1 //===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==// 2 // 3 // This family of functions perform manipulations on basic blocks, and 4 // instructions contained within basic blocks. 5 // 6 //===----------------------------------------------------------------------===// 7 8 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 9 #include "llvm/Function.h" 10 #include "llvm/iTerminators.h" 11 #include "llvm/Constant.h" 12 #include "llvm/Type.h" 13 #include <algorithm> 14 15 // ReplaceInstWithValue - Replace all uses of an instruction (specified by BI) 16 // with a value, then remove and delete the original instruction. 17 // 18 void ReplaceInstWithValue(BasicBlock::InstListType &BIL, 19 BasicBlock::iterator &BI, Value *V) { 20 Instruction &I = *BI; 21 // Replaces all of the uses of the instruction with uses of the value 22 I.replaceAllUsesWith(V); 23 24 std::string OldName = I.getName(); 25 26 // Delete the unnecessary instruction now... 27 BI = BIL.erase(BI); 28 29 // Make sure to propagate a name if there is one already... 30 if (OldName.size() && !V->hasName()) 31 V->setName(OldName, &BIL.getParent()->getSymbolTable()); 32 } 33 34 35 // ReplaceInstWithInst - Replace the instruction specified by BI with the 36 // instruction specified by I. The original instruction is deleted and BI is 37 // updated to point to the new instruction. 38 // 39 void ReplaceInstWithInst(BasicBlock::InstListType &BIL, 40 BasicBlock::iterator &BI, Instruction *I) { 41 assert(I->getParent() == 0 && 42 "ReplaceInstWithInst: Instruction already inserted into basic block!"); 43 44 // Insert the new instruction into the basic block... 45 BasicBlock::iterator New = BIL.insert(BI, I); 46 47 // Replace all uses of the old instruction, and delete it. 48 ReplaceInstWithValue(BIL, BI, I); 49 50 // Move BI back to point to the newly inserted instruction 51 BI = New; 52 } 53 54 // ReplaceInstWithInst - Replace the instruction specified by From with the 55 // instruction specified by To. 56 // 57 void ReplaceInstWithInst(Instruction *From, Instruction *To) { 58 BasicBlock::iterator BI(From); 59 ReplaceInstWithInst(From->getParent()->getInstList(), BI, To); 60 } 61 62 // RemoveSuccessor - Change the specified terminator instruction such that its 63 // successor #SuccNum no longer exists. Because this reduces the outgoing 64 // degree of the current basic block, the actual terminator instruction itself 65 // may have to be changed. In the case where the last successor of the block is 66 // deleted, a return instruction is inserted in its place which can cause a 67 // suprising change in program behavior if it is not expected. 68 // 69 void RemoveSuccessor(TerminatorInst *TI, unsigned SuccNum) { 70 assert(SuccNum < TI->getNumSuccessors() && 71 "Trying to remove a nonexistant successor!"); 72 73 // If our old successor block contains any PHI nodes, remove the entry in the 74 // PHI nodes that comes from this branch... 75 // 76 BasicBlock *BB = TI->getParent(); 77 TI->getSuccessor(SuccNum)->removePredecessor(BB); 78 79 TerminatorInst *NewTI = 0; 80 switch (TI->getOpcode()) { 81 case Instruction::Br: 82 // If this is a conditional branch... convert to unconditional branch. 83 if (TI->getNumSuccessors() == 2) { 84 cast<BranchInst>(TI)->setUnconditionalDest(TI->getSuccessor(1-SuccNum)); 85 } else { // Otherwise convert to a return instruction... 86 Value *RetVal = 0; 87 88 // Create a value to return... if the function doesn't return null... 89 if (BB->getParent()->getReturnType() != Type::VoidTy) 90 RetVal = Constant::getNullValue(BB->getParent()->getReturnType()); 91 92 // Create the return... 93 NewTI = new ReturnInst(RetVal); 94 } 95 break; 96 97 case Instruction::Invoke: // Should convert to call 98 case Instruction::Switch: // Should remove entry 99 default: 100 case Instruction::Ret: // Cannot happen, has no successors! 101 assert(0 && "Unhandled terminator instruction type in RemoveSuccessor!"); 102 abort(); 103 } 104 105 if (NewTI) // If it's a different instruction, replace. 106 ReplaceInstWithInst(TI, NewTI); 107 } 108