(this);
if (SI == E) return NULL; // No successors
BasicBlock *SuccBB = *SI;
++SI;
for (;SI != E; ++SI) {
if (*SI != SuccBB)
return NULL;
// The same successor appears multiple times in the successor list.
// This is OK.
}
return SuccBB;
}
/// 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->getIncomingValue(0) != PN)
PN->replaceAllUsesWith(PN->getIncomingValue(0));
else
// We are left with an infinite loop with no entries: kill the PHI.
PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
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)); ) {
++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 = nullptr;
if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue()))
if (PNV != PN) {
PN->replaceAllUsesWith(PNV);
PN->eraseFromParent();
}
}
}
}
/// 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 Twine &BBName) {
assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
assert(I != InstList.end() &&
"Trying to get me to create degenerate basic block!");
BasicBlock *InsertBefore = std::next(Function::iterator(this))
.getNodePtrUnchecked();
BasicBlock *New = BasicBlock::Create(getContext(), BBName,
getParent(), InsertBefore);
// 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.
BranchInst::Create(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;
}
void BasicBlock::replaceSuccessorsPhiUsesWith(BasicBlock *New) {
TerminatorInst *TI = getTerminator();
if (!TI)
// Cope with being called on a BasicBlock that doesn't have a terminator
// yet. Clang's CodeGenFunction::EmitReturnBlock() likes to do this.
return;
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
BasicBlock *Succ = TI->getSuccessor(i);
// N.B. Succ might not be a complete BasicBlock, so don't assume
// that it ends with a non-phi instruction.
for (iterator II = Succ->begin(), IE = Succ->end(); II != IE; ++II) {
PHINode *PN = dyn_cast<PHINode>(II);
if (!PN)
break;
int i;
while ((i = PN->getBasicBlockIndex(this)) >= 0)
PN->setIncomingBlock(i, New);
}
}
}
/// Return true if this basic block is a landing pad. I.e., it's
/// the destination of the 'unwind' edge of an invoke instruction.
bool BasicBlock::isLandingPad() const {
return isa<LandingPadInst>(getFirstNonPHI());
}
/// Return the landingpad instruction associated with the landing pad.
LandingPadInst *BasicBlock::getLandingPadInst() {
return dyn_cast<LandingPadInst>(getFirstNonPHI());
}
const LandingPadInst *BasicBlock::getLandingPadInst() const {
return dyn_cast<LandingPadInst>(getFirstNonPHI());
}