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 "llvm/Support/Compiler.h"
21 #include "SymbolTableListTraitsImpl.h"
26 /// DummyInst - An instance of this class is used to mark the end of the
27 /// instruction list. This is not a real instruction.
28 struct VISIBILITY_HIDDEN DummyInst : public Instruction {
29 DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd, 0, 0) {
30 // This should not be garbage monitored.
31 LeakDetector::removeGarbageObject(this);
34 virtual Instruction *clone() const {
35 assert(0 && "Cannot clone EOL");abort();
38 virtual const char *getOpcodeName() const { return "*end-of-list-inst*"; }
40 // Methods for support type inquiry through isa, cast, and dyn_cast...
41 static inline bool classof(const DummyInst *) { return true; }
42 static inline bool classof(const Instruction *I) {
43 return I->getOpcode() == OtherOpsEnd;
45 static inline bool classof(const Value *V) {
46 return isa<Instruction>(V) && classof(cast<Instruction>(V));
51 Instruction *ilist_traits<Instruction>::createSentinel() {
52 return new DummyInst();
54 iplist<Instruction> &ilist_traits<Instruction>::getList(BasicBlock *BB) {
55 return BB->getInstList();
58 // Explicit instantiation of SymbolTableListTraits since some of the methods
59 // are not in the public header file...
60 template class SymbolTableListTraits<Instruction, BasicBlock, Function>;
63 BasicBlock::BasicBlock(const std::string &Name, Function *Parent,
64 BasicBlock *InsertBefore)
65 : Value(Type::LabelTy, Value::BasicBlockVal) {
66 // Initialize the instlist...
67 InstList.setItemParent(this);
69 // Make sure that we get added to a function
70 LeakDetector::addGarbageObject(this);
74 "Cannot insert block before another block with no function!");
75 Parent->getBasicBlockList().insert(InsertBefore, this);
77 Parent->getBasicBlockList().push_back(this);
84 BasicBlock::~BasicBlock() {
85 assert(getParent() == 0 && "BasicBlock still linked into the program!");
90 void BasicBlock::setParent(Function *parent) {
92 LeakDetector::addGarbageObject(this);
94 InstList.setParent(parent);
97 LeakDetector::removeGarbageObject(this);
100 void BasicBlock::removeFromParent() {
101 getParent()->getBasicBlockList().remove(this);
104 void BasicBlock::eraseFromParent() {
105 getParent()->getBasicBlockList().erase(this);
108 /// moveBefore - Unlink this basic block from its current function and
109 /// insert it into the function that MovePos lives in, right before MovePos.
110 void BasicBlock::moveBefore(BasicBlock *MovePos) {
111 MovePos->getParent()->getBasicBlockList().splice(MovePos,
112 getParent()->getBasicBlockList(), this);
115 /// moveAfter - Unlink this basic block from its current function and
116 /// insert it into the function that MovePos lives in, right after MovePos.
117 void BasicBlock::moveAfter(BasicBlock *MovePos) {
118 Function::iterator I = MovePos;
119 MovePos->getParent()->getBasicBlockList().splice(++I,
120 getParent()->getBasicBlockList(), this);
124 TerminatorInst *BasicBlock::getTerminator() {
125 if (InstList.empty()) return 0;
126 return dyn_cast<TerminatorInst>(&InstList.back());
129 const TerminatorInst *const BasicBlock::getTerminator() const {
130 if (InstList.empty()) return 0;
131 return dyn_cast<TerminatorInst>(&InstList.back());
134 Instruction* BasicBlock::getFirstNonPHI()
136 BasicBlock::iterator i = begin();
137 // All valid basic blocks should have a terminator,
138 // which is not a PHINode. If we have invalid basic
139 // block we'll get assert when dereferencing past-the-end
141 while (isa<PHINode>(i)) ++i;
145 void BasicBlock::dropAllReferences() {
146 for(iterator I = begin(), E = end(); I != E; ++I)
147 I->dropAllReferences();
150 /// getSinglePredecessor - If this basic block has a single predecessor block,
151 /// return the block, otherwise return a null pointer.
152 BasicBlock *BasicBlock::getSinglePredecessor() {
153 pred_iterator PI = pred_begin(this), E = pred_end(this);
154 if (PI == E) return 0; // No preds.
155 BasicBlock *ThePred = *PI;
157 return (PI == E) ? ThePred : 0 /*multiple preds*/;
160 /// removePredecessor - This method is used to notify a BasicBlock that the
161 /// specified Predecessor of the block is no longer able to reach it. This is
162 /// actually not used to update the Predecessor list, but is actually used to
163 /// update the PHI nodes that reside in the block. Note that this should be
164 /// called while the predecessor still refers to this block.
166 void BasicBlock::removePredecessor(BasicBlock *Pred,
167 bool DontDeleteUselessPHIs) {
168 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
169 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
170 "removePredecessor: BB is not a predecessor!");
172 if (InstList.empty()) return;
173 PHINode *APN = dyn_cast<PHINode>(&front());
174 if (!APN) return; // Quick exit.
176 // If there are exactly two predecessors, then we want to nuke the PHI nodes
177 // altogether. However, we cannot do this, if this in this case:
180 // %x = phi [X, Loop]
181 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
182 // br Loop ;; %x2 does not dominate all uses
184 // This is because the PHI node input is actually taken from the predecessor
185 // basic block. The only case this can happen is with a self loop, so we
186 // check for this case explicitly now.
188 unsigned max_idx = APN->getNumIncomingValues();
189 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
191 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
193 // Disable PHI elimination!
194 if (this == Other) max_idx = 3;
197 // <= Two predecessors BEFORE I remove one?
198 if (max_idx <= 2 && !DontDeleteUselessPHIs) {
199 // Yup, loop through and nuke the PHI nodes
200 while (PHINode *PN = dyn_cast<PHINode>(&front())) {
201 // Remove the predecessor first.
202 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
204 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
206 if (PN->getOperand(0) != PN)
207 PN->replaceAllUsesWith(PN->getOperand(0));
209 // We are left with an infinite loop with no entries: kill the PHI.
210 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
211 getInstList().pop_front(); // Remove the PHI node
214 // If the PHI node already only had one entry, it got deleted by
215 // removeIncomingValue.
218 // Okay, now we know that we need to remove predecessor #pred_idx from all
219 // PHI nodes. Iterate over each PHI node fixing them up
221 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
223 PN->removeIncomingValue(Pred, false);
224 // If all incoming values to the Phi are the same, we can replace the Phi
227 if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue())) {
228 PN->replaceAllUsesWith(PNV);
229 PN->eraseFromParent();
236 /// splitBasicBlock - This splits a basic block into two at the specified
237 /// instruction. Note that all instructions BEFORE the specified iterator stay
238 /// as part of the original basic block, an unconditional branch is added to
239 /// the new BB, and the rest of the instructions in the BB are moved to the new
240 /// BB, including the old terminator. This invalidates the iterator.
242 /// Note that this only works on well formed basic blocks (must have a
243 /// terminator), and 'I' must not be the end of instruction list (which would
244 /// cause a degenerate basic block to be formed, having a terminator inside of
245 /// the basic block).
247 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) {
248 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
249 assert(I != InstList.end() &&
250 "Trying to get me to create degenerate basic block!");
252 BasicBlock *New = new BasicBlock(BBName, getParent(), getNext());
254 // Move all of the specified instructions from the original basic block into
255 // the new basic block.
256 New->getInstList().splice(New->end(), this->getInstList(), I, end());
258 // Add a branch instruction to the newly formed basic block.
259 new BranchInst(New, this);
261 // Now we must loop through all of the successors of the New block (which
262 // _were_ the successors of the 'this' block), and update any PHI nodes in
263 // successors. If there were PHI nodes in the successors, then they need to
264 // know that incoming branches will be from New, not from Old.
266 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
267 // Loop over any phi nodes in the basic block, updating the BB field of
268 // incoming values...
269 BasicBlock *Successor = *I;
271 for (BasicBlock::iterator II = Successor->begin();
272 (PN = dyn_cast<PHINode>(II)); ++II) {
273 int IDX = PN->getBasicBlockIndex(this);
275 PN->setIncomingBlock((unsigned)IDX, New);
276 IDX = PN->getBasicBlockIndex(this);