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/ADT/Triple.h"
20 #include "llvm/IR/Constant.h"
21 #include "llvm/IR/Constants.h"
22 #include "llvm/IR/GlobalVariable.h"
23 #include "llvm/IR/IRBuilder.h"
24 #include "llvm/IR/Instructions.h"
25 #include "llvm/IR/Intrinsics.h"
26 #include "llvm/IR/Module.h"
27 #include "llvm/IR/Operator.h"
28 #include "llvm/Pass.h"
29 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
33 #define DEBUG_TYPE "lowerbitsets"
35 STATISTIC(ByteArraySizeBits, "Byte array size in bits");
36 STATISTIC(ByteArraySizeBytes, "Byte array size in bytes");
37 STATISTIC(NumByteArraysCreated, "Number of byte arrays created");
38 STATISTIC(NumBitSetCallsLowered, "Number of bitset calls lowered");
39 STATISTIC(NumBitSetDisjointSets, "Number of disjoint sets of bitsets");
41 static cl::opt<bool> AvoidReuse(
42 "lowerbitsets-avoid-reuse",
43 cl::desc("Try to avoid reuse of byte array addresses using aliases"),
44 cl::Hidden, cl::init(true));
46 bool BitSetInfo::containsGlobalOffset(uint64_t Offset) const {
47 if (Offset < ByteOffset)
50 if ((Offset - ByteOffset) % (uint64_t(1) << AlignLog2) != 0)
53 uint64_t BitOffset = (Offset - ByteOffset) >> AlignLog2;
54 if (BitOffset >= BitSize)
57 return Bits.count(BitOffset);
60 bool BitSetInfo::containsValue(
62 const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout, Value *V,
63 uint64_t COffset) const {
64 if (auto GV = dyn_cast<GlobalVariable>(V)) {
65 auto I = GlobalLayout.find(GV);
66 if (I == GlobalLayout.end())
68 return containsGlobalOffset(I->second + COffset);
71 if (auto GEP = dyn_cast<GEPOperator>(V)) {
72 APInt APOffset(DL.getPointerSizeInBits(0), 0);
73 bool Result = GEP->accumulateConstantOffset(DL, APOffset);
76 COffset += APOffset.getZExtValue();
77 return containsValue(DL, GlobalLayout, GEP->getPointerOperand(),
81 if (auto Op = dyn_cast<Operator>(V)) {
82 if (Op->getOpcode() == Instruction::BitCast)
83 return containsValue(DL, GlobalLayout, Op->getOperand(0), COffset);
85 if (Op->getOpcode() == Instruction::Select)
86 return containsValue(DL, GlobalLayout, Op->getOperand(1), COffset) &&
87 containsValue(DL, GlobalLayout, Op->getOperand(2), COffset);
93 BitSetInfo BitSetBuilder::build() {
97 // Normalize each offset against the minimum observed offset, and compute
98 // the bitwise OR of each of the offsets. The number of trailing zeros
99 // in the mask gives us the log2 of the alignment of all offsets, which
100 // allows us to compress the bitset by only storing one bit per aligned
103 for (uint64_t &Offset : Offsets) {
109 BSI.ByteOffset = Min;
113 BSI.AlignLog2 = countTrailingZeros(Mask, ZB_Undefined);
115 // Build the compressed bitset while normalizing the offsets against the
116 // computed alignment.
117 BSI.BitSize = ((Max - Min) >> BSI.AlignLog2) + 1;
118 for (uint64_t Offset : Offsets) {
119 Offset >>= BSI.AlignLog2;
120 BSI.Bits.insert(Offset);
126 void GlobalLayoutBuilder::addFragment(const std::set<uint64_t> &F) {
127 // Create a new fragment to hold the layout for F.
128 Fragments.emplace_back();
129 std::vector<uint64_t> &Fragment = Fragments.back();
130 uint64_t FragmentIndex = Fragments.size() - 1;
132 for (auto ObjIndex : F) {
133 uint64_t OldFragmentIndex = FragmentMap[ObjIndex];
134 if (OldFragmentIndex == 0) {
135 // We haven't seen this object index before, so just add it to the current
137 Fragment.push_back(ObjIndex);
139 // This index belongs to an existing fragment. Copy the elements of the
140 // old fragment into this one and clear the old fragment. We don't update
141 // the fragment map just yet, this ensures that any further references to
142 // indices from the old fragment in this fragment do not insert any more
144 std::vector<uint64_t> &OldFragment = Fragments[OldFragmentIndex];
145 Fragment.insert(Fragment.end(), OldFragment.begin(), OldFragment.end());
150 // Update the fragment map to point our object indices to this fragment.
151 for (uint64_t ObjIndex : Fragment)
152 FragmentMap[ObjIndex] = FragmentIndex;
155 void ByteArrayBuilder::allocate(const std::set<uint64_t> &Bits,
156 uint64_t BitSize, uint64_t &AllocByteOffset,
157 uint8_t &AllocMask) {
158 // Find the smallest current allocation.
160 for (unsigned I = 1; I != BitsPerByte; ++I)
161 if (BitAllocs[I] < BitAllocs[Bit])
164 AllocByteOffset = BitAllocs[Bit];
166 // Add our size to it.
167 unsigned ReqSize = AllocByteOffset + BitSize;
168 BitAllocs[Bit] = ReqSize;
169 if (Bytes.size() < ReqSize)
170 Bytes.resize(ReqSize);
173 AllocMask = 1 << Bit;
174 for (uint64_t B : Bits)
175 Bytes[AllocByteOffset + B] |= AllocMask;
180 struct ByteArrayInfo {
181 std::set<uint64_t> Bits;
183 GlobalVariable *ByteArray;
187 struct LowerBitSets : public ModulePass {
189 LowerBitSets() : ModulePass(ID) {
190 initializeLowerBitSetsPass(*PassRegistry::getPassRegistry());
195 bool LinkerSubsectionsViaSymbols;
198 IntegerType *Int32Ty;
200 IntegerType *Int64Ty;
203 // The llvm.bitsets named metadata.
204 NamedMDNode *BitSetNM;
206 // Mapping from bitset mdstrings to the call sites that test them.
207 DenseMap<MDString *, std::vector<CallInst *>> BitSetTestCallSites;
209 std::vector<ByteArrayInfo> ByteArrayInfos;
212 buildBitSet(MDString *BitSet,
213 const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout);
214 ByteArrayInfo *createByteArray(BitSetInfo &BSI);
215 void allocateByteArrays();
216 Value *createBitSetTest(IRBuilder<> &B, BitSetInfo &BSI, ByteArrayInfo *&BAI,
219 lowerBitSetCall(CallInst *CI, BitSetInfo &BSI, ByteArrayInfo *&BAI,
220 GlobalVariable *CombinedGlobal,
221 const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout);
222 void buildBitSetsFromGlobals(const std::vector<MDString *> &BitSets,
223 const std::vector<GlobalVariable *> &Globals);
225 bool eraseBitSetMetadata();
227 bool doInitialization(Module &M) override;
228 bool runOnModule(Module &M) override;
233 INITIALIZE_PASS_BEGIN(LowerBitSets, "lowerbitsets",
234 "Lower bitset metadata", false, false)
235 INITIALIZE_PASS_END(LowerBitSets, "lowerbitsets",
236 "Lower bitset metadata", false, false)
237 char LowerBitSets::ID = 0;
239 ModulePass *llvm::createLowerBitSetsPass() { return new LowerBitSets; }
241 bool LowerBitSets::doInitialization(Module &Mod) {
243 const DataLayout &DL = Mod.getDataLayout();
245 Triple TargetTriple(M->getTargetTriple());
246 LinkerSubsectionsViaSymbols = TargetTriple.isMacOSX();
248 Int1Ty = Type::getInt1Ty(M->getContext());
249 Int8Ty = Type::getInt8Ty(M->getContext());
250 Int32Ty = Type::getInt32Ty(M->getContext());
251 Int32PtrTy = PointerType::getUnqual(Int32Ty);
252 Int64Ty = Type::getInt64Ty(M->getContext());
253 IntPtrTy = DL.getIntPtrType(M->getContext(), 0);
255 BitSetNM = M->getNamedMetadata("llvm.bitsets");
257 BitSetTestCallSites.clear();
262 /// Build a bit set for BitSet using the object layouts in
264 BitSetInfo LowerBitSets::buildBitSet(
266 const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout) {
269 // Compute the byte offset of each element of this bitset.
271 for (MDNode *Op : BitSetNM->operands()) {
272 if (Op->getOperand(0) != BitSet || !Op->getOperand(1))
274 auto OpGlobal = cast<GlobalVariable>(
275 cast<ConstantAsMetadata>(Op->getOperand(1))->getValue());
277 cast<ConstantInt>(cast<ConstantAsMetadata>(Op->getOperand(2))
278 ->getValue())->getZExtValue();
280 Offset += GlobalLayout.find(OpGlobal)->second;
282 BSB.addOffset(Offset);
289 /// Build a test that bit BitOffset mod sizeof(Bits)*8 is set in
290 /// Bits. This pattern matches to the bt instruction on x86.
291 static Value *createMaskedBitTest(IRBuilder<> &B, Value *Bits,
293 auto BitsType = cast<IntegerType>(Bits->getType());
294 unsigned BitWidth = BitsType->getBitWidth();
296 BitOffset = B.CreateZExtOrTrunc(BitOffset, BitsType);
298 B.CreateAnd(BitOffset, ConstantInt::get(BitsType, BitWidth - 1));
299 Value *BitMask = B.CreateShl(ConstantInt::get(BitsType, 1), BitIndex);
300 Value *MaskedBits = B.CreateAnd(Bits, BitMask);
301 return B.CreateICmpNE(MaskedBits, ConstantInt::get(BitsType, 0));
304 ByteArrayInfo *LowerBitSets::createByteArray(BitSetInfo &BSI) {
305 // Create globals to stand in for byte arrays and masks. These never actually
306 // get initialized, we RAUW and erase them later in allocateByteArrays() once
307 // we know the offset and mask to use.
308 auto ByteArrayGlobal = new GlobalVariable(
309 *M, Int8Ty, /*isConstant=*/true, GlobalValue::PrivateLinkage, nullptr);
310 auto MaskGlobal = new GlobalVariable(
311 *M, Int8Ty, /*isConstant=*/true, GlobalValue::PrivateLinkage, nullptr);
313 ByteArrayInfos.emplace_back();
314 ByteArrayInfo *BAI = &ByteArrayInfos.back();
316 BAI->Bits = BSI.Bits;
317 BAI->BitSize = BSI.BitSize;
318 BAI->ByteArray = ByteArrayGlobal;
319 BAI->Mask = ConstantExpr::getPtrToInt(MaskGlobal, Int8Ty);
323 void LowerBitSets::allocateByteArrays() {
324 std::stable_sort(ByteArrayInfos.begin(), ByteArrayInfos.end(),
325 [](const ByteArrayInfo &BAI1, const ByteArrayInfo &BAI2) {
326 return BAI1.BitSize > BAI2.BitSize;
329 std::vector<uint64_t> ByteArrayOffsets(ByteArrayInfos.size());
331 ByteArrayBuilder BAB;
332 for (unsigned I = 0; I != ByteArrayInfos.size(); ++I) {
333 ByteArrayInfo *BAI = &ByteArrayInfos[I];
336 BAB.allocate(BAI->Bits, BAI->BitSize, ByteArrayOffsets[I], Mask);
338 BAI->Mask->replaceAllUsesWith(ConstantInt::get(Int8Ty, Mask));
339 cast<GlobalVariable>(BAI->Mask->getOperand(0))->eraseFromParent();
342 Constant *ByteArrayConst = ConstantDataArray::get(M->getContext(), BAB.Bytes);
344 new GlobalVariable(*M, ByteArrayConst->getType(), /*isConstant=*/true,
345 GlobalValue::PrivateLinkage, ByteArrayConst);
347 for (unsigned I = 0; I != ByteArrayInfos.size(); ++I) {
348 ByteArrayInfo *BAI = &ByteArrayInfos[I];
350 Constant *Idxs[] = {ConstantInt::get(IntPtrTy, 0),
351 ConstantInt::get(IntPtrTy, ByteArrayOffsets[I])};
352 Constant *GEP = ConstantExpr::getInBoundsGetElementPtr(
353 ByteArrayConst->getType(), ByteArray, Idxs);
355 // Create an alias instead of RAUW'ing the gep directly. On x86 this ensures
356 // that the pc-relative displacement is folded into the lea instead of the
357 // test instruction getting another displacement.
358 if (LinkerSubsectionsViaSymbols) {
359 BAI->ByteArray->replaceAllUsesWith(GEP);
361 GlobalAlias *Alias = GlobalAlias::create(
362 Int8Ty, 0, GlobalValue::PrivateLinkage, "bits", GEP, M);
363 BAI->ByteArray->replaceAllUsesWith(Alias);
365 BAI->ByteArray->eraseFromParent();
368 ByteArraySizeBits = BAB.BitAllocs[0] + BAB.BitAllocs[1] + BAB.BitAllocs[2] +
369 BAB.BitAllocs[3] + BAB.BitAllocs[4] + BAB.BitAllocs[5] +
370 BAB.BitAllocs[6] + BAB.BitAllocs[7];
371 ByteArraySizeBytes = BAB.Bytes.size();
374 /// Build a test that bit BitOffset is set in BSI, where
375 /// BitSetGlobal is a global containing the bits in BSI.
376 Value *LowerBitSets::createBitSetTest(IRBuilder<> &B, BitSetInfo &BSI,
377 ByteArrayInfo *&BAI, Value *BitOffset) {
378 if (BSI.BitSize <= 64) {
379 // If the bit set is sufficiently small, we can avoid a load by bit testing
382 if (BSI.BitSize <= 32)
388 for (auto Bit : BSI.Bits)
389 Bits |= uint64_t(1) << Bit;
390 Constant *BitsConst = ConstantInt::get(BitsTy, Bits);
391 return createMaskedBitTest(B, BitsConst, BitOffset);
394 ++NumByteArraysCreated;
395 BAI = createByteArray(BSI);
398 Constant *ByteArray = BAI->ByteArray;
399 Type *Ty = BAI->ByteArray->getValueType();
400 if (!LinkerSubsectionsViaSymbols && AvoidReuse) {
401 // Each use of the byte array uses a different alias. This makes the
402 // backend less likely to reuse previously computed byte array addresses,
403 // improving the security of the CFI mechanism based on this pass.
404 ByteArray = GlobalAlias::create(BAI->ByteArray->getValueType(), 0,
405 GlobalValue::PrivateLinkage, "bits_use",
409 Value *ByteAddr = B.CreateGEP(Ty, ByteArray, BitOffset);
410 Value *Byte = B.CreateLoad(ByteAddr);
412 Value *ByteAndMask = B.CreateAnd(Byte, BAI->Mask);
413 return B.CreateICmpNE(ByteAndMask, ConstantInt::get(Int8Ty, 0));
417 /// Lower a llvm.bitset.test call to its implementation. Returns the value to
418 /// replace the call with.
419 Value *LowerBitSets::lowerBitSetCall(
420 CallInst *CI, BitSetInfo &BSI, ByteArrayInfo *&BAI,
421 GlobalVariable *CombinedGlobal,
422 const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout) {
423 Value *Ptr = CI->getArgOperand(0);
424 const DataLayout &DL = M->getDataLayout();
426 if (BSI.containsValue(DL, GlobalLayout, Ptr))
427 return ConstantInt::getTrue(CombinedGlobal->getParent()->getContext());
429 Constant *GlobalAsInt = ConstantExpr::getPtrToInt(CombinedGlobal, IntPtrTy);
430 Constant *OffsetedGlobalAsInt = ConstantExpr::getAdd(
431 GlobalAsInt, ConstantInt::get(IntPtrTy, BSI.ByteOffset));
433 BasicBlock *InitialBB = CI->getParent();
437 Value *PtrAsInt = B.CreatePtrToInt(Ptr, IntPtrTy);
439 if (BSI.isSingleOffset())
440 return B.CreateICmpEQ(PtrAsInt, OffsetedGlobalAsInt);
442 Value *PtrOffset = B.CreateSub(PtrAsInt, OffsetedGlobalAsInt);
445 if (BSI.AlignLog2 == 0) {
446 BitOffset = PtrOffset;
448 // We need to check that the offset both falls within our range and is
449 // suitably aligned. We can check both properties at the same time by
450 // performing a right rotate by log2(alignment) followed by an integer
451 // comparison against the bitset size. The rotate will move the lower
452 // order bits that need to be zero into the higher order bits of the
453 // result, causing the comparison to fail if they are nonzero. The rotate
454 // also conveniently gives us a bit offset to use during the load from
457 B.CreateLShr(PtrOffset, ConstantInt::get(IntPtrTy, BSI.AlignLog2));
458 Value *OffsetSHL = B.CreateShl(
460 ConstantInt::get(IntPtrTy, DL.getPointerSizeInBits(0) - BSI.AlignLog2));
461 BitOffset = B.CreateOr(OffsetSHR, OffsetSHL);
464 Constant *BitSizeConst = ConstantInt::get(IntPtrTy, BSI.BitSize);
465 Value *OffsetInRange = B.CreateICmpULT(BitOffset, BitSizeConst);
467 // If the bit set is all ones, testing against it is unnecessary.
469 return OffsetInRange;
471 TerminatorInst *Term = SplitBlockAndInsertIfThen(OffsetInRange, CI, false);
472 IRBuilder<> ThenB(Term);
474 // Now that we know that the offset is in range and aligned, load the
475 // appropriate bit from the bitset.
476 Value *Bit = createBitSetTest(ThenB, BSI, BAI, BitOffset);
478 // The value we want is 0 if we came directly from the initial block
479 // (having failed the range or alignment checks), or the loaded bit if
480 // we came from the block in which we loaded it.
481 B.SetInsertPoint(CI);
482 PHINode *P = B.CreatePHI(Int1Ty, 2);
483 P->addIncoming(ConstantInt::get(Int1Ty, 0), InitialBB);
484 P->addIncoming(Bit, ThenB.GetInsertBlock());
488 /// Given a disjoint set of bitsets and globals, layout the globals, build the
489 /// bit sets and lower the llvm.bitset.test calls.
490 void LowerBitSets::buildBitSetsFromGlobals(
491 const std::vector<MDString *> &BitSets,
492 const std::vector<GlobalVariable *> &Globals) {
493 // Build a new global with the combined contents of the referenced globals.
494 std::vector<Constant *> GlobalInits;
495 const DataLayout &DL = M->getDataLayout();
496 for (GlobalVariable *G : Globals) {
497 GlobalInits.push_back(G->getInitializer());
498 uint64_t InitSize = DL.getTypeAllocSize(G->getInitializer()->getType());
500 // Compute the amount of padding required to align the next element to the
502 uint64_t Padding = NextPowerOf2(InitSize - 1) - InitSize;
504 // Cap at 128 was found experimentally to have a good data/instruction
505 // overhead tradeoff.
507 Padding = RoundUpToAlignment(InitSize, 128) - InitSize;
509 GlobalInits.push_back(
510 ConstantAggregateZero::get(ArrayType::get(Int8Ty, Padding)));
512 if (!GlobalInits.empty())
513 GlobalInits.pop_back();
514 Constant *NewInit = ConstantStruct::getAnon(M->getContext(), GlobalInits);
515 auto CombinedGlobal =
516 new GlobalVariable(*M, NewInit->getType(), /*isConstant=*/true,
517 GlobalValue::PrivateLinkage, NewInit);
519 const StructLayout *CombinedGlobalLayout =
520 DL.getStructLayout(cast<StructType>(NewInit->getType()));
522 // Compute the offsets of the original globals within the new global.
523 DenseMap<GlobalVariable *, uint64_t> GlobalLayout;
524 for (unsigned I = 0; I != Globals.size(); ++I)
525 // Multiply by 2 to account for padding elements.
526 GlobalLayout[Globals[I]] = CombinedGlobalLayout->getElementOffset(I * 2);
528 // For each bitset in this disjoint set...
529 for (MDString *BS : BitSets) {
531 BitSetInfo BSI = buildBitSet(BS, GlobalLayout);
533 ByteArrayInfo *BAI = 0;
535 // Lower each call to llvm.bitset.test for this bitset.
536 for (CallInst *CI : BitSetTestCallSites[BS]) {
537 ++NumBitSetCallsLowered;
538 Value *Lowered = lowerBitSetCall(CI, BSI, BAI, CombinedGlobal, GlobalLayout);
539 CI->replaceAllUsesWith(Lowered);
540 CI->eraseFromParent();
544 // Build aliases pointing to offsets into the combined global for each
545 // global from which we built the combined global, and replace references
546 // to the original globals with references to the aliases.
547 for (unsigned I = 0; I != Globals.size(); ++I) {
548 // Multiply by 2 to account for padding elements.
549 Constant *CombinedGlobalIdxs[] = {ConstantInt::get(Int32Ty, 0),
550 ConstantInt::get(Int32Ty, I * 2)};
551 Constant *CombinedGlobalElemPtr = ConstantExpr::getGetElementPtr(
552 NewInit->getType(), CombinedGlobal, CombinedGlobalIdxs);
553 if (LinkerSubsectionsViaSymbols) {
554 Globals[I]->replaceAllUsesWith(CombinedGlobalElemPtr);
556 GlobalAlias *GAlias = GlobalAlias::create(
557 Globals[I]->getType()->getElementType(),
558 Globals[I]->getType()->getAddressSpace(), Globals[I]->getLinkage(),
559 "", CombinedGlobalElemPtr, M);
560 GAlias->takeName(Globals[I]);
561 Globals[I]->replaceAllUsesWith(GAlias);
563 Globals[I]->eraseFromParent();
567 /// Lower all bit sets in this module.
568 bool LowerBitSets::buildBitSets() {
569 Function *BitSetTestFunc =
570 M->getFunction(Intrinsic::getName(Intrinsic::bitset_test));
574 // Equivalence class set containing bitsets and the globals they reference.
575 // This is used to partition the set of bitsets in the module into disjoint
577 typedef EquivalenceClasses<PointerUnion<GlobalVariable *, MDString *>>
579 GlobalClassesTy GlobalClasses;
581 for (const Use &U : BitSetTestFunc->uses()) {
582 auto CI = cast<CallInst>(U.getUser());
584 auto BitSetMDVal = dyn_cast<MetadataAsValue>(CI->getArgOperand(1));
585 if (!BitSetMDVal || !isa<MDString>(BitSetMDVal->getMetadata()))
587 "Second argument of llvm.bitset.test must be metadata string");
588 auto BitSet = cast<MDString>(BitSetMDVal->getMetadata());
590 // Add the call site to the list of call sites for this bit set. We also use
591 // BitSetTestCallSites to keep track of whether we have seen this bit set
592 // before. If we have, we don't need to re-add the referenced globals to the
593 // equivalence class.
594 std::pair<DenseMap<MDString *, std::vector<CallInst *>>::iterator,
596 BitSetTestCallSites.insert(
597 std::make_pair(BitSet, std::vector<CallInst *>()));
598 Ins.first->second.push_back(CI);
602 // Add the bitset to the equivalence class.
603 GlobalClassesTy::iterator GCI = GlobalClasses.insert(BitSet);
604 GlobalClassesTy::member_iterator CurSet = GlobalClasses.findLeader(GCI);
609 // Verify the bitset metadata and add the referenced globals to the bitset's
610 // equivalence class.
611 for (MDNode *Op : BitSetNM->operands()) {
612 if (Op->getNumOperands() != 3)
614 "All operands of llvm.bitsets metadata must have 3 elements");
616 if (Op->getOperand(0) != BitSet || !Op->getOperand(1))
619 auto OpConstMD = dyn_cast<ConstantAsMetadata>(Op->getOperand(1));
621 report_fatal_error("Bit set element must be a constant");
622 auto OpGlobal = dyn_cast<GlobalVariable>(OpConstMD->getValue());
624 report_fatal_error("Bit set element must refer to global");
626 auto OffsetConstMD = dyn_cast<ConstantAsMetadata>(Op->getOperand(2));
628 report_fatal_error("Bit set element offset must be a constant");
629 auto OffsetInt = dyn_cast<ConstantInt>(OffsetConstMD->getValue());
632 "Bit set element offset must be an integer constant");
634 CurSet = GlobalClasses.unionSets(
635 CurSet, GlobalClasses.findLeader(GlobalClasses.insert(OpGlobal)));
639 if (GlobalClasses.empty())
642 // For each disjoint set we found...
643 for (GlobalClassesTy::iterator I = GlobalClasses.begin(),
644 E = GlobalClasses.end();
646 if (!I->isLeader()) continue;
648 ++NumBitSetDisjointSets;
650 // Build the list of bitsets and referenced globals in this disjoint set.
651 std::vector<MDString *> BitSets;
652 std::vector<GlobalVariable *> Globals;
653 llvm::DenseMap<MDString *, uint64_t> BitSetIndices;
654 llvm::DenseMap<GlobalVariable *, uint64_t> GlobalIndices;
655 for (GlobalClassesTy::member_iterator MI = GlobalClasses.member_begin(I);
656 MI != GlobalClasses.member_end(); ++MI) {
657 if ((*MI).is<MDString *>()) {
658 BitSetIndices[MI->get<MDString *>()] = BitSets.size();
659 BitSets.push_back(MI->get<MDString *>());
661 GlobalIndices[MI->get<GlobalVariable *>()] = Globals.size();
662 Globals.push_back(MI->get<GlobalVariable *>());
666 // For each bitset, build a set of indices that refer to globals referenced
668 std::vector<std::set<uint64_t>> BitSetMembers(BitSets.size());
670 for (MDNode *Op : BitSetNM->operands()) {
671 // Op = { bitset name, global, offset }
672 if (!Op->getOperand(1))
674 auto I = BitSetIndices.find(cast<MDString>(Op->getOperand(0)));
675 if (I == BitSetIndices.end())
678 auto OpGlobal = cast<GlobalVariable>(
679 cast<ConstantAsMetadata>(Op->getOperand(1))->getValue());
680 BitSetMembers[I->second].insert(GlobalIndices[OpGlobal]);
684 // Order the sets of indices by size. The GlobalLayoutBuilder works best
685 // when given small index sets first.
687 BitSetMembers.begin(), BitSetMembers.end(),
688 [](const std::set<uint64_t> &O1, const std::set<uint64_t> &O2) {
689 return O1.size() < O2.size();
692 // Create a GlobalLayoutBuilder and provide it with index sets as layout
693 // fragments. The GlobalLayoutBuilder tries to lay out members of fragments
694 // as close together as possible.
695 GlobalLayoutBuilder GLB(Globals.size());
696 for (auto &&MemSet : BitSetMembers)
697 GLB.addFragment(MemSet);
699 // Build a vector of globals with the computed layout.
700 std::vector<GlobalVariable *> OrderedGlobals(Globals.size());
701 auto OGI = OrderedGlobals.begin();
702 for (auto &&F : GLB.Fragments)
703 for (auto &&Offset : F)
704 *OGI++ = Globals[Offset];
706 // Order bitsets by name for determinism.
707 std::sort(BitSets.begin(), BitSets.end(), [](MDString *S1, MDString *S2) {
708 return S1->getString() < S2->getString();
711 // Build the bitsets from this disjoint set.
712 buildBitSetsFromGlobals(BitSets, OrderedGlobals);
715 allocateByteArrays();
720 bool LowerBitSets::eraseBitSetMetadata() {
724 M->eraseNamedMetadata(BitSetNM);
728 bool LowerBitSets::runOnModule(Module &M) {
729 bool Changed = buildBitSets();
730 Changed |= eraseBitSetMetadata();