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, Name) {
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);
82 BasicBlock::~BasicBlock() {
83 assert(getParent() == 0 && "BasicBlock still linked into the program!");
88 void BasicBlock::setParent(Function *parent) {
90 LeakDetector::addGarbageObject(this);
92 InstList.setParent(parent);
95 LeakDetector::removeGarbageObject(this);
98 void BasicBlock::removeFromParent() {
99 getParent()->getBasicBlockList().remove(this);
102 void BasicBlock::eraseFromParent() {
103 getParent()->getBasicBlockList().erase(this);
106 /// moveBefore - Unlink this basic block from its current function and
107 /// insert it into the function that MovePos lives in, right before MovePos.
108 void BasicBlock::moveBefore(BasicBlock *MovePos) {
109 MovePos->getParent()->getBasicBlockList().splice(MovePos,
110 getParent()->getBasicBlockList(), this);
113 /// moveAfter - Unlink this basic block from its current function and
114 /// insert it into the function that MovePos lives in, right after MovePos.
115 void BasicBlock::moveAfter(BasicBlock *MovePos) {
116 Function::iterator I = MovePos;
117 MovePos->getParent()->getBasicBlockList().splice(++I,
118 getParent()->getBasicBlockList(), this);
122 TerminatorInst *BasicBlock::getTerminator() {
123 if (InstList.empty()) return 0;
124 return dyn_cast<TerminatorInst>(&InstList.back());
127 const TerminatorInst *const BasicBlock::getTerminator() const {
128 if (InstList.empty()) return 0;
129 return dyn_cast<TerminatorInst>(&InstList.back());
132 Instruction* BasicBlock::getFirstNonPHI()
134 BasicBlock::iterator i = begin();
135 // All valid basic blocks should have a terminator,
136 // which is not a PHINode. If we have invalid basic
137 // block we'll get assert when dereferencing past-the-end
139 while (isa<PHINode>(i)) ++i;
143 void BasicBlock::dropAllReferences() {
144 for(iterator I = begin(), E = end(); I != E; ++I)
145 I->dropAllReferences();
148 /// getSinglePredecessor - If this basic block has a single predecessor block,
149 /// return the block, otherwise return a null pointer.
150 BasicBlock *BasicBlock::getSinglePredecessor() {
151 pred_iterator PI = pred_begin(this), E = pred_end(this);
152 if (PI == E) return 0; // No preds.
153 BasicBlock *ThePred = *PI;
155 return (PI == E) ? ThePred : 0 /*multiple preds*/;
158 /// removePredecessor - This method is used to notify a BasicBlock that the
159 /// specified Predecessor of the block is no longer able to reach it. This is
160 /// actually not used to update the Predecessor list, but is actually used to
161 /// update the PHI nodes that reside in the block. Note that this should be
162 /// called while the predecessor still refers to this block.
164 void BasicBlock::removePredecessor(BasicBlock *Pred,
165 bool DontDeleteUselessPHIs) {
166 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
167 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
168 "removePredecessor: BB is not a predecessor!");
170 if (InstList.empty()) return;
171 PHINode *APN = dyn_cast<PHINode>(&front());
172 if (!APN) return; // Quick exit.
174 // If there are exactly two predecessors, then we want to nuke the PHI nodes
175 // altogether. However, we cannot do this, if this in this case:
178 // %x = phi [X, Loop]
179 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
180 // br Loop ;; %x2 does not dominate all uses
182 // This is because the PHI node input is actually taken from the predecessor
183 // basic block. The only case this can happen is with a self loop, so we
184 // check for this case explicitly now.
186 unsigned max_idx = APN->getNumIncomingValues();
187 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
189 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
191 // Disable PHI elimination!
192 if (this == Other) max_idx = 3;
195 // <= Two predecessors BEFORE I remove one?
196 if (max_idx <= 2 && !DontDeleteUselessPHIs) {
197 // Yup, loop through and nuke the PHI nodes
198 while (PHINode *PN = dyn_cast<PHINode>(&front())) {
199 // Remove the predecessor first.
200 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
202 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
204 if (PN->getOperand(0) != PN)
205 PN->replaceAllUsesWith(PN->getOperand(0));
207 // We are left with an infinite loop with no entries: kill the PHI.
208 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
209 getInstList().pop_front(); // Remove the PHI node
212 // If the PHI node already only had one entry, it got deleted by
213 // removeIncomingValue.
216 // Okay, now we know that we need to remove predecessor #pred_idx from all
217 // PHI nodes. Iterate over each PHI node fixing them up
219 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
221 PN->removeIncomingValue(Pred, false);
222 // If all incoming values to the Phi are the same, we can replace the Phi
225 if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue())) {
226 PN->replaceAllUsesWith(PNV);
227 PN->eraseFromParent();
234 /// splitBasicBlock - This splits a basic block into two at the specified
235 /// instruction. Note that all instructions BEFORE the specified iterator stay
236 /// as part of the original basic block, an unconditional branch is added to
237 /// the new BB, and the rest of the instructions in the BB are moved to the new
238 /// BB, including the old terminator. This invalidates the iterator.
240 /// Note that this only works on well formed basic blocks (must have a
241 /// terminator), and 'I' must not be the end of instruction list (which would
242 /// cause a degenerate basic block to be formed, having a terminator inside of
243 /// the basic block).
245 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) {
246 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
247 assert(I != InstList.end() &&
248 "Trying to get me to create degenerate basic block!");
250 BasicBlock *New = new BasicBlock(BBName, getParent(), getNext());
252 // Move all of the specified instructions from the original basic block into
253 // the new basic block.
254 New->getInstList().splice(New->end(), this->getInstList(), I, end());
256 // Add a branch instruction to the newly formed basic block.
257 new BranchInst(New, this);
259 // Now we must loop through all of the successors of the New block (which
260 // _were_ the successors of the 'this' block), and update any PHI nodes in
261 // successors. If there were PHI nodes in the successors, then they need to
262 // know that incoming branches will be from New, not from Old.
264 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
265 // Loop over any phi nodes in the basic block, updating the BB field of
266 // incoming values...
267 BasicBlock *Successor = *I;
269 for (BasicBlock::iterator II = Successor->begin();
270 (PN = dyn_cast<PHINode>(II)); ++II) {
271 int IDX = PN->getBasicBlockIndex(this);
273 PN->setIncomingBlock((unsigned)IDX, New);
274 IDX = PN->getBasicBlockIndex(this);