1 //===-- LowerBitSets.cpp - Bitset lowering pass ---------------------------===//
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 lowers bitset metadata and calls to the llvm.bitset.test intrinsic.
11 // See http://llvm.org/docs/LangRef.html#bitsets for more information.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Transforms/IPO/LowerBitSets.h"
16 #include "llvm/Transforms/IPO.h"
17 #include "llvm/ADT/EquivalenceClasses.h"
18 #include "llvm/ADT/Statistic.h"
19 #include "llvm/IR/Constant.h"
20 #include "llvm/IR/Constants.h"
21 #include "llvm/IR/GlobalVariable.h"
22 #include "llvm/IR/IRBuilder.h"
23 #include "llvm/IR/Instructions.h"
24 #include "llvm/IR/Intrinsics.h"
25 #include "llvm/IR/Module.h"
26 #include "llvm/IR/Operator.h"
27 #include "llvm/Pass.h"
28 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
32 #define DEBUG_TYPE "lowerbitsets"
34 STATISTIC(ByteArraySizeBits, "Byte array size in bits");
35 STATISTIC(ByteArraySizeBytes, "Byte array size in bytes");
36 STATISTIC(NumByteArraysCreated, "Number of byte arrays created");
37 STATISTIC(NumBitSetCallsLowered, "Number of bitset calls lowered");
38 STATISTIC(NumBitSetDisjointSets, "Number of disjoint sets of bitsets");
40 bool BitSetInfo::containsGlobalOffset(uint64_t Offset) const {
41 if (Offset < ByteOffset)
44 if ((Offset - ByteOffset) % (uint64_t(1) << AlignLog2) != 0)
47 uint64_t BitOffset = (Offset - ByteOffset) >> AlignLog2;
48 if (BitOffset >= BitSize)
51 return Bits.count(BitOffset);
54 bool BitSetInfo::containsValue(
56 const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout, Value *V,
57 uint64_t COffset) const {
58 if (auto GV = dyn_cast<GlobalVariable>(V)) {
59 auto I = GlobalLayout.find(GV);
60 if (I == GlobalLayout.end())
62 return containsGlobalOffset(I->second + COffset);
65 if (auto GEP = dyn_cast<GEPOperator>(V)) {
66 APInt APOffset(DL.getPointerSizeInBits(0), 0);
67 bool Result = GEP->accumulateConstantOffset(DL, APOffset);
70 COffset += APOffset.getZExtValue();
71 return containsValue(DL, GlobalLayout, GEP->getPointerOperand(),
75 if (auto Op = dyn_cast<Operator>(V)) {
76 if (Op->getOpcode() == Instruction::BitCast)
77 return containsValue(DL, GlobalLayout, Op->getOperand(0), COffset);
79 if (Op->getOpcode() == Instruction::Select)
80 return containsValue(DL, GlobalLayout, Op->getOperand(1), COffset) &&
81 containsValue(DL, GlobalLayout, Op->getOperand(2), COffset);
87 BitSetInfo BitSetBuilder::build() {
91 // Normalize each offset against the minimum observed offset, and compute
92 // the bitwise OR of each of the offsets. The number of trailing zeros
93 // in the mask gives us the log2 of the alignment of all offsets, which
94 // allows us to compress the bitset by only storing one bit per aligned
97 for (uint64_t &Offset : Offsets) {
103 BSI.ByteOffset = Min;
107 BSI.AlignLog2 = countTrailingZeros(Mask, ZB_Undefined);
109 // Build the compressed bitset while normalizing the offsets against the
110 // computed alignment.
111 BSI.BitSize = ((Max - Min) >> BSI.AlignLog2) + 1;
112 for (uint64_t Offset : Offsets) {
113 Offset >>= BSI.AlignLog2;
114 BSI.Bits.insert(Offset);
120 void GlobalLayoutBuilder::addFragment(const std::set<uint64_t> &F) {
121 // Create a new fragment to hold the layout for F.
122 Fragments.emplace_back();
123 std::vector<uint64_t> &Fragment = Fragments.back();
124 uint64_t FragmentIndex = Fragments.size() - 1;
126 for (auto ObjIndex : F) {
127 uint64_t OldFragmentIndex = FragmentMap[ObjIndex];
128 if (OldFragmentIndex == 0) {
129 // We haven't seen this object index before, so just add it to the current
131 Fragment.push_back(ObjIndex);
133 // This index belongs to an existing fragment. Copy the elements of the
134 // old fragment into this one and clear the old fragment. We don't update
135 // the fragment map just yet, this ensures that any further references to
136 // indices from the old fragment in this fragment do not insert any more
138 std::vector<uint64_t> &OldFragment = Fragments[OldFragmentIndex];
139 Fragment.insert(Fragment.end(), OldFragment.begin(), OldFragment.end());
144 // Update the fragment map to point our object indices to this fragment.
145 for (uint64_t ObjIndex : Fragment)
146 FragmentMap[ObjIndex] = FragmentIndex;
149 void ByteArrayBuilder::allocate(const std::set<uint64_t> &Bits,
150 uint64_t BitSize, uint64_t &AllocByteOffset,
151 uint8_t &AllocMask) {
152 // Find the smallest current allocation.
154 for (unsigned I = 1; I != BitsPerByte; ++I)
155 if (BitAllocs[I] < BitAllocs[Bit])
158 AllocByteOffset = BitAllocs[Bit];
160 // Add our size to it.
161 unsigned ReqSize = AllocByteOffset + BitSize;
162 BitAllocs[Bit] = ReqSize;
163 if (Bytes.size() < ReqSize)
164 Bytes.resize(ReqSize);
167 AllocMask = 1 << Bit;
168 for (uint64_t B : Bits)
169 Bytes[AllocByteOffset + B] |= AllocMask;
174 struct ByteArrayInfo {
175 std::set<uint64_t> Bits;
177 GlobalVariable *ByteArray;
181 struct LowerBitSets : public ModulePass {
183 LowerBitSets() : ModulePass(ID) {
184 initializeLowerBitSetsPass(*PassRegistry::getPassRegistry());
191 IntegerType *Int32Ty;
193 IntegerType *Int64Ty;
196 // The llvm.bitsets named metadata.
197 NamedMDNode *BitSetNM;
199 // Mapping from bitset mdstrings to the call sites that test them.
200 DenseMap<MDString *, std::vector<CallInst *>> BitSetTestCallSites;
202 std::vector<ByteArrayInfo> ByteArrayInfos;
205 buildBitSet(MDString *BitSet,
206 const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout);
207 ByteArrayInfo *createByteArray(BitSetInfo &BSI);
208 void allocateByteArrays();
209 Value *createBitSetTest(IRBuilder<> &B, BitSetInfo &BSI, ByteArrayInfo *&BAI,
212 lowerBitSetCall(CallInst *CI, BitSetInfo &BSI, ByteArrayInfo *&BAI,
213 GlobalVariable *CombinedGlobal,
214 const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout);
215 void buildBitSetsFromGlobals(const std::vector<MDString *> &BitSets,
216 const std::vector<GlobalVariable *> &Globals);
218 bool eraseBitSetMetadata();
220 bool doInitialization(Module &M) override;
221 bool runOnModule(Module &M) override;
226 INITIALIZE_PASS_BEGIN(LowerBitSets, "lowerbitsets",
227 "Lower bitset metadata", false, false)
228 INITIALIZE_PASS_END(LowerBitSets, "lowerbitsets",
229 "Lower bitset metadata", false, false)
230 char LowerBitSets::ID = 0;
232 ModulePass *llvm::createLowerBitSetsPass() { return new LowerBitSets; }
234 bool LowerBitSets::doInitialization(Module &Mod) {
236 const DataLayout &DL = Mod.getDataLayout();
238 Int1Ty = Type::getInt1Ty(M->getContext());
239 Int8Ty = Type::getInt8Ty(M->getContext());
240 Int32Ty = Type::getInt32Ty(M->getContext());
241 Int32PtrTy = PointerType::getUnqual(Int32Ty);
242 Int64Ty = Type::getInt64Ty(M->getContext());
243 IntPtrTy = DL.getIntPtrType(M->getContext(), 0);
245 BitSetNM = M->getNamedMetadata("llvm.bitsets");
247 BitSetTestCallSites.clear();
252 /// Build a bit set for BitSet using the object layouts in
254 BitSetInfo LowerBitSets::buildBitSet(
256 const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout) {
259 // Compute the byte offset of each element of this bitset.
261 for (MDNode *Op : BitSetNM->operands()) {
262 if (Op->getOperand(0) != BitSet || !Op->getOperand(1))
264 auto OpGlobal = cast<GlobalVariable>(
265 cast<ConstantAsMetadata>(Op->getOperand(1))->getValue());
267 cast<ConstantInt>(cast<ConstantAsMetadata>(Op->getOperand(2))
268 ->getValue())->getZExtValue();
270 Offset += GlobalLayout.find(OpGlobal)->second;
272 BSB.addOffset(Offset);
279 /// Build a test that bit BitOffset mod sizeof(Bits)*8 is set in
280 /// Bits. This pattern matches to the bt instruction on x86.
281 static Value *createMaskedBitTest(IRBuilder<> &B, Value *Bits,
283 auto BitsType = cast<IntegerType>(Bits->getType());
284 unsigned BitWidth = BitsType->getBitWidth();
286 BitOffset = B.CreateZExtOrTrunc(BitOffset, BitsType);
288 B.CreateAnd(BitOffset, ConstantInt::get(BitsType, BitWidth - 1));
289 Value *BitMask = B.CreateShl(ConstantInt::get(BitsType, 1), BitIndex);
290 Value *MaskedBits = B.CreateAnd(Bits, BitMask);
291 return B.CreateICmpNE(MaskedBits, ConstantInt::get(BitsType, 0));
294 ByteArrayInfo *LowerBitSets::createByteArray(BitSetInfo &BSI) {
295 // Create globals to stand in for byte arrays and masks. These never actually
296 // get initialized, we RAUW and erase them later in allocateByteArrays() once
297 // we know the offset and mask to use.
298 auto ByteArrayGlobal = new GlobalVariable(
299 *M, Int8Ty, /*isConstant=*/true, GlobalValue::PrivateLinkage, nullptr);
300 auto MaskGlobal = new GlobalVariable(
301 *M, Int8Ty, /*isConstant=*/true, GlobalValue::PrivateLinkage, nullptr);
303 ByteArrayInfos.emplace_back();
304 ByteArrayInfo *BAI = &ByteArrayInfos.back();
306 BAI->Bits = BSI.Bits;
307 BAI->BitSize = BSI.BitSize;
308 BAI->ByteArray = ByteArrayGlobal;
309 BAI->Mask = ConstantExpr::getPtrToInt(MaskGlobal, Int8Ty);
313 void LowerBitSets::allocateByteArrays() {
314 std::stable_sort(ByteArrayInfos.begin(), ByteArrayInfos.end(),
315 [](const ByteArrayInfo &BAI1, const ByteArrayInfo &BAI2) {
316 return BAI1.BitSize > BAI2.BitSize;
319 std::vector<uint64_t> ByteArrayOffsets(ByteArrayInfos.size());
321 ByteArrayBuilder BAB;
322 for (unsigned I = 0; I != ByteArrayInfos.size(); ++I) {
323 ByteArrayInfo *BAI = &ByteArrayInfos[I];
326 BAB.allocate(BAI->Bits, BAI->BitSize, ByteArrayOffsets[I], Mask);
328 BAI->Mask->replaceAllUsesWith(ConstantInt::get(Int8Ty, Mask));
329 cast<GlobalVariable>(BAI->Mask->getOperand(0))->eraseFromParent();
332 Constant *ByteArrayConst = ConstantDataArray::get(M->getContext(), BAB.Bytes);
334 new GlobalVariable(*M, ByteArrayConst->getType(), /*isConstant=*/true,
335 GlobalValue::PrivateLinkage, ByteArrayConst);
337 for (unsigned I = 0; I != ByteArrayInfos.size(); ++I) {
338 ByteArrayInfo *BAI = &ByteArrayInfos[I];
340 Constant *Idxs[] = {ConstantInt::get(IntPtrTy, 0),
341 ConstantInt::get(IntPtrTy, ByteArrayOffsets[I])};
342 Constant *GEP = ConstantExpr::getInBoundsGetElementPtr(ByteArray, Idxs);
344 // Create an alias instead of RAUW'ing the gep directly. On x86 this ensures
345 // that the pc-relative displacement is folded into the lea instead of the
346 // test instruction getting another displacement.
347 GlobalAlias *Alias = GlobalAlias::create(
348 Int8Ty, 0, GlobalValue::PrivateLinkage, "bits", GEP, M);
349 BAI->ByteArray->replaceAllUsesWith(Alias);
350 BAI->ByteArray->eraseFromParent();
353 ByteArraySizeBits = BAB.BitAllocs[0] + BAB.BitAllocs[1] + BAB.BitAllocs[2] +
354 BAB.BitAllocs[3] + BAB.BitAllocs[4] + BAB.BitAllocs[5] +
355 BAB.BitAllocs[6] + BAB.BitAllocs[7];
356 ByteArraySizeBytes = BAB.Bytes.size();
359 /// Build a test that bit BitOffset is set in BSI, where
360 /// BitSetGlobal is a global containing the bits in BSI.
361 Value *LowerBitSets::createBitSetTest(IRBuilder<> &B, BitSetInfo &BSI,
362 ByteArrayInfo *&BAI, Value *BitOffset) {
363 if (BSI.BitSize <= 64) {
364 // If the bit set is sufficiently small, we can avoid a load by bit testing
367 if (BSI.BitSize <= 32)
373 for (auto Bit : BSI.Bits)
374 Bits |= uint64_t(1) << Bit;
375 Constant *BitsConst = ConstantInt::get(BitsTy, Bits);
376 return createMaskedBitTest(B, BitsConst, BitOffset);
379 ++NumByteArraysCreated;
380 BAI = createByteArray(BSI);
383 Value *ByteAddr = B.CreateGEP(BAI->ByteArray, BitOffset);
384 Value *Byte = B.CreateLoad(ByteAddr);
386 Value *ByteAndMask = B.CreateAnd(Byte, BAI->Mask);
387 return B.CreateICmpNE(ByteAndMask, ConstantInt::get(Int8Ty, 0));
391 /// Lower a llvm.bitset.test call to its implementation. Returns the value to
392 /// replace the call with.
393 Value *LowerBitSets::lowerBitSetCall(
394 CallInst *CI, BitSetInfo &BSI, ByteArrayInfo *&BAI,
395 GlobalVariable *CombinedGlobal,
396 const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout) {
397 Value *Ptr = CI->getArgOperand(0);
398 const DataLayout &DL = M->getDataLayout();
400 if (BSI.containsValue(DL, GlobalLayout, Ptr))
401 return ConstantInt::getTrue(CombinedGlobal->getParent()->getContext());
403 Constant *GlobalAsInt = ConstantExpr::getPtrToInt(CombinedGlobal, IntPtrTy);
404 Constant *OffsetedGlobalAsInt = ConstantExpr::getAdd(
405 GlobalAsInt, ConstantInt::get(IntPtrTy, BSI.ByteOffset));
407 BasicBlock *InitialBB = CI->getParent();
411 Value *PtrAsInt = B.CreatePtrToInt(Ptr, IntPtrTy);
413 if (BSI.isSingleOffset())
414 return B.CreateICmpEQ(PtrAsInt, OffsetedGlobalAsInt);
416 Value *PtrOffset = B.CreateSub(PtrAsInt, OffsetedGlobalAsInt);
419 if (BSI.AlignLog2 == 0) {
420 BitOffset = PtrOffset;
422 // We need to check that the offset both falls within our range and is
423 // suitably aligned. We can check both properties at the same time by
424 // performing a right rotate by log2(alignment) followed by an integer
425 // comparison against the bitset size. The rotate will move the lower
426 // order bits that need to be zero into the higher order bits of the
427 // result, causing the comparison to fail if they are nonzero. The rotate
428 // also conveniently gives us a bit offset to use during the load from
431 B.CreateLShr(PtrOffset, ConstantInt::get(IntPtrTy, BSI.AlignLog2));
432 Value *OffsetSHL = B.CreateShl(
434 ConstantInt::get(IntPtrTy, DL.getPointerSizeInBits(0) - BSI.AlignLog2));
435 BitOffset = B.CreateOr(OffsetSHR, OffsetSHL);
438 Constant *BitSizeConst = ConstantInt::get(IntPtrTy, BSI.BitSize);
439 Value *OffsetInRange = B.CreateICmpULT(BitOffset, BitSizeConst);
441 // If the bit set is all ones, testing against it is unnecessary.
443 return OffsetInRange;
445 TerminatorInst *Term = SplitBlockAndInsertIfThen(OffsetInRange, CI, false);
446 IRBuilder<> ThenB(Term);
448 // Now that we know that the offset is in range and aligned, load the
449 // appropriate bit from the bitset.
450 Value *Bit = createBitSetTest(ThenB, BSI, BAI, BitOffset);
452 // The value we want is 0 if we came directly from the initial block
453 // (having failed the range or alignment checks), or the loaded bit if
454 // we came from the block in which we loaded it.
455 B.SetInsertPoint(CI);
456 PHINode *P = B.CreatePHI(Int1Ty, 2);
457 P->addIncoming(ConstantInt::get(Int1Ty, 0), InitialBB);
458 P->addIncoming(Bit, ThenB.GetInsertBlock());
462 /// Given a disjoint set of bitsets and globals, layout the globals, build the
463 /// bit sets and lower the llvm.bitset.test calls.
464 void LowerBitSets::buildBitSetsFromGlobals(
465 const std::vector<MDString *> &BitSets,
466 const std::vector<GlobalVariable *> &Globals) {
467 // Build a new global with the combined contents of the referenced globals.
468 std::vector<Constant *> GlobalInits;
469 const DataLayout &DL = M->getDataLayout();
470 for (GlobalVariable *G : Globals) {
471 GlobalInits.push_back(G->getInitializer());
472 uint64_t InitSize = DL.getTypeAllocSize(G->getInitializer()->getType());
474 // Compute the amount of padding required to align the next element to the
476 uint64_t Padding = NextPowerOf2(InitSize - 1) - InitSize;
478 // Cap at 128 was found experimentally to have a good data/instruction
479 // overhead tradeoff.
481 Padding = RoundUpToAlignment(InitSize, 128) - InitSize;
483 GlobalInits.push_back(
484 ConstantAggregateZero::get(ArrayType::get(Int8Ty, Padding)));
486 if (!GlobalInits.empty())
487 GlobalInits.pop_back();
488 Constant *NewInit = ConstantStruct::getAnon(M->getContext(), GlobalInits);
489 auto CombinedGlobal =
490 new GlobalVariable(*M, NewInit->getType(), /*isConstant=*/true,
491 GlobalValue::PrivateLinkage, NewInit);
493 const StructLayout *CombinedGlobalLayout =
494 DL.getStructLayout(cast<StructType>(NewInit->getType()));
496 // Compute the offsets of the original globals within the new global.
497 DenseMap<GlobalVariable *, uint64_t> GlobalLayout;
498 for (unsigned I = 0; I != Globals.size(); ++I)
499 // Multiply by 2 to account for padding elements.
500 GlobalLayout[Globals[I]] = CombinedGlobalLayout->getElementOffset(I * 2);
502 // For each bitset in this disjoint set...
503 for (MDString *BS : BitSets) {
505 BitSetInfo BSI = buildBitSet(BS, GlobalLayout);
507 ByteArrayInfo *BAI = 0;
509 // Lower each call to llvm.bitset.test for this bitset.
510 for (CallInst *CI : BitSetTestCallSites[BS]) {
511 ++NumBitSetCallsLowered;
512 Value *Lowered = lowerBitSetCall(CI, BSI, BAI, CombinedGlobal, GlobalLayout);
513 CI->replaceAllUsesWith(Lowered);
514 CI->eraseFromParent();
518 // Build aliases pointing to offsets into the combined global for each
519 // global from which we built the combined global, and replace references
520 // to the original globals with references to the aliases.
521 for (unsigned I = 0; I != Globals.size(); ++I) {
522 // Multiply by 2 to account for padding elements.
523 Constant *CombinedGlobalIdxs[] = {ConstantInt::get(Int32Ty, 0),
524 ConstantInt::get(Int32Ty, I * 2)};
525 Constant *CombinedGlobalElemPtr =
526 ConstantExpr::getGetElementPtr(CombinedGlobal, CombinedGlobalIdxs);
527 GlobalAlias *GAlias = GlobalAlias::create(
528 Globals[I]->getType()->getElementType(),
529 Globals[I]->getType()->getAddressSpace(), Globals[I]->getLinkage(),
530 "", CombinedGlobalElemPtr, M);
531 GAlias->takeName(Globals[I]);
532 Globals[I]->replaceAllUsesWith(GAlias);
533 Globals[I]->eraseFromParent();
537 /// Lower all bit sets in this module.
538 bool LowerBitSets::buildBitSets() {
539 Function *BitSetTestFunc =
540 M->getFunction(Intrinsic::getName(Intrinsic::bitset_test));
544 // Equivalence class set containing bitsets and the globals they reference.
545 // This is used to partition the set of bitsets in the module into disjoint
547 typedef EquivalenceClasses<PointerUnion<GlobalVariable *, MDString *>>
549 GlobalClassesTy GlobalClasses;
551 for (const Use &U : BitSetTestFunc->uses()) {
552 auto CI = cast<CallInst>(U.getUser());
554 auto BitSetMDVal = dyn_cast<MetadataAsValue>(CI->getArgOperand(1));
555 if (!BitSetMDVal || !isa<MDString>(BitSetMDVal->getMetadata()))
557 "Second argument of llvm.bitset.test must be metadata string");
558 auto BitSet = cast<MDString>(BitSetMDVal->getMetadata());
560 // Add the call site to the list of call sites for this bit set. We also use
561 // BitSetTestCallSites to keep track of whether we have seen this bit set
562 // before. If we have, we don't need to re-add the referenced globals to the
563 // equivalence class.
564 std::pair<DenseMap<MDString *, std::vector<CallInst *>>::iterator,
566 BitSetTestCallSites.insert(
567 std::make_pair(BitSet, std::vector<CallInst *>()));
568 Ins.first->second.push_back(CI);
572 // Add the bitset to the equivalence class.
573 GlobalClassesTy::iterator GCI = GlobalClasses.insert(BitSet);
574 GlobalClassesTy::member_iterator CurSet = GlobalClasses.findLeader(GCI);
579 // Verify the bitset metadata and add the referenced globals to the bitset's
580 // equivalence class.
581 for (MDNode *Op : BitSetNM->operands()) {
582 if (Op->getNumOperands() != 3)
584 "All operands of llvm.bitsets metadata must have 3 elements");
586 if (Op->getOperand(0) != BitSet || !Op->getOperand(1))
589 auto OpConstMD = dyn_cast<ConstantAsMetadata>(Op->getOperand(1));
591 report_fatal_error("Bit set element must be a constant");
592 auto OpGlobal = dyn_cast<GlobalVariable>(OpConstMD->getValue());
594 report_fatal_error("Bit set element must refer to global");
596 auto OffsetConstMD = dyn_cast<ConstantAsMetadata>(Op->getOperand(2));
598 report_fatal_error("Bit set element offset must be a constant");
599 auto OffsetInt = dyn_cast<ConstantInt>(OffsetConstMD->getValue());
602 "Bit set element offset must be an integer constant");
604 CurSet = GlobalClasses.unionSets(
605 CurSet, GlobalClasses.findLeader(GlobalClasses.insert(OpGlobal)));
609 if (GlobalClasses.empty())
612 // For each disjoint set we found...
613 for (GlobalClassesTy::iterator I = GlobalClasses.begin(),
614 E = GlobalClasses.end();
616 if (!I->isLeader()) continue;
618 ++NumBitSetDisjointSets;
620 // Build the list of bitsets and referenced globals in this disjoint set.
621 std::vector<MDString *> BitSets;
622 std::vector<GlobalVariable *> Globals;
623 llvm::DenseMap<MDString *, uint64_t> BitSetIndices;
624 llvm::DenseMap<GlobalVariable *, uint64_t> GlobalIndices;
625 for (GlobalClassesTy::member_iterator MI = GlobalClasses.member_begin(I);
626 MI != GlobalClasses.member_end(); ++MI) {
627 if ((*MI).is<MDString *>()) {
628 BitSetIndices[MI->get<MDString *>()] = BitSets.size();
629 BitSets.push_back(MI->get<MDString *>());
631 GlobalIndices[MI->get<GlobalVariable *>()] = Globals.size();
632 Globals.push_back(MI->get<GlobalVariable *>());
636 // For each bitset, build a set of indices that refer to globals referenced
638 std::vector<std::set<uint64_t>> BitSetMembers(BitSets.size());
640 for (MDNode *Op : BitSetNM->operands()) {
641 // Op = { bitset name, global, offset }
642 if (!Op->getOperand(1))
644 auto I = BitSetIndices.find(cast<MDString>(Op->getOperand(0)));
645 if (I == BitSetIndices.end())
648 auto OpGlobal = cast<GlobalVariable>(
649 cast<ConstantAsMetadata>(Op->getOperand(1))->getValue());
650 BitSetMembers[I->second].insert(GlobalIndices[OpGlobal]);
654 // Order the sets of indices by size. The GlobalLayoutBuilder works best
655 // when given small index sets first.
657 BitSetMembers.begin(), BitSetMembers.end(),
658 [](const std::set<uint64_t> &O1, const std::set<uint64_t> &O2) {
659 return O1.size() < O2.size();
662 // Create a GlobalLayoutBuilder and provide it with index sets as layout
663 // fragments. The GlobalLayoutBuilder tries to lay out members of fragments
664 // as close together as possible.
665 GlobalLayoutBuilder GLB(Globals.size());
666 for (auto &&MemSet : BitSetMembers)
667 GLB.addFragment(MemSet);
669 // Build a vector of globals with the computed layout.
670 std::vector<GlobalVariable *> OrderedGlobals(Globals.size());
671 auto OGI = OrderedGlobals.begin();
672 for (auto &&F : GLB.Fragments)
673 for (auto &&Offset : F)
674 *OGI++ = Globals[Offset];
676 // Order bitsets by name for determinism.
677 std::sort(BitSets.begin(), BitSets.end(), [](MDString *S1, MDString *S2) {
678 return S1->getString() < S2->getString();
681 // Build the bitsets from this disjoint set.
682 buildBitSetsFromGlobals(BitSets, OrderedGlobals);
685 allocateByteArrays();
690 bool LowerBitSets::eraseBitSetMetadata() {
694 M->eraseNamedMetadata(BitSetNM);
698 bool LowerBitSets::runOnModule(Module &M) {
699 bool Changed = buildBitSets();
700 Changed |= eraseBitSetMetadata();