InlineFunction.cpp revision ee5457cbe88b7f691f774de8515d9a94226d1b00
1//===- InlineFunction.cpp - Code to perform function inlining -------------===// 2// 3// This file implements inlining of a function into a call site, resolving 4// parameters and the return value as appropriate. 5// 6// FIXME: This pass should transform alloca instructions in the called function 7// into malloc/free pairs! Or perhaps it should refuse to inline them! 8// 9//===----------------------------------------------------------------------===// 10 11#include "llvm/Transforms/Utils/Cloning.h" 12#include "llvm/Constant.h" 13#include "llvm/DerivedTypes.h" 14#include "llvm/Module.h" 15#include "llvm/Instructions.h" 16#include "llvm/Intrinsics.h" 17#include "llvm/Support/CallSite.h" 18#include "llvm/Transforms/Utils/Local.h" 19 20bool InlineFunction(CallInst *CI) { return InlineFunction(CallSite(CI)); } 21bool InlineFunction(InvokeInst *II) { return InlineFunction(CallSite(II)); } 22 23// InlineFunction - This function inlines the called function into the basic 24// block of the caller. This returns false if it is not possible to inline this 25// call. The program is still in a well defined state if this occurs though. 26// 27// Note that this only does one level of inlining. For example, if the 28// instruction 'call B' is inlined, and 'B' calls 'C', then the call to 'C' now 29// exists in the instruction stream. Similiarly this will inline a recursive 30// function by one level. 31// 32bool InlineFunction(CallSite CS) { 33 Instruction *TheCall = CS.getInstruction(); 34 assert(TheCall->getParent() && TheCall->getParent()->getParent() && 35 "Instruction not in function!"); 36 37 const Function *CalledFunc = CS.getCalledFunction(); 38 if (CalledFunc == 0 || // Can't inline external function or indirect 39 CalledFunc->isExternal() || // call, or call to a vararg function! 40 CalledFunc->getFunctionType()->isVarArg()) return false; 41 42 BasicBlock *OrigBB = TheCall->getParent(); 43 Function *Caller = OrigBB->getParent(); 44 45 // We want to clone the entire callee function into the whole between the 46 // "starter" and "ender" blocks. How we accomplish this depends on whether 47 // this is an invoke instruction or a call instruction. 48 49 BasicBlock *InvokeDest = 0; // Exception handling destination 50 BasicBlock *AfterCallBB; 51 if (InvokeInst *II = dyn_cast<InvokeInst>(TheCall)) { 52 AfterCallBB = II->getNormalDest(); 53 InvokeDest = II->getExceptionalDest(); 54 55 // Add an unconditional branch to make this look like the CallInst case... 56 new BranchInst(AfterCallBB, TheCall); 57 58 // Remove (unlink) the InvokeInst from the function... 59 OrigBB->getInstList().remove(TheCall); 60 } else { // It's a call 61 // If this is a call instruction, we need to split the basic block that the 62 // call lives in. 63 // 64 AfterCallBB = OrigBB->splitBasicBlock(TheCall, 65 CalledFunc->getName()+".entry"); 66 // Remove (unlink) the CallInst from the function... 67 AfterCallBB->getInstList().remove(TheCall); 68 } 69 70 // If we have a return value generated by this call, convert it into a PHI 71 // node that gets values from each of the old RET instructions in the original 72 // function. 73 // 74 PHINode *PHI = 0; 75 if (!TheCall->use_empty()) { 76 // The PHI node should go at the front of the new basic block to merge all 77 // possible incoming values. 78 // 79 PHI = new PHINode(CalledFunc->getReturnType(), TheCall->getName(), 80 AfterCallBB->begin()); 81 82 // Anything that used the result of the function call should now use the PHI 83 // node as their operand. 84 // 85 TheCall->replaceAllUsesWith(PHI); 86 } 87 88 // Get an iterator to the last basic block in the function, which will have 89 // the new function inlined after it. 90 // 91 Function::iterator LastBlock = &Caller->back(); 92 93 // Calculate the vector of arguments to pass into the function cloner... 94 std::map<const Value*, Value*> ValueMap; 95 assert(std::distance(CalledFunc->abegin(), CalledFunc->aend()) == 96 std::distance(CS.arg_begin(), CS.arg_end()) && 97 "No varargs calls can be inlined!"); 98 99 CallSite::arg_iterator AI = CS.arg_begin(); 100 for (Function::const_aiterator I = CalledFunc->abegin(), E=CalledFunc->aend(); 101 I != E; ++I, ++AI) 102 ValueMap[I] = *AI; 103 104 // Since we are now done with the Call/Invoke, we can delete it. 105 delete TheCall; 106 107 // Make a vector to capture the return instructions in the cloned function... 108 std::vector<ReturnInst*> Returns; 109 110 // Populate the value map with all of the globals in the program. 111 // FIXME: This should be the default for CloneFunctionInto! 112 Module &M = *Caller->getParent(); 113 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) 114 ValueMap[I] = I; 115 for (Module::giterator I = M.gbegin(), E = M.gend(); I != E; ++I) 116 ValueMap[I] = I; 117 118 // Do all of the hard part of cloning the callee into the caller... 119 CloneFunctionInto(Caller, CalledFunc, ValueMap, Returns, ".i"); 120 121 // Loop over all of the return instructions, turning them into unconditional 122 // branches to the merge point now... 123 for (unsigned i = 0, e = Returns.size(); i != e; ++i) { 124 ReturnInst *RI = Returns[i]; 125 BasicBlock *BB = RI->getParent(); 126 127 // Add a branch to the merge point where the PHI node lives if it exists. 128 new BranchInst(AfterCallBB, RI); 129 130 if (PHI) { // The PHI node should include this value! 131 assert(RI->getReturnValue() && "Ret should have value!"); 132 assert(RI->getReturnValue()->getType() == PHI->getType() && 133 "Ret value not consistent in function!"); 134 PHI->addIncoming(RI->getReturnValue(), BB); 135 } 136 137 // Delete the return instruction now 138 BB->getInstList().erase(RI); 139 } 140 141 // Check to see if the PHI node only has one argument. This is a common 142 // case resulting from there only being a single return instruction in the 143 // function call. Because this is so common, eliminate the PHI node. 144 // 145 if (PHI && PHI->getNumIncomingValues() == 1) { 146 PHI->replaceAllUsesWith(PHI->getIncomingValue(0)); 147 PHI->getParent()->getInstList().erase(PHI); 148 } 149 150 // Change the branch that used to go to AfterCallBB to branch to the first 151 // basic block of the inlined function. 152 // 153 TerminatorInst *Br = OrigBB->getTerminator(); 154 assert(Br && Br->getOpcode() == Instruction::Br && 155 "splitBasicBlock broken!"); 156 Br->setOperand(0, ++LastBlock); 157 158 // If there are any alloca instructions in the block that used to be the entry 159 // block for the callee, move them to the entry block of the caller. First 160 // calculate which instruction they should be inserted before. We insert the 161 // instructions at the end of the current alloca list. 162 // 163 if (isa<AllocaInst>(LastBlock->begin())) { 164 BasicBlock::iterator InsertPoint = Caller->begin()->begin(); 165 while (isa<AllocaInst>(InsertPoint)) ++InsertPoint; 166 167 for (BasicBlock::iterator I = LastBlock->begin(), E = LastBlock->end(); 168 I != E; ) 169 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) { 170 ++I; // Move to the next instruction 171 LastBlock->getInstList().remove(AI); 172 Caller->front().getInstList().insert(InsertPoint, AI); 173 } else { 174 ++I; 175 } 176 } 177 178 // If we just inlined a call due to an invoke instruction, scan the inlined 179 // function checking for function calls that should now be made into invoke 180 // instructions, and for unwind's which should be turned into branches. 181 if (InvokeDest) 182 for (Function::iterator BB = LastBlock, E = Caller->end(); BB != E; ++BB) { 183 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) { 184 // We only need to check for function calls: inlined invoke instructions 185 // require no special handling... 186 if (CallInst *CI = dyn_cast<CallInst>(I)) { 187 // Convert this function call into an invoke instruction... 188 189 // First, split the basic block... 190 BasicBlock *Split = BB->splitBasicBlock(CI, CI->getName()+".noexc"); 191 192 // Next, create the new invoke instruction, inserting it at the end 193 // of the old basic block. 194 new InvokeInst(CI->getCalledValue(), Split, InvokeDest, 195 std::vector<Value*>(CI->op_begin()+1, CI->op_end()), 196 CI->getName(), BB->getTerminator()); 197 198 // Delete the unconditional branch inserted by splitBasicBlock 199 BB->getInstList().pop_back(); 200 Split->getInstList().pop_front(); // Delete the original call 201 202 // This basic block is now complete, start scanning the next one. 203 break; 204 } else { 205 ++I; 206 } 207 } 208 209 if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) { 210 // An UnwindInst requires special handling when it gets inlined into an 211 // invoke site. Once this happens, we know that the unwind would cause 212 // a control transfer to the invoke exception destination, so we can 213 // transform it into a direct branch to the exception destination. 214 BranchInst *BI = new BranchInst(InvokeDest, UI); 215 216 // Delete the unwind instruction! 217 UI->getParent()->getInstList().pop_back(); 218 } 219 } 220 221 // Now that the function is correct, make it a little bit nicer. In 222 // particular, move the basic blocks inserted from the end of the function 223 // into the space made by splitting the source basic block. 224 // 225 Caller->getBasicBlockList().splice(AfterCallBB, Caller->getBasicBlockList(), 226 LastBlock, Caller->end()); 227 228 // We should always be able to fold the entry block of the function into the 229 // single predecessor of the block... 230 assert(cast<BranchInst>(Br)->isUnconditional() && "splitBasicBlock broken!"); 231 BasicBlock *CalleeEntry = cast<BranchInst>(Br)->getSuccessor(0); 232 SimplifyCFG(CalleeEntry); 233 234 // Okay, continue the CFG cleanup. It's often the case that there is only a 235 // single return instruction in the callee function. If this is the case, 236 // then we have an unconditional branch from the return block to the 237 // 'AfterCallBB'. Check for this case, and eliminate the branch is possible. 238 SimplifyCFG(AfterCallBB); 239 return true; 240} 241