Inliner.cpp revision f9c3b228e5579e0d2a9cd05a2191fe17b4c58b23
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 44Inliner::Inliner(void *ID) 45 : CallGraphSCCPass(ID), InlineThreshold(InlineLimit) {} 46 47Inliner::Inliner(void *ID, int Threshold) 48 : CallGraphSCCPass(ID), InlineThreshold(Threshold) {} 49 50/// getAnalysisUsage - For this class, we declare that we require and preserve 51/// the call graph. If the derived class implements this method, it should 52/// always explicitly call the implementation here. 53void Inliner::getAnalysisUsage(AnalysisUsage &Info) const { 54 CallGraphSCCPass::getAnalysisUsage(Info); 55} 56 57 58typedef DenseMap<const ArrayType*, std::vector<AllocaInst*> > 59InlinedArrayAllocasTy; 60 61/// InlineCallIfPossible - If it is possible to inline the specified call site, 62/// do so and update the CallGraph for this operation. 63/// 64/// This function also does some basic book-keeping to update the IR. The 65/// InlinedArrayAllocas map keeps track of any allocas that are already 66/// available from other functions inlined into the caller. If we are able to 67/// inline this call site we attempt to reuse already available allocas or add 68/// any new allocas to the set if not possible. 69static bool InlineCallIfPossible(CallSite CS, CallGraph &CG, 70 const TargetData *TD, 71 InlinedArrayAllocasTy &InlinedArrayAllocas) { 72 Function *Callee = CS.getCalledFunction(); 73 Function *Caller = CS.getCaller(); 74 75 // Try to inline the function. Get the list of static allocas that were 76 // inlined. 77 SmallVector<AllocaInst*, 16> StaticAllocas; 78 if (!InlineFunction(CS, &CG, TD, &StaticAllocas)) 79 return false; 80 81 // If the inlined function had a higher stack protection level than the 82 // calling function, then bump up the caller's stack protection level. 83 if (Callee->hasFnAttr(Attribute::StackProtectReq)) 84 Caller->addFnAttr(Attribute::StackProtectReq); 85 else if (Callee->hasFnAttr(Attribute::StackProtect) && 86 !Caller->hasFnAttr(Attribute::StackProtectReq)) 87 Caller->addFnAttr(Attribute::StackProtect); 88 89 90 // Look at all of the allocas that we inlined through this call site. If we 91 // have already inlined other allocas through other calls into this function, 92 // then we know that they have disjoint lifetimes and that we can merge them. 93 // 94 // There are many heuristics possible for merging these allocas, and the 95 // different options have different tradeoffs. One thing that we *really* 96 // don't want to hurt is SRoA: once inlining happens, often allocas are no 97 // longer address taken and so they can be promoted. 98 // 99 // Our "solution" for that is to only merge allocas whose outermost type is an 100 // array type. These are usually not promoted because someone is using a 101 // variable index into them. These are also often the most important ones to 102 // merge. 103 // 104 // A better solution would be to have real memory lifetime markers in the IR 105 // and not have the inliner do any merging of allocas at all. This would 106 // allow the backend to do proper stack slot coloring of all allocas that 107 // *actually make it to the backend*, which is really what we want. 108 // 109 // Because we don't have this information, we do this simple and useful hack. 110 // 111 SmallPtrSet<AllocaInst*, 16> UsedAllocas; 112 113 // Loop over all the allocas we have so far and see if they can be merged with 114 // a previously inlined alloca. If not, remember that we had it. 115 for (unsigned AllocaNo = 0, e = StaticAllocas.size(); 116 AllocaNo != e; ++AllocaNo) { 117 AllocaInst *AI = StaticAllocas[AllocaNo]; 118 119 // Don't bother trying to merge array allocations (they will usually be 120 // canonicalized to be an allocation *of* an array), or allocations whose 121 // type is not itself an array (because we're afraid of pessimizing SRoA). 122 const ArrayType *ATy = dyn_cast<ArrayType>(AI->getAllocatedType()); 123 if (ATy == 0 || AI->isArrayAllocation()) 124 continue; 125 126 // Get the list of all available allocas for this array type. 127 std::vector<AllocaInst*> &AllocasForType = InlinedArrayAllocas[ATy]; 128 129 // Loop over the allocas in AllocasForType to see if we can reuse one. Note 130 // that we have to be careful not to reuse the same "available" alloca for 131 // multiple different allocas that we just inlined, we use the 'UsedAllocas' 132 // set to keep track of which "available" allocas are being used by this 133 // function. Also, AllocasForType can be empty of course! 134 bool MergedAwayAlloca = false; 135 for (unsigned i = 0, e = AllocasForType.size(); i != e; ++i) { 136 AllocaInst *AvailableAlloca = AllocasForType[i]; 137 138 // The available alloca has to be in the right function, not in some other 139 // function in this SCC. 140 if (AvailableAlloca->getParent() != AI->getParent()) 141 continue; 142 143 // If the inlined function already uses this alloca then we can't reuse 144 // it. 145 if (!UsedAllocas.insert(AvailableAlloca)) 146 continue; 147 148 // Otherwise, we *can* reuse it, RAUW AI into AvailableAlloca and declare 149 // success! 150 DEBUG(dbgs() << " ***MERGED ALLOCA: " << *AI); 151 152 AI->replaceAllUsesWith(AvailableAlloca); 153 AI->eraseFromParent(); 154 MergedAwayAlloca = true; 155 ++NumMergedAllocas; 156 break; 157 } 158 159 // If we already nuked the alloca, we're done with it. 160 if (MergedAwayAlloca) 161 continue; 162 163 // If we were unable to merge away the alloca either because there are no 164 // allocas of the right type available or because we reused them all 165 // already, remember that this alloca came from an inlined function and mark 166 // it used so we don't reuse it for other allocas from this inline 167 // operation. 168 AllocasForType.push_back(AI); 169 UsedAllocas.insert(AI); 170 } 171 172 return true; 173} 174 175unsigned Inliner::getInlineThreshold(Function* Caller) const { 176 if (Caller && !Caller->isDeclaration() && 177 Caller->hasFnAttr(Attribute::OptimizeForSize) && 178 InlineLimit.getNumOccurrences() == 0) 179 return 75; 180 else 181 return InlineThreshold; 182} 183 184/// shouldInline - Return true if the inliner should attempt to inline 185/// at the given CallSite. 186bool Inliner::shouldInline(CallSite CS) { 187 InlineCost IC = getInlineCost(CS); 188 189 if (IC.isAlways()) { 190 DEBUG(dbgs() << " Inlining: cost=always" 191 << ", Call: " << *CS.getInstruction() << "\n"); 192 return true; 193 } 194 195 if (IC.isNever()) { 196 DEBUG(dbgs() << " NOT Inlining: cost=never" 197 << ", Call: " << *CS.getInstruction() << "\n"); 198 return false; 199 } 200 201 int Cost = IC.getValue(); 202 Function *Caller = CS.getCaller(); 203 int CurrentThreshold = getInlineThreshold(Caller); 204 float FudgeFactor = getInlineFudgeFactor(CS); 205 if (Cost >= (int)(CurrentThreshold * FudgeFactor)) { 206 DEBUG(dbgs() << " NOT Inlining: cost=" << Cost 207 << ", Call: " << *CS.getInstruction() << "\n"); 208 return false; 209 } 210 211 // Try to detect the case where the current inlining candidate caller 212 // (call it B) is a static function and is an inlining candidate elsewhere, 213 // and the current candidate callee (call it C) is large enough that 214 // inlining it into B would make B too big to inline later. In these 215 // circumstances it may be best not to inline C into B, but to inline B 216 // into its callers. 217 if (Caller->hasLocalLinkage()) { 218 int TotalSecondaryCost = 0; 219 bool outerCallsFound = false; 220 bool allOuterCallsWillBeInlined = true; 221 bool someOuterCallWouldNotBeInlined = false; 222 for (Value::use_iterator I = Caller->use_begin(), E =Caller->use_end(); 223 I != E; ++I) { 224 CallSite CS2 = CallSite::get(*I); 225 226 // If this isn't a call to Caller (it could be some other sort 227 // of reference) skip it. 228 if (CS2.getInstruction() == 0 || CS2.getCalledFunction() != Caller) 229 continue; 230 231 InlineCost IC2 = getInlineCost(CS2); 232 if (IC2.isNever()) 233 allOuterCallsWillBeInlined = false; 234 if (IC2.isAlways() || IC2.isNever()) 235 continue; 236 237 outerCallsFound = true; 238 int Cost2 = IC2.getValue(); 239 Function *Caller2 = CS2.getCaller(); 240 int CurrentThreshold2 = getInlineThreshold(Caller2); 241 float FudgeFactor2 = getInlineFudgeFactor(CS2); 242 243 if (Cost2 >= (int)(CurrentThreshold2 * FudgeFactor2)) 244 allOuterCallsWillBeInlined = false; 245 246 // See if we have this case. We subtract off the penalty 247 // for the call instruction, which we would be deleting. 248 if (Cost2 < (int)(CurrentThreshold2 * FudgeFactor2) && 249 Cost2 + Cost - (InlineConstants::CallPenalty + 1) >= 250 (int)(CurrentThreshold2 * FudgeFactor2)) { 251 someOuterCallWouldNotBeInlined = true; 252 TotalSecondaryCost += Cost2; 253 } 254 } 255 // If all outer calls to Caller would get inlined, the cost for the last 256 // one is set very low by getInlineCost, in anticipation that Caller will 257 // be removed entirely. We did not account for this above unless there 258 // is only one caller of Caller. 259 if (allOuterCallsWillBeInlined && Caller->use_begin() != Caller->use_end()) 260 TotalSecondaryCost += InlineConstants::LastCallToStaticBonus; 261 262 if (outerCallsFound && someOuterCallWouldNotBeInlined && 263 TotalSecondaryCost < Cost) { 264 DEBUG(dbgs() << " NOT Inlining: " << *CS.getInstruction() << 265 " Cost = " << Cost << 266 ", outer Cost = " << TotalSecondaryCost << '\n'); 267 return false; 268 } 269 } 270 271 DEBUG(dbgs() << " Inlining: cost=" << Cost 272 << ", Call: " << *CS.getInstruction() << '\n'); 273 return true; 274} 275 276bool Inliner::runOnSCC(std::vector<CallGraphNode*> &SCC) { 277 CallGraph &CG = getAnalysis<CallGraph>(); 278 const TargetData *TD = getAnalysisIfAvailable<TargetData>(); 279 280 SmallPtrSet<Function*, 8> SCCFunctions; 281 DEBUG(dbgs() << "Inliner visiting SCC:"); 282 for (unsigned i = 0, e = SCC.size(); i != e; ++i) { 283 Function *F = SCC[i]->getFunction(); 284 if (F) SCCFunctions.insert(F); 285 DEBUG(dbgs() << " " << (F ? F->getName() : "INDIRECTNODE")); 286 } 287 288 // Scan through and identify all call sites ahead of time so that we only 289 // inline call sites in the original functions, not call sites that result 290 // from inlining other functions. 291 SmallVector<CallSite, 16> CallSites; 292 293 for (unsigned i = 0, e = SCC.size(); i != e; ++i) { 294 Function *F = SCC[i]->getFunction(); 295 if (!F) continue; 296 297 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) 298 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 299 CallSite CS = CallSite::get(I); 300 // If this isn't a call, or it is a call to an intrinsic, it can 301 // never be inlined. 302 if (CS.getInstruction() == 0 || isa<IntrinsicInst>(I)) 303 continue; 304 305 // If this is a direct call to an external function, we can never inline 306 // it. If it is an indirect call, inlining may resolve it to be a 307 // direct call, so we keep it. 308 if (CS.getCalledFunction() && CS.getCalledFunction()->isDeclaration()) 309 continue; 310 311 CallSites.push_back(CS); 312 } 313 } 314 315 DEBUG(dbgs() << ": " << CallSites.size() << " call sites.\n"); 316 317 // Now that we have all of the call sites, move the ones to functions in the 318 // current SCC to the end of the list. 319 unsigned FirstCallInSCC = CallSites.size(); 320 for (unsigned i = 0; i < FirstCallInSCC; ++i) 321 if (Function *F = CallSites[i].getCalledFunction()) 322 if (SCCFunctions.count(F)) 323 std::swap(CallSites[i--], CallSites[--FirstCallInSCC]); 324 325 326 InlinedArrayAllocasTy InlinedArrayAllocas; 327 328 // Now that we have all of the call sites, loop over them and inline them if 329 // it looks profitable to do so. 330 bool Changed = false; 331 bool LocalChange; 332 do { 333 LocalChange = false; 334 // Iterate over the outer loop because inlining functions can cause indirect 335 // calls to become direct calls. 336 for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) { 337 CallSite CS = CallSites[CSi]; 338 339 Function *Caller = CS.getCaller(); 340 Function *Callee = CS.getCalledFunction(); 341 342 // If this call site is dead and it is to a readonly function, we should 343 // just delete the call instead of trying to inline it, regardless of 344 // size. This happens because IPSCCP propagates the result out of the 345 // call and then we're left with the dead call. 346 if (isInstructionTriviallyDead(CS.getInstruction())) { 347 DEBUG(dbgs() << " -> Deleting dead call: " 348 << *CS.getInstruction() << "\n"); 349 // Update the call graph by deleting the edge from Callee to Caller. 350 CG[Caller]->removeCallEdgeFor(CS); 351 CS.getInstruction()->eraseFromParent(); 352 ++NumCallsDeleted; 353 } else { 354 // We can only inline direct calls to non-declarations. 355 if (Callee == 0 || Callee->isDeclaration()) continue; 356 357 // If the policy determines that we should inline this function, 358 // try to do so. 359 if (!shouldInline(CS)) 360 continue; 361 362 // Attempt to inline the function... 363 if (!InlineCallIfPossible(CS, CG, TD, InlinedArrayAllocas)) 364 continue; 365 ++NumInlined; 366 } 367 368 // If we inlined or deleted the last possible call site to the function, 369 // delete the function body now. 370 if (Callee && Callee->use_empty() && Callee->hasLocalLinkage() && 371 // TODO: Can remove if in SCC now. 372 !SCCFunctions.count(Callee) && 373 374 // The function may be apparently dead, but if there are indirect 375 // callgraph references to the node, we cannot delete it yet, this 376 // could invalidate the CGSCC iterator. 377 CG[Callee]->getNumReferences() == 0) { 378 DEBUG(dbgs() << " -> Deleting dead function: " 379 << Callee->getName() << "\n"); 380 CallGraphNode *CalleeNode = CG[Callee]; 381 382 // Remove any call graph edges from the callee to its callees. 383 CalleeNode->removeAllCalledFunctions(); 384 385 resetCachedCostInfo(Callee); 386 387 // Removing the node for callee from the call graph and delete it. 388 delete CG.removeFunctionFromModule(CalleeNode); 389 ++NumDeleted; 390 } 391 392 // Remove any cached cost info for this caller, as inlining the 393 // callee has increased the size of the caller (which may be the 394 // same as the callee). 395 resetCachedCostInfo(Caller); 396 397 // Remove this call site from the list. If possible, use 398 // swap/pop_back for efficiency, but do not use it if doing so would 399 // move a call site to a function in this SCC before the 400 // 'FirstCallInSCC' barrier. 401 if (SCC.size() == 1) { 402 std::swap(CallSites[CSi], CallSites.back()); 403 CallSites.pop_back(); 404 } else { 405 CallSites.erase(CallSites.begin()+CSi); 406 } 407 --CSi; 408 409 Changed = true; 410 LocalChange = true; 411 } 412 } while (LocalChange); 413 414 return Changed; 415} 416 417// doFinalization - Remove now-dead linkonce functions at the end of 418// processing to avoid breaking the SCC traversal. 419bool Inliner::doFinalization(CallGraph &CG) { 420 return removeDeadFunctions(CG); 421} 422 423/// removeDeadFunctions - Remove dead functions that are not included in 424/// DNR (Do Not Remove) list. 425bool Inliner::removeDeadFunctions(CallGraph &CG, 426 SmallPtrSet<const Function *, 16> *DNR) { 427 SmallPtrSet<CallGraphNode*, 16> FunctionsToRemove; 428 429 // Scan for all of the functions, looking for ones that should now be removed 430 // from the program. Insert the dead ones in the FunctionsToRemove set. 431 for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) { 432 CallGraphNode *CGN = I->second; 433 if (CGN->getFunction() == 0) 434 continue; 435 436 Function *F = CGN->getFunction(); 437 438 // If the only remaining users of the function are dead constants, remove 439 // them. 440 F->removeDeadConstantUsers(); 441 442 if (DNR && DNR->count(F)) 443 continue; 444 if (!F->hasLinkOnceLinkage() && !F->hasLocalLinkage() && 445 !F->hasAvailableExternallyLinkage()) 446 continue; 447 if (!F->use_empty()) 448 continue; 449 450 // Remove any call graph edges from the function to its callees. 451 CGN->removeAllCalledFunctions(); 452 453 // Remove any edges from the external node to the function's call graph 454 // node. These edges might have been made irrelegant due to 455 // optimization of the program. 456 CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN); 457 458 // Removing the node for callee from the call graph and delete it. 459 FunctionsToRemove.insert(CGN); 460 } 461 462 // Now that we know which functions to delete, do so. We didn't want to do 463 // this inline, because that would invalidate our CallGraph::iterator 464 // objects. :( 465 // 466 // Note that it doesn't matter that we are iterating over a non-stable set 467 // here to do this, it doesn't matter which order the functions are deleted 468 // in. 469 bool Changed = false; 470 for (SmallPtrSet<CallGraphNode*, 16>::iterator I = FunctionsToRemove.begin(), 471 E = FunctionsToRemove.end(); I != E; ++I) { 472 resetCachedCostInfo((*I)->getFunction()); 473 delete CG.removeFunctionFromModule(*I); 474 ++NumDeleted; 475 Changed = true; 476 } 477 478 return Changed; 479} 480