Introduce bitset metadata format and bitset lowering pass.

This patch introduces a new mechanism that allows IR modules to co-operatively
build pointer sets corresponding to addresses within a given set of
globals. One particular use case for this is to allow a C++ program to
efficiently verify (at each call site) that a vtable pointer is in the set
of valid vtable pointers for the class or its derived classes. One way of
doing this is for a toolchain component to build, for each class, a bit set
that maps to the memory region allocated for the vtables, such that each 1
bit in the bit set maps to a valid vtable for that class, and lay out the
vtables next to each other, to minimize the total size of the bit sets.

The patch introduces a metadata format for representing pointer sets, an
'@llvm.bitset.test' intrinsic and an LTO lowering pass that lays out the globals
and builds the bitsets, and documents the new feature.

Differential Revision: http://reviews.llvm.org/D7288

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230054 91177308-0d34-0410-b5e6-96231b3b80d8

docs/BitSets.rst

@@ -0,0 +1,66 @@
+=======
+Bitsets
+=======
+
+This is a mechanism that allows IR modules to co-operatively build pointer
+sets corresponding to addresses within a given set of globals. One example
+of a use case for this is to allow a C++ program to efficiently verify (at
+each call site) that a vtable pointer is in the set of valid vtable pointers
+for the type of the class or its derived classes.
+
+To use the mechanism, a client creates a global metadata node named
+``llvm.bitsets``.  Each element is a metadata node with three elements:
+the first is a metadata string containing an identifier for the bitset,
+the second is a global variable and the third is a byte offset into the
+global variable.
+
+This will cause a link-time optimization pass to generate bitsets from the
+memory addresses referenced from the elements of the bitset metadata. The pass
+will lay out the referenced globals consecutively, so their definitions must
+be available at LTO time. An intrinsic, :ref:`llvm.bitset.test <bitset.test>`,
+generates code to test whether a given pointer is a member of a bitset.
+
+:Example:
+
+::
+
+    target datalayout = "e-p:32:32"
+
+    @a = internal global i32 0
+    @b = internal global i32 0
+    @c = internal global i32 0
+    @d = internal global [2 x i32] [i32 0, i32 0]
+
+    !llvm.bitsets = !{!0, !1, !2, !3, !4}
+
+    !0 = !{!"bitset1", i32* @a, i32 0}
+    !1 = !{!"bitset1", i32* @b, i32 0}
+    !2 = !{!"bitset2", i32* @b, i32 0}
+    !3 = !{!"bitset2", i32* @c, i32 0}
+    !4 = !{!"bitset2", i32* @d, i32 4}
+
+    declare i1 @llvm.bitset.test(i8* %ptr, metadata %bitset) nounwind readnone
+
+    define i1 @foo(i32* %p) {
+      %pi8 = bitcast i32* %p to i8*
+      %x = call i1 @llvm.bitset.test(i8* %pi8, metadata !"bitset1")
+      ret i1 %x
+    }
+
+    define i1 @bar(i32* %p) {
+      %pi8 = bitcast i32* %p to i8*
+      %x = call i1 @llvm.bitset.test(i8* %pi8, metadata !"bitset2")
+      ret i1 %x
+    }
+
+    define void @main() {
+      %a1 = call i1 @foo(i32* @a) ; returns 1
+      %b1 = call i1 @foo(i32* @b) ; returns 1
+      %c1 = call i1 @foo(i32* @c) ; returns 0
+      %a2 = call i1 @bar(i32* @a) ; returns 0
+      %b2 = call i1 @bar(i32* @b) ; returns 1
+      %c2 = call i1 @bar(i32* @c) ; returns 1
+      %d02 = call i1 @bar(i32* getelementptr ([2 x i32]* @d, i32 0, i32 0)) ; returns 0
+      %d12 = call i1 @bar(i32* getelementptr ([2 x i32]* @d, i32 0, i32 1)) ; returns 1
+      ret void
+    }

docs/LangRef.rst

@@ -3308,6 +3308,12 @@ the loop identifier metadata node directly:
    !1 = !{!1} ; an identifier for the inner loop
    !2 = !{!2} ; an identifier for the outer loop
 
+'``llvm.bitsets``'
+^^^^^^^^^^^^^^^^^^
+
+The ``llvm.bitsets`` global metadata is used to implement
+:doc:`bitsets <BitSets>`.
+
 Module Flags Metadata
 =====================
 
@@ -9891,6 +9897,31 @@ sufficient overall improvement in code quality. For this reason,
 that the optimizer can otherwise deduce or facts that are of little use to the
 optimizer.
 
+.. _bitset.test:
+
+'``llvm.bitset.test``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+      declare i1 @llvm.bitset.test(i8* %ptr, metadata %bitset) nounwind readnone
+
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to be tested. The second argument is a
+metadata string containing the name of a :doc:`bitset <BitSets>`.
+
+Overview:
+"""""""""
+
+The ``llvm.bitset.test`` intrinsic tests whether the given pointer is a
+member of the given bitset.
+
 '``llvm.donothing``' Intrinsic
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

docs/index.rst

@@ -244,6 +244,7 @@ For API clients and LLVM developers.
    CoverageMappingFormat
    Statepoints
    MergeFunctions
+   BitSets
 
 :doc:`WritingAnLLVMPass`
    Information on how to write LLVM transformations and analyses.

include/llvm/ADT/EquivalenceClasses.h

@@ -255,7 +255,7 @@ public:
       assert(Node != nullptr && "Dereferencing end()!");
       return Node->getData();
     }
-    reference operator->() const { return operator*(); }
+    pointer operator->() const { return &operator*(); }
 
     member_iterator &operator++() {
       assert(Node != nullptr && "++'d off the end of the list!");

include/llvm/ADT/PointerUnion.h

@@ -195,6 +195,12 @@ namespace llvm {
     return lhs.getOpaqueValue() != rhs.getOpaqueValue();
   }
 
+  template<typename PT1, typename PT2>
+  static bool operator<(PointerUnion<PT1, PT2> lhs,
+                        PointerUnion<PT1, PT2> rhs) {
+    return lhs.getOpaqueValue() < rhs.getOpaqueValue();
+  }
+
   // Teach SmallPtrSet that PointerUnion is "basically a pointer", that has
   // # low bits available = min(PT1bits,PT2bits)-1.
   template<typename PT1, typename PT2>

include/llvm/IR/Intrinsics.td

@@ -603,6 +603,10 @@ def int_masked_scatter: Intrinsic<[],
                                    LLVMVectorSameWidth<0, llvm_i1_ty>],
                                   [IntrReadWriteArgMem]>;
 
+// Intrinsics to support bit sets.
+def int_bitset_test : Intrinsic<[llvm_i1_ty], [llvm_ptr_ty, llvm_metadata_ty],
+                                [IntrNoMem]>;
+
 //===----------------------------------------------------------------------===//
 // Target-specific intrinsics
 //===----------------------------------------------------------------------===//

include/llvm/InitializePasses.h

@@ -178,6 +178,7 @@ void initializeLoopUnrollPass(PassRegistry&);
 void initializeLoopUnswitchPass(PassRegistry&);
 void initializeLoopIdiomRecognizePass(PassRegistry&);
 void initializeLowerAtomicPass(PassRegistry&);
+void initializeLowerBitSetsPass(PassRegistry&);
 void initializeLowerExpectIntrinsicPass(PassRegistry&);
 void initializeLowerIntrinsicsPass(PassRegistry&);
 void initializeLowerInvokePass(PassRegistry&);

include/llvm/Transforms/IPO.h

@@ -199,6 +199,10 @@ ModulePass *createMetaRenamerPass();
 /// manager.
 ModulePass *createBarrierNoopPass();
 
+/// \brief This pass lowers bitset metadata and the llvm.bitset.test intrinsic
+/// to bitsets.
+ModulePass *createLowerBitSetsPass();
+
 } // End llvm namespace
 
 #endif

include/llvm/Transforms/IPO/LowerBitSets.h

@@ -0,0 +1,78 @@
+//===- LowerBitSets.h - Bitset lowering pass --------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines parts of the bitset lowering pass implementation that may
+// be usefully unit tested.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_IPO_LOWERBITSETS_H
+#define LLVM_TRANSFORMS_IPO_LOWERBITSETS_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallVector.h"
+
+#include <stdint.h>
+#include <limits>
+#include <vector>
+
+namespace llvm {
+
+class DataLayout;
+class GlobalVariable;
+class Value;
+
+struct BitSetInfo {
+  // The actual bitset.
+  std::vector<uint8_t> Bits;
+
+  // The byte offset into the combined global represented by the bitset.
+  uint64_t ByteOffset;
+
+  // The size of the bitset in bits.
+  uint64_t BitSize;
+
+  // Log2 alignment of the bit set relative to the combined global.
+  // For example, a log2 alignment of 3 means that bits in the bitset
+  // represent addresses 8 bytes apart.
+  unsigned AlignLog2;
+
+  bool isSingleOffset() const {
+    return Bits.size() == 1 && Bits[0] == 1;
+  }
+
+  bool containsGlobalOffset(uint64_t Offset) const;
+
+  bool containsValue(const DataLayout *DL,
+                     const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout,
+                     Value *V, uint64_t COffset = 0) const;
+
+};
+
+struct BitSetBuilder {
+  SmallVector<uint64_t, 16> Offsets;
+  uint64_t Min, Max;
+
+  BitSetBuilder() : Min(std::numeric_limits<uint64_t>::max()), Max(0) {}
+
+  void addOffset(uint64_t Offset) {
+    if (Min > Offset)
+      Min = Offset;
+    if (Max < Offset)
+      Max = Offset;
+
+    Offsets.push_back(Offset);
+  }
+
+  BitSetInfo build();
+};
+
+} // namespace llvm
+
+#endif

lib/Transforms/IPO/CMakeLists.txt

@@ -14,6 +14,7 @@ add_llvm_library(LLVMipo
   Inliner.cpp
   Internalize.cpp
   LoopExtractor.cpp
+  LowerBitSets.cpp
   MergeFunctions.cpp
   PartialInlining.cpp
   PassManagerBuilder.cpp

lib/Transforms/IPO/IPO.cpp

@@ -36,6 +36,7 @@ void llvm::initializeIPO(PassRegistry &Registry) {
   initializeLoopExtractorPass(Registry);
   initializeBlockExtractorPassPass(Registry);
   initializeSingleLoopExtractorPass(Registry);
+  initializeLowerBitSetsPass(Registry);
   initializeMergeFunctionsPass(Registry);
   initializePartialInlinerPass(Registry);
   initializePruneEHPass(Registry);

lib/Transforms/IPO/LowerBitSets.cpp

@@ -0,0 +1,526 @@
+//===-- LowerBitSets.cpp - Bitset lowering pass ---------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass lowers bitset metadata and calls to the llvm.bitset.test intrinsic.
+// See http://llvm.org/docs/LangRef.html#bitsets for more information.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/IPO/LowerBitSets.h"
+#include "llvm/Transforms/IPO.h"
+#include "llvm/ADT/EquivalenceClasses.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/IR/Constant.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Operator.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "lowerbitsets"
+
+STATISTIC(NumBitSetsCreated, "Number of bitsets created");
+STATISTIC(NumBitSetCallsLowered, "Number of bitset calls lowered");
+STATISTIC(NumBitSetDisjointSets, "Number of disjoint sets of bitsets");
+
+bool BitSetInfo::containsGlobalOffset(uint64_t Offset) const {
+  if (Offset < ByteOffset)
+    return false;
+
+  if ((Offset - ByteOffset) % (uint64_t(1) << AlignLog2) != 0)
+    return false;
+
+  uint64_t BitOffset = (Offset - ByteOffset) >> AlignLog2;
+  if (BitOffset >= BitSize)
+    return false;
+
+  return (Bits[BitOffset / 8] >> (BitOffset % 8)) & 1;
+}
+
+bool BitSetInfo::containsValue(
+    const DataLayout *DL,
+    const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout, Value *V,
+    uint64_t COffset) const {
+  if (auto GV = dyn_cast<GlobalVariable>(V)) {
+    auto I = GlobalLayout.find(GV);
+    if (I == GlobalLayout.end())
+      return false;
+    return containsGlobalOffset(I->second + COffset);
+  }
+
+  if (auto GEP = dyn_cast<GEPOperator>(V)) {
+    APInt APOffset(DL->getPointerSizeInBits(0), 0);
+    bool Result = GEP->accumulateConstantOffset(*DL, APOffset);
+    if (!Result)
+      return false;
+    COffset += APOffset.getZExtValue();
+    return containsValue(DL, GlobalLayout, GEP->getPointerOperand(),
+                         COffset);
+  }
+
+  if (auto Op = dyn_cast<Operator>(V)) {
+    if (Op->getOpcode() == Instruction::BitCast)
+      return containsValue(DL, GlobalLayout, Op->getOperand(0), COffset);
+
+    if (Op->getOpcode() == Instruction::Select)
+      return containsValue(DL, GlobalLayout, Op->getOperand(1), COffset) &&
+             containsValue(DL, GlobalLayout, Op->getOperand(2), COffset);
+  }
+
+  return false;
+}
+
+BitSetInfo BitSetBuilder::build() {
+  if (Min > Max)
+    Min = 0;
+
+  // Normalize each offset against the minimum observed offset, and compute
+  // the bitwise OR of each of the offsets. The number of trailing zeros
+  // in the mask gives us the log2 of the alignment of all offsets, which
+  // allows us to compress the bitset by only storing one bit per aligned
+  // address.
+  uint64_t Mask = 0;
+  for (uint64_t &Offset : Offsets) {
+    Offset -= Min;
+    Mask |= Offset;
+  }
+
+  BitSetInfo BSI;
+  BSI.ByteOffset = Min;
+
+  BSI.AlignLog2 = 0;
+  // FIXME: Can probably do something smarter if all offsets are 0.
+  if (Mask != 0)
+    BSI.AlignLog2 = countTrailingZeros(Mask, ZB_Undefined);
+
+  // Build the compressed bitset while normalizing the offsets against the
+  // computed alignment.
+  BSI.BitSize = ((Max - Min) >> BSI.AlignLog2) + 1;
+  uint64_t ByteSize = (BSI.BitSize + 7) / 8;
+  BSI.Bits.resize(ByteSize);
+  for (uint64_t Offset : Offsets) {
+    Offset >>= BSI.AlignLog2;
+    BSI.Bits[Offset / 8] |= 1 << (Offset % 8);
+  }
+
+  return BSI;
+}
+
+namespace {
+
+struct LowerBitSets : public ModulePass {
+  static char ID;
+  LowerBitSets() : ModulePass(ID) {
+    initializeLowerBitSetsPass(*PassRegistry::getPassRegistry());
+  }
+
+  const DataLayout *DL;
+  IntegerType *Int1Ty;
+  IntegerType *Int32Ty;
+  Type *Int32PtrTy;
+  IntegerType *Int64Ty;
+  Type *IntPtrTy;
+
+  // The llvm.bitsets named metadata.
+  NamedMDNode *BitSetNM;
+
+  // Mapping from bitset mdstrings to the call sites that test them.
+  DenseMap<MDString *, std::vector<CallInst *>> BitSetTestCallSites;
+
+  BitSetInfo
+  buildBitSet(MDString *BitSet,
+              const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout);
+  Value *createBitSetTest(IRBuilder<> &B, const BitSetInfo &BSI,
+                          GlobalVariable *BitSetGlobal, Value *BitOffset);
+  void
+  lowerBitSetCall(CallInst *CI, const BitSetInfo &BSI,
+                  GlobalVariable *BitSetGlobal, GlobalVariable *CombinedGlobal,
+                  const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout);
+  void buildBitSetsFromGlobals(Module &M,
+                               const std::vector<MDString *> &BitSets,
+                               const std::vector<GlobalVariable *> &Globals);
+  bool buildBitSets(Module &M);
+  bool eraseBitSetMetadata(Module &M);
+
+  bool doInitialization(Module &M) override;
+  bool runOnModule(Module &M) override;
+};
+
+} // namespace
+
+INITIALIZE_PASS_BEGIN(LowerBitSets, "lowerbitsets",
+                "Lower bitset metadata", false, false)
+INITIALIZE_PASS_END(LowerBitSets, "lowerbitsets",
+                "Lower bitset metadata", false, false)
+char LowerBitSets::ID = 0;
+
+ModulePass *llvm::createLowerBitSetsPass() { return new LowerBitSets; }
+
+bool LowerBitSets::doInitialization(Module &M) {
+  DL = M.getDataLayout();
+  if (!DL)
+    report_fatal_error("Data layout required");
+
+  Int1Ty = Type::getInt1Ty(M.getContext());
+  Int32Ty = Type::getInt32Ty(M.getContext());
+  Int32PtrTy = PointerType::getUnqual(Int32Ty);
+  Int64Ty = Type::getInt64Ty(M.getContext());
+  IntPtrTy = DL->getIntPtrType(M.getContext(), 0);
+
+  BitSetNM = M.getNamedMetadata("llvm.bitsets");
+
+  BitSetTestCallSites.clear();
+
+  return false;
+}
+
+/// Build a bit set for \param BitSet using the object layouts in
+/// \param GlobalLayout.
+BitSetInfo LowerBitSets::buildBitSet(
+    MDString *BitSet,
+    const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout) {
+  BitSetBuilder BSB;
+
+  // Compute the byte offset of each element of this bitset.
+  if (BitSetNM) {
+    for (MDNode *Op : BitSetNM->operands()) {
+      if (Op->getOperand(0) != BitSet || !Op->getOperand(1))
+        continue;
+      auto OpGlobal = cast<GlobalVariable>(
+          cast<ConstantAsMetadata>(Op->getOperand(1))->getValue());
+      uint64_t Offset =
+          cast<ConstantInt>(cast<ConstantAsMetadata>(Op->getOperand(2))
+                                ->getValue())->getZExtValue();
+
+      Offset += GlobalLayout.find(OpGlobal)->second;
+
+      BSB.addOffset(Offset);
+    }
+  }
+
+  return BSB.build();
+}
+
+/// Build a test that bit \param BitOffset mod sizeof(Bits)*8 is set in
+/// \param Bits. This pattern matches to the bt instruction on x86.
+static Value *createMaskedBitTest(IRBuilder<> &B, Value *Bits,
+                                  Value *BitOffset) {
+  auto BitsType = cast<IntegerType>(Bits->getType());
+  unsigned BitWidth = BitsType->getBitWidth();
+
+  BitOffset = B.CreateZExtOrTrunc(BitOffset, BitsType);
+  Value *BitIndex =
+      B.CreateAnd(BitOffset, ConstantInt::get(BitsType, BitWidth - 1));
+  Value *BitMask = B.CreateShl(ConstantInt::get(BitsType, 1), BitIndex);
+  Value *MaskedBits = B.CreateAnd(Bits, BitMask);
+  return B.CreateICmpNE(MaskedBits, ConstantInt::get(BitsType, 0));
+}
+
+/// Build a test that bit \param BitOffset is set in \param BSI, where
+/// \param BitSetGlobal is a global containing the bits in \param BSI.
+Value *LowerBitSets::createBitSetTest(IRBuilder<> &B, const BitSetInfo &BSI,
+                                      GlobalVariable *BitSetGlobal,
+                                      Value *BitOffset) {
+  if (BSI.Bits.size() <= 8) {
+    // If the bit set is sufficiently small, we can avoid a load by bit testing
+    // a constant.
+    IntegerType *BitsTy;
+    if (BSI.Bits.size() <= 4)
+      BitsTy = Int32Ty;
+    else
+      BitsTy = Int64Ty;
+
+    uint64_t Bits = 0;
+    for (auto I = BSI.Bits.rbegin(), E = BSI.Bits.rend(); I != E; ++I) {
+      Bits <<= 8;
+      Bits |= *I;
+    }
+    Constant *BitsConst = ConstantInt::get(BitsTy, Bits);
+    return createMaskedBitTest(B, BitsConst, BitOffset);
+  } else {
+    // TODO: We might want to use the memory variant of the bt instruction
+    // with the previously computed bit offset at -Os. This instruction does
+    // exactly what we want but has been benchmarked as being slower than open
+    // coding the load+bt.
+    Value *BitSetGlobalOffset =
+        B.CreateLShr(BitOffset, ConstantInt::get(IntPtrTy, 5));
+    Value *BitSetEntryAddr = B.CreateGEP(
+        ConstantExpr::getBitCast(BitSetGlobal, Int32PtrTy), BitSetGlobalOffset);
+    Value *BitSetEntry = B.CreateLoad(BitSetEntryAddr);
+
+    return createMaskedBitTest(B, BitSetEntry, BitOffset);
+  }
+}
+
+/// Lower a llvm.bitset.test call to its implementation.
+void LowerBitSets::lowerBitSetCall(
+    CallInst *CI, const BitSetInfo &BSI, GlobalVariable *BitSetGlobal,
+    GlobalVariable *CombinedGlobal,
+    const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout) {
+  Value *Ptr = CI->getArgOperand(0);
+
+  if (BSI.containsValue(DL, GlobalLayout, Ptr)) {
+    CI->replaceAllUsesWith(
+        ConstantInt::getTrue(BitSetGlobal->getParent()->getContext()));
+    CI->eraseFromParent();
+    return;
+  }
+
+  Constant *GlobalAsInt = ConstantExpr::getPtrToInt(CombinedGlobal, IntPtrTy);
+  Constant *OffsetedGlobalAsInt = ConstantExpr::getAdd(
+      GlobalAsInt, ConstantInt::get(IntPtrTy, BSI.ByteOffset));
+
+  BasicBlock *InitialBB = CI->getParent();
+
+  IRBuilder<> B(CI);
+
+  Value *PtrAsInt = B.CreatePtrToInt(Ptr, IntPtrTy);
+
+  if (BSI.isSingleOffset()) {
+    Value *Eq = B.CreateICmpEQ(PtrAsInt, OffsetedGlobalAsInt);
+    CI->replaceAllUsesWith(Eq);
+    CI->eraseFromParent();
+    return;
+  }
+
+  Value *PtrOffset = B.CreateSub(PtrAsInt, OffsetedGlobalAsInt);
+
+  Value *BitOffset;
+  if (BSI.AlignLog2 == 0) {
+    BitOffset = PtrOffset;
+  } else {
+    // We need to check that the offset both falls within our range and is
+    // suitably aligned. We can check both properties at the same time by
+    // performing a right rotate by log2(alignment) followed by an integer
+    // comparison against the bitset size. The rotate will move the lower
+    // order bits that need to be zero into the higher order bits of the
+    // result, causing the comparison to fail if they are nonzero. The rotate
+    // also conveniently gives us a bit offset to use during the load from
+    // the bitset.
+    Value *OffsetSHR =
+        B.CreateLShr(PtrOffset, ConstantInt::get(IntPtrTy, BSI.AlignLog2));
+    Value *OffsetSHL = B.CreateShl(
+        PtrOffset, ConstantInt::get(IntPtrTy, DL->getPointerSizeInBits(0) -
+                                                  BSI.AlignLog2));
+    BitOffset = B.CreateOr(OffsetSHR, OffsetSHL);
+  }
+
+  Constant *BitSizeConst = ConstantInt::get(IntPtrTy, BSI.BitSize);
+  Value *OffsetInRange = B.CreateICmpULT(BitOffset, BitSizeConst);
+
+  TerminatorInst *Term = SplitBlockAndInsertIfThen(OffsetInRange, CI, false);
+  IRBuilder<> ThenB(Term);
+
+  // Now that we know that the offset is in range and aligned, load the
+  // appropriate bit from the bitset.
+  Value *Bit = createBitSetTest(ThenB, BSI, BitSetGlobal, BitOffset);
+
+  // The value we want is 0 if we came directly from the initial block
+  // (having failed the range or alignment checks), or the loaded bit if
+  // we came from the block in which we loaded it.
+  B.SetInsertPoint(CI);
+  PHINode *P = B.CreatePHI(Int1Ty, 2);
+  P->addIncoming(ConstantInt::get(Int1Ty, 0), InitialBB);
+  P->addIncoming(Bit, ThenB.GetInsertBlock());
+
+  CI->replaceAllUsesWith(P);
+  CI->eraseFromParent();
+}
+
+/// Given a disjoint set of bitsets and globals, layout the globals, build the
+/// bit sets and lower the llvm.bitset.test calls.
+void LowerBitSets::buildBitSetsFromGlobals(
+    Module &M,
+    const std::vector<MDString *> &BitSets,
+    const std::vector<GlobalVariable *> &Globals) {
+  // Build a new global with the combined contents of the referenced globals.
+  std::vector<Constant *> GlobalInits;
+  for (GlobalVariable *G : Globals)
+    GlobalInits.push_back(G->getInitializer());
+  Constant *NewInit = ConstantStruct::getAnon(M.getContext(), GlobalInits);
+  auto CombinedGlobal =
+      new GlobalVariable(M, NewInit->getType(), /*isConstant=*/true,
+                         GlobalValue::PrivateLinkage, NewInit);
+
+  const StructLayout *CombinedGlobalLayout =
+      DL->getStructLayout(cast<StructType>(NewInit->getType()));
+
+  // Compute the offsets of the original globals within the new global.
+  DenseMap<GlobalVariable *, uint64_t> GlobalLayout;
+  for (unsigned I = 0; I != Globals.size(); ++I)
+    GlobalLayout[Globals[I]] = CombinedGlobalLayout->getElementOffset(I);
+
+  // For each bitset in this disjoint set...
+  for (MDString *BS : BitSets) {
+    // Build the bitset.
+    BitSetInfo BSI = buildBitSet(BS, GlobalLayout);
+
+    // Create a global in which to store it.
+    ++NumBitSetsCreated;
+    Constant *BitsConst = ConstantDataArray::get(M.getContext(), BSI.Bits);
+    auto BitSetGlobal = new GlobalVariable(
+        M, BitsConst->getType(), /*isConstant=*/true,
+        GlobalValue::PrivateLinkage, BitsConst, BS->getString() + ".bits");
+
+    // Lower each call to llvm.bitset.test for this bitset.
+    for (CallInst *CI : BitSetTestCallSites[BS]) {
+      ++NumBitSetCallsLowered;
+      lowerBitSetCall(CI, BSI, BitSetGlobal, CombinedGlobal, GlobalLayout);
+    }
+  }
+
+  // Build aliases pointing to offsets into the combined global for each
+  // global from which we built the combined global, and replace references
+  // to the original globals with references to the aliases.
+  for (unsigned I = 0; I != Globals.size(); ++I) {
+    Constant *CombinedGlobalIdxs[] = {ConstantInt::get(Int32Ty, 0),
+                                      ConstantInt::get(Int32Ty, I)};
+    Constant *CombinedGlobalElemPtr =
+        ConstantExpr::getGetElementPtr(CombinedGlobal, CombinedGlobalIdxs);
+    GlobalAlias *GAlias = GlobalAlias::create(
+        Globals[I]->getType()->getElementType(),
+        Globals[I]->getType()->getAddressSpace(), Globals[I]->getLinkage(),
+        "", CombinedGlobalElemPtr, &M);
+    GAlias->takeName(Globals[I]);
+    Globals[I]->replaceAllUsesWith(GAlias);
+    Globals[I]->eraseFromParent();
+  }
+}
+
+/// Lower all bit sets in this module.
+bool LowerBitSets::buildBitSets(Module &M) {
+  Function *BitSetTestFunc =
+      M.getFunction(Intrinsic::getName(Intrinsic::bitset_test));
+  if (!BitSetTestFunc)
+    return false;
+
+  // Equivalence class set containing bitsets and the globals they reference.
+  // This is used to partition the set of bitsets in the module into disjoint
+  // sets.
+  typedef EquivalenceClasses<PointerUnion<GlobalVariable *, MDString *>>
+      GlobalClassesTy;
+  GlobalClassesTy GlobalClasses;
+
+  for (const Use &U : BitSetTestFunc->uses()) {
+    auto CI = cast<CallInst>(U.getUser());
+
+    auto BitSetMDVal = dyn_cast<MetadataAsValue>(CI->getArgOperand(1));
+    if (!BitSetMDVal || !isa<MDString>(BitSetMDVal->getMetadata()))
+      report_fatal_error(
+          "Second argument of llvm.bitset.test must be metadata string");
+    auto BitSet = cast<MDString>(BitSetMDVal->getMetadata());
+
+    // Add the call site to the list of call sites for this bit set. We also use
+    // BitSetTestCallSites to keep track of whether we have seen this bit set
+    // before. If we have, we don't need to re-add the referenced globals to the
+    // equivalence class.
+    std::pair<DenseMap<MDString *, std::vector<CallInst *>>::iterator,
+              bool> Ins =
+        BitSetTestCallSites.insert(
+            std::make_pair(BitSet, std::vector<CallInst *>()));
+    Ins.first->second.push_back(CI);
+    if (!Ins.second)
+      continue;
+
+    // Add the bitset to the equivalence class.
+    GlobalClassesTy::iterator GCI = GlobalClasses.insert(BitSet);
+    GlobalClassesTy::member_iterator CurSet = GlobalClasses.findLeader(GCI);
+
+    if (!BitSetNM)
+      continue;
+
+    // Verify the bitset metadata and add the referenced globals to the bitset's
+    // equivalence class.
+    for (MDNode *Op : BitSetNM->operands()) {
+      if (Op->getNumOperands() != 3)
+        report_fatal_error(
+            "All operands of llvm.bitsets metadata must have 3 elements");
+
+      if (Op->getOperand(0) != BitSet || !Op->getOperand(1))
+        continue;
+
+      auto OpConstMD = dyn_cast<ConstantAsMetadata>(Op->getOperand(1));
+      if (!OpConstMD)
+        report_fatal_error("Bit set element must be a constant");
+      auto OpGlobal = dyn_cast<GlobalVariable>(OpConstMD->getValue());
+      if (!OpGlobal)
+        report_fatal_error("Bit set element must refer to global");
+
+      auto OffsetConstMD = dyn_cast<ConstantAsMetadata>(Op->getOperand(2));
+      if (!OffsetConstMD)
+        report_fatal_error("Bit set element offset must be a constant");
+      auto OffsetInt = dyn_cast<ConstantInt>(OffsetConstMD->getValue());
+      if (!OffsetInt)
+        report_fatal_error(
+            "Bit set element offset must be an integer constant");
+
+      CurSet = GlobalClasses.unionSets(
+          CurSet, GlobalClasses.findLeader(GlobalClasses.insert(OpGlobal)));
+    }
+  }
+
+  if (GlobalClasses.empty())
+    return false;
+
+  // For each disjoint set we found...
+  for (GlobalClassesTy::iterator I = GlobalClasses.begin(),
+                                 E = GlobalClasses.end();
+       I != E; ++I) {
+    if (!I->isLeader()) continue;
+
+    ++NumBitSetDisjointSets;
+
+    // Build the list of bitsets and referenced globals in this disjoint set.
+    std::vector<MDString *> BitSets;
+    std::vector<GlobalVariable *> Globals;
+    for (GlobalClassesTy::member_iterator MI = GlobalClasses.member_begin(I);
+         MI != GlobalClasses.member_end(); ++MI) {
+      if ((*MI).is<MDString *>())
+        BitSets.push_back(MI->get<MDString *>());
+      else
+        Globals.push_back(MI->get<GlobalVariable *>());
+    }
+
+    // Order bitsets and globals by name for determinism. TODO: We may later
+    // want to use a more sophisticated ordering that lays out globals so as to
+    // minimize the sizes of the bitsets.
+    std::sort(BitSets.begin(), BitSets.end(), [](MDString *S1, MDString *S2) {
+      return S1->getString() < S2->getString();
+    });
+    std::sort(Globals.begin(), Globals.end(),
+              [](GlobalVariable *GV1, GlobalVariable *GV2) {
+                return GV1->getName() < GV2->getName();
+              });
+
+    // Build the bitsets from this disjoint set.
+    buildBitSetsFromGlobals(M, BitSets, Globals);
+  }
+
+  return true;
+}
+
+bool LowerBitSets::eraseBitSetMetadata(Module &M) {
+  if (!BitSetNM)
+    return false;
+
+  M.eraseNamedMetadata(BitSetNM);
+  return true;
+}
+
+bool LowerBitSets::runOnModule(Module &M) {
+  bool Changed = buildBitSets(M);
+  Changed |= eraseBitSetMetadata(M);
+  return Changed;
+}

lib/Transforms/IPO/PassManagerBuilder.cpp

@@ -474,6 +474,9 @@ void PassManagerBuilder::addLTOOptimizationPasses(legacy::PassManagerBase &PM) {
 
   PM.add(createJumpThreadingPass());
 
+  // Lower bitset metadata to bitsets.
+  PM.add(createLowerBitSetsPass());
+
   // Delete basic blocks, which optimization passes may have killed.
   PM.add(createCFGSimplificationPass());
 

test/Transforms/LowerBitSets/constant.ll

@@ -0,0 +1,34 @@
+; RUN: opt -S -lowerbitsets < %s | FileCheck %s
+
+target datalayout = "e-p:32:32"
+
+@a = constant i32 1
+@b = constant [2 x i32] [i32 2, i32 3]
+
+!0 = !{!"bitset1", i32* @a, i32 0}
+!1 = !{!"bitset1", [2 x i32]* @b, i32 4}
+
+!llvm.bitsets = !{ !0, !1 }
+
+declare i1 @llvm.bitset.test(i8* %ptr, metadata %bitset) nounwind readnone
+
+; CHECK: @foo(
+define i1 @foo() {
+  ; CHECK: ret i1 true
+  %x = call i1 @llvm.bitset.test(i8* bitcast (i32* @a to i8*), metadata !"bitset1")
+  ret i1 %x
+}
+
+; CHECK: @bar(
+define i1 @bar() {
+  ; CHECK: ret i1 true
+  %x = call i1 @llvm.bitset.test(i8* bitcast (i32* getelementptr ([2 x i32]* @b, i32 0, i32 1) to i8*), metadata !"bitset1")
+  ret i1 %x
+}
+
+; CHECK: @baz(
+define i1 @baz() {
+  ; CHECK-NOT: ret i1 true
+  %x = call i1 @llvm.bitset.test(i8* bitcast (i32* getelementptr ([2 x i32]* @b, i32 0, i32 0) to i8*), metadata !"bitset1")
+  ret i1 %x
+}

test/Transforms/LowerBitSets/simple.ll

@@ -0,0 +1,127 @@
+; RUN: opt -S -lowerbitsets < %s | FileCheck %s
+; RUN: opt -S -O3 < %s | FileCheck -check-prefix=CHECK-NODISCARD %s
+
+target datalayout = "e-p:32:32"
+
+; CHECK: [[G:@[^ ]*]] = private constant { i32, [63 x i32], i32, [2 x i32] } { i32 1, [63 x i32] zeroinitializer, i32 3, [2 x i32] [i32 4, i32 5] }
+@a = constant i32 1
+@b = constant [63 x i32] zeroinitializer
+@c = constant i32 3
+@d = constant [2 x i32] [i32 4, i32 5]
+
+; Offset 0, 4 byte alignment
+; CHECK: @bitset1.bits = private constant [9 x i8] c"\03\00\00\00\00\00\00\00\04"
+!0 = !{!"bitset1", i32* @a, i32 0}
+; CHECK-NODISCARD-DAG: !{!"bitset1", i32* @a, i32 0}
+!1 = !{!"bitset1", [63 x i32]* @b, i32 0}
+; CHECK-NODISCARD-DAG: !{!"bitset1", [63 x i32]* @b, i32 0}
+!2 = !{!"bitset1", [2 x i32]* @d, i32 4}
+; CHECK-NODISCARD-DAG: !{!"bitset1", [2 x i32]* @d, i32 4}
+
+; Offset 4, 4 byte alignment
+; CHECK: @bitset2.bits = private constant [8 x i8] c"\01\00\00\00\00\00\00\80"
+!3 = !{!"bitset2", [63 x i32]* @b, i32 0}
+; CHECK-NODISCARD-DAG: !{!"bitset2", [63 x i32]* @b, i32 0}
+!4 = !{!"bitset2", i32* @c, i32 0}
+; CHECK-NODISCARD-DAG: !{!"bitset2", i32* @c, i32 0}
+
+; Offset 0, 256 byte alignment
+; CHECK: @bitset3.bits = private constant [1 x i8] c"\03"
+!5 = !{!"bitset3", i32* @a, i32 0}
+; CHECK-NODISCARD-DAG: !{!"bitset3", i32* @a, i32 0}
+!6 = !{!"bitset3", i32* @c, i32 0}
+; CHECK-NODISCARD-DAG: !{!"bitset3", i32* @c, i32 0}
+
+; Entries whose second operand is null (the result of a global being DCE'd)
+; should be ignored.
+!7 = !{!"bitset2", null, i32 0}
+
+!llvm.bitsets = !{ !0, !1, !2, !3, !4, !5, !6, !7 }
+
+; CHECK: @a = alias getelementptr inbounds ({ i32, [63 x i32], i32, [2 x i32] }* [[G]], i32 0, i32 0)
+; CHECK: @b = alias getelementptr inbounds ({ i32, [63 x i32], i32, [2 x i32] }* [[G]], i32 0, i32 1)
+; CHECK: @c = alias getelementptr inbounds ({ i32, [63 x i32], i32, [2 x i32] }* [[G]], i32 0, i32 2)
+; CHECK: @d = alias getelementptr inbounds ({ i32, [63 x i32], i32, [2 x i32] }* [[G]], i32 0, i32 3)
+
+declare i1 @llvm.bitset.test(i8* %ptr, metadata %bitset) nounwind readnone
+
+; CHECK: @foo(i32* [[A0:%[^ ]*]])
+define i1 @foo(i32* %p) {
+  ; CHECK-NOT: llvm.bitset.test
+
+  ; CHECK: [[R0:%[^ ]*]] = bitcast i32* [[A0]] to i8*
+  %pi8 = bitcast i32* %p to i8*
+  ; CHECK: [[R1:%[^ ]*]] = ptrtoint i8* [[R0]] to i32
+  ; CHECK: [[R2:%[^ ]*]] = sub i32 [[R1]], ptrtoint ({ i32, [63 x i32], i32, [2 x i32] }* [[G]] to i32)
+  ; CHECK: [[R3:%[^ ]*]] = lshr i32 [[R2]], 2
+  ; CHECK: [[R4:%[^ ]*]] = shl i32 [[R2]], 30
+  ; CHECK: [[R5:%[^ ]*]] = or i32 [[R3]], [[R4]]
+  ; CHECK: [[R6:%[^ ]*]] = icmp ult i32 [[R5]], 67
+  ; CHECK: br i1 [[R6]]
+
+  ; CHECK: [[R8:%[^ ]*]] = lshr i32 [[R5]], 5
+  ; CHECK: [[R9:%[^ ]*]] = getelementptr i32* bitcast ([9 x i8]* @bitset1.bits to i32*), i32 [[R8]]
+  ; CHECK: [[R10:%[^ ]*]] = load i32* [[R9]]
+  ; CHECK: [[R11:%[^ ]*]] = and i32 [[R5]], 31
+  ; CHECK: [[R12:%[^ ]*]] = shl i32 1, [[R11]]
+  ; CHECK: [[R13:%[^ ]*]] = and i32 [[R10]], [[R12]]
+  ; CHECK: [[R14:%[^ ]*]] = icmp ne i32 [[R13]], 0
+
+  ; CHECK: [[R16:%[^ ]*]] = phi i1 [ false, {{%[^ ]*}} ], [ [[R14]], {{%[^ ]*}} ]
+  %x = call i1 @llvm.bitset.test(i8* %pi8, metadata !"bitset1")
+
+  ; CHECK-NOT: llvm.bitset.test
+  %y = call i1 @llvm.bitset.test(i8* %pi8, metadata !"bitset1")
+
+  ; CHECK: ret i1 [[R16]]
+  ret i1 %x
+}
+
+; CHECK: @bar(i32* [[B0:%[^ ]*]])
+define i1 @bar(i32* %p) {
+  ; CHECK: [[S0:%[^ ]*]] = bitcast i32* [[B0]] to i8*
+  %pi8 = bitcast i32* %p to i8*
+  ; CHECK: [[S1:%[^ ]*]] = ptrtoint i8* [[S0]] to i32
+  ; CHECK: [[S2:%[^ ]*]] = sub i32 [[S1]], add (i32 ptrtoint ({ i32, [63 x i32], i32, [2 x i32] }* [[G]] to i32), i32 4)
+  ; CHECK: [[S3:%[^ ]*]] = lshr i32 [[S2]], 2
+  ; CHECK: [[S4:%[^ ]*]] = shl i32 [[S2]], 30
+  ; CHECK: [[S5:%[^ ]*]] = or i32 [[S3]], [[S4]]
+  ; CHECK: [[S6:%[^ ]*]] = icmp ult i32 [[S5]], 64
+  ; CHECK: br i1 [[S6]]
+
+  ; CHECK: [[S8:%[^ ]*]] = zext i32 [[S5]] to i64
+  ; CHECK: [[S9:%[^ ]*]] = and i64 [[S8]], 63
+  ; CHECK: [[S10:%[^ ]*]] = shl i64 1, [[S9]]
+  ; CHECK: [[S11:%[^ ]*]] = and i64 -9223372036854775807, [[S10]]
+  ; CHECK: [[S12:%[^ ]*]] = icmp ne i64 [[S11]], 0
+
+  ; CHECK: [[S16:%[^ ]*]] = phi i1 [ false, {{%[^ ]*}} ], [ [[S12]], {{%[^ ]*}} ]
+  %x = call i1 @llvm.bitset.test(i8* %pi8, metadata !"bitset2")
+  ; CHECK: ret i1 [[S16]]
+  ret i1 %x
+}
+
+; CHECK: @baz(i32* [[C0:%[^ ]*]])
+define i1 @baz(i32* %p) {
+  ; CHECK: [[T0:%[^ ]*]] = bitcast i32* [[C0]] to i8*
+  %pi8 = bitcast i32* %p to i8*
+  ; CHECK: [[T1:%[^ ]*]] = ptrtoint i8* [[T0]] to i32
+  ; CHECK: [[T2:%[^ ]*]] = sub i32 [[T1]], ptrtoint ({ i32, [63 x i32], i32, [2 x i32] }* [[G]] to i32)
+  ; CHECK: [[T3:%[^ ]*]] = lshr i32 [[T2]], 8
+  ; CHECK: [[T4:%[^ ]*]] = shl i32 [[T2]], 24
+  ; CHECK: [[T5:%[^ ]*]] = or i32 [[T3]], [[T4]]
+  ; CHECK: [[T6:%[^ ]*]] = icmp ult i32 [[T5]], 2
+  ; CHECK: br i1 [[T6]]
+
+  ; CHECK: [[T8:%[^ ]*]] = and i32 [[T5]], 31
+  ; CHECK: [[T9:%[^ ]*]] = shl i32 1, [[T8]]
+  ; CHECK: [[T10:%[^ ]*]] = and i32 3, [[T9]]
+  ; CHECK: [[T11:%[^ ]*]] = icmp ne i32 [[T10]], 0
+
+  ; CHECK: [[T16:%[^ ]*]] = phi i1 [ false, {{%[^ ]*}} ], [ [[T11]], {{%[^ ]*}} ]
+  %x = call i1 @llvm.bitset.test(i8* %pi8, metadata !"bitset3")
+  ; CHECK: ret i1 [[T16]]
+  ret i1 %x
+}
+
+; CHECK-NOT: !llvm.bitsets

test/Transforms/LowerBitSets/single-offset.ll

@@ -0,0 +1,40 @@
+; RUN: opt -S -lowerbitsets < %s | FileCheck %s
+
+target datalayout = "e-p:32:32"
+
+; CHECK: [[G:@[^ ]*]] = private constant { i32, i32 }
+@a = constant i32 1
+@b = constant i32 2
+
+!0 = !{!"bitset1", i32* @a, i32 0}
+!1 = !{!"bitset1", i32* @b, i32 0}
+!2 = !{!"bitset2", i32* @a, i32 0}
+!3 = !{!"bitset3", i32* @b, i32 0}
+
+!llvm.bitsets = !{ !0, !1, !2, !3 }
+
+declare i1 @llvm.bitset.test(i8* %ptr, metadata %bitset) nounwind readnone
+
+; CHECK: @foo(i8* [[A0:%[^ ]*]])
+define i1 @foo(i8* %p) {
+  ; CHECK: [[R0:%[^ ]*]] = ptrtoint i8* [[A0]] to i32
+  ; CHECK: [[R1:%[^ ]*]] = icmp eq i32 [[R0]], ptrtoint ({ i32, i32 }* [[G]] to i32)
+  %x = call i1 @llvm.bitset.test(i8* %p, metadata !"bitset2")
+  ; CHECK: ret i1 [[R1]]
+  ret i1 %x
+}
+
+; CHECK: @bar(i8* [[B0:%[^ ]*]])
+define i1 @bar(i8* %p) {
+  ; CHECK: [[S0:%[^ ]*]] = ptrtoint i8* [[B0]] to i32
+  ; CHECK: [[S1:%[^ ]*]] = icmp eq i32 [[S0]], add (i32 ptrtoint ({ i32, i32 }* [[G]] to i32), i32 4)
+  %x = call i1 @llvm.bitset.test(i8* %p, metadata !"bitset3")
+  ; CHECK: ret i1 [[S1]]
+  ret i1 %x
+}
+
+; CHECK: @x(
+define i1 @x(i8* %p) {
+  %x = call i1 @llvm.bitset.test(i8* %p, metadata !"bitset1")
+  ret i1 %x
+}

unittests/Transforms/CMakeLists.txt

@@ -1 +1,2 @@
+add_subdirectory(IPO)
 add_subdirectory(Utils)

unittests/Transforms/IPO/CMakeLists.txt

@@ -0,0 +1,9 @@
+set(LLVM_LINK_COMPONENTS
+  Core
+  Support
+  IPO
+  )
+
+add_llvm_unittest(IPOTests
+  LowerBitSets.cpp
+  )

unittests/Transforms/IPO/LowerBitSets.cpp

@@ -0,0 +1,64 @@
+//===- LowerBitSets.cpp - Unit tests for bitset lowering ------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/IPO/LowerBitSets.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+TEST(LowerBitSets, BitSetBuilder) {
+  struct {
+    std::vector<uint64_t> Offsets;
+    std::vector<uint8_t> Bits;
+    uint64_t ByteOffset;
+    uint64_t BitSize;
+    unsigned AlignLog2;
+    bool IsSingleOffset;
+  } BSBTests[] = {
+      {{}, {0}, 0, 1, 0, false},
+      {{0}, {1}, 0, 1, 0, true},
+      {{4}, {1}, 4, 1, 0, true},
+      {{37}, {1}, 37, 1, 0, true},
+      {{0, 1}, {3}, 0, 2, 0, false},
+      {{0, 4}, {3}, 0, 2, 2, false},
+      {{0, uint64_t(1) << 33}, {3}, 0, 2, 33, false},
+      {{3, 7}, {3}, 3, 2, 2, false},
+      {{0, 1, 7}, {131}, 0, 8, 0, false},
+      {{0, 2, 14}, {131}, 0, 8, 1, false},
+      {{0, 1, 8}, {3, 1}, 0, 9, 0, false},
+      {{0, 2, 16}, {3, 1}, 0, 9, 1, false},
+  };
+
+  for (auto &&T : BSBTests) {
+    BitSetBuilder BSB;
+    for (auto Offset : T.Offsets)
+      BSB.addOffset(Offset);
+
+    BitSetInfo BSI = BSB.build();
+
+    EXPECT_EQ(T.Bits, BSI.Bits);
+    EXPECT_EQ(T.ByteOffset, BSI.ByteOffset);
+    EXPECT_EQ(T.BitSize, BSI.BitSize);
+    EXPECT_EQ(T.AlignLog2, BSI.AlignLog2);
+    EXPECT_EQ(T.IsSingleOffset, BSI.isSingleOffset());
+
+    for (auto Offset : T.Offsets)
+      EXPECT_TRUE(BSI.containsGlobalOffset(Offset));
+
+    auto I = T.Offsets.begin();
+    for (uint64_t NonOffset = 0; NonOffset != 256; ++NonOffset) {
+      if (I != T.Offsets.end() && *I == NonOffset) {
+        ++I;
+        continue;
+      }
+
+      EXPECT_FALSE(BSI.containsGlobalOffset(NonOffset));
+    }
+  }
+}

unittests/Transforms/IPO/Makefile

@@ -0,0 +1,15 @@
+##===- unittests/Transforms/IPO/Makefile -------------------*- Makefile -*-===##
+#
+#                     The LLVM Compiler Infrastructure
+#
+# This file is distributed under the University of Illinois Open Source
+# License. See LICENSE.TXT for details.
+#
+##===----------------------------------------------------------------------===##
+
+LEVEL = ../../..
+TESTNAME = IPO
+LINK_COMPONENTS := IPO
+
+include $(LEVEL)/Makefile.config
+include $(LLVM_SRC_ROOT)/unittests/Makefile.unittest

unittests/Transforms/Makefile

@@ -9,7 +9,7 @@
 
 LEVEL = ../..
 
-PARALLEL_DIRS = Utils
+PARALLEL_DIRS = IPO Utils
 
 include $(LEVEL)/Makefile.common