3 files changed, 46 insertions, 42 deletions

diff --git a/clang/lib/CodeGen/CGCXX.cpp b/clang/lib/CodeGen/CGCXX.cpp
index 08b74a3c30d..0a73550c7a2 100644
--- a/clang/lib/CodeGen/CGCXX.cpp
+++ b/clang/lib/CodeGen/CGCXX.cpp
@@ -138,12 +138,12 @@ bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
   // which case the caller is responsible for ensuring the soundness
   // of these semantics.
   auto *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
-  llvm::Constant *Aliasee = Ref;
-  if (Ref->getType() != AliasType)
-    Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType);
+  auto *Aliasee = dyn_cast<llvm::GlobalObject>(Ref);
+  if (!Aliasee)
+    Aliasee = cast<llvm::GlobalAlias>(Ref)->getAliasee();
 
   // Instead of creating as alias to a linkonce_odr, replace all of the uses
-  // of the aliassee.
+  // of the aliasee.
   if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) &&
      (TargetLinkage != llvm::GlobalValue::AvailableExternallyLinkage ||
       !TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) {
@@ -152,7 +152,10 @@ bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
     // members with attribute "AlwaysInline" and expect no reference to
     // be generated. It is desirable to reenable this optimisation after
     // corresponding LLVM changes.
-    Replacements[MangledName] = Aliasee;
+    llvm::Constant *Replacement = Aliasee;
+    if (Aliasee->getType() != AliasType)
+      Replacement = llvm::ConstantExpr::getBitCast(Aliasee, AliasType);
+    Replacements[MangledName] = Replacement;
     return false;
   }
 
@@ -160,7 +163,7 @@ bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
     /// If we don't have a definition for the destructor yet, don't
     /// emit.  We can't emit aliases to declarations; that's just not
     /// how aliases work.
-    if (Ref->isDeclaration())
+    if (Aliasee->isDeclaration())
       return true;
   }
 
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 769b01c825e..fa9ddf02221 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -238,46 +238,18 @@ void CodeGenModule::checkAliases() {
     llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
     auto *Alias = cast<llvm::GlobalAlias>(Entry);
     llvm::GlobalValue *GV = Alias->getAliasedGlobal();
-    if (!GV) {
-      Error = true;
-      Diags.Report(AA->getLocation(), diag::err_cyclic_alias);
-    } else if (GV->isDeclaration()) {
+    if (GV->isDeclaration()) {
       Error = true;
       Diags.Report(AA->getLocation(), diag::err_alias_to_undefined);
     }
 
-    llvm::Constant *Aliasee = Alias->getAliasee();
-    llvm::GlobalValue *AliaseeGV;
-    if (auto CE = dyn_cast<llvm::ConstantExpr>(Aliasee)) {
-      assert((CE->getOpcode() == llvm::Instruction::BitCast ||
-              CE->getOpcode() == llvm::Instruction::AddrSpaceCast) &&
-             "Unsupported aliasee");
-      AliaseeGV = cast<llvm::GlobalValue>(CE->getOperand(0));
-    } else {
-      AliaseeGV = cast<llvm::GlobalValue>(Aliasee);
-    }
-
+    llvm::GlobalObject *Aliasee = Alias->getAliasee();
     if (const SectionAttr *SA = D->getAttr<SectionAttr>()) {
       StringRef AliasSection = SA->getName();
-      if (AliasSection != AliaseeGV->getSection())
+      if (AliasSection != Aliasee->getSection())
         Diags.Report(SA->getLocation(), diag::warn_alias_with_section)
             << AliasSection;
     }
-
-    // We have to handle alias to weak aliases in here. LLVM itself disallows
-    // this since the object semantics would not match the IL one. For
-    // compatibility with gcc we implement it by just pointing the alias
-    // to its aliasee's aliasee. We also warn, since the user is probably
-    // expecting the link to be weak.
-    if (auto GA = dyn_cast<llvm::GlobalAlias>(AliaseeGV)) {
-      if (GA->mayBeOverridden()) {
-        Diags.Report(AA->getLocation(), diag::warn_alias_to_weak_alias)
-          << GA->getAliasedGlobal()->getName() << GA->getName();
-        Aliasee = llvm::ConstantExpr::getPointerBitCastOrAddrSpaceCast(
-            GA->getAliasee(), Alias->getType());
-        Alias->setAliasee(Aliasee);
-      }
-    }
   }
   if (!Error)
     return;
@@ -2246,6 +2218,29 @@ void CodeGenModule::EmitGlobalFunctionDefinition(GlobalDecl GD,
     AddGlobalAnnotations(D, Fn);
 }
 
+static llvm::GlobalObject &getGlobalObjectInExpr(DiagnosticsEngine &Diags,
+                                                 const AliasAttr *AA,
+                                                 llvm::Constant *C) {
+  if (auto *GO = dyn_cast<llvm::GlobalObject>(C))
+    return *GO;
+
+  auto *GA = dyn_cast<llvm::GlobalAlias>(C);
+  if (GA) {
+    if (GA->mayBeOverridden()) {
+      Diags.Report(AA->getLocation(), diag::warn_alias_to_weak_alias)
+          << GA->getAliasee()->getName() << GA->getName();
+    }
+
+    return *GA->getAliasee();
+  }
+
+  auto *CE = cast<llvm::ConstantExpr>(C);
+  assert(CE->getOpcode() == llvm::Instruction::BitCast ||
+         CE->getOpcode() == llvm::Instruction::GetElementPtr ||
+         CE->getOpcode() == llvm::Instruction::AddrSpaceCast);
+  return *cast<llvm::GlobalObject>(CE->getOperand(0));
+}
+
 void CodeGenModule::EmitAliasDefinition(GlobalDecl GD) {
   const auto *D = cast<ValueDecl>(GD.getDecl());
   const AliasAttr *AA = D->getAttr<AliasAttr>();
@@ -2276,9 +2271,15 @@ void CodeGenModule::EmitAliasDefinition(GlobalDecl GD) {
   // Create the new alias itself, but don't set a name yet.
   auto *GA = new llvm::GlobalAlias(
       cast<llvm::PointerType>(Aliasee->getType())->getElementType(),
-      llvm::Function::ExternalLinkage, "", Aliasee, &getModule());
+      llvm::Function::ExternalLinkage, "",
+      &getGlobalObjectInExpr(Diags, AA, Aliasee), &getModule());
 
   if (Entry) {
+    if (GA->getAliasee() == Entry) {
+      Diags.Report(AA->getLocation(), diag::err_cyclic_alias);
+      return;
+    }
+
     assert(Entry->isDeclaration());
 
     // If there is a declaration in the module, then we had an extern followed
@@ -3196,9 +3197,9 @@ void CodeGenModule::EmitStaticExternCAliases() {
     IdentifierInfo *Name = I->first;
     llvm::GlobalValue *Val = I->second;
     if (Val && !getModule().getNamedValue(Name->getName()))
-      addUsedGlobal(new llvm::GlobalAlias(Val->getType()->getElementType(),
-                                          Val->getLinkage(), Name->getName(),
-                                          Val, &getModule()));
+      addUsedGlobal(new llvm::GlobalAlias(
+          Val->getType()->getElementType(), Val->getLinkage(), Name->getName(),
+          cast<llvm::GlobalObject>(Val), &getModule()));
   }
 }
 
diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index 0ed23ed371d..9e5849328b9 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -5213,7 +5213,7 @@ void MSP430TargetCodeGenInfo::SetTargetAttributes(const Decl *D,
       unsigned Num = attr->getNumber() / 2;
       new llvm::GlobalAlias(GV->getType()->getElementType(),
                             llvm::Function::ExternalLinkage,
-                            "__isr_" + Twine(Num), GV, &M.getModule());
+                            "__isr_" + Twine(Num), F, &M.getModule());
     }
   }
 }