Revert "Prevent alias from pointing to weak aliases."

This reverts commit r204781.

I will follow up to with msan folks to see what is what they
were trying to do with aliases to weak aliases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204784 91177308-0d34-0410-b5e6-96231b3b80d8

docs/LangRef.rst

@@ -681,10 +681,6 @@ the aliasee.
 
 The aliasee must be a definition.
 
-Aliases are not allowed to point to aliases with linkages that can be
-overridden. Since they are only a second name, the possibility of the
-intermediate alias being overridden cannot be represented in an object file.
-
 .. _namedmetadatastructure:
 
 Named Metadata

include/llvm/IR/GlobalAlias.h

@@ -64,15 +64,23 @@ public:
   Constant *getAliasee() {
     return getOperand(0);
   }
-
-  /// This method tries to ultimately resolve the alias by going through the
-  /// aliasing chain and trying to find the very last global. Returns NULL if a
-  /// cycle was found.
+  /// getAliasedGlobal() - Aliasee can be either global or bitcast of
+  /// global. This method retrives the global for both aliasee flavours.
   GlobalValue *getAliasedGlobal();
   const GlobalValue *getAliasedGlobal() const {
     return const_cast<GlobalAlias *>(this)->getAliasedGlobal();
   }
 
+  /// resolveAliasedGlobal() - This method tries to ultimately resolve the alias
+  /// by going through the aliasing chain and trying to find the very last
+  /// global. Returns NULL if a cycle was found. If stopOnWeak is false, then
+  /// the whole chain aliasing chain is traversed, otherwise - only strong
+  /// aliases.
+  GlobalValue *resolveAliasedGlobal(bool stopOnWeak = true);
+  const GlobalValue *resolveAliasedGlobal(bool stopOnWeak = true) const {
+    return const_cast<GlobalAlias *>(this)->resolveAliasedGlobal(stopOnWeak);
+  }
+
   static bool isValidLinkage(LinkageTypes L) {
     return isExternalLinkage(L) || isLocalLinkage(L) ||
       isWeakLinkage(L) || isLinkOnceLinkage(L);

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -1172,7 +1172,7 @@ SDValue SelectionDAG::getGlobalAddress(const GlobalValue *GV, SDLoc DL,
   if (!GVar) {
     // If GV is an alias then use the aliasee for determining thread-localness.
     if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(GV))
-      GVar = dyn_cast_or_null<GlobalVariable>(GA->getAliasedGlobal());
+      GVar = dyn_cast_or_null<GlobalVariable>(GA->resolveAliasedGlobal(false));
   }
 
   unsigned Opc;

lib/ExecutionEngine/JIT/JITEmitter.cpp

@@ -688,7 +688,7 @@ void *JITEmitter::getPointerToGlobal(GlobalValue *V, void *Reference,
     return TheJIT->getOrEmitGlobalVariable(GV);
 
   if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V))
-    return TheJIT->getPointerToGlobal(GA->getAliasedGlobal());
+    return TheJIT->getPointerToGlobal(GA->resolveAliasedGlobal(false));
 
   // If we have already compiled the function, return a pointer to its body.
   Function *F = cast<Function>(V);

lib/IR/Globals.cpp

@@ -236,10 +236,10 @@ void GlobalAlias::setAliasee(Constant *Aliasee) {
   setOperand(0, Aliasee);
 }
 
-static GlobalValue *getAliaseeGV(GlobalAlias *GA) {
-  Constant *C = GA->getAliasee();
-  assert(C && "Must alias something");
-
+GlobalValue *GlobalAlias::getAliasedGlobal() {
+  Constant *C = getAliasee();
+  if (C == 0) return 0;
+  
   if (GlobalValue *GV = dyn_cast<GlobalValue>(C))
     return GV;
 
@@ -248,23 +248,30 @@ static GlobalValue *getAliaseeGV(GlobalAlias *GA) {
           CE->getOpcode() == Instruction::AddrSpaceCast ||
           CE->getOpcode() == Instruction::GetElementPtr) &&
          "Unsupported aliasee");
-
+  
   return cast<GlobalValue>(CE->getOperand(0));
 }
 
-GlobalValue *GlobalAlias::getAliasedGlobal() {
+GlobalValue *GlobalAlias::resolveAliasedGlobal(bool stopOnWeak) {
   SmallPtrSet<GlobalValue*, 3> Visited;
 
-  GlobalAlias *GA = this;
+  // Check if we need to stop early.
+  if (stopOnWeak && mayBeOverridden())
+    return this;
+
+  GlobalValue *GV = getAliasedGlobal();
+  Visited.insert(GV);
+
+  // Iterate over aliasing chain, stopping on weak alias if necessary.
+  while (GlobalAlias *GA = dyn_cast<GlobalAlias>(GV)) {
+    if (stopOnWeak && GA->mayBeOverridden())
+      break;
+
+    GV = GA->getAliasedGlobal();
 
-  for (;;) {
-    GlobalValue *GV = getAliaseeGV(GA);
     if (!Visited.insert(GV))
       return 0;
-
-    // Iterate over aliasing chain.
-    GA = dyn_cast<GlobalAlias>(GV);
-    if (!GA)
-      return GV;
   }
+
+  return GV;
 }

lib/IR/Verifier.cpp

@@ -502,14 +502,10 @@ void Verifier::visitGlobalAlias(const GlobalAlias &GA) {
     }
   }
   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);
-  }
 
-  const GlobalValue *AG = GA.getAliasedGlobal();
-  Assert1(AG, "Aliasing chain should end with function or global variable",
-          &GA);
+  const GlobalValue* Resolved = GA.resolveAliasedGlobal(/*stopOnWeak*/ false);
+  Assert1(Resolved,
+          "Aliasing chain should end with function or global variable", &GA);
 
   visitGlobalValue(GA);
 }

lib/Target/PowerPC/PPCAsmPrinter.cpp

@@ -381,8 +381,8 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
     if (MO.isGlobal()) {
       const GlobalValue *GValue = MO.getGlobal();
       const GlobalAlias *GAlias = dyn_cast<GlobalAlias>(GValue);
-      const GlobalValue *RealGValue =
-          GAlias ? GAlias->getAliasedGlobal() : GValue;
+      const GlobalValue *RealGValue = GAlias ?
+        GAlias->resolveAliasedGlobal(false) : GValue;
       MOSymbol = getSymbol(RealGValue);
       const GlobalVariable *GVar = dyn_cast<GlobalVariable>(RealGValue);
       IsExternal = GVar && !GVar->hasInitializer();
@@ -428,8 +428,8 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
     else if (MO.isGlobal()) {
       const GlobalValue *GValue = MO.getGlobal();
       const GlobalAlias *GAlias = dyn_cast<GlobalAlias>(GValue);
-      const GlobalValue *RealGValue =
-          GAlias ? GAlias->getAliasedGlobal() : GValue;
+      const GlobalValue *RealGValue = GAlias ?
+        GAlias->resolveAliasedGlobal(false) : GValue;
       MOSymbol = getSymbol(RealGValue);
       const GlobalVariable *GVar = dyn_cast<GlobalVariable>(RealGValue);
     
@@ -463,8 +463,8 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
     if (MO.isGlobal()) {
       const GlobalValue *GValue = MO.getGlobal();
       const GlobalAlias *GAlias = dyn_cast<GlobalAlias>(GValue);
-      const GlobalValue *RealGValue =
-          GAlias ? GAlias->getAliasedGlobal() : GValue;
+      const GlobalValue *RealGValue = GAlias ?
+        GAlias->resolveAliasedGlobal(false) : GValue;
       MOSymbol = getSymbol(RealGValue);
       const GlobalVariable *GVar = dyn_cast<GlobalVariable>(RealGValue);
       IsExternal = GVar && !GVar->hasInitializer();

lib/Target/PowerPC/PPCFastISel.cpp

@@ -1863,7 +1863,7 @@ unsigned PPCFastISel::PPCMaterializeGV(const GlobalValue *GV, MVT VT) {
   if (!GVar) {
     // If GV is an alias, use the aliasee for determining thread-locality.
     if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(GV))
-      GVar = dyn_cast_or_null<GlobalVariable>(GA->getAliasedGlobal());
+      GVar = dyn_cast_or_null<GlobalVariable>(GA->resolveAliasedGlobal(false));
   }
 
   // FIXME: We don't yet handle the complexity of TLS.

lib/Target/PowerPC/PPCISelDAGToDAG.cpp

@@ -1413,8 +1413,8 @@ SDNode *PPCDAGToDAGISel::Select(SDNode *N) {
     if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(GA)) {
       const GlobalValue *GValue = G->getGlobal();
       const GlobalAlias *GAlias = dyn_cast<GlobalAlias>(GValue);
-      const GlobalValue *RealGValue =
-          GAlias ? GAlias->getAliasedGlobal() : GValue;
+      const GlobalValue *RealGValue = GAlias ?
+        GAlias->resolveAliasedGlobal(false) : GValue;
       const GlobalVariable *GVar = dyn_cast<GlobalVariable>(RealGValue);
       assert((GVar || isa<Function>(RealGValue)) &&
              "Unexpected global value subclass!");

lib/Target/TargetMachine.cpp

@@ -129,7 +129,7 @@ TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
   // If GV is an alias then use the aliasee for determining
   // thread-localness.
   if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(GV))
-    GV = GA->getAliasedGlobal();
+    GV = GA->resolveAliasedGlobal(false);
   const GlobalVariable *Var = cast<GlobalVariable>(GV);
 
   bool isLocal = Var->hasLocalLinkage();

lib/Target/X86/X86FastISel.cpp

@@ -363,7 +363,7 @@ bool X86FastISel::handleConstantAddresses(const Value *V, X86AddressMode &AM) {
     // it works...).
     if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(GV))
       if (const GlobalVariable *GVar =
-              dyn_cast_or_null<GlobalVariable>(GA->getAliasedGlobal()))
+            dyn_cast_or_null<GlobalVariable>(GA->resolveAliasedGlobal(false)))
         if (GVar->isThreadLocal())
           return false;
 

lib/Target/X86/X86ISelLowering.cpp

@@ -8509,7 +8509,7 @@ X86TargetLowering::LowerGlobalTLSAddress(SDValue Op, SelectionDAG &DAG) const {
     // If GV is an alias then use the aliasee for determining
     // thread-localness.
     if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(GV))
-      GV = GA->getAliasedGlobal();
+      GV = GA->resolveAliasedGlobal(false);
     SDLoc dl(GA);
     SDValue Chain = DAG.getEntryNode();
 

lib/Target/XCore/XCoreISelLowering.cpp

@@ -277,7 +277,7 @@ getGlobalAddressWrapper(SDValue GA, const GlobalValue *GV,
   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->getAliasedGlobal();
+    UnderlyingGV = GA->resolveAliasedGlobal();
   if (const GlobalVariable *GVar = dyn_cast<GlobalVariable>(UnderlyingGV)) {
     if (  ( GVar->isConstant() &&
             UnderlyingGV->isLocalLinkage(GV->getLinkage()) )

lib/Transforms/Instrumentation/DataFlowSanitizer.cpp

@@ -554,7 +554,8 @@ bool DataFlowSanitizer::runOnModule(Module &M) {
     ++i;
     // Don't stop on weak.  We assume people aren't playing games with the
     // instrumentedness of overridden weak aliases.
-    if (Function *F = dyn_cast<Function>(GA->getAliasedGlobal())) {
+    if (Function *F = dyn_cast<Function>(
+            GA->resolveAliasedGlobal(/*stopOnWeak=*/false))) {
       bool GAInst = isInstrumented(GA), FInst = isInstrumented(F);
       if (GAInst && FInst) {
         addGlobalNamePrefix(GA);

test/CodeGen/X86/dllexport-x86_64.ll

@@ -65,7 +65,7 @@ define weak_odr dllexport void @weak1() {
 @alias2 = dllexport alias void()* @f1
 
 ; CHECK: .globl alias3
-; CHECK: alias3 = notExported
+; CHECK: alias3 = alias
 @alias3 = dllexport alias void()* @alias
 
 ; CHECK: .weak weak_alias

test/CodeGen/X86/dllexport.ll

@@ -80,7 +80,7 @@ define weak_odr dllexport void @weak1() {
 @alias2 = dllexport alias void()* @f1
 
 ; CHECK: .globl _alias3
-; CHECK: _alias3 = _notExported
+; CHECK: _alias3 = _alias
 @alias3 = dllexport alias void()* @alias
 
 ; CHECK: .weak _weak_alias

test/Feature/aliases.ll

@@ -14,7 +14,7 @@
 define i32 @foo_f() {
   ret i32 0
 }
-@bar_f = alias weak_odr %FunTy* @foo_f
+@bar_f = alias weak %FunTy* @foo_f
 @bar_ff = alias i32()* @bar_f
 
 @bar_i = alias internal i32* @bar

test/Transforms/GlobalOpt/alias-resolve.ll

@@ -1,17 +1,14 @@
 ; RUN: opt < %s -globalopt -S | FileCheck %s
 
 @foo1 = alias void ()* @foo2
-; CHECK: @foo1 = alias void ()* @bar2
+; CHECK: @foo1 = alias void ()* @foo2
 
-@foo2 = alias void()* @bar1
-; CHECK: @foo2 = alias void ()* @bar2
+@foo2 = alias weak void()* @bar1
+; CHECK: @foo2 = alias weak void ()* @bar2
 
 @bar1  = alias void ()* @bar2
 ; CHECK: @bar1 = alias void ()* @bar2
 
-@weak1 = alias weak void ()* @bar2
-; CHECK: @weak1 = alias weak void ()* @bar2
-
 define void @bar2() {
   ret void
 }
@@ -20,16 +17,14 @@ define void @bar2() {
 define void @baz() {
 entry:
          call void @foo1()
-; CHECK: call void @bar2()
+; CHECK: call void @foo2()
 
          call void @foo2()
-; CHECK: call void @bar2()
+; CHECK: call void @foo2()
 
          call void @bar1()
 ; CHECK: call void @bar2()
 
-         call void @weak1()
-; CHECK: call void @weak1()
          ret void
 }