Inliner.cpp revision 1446c29e9ddfd7756b5e5374f9e877039b667537
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/Target/TargetData.h" 23#include "llvm/Transforms/IPO/InlinerPass.h" 24#include "llvm/Transforms/Utils/Cloning.h" 25#include "llvm/Transforms/Utils/Local.h" 26#include "llvm/Support/CallSite.h" 27#include "llvm/Support/CommandLine.h" 28#include "llvm/Support/Debug.h" 29#include "llvm/Support/raw_ostream.h" 30#include "llvm/ADT/SmallPtrSet.h" 31#include "llvm/ADT/Statistic.h" 32#include <set> 33using namespace llvm; 34 35STATISTIC(NumInlined, "Number of functions inlined"); 36STATISTIC(NumCallsDeleted, "Number of call sites deleted, not inlined"); 37STATISTIC(NumDeleted, "Number of functions deleted because all callers found"); 38STATISTIC(NumMergedAllocas, "Number of allocas merged together"); 39 40static cl::opt<int> 41InlineLimit("inline-threshold", cl::Hidden, cl::init(225), cl::ZeroOrMore, 42 cl::desc("Control the amount of inlining to perform (default = 225)")); 43 44static cl::opt<int> 45HintThreshold("inlinehint-threshold", cl::Hidden, cl::init(325), 46 cl::desc("Threshold for inlining functions with inline hint")); 47 48// Threshold to use when optsize is specified (and there is no -inline-limit). 49const int OptSizeThreshold = 75; 50 51Inliner::Inliner(char &ID) 52 : CallGraphSCCPass(ID), InlineThreshold(InlineLimit) {} 53 54Inliner::Inliner(char &ID, int Threshold) 55 : CallGraphSCCPass(ID), InlineThreshold(InlineLimit.getNumOccurrences() > 0 ? 56 InlineLimit : Threshold) {} 57 58/// getAnalysisUsage - For this class, we declare that we require and preserve 59/// the call graph. If the derived class implements this method, it should 60/// always explicitly call the implementation here. 61void Inliner::getAnalysisUsage(AnalysisUsage &Info) const { 62 CallGraphSCCPass::getAnalysisUsage(Info); 63} 64 65 66typedef DenseMap<const ArrayType*, std::vector<AllocaInst*> > 67InlinedArrayAllocasTy; 68 69/// InlineCallIfPossible - If it is possible to inline the specified call site, 70/// do so and update the CallGraph for this operation. 71/// 72/// This function also does some basic book-keeping to update the IR. The 73/// InlinedArrayAllocas map keeps track of any allocas that are already 74/// available from other functions inlined into the caller. If we are able to 75/// inline this call site we attempt to reuse already available allocas or add 76/// any new allocas to the set if not possible. 77static bool InlineCallIfPossible(CallSite CS, InlineFunctionInfo &IFI, 78 InlinedArrayAllocasTy &InlinedArrayAllocas) { 79 Function *Callee = CS.getCalledFunction(); 80 Function *Caller = CS.getCaller(); 81 82 // Try to inline the function. Get the list of static allocas that were 83 // inlined. 84 if (!InlineFunction(CS, IFI)) 85 return false; 86 87 // If the inlined function had a higher stack protection level than the 88 // calling function, then bump up the caller's stack protection level. 89 if (Callee->hasFnAttr(Attribute::StackProtectReq)) 90 Caller->addFnAttr(Attribute::StackProtectReq); 91 else if (Callee->hasFnAttr(Attribute::StackProtect) && 92 !Caller->hasFnAttr(Attribute::StackProtectReq)) 93 Caller->addFnAttr(Attribute::StackProtect); 94 95 96 // Look at all of the allocas that we inlined through this call site. If we 97 // have already inlined other allocas through other calls into this function, 98 // then we know that they have disjoint lifetimes and that we can merge them. 99 // 100 // There are many heuristics possible for merging these allocas, and the 101 // different options have different tradeoffs. One thing that we *really* 102 // don't want to hurt is SRoA: once inlining happens, often allocas are no 103 // longer address taken and so they can be promoted. 104 // 105 // Our "solution" for that is to only merge allocas whose outermost type is an 106 // array type. These are usually not promoted because someone is using a 107 // variable index into them. These are also often the most important ones to 108 // merge. 109 // 110 // A better solution would be to have real memory lifetime markers in the IR 111 // and not have the inliner do any merging of allocas at all. This would 112 // allow the backend to do proper stack slot coloring of all allocas that 113 // *actually make it to the backend*, which is really what we want. 114 // 115 // Because we don't have this information, we do this simple and useful hack. 116 // 117 SmallPtrSet<AllocaInst*, 16> UsedAllocas; 118 119 // Loop over all the allocas we have so far and see if they can be merged with 120 // a previously inlined alloca. If not, remember that we had it. 121 for (unsigned AllocaNo = 0, e = IFI.StaticAllocas.size(); 122 AllocaNo != e; ++AllocaNo) { 123 AllocaInst *AI = IFI.StaticAllocas[AllocaNo]; 124 125 // Don't bother trying to merge array allocations (they will usually be 126 // canonicalized to be an allocation *of* an array), or allocations whose 127 // type is not itself an array (because we're afraid of pessimizing SRoA). 128 const ArrayType *ATy = dyn_cast<ArrayType>(AI->getAllocatedType()); 129 if (ATy == 0 || AI->isArrayAllocation()) 130 continue; 131 132 // Get the list of all available allocas for this array type. 133 std::vector<AllocaInst*> &AllocasForType = InlinedArrayAllocas[ATy]; 134 135 // Loop over the allocas in AllocasForType to see if we can reuse one. Note 136 // that we have to be careful not to reuse the same "available" alloca for 137 // multiple different allocas that we just inlined, we use the 'UsedAllocas' 138 // set to keep track of which "available" allocas are being used by this 139 // function. Also, AllocasForType can be empty of course! 140 bool MergedAwayAlloca = false; 141 for (unsigned i = 0, e = AllocasForType.size(); i != e; ++i) { 142 AllocaInst *AvailableAlloca = AllocasForType[i]; 143 144 // The available alloca has to be in the right function, not in some other 145 // function in this SCC. 146 if (AvailableAlloca->getParent() != AI->getParent()) 147 continue; 148 149 // If the inlined function already uses this alloca then we can't reuse 150 // it. 151 if (!UsedAllocas.insert(AvailableAlloca)) 152 continue; 153 154 // Otherwise, we *can* reuse it, RAUW AI into AvailableAlloca and declare 155 // success! 156 DEBUG(dbgs() << " ***MERGED ALLOCA: " << *AI); 157 158 AI->replaceAllUsesWith(AvailableAlloca); 159 AI->eraseFromParent(); 160 MergedAwayAlloca = true; 161 ++NumMergedAllocas; 162 break; 163 } 164 165 // If we already nuked the alloca, we're done with it. 166 if (MergedAwayAlloca) 167 continue; 168 169 // If we were unable to merge away the alloca either because there are no 170 // allocas of the right type available or because we reused them all 171 // already, remember that this alloca came from an inlined function and mark 172 // it used so we don't reuse it for other allocas from this inline 173 // operation. 174 AllocasForType.push_back(AI); 175 UsedAllocas.insert(AI); 176 } 177 178 return true; 179} 180 181unsigned Inliner::getInlineThreshold(CallSite CS) const { 182 int thres = InlineThreshold; 183 184 // Listen to optsize when -inline-limit is not given. 185 Function *Caller = CS.getCaller(); 186 if (Caller && !Caller->isDeclaration() && 187 Caller->hasFnAttr(Attribute::OptimizeForSize) && 188 InlineLimit.getNumOccurrences() == 0) 189 thres = OptSizeThreshold; 190 191 // Listen to inlinehint when it would increase the threshold. 192 Function *Callee = CS.getCalledFunction(); 193 if (HintThreshold > thres && Callee && !Callee->isDeclaration() && 194 Callee->hasFnAttr(Attribute::InlineHint)) 195 thres = HintThreshold; 196 197 return thres; 198} 199 200/// shouldInline - Return true if the inliner should attempt to inline 201/// at the given CallSite. 202bool Inliner::shouldInline(CallSite CS) { 203 InlineCost IC = getInlineCost(CS); 204 205 if (IC.isAlways()) { 206 DEBUG(dbgs() << " Inlining: cost=always" 207 << ", Call: " << *CS.getInstruction() << "\n"); 208 return true; 209 } 210 211 if (IC.isNever()) { 212 DEBUG(dbgs() << " NOT Inlining: cost=never" 213 << ", Call: " << *CS.getInstruction() << "\n"); 214 return false; 215 } 216 217 int Cost = IC.getValue(); 218 Function *Caller = CS.getCaller(); 219 int CurrentThreshold = getInlineThreshold(CS); 220 float FudgeFactor = getInlineFudgeFactor(CS); 221 int AdjThreshold = (int)(CurrentThreshold * FudgeFactor); 222 if (Cost >= AdjThreshold) { 223 DEBUG(dbgs() << " NOT Inlining: cost=" << Cost 224 << ", thres=" << AdjThreshold 225 << ", Call: " << *CS.getInstruction() << "\n"); 226 return false; 227 } 228 229 // Try to detect the case where the current inlining candidate caller 230 // (call it B) is a static function and is an inlining candidate elsewhere, 231 // and the current candidate callee (call it C) is large enough that 232 // inlining it into B would make B too big to inline later. In these 233 // circumstances it may be best not to inline C into B, but to inline B 234 // into its callers. 235 if (Caller->hasLocalLinkage()) { 236 int TotalSecondaryCost = 0; 237 bool outerCallsFound = false; 238 bool allOuterCallsWillBeInlined = true; 239 bool someOuterCallWouldNotBeInlined = false; 240 for (Value::use_iterator I = Caller->use_begin(), E =Caller->use_end(); 241 I != E; ++I) { 242 CallSite CS2(*I); 243 244 // If this isn't a call to Caller (it could be some other sort 245 // of reference) skip it. 246 if (!CS2 || CS2.getCalledFunction() != Caller) 247 continue; 248 249 InlineCost IC2 = getInlineCost(CS2); 250 if (IC2.isNever()) 251 allOuterCallsWillBeInlined = false; 252 if (IC2.isAlways() || IC2.isNever()) 253 continue; 254 255 outerCallsFound = true; 256 int Cost2 = IC2.getValue(); 257 int CurrentThreshold2 = getInlineThreshold(CS2); 258 float FudgeFactor2 = getInlineFudgeFactor(CS2); 259 260 if (Cost2 >= (int)(CurrentThreshold2 * FudgeFactor2)) 261 allOuterCallsWillBeInlined = false; 262 263 // See if we have this case. We subtract off the penalty 264 // for the call instruction, which we would be deleting. 265 if (Cost2 < (int)(CurrentThreshold2 * FudgeFactor2) && 266 Cost2 + Cost - (InlineConstants::CallPenalty + 1) >= 267 (int)(CurrentThreshold2 * FudgeFactor2)) { 268 someOuterCallWouldNotBeInlined = true; 269 TotalSecondaryCost += Cost2; 270 } 271 } 272 // If all outer calls to Caller would get inlined, the cost for the last 273 // one is set very low by getInlineCost, in anticipation that Caller will 274 // be removed entirely. We did not account for this above unless there 275 // is only one caller of Caller. 276 if (allOuterCallsWillBeInlined && Caller->use_begin() != Caller->use_end()) 277 TotalSecondaryCost += InlineConstants::LastCallToStaticBonus; 278 279 if (outerCallsFound && someOuterCallWouldNotBeInlined && 280 TotalSecondaryCost < Cost) { 281 DEBUG(dbgs() << " NOT Inlining: " << *CS.getInstruction() << 282 " Cost = " << Cost << 283 ", outer Cost = " << TotalSecondaryCost << '\n'); 284 return false; 285 } 286 } 287 288 DEBUG(dbgs() << " Inlining: cost=" << Cost 289 << ", thres=" << AdjThreshold 290 << ", Call: " << *CS.getInstruction() << '\n'); 291 return true; 292} 293 294/// InlineHistoryIncludes - Return true if the specified inline history ID 295/// indicates an inline history that includes the specified function. 296static bool InlineHistoryIncludes(Function *F, int InlineHistoryID, 297 const SmallVectorImpl<std::pair<Function*, int> > &InlineHistory) { 298 while (InlineHistoryID != -1) { 299 assert(unsigned(InlineHistoryID) < InlineHistory.size() && 300 "Invalid inline history ID"); 301 if (InlineHistory[InlineHistoryID].first == F) 302 return true; 303 InlineHistoryID = InlineHistory[InlineHistoryID].second; 304 } 305 return false; 306} 307 308 309bool Inliner::runOnSCC(CallGraphSCC &SCC) { 310 CallGraph &CG = getAnalysis<CallGraph>(); 311 const TargetData *TD = getAnalysisIfAvailable<TargetData>(); 312 313 SmallPtrSet<Function*, 8> SCCFunctions; 314 DEBUG(dbgs() << "Inliner visiting SCC:"); 315 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) { 316 Function *F = (*I)->getFunction(); 317 if (F) SCCFunctions.insert(F); 318 DEBUG(dbgs() << " " << (F ? F->getName() : "INDIRECTNODE")); 319 } 320 321 // Scan through and identify all call sites ahead of time so that we only 322 // inline call sites in the original functions, not call sites that result 323 // from inlining other functions. 324 SmallVector<std::pair<CallSite, int>, 16> CallSites; 325 326 // When inlining a callee produces new call sites, we want to keep track of 327 // the fact that they were inlined from the callee. This allows us to avoid 328 // infinite inlining in some obscure cases. To represent this, we use an 329 // index into the InlineHistory vector. 330 SmallVector<std::pair<Function*, int>, 8> InlineHistory; 331 332 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) { 333 Function *F = (*I)->getFunction(); 334 if (!F) continue; 335 336 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) 337 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 338 CallSite CS(cast<Value>(I)); 339 // If this isn't a call, or it is a call to an intrinsic, it can 340 // never be inlined. 341 if (!CS || isa<IntrinsicInst>(I)) 342 continue; 343 344 // If this is a direct call to an external function, we can never inline 345 // it. If it is an indirect call, inlining may resolve it to be a 346 // direct call, so we keep it. 347 if (CS.getCalledFunction() && CS.getCalledFunction()->isDeclaration()) 348 continue; 349 350 CallSites.push_back(std::make_pair(CS, -1)); 351 } 352 } 353 354 DEBUG(dbgs() << ": " << CallSites.size() << " call sites.\n"); 355 356 // If there are no calls in this function, exit early. 357 if (CallSites.empty()) 358 return false; 359 360 // Now that we have all of the call sites, move the ones to functions in the 361 // current SCC to the end of the list. 362 unsigned FirstCallInSCC = CallSites.size(); 363 for (unsigned i = 0; i < FirstCallInSCC; ++i) 364 if (Function *F = CallSites[i].first.getCalledFunction()) 365 if (SCCFunctions.count(F)) 366 std::swap(CallSites[i--], CallSites[--FirstCallInSCC]); 367 368 369 InlinedArrayAllocasTy InlinedArrayAllocas; 370 InlineFunctionInfo InlineInfo(&CG, TD); 371 372 // Now that we have all of the call sites, loop over them and inline them if 373 // it looks profitable to do so. 374 bool Changed = false; 375 bool LocalChange; 376 do { 377 LocalChange = false; 378 // Iterate over the outer loop because inlining functions can cause indirect 379 // calls to become direct calls. 380 for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) { 381 CallSite CS = CallSites[CSi].first; 382 383 Function *Caller = CS.getCaller(); 384 Function *Callee = CS.getCalledFunction(); 385 386 // If this call site is dead and it is to a readonly function, we should 387 // just delete the call instead of trying to inline it, regardless of 388 // size. This happens because IPSCCP propagates the result out of the 389 // call and then we're left with the dead call. 390 if (isInstructionTriviallyDead(CS.getInstruction())) { 391 DEBUG(dbgs() << " -> Deleting dead call: " 392 << *CS.getInstruction() << "\n"); 393 // Update the call graph by deleting the edge from Callee to Caller. 394 CG[Caller]->removeCallEdgeFor(CS); 395 CS.getInstruction()->eraseFromParent(); 396 ++NumCallsDeleted; 397 // Update the cached cost info with the missing call 398 growCachedCostInfo(Caller, NULL); 399 } else { 400 // We can only inline direct calls to non-declarations. 401 if (Callee == 0 || Callee->isDeclaration()) continue; 402 403 // If this call site was obtained by inlining another function, verify 404 // that the include path for the function did not include the callee 405 // itself. If so, we'd be recursively inlinling the same function, 406 // which would provide the same callsites, which would cause us to 407 // infinitely inline. 408 int InlineHistoryID = CallSites[CSi].second; 409 if (InlineHistoryID != -1 && 410 InlineHistoryIncludes(Callee, InlineHistoryID, InlineHistory)) 411 continue; 412 413 414 // If the policy determines that we should inline this function, 415 // try to do so. 416 if (!shouldInline(CS)) 417 continue; 418 419 // Attempt to inline the function. 420 if (!InlineCallIfPossible(CS, InlineInfo, InlinedArrayAllocas)) 421 continue; 422 ++NumInlined; 423 424 // If inlining this function gave us any new call sites, throw them 425 // onto our worklist to process. They are useful inline candidates. 426 if (!InlineInfo.InlinedCalls.empty()) { 427 // Create a new inline history entry for this, so that we remember 428 // that these new callsites came about due to inlining Callee. 429 int NewHistoryID = InlineHistory.size(); 430 InlineHistory.push_back(std::make_pair(Callee, InlineHistoryID)); 431 432 for (unsigned i = 0, e = InlineInfo.InlinedCalls.size(); 433 i != e; ++i) { 434 Value *Ptr = InlineInfo.InlinedCalls[i]; 435 CallSites.push_back(std::make_pair(CallSite(Ptr), NewHistoryID)); 436 } 437 } 438 439 // Update the cached cost info with the inlined call. 440 growCachedCostInfo(Caller, Callee); 441 } 442 443 // If we inlined or deleted the last possible call site to the function, 444 // delete the function body now. 445 if (Callee && Callee->use_empty() && Callee->hasLocalLinkage() && 446 // TODO: Can remove if in SCC now. 447 !SCCFunctions.count(Callee) && 448 449 // The function may be apparently dead, but if there are indirect 450 // callgraph references to the node, we cannot delete it yet, this 451 // could invalidate the CGSCC iterator. 452 CG[Callee]->getNumReferences() == 0) { 453 DEBUG(dbgs() << " -> Deleting dead function: " 454 << Callee->getName() << "\n"); 455 CallGraphNode *CalleeNode = CG[Callee]; 456 457 // Remove any call graph edges from the callee to its callees. 458 CalleeNode->removeAllCalledFunctions(); 459 460 resetCachedCostInfo(Callee); 461 462 // Removing the node for callee from the call graph and delete it. 463 delete CG.removeFunctionFromModule(CalleeNode); 464 ++NumDeleted; 465 } 466 467 // Remove this call site from the list. If possible, use 468 // swap/pop_back for efficiency, but do not use it if doing so would 469 // move a call site to a function in this SCC before the 470 // 'FirstCallInSCC' barrier. 471 if (SCC.isSingular()) { 472 CallSites[CSi] = CallSites.back(); 473 CallSites.pop_back(); 474 } else { 475 CallSites.erase(CallSites.begin()+CSi); 476 } 477 --CSi; 478 479 Changed = true; 480 LocalChange = true; 481 } 482 } while (LocalChange); 483 484 return Changed; 485} 486 487// doFinalization - Remove now-dead linkonce functions at the end of 488// processing to avoid breaking the SCC traversal. 489bool Inliner::doFinalization(CallGraph &CG) { 490 return removeDeadFunctions(CG); 491} 492 493/// removeDeadFunctions - Remove dead functions that are not included in 494/// DNR (Do Not Remove) list. 495bool Inliner::removeDeadFunctions(CallGraph &CG, 496 SmallPtrSet<const Function *, 16> *DNR) { 497 SmallPtrSet<CallGraphNode*, 16> FunctionsToRemove; 498 499 // Scan for all of the functions, looking for ones that should now be removed 500 // from the program. Insert the dead ones in the FunctionsToRemove set. 501 for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) { 502 CallGraphNode *CGN = I->second; 503 if (CGN->getFunction() == 0) 504 continue; 505 506 Function *F = CGN->getFunction(); 507 508 // If the only remaining users of the function are dead constants, remove 509 // them. 510 F->removeDeadConstantUsers(); 511 512 if (DNR && DNR->count(F)) 513 continue; 514 if (!F->hasLinkOnceLinkage() && !F->hasLocalLinkage() && 515 !F->hasAvailableExternallyLinkage()) 516 continue; 517 if (!F->use_empty()) 518 continue; 519 520 // Remove any call graph edges from the function to its callees. 521 CGN->removeAllCalledFunctions(); 522 523 // Remove any edges from the external node to the function's call graph 524 // node. These edges might have been made irrelegant due to 525 // optimization of the program. 526 CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN); 527 528 // Removing the node for callee from the call graph and delete it. 529 FunctionsToRemove.insert(CGN); 530 } 531 532 // Now that we know which functions to delete, do so. We didn't want to do 533 // this inline, because that would invalidate our CallGraph::iterator 534 // objects. :( 535 // 536 // Note that it doesn't matter that we are iterating over a non-stable set 537 // here to do this, it doesn't matter which order the functions are deleted 538 // in. 539 bool Changed = false; 540 for (SmallPtrSet<CallGraphNode*, 16>::iterator I = FunctionsToRemove.begin(), 541 E = FunctionsToRemove.end(); I != E; ++I) { 542 resetCachedCostInfo((*I)->getFunction()); 543 delete CG.removeFunctionFromModule(*I); 544 ++NumDeleted; 545 Changed = true; 546 } 547 548 return Changed; 549} 550