Merge commit 'b3201c5cf1e183d840f7c99ff779d57f1549d8e5' into merge_20130226

Conflicts:
	include/llvm/Support/ELF.h
	lib/Support/DeltaAlgorithm.cpp

Change-Id: I24a4fbce62eb39d924efee3c687b55e1e17b30cd

6 files changed, 129 insertions, 652 deletions

diff --git a/lib/Linker/CMakeLists.txt b/lib/Linker/CMakeLists.txt
index 0b6d2f4..28f1262 100644
--- a/lib/Linker/CMakeLists.txt
+++ b/lib/Linker/CMakeLists.txt
@@ -1,6 +1,4 @@
 add_llvm_library(LLVMLinker
-  LinkArchives.cpp
-  LinkItems.cpp
   LinkModules.cpp
   Linker.cpp
   )
diff --git a/lib/Linker/LLVMBuild.txt b/lib/Linker/LLVMBuild.txt
index 2b4c232..0bb26d0 100644
--- a/lib/Linker/LLVMBuild.txt
+++ b/lib/Linker/LLVMBuild.txt
@@ -19,4 +19,4 @@
 type = Library
 name = Linker
 parent = Libraries
-required_libraries = Archive BitReader Core Support TransformUtils
+required_libraries = Core Support TransformUtils
diff --git a/lib/Linker/LinkArchives.cpp b/lib/Linker/LinkArchives.cpp
deleted file mode 100644
index a35991c..0000000
--- a/lib/Linker/LinkArchives.cpp
+++ /dev/null
@@ -1,197 +0,0 @@
-//===- lib/Linker/LinkArchives.cpp - Link LLVM objects and libraries ------===//
-//
-//                     The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-//
-// This file contains routines to handle linking together LLVM bitcode files,
-// and to handle annoying things like static libraries.
-//
-//===----------------------------------------------------------------------===//
-
-#include "llvm/Linker.h"
-#include "llvm/ADT/SetOperations.h"
-#include "llvm/Bitcode/Archive.h"
-#include "llvm/IR/Module.h"
-#include <memory>
-#include <set>
-using namespace llvm;
-
-/// GetAllUndefinedSymbols - calculates the set of undefined symbols that still
-/// exist in an LLVM module. This is a bit tricky because there may be two
-/// symbols with the same name but different LLVM types that will be resolved to
-/// each other but aren't currently (thus we need to treat it as resolved).
-///
-/// Inputs:
-///  M - The module in which to find undefined symbols.
-///
-/// Outputs:
-///  UndefinedSymbols - A set of C++ strings containing the name of all
-///                     undefined symbols.
-///
-static void
-GetAllUndefinedSymbols(Module *M, std::set<std::string> &UndefinedSymbols) {
-  std::set<std::string> DefinedSymbols;
-  UndefinedSymbols.clear();
-
-  // If the program doesn't define a main, try pulling one in from a .a file.
-  // This is needed for programs where the main function is defined in an
-  // archive, such f2c'd programs.
-  Function *Main = M->getFunction("main");
-  if (Main == 0 || Main->isDeclaration())
-    UndefinedSymbols.insert("main");
-
-  for (Module::iterator I = M->begin(), E = M->end(); I != E; ++I)
-    if (I->hasName()) {
-      if (I->isDeclaration())
-        UndefinedSymbols.insert(I->getName());
-      else if (!I->hasLocalLinkage()) {
-        assert(!I->hasDLLImportLinkage()
-               && "Found dllimported non-external symbol!");
-        DefinedSymbols.insert(I->getName());
-      }      
-    }
-
-  for (Module::global_iterator I = M->global_begin(), E = M->global_end();
-       I != E; ++I)
-    if (I->hasName()) {
-      if (I->isDeclaration())
-        UndefinedSymbols.insert(I->getName());
-      else if (!I->hasLocalLinkage()) {
-        assert(!I->hasDLLImportLinkage()
-               && "Found dllimported non-external symbol!");
-        DefinedSymbols.insert(I->getName());
-      }      
-    }
-
-  for (Module::alias_iterator I = M->alias_begin(), E = M->alias_end();
-       I != E; ++I)
-    if (I->hasName())
-      DefinedSymbols.insert(I->getName());
-
-  // Prune out any defined symbols from the undefined symbols set...
-  for (std::set<std::string>::iterator I = UndefinedSymbols.begin();
-       I != UndefinedSymbols.end(); )
-    if (DefinedSymbols.count(*I))
-      UndefinedSymbols.erase(I++);  // This symbol really is defined!
-    else
-      ++I; // Keep this symbol in the undefined symbols list
-}
-
-/// LinkInArchive - opens an archive library and link in all objects which
-/// provide symbols that are currently undefined.
-///
-/// Inputs:
-///  Filename - The pathname of the archive.
-///
-/// Return Value:
-///  TRUE  - An error occurred.
-///  FALSE - No errors.
-bool
-Linker::LinkInArchive(const sys::Path &Filename, bool &is_native) {
-  // Make sure this is an archive file we're dealing with
-  if (!Filename.isArchive())
-    return error("File '" + Filename.str() + "' is not an archive.");
-
-  // Open the archive file
-  verbose("Linking archive file '" + Filename.str() + "'");
-
-  // Find all of the symbols currently undefined in the bitcode program.
-  // If all the symbols are defined, the program is complete, and there is
-  // no reason to link in any archive files.
-  std::set<std::string> UndefinedSymbols;
-  GetAllUndefinedSymbols(Composite, UndefinedSymbols);
-
-  if (UndefinedSymbols.empty()) {
-    verbose("No symbols undefined, skipping library '" + Filename.str() + "'");
-    return false;  // No need to link anything in!
-  }
-
-  std::string ErrMsg;
-  std::auto_ptr<Archive> AutoArch (
-    Archive::OpenAndLoadSymbols(Filename, Context, &ErrMsg));
-
-  Archive* arch = AutoArch.get();
-
-  if (!arch)
-    return error("Cannot read archive '" + Filename.str() +
-                 "': " + ErrMsg);
-  if (!arch->isBitcodeArchive()) {
-    is_native = true;
-    return false;
-  }
-  is_native = false;
-
-  // Save a set of symbols that are not defined by the archive. Since we're
-  // entering a loop, there's no point searching for these multiple times. This
-  // variable is used to "set_subtract" from the set of undefined symbols.
-  std::set<std::string> NotDefinedByArchive;
-
-  // Save the current set of undefined symbols, because we may have to make
-  // multiple passes over the archive:
-  std::set<std::string> CurrentlyUndefinedSymbols;
-
-  do {
-    CurrentlyUndefinedSymbols = UndefinedSymbols;
-
-    // Find the modules we need to link into the target module.  Note that arch
-    // keeps ownership of these modules and may return the same Module* from a
-    // subsequent call.
-    SmallVector<Module*, 16> Modules;
-    if (!arch->findModulesDefiningSymbols(UndefinedSymbols, Modules, &ErrMsg))
-      return error("Cannot find symbols in '" + Filename.str() + 
-                   "': " + ErrMsg);
-
-    // If we didn't find any more modules to link this time, we are done
-    // searching this archive.
-    if (Modules.empty())
-      break;
-
-    // Any symbols remaining in UndefinedSymbols after
-    // findModulesDefiningSymbols are ones that the archive does not define. So
-    // we add them to the NotDefinedByArchive variable now.
-    NotDefinedByArchive.insert(UndefinedSymbols.begin(),
-        UndefinedSymbols.end());
-
-    // Loop over all the Modules that we got back from the archive
-    for (SmallVectorImpl<Module*>::iterator I=Modules.begin(), E=Modules.end();
-         I != E; ++I) {
-
-      // Get the module we must link in.
-      std::string moduleErrorMsg;
-      Module* aModule = *I;
-      if (aModule != NULL) {
-        if (aModule->MaterializeAll(&moduleErrorMsg))
-          return error("Could not load a module: " + moduleErrorMsg);
-
-        verbose("  Linking in module: " + aModule->getModuleIdentifier());
-
-        // Link it in
-        if (LinkInModule(aModule, &moduleErrorMsg))
-          return error("Cannot link in module '" +
-                       aModule->getModuleIdentifier() + "': " + moduleErrorMsg);
-      } 
-    }
-    
-    // Get the undefined symbols from the aggregate module. This recomputes the
-    // symbols we still need after the new modules have been linked in.
-    GetAllUndefinedSymbols(Composite, UndefinedSymbols);
-
-    // At this point we have two sets of undefined symbols: UndefinedSymbols
-    // which holds the undefined symbols from all the modules, and
-    // NotDefinedByArchive which holds symbols we know the archive doesn't
-    // define. There's no point searching for symbols that we won't find in the
-    // archive so we subtract these sets.
-    set_subtract(UndefinedSymbols, NotDefinedByArchive);
-
-    // If there's no symbols left, no point in continuing to search the
-    // archive.
-    if (UndefinedSymbols.empty())
-      break;
-  } while (CurrentlyUndefinedSymbols != UndefinedSymbols);
-
-  return false;
-}
diff --git a/lib/Linker/LinkItems.cpp b/lib/Linker/LinkItems.cpp
deleted file mode 100644
index 8c6ed42..0000000
--- a/lib/Linker/LinkItems.cpp
+++ /dev/null
@@ -1,216 +0,0 @@
-//===- lib/Linker/LinkItems.cpp - Link LLVM objects and libraries ---------===//
-//
-//                     The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-//
-// This file contains routines to handle linking together LLVM bitcode files,
-// and to handle annoying things like static libraries.
-//
-//===----------------------------------------------------------------------===//
-
-#include "llvm/Linker.h"
-#include "llvm/Bitcode/ReaderWriter.h"
-#include "llvm/IR/Module.h"
-#include "llvm/Support/ErrorHandling.h"
-#include "llvm/Support/MemoryBuffer.h"
-#include "llvm/Support/Path.h"
-#include "llvm/Support/system_error.h"
-using namespace llvm;
-
-// LinkItems - This function is the main entry point into linking. It takes a
-// list of LinkItem which indicates the order the files should be linked and
-// how each file should be treated (plain file or with library search). The
-// function only links bitcode and produces a result list of items that are
-// native objects. 
-bool
-Linker::LinkInItems(const ItemList& Items, ItemList& NativeItems) {
-  // Clear the NativeItems just in case
-  NativeItems.clear();
-
-  // For each linkage item ...
-  for (ItemList::const_iterator I = Items.begin(), E = Items.end();
-       I != E; ++I) {
-    if (I->second) {
-      // Link in the library suggested.
-      bool is_native = false;
-      if (LinkInLibrary(I->first, is_native))
-        return true;
-      if (is_native)
-        NativeItems.push_back(*I);
-    } else {
-      // Link in the file suggested
-      bool is_native = false;
-      if (LinkInFile(sys::Path(I->first), is_native))
-        return true;
-      if (is_native)
-        NativeItems.push_back(*I);
-    }
-  }
-
-  return false;
-}
-
-
-/// LinkInLibrary - links one library into the HeadModule.
-///
-bool Linker::LinkInLibrary(StringRef Lib, bool& is_native) {
-  is_native = false;
-  // Determine where this library lives.
-  sys::Path Pathname = FindLib(Lib);
-  if (Pathname.isEmpty())
-    return error("Cannot find library '" + Lib.str() + "'");
-
-  // If its an archive, try to link it in
-  std::string Magic;
-  Pathname.getMagicNumber(Magic, 64);
-  switch (sys::IdentifyFileType(Magic.c_str(), 64)) {
-    default: llvm_unreachable("Bad file type identification");
-    case sys::Unknown_FileType:
-      return warning("Supposed library '" + Lib.str() + "' isn't a library.");
-
-    case sys::Bitcode_FileType:
-      // LLVM ".so" file.
-      if (LinkInFile(Pathname, is_native))
-        return true;
-      break;
-
-    case sys::Archive_FileType:
-      if (LinkInArchive(Pathname, is_native))
-        return error("Cannot link archive '" + Pathname.str() + "'");
-      break;
-
-    case sys::ELF_Relocatable_FileType:
-    case sys::ELF_SharedObject_FileType:
-    case sys::Mach_O_Object_FileType:
-    case sys::Mach_O_FixedVirtualMemorySharedLib_FileType:
-    case sys::Mach_O_DynamicallyLinkedSharedLib_FileType:
-    case sys::Mach_O_DynamicallyLinkedSharedLibStub_FileType:
-    case sys::COFF_FileType:
-      is_native = true;
-      break;
-  }
-  return false;
-}
-
-/// LinkLibraries - takes the specified library files and links them into the
-/// main bitcode object file.
-///
-/// Inputs:
-///  Libraries  - The list of libraries to link into the module.
-///
-/// Return value:
-///  FALSE - No error.
-///  TRUE  - Error.
-///
-bool Linker::LinkInLibraries(const std::vector<std::string> &Libraries) {
-
-  // Process the set of libraries we've been provided.
-  bool is_native = false;
-  for (unsigned i = 0; i < Libraries.size(); ++i)
-    if (LinkInLibrary(Libraries[i], is_native))
-      return true;
-
-  return false;
-}
-
-/// LinkInFile - opens a bitcode file and links in all objects which
-/// provide symbols that are currently undefined.
-///
-/// Inputs:
-///  File - The pathname of the bitcode file.
-///
-/// Outputs:
-///  ErrorMessage - A C++ string detailing what error occurred, if any.
-///
-/// Return Value:
-///  TRUE  - An error occurred.
-///  FALSE - No errors.
-///
-bool Linker::LinkInFile(const sys::Path &File, bool &is_native) {
-  is_native = false;
-  
-  // Check for a file of name "-", which means "read standard input"
-  if (File.str() == "-") {
-    std::auto_ptr<Module> M;
-    OwningPtr<MemoryBuffer> Buffer;
-    error_code ec;
-    if (!(ec = MemoryBuffer::getSTDIN(Buffer))) {
-      if (!Buffer->getBufferSize()) {
-        Error = "standard input is empty";
-      } else {
-        M.reset(ParseBitcodeFile(Buffer.get(), Context, &Error));
-        if (M.get())
-          if (!LinkInModule(M.get(), &Error))
-            return false;
-      }
-    }
-    return error("Cannot link stdin: " + ec.message());
-  }
-
-  // Determine what variety of file it is.
-  std::string Magic;
-  if (!File.getMagicNumber(Magic, 64))
-    return error("Cannot find linker input '" + File.str() + "'");
-
-  switch (sys::IdentifyFileType(Magic.c_str(), 64)) {
-    default: llvm_unreachable("Bad file type identification");
-    case sys::Unknown_FileType:
-      return warning("Ignoring file '" + File.str() + 
-                   "' because does not contain bitcode.");
-
-    case sys::Archive_FileType:
-      // A user may specify an ar archive without -l, perhaps because it
-      // is not installed as a library. Detect that and link the archive.
-      if (LinkInArchive(File, is_native))
-        return true;
-      break;
-
-    case sys::Bitcode_FileType: {
-      verbose("Linking bitcode file '" + File.str() + "'");
-      std::auto_ptr<Module> M(LoadObject(File));
-      if (M.get() == 0)
-        return error("Cannot load file '" + File.str() + "': " + Error);
-      if (LinkInModule(M.get(), &Error))
-        return error("Cannot link file '" + File.str() + "': " + Error);
-
-      verbose("Linked in file '" + File.str() + "'");
-      break;
-    }
-
-    case sys::ELF_Relocatable_FileType:
-    case sys::ELF_SharedObject_FileType:
-    case sys::Mach_O_Object_FileType:
-    case sys::Mach_O_FixedVirtualMemorySharedLib_FileType:
-    case sys::Mach_O_DynamicallyLinkedSharedLib_FileType:
-    case sys::Mach_O_DynamicallyLinkedSharedLibStub_FileType:
-    case sys::COFF_FileType:
-      is_native = true;
-      break;
-  }
-  return false;
-}
-
-/// LinkFiles - takes a module and a list of files and links them all together.
-/// It locates the file either in the current directory, as its absolute
-/// or relative pathname, or as a file somewhere in LLVM_LIB_SEARCH_PATH.
-///
-/// Inputs:
-///  Files      - A vector of sys::Path indicating the LLVM bitcode filenames
-///               to be linked.  The names can refer to a mixture of pure LLVM
-///               bitcode files and archive (ar) formatted files.
-///
-/// Return value:
-///  FALSE - No errors.
-///  TRUE  - Some error occurred.
-///
-bool Linker::LinkInFiles(const std::vector<sys::Path> &Files) {
-  bool is_native;
-  for (unsigned i = 0; i < Files.size(); ++i)
-    if (LinkInFile(Files[i], is_native))
-      return true;
-  return false;
-}
diff --git a/lib/Linker/LinkModules.cpp b/lib/Linker/LinkModules.cpp
index e973919..c358a0a 100644
--- a/lib/Linker/LinkModules.cpp
+++ b/lib/Linker/LinkModules.cpp
@@ -180,7 +180,7 @@ bool TypeMapTy::areTypesIsomorphic(Type *DstTy, Type *SrcTy) {
     if (DATy->getNumElements() != cast<ArrayType>(SrcTy)->getNumElements())
       return false;
   } else if (VectorType *DVTy = dyn_cast<VectorType>(DstTy)) {
-    if (DVTy->getNumElements() != cast<ArrayType>(SrcTy)->getNumElements())
+    if (DVTy->getNumElements() != cast<VectorType>(SrcTy)->getNumElements())
       return false;
   }
 
@@ -421,13 +421,6 @@ namespace {
     }
     
     void computeTypeMapping();
-    bool categorizeModuleFlagNodes(const NamedMDNode *ModFlags,
-                                   DenseMap<MDString*, MDNode*> &ErrorNode,
-                                   DenseMap<MDString*, MDNode*> &WarningNode,
-                                   DenseMap<MDString*, MDNode*> &OverrideNode,
-                                   DenseMap<MDString*,
-                                   SmallSetVector<MDNode*, 8> > &RequireNodes,
-                                   SmallSetVector<MDString*, 16> &SeenIDs);
     
     bool linkAppendingVarProto(GlobalVariable *DstGV, GlobalVariable *SrcGV);
     bool linkGlobalProto(GlobalVariable *SrcGV);
@@ -613,7 +606,8 @@ void ModuleLinker::computeTypeMapping() {
     // Check to see if there is a dot in the name followed by a digit.
     size_t DotPos = ST->getName().rfind('.');
     if (DotPos == 0 || DotPos == StringRef::npos ||
-        ST->getName().back() == '.' || !isdigit(ST->getName()[DotPos+1]))
+        ST->getName().back() == '.' ||
+        !isdigit(static_cast<unsigned char>(ST->getName()[DotPos+1])))
       continue;
     
     // Check to see if the destination module has a struct with the prefix name.
@@ -987,76 +981,16 @@ void ModuleLinker::linkNamedMDNodes() {
   }
 }
 
-/// categorizeModuleFlagNodes - Categorize the module flags according to their
-/// type: Error, Warning, Override, and Require.
-bool ModuleLinker::
-categorizeModuleFlagNodes(const NamedMDNode *ModFlags,
-                          DenseMap<MDString*, MDNode*> &ErrorNode,
-                          DenseMap<MDString*, MDNode*> &WarningNode,
-                          DenseMap<MDString*, MDNode*> &OverrideNode,
-                          DenseMap<MDString*,
-                            SmallSetVector<MDNode*, 8> > &RequireNodes,
-                          SmallSetVector<MDString*, 16> &SeenIDs) {
-  bool HasErr = false;
-
-  for (unsigned I = 0, E = ModFlags->getNumOperands(); I != E; ++I) {
-    MDNode *Op = ModFlags->getOperand(I);
-    assert(Op->getNumOperands() == 3 && "Invalid module flag metadata!");
-    assert(isa<ConstantInt>(Op->getOperand(0)) &&
-           "Module flag's first operand must be an integer!");
-    assert(isa<MDString>(Op->getOperand(1)) &&
-           "Module flag's second operand must be an MDString!");
-
-    ConstantInt *Behavior = cast<ConstantInt>(Op->getOperand(0));
-    MDString *ID = cast<MDString>(Op->getOperand(1));
-    Value *Val = Op->getOperand(2);
-    switch (Behavior->getZExtValue()) {
-    default:
-      assert(false && "Invalid behavior in module flag metadata!");
-      break;
-    case Module::Error: {
-      MDNode *&ErrNode = ErrorNode[ID];
-      if (!ErrNode) ErrNode = Op;
-      if (ErrNode->getOperand(2) != Val)
-        HasErr = emitError("linking module flags '" + ID->getString() +
-                           "': IDs have conflicting values");
-      break;
-    }
-    case Module::Warning: {
-      MDNode *&WarnNode = WarningNode[ID];
-      if (!WarnNode) WarnNode = Op;
-      if (WarnNode->getOperand(2) != Val)
-        errs() << "WARNING: linking module flags '" << ID->getString()
-               << "': IDs have conflicting values";
-      break;
-    }
-    case Module::Require:  RequireNodes[ID].insert(Op);     break;
-    case Module::Override: {
-      MDNode *&OvrNode = OverrideNode[ID];
-      if (!OvrNode) OvrNode = Op;
-      if (OvrNode->getOperand(2) != Val)
-        HasErr = emitError("linking module flags '" + ID->getString() +
-                           "': IDs have conflicting override values");
-      break;
-    }
-    }
-
-    SeenIDs.insert(ID);
-  }
-
-  return HasErr;
-}
-
 /// linkModuleFlagsMetadata - Merge the linker flags in Src into the Dest
 /// module.
 bool ModuleLinker::linkModuleFlagsMetadata() {
+  // If the source module has no module flags, we are done.
   const NamedMDNode *SrcModFlags = SrcM->getModuleFlagsMetadata();
   if (!SrcModFlags) return false;
 
-  NamedMDNode *DstModFlags = DstM->getOrInsertModuleFlagsMetadata();
-
   // If the destination module doesn't have module flags yet, then just copy
   // over the source module's flags.
+  NamedMDNode *DstModFlags = DstM->getOrInsertModuleFlagsMetadata();
   if (DstModFlags->getNumOperands() == 0) {
     for (unsigned I = 0, E = SrcModFlags->getNumOperands(); I != E; ++I)
       DstModFlags->addOperand(SrcModFlags->getOperand(I));
@@ -1064,89 +998,137 @@ bool ModuleLinker::linkModuleFlagsMetadata() {
     return false;
   }
 
-  bool HasErr = false;
+  // First build a map of the existing module flags and requirements.
+  DenseMap<MDString*, MDNode*> Flags;
+  SmallSetVector<MDNode*, 16> Requirements;
+  for (unsigned I = 0, E = DstModFlags->getNumOperands(); I != E; ++I) {
+    MDNode *Op = DstModFlags->getOperand(I);
+    ConstantInt *Behavior = cast<ConstantInt>(Op->getOperand(0));
+    MDString *ID = cast<MDString>(Op->getOperand(1));
 
-  // Otherwise, we have to merge them based on their behaviors. First,
-  // categorize all of the nodes in the modules' module flags. If an error or
-  // warning occurs, then emit the appropriate message(s).
-  DenseMap<MDString*, MDNode*> ErrorNode;
-  DenseMap<MDString*, MDNode*> WarningNode;
-  DenseMap<MDString*, MDNode*> OverrideNode;
-  DenseMap<MDString*, SmallSetVector<MDNode*, 8> > RequireNodes;
-  SmallSetVector<MDString*, 16> SeenIDs;
-
-  HasErr |= categorizeModuleFlagNodes(SrcModFlags, ErrorNode, WarningNode,
-                                      OverrideNode, RequireNodes, SeenIDs);
-  HasErr |= categorizeModuleFlagNodes(DstModFlags, ErrorNode, WarningNode,
-                                      OverrideNode, RequireNodes, SeenIDs);
-
-  // Check that there isn't both an error and warning node for a flag.
-  for (SmallSetVector<MDString*, 16>::iterator
-         I = SeenIDs.begin(), E = SeenIDs.end(); I != E; ++I) {
-    MDString *ID = *I;
-    if (ErrorNode[ID] && WarningNode[ID])
-      HasErr = emitError("linking module flags '" + ID->getString() +
-                         "': IDs have conflicting behaviors");
+    if (Behavior->getZExtValue() == Module::Require) {
+      Requirements.insert(cast<MDNode>(Op->getOperand(2)));
+    } else {
+      Flags[ID] = Op;
+    }
   }
 
-  // Early exit if we had an error.
-  if (HasErr) return true;
-
-  // Get the destination's module flags ready for new operands.
-  DstModFlags->dropAllReferences();
-
-  // Add all of the module flags to the destination module.
-  DenseMap<MDString*, SmallVector<MDNode*, 4> > AddedNodes;
-  for (SmallSetVector<MDString*, 16>::iterator
-         I = SeenIDs.begin(), E = SeenIDs.end(); I != E; ++I) {
-    MDString *ID = *I;
-    if (OverrideNode[ID]) {
-      DstModFlags->addOperand(OverrideNode[ID]);
-      AddedNodes[ID].push_back(OverrideNode[ID]);
-    } else if (ErrorNode[ID]) {
-      DstModFlags->addOperand(ErrorNode[ID]);
-      AddedNodes[ID].push_back(ErrorNode[ID]);
-    } else if (WarningNode[ID]) {
-      DstModFlags->addOperand(WarningNode[ID]);
-      AddedNodes[ID].push_back(WarningNode[ID]);
+  // Merge in the flags from the source module, and also collect its set of
+  // requirements.
+  bool HasErr = false;
+  for (unsigned I = 0, E = SrcModFlags->getNumOperands(); I != E; ++I) {
+    MDNode *SrcOp = SrcModFlags->getOperand(I);
+    ConstantInt *SrcBehavior = cast<ConstantInt>(SrcOp->getOperand(0));
+    MDString *ID = cast<MDString>(SrcOp->getOperand(1));
+    MDNode *DstOp = Flags.lookup(ID);
+    unsigned SrcBehaviorValue = SrcBehavior->getZExtValue();
+
+    // If this is a requirement, add it and continue.
+    if (SrcBehaviorValue == Module::Require) {
+      // If the destination module does not already have this requirement, add
+      // it.
+      if (Requirements.insert(cast<MDNode>(SrcOp->getOperand(2)))) {
+        DstModFlags->addOperand(SrcOp);
+      }
+      continue;
+    }
+
+    // If there is no existing flag with this ID, just add it.
+    if (!DstOp) {
+      Flags[ID] = SrcOp;
+      DstModFlags->addOperand(SrcOp);
+      continue;
     }
 
-    for (SmallSetVector<MDNode*, 8>::iterator
-           II = RequireNodes[ID].begin(), IE = RequireNodes[ID].end();
-         II != IE; ++II)
-      DstModFlags->addOperand(*II);
-  }
+    // Otherwise, perform a merge.
+    ConstantInt *DstBehavior = cast<ConstantInt>(DstOp->getOperand(0));
+    unsigned DstBehaviorValue = DstBehavior->getZExtValue();
+
+    // If either flag has override behavior, handle it first.
+    if (DstBehaviorValue == Module::Override) {
+      // Diagnose inconsistent flags which both have override behavior.
+      if (SrcBehaviorValue == Module::Override &&
+          SrcOp->getOperand(2) != DstOp->getOperand(2)) {
+        HasErr |= emitError("linking module flags '" + ID->getString() +
+                            "': IDs have conflicting override values");
+      }
+      continue;
+    } else if (SrcBehaviorValue == Module::Override) {
+      // Update the destination flag to that of the source.
+      DstOp->replaceOperandWith(0, SrcBehavior);
+      DstOp->replaceOperandWith(2, SrcOp->getOperand(2));
+      continue;
+    }
 
-  // Now check that all of the requirements have been satisfied.
-  for (SmallSetVector<MDString*, 16>::iterator
-         I = SeenIDs.begin(), E = SeenIDs.end(); I != E; ++I) {
-    MDString *ID = *I;
-    SmallSetVector<MDNode*, 8> &Set = RequireNodes[ID];
-
-    for (SmallSetVector<MDNode*, 8>::iterator
-           II = Set.begin(), IE = Set.end(); II != IE; ++II) {
-      MDNode *Node = *II;
-      assert(isa<MDNode>(Node->getOperand(2)) &&
-             "Module flag's third operand must be an MDNode!");
-      MDNode *Val = cast<MDNode>(Node->getOperand(2));
-
-      MDString *ReqID = cast<MDString>(Val->getOperand(0));
-      Value *ReqVal = Val->getOperand(1);
-
-      bool HasValue = false;
-      for (SmallVectorImpl<MDNode*>::iterator
-             RI = AddedNodes[ReqID].begin(), RE = AddedNodes[ReqID].end();
-           RI != RE; ++RI) {
-        MDNode *ReqNode = *RI;
-        if (ReqNode->getOperand(2) == ReqVal) {
-          HasValue = true;
-          break;
-        }
+    // Diagnose inconsistent merge behavior types.
+    if (SrcBehaviorValue != DstBehaviorValue) {
+      HasErr |= emitError("linking module flags '" + ID->getString() +
+                          "': IDs have conflicting behaviors");
+      continue;
+    }
+
+    // Perform the merge for standard behavior types.
+    switch (SrcBehaviorValue) {
+    case Module::Require:
+    case Module::Override: assert(0 && "not possible"); break;
+    case Module::Error: {
+      // Emit an error if the values differ.
+      if (SrcOp->getOperand(2) != DstOp->getOperand(2)) {
+        HasErr |= emitError("linking module flags '" + ID->getString() +
+                            "': IDs have conflicting values");
       }
+      continue;
+    }
+    case Module::Warning: {
+      // Emit a warning if the values differ.
+      if (SrcOp->getOperand(2) != DstOp->getOperand(2)) {
+        errs() << "WARNING: linking module flags '" << ID->getString()
+               << "': IDs have conflicting values";
+      }
+      continue;
+    }
+    case Module::Append: {
+      MDNode *DstValue = cast<MDNode>(DstOp->getOperand(2));
+      MDNode *SrcValue = cast<MDNode>(SrcOp->getOperand(2));
+      unsigned NumOps = DstValue->getNumOperands() + SrcValue->getNumOperands();
+      Value **VP, **Values = VP = new Value*[NumOps];
+      for (unsigned i = 0, e = DstValue->getNumOperands(); i != e; ++i, ++VP)
+        *VP = DstValue->getOperand(i);
+      for (unsigned i = 0, e = SrcValue->getNumOperands(); i != e; ++i, ++VP)
+        *VP = SrcValue->getOperand(i);
+      DstOp->replaceOperandWith(2, MDNode::get(DstM->getContext(),
+                                               ArrayRef<Value*>(Values,
+                                                                NumOps)));
+      delete[] Values;
+      break;
+    }
+    case Module::AppendUnique: {
+      SmallSetVector<Value*, 16> Elts;
+      MDNode *DstValue = cast<MDNode>(DstOp->getOperand(2));
+      MDNode *SrcValue = cast<MDNode>(SrcOp->getOperand(2));
+      for (unsigned i = 0, e = DstValue->getNumOperands(); i != e; ++i)
+        Elts.insert(DstValue->getOperand(i));
+      for (unsigned i = 0, e = SrcValue->getNumOperands(); i != e; ++i)
+        Elts.insert(SrcValue->getOperand(i));
+      DstOp->replaceOperandWith(2, MDNode::get(DstM->getContext(),
+                                               ArrayRef<Value*>(Elts.begin(),
+                                                                Elts.end())));
+      break;
+    }
+    }
+  }
 
-      if (!HasValue)
-        HasErr = emitError("linking module flags '" + ReqID->getString() +
-                           "': does not have the required value");
+  // Check all of the requirements.
+  for (unsigned I = 0, E = Requirements.size(); I != E; ++I) {
+    MDNode *Requirement = Requirements[I];
+    MDString *Flag = cast<MDString>(Requirement->getOperand(0));
+    Value *ReqValue = Requirement->getOperand(1);
+
+    MDNode *Op = Flags[Flag];
+    if (!Op || Op->getOperand(2) != ReqValue) {
+      HasErr |= emitError("linking module flags '" + Flag->getString() +
+                          "': does not have the required value");
+      continue;
     }
   }
 
diff --git a/lib/Linker/Linker.cpp b/lib/Linker/Linker.cpp
index a30363d..c8ea8ff 100644
--- a/lib/Linker/Linker.cpp
+++ b/lib/Linker/Linker.cpp
@@ -89,93 +89,3 @@ Linker::releaseModule() {
   Flags = 0;
   return result;
 }
-
-// LoadObject - Read in and parse the bitcode file named by FN and return the
-// module it contains (wrapped in an auto_ptr), or auto_ptr<Module>() and set
-// Error if an error occurs.
-std::auto_ptr<Module>
-Linker::LoadObject(const sys::Path &FN) {
-  std::string ParseErrorMessage;
-  Module *Result = 0;
-
-  OwningPtr<MemoryBuffer> Buffer;
-  if (error_code ec = MemoryBuffer::getFileOrSTDIN(FN.c_str(), Buffer))
-    ParseErrorMessage = "Error reading file '" + FN.str() + "'" + ": "
-                      + ec.message();
-  else
-    Result = ParseBitcodeFile(Buffer.get(), Context, &ParseErrorMessage);
-
-  if (Result)
-    return std::auto_ptr<Module>(Result);
-  Error = "Bitcode file '" + FN.str() + "' could not be loaded";
-  if (ParseErrorMessage.size())
-    Error += ": " + ParseErrorMessage;
-  return std::auto_ptr<Module>();
-}
-
-// IsLibrary - Determine if "Name" is a library in "Directory". Return
-// a non-empty sys::Path if its found, an empty one otherwise.
-static inline sys::Path IsLibrary(StringRef Name,
-                                  const sys::Path &Directory) {
-
-  sys::Path FullPath(Directory);
-
-  // Try the libX.a form
-  FullPath.appendComponent(("lib" + Name).str());
-  FullPath.appendSuffix("a");
-  if (FullPath.isArchive())
-    return FullPath;
-
-  // Try the libX.bca form
-  FullPath.eraseSuffix();
-  FullPath.appendSuffix("bca");
-  if (FullPath.isArchive())
-    return FullPath;
-
-  // Try the libX.so (or .dylib) form
-  FullPath.eraseSuffix();
-  FullPath.appendSuffix(sys::Path::GetDLLSuffix());
-  if (FullPath.isDynamicLibrary())  // Native shared library?
-    return FullPath;
-  if (FullPath.isBitcodeFile())    // .so file containing bitcode?
-    return FullPath;
-
-  // Try libX form, to make it possible to add dependency on the
-  // specific version of .so, like liblzma.so.1.0.0
-  FullPath.eraseSuffix();
-  if (FullPath.isDynamicLibrary())  // Native shared library?
-    return FullPath;
-  if (FullPath.isBitcodeFile())    // .so file containing bitcode?
-    return FullPath;
-
-  // Not found .. fall through
-
-  // Indicate that the library was not found in the directory.
-  FullPath.clear();
-  return FullPath;
-}
-
-/// FindLib - Try to convert Filename into the name of a file that we can open,
-/// if it does not already name a file we can open, by first trying to open
-/// Filename, then libFilename.[suffix] for each of a set of several common
-/// library suffixes, in each of the directories in LibPaths. Returns an empty
-/// Path if no matching file can be found.
-///
-sys::Path
-Linker::FindLib(StringRef Filename) {
-  // Determine if the pathname can be found as it stands.
-  sys::Path FilePath(Filename);
-  if (FilePath.canRead() &&
-      (FilePath.isArchive() || FilePath.isDynamicLibrary()))
-    return FilePath;
-
-  // Iterate over the directories in Paths to see if we can find the library
-  // there.
-  for (unsigned Index = 0; Index != LibPaths.size(); ++Index) {
-    sys::Path Directory(LibPaths[Index]);
-    sys::Path FullPath = IsLibrary(Filename, Directory);
-    if (!FullPath.isEmpty())
-      return FullPath;
-  }
-  return sys::Path();
-}