BasicBlock.cpp revision 0b16ae209a1d0876a7ea6800bb567d925443cba3
1//===-- BasicBlock.cpp - Implement BasicBlock related methods -------------===// 2// 3// This file implements the BasicBlock class for the VMCore library. 4// 5//===----------------------------------------------------------------------===// 6 7#include "llvm/BasicBlock.h" 8#include "llvm/iTerminators.h" 9#include "llvm/Type.h" 10#include "llvm/Support/CFG.h" 11#include "llvm/Constant.h" 12#include "llvm/iPHINode.h" 13#include "llvm/SymbolTable.h" 14#include "Support/LeakDetector.h" 15#include "SymbolTableListTraitsImpl.h" 16#include <algorithm> 17 18// DummyInst - An instance of this class is used to mark the end of the 19// instruction list. This is not a real instruction. 20// 21struct DummyInst : public Instruction { 22 DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd) { 23 // This should not be garbage monitored. 24 LeakDetector::removeGarbageObject(this); 25 } 26 27 virtual Instruction *clone() const { 28 assert(0 && "Cannot clone EOL");abort(); 29 return 0; 30 } 31 virtual const char *getOpcodeName() const { return "*end-of-list-inst*"; } 32 33 // Methods for support type inquiry through isa, cast, and dyn_cast... 34 static inline bool classof(const DummyInst *) { return true; } 35 static inline bool classof(const Instruction *I) { 36 return I->getOpcode() == OtherOpsEnd; 37 } 38 static inline bool classof(const Value *V) { 39 return isa<Instruction>(V) && classof(cast<Instruction>(V)); 40 } 41}; 42 43Instruction *ilist_traits<Instruction>::createNode() { 44 return new DummyInst(); 45} 46iplist<Instruction> &ilist_traits<Instruction>::getList(BasicBlock *BB) { 47 return BB->getInstList(); 48} 49 50// Explicit instantiation of SymbolTableListTraits since some of the methods 51// are not in the public header file... 52template SymbolTableListTraits<Instruction, BasicBlock, Function>; 53 54 55// BasicBlock ctor - If the function parameter is specified, the basic block is 56// automatically inserted at the end of the function. 57// 58BasicBlock::BasicBlock(const std::string &name, Function *Parent) 59 : Value(Type::LabelTy, Value::BasicBlockVal, name) { 60 // Initialize the instlist... 61 InstList.setItemParent(this); 62 63 // Make sure that we get added to a function 64 LeakDetector::addGarbageObject(this); 65 66 if (Parent) 67 Parent->getBasicBlockList().push_back(this); 68} 69 70/// BasicBlock ctor - If the InsertBefore parameter is specified, the basic 71/// block is automatically inserted right before the specified block. 72/// 73BasicBlock::BasicBlock(const std::string &Name, BasicBlock *InsertBefore) 74 : Value(Type::LabelTy, Value::BasicBlockVal, Name) { 75 // Initialize the instlist... 76 InstList.setItemParent(this); 77 78 // Make sure that we get added to a function 79 LeakDetector::addGarbageObject(this); 80 81 if (InsertBefore) { 82 assert(InsertBefore->getParent() && 83 "Cannot insert block before another block that is not embedded into" 84 " a function yet!"); 85 InsertBefore->getParent()->getBasicBlockList().insert(InsertBefore, this); 86 } 87} 88 89 90BasicBlock::~BasicBlock() { 91 dropAllReferences(); 92 InstList.clear(); 93} 94 95void BasicBlock::setParent(Function *parent) { 96 if (getParent()) 97 LeakDetector::addGarbageObject(this); 98 99 InstList.setParent(parent); 100 101 if (getParent()) 102 LeakDetector::removeGarbageObject(this); 103} 104 105// Specialize setName to take care of symbol table majik 106void BasicBlock::setName(const std::string &name, SymbolTable *ST) { 107 Function *P; 108 assert((ST == 0 || (!getParent() || ST == getParent()->getSymbolTable())) && 109 "Invalid symtab argument!"); 110 if ((P = getParent()) && hasName()) P->getSymbolTable()->remove(this); 111 Value::setName(name); 112 if (P && hasName()) P->getSymbolTable()->insert(this); 113} 114 115TerminatorInst *BasicBlock::getTerminator() { 116 if (InstList.empty()) return 0; 117 return dyn_cast<TerminatorInst>(&InstList.back()); 118} 119 120const TerminatorInst *const BasicBlock::getTerminator() const { 121 if (InstList.empty()) return 0; 122 return dyn_cast<TerminatorInst>(&InstList.back()); 123} 124 125void BasicBlock::dropAllReferences() { 126 for(iterator I = begin(), E = end(); I != E; ++I) 127 I->dropAllReferences(); 128} 129 130// hasConstantReferences() - This predicate is true if there is a 131// reference to this basic block in the constant pool for this method. For 132// example, if a block is reached through a switch table, that table resides 133// in the constant pool, and the basic block is reference from it. 134// 135bool BasicBlock::hasConstantReferences() const { 136 for (use_const_iterator I = use_begin(), E = use_end(); I != E; ++I) 137 if (::isa<Constant>((Value*)*I)) 138 return true; 139 140 return false; 141} 142 143// removePredecessor - This method is used to notify a BasicBlock that the 144// specified Predecessor of the block is no longer able to reach it. This is 145// actually not used to update the Predecessor list, but is actually used to 146// update the PHI nodes that reside in the block. Note that this should be 147// called while the predecessor still refers to this block. 148// 149void BasicBlock::removePredecessor(BasicBlock *Pred) { 150 assert(find(pred_begin(this), pred_end(this), Pred) != pred_end(this) && 151 "removePredecessor: BB is not a predecessor!"); 152 if (!isa<PHINode>(front())) return; // Quick exit. 153 154 pred_iterator PI(pred_begin(this)), EI(pred_end(this)); 155 unsigned max_idx; 156 157 // Loop over the rest of the predecessors until we run out, or until we find 158 // out that there are more than 2 predecessors. 159 for (max_idx = 0; PI != EI && max_idx < 3; ++PI, ++max_idx) /*empty*/; 160 161 // If there are exactly two predecessors, then we want to nuke the PHI nodes 162 // altogether. We cannot do this, however if this in this case however: 163 // 164 // Loop: 165 // %x = phi [X, Loop] 166 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1 167 // br Loop ;; %x2 does not dominate all uses 168 // 169 // This is because the PHI node input is actually taken from the predecessor 170 // basic block. The only case this can happen is with a self loop, so we 171 // check for this case explicitly now. 172 // 173 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!"); 174 if (max_idx == 2) { 175 PI = pred_begin(this); 176 BasicBlock *Other = *PI == Pred ? *++PI : *PI; 177 178 // Disable PHI elimination! 179 if (this == Other) max_idx = 3; 180 } 181 182 if (max_idx <= 2) { // <= Two predecessors BEFORE I remove one? 183 // Yup, loop through and nuke the PHI nodes 184 while (PHINode *PN = dyn_cast<PHINode>(&front())) { 185 PN->removeIncomingValue(Pred); // Remove the predecessor first... 186 187 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value 188 if (max_idx == 2) { 189 PN->replaceAllUsesWith(PN->getOperand(0)); 190 getInstList().pop_front(); // Remove the PHI node 191 } 192 193 // If the PHI node already only had one entry, it got deleted by 194 // removeIncomingValue. 195 } 196 } else { 197 // Okay, now we know that we need to remove predecessor #pred_idx from all 198 // PHI nodes. Iterate over each PHI node fixing them up 199 for (iterator II = begin(); PHINode *PN = dyn_cast<PHINode>(&*II); ++II) 200 PN->removeIncomingValue(Pred); 201 } 202} 203 204 205// splitBasicBlock - This splits a basic block into two at the specified 206// instruction. Note that all instructions BEFORE the specified iterator stay 207// as part of the original basic block, an unconditional branch is added to 208// the new BB, and the rest of the instructions in the BB are moved to the new 209// BB, including the old terminator. This invalidates the iterator. 210// 211// Note that this only works on well formed basic blocks (must have a 212// terminator), and 'I' must not be the end of instruction list (which would 213// cause a degenerate basic block to be formed, having a terminator inside of 214// the basic block). 215// 216BasicBlock *BasicBlock::splitBasicBlock(iterator I) { 217 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!"); 218 assert(I != InstList.end() && 219 "Trying to get me to create degenerate basic block!"); 220 221 BasicBlock *New = new BasicBlock("", getParent()); 222 223 // Go from the end of the basic block through to the iterator pointer, moving 224 // to the new basic block... 225 Instruction *Inst = 0; 226 do { 227 iterator EndIt = end(); 228 Inst = InstList.remove(--EndIt); // Remove from end 229 New->InstList.push_front(Inst); // Add to front 230 } while (Inst != &*I); // Loop until we move the specified instruction. 231 232 // Add a branch instruction to the newly formed basic block. 233 InstList.push_back(new BranchInst(New)); 234 235 // Now we must loop through all of the successors of the New block (which 236 // _were_ the successors of the 'this' block), and update any PHI nodes in 237 // successors. If there were PHI nodes in the successors, then they need to 238 // know that incoming branches will be from New, not from Old. 239 // 240 for (BasicBlock::succ_iterator I = succ_begin(New), E = succ_end(New); 241 I != E; ++I) { 242 // Loop over any phi nodes in the basic block, updating the BB field of 243 // incoming values... 244 BasicBlock *Successor = *I; 245 for (BasicBlock::iterator II = Successor->begin(); 246 PHINode *PN = dyn_cast<PHINode>(&*II); ++II) { 247 int IDX = PN->getBasicBlockIndex(this); 248 while (IDX != -1) { 249 PN->setIncomingBlock((unsigned)IDX, New); 250 IDX = PN->getBasicBlockIndex(this); 251 } 252 } 253 } 254 return New; 255} 256