InlineSimple.cpp revision bdccb0097061e05b506592c25b3b5e9e0692c950
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/Pass.h" 24#include "llvm/iTerminators.h" 25#include "llvm/iPHINode.h" 26#include "llvm/iOther.h" 27#include "llvm/Type.h" 28#include "Support/StatisticReporter.h" 29#include <algorithm> 30#include <iostream> 31 32static Statistic<> NumInlined("inline\t\t- Number of functions inlined"); 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(CallInst *CI) { 67 assert(isa<CallInst>(CI) && "InlineFunction only works on CallInst nodes"); 68 assert(CI->getParent() && "Instruction not embedded in basic block!"); 69 assert(CI->getParent()->getParent() && "Instruction not in function!"); 70 71 const Function *CalledFunc = CI->getCalledFunction(); 72 if (CalledFunc == 0 || // Can't inline external function or indirect call! 73 CalledFunc->isExternal()) return false; 74 75 //cerr << "Inlining " << CalledFunc->getName() << " into " 76 // << CurrentMeth->getName() << "\n"; 77 78 BasicBlock *OrigBB = CI->getParent(); 79 80 // Call splitBasicBlock - The original basic block now ends at the instruction 81 // immediately before the call. The original basic block now ends with an 82 // unconditional branch to NewBB, and NewBB starts with the call instruction. 83 // 84 BasicBlock *NewBB = OrigBB->splitBasicBlock(CI); 85 NewBB->setName("InlinedFunctionReturnNode"); 86 87 // Remove (unlink) the CallInst from the start of the new basic block. 88 NewBB->getInstList().remove(CI); 89 90 // If we have a return value generated by this call, convert it into a PHI 91 // node that gets values from each of the old RET instructions in the original 92 // function. 93 // 94 PHINode *PHI = 0; 95 if (CalledFunc->getReturnType() != Type::VoidTy) { 96 // The PHI node should go at the front of the new basic block to merge all 97 // possible incoming values. 98 // 99 PHI = new PHINode(CalledFunc->getReturnType(), CI->getName(), 100 NewBB->begin()); 101 102 // Anything that used the result of the function call should now use the PHI 103 // node as their operand. 104 // 105 CI->replaceAllUsesWith(PHI); 106 } 107 108 // Keep a mapping between the original function's values and the new 109 // duplicated code's values. This includes all of: Function arguments, 110 // instruction values, constant pool entries, and basic blocks. 111 // 112 std::map<const Value *, Value*> ValueMap; 113 114 // Add the function arguments to the mapping: (start counting at 1 to skip the 115 // function reference itself) 116 // 117 Function::const_aiterator PTI = CalledFunc->abegin(); 118 for (unsigned a = 1, E = CI->getNumOperands(); a != E; ++a, ++PTI) 119 ValueMap[PTI] = CI->getOperand(a); 120 121 ValueMap[NewBB] = NewBB; // Returns get converted to reference NewBB 122 123 // Loop over all of the basic blocks in the function, inlining them as 124 // appropriate. Keep track of the first basic block of the function... 125 // 126 for (Function::const_iterator BB = CalledFunc->begin(); 127 BB != CalledFunc->end(); ++BB) { 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(); ++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<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(), 162 (BasicBlock*)cast<BasicBlock>(&*BB)); 163 } 164 165 // Add a branch to the code that was after the original Call. 166 IBB->getInstList().push_back(new BranchInst(NewBB)); 167 break; 168 } 169 case Instruction::Br: 170 IBB->getInstList().push_back(TI->clone()); 171 break; 172 173 default: 174 cerr << "FunctionInlining: Don't know how to handle terminator: " << TI; 175 abort(); 176 } 177 } 178 179 180 // Loop over all of the instructions in the function, fixing up operand 181 // references as we go. This uses ValueMap to do all the hard work. 182 // 183 for (Function::const_iterator BB = CalledFunc->begin(); 184 BB != CalledFunc->end(); ++BB) { 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) { 194 RemapInstruction(PHI, ValueMap); // Fix the PHI node also... 195 196 // Check to see if the PHI node only has one argument. This is a common 197 // case resulting from there only being a single return instruction in the 198 // function call. Because this is so common, eliminate the PHI node. 199 // 200 if (PHI->getNumIncomingValues() == 1) { 201 PHI->replaceAllUsesWith(PHI->getIncomingValue(0)); 202 PHI->getParent()->getInstList().erase(PHI); 203 } 204 } 205 206 // Change the branch that used to go to NewBB to branch to the first basic 207 // block of the inlined function. 208 // 209 TerminatorInst *Br = OrigBB->getTerminator(); 210 assert(Br && Br->getOpcode() == Instruction::Br && 211 "splitBasicBlock broken!"); 212 Br->setOperand(0, ValueMap[&CalledFunc->front()]); 213 214 // Since we are now done with the CallInst, we can finally delete it. 215 delete CI; 216 return true; 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 function!"); 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 InlineFunction(CI); 244 } 245 } 246 } 247 return false; 248} 249 250// doFunctionInlining - Use a heuristic based approach to inline functions that 251// seem to look good. 252// 253static bool doFunctionInlining(Function &F) { 254 bool Changed = false; 255 256 // Loop through now and inline instructions a basic block at a time... 257 for (Function::iterator I = F.begin(); I != F.end(); ) 258 if (DoFunctionInlining(I)) { 259 ++NumInlined; 260 Changed = true; 261 } else { 262 ++I; 263 } 264 265 return Changed; 266} 267 268namespace { 269 struct FunctionInlining : public FunctionPass { 270 virtual bool runOnFunction(Function &F) { 271 return doFunctionInlining(F); 272 } 273 }; 274 RegisterOpt<FunctionInlining> X("inline", "Function Integration/Inlining"); 275} 276 277Pass *createFunctionInliningPass() { return new FunctionInlining(); } 278