InlineFunction.cpp revision f8485c643412dbff46fe87ea2867445169a5c28e
1//===- InlineFunction.cpp - Code to perform function inlining -------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the LLVM research group and is distributed under 6// the University of Illinois Open Source License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file implements inlining of a function into a call site, resolving 11// parameters and the return value as appropriate. 12// 13// FIXME: This pass should transform alloca instructions in the called function 14// into malloc/free pairs! Or perhaps it should refuse to inline them! 15// 16//===----------------------------------------------------------------------===// 17 18#include "llvm/Transforms/Utils/Cloning.h" 19#include "llvm/Constant.h" 20#include "llvm/DerivedTypes.h" 21#include "llvm/Module.h" 22#include "llvm/Instructions.h" 23#include "llvm/Intrinsics.h" 24#include "llvm/Support/CallSite.h" 25#include "llvm/Transforms/Utils/Local.h" 26 27namespace llvm { 28 29bool InlineFunction(CallInst *CI) { return InlineFunction(CallSite(CI)); } 30bool InlineFunction(InvokeInst *II) { return InlineFunction(CallSite(II)); } 31 32// InlineFunction - This function inlines the called function into the basic 33// block of the caller. This returns false if it is not possible to inline this 34// call. The program is still in a well defined state if this occurs though. 35// 36// Note that this only does one level of inlining. For example, if the 37// instruction 'call B' is inlined, and 'B' calls 'C', then the call to 'C' now 38// exists in the instruction stream. Similiarly this will inline a recursive 39// function by one level. 40// 41bool InlineFunction(CallSite CS) { 42 Instruction *TheCall = CS.getInstruction(); 43 assert(TheCall->getParent() && TheCall->getParent()->getParent() && 44 "Instruction not in function!"); 45 46 const Function *CalledFunc = CS.getCalledFunction(); 47 if (CalledFunc == 0 || // Can't inline external function or indirect 48 CalledFunc->isExternal() || // call, or call to a vararg function! 49 CalledFunc->getFunctionType()->isVarArg()) return false; 50 51 BasicBlock *OrigBB = TheCall->getParent(); 52 Function *Caller = OrigBB->getParent(); 53 54 // We want to clone the entire callee function into the whole between the 55 // "starter" and "ender" blocks. How we accomplish this depends on whether 56 // this is an invoke instruction or a call instruction. 57 58 BasicBlock *InvokeDest = 0; // Exception handling destination 59 std::vector<Value*> InvokeDestPHIValues; // Values for PHI nodes in InvokeDest 60 BasicBlock *AfterCallBB; 61 62 if (InvokeInst *II = dyn_cast<InvokeInst>(TheCall)) { 63 InvokeDest = II->getExceptionalDest(); 64 65 // If there are PHI nodes in the exceptional destination block, we need to 66 // keep track of which values came into them from this invoke, then remove 67 // the entry for this block. 68 for (BasicBlock::iterator I = InvokeDest->begin(); 69 PHINode *PN = dyn_cast<PHINode>(I); ++I) { 70 // Save the value to use for this edge... 71 InvokeDestPHIValues.push_back(PN->getIncomingValueForBlock(OrigBB)); 72 } 73 74 // Add an unconditional branch to make this look like the CallInst case... 75 BranchInst *NewBr = new BranchInst(II->getNormalDest(), TheCall); 76 77 // Split the basic block. This guarantees that no PHI nodes will have to be 78 // updated due to new incoming edges, and make the invoke case more 79 // symmetric to the call case. 80 AfterCallBB = OrigBB->splitBasicBlock(NewBr, 81 CalledFunc->getName()+".entry"); 82 83 // Remove (unlink) the InvokeInst from the function... 84 OrigBB->getInstList().remove(TheCall); 85 86 } else { // It's a call 87 // If this is a call instruction, we need to split the basic block that the 88 // call lives in. 89 // 90 AfterCallBB = OrigBB->splitBasicBlock(TheCall, 91 CalledFunc->getName()+".entry"); 92 // Remove (unlink) the CallInst from the function... 93 AfterCallBB->getInstList().remove(TheCall); 94 } 95 96 // If we have a return value generated by this call, convert it into a PHI 97 // node that gets values from each of the old RET instructions in the original 98 // function. 99 // 100 PHINode *PHI = 0; 101 if (!TheCall->use_empty()) { 102 // The PHI node should go at the front of the new basic block to merge all 103 // possible incoming values. 104 // 105 PHI = new PHINode(CalledFunc->getReturnType(), TheCall->getName(), 106 AfterCallBB->begin()); 107 108 // Anything that used the result of the function call should now use the PHI 109 // node as their operand. 110 // 111 TheCall->replaceAllUsesWith(PHI); 112 } 113 114 // Get an iterator to the last basic block in the function, which will have 115 // the new function inlined after it. 116 // 117 Function::iterator LastBlock = &Caller->back(); 118 119 // Calculate the vector of arguments to pass into the function cloner... 120 std::map<const Value*, Value*> ValueMap; 121 assert(std::distance(CalledFunc->abegin(), CalledFunc->aend()) == 122 std::distance(CS.arg_begin(), CS.arg_end()) && 123 "No varargs calls can be inlined!"); 124 125 CallSite::arg_iterator AI = CS.arg_begin(); 126 for (Function::const_aiterator I = CalledFunc->abegin(), E=CalledFunc->aend(); 127 I != E; ++I, ++AI) 128 ValueMap[I] = *AI; 129 130 // Since we are now done with the Call/Invoke, we can delete it. 131 delete TheCall; 132 133 // Make a vector to capture the return instructions in the cloned function... 134 std::vector<ReturnInst*> Returns; 135 136 // Do all of the hard part of cloning the callee into the caller... 137 CloneFunctionInto(Caller, CalledFunc, ValueMap, Returns, ".i"); 138 139 // Loop over all of the return instructions, turning them into unconditional 140 // branches to the merge point now... 141 for (unsigned i = 0, e = Returns.size(); i != e; ++i) { 142 ReturnInst *RI = Returns[i]; 143 BasicBlock *BB = RI->getParent(); 144 145 // Add a branch to the merge point where the PHI node lives if it exists. 146 new BranchInst(AfterCallBB, RI); 147 148 if (PHI) { // The PHI node should include this value! 149 assert(RI->getReturnValue() && "Ret should have value!"); 150 assert(RI->getReturnValue()->getType() == PHI->getType() && 151 "Ret value not consistent in function!"); 152 PHI->addIncoming(RI->getReturnValue(), BB); 153 } 154 155 // Delete the return instruction now 156 BB->getInstList().erase(RI); 157 } 158 159 // Check to see if the PHI node only has one argument. This is a common 160 // case resulting from there only being a single return instruction in the 161 // function call. Because this is so common, eliminate the PHI node. 162 // 163 if (PHI && PHI->getNumIncomingValues() == 1) { 164 PHI->replaceAllUsesWith(PHI->getIncomingValue(0)); 165 PHI->getParent()->getInstList().erase(PHI); 166 } 167 168 // Change the branch that used to go to AfterCallBB to branch to the first 169 // basic block of the inlined function. 170 // 171 TerminatorInst *Br = OrigBB->getTerminator(); 172 assert(Br && Br->getOpcode() == Instruction::Br && 173 "splitBasicBlock broken!"); 174 Br->setOperand(0, ++LastBlock); 175 176 // If there are any alloca instructions in the block that used to be the entry 177 // block for the callee, move them to the entry block of the caller. First 178 // calculate which instruction they should be inserted before. We insert the 179 // instructions at the end of the current alloca list. 180 // 181 if (isa<AllocaInst>(LastBlock->begin())) { 182 BasicBlock::iterator InsertPoint = Caller->begin()->begin(); 183 while (isa<AllocaInst>(InsertPoint)) ++InsertPoint; 184 185 for (BasicBlock::iterator I = LastBlock->begin(), E = LastBlock->end(); 186 I != E; ) 187 if (AllocaInst *AI = dyn_cast<AllocaInst>(I++)) 188 if (isa<Constant>(AI->getArraySize())) { 189 LastBlock->getInstList().remove(AI); 190 Caller->front().getInstList().insert(InsertPoint, AI); 191 } 192 } 193 194 // If we just inlined a call due to an invoke instruction, scan the inlined 195 // function checking for function calls that should now be made into invoke 196 // instructions, and for unwind's which should be turned into branches. 197 if (InvokeDest) { 198 for (Function::iterator BB = LastBlock, E = Caller->end(); BB != E; ++BB) { 199 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) { 200 // We only need to check for function calls: inlined invoke instructions 201 // require no special handling... 202 if (CallInst *CI = dyn_cast<CallInst>(I)) { 203 // Convert this function call into an invoke instruction... 204 205 // First, split the basic block... 206 BasicBlock *Split = BB->splitBasicBlock(CI, CI->getName()+".noexc"); 207 208 // Next, create the new invoke instruction, inserting it at the end 209 // of the old basic block. 210 InvokeInst *II = 211 new InvokeInst(CI->getCalledValue(), Split, InvokeDest, 212 std::vector<Value*>(CI->op_begin()+1, CI->op_end()), 213 CI->getName(), BB->getTerminator()); 214 215 // Make sure that anything using the call now uses the invoke! 216 CI->replaceAllUsesWith(II); 217 218 // Delete the unconditional branch inserted by splitBasicBlock 219 BB->getInstList().pop_back(); 220 Split->getInstList().pop_front(); // Delete the original call 221 222 // Update any PHI nodes in the exceptional block to indicate that 223 // there is now a new entry in them. 224 unsigned i = 0; 225 for (BasicBlock::iterator I = InvokeDest->begin(); 226 PHINode *PN = dyn_cast<PHINode>(I); ++I, ++i) 227 PN->addIncoming(InvokeDestPHIValues[i], BB); 228 229 // This basic block is now complete, start scanning the next one. 230 break; 231 } else { 232 ++I; 233 } 234 } 235 236 if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) { 237 // An UnwindInst requires special handling when it gets inlined into an 238 // invoke site. Once this happens, we know that the unwind would cause 239 // a control transfer to the invoke exception destination, so we can 240 // transform it into a direct branch to the exception destination. 241 new BranchInst(InvokeDest, UI); 242 243 // Delete the unwind instruction! 244 UI->getParent()->getInstList().pop_back(); 245 246 // Update any PHI nodes in the exceptional block to indicate that 247 // there is now a new entry in them. 248 unsigned i = 0; 249 for (BasicBlock::iterator I = InvokeDest->begin(); 250 PHINode *PN = dyn_cast<PHINode>(I); ++I, ++i) 251 PN->addIncoming(InvokeDestPHIValues[i], BB); 252 } 253 } 254 255 // Now that everything is happy, we have one final detail. The PHI nodes in 256 // the exception destination block still have entries due to the original 257 // invoke instruction. Eliminate these entries (which might even delete the 258 // PHI node) now. 259 for (BasicBlock::iterator I = InvokeDest->begin(); 260 PHINode *PN = dyn_cast<PHINode>(I); ++I) 261 PN->removeIncomingValue(AfterCallBB); 262 } 263 // Now that the function is correct, make it a little bit nicer. In 264 // particular, move the basic blocks inserted from the end of the function 265 // into the space made by splitting the source basic block. 266 // 267 Caller->getBasicBlockList().splice(AfterCallBB, Caller->getBasicBlockList(), 268 LastBlock, Caller->end()); 269 270 // We should always be able to fold the entry block of the function into the 271 // single predecessor of the block... 272 assert(cast<BranchInst>(Br)->isUnconditional() && "splitBasicBlock broken!"); 273 BasicBlock *CalleeEntry = cast<BranchInst>(Br)->getSuccessor(0); 274 SimplifyCFG(CalleeEntry); 275 276 // Okay, continue the CFG cleanup. It's often the case that there is only a 277 // single return instruction in the callee function. If this is the case, 278 // then we have an unconditional branch from the return block to the 279 // 'AfterCallBB'. Check for this case, and eliminate the branch is possible. 280 SimplifyCFG(AfterCallBB); 281 return true; 282} 283 284} // End llvm namespace 285