CloneFunction.cpp revision 9e9a0d5fc26878e51a58a8b57900fcbf952c2691
1//===- CloneFunction.cpp - Clone a function into another function ---------===// 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 file implements the CloneFunctionInto interface, which is used as the 11// low-level function cloner. This is used by the CloneFunction and function 12// inliner to do the dirty work of copying the body of a function around. 13// 14//===----------------------------------------------------------------------===// 15 16#include "llvm/Transforms/Utils/Cloning.h" 17#include "llvm/Constants.h" 18#include "llvm/DerivedTypes.h" 19#include "llvm/Instructions.h" 20#include "llvm/IntrinsicInst.h" 21#include "llvm/GlobalVariable.h" 22#include "llvm/Function.h" 23#include "llvm/LLVMContext.h" 24#include "llvm/Support/CFG.h" 25#include "llvm/Support/Compiler.h" 26#include "llvm/Transforms/Utils/ValueMapper.h" 27#include "llvm/Analysis/ConstantFolding.h" 28#include "llvm/Analysis/DebugInfo.h" 29#include "llvm/ADT/SmallVector.h" 30#include <map> 31using namespace llvm; 32 33// CloneBasicBlock - See comments in Cloning.h 34BasicBlock *llvm::CloneBasicBlock(const BasicBlock *BB, 35 DenseMap<const Value*, Value*> &ValueMap, 36 const char *NameSuffix, Function *F, 37 ClonedCodeInfo *CodeInfo) { 38 BasicBlock *NewBB = BasicBlock::Create("", F); 39 if (BB->hasName()) NewBB->setName(BB->getName()+NameSuffix); 40 41 bool hasCalls = false, hasDynamicAllocas = false, hasStaticAllocas = false; 42 43 // Loop over all instructions, and copy them over. 44 for (BasicBlock::const_iterator II = BB->begin(), IE = BB->end(); 45 II != IE; ++II) { 46 Instruction *NewInst = II->clone(BB->getContext()); 47 if (II->hasName()) 48 NewInst->setName(II->getName()+NameSuffix); 49 NewBB->getInstList().push_back(NewInst); 50 ValueMap[II] = NewInst; // Add instruction map to value. 51 52 hasCalls |= (isa<CallInst>(II) && !isa<DbgInfoIntrinsic>(II)); 53 if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) { 54 if (isa<ConstantInt>(AI->getArraySize())) 55 hasStaticAllocas = true; 56 else 57 hasDynamicAllocas = true; 58 } 59 } 60 61 if (CodeInfo) { 62 CodeInfo->ContainsCalls |= hasCalls; 63 CodeInfo->ContainsUnwinds |= isa<UnwindInst>(BB->getTerminator()); 64 CodeInfo->ContainsDynamicAllocas |= hasDynamicAllocas; 65 CodeInfo->ContainsDynamicAllocas |= hasStaticAllocas && 66 BB != &BB->getParent()->getEntryBlock(); 67 } 68 return NewBB; 69} 70 71// Clone OldFunc into NewFunc, transforming the old arguments into references to 72// ArgMap values. 73// 74void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc, 75 DenseMap<const Value*, Value*> &ValueMap, 76 std::vector<ReturnInst*> &Returns, 77 const char *NameSuffix, ClonedCodeInfo *CodeInfo) { 78 assert(NameSuffix && "NameSuffix cannot be null!"); 79 80#ifndef NDEBUG 81 for (Function::const_arg_iterator I = OldFunc->arg_begin(), 82 E = OldFunc->arg_end(); I != E; ++I) 83 assert(ValueMap.count(I) && "No mapping from source argument specified!"); 84#endif 85 86 // Clone any attributes. 87 if (NewFunc->arg_size() == OldFunc->arg_size()) 88 NewFunc->copyAttributesFrom(OldFunc); 89 else { 90 //Some arguments were deleted with the ValueMap. Copy arguments one by one 91 for (Function::const_arg_iterator I = OldFunc->arg_begin(), 92 E = OldFunc->arg_end(); I != E; ++I) 93 if (Argument* Anew = dyn_cast<Argument>(ValueMap[I])) 94 Anew->addAttr( OldFunc->getAttributes() 95 .getParamAttributes(I->getArgNo() + 1)); 96 NewFunc->setAttributes(NewFunc->getAttributes() 97 .addAttr(0, OldFunc->getAttributes() 98 .getRetAttributes())); 99 NewFunc->setAttributes(NewFunc->getAttributes() 100 .addAttr(~0, OldFunc->getAttributes() 101 .getFnAttributes())); 102 103 } 104 105 // Loop over all of the basic blocks in the function, cloning them as 106 // appropriate. Note that we save BE this way in order to handle cloning of 107 // recursive functions into themselves. 108 // 109 for (Function::const_iterator BI = OldFunc->begin(), BE = OldFunc->end(); 110 BI != BE; ++BI) { 111 const BasicBlock &BB = *BI; 112 113 // Create a new basic block and copy instructions into it! 114 BasicBlock *CBB = CloneBasicBlock(&BB, ValueMap, NameSuffix, NewFunc, 115 CodeInfo); 116 ValueMap[&BB] = CBB; // Add basic block mapping. 117 118 if (ReturnInst *RI = dyn_cast<ReturnInst>(CBB->getTerminator())) 119 Returns.push_back(RI); 120 } 121 122 // Loop over all of the instructions in the function, fixing up operand 123 // references as we go. This uses ValueMap to do all the hard work. 124 // 125 for (Function::iterator BB = cast<BasicBlock>(ValueMap[OldFunc->begin()]), 126 BE = NewFunc->end(); BB != BE; ++BB) 127 // Loop over all instructions, fixing each one as we find it... 128 for (BasicBlock::iterator II = BB->begin(); II != BB->end(); ++II) 129 RemapInstruction(II, ValueMap); 130} 131 132/// CloneFunction - Return a copy of the specified function, but without 133/// embedding the function into another module. Also, any references specified 134/// in the ValueMap are changed to refer to their mapped value instead of the 135/// original one. If any of the arguments to the function are in the ValueMap, 136/// the arguments are deleted from the resultant function. The ValueMap is 137/// updated to include mappings from all of the instructions and basicblocks in 138/// the function from their old to new values. 139/// 140Function *llvm::CloneFunction(const Function *F, 141 DenseMap<const Value*, Value*> &ValueMap, 142 ClonedCodeInfo *CodeInfo) { 143 std::vector<const Type*> ArgTypes; 144 145 // The user might be deleting arguments to the function by specifying them in 146 // the ValueMap. If so, we need to not add the arguments to the arg ty vector 147 // 148 for (Function::const_arg_iterator I = F->arg_begin(), E = F->arg_end(); 149 I != E; ++I) 150 if (ValueMap.count(I) == 0) // Haven't mapped the argument to anything yet? 151 ArgTypes.push_back(I->getType()); 152 153 // Create a new function type... 154 FunctionType *FTy = FunctionType::get(F->getFunctionType()->getReturnType(), 155 ArgTypes, F->getFunctionType()->isVarArg()); 156 157 // Create the new function... 158 Function *NewF = Function::Create(FTy, F->getLinkage(), F->getName()); 159 160 // Loop over the arguments, copying the names of the mapped arguments over... 161 Function::arg_iterator DestI = NewF->arg_begin(); 162 for (Function::const_arg_iterator I = F->arg_begin(), E = F->arg_end(); 163 I != E; ++I) 164 if (ValueMap.count(I) == 0) { // Is this argument preserved? 165 DestI->setName(I->getName()); // Copy the name over... 166 ValueMap[I] = DestI++; // Add mapping to ValueMap 167 } 168 169 std::vector<ReturnInst*> Returns; // Ignore returns cloned... 170 CloneFunctionInto(NewF, F, ValueMap, Returns, "", CodeInfo); 171 return NewF; 172} 173 174 175 176namespace { 177 /// PruningFunctionCloner - This class is a private class used to implement 178 /// the CloneAndPruneFunctionInto method. 179 struct VISIBILITY_HIDDEN PruningFunctionCloner { 180 Function *NewFunc; 181 const Function *OldFunc; 182 DenseMap<const Value*, Value*> &ValueMap; 183 std::vector<ReturnInst*> &Returns; 184 const char *NameSuffix; 185 ClonedCodeInfo *CodeInfo; 186 const TargetData *TD; 187 Value *DbgFnStart; 188 public: 189 PruningFunctionCloner(Function *newFunc, const Function *oldFunc, 190 DenseMap<const Value*, Value*> &valueMap, 191 std::vector<ReturnInst*> &returns, 192 const char *nameSuffix, 193 ClonedCodeInfo *codeInfo, 194 const TargetData *td) 195 : NewFunc(newFunc), OldFunc(oldFunc), ValueMap(valueMap), Returns(returns), 196 NameSuffix(nameSuffix), CodeInfo(codeInfo), TD(td), DbgFnStart(NULL) { 197 } 198 199 /// CloneBlock - The specified block is found to be reachable, clone it and 200 /// anything that it can reach. 201 void CloneBlock(const BasicBlock *BB, 202 std::vector<const BasicBlock*> &ToClone); 203 204 public: 205 /// ConstantFoldMappedInstruction - Constant fold the specified instruction, 206 /// mapping its operands through ValueMap if they are available. 207 Constant *ConstantFoldMappedInstruction(const Instruction *I); 208 }; 209} 210 211/// CloneBlock - The specified block is found to be reachable, clone it and 212/// anything that it can reach. 213void PruningFunctionCloner::CloneBlock(const BasicBlock *BB, 214 std::vector<const BasicBlock*> &ToClone){ 215 Value *&BBEntry = ValueMap[BB]; 216 217 // Have we already cloned this block? 218 if (BBEntry) return; 219 220 // Nope, clone it now. 221 BasicBlock *NewBB; 222 BBEntry = NewBB = BasicBlock::Create(); 223 if (BB->hasName()) NewBB->setName(BB->getName()+NameSuffix); 224 225 bool hasCalls = false, hasDynamicAllocas = false, hasStaticAllocas = false; 226 227 // Loop over all instructions, and copy them over, DCE'ing as we go. This 228 // loop doesn't include the terminator. 229 for (BasicBlock::const_iterator II = BB->begin(), IE = --BB->end(); 230 II != IE; ++II) { 231 // If this instruction constant folds, don't bother cloning the instruction, 232 // instead, just add the constant to the value map. 233 if (Constant *C = ConstantFoldMappedInstruction(II)) { 234 ValueMap[II] = C; 235 continue; 236 } 237 238 // Do not clone llvm.dbg.region.end. It will be adjusted by the inliner. 239 if (const DbgFuncStartInst *DFSI = dyn_cast<DbgFuncStartInst>(II)) { 240 if (DbgFnStart == NULL) { 241 DISubprogram SP(cast<GlobalVariable>(DFSI->getSubprogram())); 242 if (SP.describes(BB->getParent())) 243 DbgFnStart = DFSI->getSubprogram(); 244 } 245 } 246 if (const DbgRegionEndInst *DREIS = dyn_cast<DbgRegionEndInst>(II)) { 247 if (DREIS->getContext() == DbgFnStart) 248 continue; 249 } 250 251 Instruction *NewInst = II->clone(BB->getContext()); 252 if (II->hasName()) 253 NewInst->setName(II->getName()+NameSuffix); 254 NewBB->getInstList().push_back(NewInst); 255 ValueMap[II] = NewInst; // Add instruction map to value. 256 257 hasCalls |= (isa<CallInst>(II) && !isa<DbgInfoIntrinsic>(II)); 258 if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) { 259 if (isa<ConstantInt>(AI->getArraySize())) 260 hasStaticAllocas = true; 261 else 262 hasDynamicAllocas = true; 263 } 264 } 265 266 // Finally, clone over the terminator. 267 const TerminatorInst *OldTI = BB->getTerminator(); 268 bool TerminatorDone = false; 269 if (const BranchInst *BI = dyn_cast<BranchInst>(OldTI)) { 270 if (BI->isConditional()) { 271 // If the condition was a known constant in the callee... 272 ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition()); 273 // Or is a known constant in the caller... 274 if (Cond == 0) 275 Cond = dyn_cast_or_null<ConstantInt>(ValueMap[BI->getCondition()]); 276 277 // Constant fold to uncond branch! 278 if (Cond) { 279 BasicBlock *Dest = BI->getSuccessor(!Cond->getZExtValue()); 280 ValueMap[OldTI] = BranchInst::Create(Dest, NewBB); 281 ToClone.push_back(Dest); 282 TerminatorDone = true; 283 } 284 } 285 } else if (const SwitchInst *SI = dyn_cast<SwitchInst>(OldTI)) { 286 // If switching on a value known constant in the caller. 287 ConstantInt *Cond = dyn_cast<ConstantInt>(SI->getCondition()); 288 if (Cond == 0) // Or known constant after constant prop in the callee... 289 Cond = dyn_cast_or_null<ConstantInt>(ValueMap[SI->getCondition()]); 290 if (Cond) { // Constant fold to uncond branch! 291 BasicBlock *Dest = SI->getSuccessor(SI->findCaseValue(Cond)); 292 ValueMap[OldTI] = BranchInst::Create(Dest, NewBB); 293 ToClone.push_back(Dest); 294 TerminatorDone = true; 295 } 296 } 297 298 if (!TerminatorDone) { 299 Instruction *NewInst = OldTI->clone(BB->getContext()); 300 if (OldTI->hasName()) 301 NewInst->setName(OldTI->getName()+NameSuffix); 302 NewBB->getInstList().push_back(NewInst); 303 ValueMap[OldTI] = NewInst; // Add instruction map to value. 304 305 // Recursively clone any reachable successor blocks. 306 const TerminatorInst *TI = BB->getTerminator(); 307 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) 308 ToClone.push_back(TI->getSuccessor(i)); 309 } 310 311 if (CodeInfo) { 312 CodeInfo->ContainsCalls |= hasCalls; 313 CodeInfo->ContainsUnwinds |= isa<UnwindInst>(OldTI); 314 CodeInfo->ContainsDynamicAllocas |= hasDynamicAllocas; 315 CodeInfo->ContainsDynamicAllocas |= hasStaticAllocas && 316 BB != &BB->getParent()->front(); 317 } 318 319 if (ReturnInst *RI = dyn_cast<ReturnInst>(NewBB->getTerminator())) 320 Returns.push_back(RI); 321} 322 323/// ConstantFoldMappedInstruction - Constant fold the specified instruction, 324/// mapping its operands through ValueMap if they are available. 325Constant *PruningFunctionCloner:: 326ConstantFoldMappedInstruction(const Instruction *I) { 327 LLVMContext &Context = I->getContext(); 328 329 SmallVector<Constant*, 8> Ops; 330 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 331 if (Constant *Op = dyn_cast_or_null<Constant>(MapValue(I->getOperand(i), 332 ValueMap, 333 Context))) 334 Ops.push_back(Op); 335 else 336 return 0; // All operands not constant! 337 338 if (const CmpInst *CI = dyn_cast<CmpInst>(I)) 339 return ConstantFoldCompareInstOperands(CI->getPredicate(), 340 &Ops[0], Ops.size(), 341 Context, TD); 342 343 if (const LoadInst *LI = dyn_cast<LoadInst>(I)) 344 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ops[0])) 345 if (!LI->isVolatile() && CE->getOpcode() == Instruction::GetElementPtr) 346 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0))) 347 if (GV->isConstant() && GV->hasDefinitiveInitializer()) 348 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), 349 CE, Context); 350 351 return ConstantFoldInstOperands(I->getOpcode(), I->getType(), &Ops[0], 352 Ops.size(), Context, TD); 353} 354 355/// CloneAndPruneFunctionInto - This works exactly like CloneFunctionInto, 356/// except that it does some simple constant prop and DCE on the fly. The 357/// effect of this is to copy significantly less code in cases where (for 358/// example) a function call with constant arguments is inlined, and those 359/// constant arguments cause a significant amount of code in the callee to be 360/// dead. Since this doesn't produce an exact copy of the input, it can't be 361/// used for things like CloneFunction or CloneModule. 362void llvm::CloneAndPruneFunctionInto(Function *NewFunc, const Function *OldFunc, 363 DenseMap<const Value*, Value*> &ValueMap, 364 std::vector<ReturnInst*> &Returns, 365 const char *NameSuffix, 366 ClonedCodeInfo *CodeInfo, 367 const TargetData *TD) { 368 assert(NameSuffix && "NameSuffix cannot be null!"); 369 LLVMContext &Context = OldFunc->getContext(); 370 371#ifndef NDEBUG 372 for (Function::const_arg_iterator II = OldFunc->arg_begin(), 373 E = OldFunc->arg_end(); II != E; ++II) 374 assert(ValueMap.count(II) && "No mapping from source argument specified!"); 375#endif 376 377 PruningFunctionCloner PFC(NewFunc, OldFunc, ValueMap, Returns, 378 NameSuffix, CodeInfo, TD); 379 380 // Clone the entry block, and anything recursively reachable from it. 381 std::vector<const BasicBlock*> CloneWorklist; 382 CloneWorklist.push_back(&OldFunc->getEntryBlock()); 383 while (!CloneWorklist.empty()) { 384 const BasicBlock *BB = CloneWorklist.back(); 385 CloneWorklist.pop_back(); 386 PFC.CloneBlock(BB, CloneWorklist); 387 } 388 389 // Loop over all of the basic blocks in the old function. If the block was 390 // reachable, we have cloned it and the old block is now in the value map: 391 // insert it into the new function in the right order. If not, ignore it. 392 // 393 // Defer PHI resolution until rest of function is resolved. 394 std::vector<const PHINode*> PHIToResolve; 395 for (Function::const_iterator BI = OldFunc->begin(), BE = OldFunc->end(); 396 BI != BE; ++BI) { 397 BasicBlock *NewBB = cast_or_null<BasicBlock>(ValueMap[BI]); 398 if (NewBB == 0) continue; // Dead block. 399 400 // Add the new block to the new function. 401 NewFunc->getBasicBlockList().push_back(NewBB); 402 403 // Loop over all of the instructions in the block, fixing up operand 404 // references as we go. This uses ValueMap to do all the hard work. 405 // 406 BasicBlock::iterator I = NewBB->begin(); 407 408 // Handle PHI nodes specially, as we have to remove references to dead 409 // blocks. 410 if (PHINode *PN = dyn_cast<PHINode>(I)) { 411 // Skip over all PHI nodes, remembering them for later. 412 BasicBlock::const_iterator OldI = BI->begin(); 413 for (; (PN = dyn_cast<PHINode>(I)); ++I, ++OldI) 414 PHIToResolve.push_back(cast<PHINode>(OldI)); 415 } 416 417 // Otherwise, remap the rest of the instructions normally. 418 for (; I != NewBB->end(); ++I) 419 RemapInstruction(I, ValueMap); 420 } 421 422 // Defer PHI resolution until rest of function is resolved, PHI resolution 423 // requires the CFG to be up-to-date. 424 for (unsigned phino = 0, e = PHIToResolve.size(); phino != e; ) { 425 const PHINode *OPN = PHIToResolve[phino]; 426 unsigned NumPreds = OPN->getNumIncomingValues(); 427 const BasicBlock *OldBB = OPN->getParent(); 428 BasicBlock *NewBB = cast<BasicBlock>(ValueMap[OldBB]); 429 430 // Map operands for blocks that are live and remove operands for blocks 431 // that are dead. 432 for (; phino != PHIToResolve.size() && 433 PHIToResolve[phino]->getParent() == OldBB; ++phino) { 434 OPN = PHIToResolve[phino]; 435 PHINode *PN = cast<PHINode>(ValueMap[OPN]); 436 for (unsigned pred = 0, e = NumPreds; pred != e; ++pred) { 437 if (BasicBlock *MappedBlock = 438 cast_or_null<BasicBlock>(ValueMap[PN->getIncomingBlock(pred)])) { 439 Value *InVal = MapValue(PN->getIncomingValue(pred), 440 ValueMap, Context); 441 assert(InVal && "Unknown input value?"); 442 PN->setIncomingValue(pred, InVal); 443 PN->setIncomingBlock(pred, MappedBlock); 444 } else { 445 PN->removeIncomingValue(pred, false); 446 --pred, --e; // Revisit the next entry. 447 } 448 } 449 } 450 451 // The loop above has removed PHI entries for those blocks that are dead 452 // and has updated others. However, if a block is live (i.e. copied over) 453 // but its terminator has been changed to not go to this block, then our 454 // phi nodes will have invalid entries. Update the PHI nodes in this 455 // case. 456 PHINode *PN = cast<PHINode>(NewBB->begin()); 457 NumPreds = std::distance(pred_begin(NewBB), pred_end(NewBB)); 458 if (NumPreds != PN->getNumIncomingValues()) { 459 assert(NumPreds < PN->getNumIncomingValues()); 460 // Count how many times each predecessor comes to this block. 461 std::map<BasicBlock*, unsigned> PredCount; 462 for (pred_iterator PI = pred_begin(NewBB), E = pred_end(NewBB); 463 PI != E; ++PI) 464 --PredCount[*PI]; 465 466 // Figure out how many entries to remove from each PHI. 467 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 468 ++PredCount[PN->getIncomingBlock(i)]; 469 470 // At this point, the excess predecessor entries are positive in the 471 // map. Loop over all of the PHIs and remove excess predecessor 472 // entries. 473 BasicBlock::iterator I = NewBB->begin(); 474 for (; (PN = dyn_cast<PHINode>(I)); ++I) { 475 for (std::map<BasicBlock*, unsigned>::iterator PCI =PredCount.begin(), 476 E = PredCount.end(); PCI != E; ++PCI) { 477 BasicBlock *Pred = PCI->first; 478 for (unsigned NumToRemove = PCI->second; NumToRemove; --NumToRemove) 479 PN->removeIncomingValue(Pred, false); 480 } 481 } 482 } 483 484 // If the loops above have made these phi nodes have 0 or 1 operand, 485 // replace them with undef or the input value. We must do this for 486 // correctness, because 0-operand phis are not valid. 487 PN = cast<PHINode>(NewBB->begin()); 488 if (PN->getNumIncomingValues() == 0) { 489 BasicBlock::iterator I = NewBB->begin(); 490 BasicBlock::const_iterator OldI = OldBB->begin(); 491 while ((PN = dyn_cast<PHINode>(I++))) { 492 Value *NV = UndefValue::get(PN->getType()); 493 PN->replaceAllUsesWith(NV); 494 assert(ValueMap[OldI] == PN && "ValueMap mismatch"); 495 ValueMap[OldI] = NV; 496 PN->eraseFromParent(); 497 ++OldI; 498 } 499 } 500 // NOTE: We cannot eliminate single entry phi nodes here, because of 501 // ValueMap. Single entry phi nodes can have multiple ValueMap entries 502 // pointing at them. Thus, deleting one would require scanning the ValueMap 503 // to update any entries in it that would require that. This would be 504 // really slow. 505 } 506 507 // Now that the inlined function body has been fully constructed, go through 508 // and zap unconditional fall-through branches. This happen all the time when 509 // specializing code: code specialization turns conditional branches into 510 // uncond branches, and this code folds them. 511 Function::iterator I = cast<BasicBlock>(ValueMap[&OldFunc->getEntryBlock()]); 512 while (I != NewFunc->end()) { 513 BranchInst *BI = dyn_cast<BranchInst>(I->getTerminator()); 514 if (!BI || BI->isConditional()) { ++I; continue; } 515 516 // Note that we can't eliminate uncond branches if the destination has 517 // single-entry PHI nodes. Eliminating the single-entry phi nodes would 518 // require scanning the ValueMap to update any entries that point to the phi 519 // node. 520 BasicBlock *Dest = BI->getSuccessor(0); 521 if (!Dest->getSinglePredecessor() || isa<PHINode>(Dest->begin())) { 522 ++I; continue; 523 } 524 525 // We know all single-entry PHI nodes in the inlined function have been 526 // removed, so we just need to splice the blocks. 527 BI->eraseFromParent(); 528 529 // Move all the instructions in the succ to the pred. 530 I->getInstList().splice(I->end(), Dest->getInstList()); 531 532 // Make all PHI nodes that referred to Dest now refer to I as their source. 533 Dest->replaceAllUsesWith(I); 534 535 // Remove the dest block. 536 Dest->eraseFromParent(); 537 538 // Do not increment I, iteratively merge all things this block branches to. 539 } 540} 541