Inliner.cpp revision 45de584b4f82fbfb9cb9c50bc1fc08931b534308
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" 32using namespace llvm; 33 34STATISTIC(NumInlined, "Number of functions inlined"); 35STATISTIC(NumCallsDeleted, "Number of call sites deleted, not inlined"); 36STATISTIC(NumDeleted, "Number of functions deleted because all callers found"); 37STATISTIC(NumMergedAllocas, "Number of allocas merged together"); 38 39static cl::opt<int> 40InlineLimit("inline-threshold", cl::Hidden, cl::init(225), cl::ZeroOrMore, 41 cl::desc("Control the amount of inlining to perform (default = 225)")); 42 43static cl::opt<int> 44HintThreshold("inlinehint-threshold", cl::Hidden, cl::init(325), 45 cl::desc("Threshold for inlining functions with inline hint")); 46 47// Threshold to use when optsize is specified (and there is no -inline-limit). 48const int OptSizeThreshold = 75; 49 50Inliner::Inliner(char &ID) 51 : CallGraphSCCPass(ID), InlineThreshold(InlineLimit), InsertLifetime(true) {} 52 53Inliner::Inliner(char &ID, int Threshold, bool InsertLifetime) 54 : CallGraphSCCPass(ID), InlineThreshold(InlineLimit.getNumOccurrences() > 0 ? 55 InlineLimit : Threshold), 56 InsertLifetime(InsertLifetime) {} 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<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 int InlineHistory, bool InsertLifetime) { 80 Function *Callee = CS.getCalledFunction(); 81 Function *Caller = CS.getCaller(); 82 83 // Try to inline the function. Get the list of static allocas that were 84 // inlined. 85 if (!InlineFunction(CS, IFI, InsertLifetime)) 86 return false; 87 88 // If the inlined function had a higher stack protection level than the 89 // calling function, then bump up the caller's stack protection level. 90 if (Callee->hasFnAttr(Attribute::StackProtectReq)) 91 Caller->addFnAttr(Attribute::StackProtectReq); 92 else if (Callee->hasFnAttr(Attribute::StackProtect) && 93 !Caller->hasFnAttr(Attribute::StackProtectReq)) 94 Caller->addFnAttr(Attribute::StackProtect); 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 // When processing our SCC, check to see if CS was inlined from some other 120 // call site. For example, if we're processing "A" in this code: 121 // A() { B() } 122 // B() { x = alloca ... C() } 123 // C() { y = alloca ... } 124 // Assume that C was not inlined into B initially, and so we're processing A 125 // and decide to inline B into A. Doing this makes an alloca available for 126 // reuse and makes a callsite (C) available for inlining. When we process 127 // the C call site we don't want to do any alloca merging between X and Y 128 // because their scopes are not disjoint. We could make this smarter by 129 // keeping track of the inline history for each alloca in the 130 // InlinedArrayAllocas but this isn't likely to be a significant win. 131 if (InlineHistory != -1) // Only do merging for top-level call sites in SCC. 132 return true; 133 134 // Loop over all the allocas we have so far and see if they can be merged with 135 // a previously inlined alloca. If not, remember that we had it. 136 for (unsigned AllocaNo = 0, e = IFI.StaticAllocas.size(); 137 AllocaNo != e; ++AllocaNo) { 138 AllocaInst *AI = IFI.StaticAllocas[AllocaNo]; 139 140 // Don't bother trying to merge array allocations (they will usually be 141 // canonicalized to be an allocation *of* an array), or allocations whose 142 // type is not itself an array (because we're afraid of pessimizing SRoA). 143 ArrayType *ATy = dyn_cast<ArrayType>(AI->getAllocatedType()); 144 if (ATy == 0 || AI->isArrayAllocation()) 145 continue; 146 147 // Get the list of all available allocas for this array type. 148 std::vector<AllocaInst*> &AllocasForType = InlinedArrayAllocas[ATy]; 149 150 // Loop over the allocas in AllocasForType to see if we can reuse one. Note 151 // that we have to be careful not to reuse the same "available" alloca for 152 // multiple different allocas that we just inlined, we use the 'UsedAllocas' 153 // set to keep track of which "available" allocas are being used by this 154 // function. Also, AllocasForType can be empty of course! 155 bool MergedAwayAlloca = false; 156 for (unsigned i = 0, e = AllocasForType.size(); i != e; ++i) { 157 AllocaInst *AvailableAlloca = AllocasForType[i]; 158 159 // The available alloca has to be in the right function, not in some other 160 // function in this SCC. 161 if (AvailableAlloca->getParent() != AI->getParent()) 162 continue; 163 164 // If the inlined function already uses this alloca then we can't reuse 165 // it. 166 if (!UsedAllocas.insert(AvailableAlloca)) 167 continue; 168 169 // Otherwise, we *can* reuse it, RAUW AI into AvailableAlloca and declare 170 // success! 171 DEBUG(dbgs() << " ***MERGED ALLOCA: " << *AI << "\n\t\tINTO: " 172 << *AvailableAlloca << '\n'); 173 174 AI->replaceAllUsesWith(AvailableAlloca); 175 AI->eraseFromParent(); 176 MergedAwayAlloca = true; 177 ++NumMergedAllocas; 178 IFI.StaticAllocas[AllocaNo] = 0; 179 break; 180 } 181 182 // If we already nuked the alloca, we're done with it. 183 if (MergedAwayAlloca) 184 continue; 185 186 // If we were unable to merge away the alloca either because there are no 187 // allocas of the right type available or because we reused them all 188 // already, remember that this alloca came from an inlined function and mark 189 // it used so we don't reuse it for other allocas from this inline 190 // operation. 191 AllocasForType.push_back(AI); 192 UsedAllocas.insert(AI); 193 } 194 195 return true; 196} 197 198unsigned Inliner::getInlineThreshold(CallSite CS) const { 199 int thres = InlineThreshold; 200 201 // Listen to optsize when -inline-limit is not given. 202 Function *Caller = CS.getCaller(); 203 if (Caller && !Caller->isDeclaration() && 204 Caller->hasFnAttr(Attribute::OptimizeForSize) && 205 InlineLimit.getNumOccurrences() == 0) 206 thres = OptSizeThreshold; 207 208 // Listen to inlinehint when it would increase the threshold. 209 Function *Callee = CS.getCalledFunction(); 210 if (HintThreshold > thres && Callee && !Callee->isDeclaration() && 211 Callee->hasFnAttr(Attribute::InlineHint)) 212 thres = HintThreshold; 213 214 return thres; 215} 216 217/// shouldInline - Return true if the inliner should attempt to inline 218/// at the given CallSite. 219bool Inliner::shouldInline(CallSite CS) { 220 InlineCost IC = getInlineCost(CS); 221 222 if (IC.isAlways()) { 223 DEBUG(dbgs() << " Inlining: cost=always" 224 << ", Call: " << *CS.getInstruction() << "\n"); 225 return true; 226 } 227 228 if (IC.isNever()) { 229 DEBUG(dbgs() << " NOT Inlining: cost=never" 230 << ", Call: " << *CS.getInstruction() << "\n"); 231 return false; 232 } 233 234 Function *Caller = CS.getCaller(); 235 if (!IC) { 236 DEBUG(dbgs() << " NOT Inlining: cost=" << IC.getCost() 237 << ", thres=" << (IC.getCostDelta() + IC.getCost()) 238 << ", Call: " << *CS.getInstruction() << "\n"); 239 return false; 240 } 241 242 // Try to detect the case where the current inlining candidate caller (call 243 // it B) is a static or linkonce-ODR function and is an inlining candidate 244 // elsewhere, and the current candidate callee (call it C) is large enough 245 // that inlining it into B would make B too big to inline later. In these 246 // circumstances it may be best not to inline C into B, but to inline B into 247 // its callers. 248 // 249 // This only applies to static and linkonce-ODR functions because those are 250 // expected to be available for inlining in the translation units where they 251 // are used. Thus we will always have the opportunity to make local inlining 252 // decisions. Importantly the linkonce-ODR linkage covers inline functions 253 // and templates in C++. 254 // 255 // FIXME: All of this logic should be sunk into getInlineCost. It relies on 256 // the internal implementation of the inline cost metrics rather than 257 // treating them as truly abstract units etc. 258 if (Caller->hasLocalLinkage() || 259 Caller->getLinkage() == GlobalValue::LinkOnceODRLinkage) { 260 int TotalSecondaryCost = 0; 261 // The candidate cost to be imposed upon the current function. 262 int CandidateCost = IC.getCost() - (InlineConstants::CallPenalty + 1); 263 // This bool tracks what happens if we do NOT inline C into B. 264 bool callerWillBeRemoved = Caller->hasLocalLinkage(); 265 // This bool tracks what happens if we DO inline C into B. 266 bool inliningPreventsSomeOuterInline = false; 267 for (Value::use_iterator I = Caller->use_begin(), E =Caller->use_end(); 268 I != E; ++I) { 269 CallSite CS2(*I); 270 271 // If this isn't a call to Caller (it could be some other sort 272 // of reference) skip it. Such references will prevent the caller 273 // from being removed. 274 if (!CS2 || CS2.getCalledFunction() != Caller) { 275 callerWillBeRemoved = false; 276 continue; 277 } 278 279 InlineCost IC2 = getInlineCost(CS2); 280 if (!IC2) { 281 callerWillBeRemoved = false; 282 continue; 283 } 284 if (IC2.isAlways()) 285 continue; 286 287 // See if inlining or original callsite would erase the cost delta of 288 // this callsite. We subtract off the penalty for the call instruction, 289 // which we would be deleting. 290 if (IC2.getCostDelta() <= CandidateCost) { 291 inliningPreventsSomeOuterInline = true; 292 TotalSecondaryCost += IC2.getCost(); 293 } 294 } 295 // If all outer calls to Caller would get inlined, the cost for the last 296 // one is set very low by getInlineCost, in anticipation that Caller will 297 // be removed entirely. We did not account for this above unless there 298 // is only one caller of Caller. 299 if (callerWillBeRemoved && Caller->use_begin() != Caller->use_end()) 300 TotalSecondaryCost += InlineConstants::LastCallToStaticBonus; 301 302 if (inliningPreventsSomeOuterInline && TotalSecondaryCost < IC.getCost()) { 303 DEBUG(dbgs() << " NOT Inlining: " << *CS.getInstruction() << 304 " Cost = " << IC.getCost() << 305 ", outer Cost = " << TotalSecondaryCost << '\n'); 306 return false; 307 } 308 } 309 310 DEBUG(dbgs() << " Inlining: cost=" << IC.getCost() 311 << ", thres=" << (IC.getCostDelta() + IC.getCost()) 312 << ", Call: " << *CS.getInstruction() << '\n'); 313 return true; 314} 315 316/// InlineHistoryIncludes - Return true if the specified inline history ID 317/// indicates an inline history that includes the specified function. 318static bool InlineHistoryIncludes(Function *F, int InlineHistoryID, 319 const SmallVectorImpl<std::pair<Function*, int> > &InlineHistory) { 320 while (InlineHistoryID != -1) { 321 assert(unsigned(InlineHistoryID) < InlineHistory.size() && 322 "Invalid inline history ID"); 323 if (InlineHistory[InlineHistoryID].first == F) 324 return true; 325 InlineHistoryID = InlineHistory[InlineHistoryID].second; 326 } 327 return false; 328} 329 330bool Inliner::runOnSCC(CallGraphSCC &SCC) { 331 CallGraph &CG = getAnalysis<CallGraph>(); 332 const TargetData *TD = getAnalysisIfAvailable<TargetData>(); 333 334 SmallPtrSet<Function*, 8> SCCFunctions; 335 DEBUG(dbgs() << "Inliner visiting SCC:"); 336 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) { 337 Function *F = (*I)->getFunction(); 338 if (F) SCCFunctions.insert(F); 339 DEBUG(dbgs() << " " << (F ? F->getName() : "INDIRECTNODE")); 340 } 341 342 // Scan through and identify all call sites ahead of time so that we only 343 // inline call sites in the original functions, not call sites that result 344 // from inlining other functions. 345 SmallVector<std::pair<CallSite, int>, 16> CallSites; 346 347 // When inlining a callee produces new call sites, we want to keep track of 348 // the fact that they were inlined from the callee. This allows us to avoid 349 // infinite inlining in some obscure cases. To represent this, we use an 350 // index into the InlineHistory vector. 351 SmallVector<std::pair<Function*, int>, 8> InlineHistory; 352 353 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) { 354 Function *F = (*I)->getFunction(); 355 if (!F) continue; 356 357 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) 358 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 359 CallSite CS(cast<Value>(I)); 360 // If this isn't a call, or it is a call to an intrinsic, it can 361 // never be inlined. 362 if (!CS || isa<IntrinsicInst>(I)) 363 continue; 364 365 // If this is a direct call to an external function, we can never inline 366 // it. If it is an indirect call, inlining may resolve it to be a 367 // direct call, so we keep it. 368 if (CS.getCalledFunction() && CS.getCalledFunction()->isDeclaration()) 369 continue; 370 371 CallSites.push_back(std::make_pair(CS, -1)); 372 } 373 } 374 375 DEBUG(dbgs() << ": " << CallSites.size() << " call sites.\n"); 376 377 // If there are no calls in this function, exit early. 378 if (CallSites.empty()) 379 return false; 380 381 // Now that we have all of the call sites, move the ones to functions in the 382 // current SCC to the end of the list. 383 unsigned FirstCallInSCC = CallSites.size(); 384 for (unsigned i = 0; i < FirstCallInSCC; ++i) 385 if (Function *F = CallSites[i].first.getCalledFunction()) 386 if (SCCFunctions.count(F)) 387 std::swap(CallSites[i--], CallSites[--FirstCallInSCC]); 388 389 390 InlinedArrayAllocasTy InlinedArrayAllocas; 391 InlineFunctionInfo InlineInfo(&CG, TD); 392 393 // Now that we have all of the call sites, loop over them and inline them if 394 // it looks profitable to do so. 395 bool Changed = false; 396 bool LocalChange; 397 do { 398 LocalChange = false; 399 // Iterate over the outer loop because inlining functions can cause indirect 400 // calls to become direct calls. 401 for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) { 402 CallSite CS = CallSites[CSi].first; 403 404 Function *Caller = CS.getCaller(); 405 Function *Callee = CS.getCalledFunction(); 406 407 // If this call site is dead and it is to a readonly function, we should 408 // just delete the call instead of trying to inline it, regardless of 409 // size. This happens because IPSCCP propagates the result out of the 410 // call and then we're left with the dead call. 411 if (isInstructionTriviallyDead(CS.getInstruction())) { 412 DEBUG(dbgs() << " -> Deleting dead call: " 413 << *CS.getInstruction() << "\n"); 414 // Update the call graph by deleting the edge from Callee to Caller. 415 CG[Caller]->removeCallEdgeFor(CS); 416 CS.getInstruction()->eraseFromParent(); 417 ++NumCallsDeleted; 418 } else { 419 // We can only inline direct calls to non-declarations. 420 if (Callee == 0 || Callee->isDeclaration()) continue; 421 422 // If this call site was obtained by inlining another function, verify 423 // that the include path for the function did not include the callee 424 // itself. If so, we'd be recursively inlining the same function, 425 // which would provide the same callsites, which would cause us to 426 // infinitely inline. 427 int InlineHistoryID = CallSites[CSi].second; 428 if (InlineHistoryID != -1 && 429 InlineHistoryIncludes(Callee, InlineHistoryID, InlineHistory)) 430 continue; 431 432 433 // If the policy determines that we should inline this function, 434 // try to do so. 435 if (!shouldInline(CS)) 436 continue; 437 438 // Attempt to inline the function. 439 if (!InlineCallIfPossible(CS, InlineInfo, InlinedArrayAllocas, 440 InlineHistoryID, InsertLifetime)) 441 continue; 442 ++NumInlined; 443 444 // If inlining this function gave us any new call sites, throw them 445 // onto our worklist to process. They are useful inline candidates. 446 if (!InlineInfo.InlinedCalls.empty()) { 447 // Create a new inline history entry for this, so that we remember 448 // that these new callsites came about due to inlining Callee. 449 int NewHistoryID = InlineHistory.size(); 450 InlineHistory.push_back(std::make_pair(Callee, InlineHistoryID)); 451 452 for (unsigned i = 0, e = InlineInfo.InlinedCalls.size(); 453 i != e; ++i) { 454 Value *Ptr = InlineInfo.InlinedCalls[i]; 455 CallSites.push_back(std::make_pair(CallSite(Ptr), NewHistoryID)); 456 } 457 } 458 } 459 460 // If we inlined or deleted the last possible call site to the function, 461 // delete the function body now. 462 if (Callee && Callee->use_empty() && Callee->hasLocalLinkage() && 463 // TODO: Can remove if in SCC now. 464 !SCCFunctions.count(Callee) && 465 466 // The function may be apparently dead, but if there are indirect 467 // callgraph references to the node, we cannot delete it yet, this 468 // could invalidate the CGSCC iterator. 469 CG[Callee]->getNumReferences() == 0) { 470 DEBUG(dbgs() << " -> Deleting dead function: " 471 << Callee->getName() << "\n"); 472 CallGraphNode *CalleeNode = CG[Callee]; 473 474 // Remove any call graph edges from the callee to its callees. 475 CalleeNode->removeAllCalledFunctions(); 476 477 // Removing the node for callee from the call graph and delete it. 478 delete CG.removeFunctionFromModule(CalleeNode); 479 ++NumDeleted; 480 } 481 482 // Remove this call site from the list. If possible, use 483 // swap/pop_back for efficiency, but do not use it if doing so would 484 // move a call site to a function in this SCC before the 485 // 'FirstCallInSCC' barrier. 486 if (SCC.isSingular()) { 487 CallSites[CSi] = CallSites.back(); 488 CallSites.pop_back(); 489 } else { 490 CallSites.erase(CallSites.begin()+CSi); 491 } 492 --CSi; 493 494 Changed = true; 495 LocalChange = true; 496 } 497 } while (LocalChange); 498 499 return Changed; 500} 501 502// doFinalization - Remove now-dead linkonce functions at the end of 503// processing to avoid breaking the SCC traversal. 504bool Inliner::doFinalization(CallGraph &CG) { 505 return removeDeadFunctions(CG); 506} 507 508/// removeDeadFunctions - Remove dead functions that are not included in 509/// DNR (Do Not Remove) list. 510bool Inliner::removeDeadFunctions(CallGraph &CG, bool AlwaysInlineOnly) { 511 SmallVector<CallGraphNode*, 16> FunctionsToRemove; 512 513 // Scan for all of the functions, looking for ones that should now be removed 514 // from the program. Insert the dead ones in the FunctionsToRemove set. 515 for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) { 516 CallGraphNode *CGN = I->second; 517 Function *F = CGN->getFunction(); 518 if (!F || F->isDeclaration()) 519 continue; 520 521 // Handle the case when this function is called and we only want to care 522 // about always-inline functions. This is a bit of a hack to share code 523 // between here and the InlineAlways pass. 524 if (AlwaysInlineOnly && !F->hasFnAttr(Attribute::AlwaysInline)) 525 continue; 526 527 // If the only remaining users of the function are dead constants, remove 528 // them. 529 F->removeDeadConstantUsers(); 530 531 if (!F->isDefTriviallyDead()) 532 continue; 533 534 // Remove any call graph edges from the function to its callees. 535 CGN->removeAllCalledFunctions(); 536 537 // Remove any edges from the external node to the function's call graph 538 // node. These edges might have been made irrelegant due to 539 // optimization of the program. 540 CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN); 541 542 // Removing the node for callee from the call graph and delete it. 543 FunctionsToRemove.push_back(CGN); 544 } 545 if (FunctionsToRemove.empty()) 546 return false; 547 548 // Now that we know which functions to delete, do so. We didn't want to do 549 // this inline, because that would invalidate our CallGraph::iterator 550 // objects. :( 551 // 552 // Note that it doesn't matter that we are iterating over a non-stable order 553 // here to do this, it doesn't matter which order the functions are deleted 554 // in. 555 std::sort(FunctionsToRemove.begin(), FunctionsToRemove.end()); 556 FunctionsToRemove.erase(std::unique(FunctionsToRemove.begin(), 557 FunctionsToRemove.end()), 558 FunctionsToRemove.end()); 559 for (SmallVectorImpl<CallGraphNode *>::iterator I = FunctionsToRemove.begin(), 560 E = FunctionsToRemove.end(); 561 I != E; ++I) { 562 delete CG.removeFunctionFromModule(*I); 563 ++NumDeleted; 564 } 565 return true; 566} 567