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 ctor - If the function parameter is specified, the basic block is
65 // automatically inserted at the end of the function.
67 BasicBlock::BasicBlock(const std::string &name, Function *Parent)
68 : Value(Type::LabelTy, Value::BasicBlockVal, name) {
69 // Initialize the instlist...
70 InstList.setItemParent(this);
72 // Make sure that we get added to a function
73 LeakDetector::addGarbageObject(this);
76 Parent->getBasicBlockList().push_back(this);
79 /// BasicBlock ctor - If the InsertBefore parameter is specified, the basic
80 /// block is automatically inserted right before the specified block.
82 BasicBlock::BasicBlock(const std::string &Name, BasicBlock *InsertBefore)
83 : Value(Type::LabelTy, Value::BasicBlockVal, Name) {
84 // Initialize the instlist...
85 InstList.setItemParent(this);
87 // Make sure that we get added to a function
88 LeakDetector::addGarbageObject(this);
91 assert(InsertBefore->getParent() &&
92 "Cannot insert block before another block that is not embedded into"
94 InsertBefore->getParent()->getBasicBlockList().insert(InsertBefore, this);
99 BasicBlock::~BasicBlock() {
104 void BasicBlock::setParent(Function *parent) {
106 LeakDetector::addGarbageObject(this);
108 InstList.setParent(parent);
111 LeakDetector::removeGarbageObject(this);
114 // Specialize setName to take care of symbol table majik
115 void BasicBlock::setName(const std::string &name, SymbolTable *ST) {
117 assert((ST == 0 || (!getParent() || ST == &getParent()->getSymbolTable())) &&
118 "Invalid symtab argument!");
119 if ((P = getParent()) && hasName()) P->getSymbolTable().remove(this);
120 Value::setName(name);
121 if (P && hasName()) P->getSymbolTable().insert(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 void BasicBlock::dropAllReferences() {
135 for(iterator I = begin(), E = end(); I != E; ++I)
136 I->dropAllReferences();
139 // hasConstantReferences() - This predicate is true if there is a
140 // reference to this basic block in the constant pool for this method. For
141 // example, if a block is reached through a switch table, that table resides
142 // in the constant pool, and the basic block is reference from it.
144 bool BasicBlock::hasConstantReferences() const {
145 for (use_const_iterator I = use_begin(), E = use_end(); I != E; ++I)
146 if (isa<Constant>((Value*)*I))
152 // removePredecessor - This method is used to notify a BasicBlock that the
153 // specified Predecessor of the block is no longer able to reach it. This is
154 // actually not used to update the Predecessor list, but is actually used to
155 // update the PHI nodes that reside in the block. Note that this should be
156 // called while the predecessor still refers to this block.
158 void BasicBlock::removePredecessor(BasicBlock *Pred) {
159 assert(find(pred_begin(this), pred_end(this), Pred) != pred_end(this) &&
160 "removePredecessor: BB is not a predecessor!");
161 if (!isa<PHINode>(front())) return; // Quick exit.
163 pred_iterator PI(pred_begin(this)), EI(pred_end(this));
166 // Loop over the rest of the predecessors until we run out, or until we find
167 // out that there are more than 2 predecessors.
168 for (max_idx = 0; PI != EI && max_idx < 3; ++PI, ++max_idx) /*empty*/;
170 // If there are exactly two predecessors, then we want to nuke the PHI nodes
171 // altogether. We cannot do this, however if this in this case however:
174 // %x = phi [X, Loop]
175 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
176 // br Loop ;; %x2 does not dominate all uses
178 // This is because the PHI node input is actually taken from the predecessor
179 // basic block. The only case this can happen is with a self loop, so we
180 // check for this case explicitly now.
182 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
184 PI = pred_begin(this);
185 BasicBlock *Other = *PI == Pred ? *++PI : *PI;
187 // Disable PHI elimination!
188 if (this == Other) max_idx = 3;
191 if (max_idx <= 2) { // <= Two predecessors BEFORE I remove one?
192 // Yup, loop through and nuke the PHI nodes
193 while (PHINode *PN = dyn_cast<PHINode>(&front())) {
194 PN->removeIncomingValue(Pred); // Remove the predecessor first...
196 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
198 if (PN->getOperand(0) != PN)
199 PN->replaceAllUsesWith(PN->getOperand(0));
201 // We are left with an infinite loop with no entries: kill the PHI.
202 PN->replaceAllUsesWith(Constant::getNullValue(PN->getType()));
203 getInstList().pop_front(); // Remove the PHI node
206 // If the PHI node already only had one entry, it got deleted by
207 // removeIncomingValue.
210 // Okay, now we know that we need to remove predecessor #pred_idx from all
211 // PHI nodes. Iterate over each PHI node fixing them up
212 for (iterator II = begin(); PHINode *PN = dyn_cast<PHINode>(II); ++II)
213 PN->removeIncomingValue(Pred);
218 // splitBasicBlock - This splits a basic block into two at the specified
219 // instruction. Note that all instructions BEFORE the specified iterator stay
220 // as part of the original basic block, an unconditional branch is added to
221 // the new BB, and the rest of the instructions in the BB are moved to the new
222 // BB, including the old terminator. This invalidates the iterator.
224 // Note that this only works on well formed basic blocks (must have a
225 // terminator), and 'I' must not be the end of instruction list (which would
226 // cause a degenerate basic block to be formed, having a terminator inside of
229 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) {
230 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
231 assert(I != InstList.end() &&
232 "Trying to get me to create degenerate basic block!");
234 BasicBlock *New = new BasicBlock(BBName, getParent());
236 // Go from the end of the basic block through to the iterator pointer, moving
237 // to the new basic block...
238 Instruction *Inst = 0;
240 iterator EndIt = end();
241 Inst = InstList.remove(--EndIt); // Remove from end
242 New->InstList.push_front(Inst); // Add to front
243 } while (Inst != &*I); // Loop until we move the specified instruction.
245 // Add a branch instruction to the newly formed basic block.
246 new BranchInst(New, this);
248 // Now we must loop through all of the successors of the New block (which
249 // _were_ the successors of the 'this' block), and update any PHI nodes in
250 // successors. If there were PHI nodes in the successors, then they need to
251 // know that incoming branches will be from New, not from Old.
253 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
254 // Loop over any phi nodes in the basic block, updating the BB field of
255 // incoming values...
256 BasicBlock *Successor = *I;
257 for (BasicBlock::iterator II = Successor->begin();
258 PHINode *PN = dyn_cast<PHINode>(II); ++II) {
259 int IDX = PN->getBasicBlockIndex(this);
261 PN->setIncomingBlock((unsigned)IDX, New);
262 IDX = PN->getBasicBlockIndex(this);