1 //===-- BasicBlock.cpp - Implement BasicBlock related methods -------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the BasicBlock class for the VMCore library.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/BasicBlock.h"
15 #include "llvm/Constants.h"
16 #include "llvm/Instructions.h"
17 #include "llvm/Type.h"
18 #include "llvm/Support/CFG.h"
19 #include "llvm/Support/LeakDetector.h"
20 #include "SymbolTableListTraitsImpl.h"
25 /// DummyInst - An instance of this class is used to mark the end of the
26 /// instruction list. This is not a real instruction.
27 struct DummyInst : public Instruction {
28 DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd, 0, 0) {
29 // This should not be garbage monitored.
30 LeakDetector::removeGarbageObject(this);
33 virtual Instruction *clone() const {
34 assert(0 && "Cannot clone EOL");abort();
37 virtual const char *getOpcodeName() const { return "*end-of-list-inst*"; }
39 // Methods for support type inquiry through isa, cast, and dyn_cast...
40 static inline bool classof(const DummyInst *) { return true; }
41 static inline bool classof(const Instruction *I) {
42 return I->getOpcode() == OtherOpsEnd;
44 static inline bool classof(const Value *V) {
45 return isa<Instruction>(V) && classof(cast<Instruction>(V));
50 Instruction *ilist_traits<Instruction>::createSentinel() {
51 return new DummyInst();
53 iplist<Instruction> &ilist_traits<Instruction>::getList(BasicBlock *BB) {
54 return BB->getInstList();
57 // Explicit instantiation of SymbolTableListTraits since some of the methods
58 // are not in the public header file...
59 template class SymbolTableListTraits<Instruction, BasicBlock, Function>;
62 BasicBlock::BasicBlock(const std::string &Name, Function *Parent,
63 BasicBlock *InsertBefore)
64 : Value(Type::LabelTy, Value::BasicBlockVal, Name) {
65 // Initialize the instlist...
66 InstList.setItemParent(this);
68 // Make sure that we get added to a function
69 LeakDetector::addGarbageObject(this);
73 "Cannot insert block before another block with no function!");
74 Parent->getBasicBlockList().insert(InsertBefore, this);
76 Parent->getBasicBlockList().push_back(this);
81 BasicBlock::~BasicBlock() {
82 assert(getParent() == 0 && "BasicBlock still linked into the program!");
87 void BasicBlock::setParent(Function *parent) {
89 LeakDetector::addGarbageObject(this);
91 InstList.setParent(parent);
94 LeakDetector::removeGarbageObject(this);
97 void BasicBlock::removeFromParent() {
98 getParent()->getBasicBlockList().remove(this);
101 void BasicBlock::eraseFromParent() {
102 getParent()->getBasicBlockList().erase(this);
105 /// moveBefore - Unlink this instruction from its current function and
106 /// insert it into the function that MovePos lives in, right before
108 void BasicBlock::moveBefore(BasicBlock *MovePos) {
109 MovePos->getParent()->getBasicBlockList().splice(MovePos,
110 getParent()->getBasicBlockList(), this);
114 TerminatorInst *BasicBlock::getTerminator() {
115 if (InstList.empty()) return 0;
116 return dyn_cast<TerminatorInst>(&InstList.back());
119 const TerminatorInst *const BasicBlock::getTerminator() const {
120 if (InstList.empty()) return 0;
121 return dyn_cast<TerminatorInst>(&InstList.back());
124 void BasicBlock::dropAllReferences() {
125 for(iterator I = begin(), E = end(); I != E; ++I)
126 I->dropAllReferences();
129 /// getSinglePredecessor - If this basic block has a single predecessor block,
130 /// return the block, otherwise return a null pointer.
131 BasicBlock *BasicBlock::getSinglePredecessor() {
132 pred_iterator PI = pred_begin(this), E = pred_end(this);
133 if (PI == E) return 0; // No preds.
134 BasicBlock *ThePred = *PI;
136 return (PI == E) ? ThePred : 0 /*multiple preds*/;
139 /// removePredecessor - This method is used to notify a BasicBlock that the
140 /// specified Predecessor of the block is no longer able to reach it. This is
141 /// actually not used to update the Predecessor list, but is actually used to
142 /// update the PHI nodes that reside in the block. Note that this should be
143 /// called while the predecessor still refers to this block.
145 void BasicBlock::removePredecessor(BasicBlock *Pred,
146 bool DontDeleteUselessPHIs) {
147 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
148 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
149 "removePredecessor: BB is not a predecessor!");
151 if (InstList.empty()) return;
152 PHINode *APN = dyn_cast<PHINode>(&front());
153 if (!APN) return; // Quick exit.
155 // If there are exactly two predecessors, then we want to nuke the PHI nodes
156 // altogether. However, we cannot do this, if this in this case:
159 // %x = phi [X, Loop]
160 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
161 // br Loop ;; %x2 does not dominate all uses
163 // This is because the PHI node input is actually taken from the predecessor
164 // basic block. The only case this can happen is with a self loop, so we
165 // check for this case explicitly now.
167 unsigned max_idx = APN->getNumIncomingValues();
168 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
170 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
172 // Disable PHI elimination!
173 if (this == Other) max_idx = 3;
176 // <= Two predecessors BEFORE I remove one?
177 if (max_idx <= 2 && !DontDeleteUselessPHIs) {
178 // Yup, loop through and nuke the PHI nodes
179 while (PHINode *PN = dyn_cast<PHINode>(&front())) {
180 // Remove the predecessor first.
181 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
183 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
185 if (PN->getOperand(0) != PN)
186 PN->replaceAllUsesWith(PN->getOperand(0));
188 // We are left with an infinite loop with no entries: kill the PHI.
189 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
190 getInstList().pop_front(); // Remove the PHI node
193 // If the PHI node already only had one entry, it got deleted by
194 // removeIncomingValue.
197 // Okay, now we know that we need to remove predecessor #pred_idx from all
198 // PHI nodes. Iterate over each PHI node fixing them up
200 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
202 PN->removeIncomingValue(Pred, false);
203 // If all incoming values to the Phi are the same, we can replace the Phi
205 if (Value *PNV = PN->hasConstantValue()) {
206 PN->replaceAllUsesWith(PNV);
207 PN->eraseFromParent();
214 /// splitBasicBlock - This splits a basic block into two at the specified
215 /// instruction. Note that all instructions BEFORE the specified iterator stay
216 /// as part of the original basic block, an unconditional branch is added to
217 /// the new BB, and the rest of the instructions in the BB are moved to the new
218 /// BB, including the old terminator. This invalidates the iterator.
220 /// Note that this only works on well formed basic blocks (must have a
221 /// terminator), and 'I' must not be the end of instruction list (which would
222 /// cause a degenerate basic block to be formed, having a terminator inside of
223 /// the basic block).
225 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) {
226 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
227 assert(I != InstList.end() &&
228 "Trying to get me to create degenerate basic block!");
230 BasicBlock *New = new BasicBlock(BBName, getParent(), getNext());
232 // Move all of the specified instructions from the original basic block into
233 // the new basic block.
234 New->getInstList().splice(New->end(), this->getInstList(), I, end());
236 // Add a branch instruction to the newly formed basic block.
237 new BranchInst(New, this);
239 // Now we must loop through all of the successors of the New block (which
240 // _were_ the successors of the 'this' block), and update any PHI nodes in
241 // successors. If there were PHI nodes in the successors, then they need to
242 // know that incoming branches will be from New, not from Old.
244 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
245 // Loop over any phi nodes in the basic block, updating the BB field of
246 // incoming values...
247 BasicBlock *Successor = *I;
249 for (BasicBlock::iterator II = Successor->begin();
250 (PN = dyn_cast<PHINode>(II)); ++II) {
251 int IDX = PN->getBasicBlockIndex(this);
253 PN->setIncomingBlock((unsigned)IDX, New);
254 IDX = PN->getBasicBlockIndex(this);