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);
106 TerminatorInst *BasicBlock::getTerminator() {
107 if (InstList.empty()) return 0;
108 return dyn_cast<TerminatorInst>(&InstList.back());
111 const TerminatorInst *const BasicBlock::getTerminator() const {
112 if (InstList.empty()) return 0;
113 return dyn_cast<TerminatorInst>(&InstList.back());
116 void BasicBlock::dropAllReferences() {
117 for(iterator I = begin(), E = end(); I != E; ++I)
118 I->dropAllReferences();
121 /// getSinglePredecessor - If this basic block has a single predecessor block,
122 /// return the block, otherwise return a null pointer.
123 BasicBlock *BasicBlock::getSinglePredecessor() {
124 pred_iterator PI = pred_begin(this), E = pred_end(this);
125 if (PI == E) return 0; // No preds.
126 BasicBlock *ThePred = *PI;
128 return (PI == E) ? ThePred : 0 /*multiple preds*/;
131 /// removePredecessor - This method is used to notify a BasicBlock that the
132 /// specified Predecessor of the block is no longer able to reach it. This is
133 /// actually not used to update the Predecessor list, but is actually used to
134 /// update the PHI nodes that reside in the block. Note that this should be
135 /// called while the predecessor still refers to this block.
137 void BasicBlock::removePredecessor(BasicBlock *Pred,
138 bool DontDeleteUselessPHIs) {
139 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
140 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
141 "removePredecessor: BB is not a predecessor!");
143 if (InstList.empty()) return;
144 PHINode *APN = dyn_cast<PHINode>(&front());
145 if (!APN) return; // Quick exit.
147 // If there are exactly two predecessors, then we want to nuke the PHI nodes
148 // altogether. However, we cannot do this, if this in this case:
151 // %x = phi [X, Loop]
152 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
153 // br Loop ;; %x2 does not dominate all uses
155 // This is because the PHI node input is actually taken from the predecessor
156 // basic block. The only case this can happen is with a self loop, so we
157 // check for this case explicitly now.
159 unsigned max_idx = APN->getNumIncomingValues();
160 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
162 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
164 // Disable PHI elimination!
165 if (this == Other) max_idx = 3;
168 // <= Two predecessors BEFORE I remove one?
169 if (max_idx <= 2 && !DontDeleteUselessPHIs) {
170 // Yup, loop through and nuke the PHI nodes
171 while (PHINode *PN = dyn_cast<PHINode>(&front())) {
172 // Remove the predecessor first.
173 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
175 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
177 if (PN->getOperand(0) != PN)
178 PN->replaceAllUsesWith(PN->getOperand(0));
180 // We are left with an infinite loop with no entries: kill the PHI.
181 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
182 getInstList().pop_front(); // Remove the PHI node
185 // If the PHI node already only had one entry, it got deleted by
186 // removeIncomingValue.
189 // Okay, now we know that we need to remove predecessor #pred_idx from all
190 // PHI nodes. Iterate over each PHI node fixing them up
192 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
194 PN->removeIncomingValue(Pred, false);
195 // If all incoming values to the Phi are the same, we can replace the Phi
197 if (Value *PNV = PN->hasConstantValue()) {
198 PN->replaceAllUsesWith(PNV);
199 PN->eraseFromParent();
206 /// splitBasicBlock - This splits a basic block into two at the specified
207 /// instruction. Note that all instructions BEFORE the specified iterator stay
208 /// as part of the original basic block, an unconditional branch is added to
209 /// the new BB, and the rest of the instructions in the BB are moved to the new
210 /// BB, including the old terminator. This invalidates the iterator.
212 /// Note that this only works on well formed basic blocks (must have a
213 /// terminator), and 'I' must not be the end of instruction list (which would
214 /// cause a degenerate basic block to be formed, having a terminator inside of
215 /// the basic block).
217 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) {
218 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
219 assert(I != InstList.end() &&
220 "Trying to get me to create degenerate basic block!");
222 BasicBlock *New = new BasicBlock(BBName, getParent(), getNext());
224 // Move all of the specified instructions from the original basic block into
225 // the new basic block.
226 New->getInstList().splice(New->end(), this->getInstList(), I, end());
228 // Add a branch instruction to the newly formed basic block.
229 new BranchInst(New, this);
231 // Now we must loop through all of the successors of the New block (which
232 // _were_ the successors of the 'this' block), and update any PHI nodes in
233 // successors. If there were PHI nodes in the successors, then they need to
234 // know that incoming branches will be from New, not from Old.
236 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
237 // Loop over any phi nodes in the basic block, updating the BB field of
238 // incoming values...
239 BasicBlock *Successor = *I;
241 for (BasicBlock::iterator II = Successor->begin();
242 (PN = dyn_cast<PHINode>(II)); ++II) {
243 int IDX = PN->getBasicBlockIndex(this);
245 PN->setIncomingBlock((unsigned)IDX, New);
246 IDX = PN->getBasicBlockIndex(this);