1 //===-- BasicBlock.cpp - Implement BasicBlock related methods -------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the BasicBlock class for the VMCore library.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/Constants.h"
15 #include "llvm/Instructions.h"
16 #include "llvm/Type.h"
17 #include "llvm/Support/CFG.h"
18 #include "llvm/Support/LeakDetector.h"
19 #include "llvm/Support/Compiler.h"
20 #include "SymbolTableListTraitsImpl.h"
24 inline ValueSymbolTable *
25 ilist_traits<Instruction>::getSymTab(BasicBlock *BB) {
27 if (Function *F = BB->getParent())
28 return &F->getValueSymbolTable();
34 /// DummyInst - An instance of this class is used to mark the end of the
35 /// instruction list. This is not a real instruction.
36 struct VISIBILITY_HIDDEN DummyInst : public Instruction {
37 // allocate space for exactly zero operands
38 void *operator new(size_t s) {
39 return User::operator new(s, 0);
41 DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd, 0, 0) {
42 // This should not be garbage monitored.
43 LeakDetector::removeGarbageObject(this);
46 Instruction *clone() const {
47 assert(0 && "Cannot clone EOL");abort();
50 const char *getOpcodeName() const { return "*end-of-list-inst*"; }
52 // Methods for support type inquiry through isa, cast, and dyn_cast...
53 static inline bool classof(const DummyInst *) { return true; }
54 static inline bool classof(const Instruction *I) {
55 return I->getOpcode() == OtherOpsEnd;
57 static inline bool classof(const Value *V) {
58 return isa<Instruction>(V) && classof(cast<Instruction>(V));
63 Instruction *ilist_traits<Instruction>::createSentinel() {
64 return new DummyInst();
66 iplist<Instruction> &ilist_traits<Instruction>::getList(BasicBlock *BB) {
67 return BB->getInstList();
70 // Explicit instantiation of SymbolTableListTraits since some of the methods
71 // are not in the public header file...
72 template class SymbolTableListTraits<Instruction, BasicBlock>;
75 BasicBlock::BasicBlock(const std::string &Name, Function *NewParent,
76 BasicBlock *InsertBefore)
77 : Value(Type::LabelTy, Value::BasicBlockVal), Parent(0) {
79 // Make sure that we get added to a function
80 LeakDetector::addGarbageObject(this);
84 "Cannot insert block before another block with no function!");
85 NewParent->getBasicBlockList().insert(InsertBefore, this);
86 } else if (NewParent) {
87 NewParent->getBasicBlockList().push_back(this);
94 BasicBlock::~BasicBlock() {
95 assert(getParent() == 0 && "BasicBlock still linked into the program!");
100 void BasicBlock::setParent(Function *parent) {
102 LeakDetector::addGarbageObject(this);
104 // Set Parent=parent, updating instruction symtab entries as appropriate.
105 InstList.setSymTabObject(&Parent, parent);
108 LeakDetector::removeGarbageObject(this);
111 void BasicBlock::removeFromParent() {
112 getParent()->getBasicBlockList().remove(this);
115 void BasicBlock::eraseFromParent() {
116 getParent()->getBasicBlockList().erase(this);
119 /// moveBefore - Unlink this basic block from its current function and
120 /// insert it into the function that MovePos lives in, right before MovePos.
121 void BasicBlock::moveBefore(BasicBlock *MovePos) {
122 MovePos->getParent()->getBasicBlockList().splice(MovePos,
123 getParent()->getBasicBlockList(), this);
126 /// moveAfter - Unlink this basic block from its current function and
127 /// insert it into the function that MovePos lives in, right after MovePos.
128 void BasicBlock::moveAfter(BasicBlock *MovePos) {
129 Function::iterator I = MovePos;
130 MovePos->getParent()->getBasicBlockList().splice(++I,
131 getParent()->getBasicBlockList(), this);
135 TerminatorInst *BasicBlock::getTerminator() {
136 if (InstList.empty()) return 0;
137 return dyn_cast<TerminatorInst>(&InstList.back());
140 const TerminatorInst *BasicBlock::getTerminator() const {
141 if (InstList.empty()) return 0;
142 return dyn_cast<TerminatorInst>(&InstList.back());
145 Instruction* BasicBlock::getFirstNonPHI() {
146 BasicBlock::iterator i = begin();
147 // All valid basic blocks should have a terminator,
148 // which is not a PHINode. If we have an invalid basic
149 // block we'll get an assertion failure when dereferencing
150 // a past-the-end iterator.
151 while (isa<PHINode>(i)) ++i;
155 void BasicBlock::dropAllReferences() {
156 for(iterator I = begin(), E = end(); I != E; ++I)
157 I->dropAllReferences();
160 /// getSinglePredecessor - If this basic block has a single predecessor block,
161 /// return the block, otherwise return a null pointer.
162 BasicBlock *BasicBlock::getSinglePredecessor() {
163 pred_iterator PI = pred_begin(this), E = pred_end(this);
164 if (PI == E) return 0; // No preds.
165 BasicBlock *ThePred = *PI;
167 return (PI == E) ? ThePred : 0 /*multiple preds*/;
170 /// removePredecessor - This method is used to notify a BasicBlock that the
171 /// specified Predecessor of the block is no longer able to reach it. This is
172 /// actually not used to update the Predecessor list, but is actually used to
173 /// update the PHI nodes that reside in the block. Note that this should be
174 /// called while the predecessor still refers to this block.
176 void BasicBlock::removePredecessor(BasicBlock *Pred,
177 bool DontDeleteUselessPHIs) {
178 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
179 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
180 "removePredecessor: BB is not a predecessor!");
182 if (InstList.empty()) return;
183 PHINode *APN = dyn_cast<PHINode>(&front());
184 if (!APN) return; // Quick exit.
186 // If there are exactly two predecessors, then we want to nuke the PHI nodes
187 // altogether. However, we cannot do this, if this in this case:
190 // %x = phi [X, Loop]
191 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
192 // br Loop ;; %x2 does not dominate all uses
194 // This is because the PHI node input is actually taken from the predecessor
195 // basic block. The only case this can happen is with a self loop, so we
196 // check for this case explicitly now.
198 unsigned max_idx = APN->getNumIncomingValues();
199 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
201 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
203 // Disable PHI elimination!
204 if (this == Other) max_idx = 3;
207 // <= Two predecessors BEFORE I remove one?
208 if (max_idx <= 2 && !DontDeleteUselessPHIs) {
209 // Yup, loop through and nuke the PHI nodes
210 while (PHINode *PN = dyn_cast<PHINode>(&front())) {
211 // Remove the predecessor first.
212 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
214 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
216 if (PN->getOperand(0) != PN)
217 PN->replaceAllUsesWith(PN->getOperand(0));
219 // We are left with an infinite loop with no entries: kill the PHI.
220 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
221 getInstList().pop_front(); // Remove the PHI node
224 // If the PHI node already only had one entry, it got deleted by
225 // removeIncomingValue.
228 // Okay, now we know that we need to remove predecessor #pred_idx from all
229 // PHI nodes. Iterate over each PHI node fixing them up
231 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
233 PN->removeIncomingValue(Pred, false);
234 // If all incoming values to the Phi are the same, we can replace the Phi
237 if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue())) {
238 PN->replaceAllUsesWith(PNV);
239 PN->eraseFromParent();
246 /// splitBasicBlock - This splits a basic block into two at the specified
247 /// instruction. Note that all instructions BEFORE the specified iterator stay
248 /// as part of the original basic block, an unconditional branch is added to
249 /// the new BB, and the rest of the instructions in the BB are moved to the new
250 /// BB, including the old terminator. This invalidates the iterator.
252 /// Note that this only works on well formed basic blocks (must have a
253 /// terminator), and 'I' must not be the end of instruction list (which would
254 /// cause a degenerate basic block to be formed, having a terminator inside of
255 /// the basic block).
257 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) {
258 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
259 assert(I != InstList.end() &&
260 "Trying to get me to create degenerate basic block!");
262 BasicBlock *New = BasicBlock::Create(BBName, getParent(), getNext());
264 // Move all of the specified instructions from the original basic block into
265 // the new basic block.
266 New->getInstList().splice(New->end(), this->getInstList(), I, end());
268 // Add a branch instruction to the newly formed basic block.
269 BranchInst::Create(New, this);
271 // Now we must loop through all of the successors of the New block (which
272 // _were_ the successors of the 'this' block), and update any PHI nodes in
273 // successors. If there were PHI nodes in the successors, then they need to
274 // know that incoming branches will be from New, not from Old.
276 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
277 // Loop over any phi nodes in the basic block, updating the BB field of
278 // incoming values...
279 BasicBlock *Successor = *I;
281 for (BasicBlock::iterator II = Successor->begin();
282 (PN = dyn_cast<PHINode>(II)); ++II) {
283 int IDX = PN->getBasicBlockIndex(this);
285 PN->setIncomingBlock((unsigned)IDX, New);
286 IDX = PN->getBasicBlockIndex(this);