Inliner.cpp revision fad07189d3c7d121a1dc1473211096a76197177d
1//===- Inliner.cpp - Code common to all inliners --------------------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file implements the mechanics required to implement inlining without 11// missing any calls and updating the call graph. The decisions of which calls 12// are profitable to inline are implemented elsewhere. 13// 14//===----------------------------------------------------------------------===// 15 16#define DEBUG_TYPE "inline" 17#include "llvm/Module.h" 18#include "llvm/Instructions.h" 19#include "llvm/IntrinsicInst.h" 20#include "llvm/Analysis/CallGraph.h" 21#include "llvm/Analysis/InlineCost.h" 22#include "llvm/Support/CallSite.h" 23#include "llvm/Target/TargetData.h" 24#include "llvm/Transforms/IPO/InlinerPass.h" 25#include "llvm/Transforms/Utils/Cloning.h" 26#include "llvm/Support/CommandLine.h" 27#include "llvm/Support/Debug.h" 28#include "llvm/Support/raw_ostream.h" 29#include "llvm/ADT/SmallPtrSet.h" 30#include "llvm/ADT/Statistic.h" 31#include <set> 32using namespace llvm; 33 34STATISTIC(NumInlined, "Number of functions inlined"); 35STATISTIC(NumDeleted, "Number of functions deleted because all callers found"); 36STATISTIC(NumMergedAllocas, "Number of allocas merged together"); 37 38static cl::opt<int> 39InlineLimit("inline-threshold", cl::Hidden, cl::init(200), cl::ZeroOrMore, 40 cl::desc("Control the amount of inlining to perform (default = 200)")); 41 42Inliner::Inliner(void *ID) 43 : CallGraphSCCPass(ID), InlineThreshold(InlineLimit) {} 44 45Inliner::Inliner(void *ID, int Threshold) 46 : CallGraphSCCPass(ID), InlineThreshold(Threshold) {} 47 48/// getAnalysisUsage - For this class, we declare that we require and preserve 49/// the call graph. If the derived class implements this method, it should 50/// always explicitly call the implementation here. 51void Inliner::getAnalysisUsage(AnalysisUsage &Info) const { 52 CallGraphSCCPass::getAnalysisUsage(Info); 53} 54 55 56typedef DenseMap<const ArrayType*, std::vector<AllocaInst*> > 57InlinedArrayAllocasTy; 58 59/// InlineCallIfPossible - If it is possible to inline the specified call site, 60/// do so and update the CallGraph for this operation. 61/// 62/// This function also does some basic book-keeping to update the IR. The 63/// InlinedArrayAllocas map keeps track of any allocas that are already 64/// available from other functions inlined into the caller. If we are able to 65/// inline this call site we attempt to reuse already available allocas or add 66/// any new allocas to the set if not possible. 67static bool InlineCallIfPossible(CallSite CS, CallGraph &CG, 68 const TargetData *TD, 69 InlinedArrayAllocasTy &InlinedArrayAllocas) { 70 Function *Callee = CS.getCalledFunction(); 71 Function *Caller = CS.getCaller(); 72 73 // Try to inline the function. Get the list of static allocas that were 74 // inlined. 75 SmallVector<AllocaInst*, 16> StaticAllocas; 76 if (!InlineFunction(CS, &CG, TD, &StaticAllocas)) 77 return false; 78 79 // If the inlined function had a higher stack protection level than the 80 // calling function, then bump up the caller's stack protection level. 81 if (Callee->hasFnAttr(Attribute::StackProtectReq)) 82 Caller->addFnAttr(Attribute::StackProtectReq); 83 else if (Callee->hasFnAttr(Attribute::StackProtect) && 84 !Caller->hasFnAttr(Attribute::StackProtectReq)) 85 Caller->addFnAttr(Attribute::StackProtect); 86 87 88 // Look at all of the allocas that we inlined through this call site. If we 89 // have already inlined other allocas through other calls into this function, 90 // then we know that they have disjoint lifetimes and that we can merge them. 91 // 92 // There are many heuristics possible for merging these allocas, and the 93 // different options have different tradeoffs. One thing that we *really* 94 // don't want to hurt is SRoA: once inlining happens, often allocas are no 95 // longer address taken and so they can be promoted. 96 // 97 // Our "solution" for that is to only merge allocas whose outermost type is an 98 // array type. These are usually not promoted because someone is using a 99 // variable index into them. These are also often the most important ones to 100 // merge. 101 // 102 // A better solution would be to have real memory lifetime markers in the IR 103 // and not have the inliner do any merging of allocas at all. This would 104 // allow the backend to do proper stack slot coloring of all allocas that 105 // *actually make it to the backend*, which is really what we want. 106 // 107 // Because we don't have this information, we do this simple and useful hack. 108 // 109 SmallPtrSet<AllocaInst*, 16> UsedAllocas; 110 111 // Loop over all the allocas we have so far and see if they can be merged with 112 // a previously inlined alloca. If not, remember that we had it. 113 for (unsigned AllocaNo = 0, e = StaticAllocas.size(); 114 AllocaNo != e; ++AllocaNo) { 115 AllocaInst *AI = StaticAllocas[AllocaNo]; 116 117 // Don't bother trying to merge array allocations (they will usually be 118 // canonicalized to be an allocation *of* an array), or allocations whose 119 // type is not itself an array (because we're afraid of pessimizing SRoA). 120 const ArrayType *ATy = dyn_cast<ArrayType>(AI->getAllocatedType()); 121 if (ATy == 0 || AI->isArrayAllocation()) 122 continue; 123 124 // Get the list of all available allocas for this array type. 125 std::vector<AllocaInst*> &AllocasForType = InlinedArrayAllocas[ATy]; 126 127 // Loop over the allocas in AllocasForType to see if we can reuse one. Note 128 // that we have to be careful not to reuse the same "available" alloca for 129 // multiple different allocas that we just inlined, we use the 'UsedAllocas' 130 // set to keep track of which "available" allocas are being used by this 131 // function. Also, AllocasForType can be empty of course! 132 bool MergedAwayAlloca = false; 133 for (unsigned i = 0, e = AllocasForType.size(); i != e; ++i) { 134 AllocaInst *AvailableAlloca = AllocasForType[i]; 135 136 // The available alloca has to be in the right function, not in some other 137 // function in this SCC. 138 if (AvailableAlloca->getParent() != AI->getParent()) 139 continue; 140 141 // If the inlined function already uses this alloca then we can't reuse 142 // it. 143 if (!UsedAllocas.insert(AvailableAlloca)) 144 continue; 145 146 // Otherwise, we *can* reuse it, RAUW AI into AvailableAlloca and declare 147 // success! 148 DEBUG(errs() << " ***MERGED ALLOCA: " << *AI); 149 150 AI->replaceAllUsesWith(AvailableAlloca); 151 AI->eraseFromParent(); 152 MergedAwayAlloca = true; 153 ++NumMergedAllocas; 154 break; 155 } 156 157 // If we already nuked the alloca, we're done with it. 158 if (MergedAwayAlloca) 159 continue; 160 161 // If we were unable to merge away the alloca either because there are no 162 // allocas of the right type available or because we reused them all 163 // already, remember that this alloca came from an inlined function and mark 164 // it used so we don't reuse it for other allocas from this inline 165 // operation. 166 AllocasForType.push_back(AI); 167 UsedAllocas.insert(AI); 168 } 169 170 return true; 171} 172 173/// shouldInline - Return true if the inliner should attempt to inline 174/// at the given CallSite. 175bool Inliner::shouldInline(CallSite CS) { 176 InlineCost IC = getInlineCost(CS); 177 178 if (IC.isAlways()) { 179 DEBUG(errs() << " Inlining: cost=always" 180 << ", Call: " << *CS.getInstruction() << "\n"); 181 return true; 182 } 183 184 if (IC.isNever()) { 185 DEBUG(errs() << " NOT Inlining: cost=never" 186 << ", Call: " << *CS.getInstruction() << "\n"); 187 return false; 188 } 189 190 int Cost = IC.getValue(); 191 int CurrentThreshold = InlineThreshold; 192 Function *Caller = CS.getCaller(); 193 if (Caller && !Caller->isDeclaration() && 194 Caller->hasFnAttr(Attribute::OptimizeForSize) && 195 InlineLimit.getNumOccurrences() == 0 && 196 InlineThreshold != 50) 197 CurrentThreshold = 50; 198 199 float FudgeFactor = getInlineFudgeFactor(CS); 200 if (Cost >= (int)(CurrentThreshold * FudgeFactor)) { 201 DEBUG(errs() << " NOT Inlining: cost=" << Cost 202 << ", Call: " << *CS.getInstruction() << "\n"); 203 return false; 204 } 205 206 // Try to detect the case where the current inlining candidate caller 207 // (call it B) is a static function and is an inlining candidate elsewhere, 208 // and the current candidate callee (call it C) is large enough that 209 // inlining it into B would make B too big to inline later. In these 210 // circumstances it may be best not to inline C into B, but to inline B 211 // into its callers. 212 if (Caller->hasLocalLinkage()) { 213 int TotalSecondaryCost = 0; 214 bool outerCallsFound = false; 215 bool allOuterCallsWillBeInlined = true; 216 bool someOuterCallWouldNotBeInlined = false; 217 for (Value::use_iterator I = Caller->use_begin(), E =Caller->use_end(); 218 I != E; ++I) { 219 CallSite CS2 = CallSite::get(*I); 220 221 // If this isn't a call to Caller (it could be some other sort 222 // of reference) skip it. 223 if (CS2.getInstruction() == 0 || CS2.getCalledFunction() != Caller) 224 continue; 225 226 InlineCost IC2 = getInlineCost(CS2); 227 if (IC2.isNever()) 228 allOuterCallsWillBeInlined = false; 229 if (IC2.isAlways() || IC2.isNever()) 230 continue; 231 232 outerCallsFound = true; 233 int Cost2 = IC2.getValue(); 234 int CurrentThreshold2 = InlineThreshold; 235 Function *Caller2 = CS2.getCaller(); 236 if (Caller2 && !Caller2->isDeclaration() && 237 Caller2->hasFnAttr(Attribute::OptimizeForSize) && 238 InlineThreshold != 50) 239 CurrentThreshold2 = 50; 240 241 float FudgeFactor2 = getInlineFudgeFactor(CS2); 242 243 if (Cost2 >= (int)(CurrentThreshold2 * FudgeFactor2)) 244 allOuterCallsWillBeInlined = false; 245 246 // See if we have this case. We subtract off the penalty 247 // for the call instruction, which we would be deleting. 248 if (Cost2 < (int)(CurrentThreshold2 * FudgeFactor2) && 249 Cost2 + Cost - (InlineConstants::CallPenalty + 1) >= 250 (int)(CurrentThreshold2 * FudgeFactor2)) { 251 someOuterCallWouldNotBeInlined = true; 252 TotalSecondaryCost += Cost2; 253 } 254 } 255 // If all outer calls to Caller would get inlined, the cost for the last 256 // one is set very low by getInlineCost, in anticipation that Caller will 257 // be removed entirely. We did not account for this above unless there 258 // is only one caller of Caller. 259 if (allOuterCallsWillBeInlined && Caller->use_begin() != Caller->use_end()) 260 TotalSecondaryCost += InlineConstants::LastCallToStaticBonus; 261 262 if (outerCallsFound && someOuterCallWouldNotBeInlined && 263 TotalSecondaryCost < Cost) { 264 DEBUG(errs() << " NOT Inlining: " << *CS.getInstruction() << 265 " Cost = " << Cost << 266 ", outer Cost = " << TotalSecondaryCost << '\n'); 267 return false; 268 } 269 } 270 271 DEBUG(errs() << " Inlining: cost=" << Cost 272 << ", Call: " << *CS.getInstruction() << '\n'); 273 return true; 274} 275 276bool Inliner::runOnSCC(std::vector<CallGraphNode*> &SCC) { 277 CallGraph &CG = getAnalysis<CallGraph>(); 278 const TargetData *TD = getAnalysisIfAvailable<TargetData>(); 279 280 SmallPtrSet<Function*, 8> SCCFunctions; 281 DEBUG(errs() << "Inliner visiting SCC:"); 282 for (unsigned i = 0, e = SCC.size(); i != e; ++i) { 283 Function *F = SCC[i]->getFunction(); 284 if (F) SCCFunctions.insert(F); 285 DEBUG(errs() << " " << (F ? F->getName() : "INDIRECTNODE")); 286 } 287 288 // Scan through and identify all call sites ahead of time so that we only 289 // inline call sites in the original functions, not call sites that result 290 // from inlining other functions. 291 SmallVector<CallSite, 16> CallSites; 292 293 for (unsigned i = 0, e = SCC.size(); i != e; ++i) { 294 Function *F = SCC[i]->getFunction(); 295 if (!F) continue; 296 297 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) 298 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 299 CallSite CS = CallSite::get(I); 300 // If this isn't a call, or it is a call to an intrinsic, it can 301 // never be inlined. 302 if (CS.getInstruction() == 0 || isa<IntrinsicInst>(I)) 303 continue; 304 305 // If this is a direct call to an external function, we can never inline 306 // it. If it is an indirect call, inlining may resolve it to be a 307 // direct call, so we keep it. 308 if (CS.getCalledFunction() && CS.getCalledFunction()->isDeclaration()) 309 continue; 310 311 CallSites.push_back(CS); 312 } 313 } 314 315 DEBUG(errs() << ": " << CallSites.size() << " call sites.\n"); 316 317 // Now that we have all of the call sites, move the ones to functions in the 318 // current SCC to the end of the list. 319 unsigned FirstCallInSCC = CallSites.size(); 320 for (unsigned i = 0; i < FirstCallInSCC; ++i) 321 if (Function *F = CallSites[i].getCalledFunction()) 322 if (SCCFunctions.count(F)) 323 std::swap(CallSites[i--], CallSites[--FirstCallInSCC]); 324 325 326 InlinedArrayAllocasTy InlinedArrayAllocas; 327 328 // Now that we have all of the call sites, loop over them and inline them if 329 // it looks profitable to do so. 330 bool Changed = false; 331 bool LocalChange; 332 do { 333 LocalChange = false; 334 // Iterate over the outer loop because inlining functions can cause indirect 335 // calls to become direct calls. 336 for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) { 337 CallSite CS = CallSites[CSi]; 338 339 Function *Callee = CS.getCalledFunction(); 340 // We can only inline direct calls to non-declarations. 341 if (Callee == 0 || Callee->isDeclaration()) continue; 342 343 // If the policy determines that we should inline this function, 344 // try to do so. 345 if (!shouldInline(CS)) 346 continue; 347 348 Function *Caller = CS.getCaller(); 349 // Attempt to inline the function... 350 if (!InlineCallIfPossible(CS, CG, TD, InlinedArrayAllocas)) 351 continue; 352 353 // If we inlined the last possible call site to the function, delete the 354 // function body now. 355 if (Callee->use_empty() && Callee->hasLocalLinkage() && 356 // TODO: Can remove if in SCC now. 357 !SCCFunctions.count(Callee) && 358 359 // The function may be apparently dead, but if there are indirect 360 // callgraph references to the node, we cannot delete it yet, this 361 // could invalidate the CGSCC iterator. 362 CG[Callee]->getNumReferences() == 0) { 363 DEBUG(errs() << " -> Deleting dead function: " 364 << Callee->getName() << "\n"); 365 CallGraphNode *CalleeNode = CG[Callee]; 366 367 // Remove any call graph edges from the callee to its callees. 368 CalleeNode->removeAllCalledFunctions(); 369 370 resetCachedCostInfo(Callee); 371 372 // Removing the node for callee from the call graph and delete it. 373 delete CG.removeFunctionFromModule(CalleeNode); 374 ++NumDeleted; 375 } 376 377 // Remove any cached cost info for this caller, as inlining the 378 // callee has increased the size of the caller (which may be the 379 // same as the callee). 380 resetCachedCostInfo(Caller); 381 382 // Remove this call site from the list. If possible, use 383 // swap/pop_back for efficiency, but do not use it if doing so would 384 // move a call site to a function in this SCC before the 385 // 'FirstCallInSCC' barrier. 386 if (SCC.size() == 1) { 387 std::swap(CallSites[CSi], CallSites.back()); 388 CallSites.pop_back(); 389 } else { 390 CallSites.erase(CallSites.begin()+CSi); 391 } 392 --CSi; 393 394 ++NumInlined; 395 Changed = true; 396 LocalChange = true; 397 } 398 } while (LocalChange); 399 400 return Changed; 401} 402 403// doFinalization - Remove now-dead linkonce functions at the end of 404// processing to avoid breaking the SCC traversal. 405bool Inliner::doFinalization(CallGraph &CG) { 406 return removeDeadFunctions(CG); 407} 408 409/// removeDeadFunctions - Remove dead functions that are not included in 410/// DNR (Do Not Remove) list. 411bool Inliner::removeDeadFunctions(CallGraph &CG, 412 SmallPtrSet<const Function *, 16> *DNR) { 413 SmallPtrSet<CallGraphNode*, 16> FunctionsToRemove; 414 415 // Scan for all of the functions, looking for ones that should now be removed 416 // from the program. Insert the dead ones in the FunctionsToRemove set. 417 for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) { 418 CallGraphNode *CGN = I->second; 419 if (CGN->getFunction() == 0) 420 continue; 421 422 Function *F = CGN->getFunction(); 423 424 // If the only remaining users of the function are dead constants, remove 425 // them. 426 F->removeDeadConstantUsers(); 427 428 if (DNR && DNR->count(F)) 429 continue; 430 if (!F->hasLinkOnceLinkage() && !F->hasLocalLinkage() && 431 !F->hasAvailableExternallyLinkage()) 432 continue; 433 if (!F->use_empty()) 434 continue; 435 436 // Remove any call graph edges from the function to its callees. 437 CGN->removeAllCalledFunctions(); 438 439 // Remove any edges from the external node to the function's call graph 440 // node. These edges might have been made irrelegant due to 441 // optimization of the program. 442 CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN); 443 444 // Removing the node for callee from the call graph and delete it. 445 FunctionsToRemove.insert(CGN); 446 } 447 448 // Now that we know which functions to delete, do so. We didn't want to do 449 // this inline, because that would invalidate our CallGraph::iterator 450 // objects. :( 451 // 452 // Note that it doesn't matter that we are iterating over a non-stable set 453 // here to do this, it doesn't matter which order the functions are deleted 454 // in. 455 bool Changed = false; 456 for (SmallPtrSet<CallGraphNode*, 16>::iterator I = FunctionsToRemove.begin(), 457 E = FunctionsToRemove.end(); I != E; ++I) { 458 resetCachedCostInfo((*I)->getFunction()); 459 delete CG.removeFunctionFromModule(*I); 460 ++NumDeleted; 461 Changed = true; 462 } 463 464 return Changed; 465} 466