234 lines
8.9 KiB
C++
234 lines
8.9 KiB
C++
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//===--- MicrosoftVBTables.cpp - Virtual Base Table Emission --------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This class generates data about MSVC virtual base tables.
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//
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//===----------------------------------------------------------------------===//
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#include "MicrosoftVBTables.h"
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#include "CodeGenModule.h"
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#include "CGCXXABI.h"
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namespace clang {
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namespace CodeGen {
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/// Holds intermediate data about a path to a vbptr inside a base subobject.
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struct VBTablePath {
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VBTablePath(const VBTableInfo &VBInfo)
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: VBInfo(VBInfo), NextBase(VBInfo.VBPtrSubobject.getBase()) { }
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/// All the data needed to build a vbtable, minus the GlobalVariable whose
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/// name we haven't computed yet.
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VBTableInfo VBInfo;
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/// Next base to use for disambiguation. Can be null if we've already
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/// disambiguated this path once.
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const CXXRecordDecl *NextBase;
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/// Path is not really a full path like a CXXBasePath. It holds the subset of
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/// records that need to be mangled into the vbtable symbol name in order to get
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/// a unique name.
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llvm::SmallVector<const CXXRecordDecl *, 1> Path;
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};
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VBTableBuilder::VBTableBuilder(CodeGenModule &CGM,
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const CXXRecordDecl *MostDerived)
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: CGM(CGM), MostDerived(MostDerived),
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DerivedLayout(CGM.getContext().getASTRecordLayout(MostDerived)) {}
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void VBTableBuilder::enumerateVBTables(VBTableVector &VBTables) {
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VBTablePathVector Paths;
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findUnambiguousPaths(MostDerived, BaseSubobject(MostDerived,
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CharUnits::Zero()), Paths);
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for (VBTablePathVector::iterator I = Paths.begin(), E = Paths.end();
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I != E; ++I) {
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VBTablePath *P = *I;
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P->VBInfo.GV = getAddrOfVBTable(P->VBInfo.ReusingBase, P->Path);
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VBTables.push_back(P->VBInfo);
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}
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}
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void VBTableBuilder::findUnambiguousPaths(const CXXRecordDecl *ReusingBase,
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BaseSubobject CurSubobject,
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VBTablePathVector &Paths) {
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size_t PathsStart = Paths.size();
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bool ReuseVBPtrFromBase = true;
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const CXXRecordDecl *CurBase = CurSubobject.getBase();
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const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(CurBase);
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// If this base has a vbptr, then we've found a path. These are not full
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// paths, so we don't use CXXBasePath.
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if (Layout.hasOwnVBPtr()) {
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ReuseVBPtrFromBase = false;
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VBTablePath *Info = new VBTablePath(
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VBTableInfo(ReusingBase, CurSubobject, /*GV=*/0));
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Paths.push_back(Info);
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}
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// Recurse onto any bases which themselves have virtual bases.
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for (CXXRecordDecl::base_class_const_iterator I = CurBase->bases_begin(),
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E = CurBase->bases_end(); I != E; ++I) {
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const CXXRecordDecl *Base = I->getType()->getAsCXXRecordDecl();
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if (!Base->getNumVBases())
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continue; // Bases without virtual bases have no vbptrs.
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CharUnits NextOffset;
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const CXXRecordDecl *NextReusingBase = Base;
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if (I->isVirtual()) {
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if (!VBasesSeen.insert(Base))
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continue; // Don't visit virtual bases twice.
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NextOffset = DerivedLayout.getVBaseClassOffset(Base);
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} else {
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NextOffset = (CurSubobject.getBaseOffset() +
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Layout.getBaseClassOffset(Base));
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// If CurBase didn't have a vbptr, then ReusingBase will reuse the vbptr
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// from the first non-virtual base with vbases for its vbptr.
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if (ReuseVBPtrFromBase) {
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NextReusingBase = ReusingBase;
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ReuseVBPtrFromBase = false;
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}
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}
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size_t NumPaths = Paths.size();
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findUnambiguousPaths(NextReusingBase, BaseSubobject(Base, NextOffset),
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Paths);
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// Tag paths through this base with the base itself. We might use it to
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// disambiguate.
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for (size_t I = NumPaths, E = Paths.size(); I != E; ++I)
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Paths[I]->NextBase = Base;
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}
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bool AmbiguousPaths = rebucketPaths(Paths, PathsStart);
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if (AmbiguousPaths)
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rebucketPaths(Paths, PathsStart, /*SecondPass=*/true);
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#ifndef NDEBUG
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// Check that the paths are in fact unique.
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for (size_t I = PathsStart + 1, E = Paths.size(); I != E; ++I) {
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assert(Paths[I]->Path != Paths[I - 1]->Path && "vbtable paths are not unique");
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}
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#endif
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}
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static bool pathCompare(VBTablePath *LHS, VBTablePath *RHS) {
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return LHS->Path < RHS->Path;
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}
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void VBTableBuilder::extendPath(VBTablePath *P, bool SecondPass) {
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assert(P->NextBase || SecondPass);
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if (P->NextBase) {
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P->Path.push_back(P->NextBase);
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P->NextBase = 0; // Prevent the path from being extended twice.
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}
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}
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bool VBTableBuilder::rebucketPaths(VBTablePathVector &Paths, size_t PathsStart,
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bool SecondPass) {
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// What we're essentially doing here is bucketing together ambiguous paths.
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// Any bucket with more than one path in it gets extended by NextBase, which
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// is usually the direct base of the inherited the vbptr. This code uses a
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// sorted vector to implement a multiset to form the buckets. Note that the
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// ordering is based on pointers, but it doesn't change our output order. The
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// current algorithm is designed to match MSVC 2012's names.
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// TODO: Implement MSVC 2010 or earlier names to avoid extra vbtable cruft.
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VBTablePathVector PathsSorted(&Paths[PathsStart], &Paths.back() + 1);
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std::sort(PathsSorted.begin(), PathsSorted.end(), pathCompare);
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bool AmbiguousPaths = false;
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for (size_t I = 0, E = PathsSorted.size(); I != E;) {
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// Scan forward to find the end of the bucket.
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size_t BucketStart = I;
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do {
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++I;
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} while (I != E && PathsSorted[BucketStart]->Path == PathsSorted[I]->Path);
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// If this bucket has multiple paths, extend them all.
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if (I - BucketStart > 1) {
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AmbiguousPaths = true;
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for (size_t II = BucketStart; II != I; ++II)
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extendPath(PathsSorted[II], SecondPass);
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}
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}
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return AmbiguousPaths;
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}
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llvm::GlobalVariable *
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VBTableBuilder::getAddrOfVBTable(const CXXRecordDecl *ReusingBase,
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ArrayRef<const CXXRecordDecl *> BasePath) {
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// Caching at this layer is redundant with the caching in EnumerateVBTables().
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SmallString<256> OutName;
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llvm::raw_svector_ostream Out(OutName);
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MicrosoftMangleContext &Mangler =
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cast<MicrosoftMangleContext>(CGM.getCXXABI().getMangleContext());
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Mangler.mangleCXXVBTable(MostDerived, BasePath, Out);
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Out.flush();
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StringRef Name = OutName.str();
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llvm::ArrayType *VBTableType =
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llvm::ArrayType::get(CGM.IntTy, 1 + ReusingBase->getNumVBases());
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assert(!CGM.getModule().getNamedGlobal(Name) &&
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"vbtable with this name already exists: mangling bug?");
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llvm::GlobalVariable *VBTable =
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CGM.CreateOrReplaceCXXRuntimeVariable(Name, VBTableType,
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llvm::GlobalValue::ExternalLinkage);
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VBTable->setUnnamedAddr(true);
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return VBTable;
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}
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void VBTableInfo::EmitVBTableDefinition(
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CodeGenModule &CGM, const CXXRecordDecl *RD,
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llvm::GlobalVariable::LinkageTypes Linkage) const {
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assert(RD->getNumVBases() && ReusingBase->getNumVBases() &&
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"should only emit vbtables for classes with vbtables");
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const ASTRecordLayout &BaseLayout =
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CGM.getContext().getASTRecordLayout(VBPtrSubobject.getBase());
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const ASTRecordLayout &DerivedLayout =
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CGM.getContext().getASTRecordLayout(RD);
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SmallVector<llvm::Constant *, 4> Offsets(1 + ReusingBase->getNumVBases(), 0);
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// The offset from ReusingBase's vbptr to itself always leads.
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CharUnits VBPtrOffset = BaseLayout.getVBPtrOffset();
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Offsets[0] = llvm::ConstantInt::get(CGM.IntTy, -VBPtrOffset.getQuantity());
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MicrosoftVTableContext &Context = CGM.getMicrosoftVTableContext();
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for (CXXRecordDecl::base_class_const_iterator I = ReusingBase->vbases_begin(),
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E = ReusingBase->vbases_end(); I != E; ++I) {
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const CXXRecordDecl *VBase = I->getType()->getAsCXXRecordDecl();
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CharUnits Offset = DerivedLayout.getVBaseClassOffset(VBase);
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assert(!Offset.isNegative());
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// Make it relative to the subobject vbptr.
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Offset -= VBPtrSubobject.getBaseOffset() + VBPtrOffset;
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unsigned VBIndex = Context.getVBTableIndex(ReusingBase, VBase);
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assert(Offsets[VBIndex] == 0 && "The same vbindex seen twice?");
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Offsets[VBIndex] = llvm::ConstantInt::get(CGM.IntTy, Offset.getQuantity());
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}
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assert(Offsets.size() ==
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cast<llvm::ArrayType>(cast<llvm::PointerType>(GV->getType())
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->getElementType())->getNumElements());
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llvm::ArrayType *VBTableType =
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llvm::ArrayType::get(CGM.IntTy, Offsets.size());
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llvm::Constant *Init = llvm::ConstantArray::get(VBTableType, Offsets);
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GV->setInitializer(Init);
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// Set the correct linkage.
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GV->setLinkage(Linkage);
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// Set the right visibility.
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CGM.setTypeVisibility(GV, RD, CodeGenModule::TVK_ForVTable);
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}
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} // namespace CodeGen
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} // namespace clang
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