InlineSimple.cpp revision 237e6d10f24863cf48821b601b4164794e89d847
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//===----------------------------------------------------------------------===// 17 18#include "llvm/Transforms/MethodInlining.h" 19#include "llvm/Module.h" 20#include "llvm/Function.h" 21#include "llvm/Pass.h" 22#include "llvm/iTerminators.h" 23#include "llvm/iPHINode.h" 24#include "llvm/iOther.h" 25#include "llvm/Type.h" 26#include <algorithm> 27#include <map> 28#include <iostream> 29using std::cerr; 30 31// RemapInstruction - Convert the instruction operands from referencing the 32// current values into those specified by ValueMap. 33// 34static inline void RemapInstruction(Instruction *I, 35 std::map<const Value *, Value*> &ValueMap) { 36 37 for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) { 38 const Value *Op = I->getOperand(op); 39 Value *V = ValueMap[Op]; 40 if (!V && (isa<GlobalValue>(Op) || isa<Constant>(Op))) 41 continue; // Globals and constants don't get relocated 42 43 if (!V) { 44 cerr << "Val = \n" << Op << "Addr = " << (void*)Op; 45 cerr << "\nInst = " << I; 46 } 47 assert(V && "Referenced value not in value map!"); 48 I->setOperand(op, V); 49 } 50} 51 52// InlineMethod - This function forcibly inlines the called function into the 53// basic block of the caller. This returns false if it is not possible to 54// inline this call. The program is still in a well defined state if this 55// occurs though. 56// 57// Note that this only does one level of inlining. For example, if the 58// instruction 'call B' is inlined, and 'B' calls 'C', then the call to 'C' now 59// exists in the instruction stream. Similiarly this will inline a recursive 60// function by one level. 61// 62bool InlineMethod(BasicBlock::iterator CIIt) { 63 assert(isa<CallInst>(*CIIt) && "InlineMethod only works on CallInst nodes!"); 64 assert((*CIIt)->getParent() && "Instruction not embedded in basic block!"); 65 assert((*CIIt)->getParent()->getParent() && "Instruction not in function!"); 66 67 CallInst *CI = cast<CallInst>(*CIIt); 68 const Function *CalledMeth = CI->getCalledFunction(); 69 if (CalledMeth == 0 || // Can't inline external function or indirect call! 70 CalledMeth->isExternal()) return false; 71 72 //cerr << "Inlining " << CalledMeth->getName() << " into " 73 // << CurrentMeth->getName() << "\n"; 74 75 BasicBlock *OrigBB = CI->getParent(); 76 77 // Call splitBasicBlock - The original basic block now ends at the instruction 78 // immediately before the call. The original basic block now ends with an 79 // unconditional branch to NewBB, and NewBB starts with the call instruction. 80 // 81 BasicBlock *NewBB = OrigBB->splitBasicBlock(CIIt); 82 NewBB->setName("InlinedFunctionReturnNode"); 83 84 // Remove (unlink) the CallInst from the start of the new basic block. 85 NewBB->getInstList().remove(CI); 86 87 // If we have a return value generated by this call, convert it into a PHI 88 // node that gets values from each of the old RET instructions in the original 89 // function. 90 // 91 PHINode *PHI = 0; 92 if (CalledMeth->getReturnType() != Type::VoidTy) { 93 PHI = new PHINode(CalledMeth->getReturnType(), CI->getName()); 94 95 // The PHI node should go at the front of the new basic block to merge all 96 // possible incoming values. 97 // 98 NewBB->getInstList().push_front(PHI); 99 100 // Anything that used the result of the function call should now use the PHI 101 // node as their operand. 102 // 103 CI->replaceAllUsesWith(PHI); 104 } 105 106 // Keep a mapping between the original function's values and the new 107 // duplicated code's values. This includes all of: Function arguments, 108 // instruction values, constant pool entries, and basic blocks. 109 // 110 std::map<const Value *, Value*> ValueMap; 111 112 // Add the function arguments to the mapping: (start counting at 1 to skip the 113 // function reference itself) 114 // 115 Function::ArgumentListType::const_iterator PTI = 116 CalledMeth->getArgumentList().begin(); 117 for (unsigned a = 1, E = CI->getNumOperands(); a != E; ++a, ++PTI) 118 ValueMap[*PTI] = CI->getOperand(a); 119 120 ValueMap[NewBB] = NewBB; // Returns get converted to reference NewBB 121 122 // Loop over all of the basic blocks in the function, inlining them as 123 // appropriate. Keep track of the first basic block of the function... 124 // 125 for (Function::const_iterator BI = CalledMeth->begin(); 126 BI != CalledMeth->end(); ++BI) { 127 const BasicBlock *BB = *BI; 128 assert(BB->getTerminator() && "BasicBlock doesn't have terminator!?!?"); 129 130 // Create a new basic block to copy instructions into! 131 BasicBlock *IBB = new BasicBlock("", NewBB->getParent()); 132 if (BB->hasName()) IBB->setName(BB->getName()+".i"); // .i = inlined once 133 134 ValueMap[BB] = IBB; // Add basic block mapping. 135 136 // Make sure to capture the mapping that a return will use... 137 // TODO: This assumes that the RET is returning a value computed in the same 138 // basic block as the return was issued from! 139 // 140 const TerminatorInst *TI = BB->getTerminator(); 141 142 // Loop over all instructions copying them over... 143 Instruction *NewInst; 144 for (BasicBlock::const_iterator II = BB->begin(); 145 II != (BB->end()-1); ++II) { 146 IBB->getInstList().push_back((NewInst = (*II)->clone())); 147 ValueMap[*II] = NewInst; // Add instruction map to value. 148 if ((*II)->hasName()) 149 NewInst->setName((*II)->getName()+".i"); // .i = inlined once 150 } 151 152 // Copy over the terminator now... 153 switch (TI->getOpcode()) { 154 case Instruction::Ret: { 155 const ReturnInst *RI = cast<const ReturnInst>(TI); 156 157 if (PHI) { // The PHI node should include this value! 158 assert(RI->getReturnValue() && "Ret should have value!"); 159 assert(RI->getReturnValue()->getType() == PHI->getType() && 160 "Ret value not consistent in function!"); 161 PHI->addIncoming((Value*)RI->getReturnValue(), cast<BasicBlock>(BB)); 162 } 163 164 // Add a branch to the code that was after the original Call. 165 IBB->getInstList().push_back(new BranchInst(NewBB)); 166 break; 167 } 168 case Instruction::Br: 169 IBB->getInstList().push_back(TI->clone()); 170 break; 171 172 default: 173 cerr << "FunctionInlining: Don't know how to handle terminator: " << TI; 174 abort(); 175 } 176 } 177 178 179 // Loop over all of the instructions in the function, fixing up operand 180 // references as we go. This uses ValueMap to do all the hard work. 181 // 182 for (Function::const_iterator BI = CalledMeth->begin(); 183 BI != CalledMeth->end(); ++BI) { 184 const BasicBlock *BB = *BI; 185 BasicBlock *NBB = (BasicBlock*)ValueMap[BB]; 186 187 // Loop over all instructions, fixing each one as we find it... 188 // 189 for (BasicBlock::iterator II = NBB->begin(); II != NBB->end(); II++) 190 RemapInstruction(*II, ValueMap); 191 } 192 193 if (PHI) RemapInstruction(PHI, ValueMap); // Fix the PHI node also... 194 195 // Change the branch that used to go to NewBB to branch to the first basic 196 // block of the inlined function. 197 // 198 TerminatorInst *Br = OrigBB->getTerminator(); 199 assert(Br && Br->getOpcode() == Instruction::Br && 200 "splitBasicBlock broken!"); 201 Br->setOperand(0, ValueMap[CalledMeth->front()]); 202 203 // Since we are now done with the CallInst, we can finally delete it. 204 delete CI; 205 return true; 206} 207 208bool InlineMethod(CallInst *CI) { 209 assert(CI->getParent() && "CallInst not embeded in BasicBlock!"); 210 BasicBlock *PBB = CI->getParent(); 211 212 BasicBlock::iterator CallIt = find(PBB->begin(), PBB->end(), CI); 213 214 assert(CallIt != PBB->end() && 215 "CallInst has parent that doesn't contain CallInst?!?"); 216 return InlineMethod(CallIt); 217} 218 219static inline bool ShouldInlineFunction(const CallInst *CI, const Function *F) { 220 assert(CI->getParent() && CI->getParent()->getParent() && 221 "Call not embedded into a method!"); 222 223 // Don't inline a recursive call. 224 if (CI->getParent()->getParent() == F) return false; 225 226 // Don't inline something too big. This is a really crappy heuristic 227 if (F->size() > 3) return false; 228 229 // Don't inline into something too big. This is a **really** crappy heuristic 230 if (CI->getParent()->getParent()->size() > 10) return false; 231 232 // Go ahead and try just about anything else. 233 return true; 234} 235 236 237static inline bool DoFunctionInlining(BasicBlock *BB) { 238 for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) { 239 if (CallInst *CI = dyn_cast<CallInst>(*I)) { 240 // Check to see if we should inline this function 241 Function *F = CI->getCalledFunction(); 242 if (F && ShouldInlineFunction(CI, F)) 243 return InlineMethod(I); 244 } 245 } 246 return false; 247} 248 249// doFunctionInlining - Use a heuristic based approach to inline functions that 250// seem to look good. 251// 252static bool doFunctionInlining(Function *F) { 253 bool Changed = false; 254 255 // Loop through now and inline instructions a basic block at a time... 256 for (Function::iterator I = F->begin(); I != F->end(); ) 257 if (DoFunctionInlining(*I)) { 258 Changed = true; 259 // Iterator is now invalidated by new basic blocks inserted 260 I = F->begin(); 261 } else { 262 ++I; 263 } 264 265 return Changed; 266} 267 268namespace { 269 struct FunctionInlining : public MethodPass { 270 virtual bool runOnMethod(Function *F) { 271 return doFunctionInlining(F); 272 } 273 }; 274} 275 276Pass *createMethodInliningPass() { return new FunctionInlining(); } 277