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/Transforms/Scalar.h"
63 #include "llvm/ADT/DenseMap.h"
64 #include "llvm/ADT/SmallBitVector.h"
65 #include "llvm/ADT/SmallPtrSet.h"
66 #include "llvm/ADT/Statistic.h"
67 #include "llvm/CodeGen/Passes.h"
68 #include "llvm/IR/Attributes.h"
69 #include "llvm/IR/Constants.h"
70 #include "llvm/IR/DataLayout.h"
71 #include "llvm/IR/DerivedTypes.h"
72 #include "llvm/IR/Function.h"
73 #include "llvm/IR/GlobalVariable.h"
74 #include "llvm/IR/Instructions.h"
75 #include "llvm/IR/Intrinsics.h"
76 #include "llvm/IR/Module.h"
77 #include "llvm/Pass.h"
78 #include "llvm/Support/CommandLine.h"
79 #include "llvm/Support/Debug.h"
80 #include "llvm/Support/raw_ostream.h"
81 #include "llvm/Target/TargetLowering.h"
82 #include "llvm/Target/TargetLoweringObjectFile.h"
83 #include "llvm/Target/TargetSubtargetInfo.h"
84 #include <algorithm>
85 using namespace llvm;
86
87 #define DEBUG_TYPE "global-merge"
88
89 // FIXME: This is only useful as a last-resort way to disable the pass.
90 cl::opt<bool>
91 EnableGlobalMerge("enable-global-merge", cl::Hidden,
92 cl::desc("Enable the global merge pass"),
93 cl::init(true));
94
95 static cl::opt<bool> GlobalMergeGroupByUse(
96 "global-merge-group-by-use", cl::Hidden,
97 cl::desc("Improve global merge pass to look at uses"), cl::init(true));
98
99 static cl::opt<bool> GlobalMergeIgnoreSingleUse(
100 "global-merge-ignore-single-use", cl::Hidden,
101 cl::desc("Improve global merge pass to ignore globals only used alone"),
102 cl::init(true));
103
104 static cl::opt<bool>
105 EnableGlobalMergeOnConst("global-merge-on-const", cl::Hidden,
106 cl::desc("Enable global merge pass on constants"),
107 cl::init(false));
108
109 // FIXME: this could be a transitional option, and we probably need to remove
110 // it if only we are sure this optimization could always benefit all targets.
111 static cl::opt<cl::boolOrDefault>
112 EnableGlobalMergeOnExternal("global-merge-on-external", cl::Hidden,
113 cl::desc("Enable global merge pass on external linkage"));
114
115 STATISTIC(NumMerged, "Number of globals merged");
116 namespace {
117 class GlobalMerge : public FunctionPass {
118 const TargetMachine *TM;
119 // FIXME: Infer the maximum possible offset depending on the actual users
120 // (these max offsets are different for the users inside Thumb or ARM
121 // functions), see the code that passes in the offset in the ARM backend
122 // for more information.
123 unsigned MaxOffset;
124
125 /// Whether we should try to optimize for size only.
126 /// Currently, this applies a dead simple heuristic: only consider globals
127 /// used in minsize functions for merging.
128 /// FIXME: This could learn about optsize, and be used in the cost model.
129 bool OnlyOptimizeForSize;
130
131 /// Whether we should merge global variables that have external linkage.
132 bool MergeExternalGlobals;
133
134 bool doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
135 Module &M, bool isConst, unsigned AddrSpace) const;
136 /// \brief Merge everything in \p Globals for which the corresponding bit
137 /// in \p GlobalSet is set.
138 bool doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
139 const BitVector &GlobalSet, Module &M, bool isConst,
140 unsigned AddrSpace) const;
141
142 /// \brief Check if the given variable has been identified as must keep
143 /// \pre setMustKeepGlobalVariables must have been called on the Module that
144 /// contains GV
isMustKeepGlobalVariable(const GlobalVariable * GV) const145 bool isMustKeepGlobalVariable(const GlobalVariable *GV) const {
146 return MustKeepGlobalVariables.count(GV);
147 }
148
149 /// Collect every variables marked as "used" or used in a landing pad
150 /// instruction for this Module.
151 void setMustKeepGlobalVariables(Module &M);
152
153 /// Collect every variables marked as "used"
154 void collectUsedGlobalVariables(Module &M);
155
156 /// Keep track of the GlobalVariable that must not be merged away
157 SmallPtrSet<const GlobalVariable *, 16> MustKeepGlobalVariables;
158
159 public:
160 static char ID; // Pass identification, replacement for typeid.
GlobalMerge(const TargetMachine * TM=nullptr,unsigned MaximalOffset=0,bool OnlyOptimizeForSize=false,bool MergeExternalGlobals=false)161 explicit GlobalMerge(const TargetMachine *TM = nullptr,
162 unsigned MaximalOffset = 0,
163 bool OnlyOptimizeForSize = false,
164 bool MergeExternalGlobals = false)
165 : FunctionPass(ID), TM(TM), MaxOffset(MaximalOffset),
166 OnlyOptimizeForSize(OnlyOptimizeForSize),
167 MergeExternalGlobals(MergeExternalGlobals) {
168 initializeGlobalMergePass(*PassRegistry::getPassRegistry());
169 }
170
171 bool doInitialization(Module &M) override;
172 bool runOnFunction(Function &F) override;
173 bool doFinalization(Module &M) override;
174
getPassName() const175 const char *getPassName() const override {
176 return "Merge internal globals";
177 }
178
getAnalysisUsage(AnalysisUsage & AU) const179 void getAnalysisUsage(AnalysisUsage &AU) const override {
180 AU.setPreservesCFG();
181 FunctionPass::getAnalysisUsage(AU);
182 }
183 };
184 } // end anonymous namespace
185
186 char GlobalMerge::ID = 0;
187 INITIALIZE_PASS_BEGIN(GlobalMerge, "global-merge", "Merge global variables",
188 false, false)
189 INITIALIZE_PASS_END(GlobalMerge, "global-merge", "Merge global variables",
190 false, false)
191
doMerge(SmallVectorImpl<GlobalVariable * > & Globals,Module & M,bool isConst,unsigned AddrSpace) const192 bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
193 Module &M, bool isConst, unsigned AddrSpace) const {
194 auto &DL = M.getDataLayout();
195 // FIXME: Find better heuristics
196 std::stable_sort(Globals.begin(), Globals.end(),
197 [&DL](const GlobalVariable *GV1, const GlobalVariable *GV2) {
198 return DL.getTypeAllocSize(GV1->getValueType()) <
199 DL.getTypeAllocSize(GV2->getValueType());
200 });
201
202 // If we want to just blindly group all globals together, do so.
203 if (!GlobalMergeGroupByUse) {
204 BitVector AllGlobals(Globals.size());
205 AllGlobals.set();
206 return doMerge(Globals, AllGlobals, M, isConst, AddrSpace);
207 }
208
209 // If we want to be smarter, look at all uses of each global, to try to
210 // discover all sets of globals used together, and how many times each of
211 // these sets occurred.
212 //
213 // Keep this reasonably efficient, by having an append-only list of all sets
214 // discovered so far (UsedGlobalSet), and mapping each "together-ness" unit of
215 // code (currently, a Function) to the set of globals seen so far that are
216 // used together in that unit (GlobalUsesByFunction).
217 //
218 // When we look at the Nth global, we now that any new set is either:
219 // - the singleton set {N}, containing this global only, or
220 // - the union of {N} and a previously-discovered set, containing some
221 // combination of the previous N-1 globals.
222 // Using that knowledge, when looking at the Nth global, we can keep:
223 // - a reference to the singleton set {N} (CurGVOnlySetIdx)
224 // - a list mapping each previous set to its union with {N} (EncounteredUGS),
225 // if it actually occurs.
226
227 // We keep track of the sets of globals used together "close enough".
228 struct UsedGlobalSet {
229 UsedGlobalSet(size_t Size) : Globals(Size), UsageCount(1) {}
230 BitVector Globals;
231 unsigned UsageCount;
232 };
233
234 // Each set is unique in UsedGlobalSets.
235 std::vector<UsedGlobalSet> UsedGlobalSets;
236
237 // Avoid repeating the create-global-set pattern.
238 auto CreateGlobalSet = [&]() -> UsedGlobalSet & {
239 UsedGlobalSets.emplace_back(Globals.size());
240 return UsedGlobalSets.back();
241 };
242
243 // The first set is the empty set.
244 CreateGlobalSet().UsageCount = 0;
245
246 // We define "close enough" to be "in the same function".
247 // FIXME: Grouping uses by function is way too aggressive, so we should have
248 // a better metric for distance between uses.
249 // The obvious alternative would be to group by BasicBlock, but that's in
250 // turn too conservative..
251 // Anything in between wouldn't be trivial to compute, so just stick with
252 // per-function grouping.
253
254 // The value type is an index into UsedGlobalSets.
255 // The default (0) conveniently points to the empty set.
256 DenseMap<Function *, size_t /*UsedGlobalSetIdx*/> GlobalUsesByFunction;
257
258 // Now, look at each merge-eligible global in turn.
259
260 // Keep track of the sets we already encountered to which we added the
261 // current global.
262 // Each element matches the same-index element in UsedGlobalSets.
263 // This lets us efficiently tell whether a set has already been expanded to
264 // include the current global.
265 std::vector<size_t> EncounteredUGS;
266
267 for (size_t GI = 0, GE = Globals.size(); GI != GE; ++GI) {
268 GlobalVariable *GV = Globals[GI];
269
270 // Reset the encountered sets for this global...
271 std::fill(EncounteredUGS.begin(), EncounteredUGS.end(), 0);
272 // ...and grow it in case we created new sets for the previous global.
273 EncounteredUGS.resize(UsedGlobalSets.size());
274
275 // We might need to create a set that only consists of the current global.
276 // Keep track of its index into UsedGlobalSets.
277 size_t CurGVOnlySetIdx = 0;
278
279 // For each global, look at all its Uses.
280 for (auto &U : GV->uses()) {
281 // This Use might be a ConstantExpr. We're interested in Instruction
282 // users, so look through ConstantExpr...
283 Use *UI, *UE;
284 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U.getUser())) {
285 if (CE->use_empty())
286 continue;
287 UI = &*CE->use_begin();
288 UE = nullptr;
289 } else if (isa<Instruction>(U.getUser())) {
290 UI = &U;
291 UE = UI->getNext();
292 } else {
293 continue;
294 }
295
296 // ...to iterate on all the instruction users of the global.
297 // Note that we iterate on Uses and not on Users to be able to getNext().
298 for (; UI != UE; UI = UI->getNext()) {
299 Instruction *I = dyn_cast<Instruction>(UI->getUser());
300 if (!I)
301 continue;
302
303 Function *ParentFn = I->getParent()->getParent();
304
305 // If we're only optimizing for size, ignore non-minsize functions.
306 if (OnlyOptimizeForSize && !ParentFn->optForMinSize())
307 continue;
308
309 size_t UGSIdx = GlobalUsesByFunction[ParentFn];
310
311 // If this is the first global the basic block uses, map it to the set
312 // consisting of this global only.
313 if (!UGSIdx) {
314 // If that set doesn't exist yet, create it.
315 if (!CurGVOnlySetIdx) {
316 CurGVOnlySetIdx = UsedGlobalSets.size();
317 CreateGlobalSet().Globals.set(GI);
318 } else {
319 ++UsedGlobalSets[CurGVOnlySetIdx].UsageCount;
320 }
321
322 GlobalUsesByFunction[ParentFn] = CurGVOnlySetIdx;
323 continue;
324 }
325
326 // If we already encountered this BB, just increment the counter.
327 if (UsedGlobalSets[UGSIdx].Globals.test(GI)) {
328 ++UsedGlobalSets[UGSIdx].UsageCount;
329 continue;
330 }
331
332 // If not, the previous set wasn't actually used in this function.
333 --UsedGlobalSets[UGSIdx].UsageCount;
334
335 // If we already expanded the previous set to include this global, just
336 // reuse that expanded set.
337 if (size_t ExpandedIdx = EncounteredUGS[UGSIdx]) {
338 ++UsedGlobalSets[ExpandedIdx].UsageCount;
339 GlobalUsesByFunction[ParentFn] = ExpandedIdx;
340 continue;
341 }
342
343 // If not, create a new set consisting of the union of the previous set
344 // and this global. Mark it as encountered, so we can reuse it later.
345 GlobalUsesByFunction[ParentFn] = EncounteredUGS[UGSIdx] =
346 UsedGlobalSets.size();
347
348 UsedGlobalSet &NewUGS = CreateGlobalSet();
349 NewUGS.Globals.set(GI);
350 NewUGS.Globals |= UsedGlobalSets[UGSIdx].Globals;
351 }
352 }
353 }
354
355 // Now we found a bunch of sets of globals used together. We accumulated
356 // the number of times we encountered the sets (i.e., the number of blocks
357 // that use that exact set of globals).
358 //
359 // Multiply that by the size of the set to give us a crude profitability
360 // metric.
361 std::sort(UsedGlobalSets.begin(), UsedGlobalSets.end(),
362 [](const UsedGlobalSet &UGS1, const UsedGlobalSet &UGS2) {
363 return UGS1.Globals.count() * UGS1.UsageCount <
364 UGS2.Globals.count() * UGS2.UsageCount;
365 });
366
367 // We can choose to merge all globals together, but ignore globals never used
368 // with another global. This catches the obviously non-profitable cases of
369 // having a single global, but is aggressive enough for any other case.
370 if (GlobalMergeIgnoreSingleUse) {
371 BitVector AllGlobals(Globals.size());
372 for (size_t i = 0, e = UsedGlobalSets.size(); i != e; ++i) {
373 const UsedGlobalSet &UGS = UsedGlobalSets[e - i - 1];
374 if (UGS.UsageCount == 0)
375 continue;
376 if (UGS.Globals.count() > 1)
377 AllGlobals |= UGS.Globals;
378 }
379 return doMerge(Globals, AllGlobals, M, isConst, AddrSpace);
380 }
381
382 // Starting from the sets with the best (=biggest) profitability, find a
383 // good combination.
384 // The ideal (and expensive) solution can only be found by trying all
385 // combinations, looking for the one with the best profitability.
386 // Don't be smart about it, and just pick the first compatible combination,
387 // starting with the sets with the best profitability.
388 BitVector PickedGlobals(Globals.size());
389 bool Changed = false;
390
391 for (size_t i = 0, e = UsedGlobalSets.size(); i != e; ++i) {
392 const UsedGlobalSet &UGS = UsedGlobalSets[e - i - 1];
393 if (UGS.UsageCount == 0)
394 continue;
395 if (PickedGlobals.anyCommon(UGS.Globals))
396 continue;
397 PickedGlobals |= UGS.Globals;
398 // If the set only contains one global, there's no point in merging.
399 // Ignore the global for inclusion in other sets though, so keep it in
400 // PickedGlobals.
401 if (UGS.Globals.count() < 2)
402 continue;
403 Changed |= doMerge(Globals, UGS.Globals, M, isConst, AddrSpace);
404 }
405
406 return Changed;
407 }
408
doMerge(const SmallVectorImpl<GlobalVariable * > & Globals,const BitVector & GlobalSet,Module & M,bool isConst,unsigned AddrSpace) const409 bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
410 const BitVector &GlobalSet, Module &M, bool isConst,
411 unsigned AddrSpace) const {
412 assert(Globals.size() > 1);
413
414 Type *Int32Ty = Type::getInt32Ty(M.getContext());
415 auto &DL = M.getDataLayout();
416
417 DEBUG(dbgs() << " Trying to merge set, starts with #"
418 << GlobalSet.find_first() << "\n");
419
420 ssize_t i = GlobalSet.find_first();
421 while (i != -1) {
422 ssize_t j = 0;
423 uint64_t MergedSize = 0;
424 std::vector<Type*> Tys;
425 std::vector<Constant*> Inits;
426
427 for (j = i; j != -1; j = GlobalSet.find_next(j)) {
428 Type *Ty = Globals[j]->getValueType();
429 MergedSize += DL.getTypeAllocSize(Ty);
430 if (MergedSize > MaxOffset) {
431 break;
432 }
433 Tys.push_back(Ty);
434 Inits.push_back(Globals[j]->getInitializer());
435 }
436
437 StructType *MergedTy = StructType::get(M.getContext(), Tys);
438 Constant *MergedInit = ConstantStruct::get(MergedTy, Inits);
439
440 GlobalVariable *MergedGV = new GlobalVariable(
441 M, MergedTy, isConst, GlobalValue::PrivateLinkage, MergedInit,
442 "_MergedGlobals", nullptr, GlobalVariable::NotThreadLocal, AddrSpace);
443
444 for (ssize_t k = i, idx = 0; k != j; k = GlobalSet.find_next(k), ++idx) {
445 GlobalValue::LinkageTypes Linkage = Globals[k]->getLinkage();
446 std::string Name = Globals[k]->getName();
447
448 Constant *Idx[2] = {
449 ConstantInt::get(Int32Ty, 0),
450 ConstantInt::get(Int32Ty, idx),
451 };
452 Constant *GEP =
453 ConstantExpr::getInBoundsGetElementPtr(MergedTy, MergedGV, Idx);
454 Globals[k]->replaceAllUsesWith(GEP);
455 Globals[k]->eraseFromParent();
456
457 // When the linkage is not internal we must emit an alias for the original
458 // variable name as it may be accessed from another object. On non-Mach-O
459 // we can also emit an alias for internal linkage as it's safe to do so.
460 // It's not safe on Mach-O as the alias (and thus the portion of the
461 // MergedGlobals variable) may be dead stripped at link time.
462 if (Linkage != GlobalValue::InternalLinkage ||
463 !TM->getTargetTriple().isOSBinFormatMachO()) {
464 GlobalAlias::create(Tys[idx], AddrSpace, Linkage, Name, GEP, &M);
465 }
466
467 NumMerged++;
468 }
469 i = j;
470 }
471
472 return true;
473 }
474
collectUsedGlobalVariables(Module & M)475 void GlobalMerge::collectUsedGlobalVariables(Module &M) {
476 // Extract global variables from llvm.used array
477 const GlobalVariable *GV = M.getGlobalVariable("llvm.used");
478 if (!GV || !GV->hasInitializer()) return;
479
480 // Should be an array of 'i8*'.
481 const ConstantArray *InitList = cast<ConstantArray>(GV->getInitializer());
482
483 for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i)
484 if (const GlobalVariable *G =
485 dyn_cast<GlobalVariable>(InitList->getOperand(i)->stripPointerCasts()))
486 MustKeepGlobalVariables.insert(G);
487 }
488
setMustKeepGlobalVariables(Module & M)489 void GlobalMerge::setMustKeepGlobalVariables(Module &M) {
490 collectUsedGlobalVariables(M);
491
492 for (Module::iterator IFn = M.begin(), IEndFn = M.end(); IFn != IEndFn;
493 ++IFn) {
494 for (Function::iterator IBB = IFn->begin(), IEndBB = IFn->end();
495 IBB != IEndBB; ++IBB) {
496 // Follow the invoke link to find the landing pad instruction
497 const InvokeInst *II = dyn_cast<InvokeInst>(IBB->getTerminator());
498 if (!II) continue;
499
500 const LandingPadInst *LPInst = II->getUnwindDest()->getLandingPadInst();
501 // Look for globals in the clauses of the landing pad instruction
502 for (unsigned Idx = 0, NumClauses = LPInst->getNumClauses();
503 Idx != NumClauses; ++Idx)
504 if (const GlobalVariable *GV =
505 dyn_cast<GlobalVariable>(LPInst->getClause(Idx)
506 ->stripPointerCasts()))
507 MustKeepGlobalVariables.insert(GV);
508 }
509 }
510 }
511
doInitialization(Module & M)512 bool GlobalMerge::doInitialization(Module &M) {
513 if (!EnableGlobalMerge)
514 return false;
515
516 auto &DL = M.getDataLayout();
517 DenseMap<unsigned, SmallVector<GlobalVariable*, 16> > Globals, ConstGlobals,
518 BSSGlobals;
519 bool Changed = false;
520 setMustKeepGlobalVariables(M);
521
522 // Grab all non-const globals.
523 for (auto &GV : M.globals()) {
524 // Merge is safe for "normal" internal or external globals only
525 if (GV.isDeclaration() || GV.isThreadLocal() || GV.hasSection())
526 continue;
527
528 if (!(MergeExternalGlobals && GV.hasExternalLinkage()) &&
529 !GV.hasInternalLinkage())
530 continue;
531
532 PointerType *PT = dyn_cast<PointerType>(GV.getType());
533 assert(PT && "Global variable is not a pointer!");
534
535 unsigned AddressSpace = PT->getAddressSpace();
536
537 // Ignore fancy-aligned globals for now.
538 unsigned Alignment = DL.getPreferredAlignment(&GV);
539 Type *Ty = GV.getValueType();
540 if (Alignment > DL.getABITypeAlignment(Ty))
541 continue;
542
543 // Ignore all 'special' globals.
544 if (GV.getName().startswith("llvm.") ||
545 GV.getName().startswith(".llvm."))
546 continue;
547
548 // Ignore all "required" globals:
549 if (isMustKeepGlobalVariable(&GV))
550 continue;
551
552 if (DL.getTypeAllocSize(Ty) < MaxOffset) {
553 if (TargetLoweringObjectFile::getKindForGlobal(&GV, *TM).isBSSLocal())
554 BSSGlobals[AddressSpace].push_back(&GV);
555 else if (GV.isConstant())
556 ConstGlobals[AddressSpace].push_back(&GV);
557 else
558 Globals[AddressSpace].push_back(&GV);
559 }
560 }
561
562 for (auto &P : Globals)
563 if (P.second.size() > 1)
564 Changed |= doMerge(P.second, M, false, P.first);
565
566 for (auto &P : BSSGlobals)
567 if (P.second.size() > 1)
568 Changed |= doMerge(P.second, M, false, P.first);
569
570 if (EnableGlobalMergeOnConst)
571 for (auto &P : ConstGlobals)
572 if (P.second.size() > 1)
573 Changed |= doMerge(P.second, M, true, P.first);
574
575 return Changed;
576 }
577
runOnFunction(Function & F)578 bool GlobalMerge::runOnFunction(Function &F) {
579 return false;
580 }
581
doFinalization(Module & M)582 bool GlobalMerge::doFinalization(Module &M) {
583 MustKeepGlobalVariables.clear();
584 return false;
585 }
586
createGlobalMergePass(const TargetMachine * TM,unsigned Offset,bool OnlyOptimizeForSize,bool MergeExternalByDefault)587 Pass *llvm::createGlobalMergePass(const TargetMachine *TM, unsigned Offset,
588 bool OnlyOptimizeForSize,
589 bool MergeExternalByDefault) {
590 bool MergeExternal = (EnableGlobalMergeOnExternal == cl::BOU_UNSET) ?
591 MergeExternalByDefault : (EnableGlobalMergeOnExternal == cl::BOU_TRUE);
592 return new GlobalMerge(TM, Offset, OnlyOptimizeForSize, MergeExternal);
593 }
594