Allow alias to point to an arbitrary ConstantExpr.

This  patch changes GlobalAlias to point to an arbitrary ConstantExpr and it is
up to MC (or the system assembler) to decide if that expression is valid or not.

This reduces our ability to diagnose invalid uses and how early we can spot
them, but it also lets us do things like

@test5 = alias inttoptr(i32 sub (i32 ptrtoint (i32* @test2 to i32),
                                 i32 ptrtoint (i32* @bar to i32)) to i32*)

An important implication of this patch is that the notion of aliased global
doesn't exist any more. The alias has to encode the information needed to
access it in its metadata (linkage, visibility, type, etc).

Another consequence to notice is that getSection has to return a "const char *".
It could return a NullTerminatedStringRef if there was such a thing, but when
that was proposed the decision was to just uses "const char*" for that.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210062 91177308-0d34-0410-b5e6-96231b3b80d8

14 files changed, 137 insertions, 200 deletions

diff --git a/lib/AsmParser/LLParser.cpp b/lib/AsmParser/LLParser.cpp
index f0efa9414d..dc151f2bf9 100644
--- a/lib/AsmParser/LLParser.cpp
+++ b/lib/AsmParser/LLParser.cpp
@@ -674,44 +674,30 @@ bool LLParser::ParseAlias(const std::string &Name, LocTy NameLoc,
     return Error(LinkageLoc,
                  "symbol with local linkage must have default visibility");
 
-  bool HasAddrSpace = Lex.getKind() == lltok::kw_addrspace;
-  unsigned AddrSpace;
-  LocTy AddrSpaceLoc = Lex.getLoc();
-  if (ParseOptionalAddrSpace(AddrSpace))
-    return true;
-
-  LocTy TyLoc = Lex.getLoc();
-  Type *Ty = nullptr;
-  if (ParseType(Ty))
-    return true;
-
-  bool DifferentType = EatIfPresent(lltok::comma);
-  if (HasAddrSpace && !DifferentType)
-    return Error(AddrSpaceLoc, "A type is required if addrspace is given");
-
-  Type *AliaseeType = nullptr;
-  if (DifferentType) {
-    if (ParseType(AliaseeType))
+  Constant *Aliasee;
+  LocTy AliaseeLoc = Lex.getLoc();
+  if (Lex.getKind() != lltok::kw_bitcast &&
+      Lex.getKind() != lltok::kw_getelementptr &&
+      Lex.getKind() != lltok::kw_addrspacecast &&
+      Lex.getKind() != lltok::kw_inttoptr) {
+    if (ParseGlobalTypeAndValue(Aliasee))
       return true;
   } else {
-    AliaseeType = Ty;
-    auto *PTy = dyn_cast<PointerType>(Ty);
-    if (!PTy)
-      return Error(TyLoc, "An alias must have pointer type");
-    Ty = PTy->getElementType();
-    AddrSpace = PTy->getAddressSpace();
+    // The bitcast dest type is not present, it is implied by the dest type.
+    ValID ID;
+    if (ParseValID(ID))
+      return true;
+    if (ID.Kind != ValID::t_Constant)
+      return Error(AliaseeLoc, "invalid aliasee");
+    Aliasee = ID.ConstantVal;
   }
 
-  LocTy AliaseeLoc = Lex.getLoc();
-  Constant *C;
-  if (ParseGlobalValue(AliaseeType, C))
-    return true;
-
-  auto *Aliasee = dyn_cast<GlobalObject>(C);
-  if (!Aliasee)
-    return Error(AliaseeLoc, "Alias must point to function or variable");
-
-  assert(Aliasee->getType()->isPointerTy());
+  Type *AliaseeType = Aliasee->getType();
+  auto *PTy = dyn_cast<PointerType>(AliaseeType);
+  if (!PTy)
+    return Error(AliaseeLoc, "An alias must have pointer type");
+  Type *Ty = PTy->getElementType();
+  unsigned AddrSpace = PTy->getAddressSpace();
 
   // Okay, create the alias but do not insert it into the module yet.
   std::unique_ptr<GlobalAlias> GA(
@@ -739,11 +725,6 @@ bool LLParser::ParseAlias(const std::string &Name, LocTy NameLoc,
 
     // If they agree, just RAUW the old value with the alias and remove the
     // forward ref info.
-    for (auto *User : Val->users()) {
-      if (auto *GA = dyn_cast<GlobalAlias>(User))
-        return Error(NameLoc, "Alias is pointed by alias " + GA->getName());
-    }
-
     Val->replaceAllUsesWith(GA.get());
     Val->eraseFromParent();
     ForwardRefVals.erase(I);
diff --git a/lib/Bitcode/Reader/BitcodeReader.cpp b/lib/Bitcode/Reader/BitcodeReader.cpp
index 3d4ae84dbd..322879b566 100644
--- a/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -1094,28 +1094,6 @@ uint64_t BitcodeReader::decodeSignRotatedValue(uint64_t V) {
   return 1ULL << 63;
 }
 
-// FIXME: Delete this in LLVM 4.0 and just assert that the aliasee is a
-// GlobalObject.
-static GlobalObject &
-getGlobalObjectInExpr(const DenseMap<GlobalAlias *, Constant *> &Map,
-                      Constant &C) {
-  auto *GO = dyn_cast<GlobalObject>(&C);
-  if (GO)
-    return *GO;
-
-  auto *GA = dyn_cast<GlobalAlias>(&C);
-  if (GA)
-    return getGlobalObjectInExpr(Map, *Map.find(GA)->second);
-
-  auto &CE = cast<ConstantExpr>(C);
-  assert(CE.getOpcode() == Instruction::BitCast ||
-         CE.getOpcode() == Instruction::GetElementPtr ||
-         CE.getOpcode() == Instruction::AddrSpaceCast);
-  if (CE.getOpcode() == Instruction::GetElementPtr)
-    assert(cast<GEPOperator>(CE).hasAllZeroIndices());
-  return getGlobalObjectInExpr(Map, *CE.getOperand(0));
-}
-
 /// ResolveGlobalAndAliasInits - Resolve all of the initializers for global
 /// values and aliases that we can.
 error_code BitcodeReader::ResolveGlobalAndAliasInits() {
@@ -1141,30 +1119,19 @@ error_code BitcodeReader::ResolveGlobalAndAliasInits() {
     GlobalInitWorklist.pop_back();
   }
 
-  // FIXME: Delete this in LLVM 4.0
-  // Older versions of llvm could write an alias pointing to another. We cannot
-  // construct those aliases, so we first collect an alias to aliasee expression
-  // and then compute the actual aliasee.
-  DenseMap<GlobalAlias *, Constant *> AliasInit;
-
   while (!AliasInitWorklist.empty()) {
     unsigned ValID = AliasInitWorklist.back().second;
     if (ValID >= ValueList.size()) {
       AliasInits.push_back(AliasInitWorklist.back());
     } else {
       if (Constant *C = dyn_cast_or_null<Constant>(ValueList[ValID]))
-        AliasInit.insert(std::make_pair(AliasInitWorklist.back().first, C));
+        AliasInitWorklist.back().first->setAliasee(C);
       else
         return Error(ExpectedConstant);
     }
     AliasInitWorklist.pop_back();
   }
 
-  for (auto &Pair : AliasInit) {
-    auto &GO = getGlobalObjectInExpr(AliasInit, *Pair.second);
-    Pair.first->setAliasee(&GO);
-  }
-
   while (!FunctionPrefixWorklist.empty()) {
     unsigned ValID = FunctionPrefixWorklist.back().second;
     if (ValID >= ValueList.size()) {
diff --git a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 7de9c6d616..6c6d0dae9e 100644
--- a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -870,6 +870,8 @@ void AsmPrinter::EmitFunctionBody() {
   OutStreamer.AddBlankLine();
 }
 
+static const MCExpr *lowerConstant(const Constant *CV, AsmPrinter &AP);
+
 bool AsmPrinter::doFinalization(Module &M) {
   // Emit global variables.
   for (const auto &G : M.globals())
@@ -932,10 +934,6 @@ bool AsmPrinter::doFinalization(Module &M) {
     for (const auto &Alias : M.aliases()) {
       MCSymbol *Name = getSymbol(&Alias);
 
-      const GlobalValue *GV = Alias.getAliasee();
-      assert(!GV->isDeclaration());
-      MCSymbol *Target = getSymbol(GV);
-
       if (Alias.hasExternalLinkage() || !MAI->getWeakRefDirective())
         OutStreamer.EmitSymbolAttribute(Name, MCSA_Global);
       else if (Alias.hasWeakLinkage() || Alias.hasLinkOnceLinkage())
@@ -947,7 +945,7 @@ bool AsmPrinter::doFinalization(Module &M) {
 
       // Emit the directives as assignments aka .set:
       OutStreamer.EmitAssignment(Name,
-                                 MCSymbolRefExpr::Create(Target, OutContext));
+                                 lowerConstant(Alias.getAliasee(), *this));
     }
   }
 
@@ -1248,7 +1246,7 @@ bool AsmPrinter::EmitSpecialLLVMGlobal(const GlobalVariable *GV) {
   }
 
   // Ignore debug and non-emitted data.  This handles llvm.compiler.used.
-  if (GV->getSection() == "llvm.metadata" ||
+  if (StringRef(GV->getSection()) == "llvm.metadata" ||
       GV->hasAvailableExternallyLinkage())
     return true;
 
diff --git a/lib/ExecutionEngine/JIT/JITEmitter.cpp b/lib/ExecutionEngine/JIT/JITEmitter.cpp
index cd7a500f51..f1c3bb274e 100644
--- a/lib/ExecutionEngine/JIT/JITEmitter.cpp
+++ b/lib/ExecutionEngine/JIT/JITEmitter.cpp
@@ -32,6 +32,7 @@
 #include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Module.h"
+#include "llvm/IR/Operator.h"
 #include "llvm/IR/ValueHandle.h"
 #include "llvm/IR/ValueMap.h"
 #include "llvm/Support/Debug.h"
@@ -684,13 +685,23 @@ void *JITResolver::JITCompilerFn(void *Stub) {
 //===----------------------------------------------------------------------===//
 // JITEmitter code.
 //
+
+static GlobalObject *getSimpleAliasee(Constant *C) {
+  C = cast<Constant>(C->stripPointerCasts());
+  return dyn_cast<GlobalObject>(C);
+}
+
 void *JITEmitter::getPointerToGlobal(GlobalValue *V, void *Reference,
                                      bool MayNeedFarStub) {
   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
     return TheJIT->getOrEmitGlobalVariable(GV);
 
-  if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V))
-    return TheJIT->getPointerToGlobal(GA->getAliasee());
+  if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
+    // We can only handle simple cases.
+    if (GlobalValue *GV = getSimpleAliasee(GA->getAliasee()))
+      return TheJIT->getPointerToGlobal(GV);
+    return nullptr;
+  }
 
   // If we have already compiled the function, return a pointer to its body.
   Function *F = cast<Function>(V);
diff --git a/lib/IR/AsmWriter.cpp b/lib/IR/AsmWriter.cpp
index 8aee77ac07..14467137aa 100644
--- a/lib/IR/AsmWriter.cpp
+++ b/lib/IR/AsmWriter.cpp
@@ -1494,16 +1494,10 @@ void AssemblyWriter::printAlias(const GlobalAlias *GA) {
 
   PrintLinkage(GA->getLinkage(), Out);
 
-  PointerType *Ty = GA->getType();
   const Constant *Aliasee = GA->getAliasee();
-  if (!Aliasee || Ty != Aliasee->getType()) {
-    if (unsigned AddressSpace = Ty->getAddressSpace())
-      Out << "addrspace(" << AddressSpace << ") ";
-    TypePrinter.print(Ty->getElementType(), Out);
-    Out << ", ";
-  }
 
   if (!Aliasee) {
+    TypePrinter.print(GA->getType(), Out);
     Out << " <<NULL ALIASEE>>";
   } else {
     writeOperand(Aliasee, !isa<ConstantExpr>(Aliasee));
diff --git a/lib/IR/Core.cpp b/lib/IR/Core.cpp
index 27ce503e1c..aa373f602a 100644
--- a/lib/IR/Core.cpp
+++ b/lib/IR/Core.cpp
@@ -1286,7 +1286,7 @@ void LLVMSetLinkage(LLVMValueRef Global, LLVMLinkage Linkage) {
 }
 
 const char *LLVMGetSection(LLVMValueRef Global) {
-  return unwrap<GlobalValue>(Global)->getSection().c_str();
+  return unwrap<GlobalValue>(Global)->getSection();
 }
 
 void LLVMSetSection(LLVMValueRef Global, const char *Section) {
diff --git a/lib/IR/Globals.cpp b/lib/IR/Globals.cpp
index 344a08d8f3..d5723c226a 100644
--- a/lib/IR/Globals.cpp
+++ b/lib/IR/Globals.cpp
@@ -20,6 +20,7 @@
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/LeakDetector.h"
 #include "llvm/IR/Module.h"
+#include "llvm/IR/Operator.h"
 #include "llvm/Support/ErrorHandling.h"
 using namespace llvm;
 
@@ -58,10 +59,22 @@ void GlobalValue::copyAttributesFrom(const GlobalValue *Src) {
   setDLLStorageClass(Src->getDLLStorageClass());
 }
 
-unsigned GlobalValue::getAlignment() const {
-  if (auto *GA = dyn_cast<GlobalAlias>(this))
-    return GA->getAliasee()->getAlignment();
+const GlobalObject *getBaseObject(const Constant &C) {
+  // FIXME: We should probably return a base + offset pair for non-zero GEPs.
+  return dyn_cast<GlobalObject>(C.stripPointerCasts());
+}
 
+unsigned GlobalValue::getAlignment() const {
+  if (auto *GA = dyn_cast<GlobalAlias>(this)) {
+    // In general we cannot compute this at the IR level, but we try.
+    if (const GlobalObject *GO = getBaseObject(*GA->getAliasee()))
+      return GO->getAlignment();
+
+    // FIXME: we should also be able to handle:
+    // Alias = Global + Offset
+    // Alias = Absolute
+    return 0;
+  }
   return cast<GlobalObject>(this)->getAlignment();
 }
 
@@ -80,9 +93,13 @@ void GlobalObject::copyAttributesFrom(const GlobalValue *Src) {
   setSection(GV->getSection());
 }
 
-const std::string &GlobalValue::getSection() const {
-  if (auto *GA = dyn_cast<GlobalAlias>(this))
-    return GA->getAliasee()->getSection();
+const char *GlobalValue::getSection() const {
+  if (auto *GA = dyn_cast<GlobalAlias>(this)) {
+    // In general we cannot compute this at the IR level, but we try.
+    if (const GlobalObject *GO = getBaseObject(*GA->getAliasee()))
+      return GO->getSection();
+    return "";
+  }
   return cast<GlobalObject>(this)->getSection();
 }
 
@@ -216,7 +233,7 @@ void GlobalVariable::copyAttributesFrom(const GlobalValue *Src) {
 //===----------------------------------------------------------------------===//
 
 GlobalAlias::GlobalAlias(Type *Ty, unsigned AddressSpace, LinkageTypes Link,
-                         const Twine &Name, GlobalObject *Aliasee,
+                         const Twine &Name, Constant *Aliasee,
                          Module *ParentModule)
     : GlobalValue(PointerType::get(Ty, AddressSpace), Value::GlobalAliasVal,
                   &Op<0>(), 1, Link, Name) {
@@ -229,7 +246,7 @@ GlobalAlias::GlobalAlias(Type *Ty, unsigned AddressSpace, LinkageTypes Link,
 
 GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
                                  LinkageTypes Link, const Twine &Name,
-                                 GlobalObject *Aliasee, Module *ParentModule) {
+                                 Constant *Aliasee, Module *ParentModule) {
   return new GlobalAlias(Ty, AddressSpace, Link, Name, Aliasee, ParentModule);
 }
 
@@ -241,18 +258,18 @@ GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
 
 GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
                                  LinkageTypes Linkage, const Twine &Name,
-                                 GlobalObject *Aliasee) {
+                                 GlobalValue *Aliasee) {
   return create(Ty, AddressSpace, Linkage, Name, Aliasee, Aliasee->getParent());
 }
 
 GlobalAlias *GlobalAlias::create(LinkageTypes Link, const Twine &Name,
-                                 GlobalObject *Aliasee) {
+                                 GlobalValue *Aliasee) {
   PointerType *PTy = Aliasee->getType();
   return create(PTy->getElementType(), PTy->getAddressSpace(), Link, Name,
                 Aliasee);
 }
 
-GlobalAlias *GlobalAlias::create(const Twine &Name, GlobalObject *Aliasee) {
+GlobalAlias *GlobalAlias::create(const Twine &Name, GlobalValue *Aliasee) {
   return create(Aliasee->getLinkage(), Name, Aliasee);
 }
 
@@ -272,4 +289,8 @@ void GlobalAlias::eraseFromParent() {
   getParent()->getAliasList().erase(this);
 }
 
-void GlobalAlias::setAliasee(GlobalObject *Aliasee) { setOperand(0, Aliasee); }
+void GlobalAlias::setAliasee(Constant *Aliasee) {
+  assert(!Aliasee || Aliasee->getType() == getType() &&
+         "Alias and aliasee types should match!");
+  setOperand(0, Aliasee);
+}
diff --git a/lib/IR/Value.cpp b/lib/IR/Value.cpp
index d734e4ea81..cc599745d5 100644
--- a/lib/IR/Value.cpp
+++ b/lib/IR/Value.cpp
@@ -301,27 +301,6 @@ void Value::takeName(Value *V) {
     ST->reinsertValue(this);
 }
 
-static GlobalObject &findReplacementForAliasUse(Value &C) {
-  if (auto *GO = dyn_cast<GlobalObject>(&C))
-    return *GO;
-  if (auto *GA = dyn_cast<GlobalAlias>(&C))
-    return *GA->getAliasee();
-  auto *CE = cast<ConstantExpr>(&C);
-  assert(CE->getOpcode() == Instruction::BitCast ||
-         CE->getOpcode() == Instruction::GetElementPtr ||
-         CE->getOpcode() == Instruction::AddrSpaceCast);
-  if (CE->getOpcode() == Instruction::GetElementPtr)
-    assert(cast<GEPOperator>(CE)->hasAllZeroIndices());
-  return findReplacementForAliasUse(*CE->getOperand(0));
-}
-
-static void replaceAliasUseWith(Use &U, Value *New) {
-  GlobalObject &Replacement = findReplacementForAliasUse(*New);
-  assert(&cast<GlobalObject>(*U) != &Replacement &&
-         "replaceAliasUseWith cannot form an alias cycle");
-  U.set(&Replacement);
-}
-
 #ifndef NDEBUG
 static bool contains(SmallPtrSet<ConstantExpr *, 4> &Cache, ConstantExpr *Expr,
                      Constant *C) {
@@ -373,10 +352,6 @@ void Value::replaceAllUsesWith(Value *New) {
     // Must handle Constants specially, we cannot call replaceUsesOfWith on a
     // constant because they are uniqued.
     if (auto *C = dyn_cast<Constant>(U.getUser())) {
-      if (isa<GlobalAlias>(C)) {
-        replaceAliasUseWith(U, New);
-        continue;
-      }
       if (!isa<GlobalValue>(C)) {
         C->replaceUsesOfWithOnConstant(this, New, &U);
         continue;
diff --git a/lib/IR/Verifier.cpp b/lib/IR/Verifier.cpp
index bcc38c1ad5..1719cb2759 100644
--- a/lib/IR/Verifier.cpp
+++ b/lib/IR/Verifier.cpp
@@ -241,6 +241,9 @@ private:
   void visitGlobalValue(const GlobalValue &GV);
   void visitGlobalVariable(const GlobalVariable &GV);
   void visitGlobalAlias(const GlobalAlias &GA);
+  void visitAliaseeSubExpr(const GlobalAlias &A, const Constant &C);
+  void visitAliaseeSubExpr(SmallPtrSet<const GlobalAlias *, 4> &Visited,
+                           const GlobalAlias &A, const Constant &C);
   void visitNamedMDNode(const NamedMDNode &NMD);
   void visitMDNode(MDNode &MD, Function *F);
   void visitModuleIdents(const Module &M);
@@ -474,36 +477,52 @@ void Verifier::visitGlobalVariable(const GlobalVariable &GV) {
   visitGlobalValue(GV);
 }
 
+void Verifier::visitAliaseeSubExpr(const GlobalAlias &GA, const Constant &C) {
+  SmallPtrSet<const GlobalAlias*, 4> Visited;
+  Visited.insert(&GA);
+  visitAliaseeSubExpr(Visited, GA, C);
+}
+
+void Verifier::visitAliaseeSubExpr(SmallPtrSet<const GlobalAlias *, 4> &Visited,
+                                   const GlobalAlias &GA, const Constant &C) {
+  if (const auto *GV = dyn_cast<GlobalValue>(&C)) {
+    Assert1(!GV->isDeclaration(), "Alias must point to a definition", &GA);
+
+    if (const auto *GA2 = dyn_cast<GlobalAlias>(GV)) {
+      Assert1(Visited.insert(GA2), "Aliases cannot form a cycle", &GA);
+
+      Assert1(!GA2->mayBeOverridden(), "Alias cannot point to a weak alias",
+              &GA);
+    }
+  }
+
+  if (const auto *CE = dyn_cast<ConstantExpr>(&C))
+    VerifyConstantExprBitcastType(CE);
+
+  for (const Use &U : C.operands()) {
+    Value *V = &*U;
+    if (const auto *GA2 = dyn_cast<GlobalAlias>(V))
+      visitAliaseeSubExpr(Visited, GA, *GA2->getAliasee());
+    else if (const auto *C2 = dyn_cast<Constant>(V))
+      visitAliaseeSubExpr(Visited, GA, *C2);
+  }
+}
+
 void Verifier::visitGlobalAlias(const GlobalAlias &GA) {
   Assert1(!GA.getName().empty(),
           "Alias name cannot be empty!", &GA);
   Assert1(GlobalAlias::isValidLinkage(GA.getLinkage()),
           "Alias should have external or external weak linkage!", &GA);
-  Assert1(GA.getAliasee(),
-          "Aliasee cannot be NULL!", &GA);
-  Assert1(!GA.hasUnnamedAddr(), "Alias cannot have unnamed_addr!", &GA);
-
   const Constant *Aliasee = GA.getAliasee();
-  const GlobalValue *GV = dyn_cast<GlobalValue>(Aliasee);
-
-  if (!GV) {
-    const ConstantExpr *CE = dyn_cast<ConstantExpr>(Aliasee);
-    if (CE && (CE->getOpcode() == Instruction::BitCast ||
-               CE->getOpcode() == Instruction::AddrSpaceCast ||
-               CE->getOpcode() == Instruction::GetElementPtr))
-      GV = dyn_cast<GlobalValue>(CE->getOperand(0));
+  Assert1(Aliasee, "Aliasee cannot be NULL!", &GA);
+  Assert1(GA.getType() == Aliasee->getType(),
+          "Alias and aliasee types should match!", &GA);
+  Assert1(!GA.hasUnnamedAddr(), "Alias cannot have unnamed_addr!", &GA);
 
-    Assert1(GV, "Aliasee should be either GlobalValue, bitcast or "
-                "addrspacecast of GlobalValue",
-            &GA);
+  Assert1(isa<GlobalValue>(Aliasee) || isa<ConstantExpr>(Aliasee),
+          "Aliasee should be either GlobalValue or ConstantExpr", &GA);
 
-    VerifyConstantExprBitcastType(CE);
-  }
-  Assert1(!GV->isDeclaration(), "Alias must point to a definition", &GA);
-  if (const GlobalAlias *GAAliasee = dyn_cast<GlobalAlias>(GV)) {
-    Assert1(!GAAliasee->mayBeOverridden(), "Alias cannot point to a weak alias",
-            &GA);
-  }
+  visitAliaseeSubExpr(GA, *Aliasee);
 
   visitGlobalValue(GA);
 }
diff --git a/lib/LTO/LTOModule.cpp b/lib/LTO/LTOModule.cpp
index d117514265..f7f6a3c4b8 100644
--- a/lib/LTO/LTOModule.cpp
+++ b/lib/LTO/LTOModule.cpp
@@ -334,21 +334,22 @@ void LTOModule::addDefinedDataSymbol(const GlobalValue *v) {
   // from the ObjC data structures generated by the front end.
 
   // special case if this data blob is an ObjC class definition
-  if (v->getSection().compare(0, 15, "__OBJC,__class,") == 0) {
+  std::string Section = v->getSection();
+  if (Section.compare(0, 15, "__OBJC,__class,") == 0) {
     if (const GlobalVariable *gv = dyn_cast<GlobalVariable>(v)) {
       addObjCClass(gv);
     }
   }
 
   // special case if this data blob is an ObjC category definition
-  else if (v->getSection().compare(0, 18, "__OBJC,__category,") == 0) {
+  else if (Section.compare(0, 18, "__OBJC,__category,") == 0) {
     if (const GlobalVariable *gv = dyn_cast<GlobalVariable>(v)) {
       addObjCCategory(gv);
     }
   }
 
   // special case if this data blob is the list of referenced classes
-  else if (v->getSection().compare(0, 18, "__OBJC,__cls_refs,") == 0) {
+  else if (Section.compare(0, 18, "__OBJC,__cls_refs,") == 0) {
     if (const GlobalVariable *gv = dyn_cast<GlobalVariable>(v)) {
       addObjCClassRef(gv);
     }
diff --git a/lib/Linker/LinkModules.cpp b/lib/Linker/LinkModules.cpp
index 45f2d4e03a..ad8e01dc1b 100644
--- a/lib/Linker/LinkModules.cpp
+++ b/lib/Linker/LinkModules.cpp
@@ -389,8 +389,6 @@ namespace {
     /// actually need, but this allows us to reuse the ValueMapper code.
     ValueToValueMapTy ValueMap;
 
-    std::vector<std::pair<GlobalValue *, GlobalAlias *>> ReplaceWithAlias;
-
     struct AppendingVarInfo {
       GlobalVariable *NewGV;  // New aggregate global in dest module.
       Constant *DstInit;      // Old initializer from dest module.
@@ -723,7 +721,7 @@ bool ModuleLinker::linkAppendingVarProto(GlobalVariable *DstGV,
     return emitError(
         "Appending variables with different unnamed_addr need to be linked!");
 
-  if (DstGV->getSection() != SrcGV->getSection())
+  if (StringRef(DstGV->getSection()) != SrcGV->getSection())
     return emitError(
           "Appending variables with different section name need to be linked!");
 
@@ -929,8 +927,11 @@ bool ModuleLinker::linkAliasProto(GlobalAlias *SGA) {
   if (NewVisibility)
     NewDA->setVisibility(*NewVisibility);
 
-  if (DGV)
-    ReplaceWithAlias.push_back(std::make_pair(DGV, NewDA));
+  if (DGV) {
+    // Any uses of DGV need to change to NewDA, with cast.
+    DGV->replaceAllUsesWith(ConstantExpr::getBitCast(NewDA, DGV->getType()));
+    DGV->eraseFromParent();
+  }
 
   ValueMap[SGA] = NewDA;
   return false;
@@ -1016,19 +1017,6 @@ void ModuleLinker::linkFunctionBody(Function *Dst, Function *Src) {
 
 }
 
-static GlobalObject &getGlobalObjectInExpr(Constant &C) {
-  auto *GO = dyn_cast<GlobalObject>(&C);
-  if (GO)
-    return *GO;
-  auto *GA = dyn_cast<GlobalAlias>(&C);
-  if (GA)
-    return *GA->getAliasee();
-  auto &CE = cast<ConstantExpr>(C);
-  assert(CE.getOpcode() == Instruction::BitCast ||
-         CE.getOpcode() == Instruction::AddrSpaceCast);
-  return getGlobalObjectInExpr(*CE.getOperand(0));
-}
-
 /// linkAliasBodies - Insert all of the aliases in Src into the Dest module.
 void ModuleLinker::linkAliasBodies() {
   for (Module::alias_iterator I = SrcM->alias_begin(), E = SrcM->alias_end();
@@ -1039,25 +1027,9 @@ void ModuleLinker::linkAliasBodies() {
       GlobalAlias *DA = cast<GlobalAlias>(ValueMap[I]);
       Constant *Val =
           MapValue(Aliasee, ValueMap, RF_None, &TypeMap, &ValMaterializer);
-      DA->setAliasee(&getGlobalObjectInExpr(*Val));
+      DA->setAliasee(Val);
     }
   }
-
-  // Any uses of DGV need to change to NewDA, with cast.
-  for (auto &Pair : ReplaceWithAlias) {
-    GlobalValue *DGV = Pair.first;
-    GlobalAlias *NewDA = Pair.second;
-
-    for (auto *User : DGV->users()) {
-      if (auto *GA = dyn_cast<GlobalAlias>(User)) {
-        if (GA == NewDA)
-          report_fatal_error("Linking these modules creates an alias cycle.");
-      }
-    }
-
-    DGV->replaceAllUsesWith(ConstantExpr::getBitCast(NewDA, DGV->getType()));
-    DGV->eraseFromParent();
-  }
 }
 
 /// linkNamedMDNodes - Insert all of the named MDNodes in Src into the Dest
diff --git a/lib/Target/NVPTX/NVPTXAsmPrinter.cpp b/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
index 4ec575ff34..e6cbf64359 100644
--- a/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
+++ b/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
@@ -1356,7 +1356,7 @@ void NVPTXAsmPrinter::printModuleLevelGV(const GlobalVariable *GVar,
 
   // Skip meta data
   if (GVar->hasSection()) {
-    if (GVar->getSection() == "llvm.metadata")
+    if (GVar->getSection() == StringRef("llvm.metadata"))
       return;
   }
 
diff --git a/lib/Target/XCore/XCoreISelLowering.cpp b/lib/Target/XCore/XCoreISelLowering.cpp
index 9d78586495..e9db2a8fa4 100644
--- a/lib/Target/XCore/XCoreISelLowering.cpp
+++ b/lib/Target/XCore/XCoreISelLowering.cpp
@@ -273,18 +273,16 @@ SDValue XCoreTargetLowering::getGlobalAddressWrapper(SDValue GA,
                                                      SelectionDAG &DAG) const {
   // FIXME there is no actual debug info here
   SDLoc dl(GA);
-  const GlobalValue *UnderlyingGV = GV;
-  // If GV is an alias then use the aliasee to determine the wrapper type
-  if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(GV))
-    UnderlyingGV = GA->getAliasee();
-  if (const GlobalVariable *GVar = dyn_cast<GlobalVariable>(UnderlyingGV)) {
-    if ((GVar->isConstant() && GV->hasLocalLinkage()) ||
-        (GVar->hasSection() &&
-         StringRef(GVar->getSection()).startswith(".cp.")))
-      return DAG.getNode(XCoreISD::CPRelativeWrapper, dl, MVT::i32, GA);
-    return DAG.getNode(XCoreISD::DPRelativeWrapper, dl, MVT::i32, GA);
-  }
-  return DAG.getNode(XCoreISD::PCRelativeWrapper, dl, MVT::i32, GA);
+
+  if (GV->getType()->getElementType()->isFunctionTy())
+    return DAG.getNode(XCoreISD::PCRelativeWrapper, dl, MVT::i32, GA);
+
+  const auto *GVar = dyn_cast<GlobalVariable>(GV);
+  if ((GV->hasSection() && StringRef(GV->getSection()).startswith(".cp.")) ||
+      (GVar && GVar->isConstant() && GV->hasLocalLinkage()))
+    return DAG.getNode(XCoreISD::CPRelativeWrapper, dl, MVT::i32, GA);
+
+  return DAG.getNode(XCoreISD::DPRelativeWrapper, dl, MVT::i32, GA);
 }
 
 static bool IsSmallObject(const GlobalValue *GV, const XCoreTargetLowering &XTL) {
diff --git a/lib/Transforms/Utils/CloneModule.cpp b/lib/Transforms/Utils/CloneModule.cpp
index eb67db1f85..3f75b3e677 100644
--- a/lib/Transforms/Utils/CloneModule.cpp
+++ b/lib/Transforms/Utils/CloneModule.cpp
@@ -107,7 +107,7 @@ Module *llvm::CloneModule(const Module *M, ValueToValueMapTy &VMap) {
   for (Module::const_alias_iterator I = M->alias_begin(), E = M->alias_end();
        I != E; ++I) {
     GlobalAlias *GA = cast<GlobalAlias>(VMap[I]);
-    if (const GlobalObject *C = I->getAliasee())
+    if (const Constant *C = I->getAliasee())
       GA->setAliasee(cast<GlobalObject>(MapValue(C, VMap)));
   }