Inliner.cpp revision 78b1040a79c64d735bc77d02db22fa589b2f2b1e
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, CallGraph &CG, 77 const TargetData *TD, 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 SmallVector<AllocaInst*, 16> StaticAllocas; 85 if (!InlineFunction(CS, &CG, TD, &StaticAllocas)) 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 97 // Look at all of the allocas that we inlined through this call site. If we 98 // have already inlined other allocas through other calls into this function, 99 // then we know that they have disjoint lifetimes and that we can merge them. 100 // 101 // There are many heuristics possible for merging these allocas, and the 102 // different options have different tradeoffs. One thing that we *really* 103 // don't want to hurt is SRoA: once inlining happens, often allocas are no 104 // longer address taken and so they can be promoted. 105 // 106 // Our "solution" for that is to only merge allocas whose outermost type is an 107 // array type. These are usually not promoted because someone is using a 108 // variable index into them. These are also often the most important ones to 109 // merge. 110 // 111 // A better solution would be to have real memory lifetime markers in the IR 112 // and not have the inliner do any merging of allocas at all. This would 113 // allow the backend to do proper stack slot coloring of all allocas that 114 // *actually make it to the backend*, which is really what we want. 115 // 116 // Because we don't have this information, we do this simple and useful hack. 117 // 118 SmallPtrSet<AllocaInst*, 16> UsedAllocas; 119 120 // Loop over all the allocas we have so far and see if they can be merged with 121 // a previously inlined alloca. If not, remember that we had it. 122 for (unsigned AllocaNo = 0, e = StaticAllocas.size(); 123 AllocaNo != e; ++AllocaNo) { 124 AllocaInst *AI = StaticAllocas[AllocaNo]; 125 126 // Don't bother trying to merge array allocations (they will usually be 127 // canonicalized to be an allocation *of* an array), or allocations whose 128 // type is not itself an array (because we're afraid of pessimizing SRoA). 129 const ArrayType *ATy = dyn_cast<ArrayType>(AI->getAllocatedType()); 130 if (ATy == 0 || AI->isArrayAllocation()) 131 continue; 132 133 // Get the list of all available allocas for this array type. 134 std::vector<AllocaInst*> &AllocasForType = InlinedArrayAllocas[ATy]; 135 136 // Loop over the allocas in AllocasForType to see if we can reuse one. Note 137 // that we have to be careful not to reuse the same "available" alloca for 138 // multiple different allocas that we just inlined, we use the 'UsedAllocas' 139 // set to keep track of which "available" allocas are being used by this 140 // function. Also, AllocasForType can be empty of course! 141 bool MergedAwayAlloca = false; 142 for (unsigned i = 0, e = AllocasForType.size(); i != e; ++i) { 143 AllocaInst *AvailableAlloca = AllocasForType[i]; 144 145 // The available alloca has to be in the right function, not in some other 146 // function in this SCC. 147 if (AvailableAlloca->getParent() != AI->getParent()) 148 continue; 149 150 // If the inlined function already uses this alloca then we can't reuse 151 // it. 152 if (!UsedAllocas.insert(AvailableAlloca)) 153 continue; 154 155 // Otherwise, we *can* reuse it, RAUW AI into AvailableAlloca and declare 156 // success! 157 DEBUG(dbgs() << " ***MERGED ALLOCA: " << *AI); 158 159 AI->replaceAllUsesWith(AvailableAlloca); 160 AI->eraseFromParent(); 161 MergedAwayAlloca = true; 162 ++NumMergedAllocas; 163 break; 164 } 165 166 // If we already nuked the alloca, we're done with it. 167 if (MergedAwayAlloca) 168 continue; 169 170 // If we were unable to merge away the alloca either because there are no 171 // allocas of the right type available or because we reused them all 172 // already, remember that this alloca came from an inlined function and mark 173 // it used so we don't reuse it for other allocas from this inline 174 // operation. 175 AllocasForType.push_back(AI); 176 UsedAllocas.insert(AI); 177 } 178 179 return true; 180} 181 182unsigned Inliner::getInlineThreshold(CallSite CS) const { 183 int thres = InlineThreshold; 184 185 // Listen to optsize when -inline-limit is not given. 186 Function *Caller = CS.getCaller(); 187 if (Caller && !Caller->isDeclaration() && 188 Caller->hasFnAttr(Attribute::OptimizeForSize) && 189 InlineLimit.getNumOccurrences() == 0) 190 thres = OptSizeThreshold; 191 192 // Listen to inlinehint when it would increase the threshold. 193 Function *Callee = CS.getCalledFunction(); 194 if (HintThreshold > thres && Callee && !Callee->isDeclaration() && 195 Callee->hasFnAttr(Attribute::InlineHint)) 196 thres = HintThreshold; 197 198 return thres; 199} 200 201/// shouldInline - Return true if the inliner should attempt to inline 202/// at the given CallSite. 203bool Inliner::shouldInline(CallSite CS) { 204 InlineCost IC = getInlineCost(CS); 205 206 if (IC.isAlways()) { 207 DEBUG(dbgs() << " Inlining: cost=always" 208 << ", Call: " << *CS.getInstruction() << "\n"); 209 return true; 210 } 211 212 if (IC.isNever()) { 213 DEBUG(dbgs() << " NOT Inlining: cost=never" 214 << ", Call: " << *CS.getInstruction() << "\n"); 215 return false; 216 } 217 218 int Cost = IC.getValue(); 219 Function *Caller = CS.getCaller(); 220 int CurrentThreshold = getInlineThreshold(CS); 221 float FudgeFactor = getInlineFudgeFactor(CS); 222 if (Cost >= (int)(CurrentThreshold * FudgeFactor)) { 223 DEBUG(dbgs() << " NOT Inlining: cost=" << Cost 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 << ", Call: " << *CS.getInstruction() << '\n'); 289 return true; 290} 291 292bool Inliner::runOnSCC(std::vector<CallGraphNode*> &SCC) { 293 CallGraph &CG = getAnalysis<CallGraph>(); 294 const TargetData *TD = getAnalysisIfAvailable<TargetData>(); 295 296 SmallPtrSet<Function*, 8> SCCFunctions; 297 DEBUG(dbgs() << "Inliner visiting SCC:"); 298 for (unsigned i = 0, e = SCC.size(); i != e; ++i) { 299 Function *F = SCC[i]->getFunction(); 300 if (F) SCCFunctions.insert(F); 301 DEBUG(dbgs() << " " << (F ? F->getName() : "INDIRECTNODE")); 302 } 303 304 // Scan through and identify all call sites ahead of time so that we only 305 // inline call sites in the original functions, not call sites that result 306 // from inlining other functions. 307 SmallVector<CallSite, 16> CallSites; 308 309 for (unsigned i = 0, e = SCC.size(); i != e; ++i) { 310 Function *F = SCC[i]->getFunction(); 311 if (!F) continue; 312 313 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) 314 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 315 CallSite CS = CallSite::get(I); 316 // If this isn't a call, or it is a call to an intrinsic, it can 317 // never be inlined. 318 if (CS.getInstruction() == 0 || isa<IntrinsicInst>(I)) 319 continue; 320 321 // If this is a direct call to an external function, we can never inline 322 // it. If it is an indirect call, inlining may resolve it to be a 323 // direct call, so we keep it. 324 if (CS.getCalledFunction() && CS.getCalledFunction()->isDeclaration()) 325 continue; 326 327 CallSites.push_back(CS); 328 } 329 } 330 331 DEBUG(dbgs() << ": " << CallSites.size() << " call sites.\n"); 332 333 // Now that we have all of the call sites, move the ones to functions in the 334 // current SCC to the end of the list. 335 unsigned FirstCallInSCC = CallSites.size(); 336 for (unsigned i = 0; i < FirstCallInSCC; ++i) 337 if (Function *F = CallSites[i].getCalledFunction()) 338 if (SCCFunctions.count(F)) 339 std::swap(CallSites[i--], CallSites[--FirstCallInSCC]); 340 341 342 InlinedArrayAllocasTy InlinedArrayAllocas; 343 344 // Now that we have all of the call sites, loop over them and inline them if 345 // it looks profitable to do so. 346 bool Changed = false; 347 bool LocalChange; 348 do { 349 LocalChange = false; 350 // Iterate over the outer loop because inlining functions can cause indirect 351 // calls to become direct calls. 352 for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) { 353 CallSite CS = CallSites[CSi]; 354 355 Function *Caller = CS.getCaller(); 356 Function *Callee = CS.getCalledFunction(); 357 358 // If this call site is dead and it is to a readonly function, we should 359 // just delete the call instead of trying to inline it, regardless of 360 // size. This happens because IPSCCP propagates the result out of the 361 // call and then we're left with the dead call. 362 if (isInstructionTriviallyDead(CS.getInstruction())) { 363 DEBUG(dbgs() << " -> Deleting dead call: " 364 << *CS.getInstruction() << "\n"); 365 // Update the call graph by deleting the edge from Callee to Caller. 366 CG[Caller]->removeCallEdgeFor(CS); 367 CS.getInstruction()->eraseFromParent(); 368 ++NumCallsDeleted; 369 } else { 370 // We can only inline direct calls to non-declarations. 371 if (Callee == 0 || Callee->isDeclaration()) continue; 372 373 // If the policy determines that we should inline this function, 374 // try to do so. 375 if (!shouldInline(CS)) 376 continue; 377 378 // Attempt to inline the function... 379 if (!InlineCallIfPossible(CS, CG, TD, InlinedArrayAllocas)) 380 continue; 381 ++NumInlined; 382 } 383 384 // If we inlined or deleted the last possible call site to the function, 385 // delete the function body now. 386 if (Callee && Callee->use_empty() && Callee->hasLocalLinkage() && 387 // TODO: Can remove if in SCC now. 388 !SCCFunctions.count(Callee) && 389 390 // The function may be apparently dead, but if there are indirect 391 // callgraph references to the node, we cannot delete it yet, this 392 // could invalidate the CGSCC iterator. 393 CG[Callee]->getNumReferences() == 0) { 394 DEBUG(dbgs() << " -> Deleting dead function: " 395 << Callee->getName() << "\n"); 396 CallGraphNode *CalleeNode = CG[Callee]; 397 398 // Remove any call graph edges from the callee to its callees. 399 CalleeNode->removeAllCalledFunctions(); 400 401 resetCachedCostInfo(Callee); 402 403 // Removing the node for callee from the call graph and delete it. 404 delete CG.removeFunctionFromModule(CalleeNode); 405 ++NumDeleted; 406 } 407 408 // Remove any cached cost info for this caller, as inlining the 409 // callee has increased the size of the caller (which may be the 410 // same as the callee). 411 resetCachedCostInfo(Caller); 412 413 // Remove this call site from the list. If possible, use 414 // swap/pop_back for efficiency, but do not use it if doing so would 415 // move a call site to a function in this SCC before the 416 // 'FirstCallInSCC' barrier. 417 if (SCC.size() == 1) { 418 std::swap(CallSites[CSi], CallSites.back()); 419 CallSites.pop_back(); 420 } else { 421 CallSites.erase(CallSites.begin()+CSi); 422 } 423 --CSi; 424 425 Changed = true; 426 LocalChange = true; 427 } 428 } while (LocalChange); 429 430 return Changed; 431} 432 433// doFinalization - Remove now-dead linkonce functions at the end of 434// processing to avoid breaking the SCC traversal. 435bool Inliner::doFinalization(CallGraph &CG) { 436 return removeDeadFunctions(CG); 437} 438 439/// removeDeadFunctions - Remove dead functions that are not included in 440/// DNR (Do Not Remove) list. 441bool Inliner::removeDeadFunctions(CallGraph &CG, 442 SmallPtrSet<const Function *, 16> *DNR) { 443 SmallPtrSet<CallGraphNode*, 16> FunctionsToRemove; 444 445 // Scan for all of the functions, looking for ones that should now be removed 446 // from the program. Insert the dead ones in the FunctionsToRemove set. 447 for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) { 448 CallGraphNode *CGN = I->second; 449 if (CGN->getFunction() == 0) 450 continue; 451 452 Function *F = CGN->getFunction(); 453 454 // If the only remaining users of the function are dead constants, remove 455 // them. 456 F->removeDeadConstantUsers(); 457 458 if (DNR && DNR->count(F)) 459 continue; 460 if (!F->hasLinkOnceLinkage() && !F->hasLocalLinkage() && 461 !F->hasAvailableExternallyLinkage()) 462 continue; 463 if (!F->use_empty()) 464 continue; 465 466 // Remove any call graph edges from the function to its callees. 467 CGN->removeAllCalledFunctions(); 468 469 // Remove any edges from the external node to the function's call graph 470 // node. These edges might have been made irrelegant due to 471 // optimization of the program. 472 CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN); 473 474 // Removing the node for callee from the call graph and delete it. 475 FunctionsToRemove.insert(CGN); 476 } 477 478 // Now that we know which functions to delete, do so. We didn't want to do 479 // this inline, because that would invalidate our CallGraph::iterator 480 // objects. :( 481 // 482 // Note that it doesn't matter that we are iterating over a non-stable set 483 // here to do this, it doesn't matter which order the functions are deleted 484 // in. 485 bool Changed = false; 486 for (SmallPtrSet<CallGraphNode*, 16>::iterator I = FunctionsToRemove.begin(), 487 E = FunctionsToRemove.end(); I != E; ++I) { 488 resetCachedCostInfo((*I)->getFunction()); 489 delete CG.removeFunctionFromModule(*I); 490 ++NumDeleted; 491 Changed = true; 492 } 493 494 return Changed; 495} 496