BasicBlock.cpp revision b2e80a69514485c36442ea849063313e6db13e09
1//===-- BasicBlock.cpp - Implement BasicBlock related functions --*- C++ -*--=// 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 "SymbolTableListTraitsImpl.h" 15#include <algorithm> 16 17// DummyInst - An instance of this class is used to mark the end of the 18// instruction list. This is not a real instruction. 19// 20struct DummyInst : public Instruction { 21 DummyInst() : Instruction(Type::VoidTy, NumOtherOps) {} 22 23 virtual Instruction *clone() const { 24 assert(0 && "Cannot clone EOL");abort(); 25 return 0; 26 } 27 virtual const char *getOpcodeName() const { return "*end-of-list-inst*"; } 28 29 // Methods for support type inquiry through isa, cast, and dyn_cast... 30 static inline bool classof(const DummyInst *) { return true; } 31 static inline bool classof(const Instruction *I) { 32 return I->getOpcode() == NumOtherOps; 33 } 34 static inline bool classof(const Value *V) { 35 return isa<Instruction>(V) && classof(cast<Instruction>(V)); 36 } 37}; 38 39Instruction *ilist_traits<Instruction>::createNode() { 40 return new DummyInst(); 41} 42iplist<Instruction> &ilist_traits<Instruction>::getList(BasicBlock *BB) { 43 return BB->getInstList(); 44} 45 46// Explicit instantiation of SymbolTableListTraits since some of the methods 47// are not in the public header file... 48template SymbolTableListTraits<Instruction, BasicBlock, Function>; 49 50 51BasicBlock::BasicBlock(const std::string &name, Function *Parent) 52 : Value(Type::LabelTy, Value::BasicBlockVal, name) { 53 // Initialize the instlist... 54 InstList.setItemParent(this); 55 56 if (Parent) 57 Parent->getBasicBlockList().push_back(this); 58} 59 60BasicBlock::~BasicBlock() { 61 dropAllReferences(); 62 InstList.clear(); 63} 64 65// Specialize setName to take care of symbol table majik 66void BasicBlock::setName(const std::string &name, SymbolTable *ST) { 67 Function *P; 68 assert((ST == 0 || (!getParent() || ST == getParent()->getSymbolTable())) && 69 "Invalid symtab argument!"); 70 if ((P = getParent()) && hasName()) P->getSymbolTable()->remove(this); 71 Value::setName(name); 72 if (P && hasName()) P->getSymbolTable()->insert(this); 73} 74 75TerminatorInst *BasicBlock::getTerminator() { 76 if (InstList.empty()) return 0; 77 return dyn_cast<TerminatorInst>(&InstList.back()); 78} 79 80const TerminatorInst *const BasicBlock::getTerminator() const { 81 if (InstList.empty()) return 0; 82 return dyn_cast<TerminatorInst>(&InstList.back()); 83} 84 85void BasicBlock::dropAllReferences() { 86 for(iterator I = begin(), E = end(); I != E; ++I) 87 I->dropAllReferences(); 88} 89 90// hasConstantReferences() - This predicate is true if there is a 91// reference to this basic block in the constant pool for this method. For 92// example, if a block is reached through a switch table, that table resides 93// in the constant pool, and the basic block is reference from it. 94// 95bool BasicBlock::hasConstantReferences() const { 96 for (use_const_iterator I = use_begin(), E = use_end(); I != E; ++I) 97 if (::isa<Constant>((Value*)*I)) 98 return true; 99 100 return false; 101} 102 103// removePredecessor - This method is used to notify a BasicBlock that the 104// specified Predecessor of the block is no longer able to reach it. This is 105// actually not used to update the Predecessor list, but is actually used to 106// update the PHI nodes that reside in the block. Note that this should be 107// called while the predecessor still refers to this block. 108// 109void BasicBlock::removePredecessor(BasicBlock *Pred) { 110 assert(find(pred_begin(this), pred_end(this), Pred) != pred_end(this) && 111 "removePredecessor: BB is not a predecessor!"); 112 if (!isa<PHINode>(front())) return; // Quick exit. 113 114 pred_iterator PI(pred_begin(this)), EI(pred_end(this)); 115 unsigned max_idx; 116 117 // Loop over the rest of the predecessors until we run out, or until we find 118 // out that there are more than 2 predecessors. 119 for (max_idx = 0; PI != EI && max_idx < 3; ++PI, ++max_idx) /*empty*/; 120 121 // If there are exactly two predecessors, then we want to nuke the PHI nodes 122 // altogether. We cannot do this, however if this in this case however: 123 // 124 // Loop: 125 // %x = phi [X, Loop] 126 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1 127 // br Loop ;; %x2 does not dominate all uses 128 // 129 // This is because the PHI node input is actually taken from the predecessor 130 // basic block. The only case this can happen is with a self loop, so we 131 // check for this case explicitly now. 132 // 133 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!"); 134 if (max_idx == 2) { 135 PI = pred_begin(this); 136 BasicBlock *Other = *PI == Pred ? *++PI : *PI; 137 138 // Disable PHI elimination! 139 if (this == Other) max_idx = 3; 140 } 141 142 if (max_idx <= 2) { // <= Two predecessors BEFORE I remove one? 143 // Yup, loop through and nuke the PHI nodes 144 while (PHINode *PN = dyn_cast<PHINode>(&front())) { 145 PN->removeIncomingValue(Pred); // Remove the predecessor first... 146 147 assert(PN->getNumIncomingValues() == max_idx-1 && 148 "PHI node shouldn't have this many values!!!"); 149 150 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value 151 if (max_idx == 2) 152 PN->replaceAllUsesWith(PN->getOperand(0)); 153 else // Otherwise there are no incoming values/edges, replace with dummy 154 PN->replaceAllUsesWith(Constant::getNullValue(PN->getType())); 155 getInstList().pop_front(); // Remove the PHI node 156 } 157 } else { 158 // Okay, now we know that we need to remove predecessor #pred_idx from all 159 // PHI nodes. Iterate over each PHI node fixing them up 160 for (iterator II = begin(); PHINode *PN = dyn_cast<PHINode>(&*II); ++II) 161 PN->removeIncomingValue(Pred); 162 } 163} 164 165 166// splitBasicBlock - This splits a basic block into two at the specified 167// instruction. Note that all instructions BEFORE the specified iterator stay 168// as part of the original basic block, an unconditional branch is added to 169// the new BB, and the rest of the instructions in the BB are moved to the new 170// BB, including the old terminator. This invalidates the iterator. 171// 172// Note that this only works on well formed basic blocks (must have a 173// terminator), and 'I' must not be the end of instruction list (which would 174// cause a degenerate basic block to be formed, having a terminator inside of 175// the basic block). 176// 177BasicBlock *BasicBlock::splitBasicBlock(iterator I) { 178 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!"); 179 assert(I != InstList.end() && 180 "Trying to get me to create degenerate basic block!"); 181 182 BasicBlock *New = new BasicBlock("", getParent()); 183 184 // Go from the end of the basic block through to the iterator pointer, moving 185 // to the new basic block... 186 Instruction *Inst = 0; 187 do { 188 iterator EndIt = end(); 189 Inst = InstList.remove(--EndIt); // Remove from end 190 New->InstList.push_front(Inst); // Add to front 191 } while (Inst != &*I); // Loop until we move the specified instruction. 192 193 // Add a branch instruction to the newly formed basic block. 194 InstList.push_back(new BranchInst(New)); 195 196 // Now we must loop through all of the successors of the New block (which 197 // _were_ the successors of the 'this' block), and update any PHI nodes in 198 // successors. If there were PHI nodes in the successors, then they need to 199 // know that incoming branches will be from New, not from Old. 200 // 201 for (BasicBlock::succ_iterator I = succ_begin(New), E = succ_end(New); 202 I != E; ++I) { 203 // Loop over any phi nodes in the basic block, updating the BB field of 204 // incoming values... 205 BasicBlock *Successor = *I; 206 for (BasicBlock::iterator II = Successor->begin(); 207 PHINode *PN = dyn_cast<PHINode>(&*II); ++II) { 208 int IDX = PN->getBasicBlockIndex(this); 209 while (IDX != -1) { 210 PN->setIncomingBlock((unsigned)IDX, New); 211 IDX = PN->getBasicBlockIndex(this); 212 } 213 } 214 } 215 return New; 216} 217