BasicBlockUtils.cpp revision 280a6e607d8eb7401749a92db624a82de47da777
1//===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This family of functions perform manipulations on basic blocks, and 11// instructions contained within basic blocks. 12// 13//===----------------------------------------------------------------------===// 14 15#include "llvm/Transforms/Utils/BasicBlockUtils.h" 16#include "llvm/Function.h" 17#include "llvm/Instructions.h" 18#include "llvm/Constant.h" 19#include "llvm/Type.h" 20#include "llvm/Analysis/AliasAnalysis.h" 21#include "llvm/Analysis/LoopInfo.h" 22#include "llvm/Analysis/Dominators.h" 23#include <algorithm> 24using namespace llvm; 25 26/// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI) 27/// with a value, then remove and delete the original instruction. 28/// 29void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL, 30 BasicBlock::iterator &BI, Value *V) { 31 Instruction &I = *BI; 32 // Replaces all of the uses of the instruction with uses of the value 33 I.replaceAllUsesWith(V); 34 35 // Make sure to propagate a name if there is one already. 36 if (I.hasName() && !V->hasName()) 37 V->takeName(&I); 38 39 // Delete the unnecessary instruction now... 40 BI = BIL.erase(BI); 41} 42 43 44/// ReplaceInstWithInst - Replace the instruction specified by BI with the 45/// instruction specified by I. The original instruction is deleted and BI is 46/// updated to point to the new instruction. 47/// 48void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL, 49 BasicBlock::iterator &BI, Instruction *I) { 50 assert(I->getParent() == 0 && 51 "ReplaceInstWithInst: Instruction already inserted into basic block!"); 52 53 // Insert the new instruction into the basic block... 54 BasicBlock::iterator New = BIL.insert(BI, I); 55 56 // Replace all uses of the old instruction, and delete it. 57 ReplaceInstWithValue(BIL, BI, I); 58 59 // Move BI back to point to the newly inserted instruction 60 BI = New; 61} 62 63/// ReplaceInstWithInst - Replace the instruction specified by From with the 64/// instruction specified by To. 65/// 66void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) { 67 BasicBlock::iterator BI(From); 68 ReplaceInstWithInst(From->getParent()->getInstList(), BI, To); 69} 70 71/// RemoveSuccessor - Change the specified terminator instruction such that its 72/// successor SuccNum no longer exists. Because this reduces the outgoing 73/// degree of the current basic block, the actual terminator instruction itself 74/// may have to be changed. In the case where the last successor of the block 75/// is deleted, a return instruction is inserted in its place which can cause a 76/// surprising change in program behavior if it is not expected. 77/// 78void llvm::RemoveSuccessor(TerminatorInst *TI, unsigned SuccNum) { 79 assert(SuccNum < TI->getNumSuccessors() && 80 "Trying to remove a nonexistant successor!"); 81 82 // If our old successor block contains any PHI nodes, remove the entry in the 83 // PHI nodes that comes from this branch... 84 // 85 BasicBlock *BB = TI->getParent(); 86 TI->getSuccessor(SuccNum)->removePredecessor(BB); 87 88 TerminatorInst *NewTI = 0; 89 switch (TI->getOpcode()) { 90 case Instruction::Br: 91 // If this is a conditional branch... convert to unconditional branch. 92 if (TI->getNumSuccessors() == 2) { 93 cast<BranchInst>(TI)->setUnconditionalDest(TI->getSuccessor(1-SuccNum)); 94 } else { // Otherwise convert to a return instruction... 95 Value *RetVal = 0; 96 97 // Create a value to return... if the function doesn't return null... 98 if (BB->getParent()->getReturnType() != Type::VoidTy) 99 RetVal = Constant::getNullValue(BB->getParent()->getReturnType()); 100 101 // Create the return... 102 NewTI = ReturnInst::Create(RetVal); 103 } 104 break; 105 106 case Instruction::Invoke: // Should convert to call 107 case Instruction::Switch: // Should remove entry 108 default: 109 case Instruction::Ret: // Cannot happen, has no successors! 110 assert(0 && "Unhandled terminator instruction type in RemoveSuccessor!"); 111 abort(); 112 } 113 114 if (NewTI) // If it's a different instruction, replace. 115 ReplaceInstWithInst(TI, NewTI); 116} 117 118/// SplitEdge - Split the edge connecting specified block. Pass P must 119/// not be NULL. 120BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) { 121 TerminatorInst *LatchTerm = BB->getTerminator(); 122 unsigned SuccNum = 0; 123 for (unsigned i = 0, e = LatchTerm->getNumSuccessors(); ; ++i) { 124 assert(i != e && "Didn't find edge?"); 125 if (LatchTerm->getSuccessor(i) == Succ) { 126 SuccNum = i; 127 break; 128 } 129 } 130 131 // If this is a critical edge, let SplitCriticalEdge do it. 132 if (SplitCriticalEdge(BB->getTerminator(), SuccNum, P)) 133 return LatchTerm->getSuccessor(SuccNum); 134 135 // If the edge isn't critical, then BB has a single successor or Succ has a 136 // single pred. Split the block. 137 BasicBlock::iterator SplitPoint; 138 if (BasicBlock *SP = Succ->getSinglePredecessor()) { 139 // If the successor only has a single pred, split the top of the successor 140 // block. 141 assert(SP == BB && "CFG broken"); 142 return SplitBlock(Succ, Succ->begin(), P); 143 } else { 144 // Otherwise, if BB has a single successor, split it at the bottom of the 145 // block. 146 assert(BB->getTerminator()->getNumSuccessors() == 1 && 147 "Should have a single succ!"); 148 return SplitBlock(BB, BB->getTerminator(), P); 149 } 150} 151 152/// SplitBlock - Split the specified block at the specified instruction - every 153/// thing before SplitPt stays in Old and everything starting with SplitPt moves 154/// to a new block. The two blocks are joined by an unconditional branch and 155/// the loop info is updated. 156/// 157BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) { 158 159 LoopInfo &LI = P->getAnalysis<LoopInfo>(); 160 BasicBlock::iterator SplitIt = SplitPt; 161 while (isa<PHINode>(SplitIt)) 162 ++SplitIt; 163 BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split"); 164 165 // The new block lives in whichever loop the old one did. 166 if (Loop *L = LI.getLoopFor(Old)) 167 L->addBasicBlockToLoop(New, LI.getBase()); 168 169 if (DominatorTree *DT = P->getAnalysisToUpdate<DominatorTree>()) 170 { 171 // Old dominates New. New node domiantes all other nodes dominated by Old. 172 DomTreeNode *OldNode = DT->getNode(Old); 173 std::vector<DomTreeNode *> Children; 174 for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end(); 175 I != E; ++I) 176 Children.push_back(*I); 177 178 DomTreeNode *NewNode = DT->addNewBlock(New,Old); 179 180 for (std::vector<DomTreeNode *>::iterator I = Children.begin(), 181 E = Children.end(); I != E; ++I) 182 DT->changeImmediateDominator(*I, NewNode); 183 } 184 185 if (DominanceFrontier *DF = P->getAnalysisToUpdate<DominanceFrontier>()) 186 DF->splitBlock(Old); 187 188 return New; 189} 190 191 192/// SplitBlockPredecessors - This method transforms BB by introducing a new 193/// basic block into the function, and moving some of the predecessors of BB to 194/// be predecessors of the new block. The new predecessors are indicated by the 195/// Preds array, which has NumPreds elements in it. The new block is given a 196/// suffix of 'Suffix'. 197/// 198/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree and 199/// DominanceFrontier, but no other analyses. 200BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB, 201 BasicBlock *const *Preds, 202 unsigned NumPreds, const char *Suffix, 203 Pass *P) { 204 // Create new basic block, insert right before the original block. 205 BasicBlock *NewBB = 206 BasicBlock::Create(BB->getName()+Suffix, BB->getParent(), BB); 207 208 // The new block unconditionally branches to the old block. 209 BranchInst *BI = BranchInst::Create(BB, NewBB); 210 211 // Move the edges from Preds to point to NewBB instead of BB. 212 for (unsigned i = 0; i != NumPreds; ++i) 213 Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB); 214 215 // Update dominator tree and dominator frontier if available. 216 DominatorTree *DT = P ? P->getAnalysisToUpdate<DominatorTree>() : 0; 217 if (DT) 218 DT->splitBlock(NewBB); 219 if (DominanceFrontier *DF = P ? P->getAnalysisToUpdate<DominanceFrontier>():0) 220 DF->splitBlock(NewBB); 221 AliasAnalysis *AA = P ? P->getAnalysisToUpdate<AliasAnalysis>() : 0; 222 223 224 // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI 225 // node becomes an incoming value for BB's phi node. However, if the Preds 226 // list is empty, we need to insert dummy entries into the PHI nodes in BB to 227 // account for the newly created predecessor. 228 if (NumPreds == 0) { 229 // Insert dummy values as the incoming value. 230 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I) 231 cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB); 232 return NewBB; 233 } 234 235 // Otherwise, create a new PHI node in NewBB for each PHI node in BB. 236 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) { 237 PHINode *PN = cast<PHINode>(I++); 238 239 // Check to see if all of the values coming in are the same. If so, we 240 // don't need to create a new PHI node. 241 Value *InVal = PN->getIncomingValueForBlock(Preds[0]); 242 for (unsigned i = 1; i != NumPreds; ++i) 243 if (InVal != PN->getIncomingValueForBlock(Preds[i])) { 244 InVal = 0; 245 break; 246 } 247 248 if (InVal) { 249 // If all incoming values for the new PHI would be the same, just don't 250 // make a new PHI. Instead, just remove the incoming values from the old 251 // PHI. 252 for (unsigned i = 0; i != NumPreds; ++i) 253 PN->removeIncomingValue(Preds[i], false); 254 } else { 255 // If the values coming into the block are not the same, we need a PHI. 256 // Create the new PHI node, insert it into NewBB at the end of the block 257 PHINode *NewPHI = 258 PHINode::Create(PN->getType(), PN->getName()+".ph", BI); 259 if (AA) AA->copyValue(PN, NewPHI); 260 261 // Move all of the PHI values for 'Preds' to the new PHI. 262 for (unsigned i = 0; i != NumPreds; ++i) { 263 Value *V = PN->removeIncomingValue(Preds[i], false); 264 NewPHI->addIncoming(V, Preds[i]); 265 } 266 InVal = NewPHI; 267 } 268 269 // Add an incoming value to the PHI node in the loop for the preheader 270 // edge. 271 PN->addIncoming(InVal, NewBB); 272 273 // Check to see if we can eliminate this phi node. 274 if (Value *V = PN->hasConstantValue(DT != 0)) { 275 Instruction *I = dyn_cast<Instruction>(V); 276 if (!I || DT == 0 || DT->dominates(I, PN)) { 277 PN->replaceAllUsesWith(V); 278 if (AA) AA->deleteValue(PN); 279 PN->eraseFromParent(); 280 } 281 } 282 } 283 284 return NewBB; 285} 286