C++ Constant类代码示例

// Create a constant for Str so that we can pass it to the run-time lib.
static GlobalVariable *createPrivateGlobalForString(Module &M, StringRef Str) {
  Constant *StrConst = ConstantDataArray::getString(M.getContext(), Str);
  return new GlobalVariable(M, StrConst->getType(), true,
                            GlobalValue::PrivateLinkage, StrConst, "");
}

void StrPrinter::bvisit(const Constant &x) {
    str_ = x.get_name();
}

bool SparcAsmPrinter::doFinalization(Module &M) {
  const TargetData *TD = TM.getTargetData();

  // Print out module-level global variables here.
  for (Module::const_global_iterator I = M.global_begin(), E = M.global_end();
       I != E; ++I)
    if (I->hasInitializer()) {   // External global require no code
      // Check to see if this is a special global used by LLVM, if so, emit it.
      if (EmitSpecialLLVMGlobal(I))
        continue;
      
      O << "\n\n";
      std::string name = Mang->getValueName(I);
      Constant *C = I->getInitializer();
      unsigned Size = TD->getABITypeSize(C->getType());
      unsigned Align = TD->getPreferredAlignment(I);

      if (C->isNullValue() &&
          (I->hasLinkOnceLinkage() || I->hasInternalLinkage() ||
           I->hasWeakLinkage() /* FIXME: Verify correct */)) {
        SwitchToDataSection(".data", I);
        if (I->hasInternalLinkage())
          O << "\t.local " << name << "\n";

        O << "\t.comm " << name << "," << TD->getABITypeSize(C->getType())
          << "," << Align;
        O << "\n";
      } else {
        switch (I->getLinkage()) {
        case GlobalValue::LinkOnceLinkage:
        case GlobalValue::WeakLinkage:   // FIXME: Verify correct for weak.
          // Nonnull linkonce -> weak
          O << "\t.weak " << name << "\n";
          SwitchToDataSection("", I);
          O << "\t.section\t\".llvm.linkonce.d." << name
            << "\",\"aw\",@progbits\n";
          break;

        case GlobalValue::AppendingLinkage:
          // FIXME: appending linkage variables should go into a section of
          // their name or something.  For now, just emit them as external.
        case GlobalValue::ExternalLinkage:
          // If external or appending, declare as a global symbol
          O << "\t.globl " << name << "\n";
          // FALL THROUGH
        case GlobalValue::InternalLinkage:
          if (C->isNullValue())
            SwitchToDataSection(".bss", I);
          else
            SwitchToDataSection(".data", I);
          break;
        case GlobalValue::GhostLinkage:
          cerr << "Should not have any unmaterialized functions!\n";
          abort();
        case GlobalValue::DLLImportLinkage:
          cerr << "DLLImport linkage is not supported by this target!\n";
          abort();
        case GlobalValue::DLLExportLinkage:
          cerr << "DLLExport linkage is not supported by this target!\n";
          abort();
        default:
          assert(0 && "Unknown linkage type!");          
        }

        O << "\t.align " << Align << "\n";
        O << "\t.type " << name << ",#object\n";
        O << "\t.size " << name << "," << Size << "\n";
        O << name << ":\n";
        EmitGlobalConstant(C);
      }
    }

  return AsmPrinter::doFinalization(M);
}

/// CleanupAndPrepareModules - Get the specified modules ready for code
/// generator testing.
///
static void CleanupAndPrepareModules(BugDriver &BD, Module *&Test,
                                     Module *Safe) {
  // Clean up the modules, removing extra cruft that we don't need anymore...
  Test = BD.performFinalCleanups(Test);

  // If we are executing the JIT, we have several nasty issues to take care of.
  if (!BD.isExecutingJIT()) return;

  // First, if the main function is in the Safe module, we must add a stub to
  // the Test module to call into it.  Thus, we create a new function `main'
  // which just calls the old one.
  if (Function *oldMain = Safe->getFunction("main"))
    if (!oldMain->isDeclaration()) {
      // Rename it
      oldMain->setName("llvm_bugpoint_old_main");
      // Create a NEW `main' function with same type in the test module.
      Function *newMain = Function::Create(oldMain->getFunctionType(),
                                           GlobalValue::ExternalLinkage,
                                           "main", Test);
      // Create an `oldmain' prototype in the test module, which will
      // corresponds to the real main function in the same module.
      Function *oldMainProto = Function::Create(oldMain->getFunctionType(),
                                                GlobalValue::ExternalLinkage,
                                                oldMain->getName(), Test);
      // Set up and remember the argument list for the main function.
      std::vector<Value*> args;
      for (Function::arg_iterator
             I = newMain->arg_begin(), E = newMain->arg_end(),
             OI = oldMain->arg_begin(); I != E; ++I, ++OI) {
        I->setName(OI->getName());    // Copy argument names from oldMain
        args.push_back(I);
      }

      // Call the old main function and return its result
      BasicBlock *BB = BasicBlock::Create(Safe->getContext(), "entry", newMain);
      CallInst *call = CallInst::Create(oldMainProto, args.begin(), args.end(),
                                        "", BB);

      // If the type of old function wasn't void, return value of call
      ReturnInst::Create(Safe->getContext(), call, BB);
    }

  // The second nasty issue we must deal with in the JIT is that the Safe
  // module cannot directly reference any functions defined in the test
  // module.  Instead, we use a JIT API call to dynamically resolve the
  // symbol.

  // Add the resolver to the Safe module.
  // Prototype: void *getPointerToNamedFunction(const char* Name)
  Constant *resolverFunc =
    Safe->getOrInsertFunction("getPointerToNamedFunction",
                    Type::getInt8PtrTy(Safe->getContext()),
                    Type::getInt8PtrTy(Safe->getContext()),
                       (Type *)0);

  // Use the function we just added to get addresses of functions we need.
  for (Module::iterator F = Safe->begin(), E = Safe->end(); F != E; ++F) {
    if (F->isDeclaration() && !F->use_empty() && &*F != resolverFunc &&
        !F->isIntrinsic() /* ignore intrinsics */) {
      Function *TestFn = Test->getFunction(F->getName());

      // Don't forward functions which are external in the test module too.
      if (TestFn && !TestFn->isDeclaration()) {
        // 1. Add a string constant with its name to the global file
        Constant *InitArray = ConstantArray::get(F->getContext(), F->getName());
        GlobalVariable *funcName =
          new GlobalVariable(*Safe, InitArray->getType(), true /*isConstant*/,
                             GlobalValue::InternalLinkage, InitArray,
                             F->getName() + "_name");

        // 2. Use `GetElementPtr *funcName, 0, 0' to convert the string to an
        // sbyte* so it matches the signature of the resolver function.

        // GetElementPtr *funcName, ulong 0, ulong 0
        std::vector<Constant*> GEPargs(2,
                     Constant::getNullValue(Type::getInt32Ty(F->getContext())));
        Value *GEP =
                ConstantExpr::getGetElementPtr(funcName, &GEPargs[0], 2);
        std::vector<Value*> ResolverArgs;
        ResolverArgs.push_back(GEP);

        // Rewrite uses of F in global initializers, etc. to uses of a wrapper
        // function that dynamically resolves the calls to F via our JIT API
        if (!F->use_empty()) {
          // Create a new global to hold the cached function pointer.
          Constant *NullPtr = ConstantPointerNull::get(F->getType());
          GlobalVariable *Cache =
            new GlobalVariable(*F->getParent(), F->getType(), 
                               false, GlobalValue::InternalLinkage,
                               NullPtr,F->getName()+".fpcache");

          // Construct a new stub function that will re-route calls to F
          const FunctionType *FuncTy = F->getFunctionType();
          Function *FuncWrapper = Function::Create(FuncTy,
                                                   GlobalValue::InternalLinkage,
                                                   F->getName() + "_wrapper",
                                                   F->getParent());
//.........这里部分代码省略.........

 inline Value::Value(const Type& aType, const Constant& val,    const char* name)
     : fpImpl( SFun_Value_ctor_T_C_d_c(aType.getImpl(), val.getImpl(), name) )
 {
     verify(fpImpl);
 }

Value *llvm::MapValue(const Value *V, ValueToValueMapTy &VM, RemapFlags Flags,
                      ValueMapTypeRemapper *TypeMapper,
                      ValueMaterializer *Materializer) {
  ValueToValueMapTy::iterator I = VM.find(V);
  
  // If the value already exists in the map, use it.
  if (I != VM.end() && I->second) return I->second;
  
  // If we have a materializer and it can materialize a value, use that.
  if (Materializer) {
    if (Value *NewV = Materializer->materializeValueFor(const_cast<Value*>(V)))
      return VM[V] = NewV;
  }

  // Global values do not need to be seeded into the VM if they
  // are using the identity mapping.
  if (isa<GlobalValue>(V))
    return VM[V] = const_cast<Value*>(V);
  
  if (const InlineAsm *IA = dyn_cast<InlineAsm>(V)) {
    // Inline asm may need *type* remapping.
    FunctionType *NewTy = IA->getFunctionType();
    if (TypeMapper) {
      NewTy = cast<FunctionType>(TypeMapper->remapType(NewTy));

      if (NewTy != IA->getFunctionType())
        V = InlineAsm::get(NewTy, IA->getAsmString(), IA->getConstraintString(),
                           IA->hasSideEffects(), IA->isAlignStack());
    }
    
    return VM[V] = const_cast<Value*>(V);
  }

  if (const auto *MDV = dyn_cast<MetadataAsValue>(V)) {
    const Metadata *MD = MDV->getMetadata();
    // If this is a module-level metadata and we know that nothing at the module
    // level is changing, then use an identity mapping.
    if (!isa<LocalAsMetadata>(MD) && (Flags & RF_NoModuleLevelChanges))
      return VM[V] = const_cast<Value *>(V);

    auto *MappedMD = MapMetadata(MD, VM, Flags, TypeMapper, Materializer);
    if (MD == MappedMD || (!MappedMD && (Flags & RF_IgnoreMissingEntries)))
      return VM[V] = const_cast<Value *>(V);

    // FIXME: This assert crashes during bootstrap, but I think it should be
    // correct.  For now, just match behaviour from before the metadata/value
    // split.
    //
    //    assert(MappedMD && "Referenced metadata value not in value map");
    return VM[V] = MetadataAsValue::get(V->getContext(), MappedMD);
  }

  // Okay, this either must be a constant (which may or may not be mappable) or
  // is something that is not in the mapping table.
  Constant *C = const_cast<Constant*>(dyn_cast<Constant>(V));
  if (!C)
    return nullptr;
  
  if (BlockAddress *BA = dyn_cast<BlockAddress>(C)) {
    Function *F = 
      cast<Function>(MapValue(BA->getFunction(), VM, Flags, TypeMapper, Materializer));
    BasicBlock *BB = cast_or_null<BasicBlock>(MapValue(BA->getBasicBlock(), VM,
                                                       Flags, TypeMapper, Materializer));
    return VM[V] = BlockAddress::get(F, BB ? BB : BA->getBasicBlock());
  }
  
  // Otherwise, we have some other constant to remap.  Start by checking to see
  // if all operands have an identity remapping.
  unsigned OpNo = 0, NumOperands = C->getNumOperands();
  Value *Mapped = nullptr;
  for (; OpNo != NumOperands; ++OpNo) {
    Value *Op = C->getOperand(OpNo);
    Mapped = MapValue(Op, VM, Flags, TypeMapper, Materializer);
    if (Mapped != C) break;
  }
  
  // See if the type mapper wants to remap the type as well.
  Type *NewTy = C->getType();
  if (TypeMapper)
    NewTy = TypeMapper->remapType(NewTy);

  // If the result type and all operands match up, then just insert an identity
  // mapping.
  if (OpNo == NumOperands && NewTy == C->getType())
    return VM[V] = C;
  
  // Okay, we need to create a new constant.  We've already processed some or
  // all of the operands, set them all up now.
  SmallVector<Constant*, 8> Ops;
  Ops.reserve(NumOperands);
  for (unsigned j = 0; j != OpNo; ++j)
    Ops.push_back(cast<Constant>(C->getOperand(j)));
  
  // If one of the operands mismatch, push it and the other mapped operands.
  if (OpNo != NumOperands) {
    Ops.push_back(cast<Constant>(Mapped));
  
    // Map the rest of the operands that aren't processed yet.
    for (++OpNo; OpNo != NumOperands; ++OpNo)
      Ops.push_back(MapValue(cast<Constant>(C->getOperand(OpNo)), VM,
//.........这里部分代码省略.........

static bool match_index_and_scale(Instruction*  instr,
                                  Instruction** index,
                                  int*          log2_scale,
                                  Instruction** instr_to_unpin) {
  *instr_to_unpin = NULL;

  // Skip conversion ops
  Convert* convert = instr->as_Convert();
  if (convert != NULL) {
    instr = convert->value();
  }

  ShiftOp* shift = instr->as_ShiftOp();
  if (shift != NULL) {
    if (shift->is_pinned()) {
      *instr_to_unpin = shift;
    }
    // Constant shift value?
    Constant* con = shift->y()->as_Constant();
    if (con == NULL) return false;
    // Well-known type and value?
    IntConstant* val = con->type()->as_IntConstant();
    if (val == NULL) return false;
    if (shift->x()->type() != intType) return false;
    *index = shift->x();
    int tmp_scale = val->value();
    if (tmp_scale >= 0 && tmp_scale < 4) {
      *log2_scale = tmp_scale;
      return true;
    } else {
      return false;
    }
  }

  ArithmeticOp* arith = instr->as_ArithmeticOp();
  if (arith != NULL) {
    if (arith->is_pinned()) {
      *instr_to_unpin = arith;
    }
    // Check for integer multiply
    if (arith->op() == Bytecodes::_imul) {
      // See if either arg is a known constant
      Constant* con = arith->x()->as_Constant();
      if (con != NULL) {
        *index = arith->y();
      } else {
        con = arith->y()->as_Constant();
        if (con == NULL) return false;
        *index = arith->x();
      }
      if ((*index)->type() != intType) return false;
      // Well-known type and value?
      IntConstant* val = con->type()->as_IntConstant();
      if (val == NULL) return false;
      switch (val->value()) {
      case 1: *log2_scale = 0; return true;
      case 2: *log2_scale = 1; return true;
      case 4: *log2_scale = 2; return true;
      case 8: *log2_scale = 3; return true;
      default:            return false;
      }
    }
  }

  // Unknown instruction sequence; don't touch it
  return false;
}

Function* TranslationContext::createFunction(Executable& executable, uint64_t baseAddress)
{
	Function* fn = functionMap->createFunction(baseAddress);
	assert(fn != nullptr);
	
	auto targetInfo = TargetInfo::getTargetInfo(*module);
	AddressToBlock blockMap(*fn);
	BasicBlock* entry = &fn->back();
	TranslationCloningDirector director(*module, *functionMap, blockMap);
	
	Argument* registers = fn->arg_begin();
	auto flags = new AllocaInst(irgen->getFlagsTy(), "flags", entry);
	
	ArrayRef<Value*> ipGepIndices = irgen->getIpOffset();
	auto ipPointer = GetElementPtrInst::CreateInBounds(registers, ipGepIndices, "", entry);
	Type* ipType = GetElementPtrInst::getIndexedType(irgen->getRegisterTy(), ipGepIndices);
	
	Function* prologue = irgen->implementationForPrologue();
	inlineFunction(fn, prologue, { configVariable, registers }, director, baseAddress);
	
	uint64_t addressToDisassemble;
	auto end = executable.end();
	auto inst = cs->alloc();
	SmallVector<Value*, 4> inliningParameters = { configVariable, nullptr, registers, flags };
	while (blockMap.getOneStub(addressToDisassemble))
	{
		if (auto begin = executable.map(addressToDisassemble))
		if (cs->disassemble(inst.get(), begin, end, addressToDisassemble))
		if (BasicBlock* thisBlock = blockMap.implementInstruction(inst->address)) // already implemented?
		{
			// store instruction pointer
			// (this needs to be the IP of the next instruction)
			auto nextInstAddress = inst->address + inst->size;
			auto ipValue = ConstantInt::get(ipType, nextInstAddress);
			new StoreInst(ipValue, ipPointer, false, thisBlock);
			
			if (Function* implementation = irgen->implementationFor(inst->id))
			{
				// We have an implementation: inline it
				Constant* detailAsConstant = irgen->constantForDetail(*inst->detail);
				inliningParameters[1] = new GlobalVariable(*module, detailAsConstant->getType(), true, GlobalValue::PrivateLinkage, detailAsConstant);
				inlineFunction(fn, implementation, inliningParameters, director, nextInstAddress);
			}
			else
			{
				createAsmCall(*targetInfo, *inst, registers, *thisBlock);
				BasicBlock* target = blockMap.blockToInstruction(nextInstAddress);
				BranchInst::Create(target, thisBlock);
			}
			continue;
		}
		break;
	}
	
#if DEBUG && 0
	// check that it still works
	if (verifyModule(*module, &errs()))
	{
		module->dump();
		abort();
	}
#endif
	
	return fn;
}

/// getKindForGlobal - This is a top-level target-independent classifier for
/// a global variable.  Given an global variable and information from TM, it
/// classifies the global in a variety of ways that make various target
/// implementations simpler.  The target implementation is free to ignore this
/// extra info of course.
SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
                                                       const TargetMachine &TM){
  assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
         "Can only be used for global definitions");

  Reloc::Model ReloModel = TM.getRelocationModel();

  // Early exit - functions should be always in text sections.
  const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
  if (GVar == 0)
    return SectionKind::getText();

  // Handle thread-local data first.
  if (GVar->isThreadLocal()) {
    if (isSuitableForBSS(GVar))
      return SectionKind::getThreadBSS();
    return SectionKind::getThreadData();
  }

  // Variables with common linkage always get classified as common.
  if (GVar->hasCommonLinkage())
    return SectionKind::getCommon();

  // Variable can be easily put to BSS section.
  if (isSuitableForBSS(GVar)) {
    if (GVar->hasLocalLinkage())
      return SectionKind::getBSSLocal();
    else if (GVar->hasExternalLinkage())
      return SectionKind::getBSSExtern();
    return SectionKind::getBSS();
  }

  Constant *C = GVar->getInitializer();

  // If the global is marked constant, we can put it into a mergable section,
  // a mergable string section, or general .data if it contains relocations.
  if (GVar->isConstant()) {
    // If the initializer for the global contains something that requires a
    // relocation, then we may have to drop this into a wriable data section
    // even though it is marked const.
    switch (C->getRelocationInfo()) {
    default: assert(0 && "unknown relocation info kind");
    case Constant::NoRelocation:
      // If initializer is a null-terminated string, put it in a "cstring"
      // section of the right width.
      if (const ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
        if (const IntegerType *ITy =
              dyn_cast<IntegerType>(ATy->getElementType())) {
          if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 ||
               ITy->getBitWidth() == 32) &&
              IsNullTerminatedString(C)) {
            if (ITy->getBitWidth() == 8)
              return SectionKind::getMergeable1ByteCString();
            if (ITy->getBitWidth() == 16)
              return SectionKind::getMergeable2ByteCString();

            assert(ITy->getBitWidth() == 32 && "Unknown width");
            return SectionKind::getMergeable4ByteCString();
          }
        }
      }

      // Otherwise, just drop it into a mergable constant section.  If we have
      // a section for this size, use it, otherwise use the arbitrary sized
      // mergable section.
      switch (TM.getTargetData()->getTypeAllocSize(C->getType())) {
      case 4:  return SectionKind::getMergeableConst4();
      case 8:  return SectionKind::getMergeableConst8();
      case 16: return SectionKind::getMergeableConst16();
      default: return SectionKind::getMergeableConst();
      }

    case Constant::LocalRelocation:
      // In static relocation model, the linker will resolve all addresses, so
      // the relocation entries will actually be constants by the time the app
      // starts up.  However, we can't put this into a mergable section, because
      // the linker doesn't take relocations into consideration when it tries to
      // merge entries in the section.
      if (ReloModel == Reloc::Static)
        return SectionKind::getReadOnly();

      // Otherwise, the dynamic linker needs to fix it up, put it in the
      // writable data.rel.local section.
      return SectionKind::getReadOnlyWithRelLocal();

    case Constant::GlobalRelocations:
      // In static relocation model, the linker will resolve all addresses, so
      // the relocation entries will actually be constants by the time the app
      // starts up.  However, we can't put this into a mergable section, because
      // the linker doesn't take relocations into consideration when it tries to
      // merge entries in the section.
      if (ReloModel == Reloc::Static)
        return SectionKind::getReadOnly();

      // Otherwise, the dynamic linker needs to fix it up, put it in the
//.........这里部分代码省略.........

//
// Method: postOrderInline()
//
// Description:
//  This methods does a post order traversal of the call graph and performs
//  bottom-up inlining of the DSGraphs.
//
void
BUDataStructures::postOrderInline (Module & M) {
  // Variables used for Tarjan SCC-finding algorithm.  These are passed into
  // the recursive function used to find SCCs.
  std::vector<const Function*> Stack;
  std::map<const Function*, unsigned> ValMap;
  unsigned NextID = 1;


  // Do post order traversal on the global ctors. Use this information to update
  // the globals graph.
  const char *Name = "llvm.global_ctors";
  GlobalVariable *GV = M.getNamedGlobal(Name);
  if (GV && !(GV->isDeclaration()) && !(GV->hasLocalLinkage())) {
    // Should be an array of '{ int, void ()* }' structs.  The first value is
    // the init priority, which we ignore.
    ConstantArray *InitList = dyn_cast<ConstantArray>(GV->getInitializer());
    if (InitList) {
      for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i)
        if (ConstantStruct *CS = dyn_cast<ConstantStruct>(InitList->getOperand(i))) {
          if (CS->getNumOperands() != 2)
            break; // Not array of 2-element structs.
          Constant *FP = CS->getOperand(1);
          if (FP->isNullValue())
            break;  // Found a null terminator, exit.

          if (ConstantExpr *CE = dyn_cast<ConstantExpr>(FP))
            if (CE->isCast())
              FP = CE->getOperand(0);
          Function *F = dyn_cast<Function>(FP);
          if (F && !F->isDeclaration() && !ValMap.count(F)) {
            calculateGraphs(F, Stack, NextID, ValMap);
            CloneAuxIntoGlobal(getDSGraph(*F));
          }
        }
      GlobalsGraph->removeTriviallyDeadNodes();
      GlobalsGraph->maskIncompleteMarkers();

      // Mark external globals incomplete.
      GlobalsGraph->markIncompleteNodes(DSGraph::IgnoreGlobals);
      GlobalsGraph->computeExternalFlags(DSGraph::DontMarkFormalsExternal);
      GlobalsGraph->computeIntPtrFlags();

      //
      // Create equivalence classes for aliasing globals so that we only need to
      // record one global per DSNode.
      //
      formGlobalECs();
      // propogte information calculated
      // from the globals graph to the other graphs.
      for (Module::iterator F = M.begin(); F != M.end(); ++F) {
        if (!(F->isDeclaration())){
          DSGraph *Graph  = getDSGraph(*F);
          cloneGlobalsInto(Graph, DSGraph::DontCloneCallNodes |
                           DSGraph::DontCloneAuxCallNodes);
          Graph->buildCallGraph(callgraph, GlobalFunctionList, filterCallees);
          Graph->maskIncompleteMarkers();
          Graph->markIncompleteNodes(DSGraph::MarkFormalArgs |
                                     DSGraph::IgnoreGlobals);
          Graph->computeExternalFlags(DSGraph::DontMarkFormalsExternal);
          Graph->computeIntPtrFlags();
        }
      }
    }
  }

  //
  // Start the post order traversal with the main() function.  If there is no
  // main() function, don't worry; we'll have a separate traversal for inlining
  // graphs for functions not reachable from main().
  //
  Function *MainFunc = M.getFunction ("main");
  if (MainFunc && !MainFunc->isDeclaration()) {
    calculateGraphs(MainFunc, Stack, NextID, ValMap);
    CloneAuxIntoGlobal(getDSGraph(*MainFunc));
  }

  //
  // Calculate the graphs for any functions that are unreachable from main...
  //
  for (Function &F : M)
    if (!F.isDeclaration() && !ValMap.count(&F)) {
      if (MainFunc)
        DEBUG(errs() << debugname << ": Function unreachable from main: "
        << F.getName() << "\n");
      calculateGraphs(&F, Stack, NextID, ValMap);     // Calculate all graphs.
      CloneAuxIntoGlobal(getDSGraph(F));

      // Mark this graph as processed.  Do this by finding all functions
      // in the graph that map to it, and mark them visited.
      // Note that this really should be handled neatly by calculateGraphs
      // itself, not here.  However this catches the worst offenders.
      DSGraph *G = getDSGraph(F);
//.........这里部分代码省略.........

/// getPredicateOnEdge - Determine whether the specified value comparison
/// with a constant is known to be true or false on the specified CFG edge.
/// Pred is a CmpInst predicate.
LazyValueInfo::Tristate
LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
                                  BasicBlock *FromBB, BasicBlock *ToBB) {
  LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
  
  // If we know the value is a constant, evaluate the conditional.
  Constant *Res = 0;
  if (Result.isConstant()) {
    Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, TD,
                                          TLI);
    if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res))
      return ResCI->isZero() ? False : True;
    return Unknown;
  }
  
  if (Result.isConstantRange()) {
    ConstantInt *CI = dyn_cast<ConstantInt>(C);
    if (!CI) return Unknown;
    
    ConstantRange CR = Result.getConstantRange();
    if (Pred == ICmpInst::ICMP_EQ) {
      if (!CR.contains(CI->getValue()))
        return False;
      
      if (CR.isSingleElement() && CR.contains(CI->getValue()))
        return True;
    } else if (Pred == ICmpInst::ICMP_NE) {
      if (!CR.contains(CI->getValue()))
        return True;
      
      if (CR.isSingleElement() && CR.contains(CI->getValue()))
        return False;
    }
    
    // Handle more complex predicates.
    ConstantRange TrueValues =
        ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue());
    if (TrueValues.contains(CR))
      return True;
    if (TrueValues.inverse().contains(CR))
      return False;
    return Unknown;
  }
  
  if (Result.isNotConstant()) {
    // If this is an equality comparison, we can try to fold it knowing that
    // "V != C1".
    if (Pred == ICmpInst::ICMP_EQ) {
      // !C1 == C -> false iff C1 == C.
      Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
                                            Result.getNotConstant(), C, TD,
                                            TLI);
      if (Res->isNullValue())
        return False;
    } else if (Pred == ICmpInst::ICMP_NE) {
      // !C1 != C -> true iff C1 == C.
      Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
                                            Result.getNotConstant(), C, TD,
                                            TLI);
      if (Res->isNullValue())
        return True;
    }
    return Unknown;
  }
  
  return Unknown;
}

PreservedAnalyses GlobalDCEPass::run(Module &M, ModuleAnalysisManager &) {
  bool Changed = false;

  // Remove empty functions from the global ctors list.
  Changed |= optimizeGlobalCtorsList(M, isEmptyFunction);

  // Collect the set of members for each comdat.
  for (Function &F : M)
    if (Comdat *C = F.getComdat())
      ComdatMembers.insert(std::make_pair(C, &F));
  for (GlobalVariable &GV : M.globals())
    if (Comdat *C = GV.getComdat())
      ComdatMembers.insert(std::make_pair(C, &GV));
  for (GlobalAlias &GA : M.aliases())
    if (Comdat *C = GA.getComdat())
      ComdatMembers.insert(std::make_pair(C, &GA));

  // Loop over the module, adding globals which are obviously necessary.
  for (GlobalObject &GO : M.global_objects()) {
    Changed |= RemoveUnusedGlobalValue(GO);
    // Functions with external linkage are needed if they have a body.
    // Externally visible & appending globals are needed, if they have an
    // initializer.
    if (!GO.isDeclaration() && !GO.hasAvailableExternallyLinkage())
      if (!GO.isDiscardableIfUnused())
        GlobalIsNeeded(&GO);
  }

  for (GlobalAlias &GA : M.aliases()) {
    Changed |= RemoveUnusedGlobalValue(GA);
    // Externally visible aliases are needed.
    if (!GA.isDiscardableIfUnused())
      GlobalIsNeeded(&GA);
  }

  for (GlobalIFunc &GIF : M.ifuncs()) {
    Changed |= RemoveUnusedGlobalValue(GIF);
    // Externally visible ifuncs are needed.
    if (!GIF.isDiscardableIfUnused())
      GlobalIsNeeded(&GIF);
  }

  // Now that all globals which are needed are in the AliveGlobals set, we loop
  // through the program, deleting those which are not alive.
  //

  // The first pass is to drop initializers of global variables which are dead.
  std::vector<GlobalVariable *> DeadGlobalVars; // Keep track of dead globals
  for (GlobalVariable &GV : M.globals())
    if (!AliveGlobals.count(&GV)) {
      DeadGlobalVars.push_back(&GV);         // Keep track of dead globals
      if (GV.hasInitializer()) {
        Constant *Init = GV.getInitializer();
        GV.setInitializer(nullptr);
        if (isSafeToDestroyConstant(Init))
          Init->destroyConstant();
      }
    }

  // The second pass drops the bodies of functions which are dead...
  std::vector<Function *> DeadFunctions;
  for (Function &F : M)
    if (!AliveGlobals.count(&F)) {
      DeadFunctions.push_back(&F);         // Keep track of dead globals
      if (!F.isDeclaration())
        F.deleteBody();
    }

  // The third pass drops targets of aliases which are dead...
  std::vector<GlobalAlias*> DeadAliases;
  for (GlobalAlias &GA : M.aliases())
    if (!AliveGlobals.count(&GA)) {
      DeadAliases.push_back(&GA);
      GA.setAliasee(nullptr);
    }

  // The third pass drops targets of ifuncs which are dead...
  std::vector<GlobalIFunc*> DeadIFuncs;
  for (GlobalIFunc &GIF : M.ifuncs())
    if (!AliveGlobals.count(&GIF)) {
      DeadIFuncs.push_back(&GIF);
      GIF.setResolver(nullptr);
    }

  // Now that all interferences have been dropped, delete the actual objects
  // themselves.
  auto EraseUnusedGlobalValue = [&](GlobalValue *GV) {
    RemoveUnusedGlobalValue(*GV);
    GV->eraseFromParent();
    Changed = true;
  };

  NumFunctions += DeadFunctions.size();
  for (Function *F : DeadFunctions)
    EraseUnusedGlobalValue(F);

  NumVariables += DeadGlobalVars.size();
  for (GlobalVariable *GV : DeadGlobalVars)
    EraseUnusedGlobalValue(GV);

//.........这里部分代码省略.........

bool GlobalDCE::runOnModule(Module &M) {
  bool Changed = false;

  // Remove empty functions from the global ctors list.
  Changed |= optimizeGlobalCtorsList(M, isEmptyFunction);

  // Loop over the module, adding globals which are obviously necessary.
  for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
    Changed |= RemoveUnusedGlobalValue(*I);
    // Functions with external linkage are needed if they have a body
    if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage()) {
      if (!I->isDiscardableIfUnused())
        GlobalIsNeeded(I);
    }
  }

  for (Module::global_iterator I = M.global_begin(), E = M.global_end();
       I != E; ++I) {
    Changed |= RemoveUnusedGlobalValue(*I);
    // Externally visible & appending globals are needed, if they have an
    // initializer.
    if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage()) {
      if (!I->isDiscardableIfUnused())
        GlobalIsNeeded(I);
    }
  }

  for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
       I != E; ++I) {
    Changed |= RemoveUnusedGlobalValue(*I);
    // Externally visible aliases are needed.
    if (!I->isDiscardableIfUnused()) {
      GlobalIsNeeded(I);
    }
  }

  // Now that all globals which are needed are in the AliveGlobals set, we loop
  // through the program, deleting those which are not alive.
  //

  // The first pass is to drop initializers of global variables which are dead.
  std::vector<GlobalVariable*> DeadGlobalVars;   // Keep track of dead globals
  for (Module::global_iterator I = M.global_begin(), E = M.global_end();
       I != E; ++I)
    if (!AliveGlobals.count(I)) {
      DeadGlobalVars.push_back(I);         // Keep track of dead globals
      if (I->hasInitializer()) {
        Constant *Init = I->getInitializer();
        I->setInitializer(nullptr);
        if (isSafeToDestroyConstant(Init))
          Init->destroyConstant();
      }
    }

  // The second pass drops the bodies of functions which are dead...
  std::vector<Function*> DeadFunctions;
  for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
    if (!AliveGlobals.count(I)) {
      DeadFunctions.push_back(I);         // Keep track of dead globals
      if (!I->isDeclaration())
        I->deleteBody();
    }

  // The third pass drops targets of aliases which are dead...
  std::vector<GlobalAlias*> DeadAliases;
  for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); I != E;
       ++I)
    if (!AliveGlobals.count(I)) {
      DeadAliases.push_back(I);
      I->setAliasee(nullptr);
    }

  if (!DeadFunctions.empty()) {
    // Now that all interferences have been dropped, delete the actual objects
    // themselves.
    for (unsigned i = 0, e = DeadFunctions.size(); i != e; ++i) {
      RemoveUnusedGlobalValue(*DeadFunctions[i]);
      M.getFunctionList().erase(DeadFunctions[i]);
    }
    NumFunctions += DeadFunctions.size();
    Changed = true;
  }

  if (!DeadGlobalVars.empty()) {
    for (unsigned i = 0, e = DeadGlobalVars.size(); i != e; ++i) {
      RemoveUnusedGlobalValue(*DeadGlobalVars[i]);
      M.getGlobalList().erase(DeadGlobalVars[i]);
    }
    NumVariables += DeadGlobalVars.size();
    Changed = true;
  }

  // Now delete any dead aliases.
  if (!DeadAliases.empty()) {
    for (unsigned i = 0, e = DeadAliases.size(); i != e; ++i) {
      RemoveUnusedGlobalValue(*DeadAliases[i]);
      M.getAliasList().erase(DeadAliases[i]);
    }
    NumAliases += DeadAliases.size();
    Changed = true;
//.........这里部分代码省略.........

//.........这里部分代码省略.........
      NewCall->takeName(II);
      NewCall->setCallingConv(II->getCallingConv());
      NewCall->setDebugLoc(II->getDebugLoc());
      NewCall->setAttributes(II->getAttributes());
      II->replaceAllUsesWith(NewCall);
      ToErase.push_back(II);

      IRB.CreateBr(II->getNormalDest());

      // Remove any PHI node entries from the exception destination
      II->getUnwindDest()->removePredecessor(&BB);
    }
  }

  // Process resume instructions
  for (BasicBlock &BB : F) {
    // Scan the body of the basic block for resumes
    for (Instruction &I : BB) {
      auto *RI = dyn_cast<ResumeInst>(&I);
      if (!RI)
        continue;

      // Split the input into legal values
      Value *Input = RI->getValue();
      IRB.SetInsertPoint(RI);
      Value *Low = IRB.CreateExtractValue(Input, 0, "low");
      // Create a call to __resumeException function
      IRB.CreateCall(ResumeF, {Low});
      // Add a terminator to the block
      IRB.CreateUnreachable();
      ToErase.push_back(RI);
    }
  }

  // Process llvm.eh.typeid.for intrinsics
  for (BasicBlock &BB : F) {
    for (Instruction &I : BB) {
      auto *CI = dyn_cast<CallInst>(&I);
      if (!CI)
        continue;
      const Function *Callee = CI->getCalledFunction();
      if (!Callee)
        continue;
      if (Callee->getIntrinsicID() != Intrinsic::eh_typeid_for)
        continue;

      IRB.SetInsertPoint(CI);
      CallInst *NewCI =
          IRB.CreateCall(EHTypeIDF, CI->getArgOperand(0), "typeid");
      CI->replaceAllUsesWith(NewCI);
      ToErase.push_back(CI);
    }
  }

  // Look for orphan landingpads, can occur in blocks with no predecessors
  for (BasicBlock &BB : F) {
    Instruction *I = BB.getFirstNonPHI();
    if (auto *LPI = dyn_cast<LandingPadInst>(I))
      LandingPads.insert(LPI);
  }

  // Handle all the landingpad for this function together, as multiple invokes
  // may share a single lp
  for (LandingPadInst *LPI : LandingPads) {
    IRB.SetInsertPoint(LPI);
    SmallVector<Value *, 16> FMCArgs;
    for (unsigned i = 0, e = LPI->getNumClauses(); i < e; ++i) {
      Constant *Clause = LPI->getClause(i);
      // As a temporary workaround for the lack of aggregate varargs support
      // in the interface between JS and wasm, break out filter operands into
      // their component elements.
      if (LPI->isFilter(i)) {
        auto *ATy = cast<ArrayType>(Clause->getType());
        for (unsigned j = 0, e = ATy->getNumElements(); j < e; ++j) {
          Value *EV = IRB.CreateExtractValue(Clause, makeArrayRef(j), "filter");
          FMCArgs.push_back(EV);
        }
      } else
        FMCArgs.push_back(Clause);
    }

    // Create a call to __cxa_find_matching_catch_N function
    Function *FMCF = getFindMatchingCatch(M, FMCArgs.size());
    CallInst *FMCI = IRB.CreateCall(FMCF, FMCArgs, "fmc");
    Value *Undef = UndefValue::get(LPI->getType());
    Value *Pair0 = IRB.CreateInsertValue(Undef, FMCI, 0, "pair0");
    Value *TempRet0 =
        IRB.CreateLoad(TempRet0GV, TempRet0GV->getName() + ".val");
    Value *Pair1 = IRB.CreateInsertValue(Pair0, TempRet0, 1, "pair1");

    LPI->replaceAllUsesWith(Pair1);
    ToErase.push_back(LPI);
  }

  // Erase everything we no longer need in this function
  for (Instruction *I : ToErase)
    I->eraseFromParent();

  return Changed;
}

bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable *> &Globals,
                          const BitVector &GlobalSet, Module &M, bool isConst,
                          unsigned AddrSpace) const {

  Type *Int32Ty = Type::getInt32Ty(M.getContext());
  auto &DL = M.getDataLayout();

  assert(Globals.size() > 1);

  DEBUG(dbgs() << " Trying to merge set, starts with #"
               << GlobalSet.find_first() << "\n");

  ssize_t i = GlobalSet.find_first();
  while (i != -1) {
    ssize_t j = 0;
    uint64_t MergedSize = 0;
    std::vector<Type*> Tys;
    std::vector<Constant*> Inits;

    bool HasExternal = false;
    GlobalVariable *TheFirstExternal = 0;
    for (j = i; j != -1; j = GlobalSet.find_next(j)) {
      Type *Ty = Globals[j]->getType()->getElementType();
      MergedSize += DL.getTypeAllocSize(Ty);
      if (MergedSize > MaxOffset) {
        break;
      }
      Tys.push_back(Ty);
      Inits.push_back(Globals[j]->getInitializer());

      if (Globals[j]->hasExternalLinkage() && !HasExternal) {
        HasExternal = true;
        TheFirstExternal = Globals[j];
      }
    }

    // If merged variables doesn't have external linkage, we needn't to expose
    // the symbol after merging.
    GlobalValue::LinkageTypes Linkage = HasExternal
                                            ? GlobalValue::ExternalLinkage
                                            : GlobalValue::InternalLinkage;

    StructType *MergedTy = StructType::get(M.getContext(), Tys);
    Constant *MergedInit = ConstantStruct::get(MergedTy, Inits);

    // If merged variables have external linkage, we use symbol name of the
    // first variable merged as the suffix of global symbol name. This would
    // be able to avoid the link-time naming conflict for globalm symbols.
    GlobalVariable *MergedGV = new GlobalVariable(
        M, MergedTy, isConst, Linkage, MergedInit,
        HasExternal ? "_MergedGlobals_" + TheFirstExternal->getName()
                    : "_MergedGlobals",
        nullptr, GlobalVariable::NotThreadLocal, AddrSpace);

    for (ssize_t k = i, idx = 0; k != j; k = GlobalSet.find_next(k)) {
      GlobalValue::LinkageTypes Linkage = Globals[k]->getLinkage();
      std::string Name = Globals[k]->getName();

      Constant *Idx[2] = {
        ConstantInt::get(Int32Ty, 0),
        ConstantInt::get(Int32Ty, idx++)
      };
      Constant *GEP =
          ConstantExpr::getInBoundsGetElementPtr(MergedTy, MergedGV, Idx);
      Globals[k]->replaceAllUsesWith(GEP);
      Globals[k]->eraseFromParent();

      if (Linkage != GlobalValue::InternalLinkage) {
        // Generate a new alias...
        auto *PTy = cast<PointerType>(GEP->getType());
        GlobalAlias::create(PTy, Linkage, Name, GEP, &M);
      }

      NumMerged++;
    }
    i = j;
  }

  return true;
}