Inliner.cpp revision 93ff359d75526a97df918f4b59085b992e302658
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(void *ID) 52 : CallGraphSCCPass(ID), InlineThreshold(InlineLimit) {} 53 54Inliner::Inliner(void *ID, int Threshold) 55 : CallGraphSCCPass(ID), InlineThreshold(Threshold) {} 56 57/// getAnalysisUsage - For this class, we declare that we require and preserve 58/// the call graph. If the derived class implements this method, it should 59/// always explicitly call the implementation here. 60void Inliner::getAnalysisUsage(AnalysisUsage &Info) const { 61 CallGraphSCCPass::getAnalysisUsage(Info); 62} 63 64 65typedef DenseMap<const ArrayType*, std::vector<AllocaInst*> > 66InlinedArrayAllocasTy; 67 68/// InlineCallIfPossible - If it is possible to inline the specified call site, 69/// do so and update the CallGraph for this operation. 70/// 71/// This function also does some basic book-keeping to update the IR. The 72/// InlinedArrayAllocas map keeps track of any allocas that are already 73/// available from other functions inlined into the caller. If we are able to 74/// inline this call site we attempt to reuse already available allocas or add 75/// any new allocas to the set if not possible. 76static bool InlineCallIfPossible(CallSite CS, InlineFunctionInfo &IFI, 77 InlinedArrayAllocasTy &InlinedArrayAllocas) { 78 Function *Callee = CS.getCalledFunction(); 79 Function *Caller = CS.getCaller(); 80 81 // Try to inline the function. Get the list of static allocas that were 82 // inlined. 83 if (!InlineFunction(CS, IFI)) 84 return false; 85 86 // If the inlined function had a higher stack protection level than the 87 // calling function, then bump up the caller's stack protection level. 88 if (Callee->hasFnAttr(Attribute::StackProtectReq)) 89 Caller->addFnAttr(Attribute::StackProtectReq); 90 else if (Callee->hasFnAttr(Attribute::StackProtect) && 91 !Caller->hasFnAttr(Attribute::StackProtectReq)) 92 Caller->addFnAttr(Attribute::StackProtect); 93 94 95 // Look at all of the allocas that we inlined through this call site. If we 96 // have already inlined other allocas through other calls into this function, 97 // then we know that they have disjoint lifetimes and that we can merge them. 98 // 99 // There are many heuristics possible for merging these allocas, and the 100 // different options have different tradeoffs. One thing that we *really* 101 // don't want to hurt is SRoA: once inlining happens, often allocas are no 102 // longer address taken and so they can be promoted. 103 // 104 // Our "solution" for that is to only merge allocas whose outermost type is an 105 // array type. These are usually not promoted because someone is using a 106 // variable index into them. These are also often the most important ones to 107 // merge. 108 // 109 // A better solution would be to have real memory lifetime markers in the IR 110 // and not have the inliner do any merging of allocas at all. This would 111 // allow the backend to do proper stack slot coloring of all allocas that 112 // *actually make it to the backend*, which is really what we want. 113 // 114 // Because we don't have this information, we do this simple and useful hack. 115 // 116 SmallPtrSet<AllocaInst*, 16> UsedAllocas; 117 118 // Loop over all the allocas we have so far and see if they can be merged with 119 // a previously inlined alloca. If not, remember that we had it. 120 for (unsigned AllocaNo = 0, e = IFI.StaticAllocas.size(); 121 AllocaNo != e; ++AllocaNo) { 122 AllocaInst *AI = IFI.StaticAllocas[AllocaNo]; 123 124 // Don't bother trying to merge array allocations (they will usually be 125 // canonicalized to be an allocation *of* an array), or allocations whose 126 // type is not itself an array (because we're afraid of pessimizing SRoA). 127 const ArrayType *ATy = dyn_cast<ArrayType>(AI->getAllocatedType()); 128 if (ATy == 0 || AI->isArrayAllocation()) 129 continue; 130 131 // Get the list of all available allocas for this array type. 132 std::vector<AllocaInst*> &AllocasForType = InlinedArrayAllocas[ATy]; 133 134 // Loop over the allocas in AllocasForType to see if we can reuse one. Note 135 // that we have to be careful not to reuse the same "available" alloca for 136 // multiple different allocas that we just inlined, we use the 'UsedAllocas' 137 // set to keep track of which "available" allocas are being used by this 138 // function. Also, AllocasForType can be empty of course! 139 bool MergedAwayAlloca = false; 140 for (unsigned i = 0, e = AllocasForType.size(); i != e; ++i) { 141 AllocaInst *AvailableAlloca = AllocasForType[i]; 142 143 // The available alloca has to be in the right function, not in some other 144 // function in this SCC. 145 if (AvailableAlloca->getParent() != AI->getParent()) 146 continue; 147 148 // If the inlined function already uses this alloca then we can't reuse 149 // it. 150 if (!UsedAllocas.insert(AvailableAlloca)) 151 continue; 152 153 // Otherwise, we *can* reuse it, RAUW AI into AvailableAlloca and declare 154 // success! 155 DEBUG(dbgs() << " ***MERGED ALLOCA: " << *AI); 156 157 AI->replaceAllUsesWith(AvailableAlloca); 158 AI->eraseFromParent(); 159 MergedAwayAlloca = true; 160 ++NumMergedAllocas; 161 break; 162 } 163 164 // If we already nuked the alloca, we're done with it. 165 if (MergedAwayAlloca) 166 continue; 167 168 // If we were unable to merge away the alloca either because there are no 169 // allocas of the right type available or because we reused them all 170 // already, remember that this alloca came from an inlined function and mark 171 // it used so we don't reuse it for other allocas from this inline 172 // operation. 173 AllocasForType.push_back(AI); 174 UsedAllocas.insert(AI); 175 } 176 177 return true; 178} 179 180unsigned Inliner::getInlineThreshold(CallSite CS) const { 181 int thres = InlineThreshold; 182 183 // Listen to optsize when -inline-limit is not given. 184 Function *Caller = CS.getCaller(); 185 if (Caller && !Caller->isDeclaration() && 186 Caller->hasFnAttr(Attribute::OptimizeForSize) && 187 InlineLimit.getNumOccurrences() == 0) 188 thres = OptSizeThreshold; 189 190 // Listen to inlinehint when it would increase the threshold. 191 Function *Callee = CS.getCalledFunction(); 192 if (HintThreshold > thres && Callee && !Callee->isDeclaration() && 193 Callee->hasFnAttr(Attribute::InlineHint)) 194 thres = HintThreshold; 195 196 return thres; 197} 198 199/// shouldInline - Return true if the inliner should attempt to inline 200/// at the given CallSite. 201bool Inliner::shouldInline(CallSite CS) { 202 InlineCost IC = getInlineCost(CS); 203 204 if (IC.isAlways()) { 205 DEBUG(dbgs() << " Inlining: cost=always" 206 << ", Call: " << *CS.getInstruction() << "\n"); 207 return true; 208 } 209 210 if (IC.isNever()) { 211 DEBUG(dbgs() << " NOT Inlining: cost=never" 212 << ", Call: " << *CS.getInstruction() << "\n"); 213 return false; 214 } 215 216 int Cost = IC.getValue(); 217 Function *Caller = CS.getCaller(); 218 int CurrentThreshold = getInlineThreshold(CS); 219 float FudgeFactor = getInlineFudgeFactor(CS); 220 int AdjThreshold = (int)(CurrentThreshold * FudgeFactor); 221 if (Cost >= AdjThreshold) { 222 DEBUG(dbgs() << " NOT Inlining: cost=" << Cost 223 << ", thres=" << AdjThreshold 224 << ", Call: " << *CS.getInstruction() << "\n"); 225 return false; 226 } 227 228 // Try to detect the case where the current inlining candidate caller 229 // (call it B) is a static function and is an inlining candidate elsewhere, 230 // and the current candidate callee (call it C) is large enough that 231 // inlining it into B would make B too big to inline later. In these 232 // circumstances it may be best not to inline C into B, but to inline B 233 // into its callers. 234 if (Caller->hasLocalLinkage()) { 235 int TotalSecondaryCost = 0; 236 bool outerCallsFound = false; 237 bool allOuterCallsWillBeInlined = true; 238 bool someOuterCallWouldNotBeInlined = false; 239 for (Value::use_iterator I = Caller->use_begin(), E =Caller->use_end(); 240 I != E; ++I) { 241 CallSite CS2 = CallSite::get(*I); 242 243 // If this isn't a call to Caller (it could be some other sort 244 // of reference) skip it. 245 if (CS2.getInstruction() == 0 || CS2.getCalledFunction() != Caller) 246 continue; 247 248 InlineCost IC2 = getInlineCost(CS2); 249 if (IC2.isNever()) 250 allOuterCallsWillBeInlined = false; 251 if (IC2.isAlways() || IC2.isNever()) 252 continue; 253 254 outerCallsFound = true; 255 int Cost2 = IC2.getValue(); 256 int CurrentThreshold2 = getInlineThreshold(CS2); 257 float FudgeFactor2 = getInlineFudgeFactor(CS2); 258 259 if (Cost2 >= (int)(CurrentThreshold2 * FudgeFactor2)) 260 allOuterCallsWillBeInlined = false; 261 262 // See if we have this case. We subtract off the penalty 263 // for the call instruction, which we would be deleting. 264 if (Cost2 < (int)(CurrentThreshold2 * FudgeFactor2) && 265 Cost2 + Cost - (InlineConstants::CallPenalty + 1) >= 266 (int)(CurrentThreshold2 * FudgeFactor2)) { 267 someOuterCallWouldNotBeInlined = true; 268 TotalSecondaryCost += Cost2; 269 } 270 } 271 // If all outer calls to Caller would get inlined, the cost for the last 272 // one is set very low by getInlineCost, in anticipation that Caller will 273 // be removed entirely. We did not account for this above unless there 274 // is only one caller of Caller. 275 if (allOuterCallsWillBeInlined && Caller->use_begin() != Caller->use_end()) 276 TotalSecondaryCost += InlineConstants::LastCallToStaticBonus; 277 278 if (outerCallsFound && someOuterCallWouldNotBeInlined && 279 TotalSecondaryCost < Cost) { 280 DEBUG(dbgs() << " NOT Inlining: " << *CS.getInstruction() << 281 " Cost = " << Cost << 282 ", outer Cost = " << TotalSecondaryCost << '\n'); 283 return false; 284 } 285 } 286 287 DEBUG(dbgs() << " Inlining: cost=" << Cost 288 << ", thres=" << AdjThreshold 289 << ", Call: " << *CS.getInstruction() << '\n'); 290 return true; 291} 292 293bool Inliner::runOnSCC(CallGraphSCC &SCC) { 294 CallGraph &CG = getAnalysis<CallGraph>(); 295 const TargetData *TD = getAnalysisIfAvailable<TargetData>(); 296 297 SmallPtrSet<Function*, 8> SCCFunctions; 298 DEBUG(dbgs() << "Inliner visiting SCC:"); 299 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) { 300 Function *F = (*I)->getFunction(); 301 if (F) SCCFunctions.insert(F); 302 DEBUG(dbgs() << " " << (F ? F->getName() : "INDIRECTNODE")); 303 } 304 305 // Scan through and identify all call sites ahead of time so that we only 306 // inline call sites in the original functions, not call sites that result 307 // from inlining other functions. 308 SmallVector<CallSite, 16> CallSites; 309 310 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) { 311 Function *F = (*I)->getFunction(); 312 if (!F) continue; 313 314 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) 315 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 316 CallSite CS = CallSite::get(I); 317 // If this isn't a call, or it is a call to an intrinsic, it can 318 // never be inlined. 319 if (CS.getInstruction() == 0 || isa<IntrinsicInst>(I)) 320 continue; 321 322 // If this is a direct call to an external function, we can never inline 323 // it. If it is an indirect call, inlining may resolve it to be a 324 // direct call, so we keep it. 325 if (CS.getCalledFunction() && CS.getCalledFunction()->isDeclaration()) 326 continue; 327 328 CallSites.push_back(CS); 329 } 330 } 331 332 DEBUG(dbgs() << ": " << CallSites.size() << " call sites.\n"); 333 334 // If there are no calls in this function, exit early. 335 if (CallSites.empty()) 336 return false; 337 338 // Now that we have all of the call sites, move the ones to functions in the 339 // current SCC to the end of the list. 340 unsigned FirstCallInSCC = CallSites.size(); 341 for (unsigned i = 0; i < FirstCallInSCC; ++i) 342 if (Function *F = CallSites[i].getCalledFunction()) 343 if (SCCFunctions.count(F)) 344 std::swap(CallSites[i--], CallSites[--FirstCallInSCC]); 345 346 347 InlinedArrayAllocasTy InlinedArrayAllocas; 348 InlineFunctionInfo InlineInfo(&CG, TD); 349 350 // Now that we have all of the call sites, loop over them and inline them if 351 // it looks profitable to do so. 352 bool Changed = false; 353 bool LocalChange; 354 do { 355 LocalChange = false; 356 // Iterate over the outer loop because inlining functions can cause indirect 357 // calls to become direct calls. 358 for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) { 359 CallSite CS = CallSites[CSi]; 360 361 Function *Caller = CS.getCaller(); 362 Function *Callee = CS.getCalledFunction(); 363 364 // If this call site is dead and it is to a readonly function, we should 365 // just delete the call instead of trying to inline it, regardless of 366 // size. This happens because IPSCCP propagates the result out of the 367 // call and then we're left with the dead call. 368 if (isInstructionTriviallyDead(CS.getInstruction())) { 369 DEBUG(dbgs() << " -> Deleting dead call: " 370 << *CS.getInstruction() << "\n"); 371 // Update the call graph by deleting the edge from Callee to Caller. 372 CG[Caller]->removeCallEdgeFor(CS); 373 CS.getInstruction()->eraseFromParent(); 374 ++NumCallsDeleted; 375 // Update the cached cost info with the missing call 376 growCachedCostInfo(Caller, NULL); 377 } else { 378 // We can only inline direct calls to non-declarations. 379 if (Callee == 0 || Callee->isDeclaration()) continue; 380 381 // If the policy determines that we should inline this function, 382 // try to do so. 383 if (!shouldInline(CS)) 384 continue; 385 386 // Attempt to inline the function. 387 if (!InlineCallIfPossible(CS, InlineInfo, InlinedArrayAllocas)) 388 continue; 389 ++NumInlined; 390 391 // If inlining this function devirtualized any call sites, throw them 392 // onto our worklist to process. They are useful inline candidates. 393#if 0 394 for (unsigned i = 0, e = InlineInfo.DevirtualizedCalls.size(); 395 i != e; ++i) 396 CallSites.push_back(CallSite(InlineInfo.DevirtualizedCalls[i])); 397#endif 398 399 // Update the cached cost info with the inlined call. 400 growCachedCostInfo(Caller, Callee); 401 } 402 403 // If we inlined or deleted the last possible call site to the function, 404 // delete the function body now. 405 if (Callee && Callee->use_empty() && Callee->hasLocalLinkage() && 406 // TODO: Can remove if in SCC now. 407 !SCCFunctions.count(Callee) && 408 409 // The function may be apparently dead, but if there are indirect 410 // callgraph references to the node, we cannot delete it yet, this 411 // could invalidate the CGSCC iterator. 412 CG[Callee]->getNumReferences() == 0) { 413 DEBUG(dbgs() << " -> Deleting dead function: " 414 << Callee->getName() << "\n"); 415 CallGraphNode *CalleeNode = CG[Callee]; 416 417 // Remove any call graph edges from the callee to its callees. 418 CalleeNode->removeAllCalledFunctions(); 419 420 resetCachedCostInfo(Callee); 421 422 // Removing the node for callee from the call graph and delete it. 423 delete CG.removeFunctionFromModule(CalleeNode); 424 ++NumDeleted; 425 } 426 427 // Remove this call site from the list. If possible, use 428 // swap/pop_back for efficiency, but do not use it if doing so would 429 // move a call site to a function in this SCC before the 430 // 'FirstCallInSCC' barrier. 431 if (SCC.isSingular()) { 432 std::swap(CallSites[CSi], CallSites.back()); 433 CallSites.pop_back(); 434 } else { 435 CallSites.erase(CallSites.begin()+CSi); 436 } 437 --CSi; 438 439 Changed = true; 440 LocalChange = true; 441 } 442 } while (LocalChange); 443 444 return Changed; 445} 446 447// doFinalization - Remove now-dead linkonce functions at the end of 448// processing to avoid breaking the SCC traversal. 449bool Inliner::doFinalization(CallGraph &CG) { 450 return removeDeadFunctions(CG); 451} 452 453/// removeDeadFunctions - Remove dead functions that are not included in 454/// DNR (Do Not Remove) list. 455bool Inliner::removeDeadFunctions(CallGraph &CG, 456 SmallPtrSet<const Function *, 16> *DNR) { 457 SmallPtrSet<CallGraphNode*, 16> FunctionsToRemove; 458 459 // Scan for all of the functions, looking for ones that should now be removed 460 // from the program. Insert the dead ones in the FunctionsToRemove set. 461 for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) { 462 CallGraphNode *CGN = I->second; 463 if (CGN->getFunction() == 0) 464 continue; 465 466 Function *F = CGN->getFunction(); 467 468 // If the only remaining users of the function are dead constants, remove 469 // them. 470 F->removeDeadConstantUsers(); 471 472 if (DNR && DNR->count(F)) 473 continue; 474 if (!F->hasLinkOnceLinkage() && !F->hasLocalLinkage() && 475 !F->hasAvailableExternallyLinkage()) 476 continue; 477 if (!F->use_empty()) 478 continue; 479 480 // Remove any call graph edges from the function to its callees. 481 CGN->removeAllCalledFunctions(); 482 483 // Remove any edges from the external node to the function's call graph 484 // node. These edges might have been made irrelegant due to 485 // optimization of the program. 486 CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN); 487 488 // Removing the node for callee from the call graph and delete it. 489 FunctionsToRemove.insert(CGN); 490 } 491 492 // Now that we know which functions to delete, do so. We didn't want to do 493 // this inline, because that would invalidate our CallGraph::iterator 494 // objects. :( 495 // 496 // Note that it doesn't matter that we are iterating over a non-stable set 497 // here to do this, it doesn't matter which order the functions are deleted 498 // in. 499 bool Changed = false; 500 for (SmallPtrSet<CallGraphNode*, 16>::iterator I = FunctionsToRemove.begin(), 501 E = FunctionsToRemove.end(); I != E; ++I) { 502 resetCachedCostInfo((*I)->getFunction()); 503 delete CG.removeFunctionFromModule(*I); 504 ++NumDeleted; 505 Changed = true; 506 } 507 508 return Changed; 509} 510