1 //===-- GlobalMerge.cpp - Internal globals merging -----------------------===// 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 // This pass merges globals with internal linkage into one. This way all the 10 // globals which were merged into a biggest one can be addressed using offsets 11 // from the same base pointer (no need for separate base pointer for each of the 12 // global). Such a transformation can significantly reduce the register pressure 13 // when many globals are involved. 14 // 15 // For example, consider the code which touches several global variables at 16 // once: 17 // 18 // static int foo[N], bar[N], baz[N]; 19 // 20 // for (i = 0; i < N; ++i) { 21 // foo[i] = bar[i] * baz[i]; 22 // } 23 // 24 // On ARM the addresses of 3 arrays should be kept in the registers, thus 25 // this code has quite large register pressure (loop body): 26 // 27 // ldr r1, [r5], #4 28 // ldr r2, [r6], #4 29 // mul r1, r2, r1 30 // str r1, [r0], #4 31 // 32 // Pass converts the code to something like: 33 // 34 // static struct { 35 // int foo[N]; 36 // int bar[N]; 37 // int baz[N]; 38 // } merged; 39 // 40 // for (i = 0; i < N; ++i) { 41 // merged.foo[i] = merged.bar[i] * merged.baz[i]; 42 // } 43 // 44 // and in ARM code this becomes: 45 // 46 // ldr r0, [r5, #40] 47 // ldr r1, [r5, #80] 48 // mul r0, r1, r0 49 // str r0, [r5], #4 50 // 51 // note that we saved 2 registers here almostly "for free". 52 // 53 // However, merging globals can have tradeoffs: 54 // - it confuses debuggers, tools, and users 55 // - it makes linker optimizations less useful (order files, LOHs, ...) 56 // - it forces usage of indexed addressing (which isn't necessarily "free") 57 // - it can increase register pressure when the uses are disparate enough. 58 // 59 // We use heuristics to discover the best global grouping we can (cf cl::opts). 60 // ===---------------------------------------------------------------------===// 61 62 #include "llvm/ADT/DenseMap.h" 63 #include "llvm/ADT/SmallBitVector.h" 64 #include "llvm/ADT/SmallPtrSet.h" 65 #include "llvm/ADT/Statistic.h" 66 #include "llvm/CodeGen/Passes.h" 67 #include "llvm/IR/Attributes.h" 68 #include "llvm/IR/Constants.h" 69 #include "llvm/IR/DataLayout.h" 70 #include "llvm/IR/DerivedTypes.h" 71 #include "llvm/IR/Function.h" 72 #include "llvm/IR/GlobalVariable.h" 73 #include "llvm/IR/Instructions.h" 74 #include "llvm/IR/Intrinsics.h" 75 #include "llvm/IR/Module.h" 76 #include "llvm/Pass.h" 77 #include "llvm/Support/CommandLine.h" 78 #include "llvm/Support/Debug.h" 79 #include "llvm/Support/raw_ostream.h" 80 #include "llvm/Target/TargetLowering.h" 81 #include "llvm/Target/TargetLoweringObjectFile.h" 82 #include "llvm/Target/TargetSubtargetInfo.h" 83 #include <algorithm> 84 using namespace llvm; 85 86 #define DEBUG_TYPE "global-merge" 87 88 // FIXME: This is only useful as a last-resort way to disable the pass. 89 cl::opt<bool> 90 EnableGlobalMerge("enable-global-merge", cl::Hidden, 91 cl::desc("Enable the global merge pass"), 92 cl::init(true)); 93 94 static cl::opt<unsigned> 95 GlobalMergeMaxOffset("global-merge-max-offset", cl::Hidden, 96 cl::desc("Set maximum offset for global merge pass"), 97 cl::init(0)); 98 99 static cl::opt<bool> GlobalMergeGroupByUse( 100 "global-merge-group-by-use", cl::Hidden, 101 cl::desc("Improve global merge pass to look at uses"), cl::init(true)); 102 103 static cl::opt<bool> GlobalMergeIgnoreSingleUse( 104 "global-merge-ignore-single-use", cl::Hidden, 105 cl::desc("Improve global merge pass to ignore globals only used alone"), 106 cl::init(true)); 107 108 static cl::opt<bool> 109 EnableGlobalMergeOnConst("global-merge-on-const", cl::Hidden, 110 cl::desc("Enable global merge pass on constants"), 111 cl::init(false)); 112 113 // FIXME: this could be a transitional option, and we probably need to remove 114 // it if only we are sure this optimization could always benefit all targets. 115 static cl::opt<cl::boolOrDefault> 116 EnableGlobalMergeOnExternal("global-merge-on-external", cl::Hidden, 117 cl::desc("Enable global merge pass on external linkage")); 118 119 STATISTIC(NumMerged, "Number of globals merged"); 120 namespace { 121 class GlobalMerge : public FunctionPass { 122 const TargetMachine *TM; 123 // FIXME: Infer the maximum possible offset depending on the actual users 124 // (these max offsets are different for the users inside Thumb or ARM 125 // functions), see the code that passes in the offset in the ARM backend 126 // for more information. 127 unsigned MaxOffset; 128 129 /// Whether we should try to optimize for size only. 130 /// Currently, this applies a dead simple heuristic: only consider globals 131 /// used in minsize functions for merging. 132 /// FIXME: This could learn about optsize, and be used in the cost model. 133 bool OnlyOptimizeForSize; 134 135 /// Whether we should merge global variables that have external linkage. 136 bool MergeExternalGlobals; 137 138 bool IsMachO; 139 140 bool doMerge(SmallVectorImpl<GlobalVariable*> &Globals, 141 Module &M, bool isConst, unsigned AddrSpace) const; 142 /// \brief Merge everything in \p Globals for which the corresponding bit 143 /// in \p GlobalSet is set. 144 bool doMerge(const SmallVectorImpl<GlobalVariable *> &Globals, 145 const BitVector &GlobalSet, Module &M, bool isConst, 146 unsigned AddrSpace) const; 147 148 /// \brief Check if the given variable has been identified as must keep 149 /// \pre setMustKeepGlobalVariables must have been called on the Module that 150 /// contains GV 151 bool isMustKeepGlobalVariable(const GlobalVariable *GV) const { 152 return MustKeepGlobalVariables.count(GV); 153 } 154 155 /// Collect every variables marked as "used" or used in a landing pad 156 /// instruction for this Module. 157 void setMustKeepGlobalVariables(Module &M); 158 159 /// Collect every variables marked as "used" 160 void collectUsedGlobalVariables(Module &M); 161 162 /// Keep track of the GlobalVariable that must not be merged away 163 SmallPtrSet<const GlobalVariable *, 16> MustKeepGlobalVariables; 164 165 public: 166 static char ID; // Pass identification, replacement for typeid. 167 explicit GlobalMerge() 168 : FunctionPass(ID), TM(nullptr), MaxOffset(GlobalMergeMaxOffset), 169 OnlyOptimizeForSize(false), MergeExternalGlobals(false) { 170 initializeGlobalMergePass(*PassRegistry::getPassRegistry()); 171 } 172 173 explicit GlobalMerge(const TargetMachine *TM, unsigned MaximalOffset, 174 bool OnlyOptimizeForSize, bool MergeExternalGlobals) 175 : FunctionPass(ID), TM(TM), MaxOffset(MaximalOffset), 176 OnlyOptimizeForSize(OnlyOptimizeForSize), 177 MergeExternalGlobals(MergeExternalGlobals) { 178 initializeGlobalMergePass(*PassRegistry::getPassRegistry()); 179 } 180 181 bool doInitialization(Module &M) override; 182 bool runOnFunction(Function &F) override; 183 bool doFinalization(Module &M) override; 184 185 const char *getPassName() const override { 186 return "Merge internal globals"; 187 } 188 189 void getAnalysisUsage(AnalysisUsage &AU) const override { 190 AU.setPreservesCFG(); 191 FunctionPass::getAnalysisUsage(AU); 192 } 193 }; 194 } // end anonymous namespace 195 196 char GlobalMerge::ID = 0; 197 INITIALIZE_PASS_BEGIN(GlobalMerge, "global-merge", "Merge global variables", 198 false, false) 199 INITIALIZE_PASS_END(GlobalMerge, "global-merge", "Merge global variables", 200 false, false) 201 202 bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable*> &Globals, 203 Module &M, bool isConst, unsigned AddrSpace) const { 204 auto &DL = M.getDataLayout(); 205 // FIXME: Find better heuristics 206 std::stable_sort(Globals.begin(), Globals.end(), 207 [&DL](const GlobalVariable *GV1, const GlobalVariable *GV2) { 208 return DL.getTypeAllocSize(GV1->getValueType()) < 209 DL.getTypeAllocSize(GV2->getValueType()); 210 }); 211 212 // If we want to just blindly group all globals together, do so. 213 if (!GlobalMergeGroupByUse) { 214 BitVector AllGlobals(Globals.size()); 215 AllGlobals.set(); 216 return doMerge(Globals, AllGlobals, M, isConst, AddrSpace); 217 } 218 219 // If we want to be smarter, look at all uses of each global, to try to 220 // discover all sets of globals used together, and how many times each of 221 // these sets occurred. 222 // 223 // Keep this reasonably efficient, by having an append-only list of all sets 224 // discovered so far (UsedGlobalSet), and mapping each "together-ness" unit of 225 // code (currently, a Function) to the set of globals seen so far that are 226 // used together in that unit (GlobalUsesByFunction). 227 // 228 // When we look at the Nth global, we now that any new set is either: 229 // - the singleton set {N}, containing this global only, or 230 // - the union of {N} and a previously-discovered set, containing some 231 // combination of the previous N-1 globals. 232 // Using that knowledge, when looking at the Nth global, we can keep: 233 // - a reference to the singleton set {N} (CurGVOnlySetIdx) 234 // - a list mapping each previous set to its union with {N} (EncounteredUGS), 235 // if it actually occurs. 236 237 // We keep track of the sets of globals used together "close enough". 238 struct UsedGlobalSet { 239 UsedGlobalSet(size_t Size) : Globals(Size), UsageCount(1) {} 240 BitVector Globals; 241 unsigned UsageCount; 242 }; 243 244 // Each set is unique in UsedGlobalSets. 245 std::vector<UsedGlobalSet> UsedGlobalSets; 246 247 // Avoid repeating the create-global-set pattern. 248 auto CreateGlobalSet = [&]() -> UsedGlobalSet & { 249 UsedGlobalSets.emplace_back(Globals.size()); 250 return UsedGlobalSets.back(); 251 }; 252 253 // The first set is the empty set. 254 CreateGlobalSet().UsageCount = 0; 255 256 // We define "close enough" to be "in the same function". 257 // FIXME: Grouping uses by function is way too aggressive, so we should have 258 // a better metric for distance between uses. 259 // The obvious alternative would be to group by BasicBlock, but that's in 260 // turn too conservative.. 261 // Anything in between wouldn't be trivial to compute, so just stick with 262 // per-function grouping. 263 264 // The value type is an index into UsedGlobalSets. 265 // The default (0) conveniently points to the empty set. 266 DenseMap<Function *, size_t /*UsedGlobalSetIdx*/> GlobalUsesByFunction; 267 268 // Now, look at each merge-eligible global in turn. 269 270 // Keep track of the sets we already encountered to which we added the 271 // current global. 272 // Each element matches the same-index element in UsedGlobalSets. 273 // This lets us efficiently tell whether a set has already been expanded to 274 // include the current global. 275 std::vector<size_t> EncounteredUGS; 276 277 for (size_t GI = 0, GE = Globals.size(); GI != GE; ++GI) { 278 GlobalVariable *GV = Globals[GI]; 279 280 // Reset the encountered sets for this global... 281 std::fill(EncounteredUGS.begin(), EncounteredUGS.end(), 0); 282 // ...and grow it in case we created new sets for the previous global. 283 EncounteredUGS.resize(UsedGlobalSets.size()); 284 285 // We might need to create a set that only consists of the current global. 286 // Keep track of its index into UsedGlobalSets. 287 size_t CurGVOnlySetIdx = 0; 288 289 // For each global, look at all its Uses. 290 for (auto &U : GV->uses()) { 291 // This Use might be a ConstantExpr. We're interested in Instruction 292 // users, so look through ConstantExpr... 293 Use *UI, *UE; 294 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U.getUser())) { 295 if (CE->use_empty()) 296 continue; 297 UI = &*CE->use_begin(); 298 UE = nullptr; 299 } else if (isa<Instruction>(U.getUser())) { 300 UI = &U; 301 UE = UI->getNext(); 302 } else { 303 continue; 304 } 305 306 // ...to iterate on all the instruction users of the global. 307 // Note that we iterate on Uses and not on Users to be able to getNext(). 308 for (; UI != UE; UI = UI->getNext()) { 309 Instruction *I = dyn_cast<Instruction>(UI->getUser()); 310 if (!I) 311 continue; 312 313 Function *ParentFn = I->getParent()->getParent(); 314 315 // If we're only optimizing for size, ignore non-minsize functions. 316 if (OnlyOptimizeForSize && !ParentFn->optForMinSize()) 317 continue; 318 319 size_t UGSIdx = GlobalUsesByFunction[ParentFn]; 320 321 // If this is the first global the basic block uses, map it to the set 322 // consisting of this global only. 323 if (!UGSIdx) { 324 // If that set doesn't exist yet, create it. 325 if (!CurGVOnlySetIdx) { 326 CurGVOnlySetIdx = UsedGlobalSets.size(); 327 CreateGlobalSet().Globals.set(GI); 328 } else { 329 ++UsedGlobalSets[CurGVOnlySetIdx].UsageCount; 330 } 331 332 GlobalUsesByFunction[ParentFn] = CurGVOnlySetIdx; 333 continue; 334 } 335 336 // If we already encountered this BB, just increment the counter. 337 if (UsedGlobalSets[UGSIdx].Globals.test(GI)) { 338 ++UsedGlobalSets[UGSIdx].UsageCount; 339 continue; 340 } 341 342 // If not, the previous set wasn't actually used in this function. 343 --UsedGlobalSets[UGSIdx].UsageCount; 344 345 // If we already expanded the previous set to include this global, just 346 // reuse that expanded set. 347 if (size_t ExpandedIdx = EncounteredUGS[UGSIdx]) { 348 ++UsedGlobalSets[ExpandedIdx].UsageCount; 349 GlobalUsesByFunction[ParentFn] = ExpandedIdx; 350 continue; 351 } 352 353 // If not, create a new set consisting of the union of the previous set 354 // and this global. Mark it as encountered, so we can reuse it later. 355 GlobalUsesByFunction[ParentFn] = EncounteredUGS[UGSIdx] = 356 UsedGlobalSets.size(); 357 358 UsedGlobalSet &NewUGS = CreateGlobalSet(); 359 NewUGS.Globals.set(GI); 360 NewUGS.Globals |= UsedGlobalSets[UGSIdx].Globals; 361 } 362 } 363 } 364 365 // Now we found a bunch of sets of globals used together. We accumulated 366 // the number of times we encountered the sets (i.e., the number of blocks 367 // that use that exact set of globals). 368 // 369 // Multiply that by the size of the set to give us a crude profitability 370 // metric. 371 std::sort(UsedGlobalSets.begin(), UsedGlobalSets.end(), 372 [](const UsedGlobalSet &UGS1, const UsedGlobalSet &UGS2) { 373 return UGS1.Globals.count() * UGS1.UsageCount < 374 UGS2.Globals.count() * UGS2.UsageCount; 375 }); 376 377 // We can choose to merge all globals together, but ignore globals never used 378 // with another global. This catches the obviously non-profitable cases of 379 // having a single global, but is aggressive enough for any other case. 380 if (GlobalMergeIgnoreSingleUse) { 381 BitVector AllGlobals(Globals.size()); 382 for (size_t i = 0, e = UsedGlobalSets.size(); i != e; ++i) { 383 const UsedGlobalSet &UGS = UsedGlobalSets[e - i - 1]; 384 if (UGS.UsageCount == 0) 385 continue; 386 if (UGS.Globals.count() > 1) 387 AllGlobals |= UGS.Globals; 388 } 389 return doMerge(Globals, AllGlobals, M, isConst, AddrSpace); 390 } 391 392 // Starting from the sets with the best (=biggest) profitability, find a 393 // good combination. 394 // The ideal (and expensive) solution can only be found by trying all 395 // combinations, looking for the one with the best profitability. 396 // Don't be smart about it, and just pick the first compatible combination, 397 // starting with the sets with the best profitability. 398 BitVector PickedGlobals(Globals.size()); 399 bool Changed = false; 400 401 for (size_t i = 0, e = UsedGlobalSets.size(); i != e; ++i) { 402 const UsedGlobalSet &UGS = UsedGlobalSets[e - i - 1]; 403 if (UGS.UsageCount == 0) 404 continue; 405 if (PickedGlobals.anyCommon(UGS.Globals)) 406 continue; 407 PickedGlobals |= UGS.Globals; 408 // If the set only contains one global, there's no point in merging. 409 // Ignore the global for inclusion in other sets though, so keep it in 410 // PickedGlobals. 411 if (UGS.Globals.count() < 2) 412 continue; 413 Changed |= doMerge(Globals, UGS.Globals, M, isConst, AddrSpace); 414 } 415 416 return Changed; 417 } 418 419 bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals, 420 const BitVector &GlobalSet, Module &M, bool isConst, 421 unsigned AddrSpace) const { 422 assert(Globals.size() > 1); 423 424 Type *Int32Ty = Type::getInt32Ty(M.getContext()); 425 auto &DL = M.getDataLayout(); 426 427 DEBUG(dbgs() << " Trying to merge set, starts with #" 428 << GlobalSet.find_first() << "\n"); 429 430 ssize_t i = GlobalSet.find_first(); 431 while (i != -1) { 432 ssize_t j = 0; 433 uint64_t MergedSize = 0; 434 std::vector<Type*> Tys; 435 std::vector<Constant*> Inits; 436 437 for (j = i; j != -1; j = GlobalSet.find_next(j)) { 438 Type *Ty = Globals[j]->getValueType(); 439 MergedSize += DL.getTypeAllocSize(Ty); 440 if (MergedSize > MaxOffset) { 441 break; 442 } 443 Tys.push_back(Ty); 444 Inits.push_back(Globals[j]->getInitializer()); 445 } 446 447 StructType *MergedTy = StructType::get(M.getContext(), Tys); 448 Constant *MergedInit = ConstantStruct::get(MergedTy, Inits); 449 450 GlobalVariable *MergedGV = new GlobalVariable( 451 M, MergedTy, isConst, GlobalValue::PrivateLinkage, MergedInit, 452 "_MergedGlobals", nullptr, GlobalVariable::NotThreadLocal, AddrSpace); 453 454 for (ssize_t k = i, idx = 0; k != j; k = GlobalSet.find_next(k), ++idx) { 455 GlobalValue::LinkageTypes Linkage = Globals[k]->getLinkage(); 456 std::string Name = Globals[k]->getName(); 457 458 Constant *Idx[2] = { 459 ConstantInt::get(Int32Ty, 0), 460 ConstantInt::get(Int32Ty, idx), 461 }; 462 Constant *GEP = 463 ConstantExpr::getInBoundsGetElementPtr(MergedTy, MergedGV, Idx); 464 Globals[k]->replaceAllUsesWith(GEP); 465 Globals[k]->eraseFromParent(); 466 467 // When the linkage is not internal we must emit an alias for the original 468 // variable name as it may be accessed from another object. On non-Mach-O 469 // we can also emit an alias for internal linkage as it's safe to do so. 470 // It's not safe on Mach-O as the alias (and thus the portion of the 471 // MergedGlobals variable) may be dead stripped at link time. 472 if (Linkage != GlobalValue::InternalLinkage || !IsMachO) { 473 GlobalAlias::create(Tys[idx], AddrSpace, Linkage, Name, GEP, &M); 474 } 475 476 NumMerged++; 477 } 478 i = j; 479 } 480 481 return true; 482 } 483 484 void GlobalMerge::collectUsedGlobalVariables(Module &M) { 485 // Extract global variables from llvm.used array 486 const GlobalVariable *GV = M.getGlobalVariable("llvm.used"); 487 if (!GV || !GV->hasInitializer()) return; 488 489 // Should be an array of 'i8*'. 490 const ConstantArray *InitList = cast<ConstantArray>(GV->getInitializer()); 491 492 for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i) 493 if (const GlobalVariable *G = 494 dyn_cast<GlobalVariable>(InitList->getOperand(i)->stripPointerCasts())) 495 MustKeepGlobalVariables.insert(G); 496 } 497 498 void GlobalMerge::setMustKeepGlobalVariables(Module &M) { 499 collectUsedGlobalVariables(M); 500 501 for (Module::iterator IFn = M.begin(), IEndFn = M.end(); IFn != IEndFn; 502 ++IFn) { 503 for (Function::iterator IBB = IFn->begin(), IEndBB = IFn->end(); 504 IBB != IEndBB; ++IBB) { 505 // Follow the invoke link to find the landing pad instruction 506 const InvokeInst *II = dyn_cast<InvokeInst>(IBB->getTerminator()); 507 if (!II) continue; 508 509 const LandingPadInst *LPInst = II->getUnwindDest()->getLandingPadInst(); 510 // Look for globals in the clauses of the landing pad instruction 511 for (unsigned Idx = 0, NumClauses = LPInst->getNumClauses(); 512 Idx != NumClauses; ++Idx) 513 if (const GlobalVariable *GV = 514 dyn_cast<GlobalVariable>(LPInst->getClause(Idx) 515 ->stripPointerCasts())) 516 MustKeepGlobalVariables.insert(GV); 517 } 518 } 519 } 520 521 bool GlobalMerge::doInitialization(Module &M) { 522 if (!EnableGlobalMerge) 523 return false; 524 525 IsMachO = Triple(M.getTargetTriple()).isOSBinFormatMachO(); 526 527 auto &DL = M.getDataLayout(); 528 DenseMap<unsigned, SmallVector<GlobalVariable*, 16> > Globals, ConstGlobals, 529 BSSGlobals; 530 bool Changed = false; 531 setMustKeepGlobalVariables(M); 532 533 // Grab all non-const globals. 534 for (auto &GV : M.globals()) { 535 // Merge is safe for "normal" internal or external globals only 536 if (GV.isDeclaration() || GV.isThreadLocal() || GV.hasSection()) 537 continue; 538 539 if (!(MergeExternalGlobals && GV.hasExternalLinkage()) && 540 !GV.hasInternalLinkage()) 541 continue; 542 543 PointerType *PT = dyn_cast<PointerType>(GV.getType()); 544 assert(PT && "Global variable is not a pointer!"); 545 546 unsigned AddressSpace = PT->getAddressSpace(); 547 548 // Ignore fancy-aligned globals for now. 549 unsigned Alignment = DL.getPreferredAlignment(&GV); 550 Type *Ty = GV.getValueType(); 551 if (Alignment > DL.getABITypeAlignment(Ty)) 552 continue; 553 554 // Ignore all 'special' globals. 555 if (GV.getName().startswith("llvm.") || 556 GV.getName().startswith(".llvm.")) 557 continue; 558 559 // Ignore all "required" globals: 560 if (isMustKeepGlobalVariable(&GV)) 561 continue; 562 563 if (DL.getTypeAllocSize(Ty) < MaxOffset) { 564 if (TM && 565 TargetLoweringObjectFile::getKindForGlobal(&GV, *TM).isBSSLocal()) 566 BSSGlobals[AddressSpace].push_back(&GV); 567 else if (GV.isConstant()) 568 ConstGlobals[AddressSpace].push_back(&GV); 569 else 570 Globals[AddressSpace].push_back(&GV); 571 } 572 } 573 574 for (auto &P : Globals) 575 if (P.second.size() > 1) 576 Changed |= doMerge(P.second, M, false, P.first); 577 578 for (auto &P : BSSGlobals) 579 if (P.second.size() > 1) 580 Changed |= doMerge(P.second, M, false, P.first); 581 582 if (EnableGlobalMergeOnConst) 583 for (auto &P : ConstGlobals) 584 if (P.second.size() > 1) 585 Changed |= doMerge(P.second, M, true, P.first); 586 587 return Changed; 588 } 589 590 bool GlobalMerge::runOnFunction(Function &F) { 591 return false; 592 } 593 594 bool GlobalMerge::doFinalization(Module &M) { 595 MustKeepGlobalVariables.clear(); 596 return false; 597 } 598 599 Pass *llvm::createGlobalMergePass(const TargetMachine *TM, unsigned Offset, 600 bool OnlyOptimizeForSize, 601 bool MergeExternalByDefault) { 602 bool MergeExternal = (EnableGlobalMergeOnExternal == cl::BOU_UNSET) ? 603 MergeExternalByDefault : (EnableGlobalMergeOnExternal == cl::BOU_TRUE); 604 return new GlobalMerge(TM, Offset, OnlyOptimizeForSize, MergeExternal); 605 } 606