InlineSimple.cpp revision 96c466b06ab0c830b07329c1b16037f585ccbe40
1//===- FunctionInlining.cpp - Code to perform function inlining -----------===// 2// 3// This file implements inlining of functions. 4// 5// Specifically, this: 6// * Exports functionality to inline any function call 7// * Inlines functions that consist of a single basic block 8// * Is able to inline ANY function call 9// . Has a smart heuristic for when to inline a function 10// 11// Notice that: 12// * This pass opens up a lot of opportunities for constant propogation. It 13// is a good idea to to run a constant propogation pass, then a DCE pass 14// sometime after running this pass. 15// 16// FIXME: This pass should transform alloca instructions in the called function 17// into malloc/free pairs! 18// 19//===----------------------------------------------------------------------===// 20 21#include "llvm/Transforms/FunctionInlining.h" 22#include "llvm/Module.h" 23#include "llvm/Function.h" 24#include "llvm/Pass.h" 25#include "llvm/iTerminators.h" 26#include "llvm/iPHINode.h" 27#include "llvm/iOther.h" 28#include "llvm/Type.h" 29#include "llvm/Argument.h" 30#include <algorithm> 31#include <map> 32#include <iostream> 33using std::cerr; 34 35// RemapInstruction - Convert the instruction operands from referencing the 36// current values into those specified by ValueMap. 37// 38static inline void RemapInstruction(Instruction *I, 39 std::map<const Value *, Value*> &ValueMap) { 40 41 for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) { 42 const Value *Op = I->getOperand(op); 43 Value *V = ValueMap[Op]; 44 if (!V && (isa<GlobalValue>(Op) || isa<Constant>(Op))) 45 continue; // Globals and constants don't get relocated 46 47 if (!V) { 48 cerr << "Val = \n" << Op << "Addr = " << (void*)Op; 49 cerr << "\nInst = " << I; 50 } 51 assert(V && "Referenced value not in value map!"); 52 I->setOperand(op, V); 53 } 54} 55 56// InlineFunction - This function forcibly inlines the called function into the 57// basic block of the caller. This returns false if it is not possible to 58// inline this call. The program is still in a well defined state if this 59// occurs though. 60// 61// Note that this only does one level of inlining. For example, if the 62// instruction 'call B' is inlined, and 'B' calls 'C', then the call to 'C' now 63// exists in the instruction stream. Similiarly this will inline a recursive 64// function by one level. 65// 66bool InlineFunction(BasicBlock::iterator CIIt) { 67 assert(isa<CallInst>(*CIIt) && "InlineFunction only works on CallInst nodes"); 68 assert((*CIIt)->getParent() && "Instruction not embedded in basic block!"); 69 assert((*CIIt)->getParent()->getParent() && "Instruction not in function!"); 70 71 CallInst *CI = cast<CallInst>(*CIIt); 72 const Function *CalledMeth = CI->getCalledFunction(); 73 if (CalledMeth == 0 || // Can't inline external function or indirect call! 74 CalledMeth->isExternal()) return false; 75 76 //cerr << "Inlining " << CalledMeth->getName() << " into " 77 // << CurrentMeth->getName() << "\n"; 78 79 BasicBlock *OrigBB = CI->getParent(); 80 81 // Call splitBasicBlock - The original basic block now ends at the instruction 82 // immediately before the call. The original basic block now ends with an 83 // unconditional branch to NewBB, and NewBB starts with the call instruction. 84 // 85 BasicBlock *NewBB = OrigBB->splitBasicBlock(CIIt); 86 NewBB->setName("InlinedFunctionReturnNode"); 87 88 // Remove (unlink) the CallInst from the start of the new basic block. 89 NewBB->getInstList().remove(CI); 90 91 // If we have a return value generated by this call, convert it into a PHI 92 // node that gets values from each of the old RET instructions in the original 93 // function. 94 // 95 PHINode *PHI = 0; 96 if (CalledMeth->getReturnType() != Type::VoidTy) { 97 PHI = new PHINode(CalledMeth->getReturnType(), CI->getName()); 98 99 // The PHI node should go at the front of the new basic block to merge all 100 // possible incoming values. 101 // 102 NewBB->getInstList().push_front(PHI); 103 104 // Anything that used the result of the function call should now use the PHI 105 // node as their operand. 106 // 107 CI->replaceAllUsesWith(PHI); 108 } 109 110 // Keep a mapping between the original function's values and the new 111 // duplicated code's values. This includes all of: Function arguments, 112 // instruction values, constant pool entries, and basic blocks. 113 // 114 std::map<const Value *, Value*> ValueMap; 115 116 // Add the function arguments to the mapping: (start counting at 1 to skip the 117 // function reference itself) 118 // 119 Function::ArgumentListType::const_iterator PTI = 120 CalledMeth->getArgumentList().begin(); 121 for (unsigned a = 1, E = CI->getNumOperands(); a != E; ++a, ++PTI) 122 ValueMap[*PTI] = CI->getOperand(a); 123 124 ValueMap[NewBB] = NewBB; // Returns get converted to reference NewBB 125 126 // Loop over all of the basic blocks in the function, inlining them as 127 // appropriate. Keep track of the first basic block of the function... 128 // 129 for (Function::const_iterator BI = CalledMeth->begin(); 130 BI != CalledMeth->end(); ++BI) { 131 const BasicBlock *BB = *BI; 132 assert(BB->getTerminator() && "BasicBlock doesn't have terminator!?!?"); 133 134 // Create a new basic block to copy instructions into! 135 BasicBlock *IBB = new BasicBlock("", NewBB->getParent()); 136 if (BB->hasName()) IBB->setName(BB->getName()+".i"); // .i = inlined once 137 138 ValueMap[BB] = IBB; // Add basic block mapping. 139 140 // Make sure to capture the mapping that a return will use... 141 // TODO: This assumes that the RET is returning a value computed in the same 142 // basic block as the return was issued from! 143 // 144 const TerminatorInst *TI = BB->getTerminator(); 145 146 // Loop over all instructions copying them over... 147 Instruction *NewInst; 148 for (BasicBlock::const_iterator II = BB->begin(); 149 II != (BB->end()-1); ++II) { 150 IBB->getInstList().push_back((NewInst = (*II)->clone())); 151 ValueMap[*II] = NewInst; // Add instruction map to value. 152 if ((*II)->hasName()) 153 NewInst->setName((*II)->getName()+".i"); // .i = inlined once 154 } 155 156 // Copy over the terminator now... 157 switch (TI->getOpcode()) { 158 case Instruction::Ret: { 159 const ReturnInst *RI = cast<const ReturnInst>(TI); 160 161 if (PHI) { // The PHI node should include this value! 162 assert(RI->getReturnValue() && "Ret should have value!"); 163 assert(RI->getReturnValue()->getType() == PHI->getType() && 164 "Ret value not consistent in function!"); 165 PHI->addIncoming((Value*)RI->getReturnValue(), cast<BasicBlock>(BB)); 166 } 167 168 // Add a branch to the code that was after the original Call. 169 IBB->getInstList().push_back(new BranchInst(NewBB)); 170 break; 171 } 172 case Instruction::Br: 173 IBB->getInstList().push_back(TI->clone()); 174 break; 175 176 default: 177 cerr << "FunctionInlining: Don't know how to handle terminator: " << TI; 178 abort(); 179 } 180 } 181 182 183 // Loop over all of the instructions in the function, fixing up operand 184 // references as we go. This uses ValueMap to do all the hard work. 185 // 186 for (Function::const_iterator BI = CalledMeth->begin(); 187 BI != CalledMeth->end(); ++BI) { 188 const BasicBlock *BB = *BI; 189 BasicBlock *NBB = (BasicBlock*)ValueMap[BB]; 190 191 // Loop over all instructions, fixing each one as we find it... 192 // 193 for (BasicBlock::iterator II = NBB->begin(); II != NBB->end(); II++) 194 RemapInstruction(*II, ValueMap); 195 } 196 197 if (PHI) RemapInstruction(PHI, ValueMap); // Fix the PHI node also... 198 199 // Change the branch that used to go to NewBB to branch to the first basic 200 // block of the inlined function. 201 // 202 TerminatorInst *Br = OrigBB->getTerminator(); 203 assert(Br && Br->getOpcode() == Instruction::Br && 204 "splitBasicBlock broken!"); 205 Br->setOperand(0, ValueMap[CalledMeth->front()]); 206 207 // Since we are now done with the CallInst, we can finally delete it. 208 delete CI; 209 return true; 210} 211 212bool InlineFunction(CallInst *CI) { 213 assert(CI->getParent() && "CallInst not embeded in BasicBlock!"); 214 BasicBlock *PBB = CI->getParent(); 215 216 BasicBlock::iterator CallIt = find(PBB->begin(), PBB->end(), CI); 217 218 assert(CallIt != PBB->end() && 219 "CallInst has parent that doesn't contain CallInst?!?"); 220 return InlineFunction(CallIt); 221} 222 223static inline bool ShouldInlineFunction(const CallInst *CI, const Function *F) { 224 assert(CI->getParent() && CI->getParent()->getParent() && 225 "Call not embedded into a function!"); 226 227 // Don't inline a recursive call. 228 if (CI->getParent()->getParent() == F) return false; 229 230 // Don't inline something too big. This is a really crappy heuristic 231 if (F->size() > 3) return false; 232 233 // Don't inline into something too big. This is a **really** crappy heuristic 234 if (CI->getParent()->getParent()->size() > 10) return false; 235 236 // Go ahead and try just about anything else. 237 return true; 238} 239 240 241static inline bool DoFunctionInlining(BasicBlock *BB) { 242 for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) { 243 if (CallInst *CI = dyn_cast<CallInst>(*I)) { 244 // Check to see if we should inline this function 245 Function *F = CI->getCalledFunction(); 246 if (F && ShouldInlineFunction(CI, F)) 247 return InlineFunction(I); 248 } 249 } 250 return false; 251} 252 253// doFunctionInlining - Use a heuristic based approach to inline functions that 254// seem to look good. 255// 256static bool doFunctionInlining(Function *F) { 257 bool Changed = false; 258 259 // Loop through now and inline instructions a basic block at a time... 260 for (Function::iterator I = F->begin(); I != F->end(); ) 261 if (DoFunctionInlining(*I)) { 262 Changed = true; 263 // Iterator is now invalidated by new basic blocks inserted 264 I = F->begin(); 265 } else { 266 ++I; 267 } 268 269 return Changed; 270} 271 272namespace { 273 struct FunctionInlining : public FunctionPass { 274 const char *getPassName() const { return "Function Inlining"; } 275 virtual bool runOnFunction(Function *F) { 276 return doFunctionInlining(F); 277 } 278 }; 279} 280 281Pass *createFunctionInliningPass() { return new FunctionInlining(); } 282