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 #include "llvm/ADT/SmallPtrSet.h" 17 #include "llvm/ADT/Statistic.h" 18 #include "llvm/Analysis/AliasAnalysis.h" 19 #include "llvm/Analysis/AssumptionCache.h" 20 #include "llvm/Analysis/BasicAliasAnalysis.h" 21 #include "llvm/Analysis/CallGraph.h" 22 #include "llvm/Analysis/InlineCost.h" 23 #include "llvm/Analysis/ProfileSummaryInfo.h" 24 #include "llvm/Analysis/TargetLibraryInfo.h" 25 #include "llvm/IR/CallSite.h" 26 #include "llvm/IR/DataLayout.h" 27 #include "llvm/IR/DiagnosticInfo.h" 28 #include "llvm/IR/Instructions.h" 29 #include "llvm/IR/IntrinsicInst.h" 30 #include "llvm/IR/Module.h" 31 #include "llvm/Support/Debug.h" 32 #include "llvm/Support/raw_ostream.h" 33 #include "llvm/Transforms/IPO/InlinerPass.h" 34 #include "llvm/Transforms/Utils/Cloning.h" 35 #include "llvm/Transforms/Utils/Local.h" 36 using namespace llvm; 37 38 #define DEBUG_TYPE "inline" 39 40 STATISTIC(NumInlined, "Number of functions inlined"); 41 STATISTIC(NumCallsDeleted, "Number of call sites deleted, not inlined"); 42 STATISTIC(NumDeleted, "Number of functions deleted because all callers found"); 43 STATISTIC(NumMergedAllocas, "Number of allocas merged together"); 44 45 // This weirdly named statistic tracks the number of times that, when attempting 46 // to inline a function A into B, we analyze the callers of B in order to see 47 // if those would be more profitable and blocked inline steps. 48 STATISTIC(NumCallerCallersAnalyzed, "Number of caller-callers analyzed"); 49 50 Inliner::Inliner(char &ID) : CallGraphSCCPass(ID), InsertLifetime(true) {} 51 52 Inliner::Inliner(char &ID, bool InsertLifetime) 53 : CallGraphSCCPass(ID), InsertLifetime(InsertLifetime) {} 54 55 /// For this class, we declare that we require and preserve the call graph. 56 /// If the derived class implements this method, it should 57 /// always explicitly call the implementation here. 58 void Inliner::getAnalysisUsage(AnalysisUsage &AU) const { 59 AU.addRequired<AssumptionCacheTracker>(); 60 AU.addRequired<ProfileSummaryInfoWrapperPass>(); 61 AU.addRequired<TargetLibraryInfoWrapperPass>(); 62 getAAResultsAnalysisUsage(AU); 63 CallGraphSCCPass::getAnalysisUsage(AU); 64 } 65 66 67 typedef DenseMap<ArrayType*, std::vector<AllocaInst*> > 68 InlinedArrayAllocasTy; 69 70 /// If it is possible to inline the specified call site, 71 /// do so and update the CallGraph for this operation. 72 /// 73 /// This function also does some basic book-keeping to update the IR. The 74 /// InlinedArrayAllocas map keeps track of any allocas that are already 75 /// available from other functions inlined into the caller. If we are able to 76 /// inline this call site we attempt to reuse already available allocas or add 77 /// any new allocas to the set if not possible. 78 static bool InlineCallIfPossible(Pass &P, CallSite CS, InlineFunctionInfo &IFI, 79 InlinedArrayAllocasTy &InlinedArrayAllocas, 80 int InlineHistory, bool InsertLifetime) { 81 Function *Callee = CS.getCalledFunction(); 82 Function *Caller = CS.getCaller(); 83 84 // We need to manually construct BasicAA directly in order to disable 85 // its use of other function analyses. 86 BasicAAResult BAR(createLegacyPMBasicAAResult(P, *Callee)); 87 88 // Construct our own AA results for this function. We do this manually to 89 // work around the limitations of the legacy pass manager. 90 AAResults AAR(createLegacyPMAAResults(P, *Callee, BAR)); 91 92 // Try to inline the function. Get the list of static allocas that were 93 // inlined. 94 if (!InlineFunction(CS, IFI, &AAR, InsertLifetime)) 95 return false; 96 97 AttributeFuncs::mergeAttributesForInlining(*Caller, *Callee); 98 99 // Look at all of the allocas that we inlined through this call site. If we 100 // have already inlined other allocas through other calls into this function, 101 // then we know that they have disjoint lifetimes and that we can merge them. 102 // 103 // There are many heuristics possible for merging these allocas, and the 104 // different options have different tradeoffs. One thing that we *really* 105 // don't want to hurt is SRoA: once inlining happens, often allocas are no 106 // longer address taken and so they can be promoted. 107 // 108 // Our "solution" for that is to only merge allocas whose outermost type is an 109 // array type. These are usually not promoted because someone is using a 110 // variable index into them. These are also often the most important ones to 111 // merge. 112 // 113 // A better solution would be to have real memory lifetime markers in the IR 114 // and not have the inliner do any merging of allocas at all. This would 115 // allow the backend to do proper stack slot coloring of all allocas that 116 // *actually make it to the backend*, which is really what we want. 117 // 118 // Because we don't have this information, we do this simple and useful hack. 119 // 120 SmallPtrSet<AllocaInst*, 16> UsedAllocas; 121 122 // When processing our SCC, check to see if CS was inlined from some other 123 // call site. For example, if we're processing "A" in this code: 124 // A() { B() } 125 // B() { x = alloca ... C() } 126 // C() { y = alloca ... } 127 // Assume that C was not inlined into B initially, and so we're processing A 128 // and decide to inline B into A. Doing this makes an alloca available for 129 // reuse and makes a callsite (C) available for inlining. When we process 130 // the C call site we don't want to do any alloca merging between X and Y 131 // because their scopes are not disjoint. We could make this smarter by 132 // keeping track of the inline history for each alloca in the 133 // InlinedArrayAllocas but this isn't likely to be a significant win. 134 if (InlineHistory != -1) // Only do merging for top-level call sites in SCC. 135 return true; 136 137 // Loop over all the allocas we have so far and see if they can be merged with 138 // a previously inlined alloca. If not, remember that we had it. 139 for (unsigned AllocaNo = 0, e = IFI.StaticAllocas.size(); 140 AllocaNo != e; ++AllocaNo) { 141 AllocaInst *AI = IFI.StaticAllocas[AllocaNo]; 142 143 // Don't bother trying to merge array allocations (they will usually be 144 // canonicalized to be an allocation *of* an array), or allocations whose 145 // type is not itself an array (because we're afraid of pessimizing SRoA). 146 ArrayType *ATy = dyn_cast<ArrayType>(AI->getAllocatedType()); 147 if (!ATy || AI->isArrayAllocation()) 148 continue; 149 150 // Get the list of all available allocas for this array type. 151 std::vector<AllocaInst*> &AllocasForType = InlinedArrayAllocas[ATy]; 152 153 // Loop over the allocas in AllocasForType to see if we can reuse one. Note 154 // that we have to be careful not to reuse the same "available" alloca for 155 // multiple different allocas that we just inlined, we use the 'UsedAllocas' 156 // set to keep track of which "available" allocas are being used by this 157 // function. Also, AllocasForType can be empty of course! 158 bool MergedAwayAlloca = false; 159 for (AllocaInst *AvailableAlloca : AllocasForType) { 160 161 unsigned Align1 = AI->getAlignment(), 162 Align2 = AvailableAlloca->getAlignment(); 163 164 // The available alloca has to be in the right function, not in some other 165 // function in this SCC. 166 if (AvailableAlloca->getParent() != AI->getParent()) 167 continue; 168 169 // If the inlined function already uses this alloca then we can't reuse 170 // it. 171 if (!UsedAllocas.insert(AvailableAlloca).second) 172 continue; 173 174 // Otherwise, we *can* reuse it, RAUW AI into AvailableAlloca and declare 175 // success! 176 DEBUG(dbgs() << " ***MERGED ALLOCA: " << *AI << "\n\t\tINTO: " 177 << *AvailableAlloca << '\n'); 178 179 // Move affected dbg.declare calls immediately after the new alloca to 180 // avoid the situation when a dbg.declare preceeds its alloca. 181 if (auto *L = LocalAsMetadata::getIfExists(AI)) 182 if (auto *MDV = MetadataAsValue::getIfExists(AI->getContext(), L)) 183 for (User *U : MDV->users()) 184 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U)) 185 DDI->moveBefore(AvailableAlloca->getNextNode()); 186 187 AI->replaceAllUsesWith(AvailableAlloca); 188 189 if (Align1 != Align2) { 190 if (!Align1 || !Align2) { 191 const DataLayout &DL = Caller->getParent()->getDataLayout(); 192 unsigned TypeAlign = DL.getABITypeAlignment(AI->getAllocatedType()); 193 194 Align1 = Align1 ? Align1 : TypeAlign; 195 Align2 = Align2 ? Align2 : TypeAlign; 196 } 197 198 if (Align1 > Align2) 199 AvailableAlloca->setAlignment(AI->getAlignment()); 200 } 201 202 AI->eraseFromParent(); 203 MergedAwayAlloca = true; 204 ++NumMergedAllocas; 205 IFI.StaticAllocas[AllocaNo] = nullptr; 206 break; 207 } 208 209 // If we already nuked the alloca, we're done with it. 210 if (MergedAwayAlloca) 211 continue; 212 213 // If we were unable to merge away the alloca either because there are no 214 // allocas of the right type available or because we reused them all 215 // already, remember that this alloca came from an inlined function and mark 216 // it used so we don't reuse it for other allocas from this inline 217 // operation. 218 AllocasForType.push_back(AI); 219 UsedAllocas.insert(AI); 220 } 221 222 return true; 223 } 224 225 static void emitAnalysis(CallSite CS, const Twine &Msg) { 226 Function *Caller = CS.getCaller(); 227 LLVMContext &Ctx = Caller->getContext(); 228 DebugLoc DLoc = CS.getInstruction()->getDebugLoc(); 229 emitOptimizationRemarkAnalysis(Ctx, DEBUG_TYPE, *Caller, DLoc, Msg); 230 } 231 232 bool Inliner::shouldBeDeferred(Function *Caller, CallSite CS, InlineCost IC, 233 int &TotalSecondaryCost) { 234 235 // For now we only handle local or inline functions. 236 if (!Caller->hasLocalLinkage() && !Caller->hasLinkOnceODRLinkage()) 237 return false; 238 // Try to detect the case where the current inlining candidate caller (call 239 // it B) is a static or linkonce-ODR function and is an inlining candidate 240 // elsewhere, and the current candidate callee (call it C) is large enough 241 // that inlining it into B would make B too big to inline later. In these 242 // circumstances it may be best not to inline C into B, but to inline B into 243 // its callers. 244 // 245 // This only applies to static and linkonce-ODR functions because those are 246 // expected to be available for inlining in the translation units where they 247 // are used. Thus we will always have the opportunity to make local inlining 248 // decisions. Importantly the linkonce-ODR linkage covers inline functions 249 // and templates in C++. 250 // 251 // FIXME: All of this logic should be sunk into getInlineCost. It relies on 252 // the internal implementation of the inline cost metrics rather than 253 // treating them as truly abstract units etc. 254 TotalSecondaryCost = 0; 255 // The candidate cost to be imposed upon the current function. 256 int CandidateCost = IC.getCost() - (InlineConstants::CallPenalty + 1); 257 // This bool tracks what happens if we do NOT inline C into B. 258 bool callerWillBeRemoved = Caller->hasLocalLinkage(); 259 // This bool tracks what happens if we DO inline C into B. 260 bool inliningPreventsSomeOuterInline = false; 261 for (User *U : Caller->users()) { 262 CallSite CS2(U); 263 264 // If this isn't a call to Caller (it could be some other sort 265 // of reference) skip it. Such references will prevent the caller 266 // from being removed. 267 if (!CS2 || CS2.getCalledFunction() != Caller) { 268 callerWillBeRemoved = false; 269 continue; 270 } 271 272 InlineCost IC2 = getInlineCost(CS2); 273 ++NumCallerCallersAnalyzed; 274 if (!IC2) { 275 callerWillBeRemoved = false; 276 continue; 277 } 278 if (IC2.isAlways()) 279 continue; 280 281 // See if inlining or original callsite would erase the cost delta of 282 // this callsite. We subtract off the penalty for the call instruction, 283 // which we would be deleting. 284 if (IC2.getCostDelta() <= CandidateCost) { 285 inliningPreventsSomeOuterInline = true; 286 TotalSecondaryCost += IC2.getCost(); 287 } 288 } 289 // If all outer calls to Caller would get inlined, the cost for the last 290 // one is set very low by getInlineCost, in anticipation that Caller will 291 // be removed entirely. We did not account for this above unless there 292 // is only one caller of Caller. 293 if (callerWillBeRemoved && !Caller->use_empty()) 294 TotalSecondaryCost += InlineConstants::LastCallToStaticBonus; 295 296 if (inliningPreventsSomeOuterInline && TotalSecondaryCost < IC.getCost()) 297 return true; 298 299 return false; 300 } 301 302 /// Return true if the inliner should attempt to inline at the given CallSite. 303 bool Inliner::shouldInline(CallSite CS) { 304 InlineCost IC = getInlineCost(CS); 305 306 if (IC.isAlways()) { 307 DEBUG(dbgs() << " Inlining: cost=always" 308 << ", Call: " << *CS.getInstruction() << "\n"); 309 emitAnalysis(CS, Twine(CS.getCalledFunction()->getName()) + 310 " should always be inlined (cost=always)"); 311 return true; 312 } 313 314 if (IC.isNever()) { 315 DEBUG(dbgs() << " NOT Inlining: cost=never" 316 << ", Call: " << *CS.getInstruction() << "\n"); 317 emitAnalysis(CS, Twine(CS.getCalledFunction()->getName() + 318 " should never be inlined (cost=never)")); 319 return false; 320 } 321 322 Function *Caller = CS.getCaller(); 323 if (!IC) { 324 DEBUG(dbgs() << " NOT Inlining: cost=" << IC.getCost() 325 << ", thres=" << (IC.getCostDelta() + IC.getCost()) 326 << ", Call: " << *CS.getInstruction() << "\n"); 327 emitAnalysis(CS, Twine(CS.getCalledFunction()->getName() + 328 " too costly to inline (cost=") + 329 Twine(IC.getCost()) + ", threshold=" + 330 Twine(IC.getCostDelta() + IC.getCost()) + ")"); 331 return false; 332 } 333 334 int TotalSecondaryCost = 0; 335 if (shouldBeDeferred(Caller, CS, IC, TotalSecondaryCost)) { 336 DEBUG(dbgs() << " NOT Inlining: " << *CS.getInstruction() 337 << " Cost = " << IC.getCost() 338 << ", outer Cost = " << TotalSecondaryCost << '\n'); 339 emitAnalysis(CS, Twine("Not inlining. Cost of inlining " + 340 CS.getCalledFunction()->getName() + 341 " increases the cost of inlining " + 342 CS.getCaller()->getName() + " in other contexts")); 343 return false; 344 } 345 346 DEBUG(dbgs() << " Inlining: cost=" << IC.getCost() 347 << ", thres=" << (IC.getCostDelta() + IC.getCost()) 348 << ", Call: " << *CS.getInstruction() << '\n'); 349 emitAnalysis( 350 CS, CS.getCalledFunction()->getName() + Twine(" can be inlined into ") + 351 CS.getCaller()->getName() + " with cost=" + Twine(IC.getCost()) + 352 " (threshold=" + Twine(IC.getCostDelta() + IC.getCost()) + ")"); 353 return true; 354 } 355 356 /// Return true if the specified inline history ID 357 /// indicates an inline history that includes the specified function. 358 static bool InlineHistoryIncludes(Function *F, int InlineHistoryID, 359 const SmallVectorImpl<std::pair<Function*, int> > &InlineHistory) { 360 while (InlineHistoryID != -1) { 361 assert(unsigned(InlineHistoryID) < InlineHistory.size() && 362 "Invalid inline history ID"); 363 if (InlineHistory[InlineHistoryID].first == F) 364 return true; 365 InlineHistoryID = InlineHistory[InlineHistoryID].second; 366 } 367 return false; 368 } 369 370 bool Inliner::runOnSCC(CallGraphSCC &SCC) { 371 if (skipSCC(SCC)) 372 return false; 373 return inlineCalls(SCC); 374 } 375 376 bool Inliner::inlineCalls(CallGraphSCC &SCC) { 377 CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph(); 378 ACT = &getAnalysis<AssumptionCacheTracker>(); 379 PSI = getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI(CG.getModule()); 380 auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(); 381 382 SmallPtrSet<Function*, 8> SCCFunctions; 383 DEBUG(dbgs() << "Inliner visiting SCC:"); 384 for (CallGraphNode *Node : SCC) { 385 Function *F = Node->getFunction(); 386 if (F) SCCFunctions.insert(F); 387 DEBUG(dbgs() << " " << (F ? F->getName() : "INDIRECTNODE")); 388 } 389 390 // Scan through and identify all call sites ahead of time so that we only 391 // inline call sites in the original functions, not call sites that result 392 // from inlining other functions. 393 SmallVector<std::pair<CallSite, int>, 16> CallSites; 394 395 // When inlining a callee produces new call sites, we want to keep track of 396 // the fact that they were inlined from the callee. This allows us to avoid 397 // infinite inlining in some obscure cases. To represent this, we use an 398 // index into the InlineHistory vector. 399 SmallVector<std::pair<Function*, int>, 8> InlineHistory; 400 401 for (CallGraphNode *Node : SCC) { 402 Function *F = Node->getFunction(); 403 if (!F) continue; 404 405 for (BasicBlock &BB : *F) 406 for (Instruction &I : BB) { 407 CallSite CS(cast<Value>(&I)); 408 // If this isn't a call, or it is a call to an intrinsic, it can 409 // never be inlined. 410 if (!CS || isa<IntrinsicInst>(I)) 411 continue; 412 413 // If this is a direct call to an external function, we can never inline 414 // it. If it is an indirect call, inlining may resolve it to be a 415 // direct call, so we keep it. 416 if (Function *Callee = CS.getCalledFunction()) 417 if (Callee->isDeclaration()) 418 continue; 419 420 CallSites.push_back(std::make_pair(CS, -1)); 421 } 422 } 423 424 DEBUG(dbgs() << ": " << CallSites.size() << " call sites.\n"); 425 426 // If there are no calls in this function, exit early. 427 if (CallSites.empty()) 428 return false; 429 430 // Now that we have all of the call sites, move the ones to functions in the 431 // current SCC to the end of the list. 432 unsigned FirstCallInSCC = CallSites.size(); 433 for (unsigned i = 0; i < FirstCallInSCC; ++i) 434 if (Function *F = CallSites[i].first.getCalledFunction()) 435 if (SCCFunctions.count(F)) 436 std::swap(CallSites[i--], CallSites[--FirstCallInSCC]); 437 438 439 InlinedArrayAllocasTy InlinedArrayAllocas; 440 InlineFunctionInfo InlineInfo(&CG, ACT); 441 442 // Now that we have all of the call sites, loop over them and inline them if 443 // it looks profitable to do so. 444 bool Changed = false; 445 bool LocalChange; 446 do { 447 LocalChange = false; 448 // Iterate over the outer loop because inlining functions can cause indirect 449 // calls to become direct calls. 450 // CallSites may be modified inside so ranged for loop can not be used. 451 for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) { 452 CallSite CS = CallSites[CSi].first; 453 454 Function *Caller = CS.getCaller(); 455 Function *Callee = CS.getCalledFunction(); 456 457 // If this call site is dead and it is to a readonly function, we should 458 // just delete the call instead of trying to inline it, regardless of 459 // size. This happens because IPSCCP propagates the result out of the 460 // call and then we're left with the dead call. 461 if (isInstructionTriviallyDead(CS.getInstruction(), &TLI)) { 462 DEBUG(dbgs() << " -> Deleting dead call: " 463 << *CS.getInstruction() << "\n"); 464 // Update the call graph by deleting the edge from Callee to Caller. 465 CG[Caller]->removeCallEdgeFor(CS); 466 CS.getInstruction()->eraseFromParent(); 467 ++NumCallsDeleted; 468 } else { 469 // We can only inline direct calls to non-declarations. 470 if (!Callee || Callee->isDeclaration()) continue; 471 472 // If this call site was obtained by inlining another function, verify 473 // that the include path for the function did not include the callee 474 // itself. If so, we'd be recursively inlining the same function, 475 // which would provide the same callsites, which would cause us to 476 // infinitely inline. 477 int InlineHistoryID = CallSites[CSi].second; 478 if (InlineHistoryID != -1 && 479 InlineHistoryIncludes(Callee, InlineHistoryID, InlineHistory)) 480 continue; 481 482 LLVMContext &CallerCtx = Caller->getContext(); 483 484 // Get DebugLoc to report. CS will be invalid after Inliner. 485 DebugLoc DLoc = CS.getInstruction()->getDebugLoc(); 486 487 // If the policy determines that we should inline this function, 488 // try to do so. 489 if (!shouldInline(CS)) { 490 emitOptimizationRemarkMissed(CallerCtx, DEBUG_TYPE, *Caller, DLoc, 491 Twine(Callee->getName() + 492 " will not be inlined into " + 493 Caller->getName())); 494 continue; 495 } 496 497 // Attempt to inline the function. 498 if (!InlineCallIfPossible(*this, CS, InlineInfo, InlinedArrayAllocas, 499 InlineHistoryID, InsertLifetime)) { 500 emitOptimizationRemarkMissed(CallerCtx, DEBUG_TYPE, *Caller, DLoc, 501 Twine(Callee->getName() + 502 " will not be inlined into " + 503 Caller->getName())); 504 continue; 505 } 506 ++NumInlined; 507 508 // Report the inline decision. 509 emitOptimizationRemark( 510 CallerCtx, DEBUG_TYPE, *Caller, DLoc, 511 Twine(Callee->getName() + " inlined into " + Caller->getName())); 512 513 // If inlining this function gave us any new call sites, throw them 514 // onto our worklist to process. They are useful inline candidates. 515 if (!InlineInfo.InlinedCalls.empty()) { 516 // Create a new inline history entry for this, so that we remember 517 // that these new callsites came about due to inlining Callee. 518 int NewHistoryID = InlineHistory.size(); 519 InlineHistory.push_back(std::make_pair(Callee, InlineHistoryID)); 520 521 for (Value *Ptr : InlineInfo.InlinedCalls) 522 CallSites.push_back(std::make_pair(CallSite(Ptr), NewHistoryID)); 523 } 524 } 525 526 // If we inlined or deleted the last possible call site to the function, 527 // delete the function body now. 528 if (Callee && Callee->use_empty() && Callee->hasLocalLinkage() && 529 // TODO: Can remove if in SCC now. 530 !SCCFunctions.count(Callee) && 531 532 // The function may be apparently dead, but if there are indirect 533 // callgraph references to the node, we cannot delete it yet, this 534 // could invalidate the CGSCC iterator. 535 CG[Callee]->getNumReferences() == 0) { 536 DEBUG(dbgs() << " -> Deleting dead function: " 537 << Callee->getName() << "\n"); 538 CallGraphNode *CalleeNode = CG[Callee]; 539 540 // Remove any call graph edges from the callee to its callees. 541 CalleeNode->removeAllCalledFunctions(); 542 543 // Removing the node for callee from the call graph and delete it. 544 delete CG.removeFunctionFromModule(CalleeNode); 545 ++NumDeleted; 546 } 547 548 // Remove this call site from the list. If possible, use 549 // swap/pop_back for efficiency, but do not use it if doing so would 550 // move a call site to a function in this SCC before the 551 // 'FirstCallInSCC' barrier. 552 if (SCC.isSingular()) { 553 CallSites[CSi] = CallSites.back(); 554 CallSites.pop_back(); 555 } else { 556 CallSites.erase(CallSites.begin()+CSi); 557 } 558 --CSi; 559 560 Changed = true; 561 LocalChange = true; 562 } 563 } while (LocalChange); 564 565 return Changed; 566 } 567 568 /// Remove now-dead linkonce functions at the end of 569 /// processing to avoid breaking the SCC traversal. 570 bool Inliner::doFinalization(CallGraph &CG) { 571 return removeDeadFunctions(CG); 572 } 573 574 /// Remove dead functions that are not included in DNR (Do Not Remove) list. 575 bool Inliner::removeDeadFunctions(CallGraph &CG, bool AlwaysInlineOnly) { 576 SmallVector<CallGraphNode*, 16> FunctionsToRemove; 577 SmallVector<CallGraphNode *, 16> DeadFunctionsInComdats; 578 SmallDenseMap<const Comdat *, int, 16> ComdatEntriesAlive; 579 580 auto RemoveCGN = [&](CallGraphNode *CGN) { 581 // Remove any call graph edges from the function to its callees. 582 CGN->removeAllCalledFunctions(); 583 584 // Remove any edges from the external node to the function's call graph 585 // node. These edges might have been made irrelegant due to 586 // optimization of the program. 587 CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN); 588 589 // Removing the node for callee from the call graph and delete it. 590 FunctionsToRemove.push_back(CGN); 591 }; 592 593 // Scan for all of the functions, looking for ones that should now be removed 594 // from the program. Insert the dead ones in the FunctionsToRemove set. 595 for (const auto &I : CG) { 596 CallGraphNode *CGN = I.second.get(); 597 Function *F = CGN->getFunction(); 598 if (!F || F->isDeclaration()) 599 continue; 600 601 // Handle the case when this function is called and we only want to care 602 // about always-inline functions. This is a bit of a hack to share code 603 // between here and the InlineAlways pass. 604 if (AlwaysInlineOnly && !F->hasFnAttribute(Attribute::AlwaysInline)) 605 continue; 606 607 // If the only remaining users of the function are dead constants, remove 608 // them. 609 F->removeDeadConstantUsers(); 610 611 if (!F->isDefTriviallyDead()) 612 continue; 613 614 // It is unsafe to drop a function with discardable linkage from a COMDAT 615 // without also dropping the other members of the COMDAT. 616 // The inliner doesn't visit non-function entities which are in COMDAT 617 // groups so it is unsafe to do so *unless* the linkage is local. 618 if (!F->hasLocalLinkage()) { 619 if (const Comdat *C = F->getComdat()) { 620 --ComdatEntriesAlive[C]; 621 DeadFunctionsInComdats.push_back(CGN); 622 continue; 623 } 624 } 625 626 RemoveCGN(CGN); 627 } 628 if (!DeadFunctionsInComdats.empty()) { 629 // Count up all the entities in COMDAT groups 630 auto ComdatGroupReferenced = [&](const Comdat *C) { 631 auto I = ComdatEntriesAlive.find(C); 632 if (I != ComdatEntriesAlive.end()) 633 ++(I->getSecond()); 634 }; 635 for (const Function &F : CG.getModule()) 636 if (const Comdat *C = F.getComdat()) 637 ComdatGroupReferenced(C); 638 for (const GlobalVariable &GV : CG.getModule().globals()) 639 if (const Comdat *C = GV.getComdat()) 640 ComdatGroupReferenced(C); 641 for (const GlobalAlias &GA : CG.getModule().aliases()) 642 if (const Comdat *C = GA.getComdat()) 643 ComdatGroupReferenced(C); 644 for (CallGraphNode *CGN : DeadFunctionsInComdats) { 645 Function *F = CGN->getFunction(); 646 const Comdat *C = F->getComdat(); 647 int NumAlive = ComdatEntriesAlive[C]; 648 // We can remove functions in a COMDAT group if the entire group is dead. 649 assert(NumAlive >= 0); 650 if (NumAlive > 0) 651 continue; 652 653 RemoveCGN(CGN); 654 } 655 } 656 657 if (FunctionsToRemove.empty()) 658 return false; 659 660 // Now that we know which functions to delete, do so. We didn't want to do 661 // this inline, because that would invalidate our CallGraph::iterator 662 // objects. :( 663 // 664 // Note that it doesn't matter that we are iterating over a non-stable order 665 // here to do this, it doesn't matter which order the functions are deleted 666 // in. 667 array_pod_sort(FunctionsToRemove.begin(), FunctionsToRemove.end()); 668 FunctionsToRemove.erase(std::unique(FunctionsToRemove.begin(), 669 FunctionsToRemove.end()), 670 FunctionsToRemove.end()); 671 for (CallGraphNode *CGN : FunctionsToRemove) { 672 delete CG.removeFunctionFromModule(CGN); 673 ++NumDeleted; 674 } 675 return true; 676 } 677