summaryrefslogtreecommitdiffstats
path: root/contrib/llvm/lib/Transforms/IPO/LowerBitSets.cpp
diff options
context:
space:
mode:
Diffstat (limited to 'contrib/llvm/lib/Transforms/IPO/LowerBitSets.cpp')
-rw-r--r--contrib/llvm/lib/Transforms/IPO/LowerBitSets.cpp1055
1 files changed, 1055 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/IPO/LowerBitSets.cpp b/contrib/llvm/lib/Transforms/IPO/LowerBitSets.cpp
new file mode 100644
index 0000000..7b51574
--- /dev/null
+++ b/contrib/llvm/lib/Transforms/IPO/LowerBitSets.cpp
@@ -0,0 +1,1055 @@
+//===-- 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/ADT/Triple.h"
+#include "llvm/IR/Constant.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/GlobalObject.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/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "lowerbitsets"
+
+STATISTIC(ByteArraySizeBits, "Byte array size in bits");
+STATISTIC(ByteArraySizeBytes, "Byte array size in bytes");
+STATISTIC(NumByteArraysCreated, "Number of byte arrays created");
+STATISTIC(NumBitSetCallsLowered, "Number of bitset calls lowered");
+STATISTIC(NumBitSetDisjointSets, "Number of disjoint sets of bitsets");
+
+static cl::opt<bool> AvoidReuse(
+ "lowerbitsets-avoid-reuse",
+ cl::desc("Try to avoid reuse of byte array addresses using aliases"),
+ cl::Hidden, cl::init(true));
+
+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.count(BitOffset);
+}
+
+bool BitSetInfo::containsValue(
+ const DataLayout &DL,
+ const DenseMap<GlobalObject *, uint64_t> &GlobalLayout, Value *V,
+ uint64_t COffset) const {
+ if (auto GV = dyn_cast<GlobalObject>(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;
+}
+
+void BitSetInfo::print(raw_ostream &OS) const {
+ OS << "offset " << ByteOffset << " size " << BitSize << " align "
+ << (1 << AlignLog2);
+
+ if (isAllOnes()) {
+ OS << " all-ones\n";
+ return;
+ }
+
+ OS << " { ";
+ for (uint64_t B : Bits)
+ OS << B << ' ';
+ OS << "}\n";
+}
+
+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;
+ 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;
+ for (uint64_t Offset : Offsets) {
+ Offset >>= BSI.AlignLog2;
+ BSI.Bits.insert(Offset);
+ }
+
+ return BSI;
+}
+
+void GlobalLayoutBuilder::addFragment(const std::set<uint64_t> &F) {
+ // Create a new fragment to hold the layout for F.
+ Fragments.emplace_back();
+ std::vector<uint64_t> &Fragment = Fragments.back();
+ uint64_t FragmentIndex = Fragments.size() - 1;
+
+ for (auto ObjIndex : F) {
+ uint64_t OldFragmentIndex = FragmentMap[ObjIndex];
+ if (OldFragmentIndex == 0) {
+ // We haven't seen this object index before, so just add it to the current
+ // fragment.
+ Fragment.push_back(ObjIndex);
+ } else {
+ // This index belongs to an existing fragment. Copy the elements of the
+ // old fragment into this one and clear the old fragment. We don't update
+ // the fragment map just yet, this ensures that any further references to
+ // indices from the old fragment in this fragment do not insert any more
+ // indices.
+ std::vector<uint64_t> &OldFragment = Fragments[OldFragmentIndex];
+ Fragment.insert(Fragment.end(), OldFragment.begin(), OldFragment.end());
+ OldFragment.clear();
+ }
+ }
+
+ // Update the fragment map to point our object indices to this fragment.
+ for (uint64_t ObjIndex : Fragment)
+ FragmentMap[ObjIndex] = FragmentIndex;
+}
+
+void ByteArrayBuilder::allocate(const std::set<uint64_t> &Bits,
+ uint64_t BitSize, uint64_t &AllocByteOffset,
+ uint8_t &AllocMask) {
+ // Find the smallest current allocation.
+ unsigned Bit = 0;
+ for (unsigned I = 1; I != BitsPerByte; ++I)
+ if (BitAllocs[I] < BitAllocs[Bit])
+ Bit = I;
+
+ AllocByteOffset = BitAllocs[Bit];
+
+ // Add our size to it.
+ unsigned ReqSize = AllocByteOffset + BitSize;
+ BitAllocs[Bit] = ReqSize;
+ if (Bytes.size() < ReqSize)
+ Bytes.resize(ReqSize);
+
+ // Set our bits.
+ AllocMask = 1 << Bit;
+ for (uint64_t B : Bits)
+ Bytes[AllocByteOffset + B] |= AllocMask;
+}
+
+namespace {
+
+struct ByteArrayInfo {
+ std::set<uint64_t> Bits;
+ uint64_t BitSize;
+ GlobalVariable *ByteArray;
+ Constant *Mask;
+};
+
+struct LowerBitSets : public ModulePass {
+ static char ID;
+ LowerBitSets() : ModulePass(ID) {
+ initializeLowerBitSetsPass(*PassRegistry::getPassRegistry());
+ }
+
+ Module *M;
+
+ bool LinkerSubsectionsViaSymbols;
+ Triple::ArchType Arch;
+ Triple::ObjectFormatType ObjectFormat;
+ IntegerType *Int1Ty;
+ IntegerType *Int8Ty;
+ IntegerType *Int32Ty;
+ Type *Int32PtrTy;
+ IntegerType *Int64Ty;
+ IntegerType *IntPtrTy;
+
+ // The llvm.bitsets named metadata.
+ NamedMDNode *BitSetNM;
+
+ // Mapping from bitset identifiers to the call sites that test them.
+ DenseMap<Metadata *, std::vector<CallInst *>> BitSetTestCallSites;
+
+ std::vector<ByteArrayInfo> ByteArrayInfos;
+
+ BitSetInfo
+ buildBitSet(Metadata *BitSet,
+ const DenseMap<GlobalObject *, uint64_t> &GlobalLayout);
+ ByteArrayInfo *createByteArray(BitSetInfo &BSI);
+ void allocateByteArrays();
+ Value *createBitSetTest(IRBuilder<> &B, BitSetInfo &BSI, ByteArrayInfo *&BAI,
+ Value *BitOffset);
+ void lowerBitSetCalls(ArrayRef<Metadata *> BitSets,
+ Constant *CombinedGlobalAddr,
+ const DenseMap<GlobalObject *, uint64_t> &GlobalLayout);
+ Value *
+ lowerBitSetCall(CallInst *CI, BitSetInfo &BSI, ByteArrayInfo *&BAI,
+ Constant *CombinedGlobal,
+ const DenseMap<GlobalObject *, uint64_t> &GlobalLayout);
+ void buildBitSetsFromGlobalVariables(ArrayRef<Metadata *> BitSets,
+ ArrayRef<GlobalVariable *> Globals);
+ unsigned getJumpTableEntrySize();
+ Type *getJumpTableEntryType();
+ Constant *createJumpTableEntry(GlobalObject *Src, Function *Dest,
+ unsigned Distance);
+ void verifyBitSetMDNode(MDNode *Op);
+ void buildBitSetsFromFunctions(ArrayRef<Metadata *> BitSets,
+ ArrayRef<Function *> Functions);
+ void buildBitSetsFromDisjointSet(ArrayRef<Metadata *> BitSets,
+ ArrayRef<GlobalObject *> Globals);
+ bool buildBitSets();
+ bool eraseBitSetMetadata();
+
+ bool doInitialization(Module &M) override;
+ bool runOnModule(Module &M) override;
+};
+
+} // anonymous 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 &Mod) {
+ M = &Mod;
+ const DataLayout &DL = Mod.getDataLayout();
+
+ Triple TargetTriple(M->getTargetTriple());
+ LinkerSubsectionsViaSymbols = TargetTriple.isMacOSX();
+ Arch = TargetTriple.getArch();
+ ObjectFormat = TargetTriple.getObjectFormat();
+
+ Int1Ty = Type::getInt1Ty(M->getContext());
+ Int8Ty = Type::getInt8Ty(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 BitSet using the object layouts in
+/// GlobalLayout.
+BitSetInfo LowerBitSets::buildBitSet(
+ Metadata *BitSet,
+ const DenseMap<GlobalObject *, 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;
+ Constant *OpConst =
+ cast<ConstantAsMetadata>(Op->getOperand(1))->getValue();
+ if (auto GA = dyn_cast<GlobalAlias>(OpConst))
+ OpConst = GA->getAliasee();
+ auto OpGlobal = dyn_cast<GlobalObject>(OpConst);
+ if (!OpGlobal)
+ continue;
+ 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 BitOffset mod sizeof(Bits)*8 is set in
+/// 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));
+}
+
+ByteArrayInfo *LowerBitSets::createByteArray(BitSetInfo &BSI) {
+ // Create globals to stand in for byte arrays and masks. These never actually
+ // get initialized, we RAUW and erase them later in allocateByteArrays() once
+ // we know the offset and mask to use.
+ auto ByteArrayGlobal = new GlobalVariable(
+ *M, Int8Ty, /*isConstant=*/true, GlobalValue::PrivateLinkage, nullptr);
+ auto MaskGlobal = new GlobalVariable(
+ *M, Int8Ty, /*isConstant=*/true, GlobalValue::PrivateLinkage, nullptr);
+
+ ByteArrayInfos.emplace_back();
+ ByteArrayInfo *BAI = &ByteArrayInfos.back();
+
+ BAI->Bits = BSI.Bits;
+ BAI->BitSize = BSI.BitSize;
+ BAI->ByteArray = ByteArrayGlobal;
+ BAI->Mask = ConstantExpr::getPtrToInt(MaskGlobal, Int8Ty);
+ return BAI;
+}
+
+void LowerBitSets::allocateByteArrays() {
+ std::stable_sort(ByteArrayInfos.begin(), ByteArrayInfos.end(),
+ [](const ByteArrayInfo &BAI1, const ByteArrayInfo &BAI2) {
+ return BAI1.BitSize > BAI2.BitSize;
+ });
+
+ std::vector<uint64_t> ByteArrayOffsets(ByteArrayInfos.size());
+
+ ByteArrayBuilder BAB;
+ for (unsigned I = 0; I != ByteArrayInfos.size(); ++I) {
+ ByteArrayInfo *BAI = &ByteArrayInfos[I];
+
+ uint8_t Mask;
+ BAB.allocate(BAI->Bits, BAI->BitSize, ByteArrayOffsets[I], Mask);
+
+ BAI->Mask->replaceAllUsesWith(ConstantInt::get(Int8Ty, Mask));
+ cast<GlobalVariable>(BAI->Mask->getOperand(0))->eraseFromParent();
+ }
+
+ Constant *ByteArrayConst = ConstantDataArray::get(M->getContext(), BAB.Bytes);
+ auto ByteArray =
+ new GlobalVariable(*M, ByteArrayConst->getType(), /*isConstant=*/true,
+ GlobalValue::PrivateLinkage, ByteArrayConst);
+
+ for (unsigned I = 0; I != ByteArrayInfos.size(); ++I) {
+ ByteArrayInfo *BAI = &ByteArrayInfos[I];
+
+ Constant *Idxs[] = {ConstantInt::get(IntPtrTy, 0),
+ ConstantInt::get(IntPtrTy, ByteArrayOffsets[I])};
+ Constant *GEP = ConstantExpr::getInBoundsGetElementPtr(
+ ByteArrayConst->getType(), ByteArray, Idxs);
+
+ // Create an alias instead of RAUW'ing the gep directly. On x86 this ensures
+ // that the pc-relative displacement is folded into the lea instead of the
+ // test instruction getting another displacement.
+ if (LinkerSubsectionsViaSymbols) {
+ BAI->ByteArray->replaceAllUsesWith(GEP);
+ } else {
+ GlobalAlias *Alias = GlobalAlias::create(
+ Int8Ty, 0, GlobalValue::PrivateLinkage, "bits", GEP, M);
+ BAI->ByteArray->replaceAllUsesWith(Alias);
+ }
+ BAI->ByteArray->eraseFromParent();
+ }
+
+ ByteArraySizeBits = BAB.BitAllocs[0] + BAB.BitAllocs[1] + BAB.BitAllocs[2] +
+ BAB.BitAllocs[3] + BAB.BitAllocs[4] + BAB.BitAllocs[5] +
+ BAB.BitAllocs[6] + BAB.BitAllocs[7];
+ ByteArraySizeBytes = BAB.Bytes.size();
+}
+
+/// Build a test that bit BitOffset is set in BSI, where
+/// BitSetGlobal is a global containing the bits in BSI.
+Value *LowerBitSets::createBitSetTest(IRBuilder<> &B, BitSetInfo &BSI,
+ ByteArrayInfo *&BAI, Value *BitOffset) {
+ if (BSI.BitSize <= 64) {
+ // If the bit set is sufficiently small, we can avoid a load by bit testing
+ // a constant.
+ IntegerType *BitsTy;
+ if (BSI.BitSize <= 32)
+ BitsTy = Int32Ty;
+ else
+ BitsTy = Int64Ty;
+
+ uint64_t Bits = 0;
+ for (auto Bit : BSI.Bits)
+ Bits |= uint64_t(1) << Bit;
+ Constant *BitsConst = ConstantInt::get(BitsTy, Bits);
+ return createMaskedBitTest(B, BitsConst, BitOffset);
+ } else {
+ if (!BAI) {
+ ++NumByteArraysCreated;
+ BAI = createByteArray(BSI);
+ }
+
+ Constant *ByteArray = BAI->ByteArray;
+ Type *Ty = BAI->ByteArray->getValueType();
+ if (!LinkerSubsectionsViaSymbols && AvoidReuse) {
+ // Each use of the byte array uses a different alias. This makes the
+ // backend less likely to reuse previously computed byte array addresses,
+ // improving the security of the CFI mechanism based on this pass.
+ ByteArray = GlobalAlias::create(BAI->ByteArray->getValueType(), 0,
+ GlobalValue::PrivateLinkage, "bits_use",
+ ByteArray, M);
+ }
+
+ Value *ByteAddr = B.CreateGEP(Ty, ByteArray, BitOffset);
+ Value *Byte = B.CreateLoad(ByteAddr);
+
+ Value *ByteAndMask = B.CreateAnd(Byte, BAI->Mask);
+ return B.CreateICmpNE(ByteAndMask, ConstantInt::get(Int8Ty, 0));
+ }
+}
+
+/// Lower a llvm.bitset.test call to its implementation. Returns the value to
+/// replace the call with.
+Value *LowerBitSets::lowerBitSetCall(
+ CallInst *CI, BitSetInfo &BSI, ByteArrayInfo *&BAI,
+ Constant *CombinedGlobalIntAddr,
+ const DenseMap<GlobalObject *, uint64_t> &GlobalLayout) {
+ Value *Ptr = CI->getArgOperand(0);
+ const DataLayout &DL = M->getDataLayout();
+
+ if (BSI.containsValue(DL, GlobalLayout, Ptr))
+ return ConstantInt::getTrue(M->getContext());
+
+ Constant *OffsetedGlobalAsInt = ConstantExpr::getAdd(
+ CombinedGlobalIntAddr, ConstantInt::get(IntPtrTy, BSI.ByteOffset));
+
+ BasicBlock *InitialBB = CI->getParent();
+
+ IRBuilder<> B(CI);
+
+ Value *PtrAsInt = B.CreatePtrToInt(Ptr, IntPtrTy);
+
+ if (BSI.isSingleOffset())
+ return B.CreateICmpEQ(PtrAsInt, OffsetedGlobalAsInt);
+
+ 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);
+
+ // If the bit set is all ones, testing against it is unnecessary.
+ if (BSI.isAllOnes())
+ return OffsetInRange;
+
+ 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, BAI, 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());
+ return P;
+}
+
+/// Given a disjoint set of bitsets and globals, layout the globals, build the
+/// bit sets and lower the llvm.bitset.test calls.
+void LowerBitSets::buildBitSetsFromGlobalVariables(
+ ArrayRef<Metadata *> BitSets, ArrayRef<GlobalVariable *> Globals) {
+ // Build a new global with the combined contents of the referenced globals.
+ // This global is a struct whose even-indexed elements contain the original
+ // contents of the referenced globals and whose odd-indexed elements contain
+ // any padding required to align the next element to the next power of 2.
+ std::vector<Constant *> GlobalInits;
+ const DataLayout &DL = M->getDataLayout();
+ for (GlobalVariable *G : Globals) {
+ GlobalInits.push_back(G->getInitializer());
+ uint64_t InitSize = DL.getTypeAllocSize(G->getValueType());
+
+ // Compute the amount of padding required.
+ uint64_t Padding = NextPowerOf2(InitSize - 1) - InitSize;
+
+ // Cap at 128 was found experimentally to have a good data/instruction
+ // overhead tradeoff.
+ if (Padding > 128)
+ Padding = RoundUpToAlignment(InitSize, 128) - InitSize;
+
+ GlobalInits.push_back(
+ ConstantAggregateZero::get(ArrayType::get(Int8Ty, Padding)));
+ }
+ if (!GlobalInits.empty())
+ GlobalInits.pop_back();
+ Constant *NewInit = ConstantStruct::getAnon(M->getContext(), GlobalInits);
+ auto *CombinedGlobal =
+ new GlobalVariable(*M, NewInit->getType(), /*isConstant=*/true,
+ GlobalValue::PrivateLinkage, NewInit);
+
+ StructType *NewTy = cast<StructType>(NewInit->getType());
+ const StructLayout *CombinedGlobalLayout = DL.getStructLayout(NewTy);
+
+ // Compute the offsets of the original globals within the new global.
+ DenseMap<GlobalObject *, uint64_t> GlobalLayout;
+ for (unsigned I = 0; I != Globals.size(); ++I)
+ // Multiply by 2 to account for padding elements.
+ GlobalLayout[Globals[I]] = CombinedGlobalLayout->getElementOffset(I * 2);
+
+ lowerBitSetCalls(BitSets, 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) {
+ // Multiply by 2 to account for padding elements.
+ Constant *CombinedGlobalIdxs[] = {ConstantInt::get(Int32Ty, 0),
+ ConstantInt::get(Int32Ty, I * 2)};
+ Constant *CombinedGlobalElemPtr = ConstantExpr::getGetElementPtr(
+ NewInit->getType(), CombinedGlobal, CombinedGlobalIdxs);
+ if (LinkerSubsectionsViaSymbols) {
+ Globals[I]->replaceAllUsesWith(CombinedGlobalElemPtr);
+ } else {
+ assert(Globals[I]->getType()->getAddressSpace() == 0);
+ GlobalAlias *GAlias = GlobalAlias::create(NewTy->getElementType(I * 2), 0,
+ Globals[I]->getLinkage(), "",
+ CombinedGlobalElemPtr, M);
+ GAlias->setVisibility(Globals[I]->getVisibility());
+ GAlias->takeName(Globals[I]);
+ Globals[I]->replaceAllUsesWith(GAlias);
+ }
+ Globals[I]->eraseFromParent();
+ }
+}
+
+void LowerBitSets::lowerBitSetCalls(
+ ArrayRef<Metadata *> BitSets, Constant *CombinedGlobalAddr,
+ const DenseMap<GlobalObject *, uint64_t> &GlobalLayout) {
+ Constant *CombinedGlobalIntAddr =
+ ConstantExpr::getPtrToInt(CombinedGlobalAddr, IntPtrTy);
+
+ // For each bitset in this disjoint set...
+ for (Metadata *BS : BitSets) {
+ // Build the bitset.
+ BitSetInfo BSI = buildBitSet(BS, GlobalLayout);
+ DEBUG({
+ if (auto BSS = dyn_cast<MDString>(BS))
+ dbgs() << BSS->getString() << ": ";
+ else
+ dbgs() << "<unnamed>: ";
+ BSI.print(dbgs());
+ });
+
+ ByteArrayInfo *BAI = nullptr;
+
+ // Lower each call to llvm.bitset.test for this bitset.
+ for (CallInst *CI : BitSetTestCallSites[BS]) {
+ ++NumBitSetCallsLowered;
+ Value *Lowered =
+ lowerBitSetCall(CI, BSI, BAI, CombinedGlobalIntAddr, GlobalLayout);
+ CI->replaceAllUsesWith(Lowered);
+ CI->eraseFromParent();
+ }
+ }
+}
+
+void LowerBitSets::verifyBitSetMDNode(MDNode *Op) {
+ if (Op->getNumOperands() != 3)
+ report_fatal_error(
+ "All operands of llvm.bitsets metadata must have 3 elements");
+ if (!Op->getOperand(1))
+ return;
+
+ auto OpConstMD = dyn_cast<ConstantAsMetadata>(Op->getOperand(1));
+ if (!OpConstMD)
+ report_fatal_error("Bit set element must be a constant");
+ auto OpGlobal = dyn_cast<GlobalObject>(OpConstMD->getValue());
+ if (!OpGlobal)
+ return;
+
+ if (OpGlobal->isThreadLocal())
+ report_fatal_error("Bit set element may not be thread-local");
+ if (OpGlobal->hasSection())
+ report_fatal_error("Bit set element may not have an explicit section");
+
+ if (isa<GlobalVariable>(OpGlobal) && OpGlobal->isDeclarationForLinker())
+ report_fatal_error("Bit set global var element must be a definition");
+
+ 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");
+}
+
+static const unsigned kX86JumpTableEntrySize = 8;
+
+unsigned LowerBitSets::getJumpTableEntrySize() {
+ if (Arch != Triple::x86 && Arch != Triple::x86_64)
+ report_fatal_error("Unsupported architecture for jump tables");
+
+ return kX86JumpTableEntrySize;
+}
+
+// Create a constant representing a jump table entry for the target. This
+// consists of an instruction sequence containing a relative branch to Dest. The
+// constant will be laid out at address Src+(Len*Distance) where Len is the
+// target-specific jump table entry size.
+Constant *LowerBitSets::createJumpTableEntry(GlobalObject *Src, Function *Dest,
+ unsigned Distance) {
+ if (Arch != Triple::x86 && Arch != Triple::x86_64)
+ report_fatal_error("Unsupported architecture for jump tables");
+
+ const unsigned kJmpPCRel32Code = 0xe9;
+ const unsigned kInt3Code = 0xcc;
+
+ ConstantInt *Jmp = ConstantInt::get(Int8Ty, kJmpPCRel32Code);
+
+ // Build a constant representing the displacement between the constant's
+ // address and Dest. This will resolve to a PC32 relocation referring to Dest.
+ Constant *DestInt = ConstantExpr::getPtrToInt(Dest, IntPtrTy);
+ Constant *SrcInt = ConstantExpr::getPtrToInt(Src, IntPtrTy);
+ Constant *Disp = ConstantExpr::getSub(DestInt, SrcInt);
+ ConstantInt *DispOffset =
+ ConstantInt::get(IntPtrTy, Distance * kX86JumpTableEntrySize + 5);
+ Constant *OffsetedDisp = ConstantExpr::getSub(Disp, DispOffset);
+ OffsetedDisp = ConstantExpr::getTruncOrBitCast(OffsetedDisp, Int32Ty);
+
+ ConstantInt *Int3 = ConstantInt::get(Int8Ty, kInt3Code);
+
+ Constant *Fields[] = {
+ Jmp, OffsetedDisp, Int3, Int3, Int3,
+ };
+ return ConstantStruct::getAnon(Fields, /*Packed=*/true);
+}
+
+Type *LowerBitSets::getJumpTableEntryType() {
+ if (Arch != Triple::x86 && Arch != Triple::x86_64)
+ report_fatal_error("Unsupported architecture for jump tables");
+
+ return StructType::get(M->getContext(),
+ {Int8Ty, Int32Ty, Int8Ty, Int8Ty, Int8Ty},
+ /*Packed=*/true);
+}
+
+/// Given a disjoint set of bitsets and functions, build a jump table for the
+/// functions, build the bit sets and lower the llvm.bitset.test calls.
+void LowerBitSets::buildBitSetsFromFunctions(ArrayRef<Metadata *> BitSets,
+ ArrayRef<Function *> Functions) {
+ // Unlike the global bitset builder, the function bitset builder cannot
+ // re-arrange functions in a particular order and base its calculations on the
+ // layout of the functions' entry points, as we have no idea how large a
+ // particular function will end up being (the size could even depend on what
+ // this pass does!) Instead, we build a jump table, which is a block of code
+ // consisting of one branch instruction for each of the functions in the bit
+ // set that branches to the target function, and redirect any taken function
+ // addresses to the corresponding jump table entry. In the object file's
+ // symbol table, the symbols for the target functions also refer to the jump
+ // table entries, so that addresses taken outside the module will pass any
+ // verification done inside the module.
+ //
+ // In more concrete terms, suppose we have three functions f, g, h which are
+ // members of a single bitset, and a function foo that returns their
+ // addresses:
+ //
+ // f:
+ // mov 0, %eax
+ // ret
+ //
+ // g:
+ // mov 1, %eax
+ // ret
+ //
+ // h:
+ // mov 2, %eax
+ // ret
+ //
+ // foo:
+ // mov f, %eax
+ // mov g, %edx
+ // mov h, %ecx
+ // ret
+ //
+ // To create a jump table for these functions, we instruct the LLVM code
+ // generator to output a jump table in the .text section. This is done by
+ // representing the instructions in the jump table as an LLVM constant and
+ // placing them in a global variable in the .text section. The end result will
+ // (conceptually) look like this:
+ //
+ // f:
+ // jmp .Ltmp0 ; 5 bytes
+ // int3 ; 1 byte
+ // int3 ; 1 byte
+ // int3 ; 1 byte
+ //
+ // g:
+ // jmp .Ltmp1 ; 5 bytes
+ // int3 ; 1 byte
+ // int3 ; 1 byte
+ // int3 ; 1 byte
+ //
+ // h:
+ // jmp .Ltmp2 ; 5 bytes
+ // int3 ; 1 byte
+ // int3 ; 1 byte
+ // int3 ; 1 byte
+ //
+ // .Ltmp0:
+ // mov 0, %eax
+ // ret
+ //
+ // .Ltmp1:
+ // mov 1, %eax
+ // ret
+ //
+ // .Ltmp2:
+ // mov 2, %eax
+ // ret
+ //
+ // foo:
+ // mov f, %eax
+ // mov g, %edx
+ // mov h, %ecx
+ // ret
+ //
+ // Because the addresses of f, g, h are evenly spaced at a power of 2, in the
+ // normal case the check can be carried out using the same kind of simple
+ // arithmetic that we normally use for globals.
+
+ assert(!Functions.empty());
+
+ // Build a simple layout based on the regular layout of jump tables.
+ DenseMap<GlobalObject *, uint64_t> GlobalLayout;
+ unsigned EntrySize = getJumpTableEntrySize();
+ for (unsigned I = 0; I != Functions.size(); ++I)
+ GlobalLayout[Functions[I]] = I * EntrySize;
+
+ // Create a constant to hold the jump table.
+ ArrayType *JumpTableType =
+ ArrayType::get(getJumpTableEntryType(), Functions.size());
+ auto JumpTable = new GlobalVariable(*M, JumpTableType,
+ /*isConstant=*/true,
+ GlobalValue::PrivateLinkage, nullptr);
+ JumpTable->setSection(ObjectFormat == Triple::MachO
+ ? "__TEXT,__text,regular,pure_instructions"
+ : ".text");
+ lowerBitSetCalls(BitSets, JumpTable, GlobalLayout);
+
+ // Build aliases pointing to offsets into the jump table, and replace
+ // references to the original functions with references to the aliases.
+ for (unsigned I = 0; I != Functions.size(); ++I) {
+ Constant *CombinedGlobalElemPtr = ConstantExpr::getBitCast(
+ ConstantExpr::getGetElementPtr(
+ JumpTableType, JumpTable,
+ ArrayRef<Constant *>{ConstantInt::get(IntPtrTy, 0),
+ ConstantInt::get(IntPtrTy, I)}),
+ Functions[I]->getType());
+ if (LinkerSubsectionsViaSymbols || Functions[I]->isDeclarationForLinker()) {
+ Functions[I]->replaceAllUsesWith(CombinedGlobalElemPtr);
+ } else {
+ assert(Functions[I]->getType()->getAddressSpace() == 0);
+ GlobalAlias *GAlias = GlobalAlias::create(Functions[I]->getValueType(), 0,
+ Functions[I]->getLinkage(), "",
+ CombinedGlobalElemPtr, M);
+ GAlias->setVisibility(Functions[I]->getVisibility());
+ GAlias->takeName(Functions[I]);
+ Functions[I]->replaceAllUsesWith(GAlias);
+ }
+ if (!Functions[I]->isDeclarationForLinker())
+ Functions[I]->setLinkage(GlobalValue::PrivateLinkage);
+ }
+
+ // Build and set the jump table's initializer.
+ std::vector<Constant *> JumpTableEntries;
+ for (unsigned I = 0; I != Functions.size(); ++I)
+ JumpTableEntries.push_back(
+ createJumpTableEntry(JumpTable, Functions[I], I));
+ JumpTable->setInitializer(
+ ConstantArray::get(JumpTableType, JumpTableEntries));
+}
+
+void LowerBitSets::buildBitSetsFromDisjointSet(
+ ArrayRef<Metadata *> BitSets, ArrayRef<GlobalObject *> Globals) {
+ llvm::DenseMap<Metadata *, uint64_t> BitSetIndices;
+ llvm::DenseMap<GlobalObject *, uint64_t> GlobalIndices;
+ for (unsigned I = 0; I != BitSets.size(); ++I)
+ BitSetIndices[BitSets[I]] = I;
+ for (unsigned I = 0; I != Globals.size(); ++I)
+ GlobalIndices[Globals[I]] = I;
+
+ // For each bitset, build a set of indices that refer to globals referenced by
+ // the bitset.
+ std::vector<std::set<uint64_t>> BitSetMembers(BitSets.size());
+ if (BitSetNM) {
+ for (MDNode *Op : BitSetNM->operands()) {
+ // Op = { bitset name, global, offset }
+ if (!Op->getOperand(1))
+ continue;
+ auto I = BitSetIndices.find(Op->getOperand(0));
+ if (I == BitSetIndices.end())
+ continue;
+
+ auto OpGlobal = dyn_cast<GlobalObject>(
+ cast<ConstantAsMetadata>(Op->getOperand(1))->getValue());
+ if (!OpGlobal)
+ continue;
+ BitSetMembers[I->second].insert(GlobalIndices[OpGlobal]);
+ }
+ }
+
+ // Order the sets of indices by size. The GlobalLayoutBuilder works best
+ // when given small index sets first.
+ std::stable_sort(
+ BitSetMembers.begin(), BitSetMembers.end(),
+ [](const std::set<uint64_t> &O1, const std::set<uint64_t> &O2) {
+ return O1.size() < O2.size();
+ });
+
+ // Create a GlobalLayoutBuilder and provide it with index sets as layout
+ // fragments. The GlobalLayoutBuilder tries to lay out members of fragments as
+ // close together as possible.
+ GlobalLayoutBuilder GLB(Globals.size());
+ for (auto &&MemSet : BitSetMembers)
+ GLB.addFragment(MemSet);
+
+ // Build the bitsets from this disjoint set.
+ if (Globals.empty() || isa<GlobalVariable>(Globals[0])) {
+ // Build a vector of global variables with the computed layout.
+ std::vector<GlobalVariable *> OrderedGVs(Globals.size());
+ auto OGI = OrderedGVs.begin();
+ for (auto &&F : GLB.Fragments) {
+ for (auto &&Offset : F) {
+ auto GV = dyn_cast<GlobalVariable>(Globals[Offset]);
+ if (!GV)
+ report_fatal_error(
+ "Bit set may not contain both global variables and functions");
+ *OGI++ = GV;
+ }
+ }
+
+ buildBitSetsFromGlobalVariables(BitSets, OrderedGVs);
+ } else {
+ // Build a vector of functions with the computed layout.
+ std::vector<Function *> OrderedFns(Globals.size());
+ auto OFI = OrderedFns.begin();
+ for (auto &&F : GLB.Fragments) {
+ for (auto &&Offset : F) {
+ auto Fn = dyn_cast<Function>(Globals[Offset]);
+ if (!Fn)
+ report_fatal_error(
+ "Bit set may not contain both global variables and functions");
+ *OFI++ = Fn;
+ }
+ }
+
+ buildBitSetsFromFunctions(BitSets, OrderedFns);
+ }
+}
+
+/// Lower all bit sets in this module.
+bool LowerBitSets::buildBitSets() {
+ 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<GlobalObject *, Metadata *>>
+ GlobalClassesTy;
+ GlobalClassesTy GlobalClasses;
+
+ // Verify the bitset metadata and build a mapping from bitset identifiers to
+ // their last observed index in BitSetNM. This will used later to
+ // deterministically order the list of bitset identifiers.
+ llvm::DenseMap<Metadata *, unsigned> BitSetIdIndices;
+ if (BitSetNM) {
+ for (unsigned I = 0, E = BitSetNM->getNumOperands(); I != E; ++I) {
+ MDNode *Op = BitSetNM->getOperand(I);
+ verifyBitSetMDNode(Op);
+ BitSetIdIndices[Op->getOperand(0)] = I;
+ }
+ }
+
+ for (const Use &U : BitSetTestFunc->uses()) {
+ auto CI = cast<CallInst>(U.getUser());
+
+ auto BitSetMDVal = dyn_cast<MetadataAsValue>(CI->getArgOperand(1));
+ if (!BitSetMDVal)
+ report_fatal_error(
+ "Second argument of llvm.bitset.test must be metadata");
+ auto BitSet = 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<Metadata *, 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;
+
+ // Add the referenced globals to the bitset's equivalence class.
+ for (MDNode *Op : BitSetNM->operands()) {
+ if (Op->getOperand(0) != BitSet || !Op->getOperand(1))
+ continue;
+
+ auto OpGlobal = dyn_cast<GlobalObject>(
+ cast<ConstantAsMetadata>(Op->getOperand(1))->getValue());
+ if (!OpGlobal)
+ continue;
+
+ CurSet = GlobalClasses.unionSets(
+ CurSet, GlobalClasses.findLeader(GlobalClasses.insert(OpGlobal)));
+ }
+ }
+
+ if (GlobalClasses.empty())
+ return false;
+
+ // Build a list of disjoint sets ordered by their maximum BitSetNM index
+ // for determinism.
+ std::vector<std::pair<GlobalClassesTy::iterator, unsigned>> Sets;
+ for (GlobalClassesTy::iterator I = GlobalClasses.begin(),
+ E = GlobalClasses.end();
+ I != E; ++I) {
+ if (!I->isLeader()) continue;
+ ++NumBitSetDisjointSets;
+
+ unsigned MaxIndex = 0;
+ for (GlobalClassesTy::member_iterator MI = GlobalClasses.member_begin(I);
+ MI != GlobalClasses.member_end(); ++MI) {
+ if ((*MI).is<Metadata *>())
+ MaxIndex = std::max(MaxIndex, BitSetIdIndices[MI->get<Metadata *>()]);
+ }
+ Sets.emplace_back(I, MaxIndex);
+ }
+ std::sort(Sets.begin(), Sets.end(),
+ [](const std::pair<GlobalClassesTy::iterator, unsigned> &S1,
+ const std::pair<GlobalClassesTy::iterator, unsigned> &S2) {
+ return S1.second < S2.second;
+ });
+
+ // For each disjoint set we found...
+ for (const auto &S : Sets) {
+ // Build the list of bitsets in this disjoint set.
+ std::vector<Metadata *> BitSets;
+ std::vector<GlobalObject *> Globals;
+ for (GlobalClassesTy::member_iterator MI =
+ GlobalClasses.member_begin(S.first);
+ MI != GlobalClasses.member_end(); ++MI) {
+ if ((*MI).is<Metadata *>())
+ BitSets.push_back(MI->get<Metadata *>());
+ else
+ Globals.push_back(MI->get<GlobalObject *>());
+ }
+
+ // Order bitsets by BitSetNM index for determinism. This ordering is stable
+ // as there is a one-to-one mapping between metadata and indices.
+ std::sort(BitSets.begin(), BitSets.end(), [&](Metadata *M1, Metadata *M2) {
+ return BitSetIdIndices[M1] < BitSetIdIndices[M2];
+ });
+
+ // Lower the bitsets in this disjoint set.
+ buildBitSetsFromDisjointSet(BitSets, Globals);
+ }
+
+ allocateByteArrays();
+
+ return true;
+}
+
+bool LowerBitSets::eraseBitSetMetadata() {
+ if (!BitSetNM)
+ return false;
+
+ M->eraseNamedMetadata(BitSetNM);
+ return true;
+}
+
+bool LowerBitSets::runOnModule(Module &M) {
+ bool Changed = buildBitSets();
+ Changed |= eraseBitSetMetadata();
+ return Changed;
+}
OpenPOWER on IntegriCloud