1 //===- GlobalMerge.cpp - Internal globals merging -------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass merges globals with internal linkage into one. This way all the
11 // globals which were merged into a biggest one can be addressed using offsets
12 // from the same base pointer (no need for separate base pointer for each of the
13 // global). Such a transformation can significantly reduce the register pressure
14 // when many globals are involved.
16 // For example, consider the code which touches several global variables at
19 // static int foo[N], bar[N], baz[N];
21 // for (i = 0; i < N; ++i) {
22 // foo[i] = bar[i] * baz[i];
25 // On ARM the addresses of 3 arrays should be kept in the registers, thus
26 // this code has quite large register pressure (loop body):
33 // Pass converts the code to something like:
41 // for (i = 0; i < N; ++i) {
42 // merged.foo[i] = merged.bar[i] * merged.baz[i];
45 // and in ARM code this becomes:
52 // note that we saved 2 registers here almostly "for free".
54 // However, merging globals can have tradeoffs:
55 // - it confuses debuggers, tools, and users
56 // - it makes linker optimizations less useful (order files, LOHs, ...)
57 // - it forces usage of indexed addressing (which isn't necessarily "free")
58 // - it can increase register pressure when the uses are disparate enough.
60 // We use heuristics to discover the best global grouping we can (cf cl::opts).
62 // ===---------------------------------------------------------------------===//
64 #include "llvm/ADT/BitVector.h"
65 #include "llvm/ADT/DenseMap.h"
66 #include "llvm/ADT/SmallPtrSet.h"
67 #include "llvm/ADT/SmallVector.h"
68 #include "llvm/ADT/Statistic.h"
69 #include "llvm/ADT/StringRef.h"
70 #include "llvm/ADT/Triple.h"
71 #include "llvm/ADT/Twine.h"
72 #include "llvm/CodeGen/Passes.h"
73 #include "llvm/IR/BasicBlock.h"
74 #include "llvm/IR/Constants.h"
75 #include "llvm/IR/DataLayout.h"
76 #include "llvm/IR/DerivedTypes.h"
77 #include "llvm/IR/Function.h"
78 #include "llvm/IR/GlobalAlias.h"
79 #include "llvm/IR/GlobalValue.h"
80 #include "llvm/IR/GlobalVariable.h"
81 #include "llvm/IR/Instruction.h"
82 #include "llvm/IR/Module.h"
83 #include "llvm/IR/Type.h"
84 #include "llvm/IR/Use.h"
85 #include "llvm/IR/User.h"
86 #include "llvm/Pass.h"
87 #include "llvm/Support/Casting.h"
88 #include "llvm/Support/CommandLine.h"
89 #include "llvm/Support/Debug.h"
90 #include "llvm/Support/raw_ostream.h"
91 #include "llvm/Target/TargetLoweringObjectFile.h"
92 #include "llvm/Target/TargetMachine.h"
100 using namespace llvm
;
102 #define DEBUG_TYPE "global-merge"
104 // FIXME: This is only useful as a last-resort way to disable the pass.
106 EnableGlobalMerge("enable-global-merge", cl::Hidden
,
107 cl::desc("Enable the global merge pass"),
110 static cl::opt
<unsigned>
111 GlobalMergeMaxOffset("global-merge-max-offset", cl::Hidden
,
112 cl::desc("Set maximum offset for global merge pass"),
115 static cl::opt
<bool> GlobalMergeGroupByUse(
116 "global-merge-group-by-use", cl::Hidden
,
117 cl::desc("Improve global merge pass to look at uses"), cl::init(true));
119 static cl::opt
<bool> GlobalMergeIgnoreSingleUse(
120 "global-merge-ignore-single-use", cl::Hidden
,
121 cl::desc("Improve global merge pass to ignore globals only used alone"),
125 EnableGlobalMergeOnConst("global-merge-on-const", cl::Hidden
,
126 cl::desc("Enable global merge pass on constants"),
129 // FIXME: this could be a transitional option, and we probably need to remove
130 // it if only we are sure this optimization could always benefit all targets.
131 static cl::opt
<cl::boolOrDefault
>
132 EnableGlobalMergeOnExternal("global-merge-on-external", cl::Hidden
,
133 cl::desc("Enable global merge pass on external linkage"));
135 STATISTIC(NumMerged
, "Number of globals merged");
139 class GlobalMerge
: public FunctionPass
{
140 const TargetMachine
*TM
= nullptr;
142 // FIXME: Infer the maximum possible offset depending on the actual users
143 // (these max offsets are different for the users inside Thumb or ARM
144 // functions), see the code that passes in the offset in the ARM backend
145 // for more information.
148 /// Whether we should try to optimize for size only.
149 /// Currently, this applies a dead simple heuristic: only consider globals
150 /// used in minsize functions for merging.
151 /// FIXME: This could learn about optsize, and be used in the cost model.
152 bool OnlyOptimizeForSize
= false;
154 /// Whether we should merge global variables that have external linkage.
155 bool MergeExternalGlobals
= false;
159 bool doMerge(SmallVectorImpl
<GlobalVariable
*> &Globals
,
160 Module
&M
, bool isConst
, unsigned AddrSpace
) const;
162 /// Merge everything in \p Globals for which the corresponding bit
163 /// in \p GlobalSet is set.
164 bool doMerge(const SmallVectorImpl
<GlobalVariable
*> &Globals
,
165 const BitVector
&GlobalSet
, Module
&M
, bool isConst
,
166 unsigned AddrSpace
) const;
168 /// Check if the given variable has been identified as must keep
169 /// \pre setMustKeepGlobalVariables must have been called on the Module that
171 bool isMustKeepGlobalVariable(const GlobalVariable
*GV
) const {
172 return MustKeepGlobalVariables
.count(GV
);
175 /// Collect every variables marked as "used" or used in a landing pad
176 /// instruction for this Module.
177 void setMustKeepGlobalVariables(Module
&M
);
179 /// Collect every variables marked as "used"
180 void collectUsedGlobalVariables(Module
&M
, StringRef Name
);
182 /// Keep track of the GlobalVariable that must not be merged away
183 SmallPtrSet
<const GlobalVariable
*, 16> MustKeepGlobalVariables
;
186 static char ID
; // Pass identification, replacement for typeid.
188 explicit GlobalMerge()
189 : FunctionPass(ID
), MaxOffset(GlobalMergeMaxOffset
) {
190 initializeGlobalMergePass(*PassRegistry::getPassRegistry());
193 explicit GlobalMerge(const TargetMachine
*TM
, unsigned MaximalOffset
,
194 bool OnlyOptimizeForSize
, bool MergeExternalGlobals
)
195 : FunctionPass(ID
), TM(TM
), MaxOffset(MaximalOffset
),
196 OnlyOptimizeForSize(OnlyOptimizeForSize
),
197 MergeExternalGlobals(MergeExternalGlobals
) {
198 initializeGlobalMergePass(*PassRegistry::getPassRegistry());
201 bool doInitialization(Module
&M
) override
;
202 bool runOnFunction(Function
&F
) override
;
203 bool doFinalization(Module
&M
) override
;
205 StringRef
getPassName() const override
{ return "Merge internal globals"; }
207 void getAnalysisUsage(AnalysisUsage
&AU
) const override
{
208 AU
.setPreservesCFG();
209 FunctionPass::getAnalysisUsage(AU
);
213 } // end anonymous namespace
215 char GlobalMerge::ID
= 0;
217 INITIALIZE_PASS(GlobalMerge
, DEBUG_TYPE
, "Merge global variables", false, false)
219 bool GlobalMerge::doMerge(SmallVectorImpl
<GlobalVariable
*> &Globals
,
220 Module
&M
, bool isConst
, unsigned AddrSpace
) const {
221 auto &DL
= M
.getDataLayout();
222 // FIXME: Find better heuristics
223 std::stable_sort(Globals
.begin(), Globals
.end(),
224 [&DL
](const GlobalVariable
*GV1
, const GlobalVariable
*GV2
) {
225 return DL
.getTypeAllocSize(GV1
->getValueType()) <
226 DL
.getTypeAllocSize(GV2
->getValueType());
229 // If we want to just blindly group all globals together, do so.
230 if (!GlobalMergeGroupByUse
) {
231 BitVector
AllGlobals(Globals
.size());
233 return doMerge(Globals
, AllGlobals
, M
, isConst
, AddrSpace
);
236 // If we want to be smarter, look at all uses of each global, to try to
237 // discover all sets of globals used together, and how many times each of
238 // these sets occurred.
240 // Keep this reasonably efficient, by having an append-only list of all sets
241 // discovered so far (UsedGlobalSet), and mapping each "together-ness" unit of
242 // code (currently, a Function) to the set of globals seen so far that are
243 // used together in that unit (GlobalUsesByFunction).
245 // When we look at the Nth global, we know that any new set is either:
246 // - the singleton set {N}, containing this global only, or
247 // - the union of {N} and a previously-discovered set, containing some
248 // combination of the previous N-1 globals.
249 // Using that knowledge, when looking at the Nth global, we can keep:
250 // - a reference to the singleton set {N} (CurGVOnlySetIdx)
251 // - a list mapping each previous set to its union with {N} (EncounteredUGS),
252 // if it actually occurs.
254 // We keep track of the sets of globals used together "close enough".
255 struct UsedGlobalSet
{
257 unsigned UsageCount
= 1;
259 UsedGlobalSet(size_t Size
) : Globals(Size
) {}
262 // Each set is unique in UsedGlobalSets.
263 std::vector
<UsedGlobalSet
> UsedGlobalSets
;
265 // Avoid repeating the create-global-set pattern.
266 auto CreateGlobalSet
= [&]() -> UsedGlobalSet
& {
267 UsedGlobalSets
.emplace_back(Globals
.size());
268 return UsedGlobalSets
.back();
271 // The first set is the empty set.
272 CreateGlobalSet().UsageCount
= 0;
274 // We define "close enough" to be "in the same function".
275 // FIXME: Grouping uses by function is way too aggressive, so we should have
276 // a better metric for distance between uses.
277 // The obvious alternative would be to group by BasicBlock, but that's in
278 // turn too conservative..
279 // Anything in between wouldn't be trivial to compute, so just stick with
280 // per-function grouping.
282 // The value type is an index into UsedGlobalSets.
283 // The default (0) conveniently points to the empty set.
284 DenseMap
<Function
*, size_t /*UsedGlobalSetIdx*/> GlobalUsesByFunction
;
286 // Now, look at each merge-eligible global in turn.
288 // Keep track of the sets we already encountered to which we added the
290 // Each element matches the same-index element in UsedGlobalSets.
291 // This lets us efficiently tell whether a set has already been expanded to
292 // include the current global.
293 std::vector
<size_t> EncounteredUGS
;
295 for (size_t GI
= 0, GE
= Globals
.size(); GI
!= GE
; ++GI
) {
296 GlobalVariable
*GV
= Globals
[GI
];
298 // Reset the encountered sets for this global...
299 std::fill(EncounteredUGS
.begin(), EncounteredUGS
.end(), 0);
300 // ...and grow it in case we created new sets for the previous global.
301 EncounteredUGS
.resize(UsedGlobalSets
.size());
303 // We might need to create a set that only consists of the current global.
304 // Keep track of its index into UsedGlobalSets.
305 size_t CurGVOnlySetIdx
= 0;
307 // For each global, look at all its Uses.
308 for (auto &U
: GV
->uses()) {
309 // This Use might be a ConstantExpr. We're interested in Instruction
310 // users, so look through ConstantExpr...
312 if (ConstantExpr
*CE
= dyn_cast
<ConstantExpr
>(U
.getUser())) {
315 UI
= &*CE
->use_begin();
317 } else if (isa
<Instruction
>(U
.getUser())) {
324 // ...to iterate on all the instruction users of the global.
325 // Note that we iterate on Uses and not on Users to be able to getNext().
326 for (; UI
!= UE
; UI
= UI
->getNext()) {
327 Instruction
*I
= dyn_cast
<Instruction
>(UI
->getUser());
331 Function
*ParentFn
= I
->getParent()->getParent();
333 // If we're only optimizing for size, ignore non-minsize functions.
334 if (OnlyOptimizeForSize
&& !ParentFn
->optForMinSize())
337 size_t UGSIdx
= GlobalUsesByFunction
[ParentFn
];
339 // If this is the first global the basic block uses, map it to the set
340 // consisting of this global only.
342 // If that set doesn't exist yet, create it.
343 if (!CurGVOnlySetIdx
) {
344 CurGVOnlySetIdx
= UsedGlobalSets
.size();
345 CreateGlobalSet().Globals
.set(GI
);
347 ++UsedGlobalSets
[CurGVOnlySetIdx
].UsageCount
;
350 GlobalUsesByFunction
[ParentFn
] = CurGVOnlySetIdx
;
354 // If we already encountered this BB, just increment the counter.
355 if (UsedGlobalSets
[UGSIdx
].Globals
.test(GI
)) {
356 ++UsedGlobalSets
[UGSIdx
].UsageCount
;
360 // If not, the previous set wasn't actually used in this function.
361 --UsedGlobalSets
[UGSIdx
].UsageCount
;
363 // If we already expanded the previous set to include this global, just
364 // reuse that expanded set.
365 if (size_t ExpandedIdx
= EncounteredUGS
[UGSIdx
]) {
366 ++UsedGlobalSets
[ExpandedIdx
].UsageCount
;
367 GlobalUsesByFunction
[ParentFn
] = ExpandedIdx
;
371 // If not, create a new set consisting of the union of the previous set
372 // and this global. Mark it as encountered, so we can reuse it later.
373 GlobalUsesByFunction
[ParentFn
] = EncounteredUGS
[UGSIdx
] =
374 UsedGlobalSets
.size();
376 UsedGlobalSet
&NewUGS
= CreateGlobalSet();
377 NewUGS
.Globals
.set(GI
);
378 NewUGS
.Globals
|= UsedGlobalSets
[UGSIdx
].Globals
;
383 // Now we found a bunch of sets of globals used together. We accumulated
384 // the number of times we encountered the sets (i.e., the number of blocks
385 // that use that exact set of globals).
387 // Multiply that by the size of the set to give us a crude profitability
389 std::stable_sort(UsedGlobalSets
.begin(), UsedGlobalSets
.end(),
390 [](const UsedGlobalSet
&UGS1
, const UsedGlobalSet
&UGS2
) {
391 return UGS1
.Globals
.count() * UGS1
.UsageCount
<
392 UGS2
.Globals
.count() * UGS2
.UsageCount
;
395 // We can choose to merge all globals together, but ignore globals never used
396 // with another global. This catches the obviously non-profitable cases of
397 // having a single global, but is aggressive enough for any other case.
398 if (GlobalMergeIgnoreSingleUse
) {
399 BitVector
AllGlobals(Globals
.size());
400 for (size_t i
= 0, e
= UsedGlobalSets
.size(); i
!= e
; ++i
) {
401 const UsedGlobalSet
&UGS
= UsedGlobalSets
[e
- i
- 1];
402 if (UGS
.UsageCount
== 0)
404 if (UGS
.Globals
.count() > 1)
405 AllGlobals
|= UGS
.Globals
;
407 return doMerge(Globals
, AllGlobals
, M
, isConst
, AddrSpace
);
410 // Starting from the sets with the best (=biggest) profitability, find a
412 // The ideal (and expensive) solution can only be found by trying all
413 // combinations, looking for the one with the best profitability.
414 // Don't be smart about it, and just pick the first compatible combination,
415 // starting with the sets with the best profitability.
416 BitVector
PickedGlobals(Globals
.size());
417 bool Changed
= false;
419 for (size_t i
= 0, e
= UsedGlobalSets
.size(); i
!= e
; ++i
) {
420 const UsedGlobalSet
&UGS
= UsedGlobalSets
[e
- i
- 1];
421 if (UGS
.UsageCount
== 0)
423 if (PickedGlobals
.anyCommon(UGS
.Globals
))
425 PickedGlobals
|= UGS
.Globals
;
426 // If the set only contains one global, there's no point in merging.
427 // Ignore the global for inclusion in other sets though, so keep it in
429 if (UGS
.Globals
.count() < 2)
431 Changed
|= doMerge(Globals
, UGS
.Globals
, M
, isConst
, AddrSpace
);
437 bool GlobalMerge::doMerge(const SmallVectorImpl
<GlobalVariable
*> &Globals
,
438 const BitVector
&GlobalSet
, Module
&M
, bool isConst
,
439 unsigned AddrSpace
) const {
440 assert(Globals
.size() > 1);
442 Type
*Int32Ty
= Type::getInt32Ty(M
.getContext());
443 Type
*Int8Ty
= Type::getInt8Ty(M
.getContext());
444 auto &DL
= M
.getDataLayout();
446 LLVM_DEBUG(dbgs() << " Trying to merge set, starts with #"
447 << GlobalSet
.find_first() << "\n");
449 bool Changed
= false;
450 ssize_t i
= GlobalSet
.find_first();
453 uint64_t MergedSize
= 0;
454 std::vector
<Type
*> Tys
;
455 std::vector
<Constant
*> Inits
;
456 std::vector
<unsigned> StructIdxs
;
458 bool HasExternal
= false;
459 StringRef FirstExternalName
;
460 unsigned MaxAlign
= 1;
462 for (j
= i
; j
!= -1; j
= GlobalSet
.find_next(j
)) {
463 Type
*Ty
= Globals
[j
]->getValueType();
465 // Make sure we use the same alignment AsmPrinter would use.
466 unsigned Align
= DL
.getPreferredAlignment(Globals
[j
]);
467 unsigned Padding
= alignTo(MergedSize
, Align
) - MergedSize
;
468 MergedSize
+= Padding
;
469 MergedSize
+= DL
.getTypeAllocSize(Ty
);
470 if (MergedSize
> MaxOffset
) {
474 Tys
.push_back(ArrayType::get(Int8Ty
, Padding
));
475 Inits
.push_back(ConstantAggregateZero::get(Tys
.back()));
479 Inits
.push_back(Globals
[j
]->getInitializer());
480 StructIdxs
.push_back(CurIdx
++);
482 MaxAlign
= std::max(MaxAlign
, Align
);
484 if (Globals
[j
]->hasExternalLinkage() && !HasExternal
) {
486 FirstExternalName
= Globals
[j
]->getName();
490 // Exit early if there is only one global to merge.
491 if (Tys
.size() < 2) {
496 // If merged variables doesn't have external linkage, we needn't to expose
497 // the symbol after merging.
498 GlobalValue::LinkageTypes Linkage
= HasExternal
499 ? GlobalValue::ExternalLinkage
500 : GlobalValue::InternalLinkage
;
501 // Use a packed struct so we can control alignment.
502 StructType
*MergedTy
= StructType::get(M
.getContext(), Tys
, true);
503 Constant
*MergedInit
= ConstantStruct::get(MergedTy
, Inits
);
505 // On Darwin external linkage needs to be preserved, otherwise
506 // dsymutil cannot preserve the debug info for the merged
507 // variables. If they have external linkage, use the symbol name
508 // of the first variable merged as the suffix of global symbol
509 // name. This avoids a link-time naming conflict for the
510 // _MergedGlobals symbols.
512 (IsMachO
&& HasExternal
)
513 ? "_MergedGlobals_" + FirstExternalName
515 auto MergedLinkage
= IsMachO
? Linkage
: GlobalValue::PrivateLinkage
;
516 auto *MergedGV
= new GlobalVariable(
517 M
, MergedTy
, isConst
, MergedLinkage
, MergedInit
, MergedName
, nullptr,
518 GlobalVariable::NotThreadLocal
, AddrSpace
);
520 MergedGV
->setAlignment(MaxAlign
);
521 MergedGV
->setSection(Globals
[i
]->getSection());
523 const StructLayout
*MergedLayout
= DL
.getStructLayout(MergedTy
);
524 for (ssize_t k
= i
, idx
= 0; k
!= j
; k
= GlobalSet
.find_next(k
), ++idx
) {
525 GlobalValue::LinkageTypes Linkage
= Globals
[k
]->getLinkage();
526 std::string Name
= Globals
[k
]->getName();
527 GlobalValue::DLLStorageClassTypes DLLStorage
=
528 Globals
[k
]->getDLLStorageClass();
530 // Copy metadata while adjusting any debug info metadata by the original
531 // global's offset within the merged global.
532 MergedGV
->copyMetadata(Globals
[k
],
533 MergedLayout
->getElementOffset(StructIdxs
[idx
]));
536 ConstantInt::get(Int32Ty
, 0),
537 ConstantInt::get(Int32Ty
, StructIdxs
[idx
]),
540 ConstantExpr::getInBoundsGetElementPtr(MergedTy
, MergedGV
, Idx
);
541 Globals
[k
]->replaceAllUsesWith(GEP
);
542 Globals
[k
]->eraseFromParent();
544 // When the linkage is not internal we must emit an alias for the original
545 // variable name as it may be accessed from another object. On non-Mach-O
546 // we can also emit an alias for internal linkage as it's safe to do so.
547 // It's not safe on Mach-O as the alias (and thus the portion of the
548 // MergedGlobals variable) may be dead stripped at link time.
549 if (Linkage
!= GlobalValue::InternalLinkage
|| !IsMachO
) {
550 GlobalAlias
*GA
= GlobalAlias::create(Tys
[StructIdxs
[idx
]], AddrSpace
,
551 Linkage
, Name
, GEP
, &M
);
552 GA
->setDLLStorageClass(DLLStorage
);
564 void GlobalMerge::collectUsedGlobalVariables(Module
&M
, StringRef Name
) {
565 // Extract global variables from llvm.used array
566 const GlobalVariable
*GV
= M
.getGlobalVariable(Name
);
567 if (!GV
|| !GV
->hasInitializer()) return;
569 // Should be an array of 'i8*'.
570 const ConstantArray
*InitList
= cast
<ConstantArray
>(GV
->getInitializer());
572 for (unsigned i
= 0, e
= InitList
->getNumOperands(); i
!= e
; ++i
)
573 if (const GlobalVariable
*G
=
574 dyn_cast
<GlobalVariable
>(InitList
->getOperand(i
)->stripPointerCasts()))
575 MustKeepGlobalVariables
.insert(G
);
578 void GlobalMerge::setMustKeepGlobalVariables(Module
&M
) {
579 collectUsedGlobalVariables(M
, "llvm.used");
580 collectUsedGlobalVariables(M
, "llvm.compiler.used");
582 for (Function
&F
: M
) {
583 for (BasicBlock
&BB
: F
) {
584 Instruction
*Pad
= BB
.getFirstNonPHI();
588 // Keep globals used by landingpads and catchpads.
589 for (const Use
&U
: Pad
->operands()) {
590 if (const GlobalVariable
*GV
=
591 dyn_cast
<GlobalVariable
>(U
->stripPointerCasts()))
592 MustKeepGlobalVariables
.insert(GV
);
598 bool GlobalMerge::doInitialization(Module
&M
) {
599 if (!EnableGlobalMerge
)
602 IsMachO
= Triple(M
.getTargetTriple()).isOSBinFormatMachO();
604 auto &DL
= M
.getDataLayout();
605 DenseMap
<std::pair
<unsigned, StringRef
>, SmallVector
<GlobalVariable
*, 16>>
606 Globals
, ConstGlobals
, BSSGlobals
;
607 bool Changed
= false;
608 setMustKeepGlobalVariables(M
);
610 // Grab all non-const globals.
611 for (auto &GV
: M
.globals()) {
612 // Merge is safe for "normal" internal or external globals only
613 if (GV
.isDeclaration() || GV
.isThreadLocal() || GV
.hasImplicitSection())
616 // It's not safe to merge globals that may be preempted
617 if (TM
&& !TM
->shouldAssumeDSOLocal(M
, &GV
))
620 if (!(MergeExternalGlobals
&& GV
.hasExternalLinkage()) &&
621 !GV
.hasInternalLinkage())
624 PointerType
*PT
= dyn_cast
<PointerType
>(GV
.getType());
625 assert(PT
&& "Global variable is not a pointer!");
627 unsigned AddressSpace
= PT
->getAddressSpace();
628 StringRef Section
= GV
.getSection();
630 // Ignore all 'special' globals.
631 if (GV
.getName().startswith("llvm.") ||
632 GV
.getName().startswith(".llvm."))
635 // Ignore all "required" globals:
636 if (isMustKeepGlobalVariable(&GV
))
639 Type
*Ty
= GV
.getValueType();
640 if (DL
.getTypeAllocSize(Ty
) < MaxOffset
) {
642 TargetLoweringObjectFile::getKindForGlobal(&GV
, *TM
).isBSS())
643 BSSGlobals
[{AddressSpace
, Section
}].push_back(&GV
);
644 else if (GV
.isConstant())
645 ConstGlobals
[{AddressSpace
, Section
}].push_back(&GV
);
647 Globals
[{AddressSpace
, Section
}].push_back(&GV
);
651 for (auto &P
: Globals
)
652 if (P
.second
.size() > 1)
653 Changed
|= doMerge(P
.second
, M
, false, P
.first
.first
);
655 for (auto &P
: BSSGlobals
)
656 if (P
.second
.size() > 1)
657 Changed
|= doMerge(P
.second
, M
, false, P
.first
.first
);
659 if (EnableGlobalMergeOnConst
)
660 for (auto &P
: ConstGlobals
)
661 if (P
.second
.size() > 1)
662 Changed
|= doMerge(P
.second
, M
, true, P
.first
.first
);
667 bool GlobalMerge::runOnFunction(Function
&F
) {
671 bool GlobalMerge::doFinalization(Module
&M
) {
672 MustKeepGlobalVariables
.clear();
676 Pass
*llvm::createGlobalMergePass(const TargetMachine
*TM
, unsigned Offset
,
677 bool OnlyOptimizeForSize
,
678 bool MergeExternalByDefault
) {
679 bool MergeExternal
= (EnableGlobalMergeOnExternal
== cl::BOU_UNSET
) ?
680 MergeExternalByDefault
: (EnableGlobalMergeOnExternal
== cl::BOU_TRUE
);
681 return new GlobalMerge(TM
, Offset
, OnlyOptimizeForSize
, MergeExternal
);