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/Constant.h"
16 #include "llvm/Instructions.h"
17 #include "llvm/Type.h"
18 #include "llvm/Support/CFG.h"
19 #include "llvm/SymbolTable.h"
20 #include "llvm/Support/LeakDetector.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 DummyInst : public Instruction {
29 DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd) {
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>::createNode() {
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 // Specialize setName to take care of symbol table majik
99 void BasicBlock::setName(const std::string &name, SymbolTable *ST) {
101 assert((ST == 0 || (!getParent() || ST == &getParent()->getSymbolTable())) &&
102 "Invalid symtab argument!");
103 if ((P = getParent()) && hasName()) P->getSymbolTable().remove(this);
104 Value::setName(name);
105 if (P && hasName()) P->getSymbolTable().insert(this);
108 TerminatorInst *BasicBlock::getTerminator() {
109 if (InstList.empty()) return 0;
110 return dyn_cast<TerminatorInst>(&InstList.back());
113 const TerminatorInst *const BasicBlock::getTerminator() const {
114 if (InstList.empty()) return 0;
115 return dyn_cast<TerminatorInst>(&InstList.back());
118 void BasicBlock::dropAllReferences() {
119 for(iterator I = begin(), E = end(); I != E; ++I)
120 I->dropAllReferences();
123 // removePredecessor - This method is used to notify a BasicBlock that the
124 // specified Predecessor of the block is no longer able to reach it. This is
125 // actually not used to update the Predecessor list, but is actually used to
126 // update the PHI nodes that reside in the block. Note that this should be
127 // called while the predecessor still refers to this block.
129 void BasicBlock::removePredecessor(BasicBlock *Pred) {
130 assert(find(pred_begin(this), pred_end(this), Pred) != pred_end(this) &&
131 "removePredecessor: BB is not a predecessor!");
132 PHINode *APN = dyn_cast<PHINode>(&front());
133 if (!APN) return; // Quick exit.
135 // If there are exactly two predecessors, then we want to nuke the PHI nodes
136 // altogether. However, we cannot do this, if this in this case:
139 // %x = phi [X, Loop]
140 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
141 // br Loop ;; %x2 does not dominate all uses
143 // This is because the PHI node input is actually taken from the predecessor
144 // basic block. The only case this can happen is with a self loop, so we
145 // check for this case explicitly now.
147 unsigned max_idx = APN->getNumIncomingValues();
148 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
150 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
152 // Disable PHI elimination!
153 if (this == Other) max_idx = 3;
156 if (max_idx <= 2) { // <= Two predecessors BEFORE I remove one?
157 // Yup, loop through and nuke the PHI nodes
158 while (PHINode *PN = dyn_cast<PHINode>(&front())) {
159 PN->removeIncomingValue(Pred); // Remove the predecessor first...
161 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
163 if (PN->getOperand(0) != PN)
164 PN->replaceAllUsesWith(PN->getOperand(0));
166 // We are left with an infinite loop with no entries: kill the PHI.
167 PN->replaceAllUsesWith(Constant::getNullValue(PN->getType()));
168 getInstList().pop_front(); // Remove the PHI node
171 // If the PHI node already only had one entry, it got deleted by
172 // removeIncomingValue.
175 // Okay, now we know that we need to remove predecessor #pred_idx from all
176 // PHI nodes. Iterate over each PHI node fixing them up
178 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ++II)
179 PN->removeIncomingValue(Pred);
184 // splitBasicBlock - This splits a basic block into two at the specified
185 // instruction. Note that all instructions BEFORE the specified iterator stay
186 // as part of the original basic block, an unconditional branch is added to
187 // the new BB, and the rest of the instructions in the BB are moved to the new
188 // BB, including the old terminator. This invalidates the iterator.
190 // Note that this only works on well formed basic blocks (must have a
191 // terminator), and 'I' must not be the end of instruction list (which would
192 // cause a degenerate basic block to be formed, having a terminator inside of
195 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) {
196 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
197 assert(I != InstList.end() &&
198 "Trying to get me to create degenerate basic block!");
200 BasicBlock *New = new BasicBlock(BBName, getParent(), getNext());
202 // Move all of the specified instructions from the original basic block into
203 // the new basic block.
204 New->getInstList().splice(New->end(), this->getInstList(), I, end());
206 // Add a branch instruction to the newly formed basic block.
207 new BranchInst(New, this);
209 // Now we must loop through all of the successors of the New block (which
210 // _were_ the successors of the 'this' block), and update any PHI nodes in
211 // successors. If there were PHI nodes in the successors, then they need to
212 // know that incoming branches will be from New, not from Old.
214 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
215 // Loop over any phi nodes in the basic block, updating the BB field of
216 // incoming values...
217 BasicBlock *Successor = *I;
219 for (BasicBlock::iterator II = Successor->begin();
220 (PN = dyn_cast<PHINode>(II)); ++II) {
221 int IDX = PN->getBasicBlockIndex(this);
223 PN->setIncomingBlock((unsigned)IDX, New);
224 IDX = PN->getBasicBlockIndex(this);