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/iTerminators.h"
16 #include "llvm/Type.h"
17 #include "llvm/Support/CFG.h"
18 #include "llvm/Constant.h"
19 #include "llvm/iPHINode.h"
20 #include "llvm/SymbolTable.h"
21 #include "Support/LeakDetector.h"
22 #include "SymbolTableListTraitsImpl.h"
27 /// DummyInst - An instance of this class is used to mark the end of the
28 /// instruction list. This is not a real instruction.
29 struct DummyInst : public Instruction {
30 DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd) {
31 // This should not be garbage monitored.
32 LeakDetector::removeGarbageObject(this);
35 virtual Instruction *clone() const {
36 assert(0 && "Cannot clone EOL");abort();
39 virtual const char *getOpcodeName() const { return "*end-of-list-inst*"; }
41 // Methods for support type inquiry through isa, cast, and dyn_cast...
42 static inline bool classof(const DummyInst *) { return true; }
43 static inline bool classof(const Instruction *I) {
44 return I->getOpcode() == OtherOpsEnd;
46 static inline bool classof(const Value *V) {
47 return isa<Instruction>(V) && classof(cast<Instruction>(V));
52 Instruction *ilist_traits<Instruction>::createNode() {
53 return new DummyInst();
55 iplist<Instruction> &ilist_traits<Instruction>::getList(BasicBlock *BB) {
56 return BB->getInstList();
59 // Explicit instantiation of SymbolTableListTraits since some of the methods
60 // are not in the public header file...
61 template class SymbolTableListTraits<Instruction, BasicBlock, Function>;
64 BasicBlock::BasicBlock(const std::string &Name, Function *Parent,
65 BasicBlock *InsertBefore)
66 : Value(Type::LabelTy, Value::BasicBlockVal, Name) {
67 // Initialize the instlist...
68 InstList.setItemParent(this);
70 // Make sure that we get added to a function
71 LeakDetector::addGarbageObject(this);
75 "Cannot insert block before another block with no function!");
76 Parent->getBasicBlockList().insert(InsertBefore, this);
78 Parent->getBasicBlockList().push_back(this);
83 BasicBlock::~BasicBlock() {
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 // hasConstantReferences() - This predicate is true if there is a
124 // reference to this basic block in the constant pool for this method. For
125 // example, if a block is reached through a switch table, that table resides
126 // in the constant pool, and the basic block is reference from it.
128 bool BasicBlock::hasConstantReferences() const {
129 for (use_const_iterator I = use_begin(), E = use_end(); I != E; ++I)
130 if (isa<Constant>((Value*)*I))
136 // removePredecessor - This method is used to notify a BasicBlock that the
137 // specified Predecessor of the block is no longer able to reach it. This is
138 // actually not used to update the Predecessor list, but is actually used to
139 // update the PHI nodes that reside in the block. Note that this should be
140 // called while the predecessor still refers to this block.
142 void BasicBlock::removePredecessor(BasicBlock *Pred) {
143 assert(find(pred_begin(this), pred_end(this), Pred) != pred_end(this) &&
144 "removePredecessor: BB is not a predecessor!");
145 if (!isa<PHINode>(front())) return; // Quick exit.
147 pred_iterator PI(pred_begin(this)), EI(pred_end(this));
150 // Loop over the rest of the predecessors until we run out, or until we find
151 // out that there are more than 2 predecessors.
152 for (max_idx = 0; PI != EI && max_idx < 3; ++PI, ++max_idx) /*empty*/;
154 // If there are exactly two predecessors, then we want to nuke the PHI nodes
155 // altogether. We cannot do this, however if this in this case however:
158 // %x = phi [X, Loop]
159 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
160 // br Loop ;; %x2 does not dominate all uses
162 // This is because the PHI node input is actually taken from the predecessor
163 // basic block. The only case this can happen is with a self loop, so we
164 // check for this case explicitly now.
166 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
168 PI = pred_begin(this);
169 BasicBlock *Other = *PI == Pred ? *++PI : *PI;
171 // Disable PHI elimination!
172 if (this == Other) max_idx = 3;
175 if (max_idx <= 2) { // <= Two predecessors BEFORE I remove one?
176 // Yup, loop through and nuke the PHI nodes
177 while (PHINode *PN = dyn_cast<PHINode>(&front())) {
178 PN->removeIncomingValue(Pred); // Remove the predecessor first...
180 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
182 if (PN->getOperand(0) != PN)
183 PN->replaceAllUsesWith(PN->getOperand(0));
185 // We are left with an infinite loop with no entries: kill the PHI.
186 PN->replaceAllUsesWith(Constant::getNullValue(PN->getType()));
187 getInstList().pop_front(); // Remove the PHI node
190 // If the PHI node already only had one entry, it got deleted by
191 // removeIncomingValue.
194 // Okay, now we know that we need to remove predecessor #pred_idx from all
195 // PHI nodes. Iterate over each PHI node fixing them up
196 for (iterator II = begin(); PHINode *PN = dyn_cast<PHINode>(II); ++II)
197 PN->removeIncomingValue(Pred);
202 // splitBasicBlock - This splits a basic block into two at the specified
203 // instruction. Note that all instructions BEFORE the specified iterator stay
204 // as part of the original basic block, an unconditional branch is added to
205 // the new BB, and the rest of the instructions in the BB are moved to the new
206 // BB, including the old terminator. This invalidates the iterator.
208 // Note that this only works on well formed basic blocks (must have a
209 // terminator), and 'I' must not be the end of instruction list (which would
210 // cause a degenerate basic block to be formed, having a terminator inside of
213 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) {
214 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
215 assert(I != InstList.end() &&
216 "Trying to get me to create degenerate basic block!");
218 BasicBlock *New = new BasicBlock(BBName, getParent(), getNext());
220 // Move all of the specified instructions from the original basic block into
221 // the new basic block.
222 New->getInstList().splice(New->end(), this->getInstList(), I, end());
224 // Add a branch instruction to the newly formed basic block.
225 new BranchInst(New, this);
227 // Now we must loop through all of the successors of the New block (which
228 // _were_ the successors of the 'this' block), and update any PHI nodes in
229 // successors. If there were PHI nodes in the successors, then they need to
230 // know that incoming branches will be from New, not from Old.
232 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
233 // Loop over any phi nodes in the basic block, updating the BB field of
234 // incoming values...
235 BasicBlock *Successor = *I;
236 for (BasicBlock::iterator II = Successor->begin();
237 PHINode *PN = dyn_cast<PHINode>(II); ++II) {
238 int IDX = PN->getBasicBlockIndex(this);
240 PN->setIncomingBlock((unsigned)IDX, New);
241 IDX = PN->getBasicBlockIndex(this);