CodeGen: Mark functions used in vtables as unnamed_addr.

[pcc]

Summary

This marks virtual function declarations, as well as runtime library functions
cxa_pure_virtual, cxa_deleted_virtual and _purecall, as unnamed_addr. This
will allow us to correctly form relative references to them from vtables in
the relative vtable ABI.

[rjmccall]

The underscore check seems over-broad; we support a lot of language dialects and runtimes besides the Itanium C++ runtime. This would be both more conservative and more convincing if it were constrained to the functions that we expect to put in v-tables.

[pcc]

Restrict to functions referenced in virtual tables

[pcc]

Done (this also affects _purecall in the MS ABI; I don't think this change should break anything there, but someone working on that might want to comment). Since this patch is now specific to virtual tables anyway, I've incorporated another relevant change, which is to mark virtual function declarations as unnamed_addr.

[rjmccall]

I see, they weren't being set on declarations, just definitions. Yes, this seems reasonable.

[rnk]

In D18071#373687, @pcc wrote:

Done (this also affects _purecall in the MS ABI; I don't think this change should break anything there, but someone working on that might want to comment). Since this patch is now specific to virtual tables anyway, I've incorporated another relevant change, which is to mark virtual function declarations as unnamed_addr.

That shouldn't matter. Virtual member functions are wrapped with a thunk, so comparisons won't actually involve pointers to __purecall.

[rjmccall]

Member function comparisons of virtual functions aren't required to work anyway. Itanium just happens to implement them in a way that kindof gets it right (for simple cases).

cfe/trunk/lib/CodeGen/CGVTables.cpp

case VTableComponent::CK_DeletingDtorPointer: {
 
       if (cast<CXXMethodDecl>(GD.getDecl())->isPure()) {
         // We have a pure virtual member function.
         if (!PureVirtualFn) {
           llvm::FunctionType *Ty = 
             llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
           StringRef PureCallName = CGM.getCXXABI().GetPureVirtualCallName();
           PureVirtualFn = CGM.CreateRuntimeFunction(Ty, PureCallName);
+          if (auto *F = dyn_cast<llvm::Function>(PureVirtualFn))
+            F->setUnnamedAddr(true);
           PureVirtualFn = llvm::ConstantExpr::getBitCast(PureVirtualFn,
                                                          CGM.Int8PtrTy);
         }
         Init = PureVirtualFn;
       } else if (cast<CXXMethodDecl>(GD.getDecl())->isDeleted()) {
         if (!DeletedVirtualFn) {
           llvm::FunctionType *Ty =
             llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
           StringRef DeletedCallName =
             CGM.getCXXABI().GetDeletedVirtualCallName();
           DeletedVirtualFn = CGM.CreateRuntimeFunction(Ty, DeletedCallName);
+          if (auto *F = dyn_cast<llvm::Function>(DeletedVirtualFn))
+            F->setUnnamedAddr(true);
           DeletedVirtualFn = llvm::ConstantExpr::getBitCast(DeletedVirtualFn,
                                                          CGM.Int8PtrTy);
         }
         Init = DeletedVirtualFn;
       } else {
         // Check if we should use a thunk.
         if (NextVTableThunkIndex < NumVTableThunks &&
             VTableThunks[NextVTableThunkIndex].first == I) {

cfe/trunk/lib/CodeGen/CodeGenModule.cpp

if (D->hasAttr<OptimizeNoneAttr>()) {
     assert(!F->hasFnAttribute(llvm::Attribute::AlwaysInline) &&
            "OptimizeNone and AlwaysInline on same function!");
 
     // Attribute 'inlinehint' has no effect on 'optnone' functions.
     // Explicitly remove it from the set of function attributes.
     F->removeFnAttr(llvm::Attribute::InlineHint);
   }
 
-  if (isa<CXXConstructorDecl>(D) || isa<CXXDestructorDecl>(D))
-    F->setUnnamedAddr(true);
-  else if (const auto *MD = dyn_cast<CXXMethodDecl>(D))
-    if (MD->isVirtual())
-      F->setUnnamedAddr(true);
-
   unsigned alignment = D->getMaxAlignment() / Context.getCharWidth();
   if (alignment)
     F->setAlignment(alignment);
 
   // Some C++ ABIs require 2-byte alignment for member functions, in order to
   // reserve a bit for differentiating between virtual and non-virtual member
   // functions. If the current target's C++ ABI requires this and this is a
   // member function, set its alignment accordingly.
if (const SectionAttr *SA = FD->getAttr<SectionAttr>())
     F->setSection(SA->getName());
 
   // A replaceable global allocation function does not act like a builtin by
   // default, only if it is invoked by a new-expression or delete-expression.
   if (FD->isReplaceableGlobalAllocationFunction())
     F->addAttribute(llvm::AttributeSet::FunctionIndex,
                     llvm::Attribute::NoBuiltin);
 
+  if (isa<CXXConstructorDecl>(FD) || isa<CXXDestructorDecl>(FD))
+    F->setUnnamedAddr(true);
+  else if (const auto *MD = dyn_cast<CXXMethodDecl>(FD))
+    if (MD->isVirtual())
+      F->setUnnamedAddr(true);
+
   CreateFunctionBitSetEntry(FD, F);
 }
 
 void CodeGenModule::addUsedGlobal(llvm::GlobalValue *GV) {
   assert(!GV->isDeclaration() &&
          "Only globals with definition can force usage.");
   LLVMUsed.emplace_back(GV);
 }

cfe/trunk/test/CodeGenCXX/virtual-function-attrs.cpp

+// RUN: %clang_cc1 %s -triple %itanium_abi_triple -std=c++11 -emit-llvm -o - | FileCheck %s
+
+class A {
+  virtual void f();
+  virtual void g();
+  virtual ~A();
+};
+
+void A::f() {}
+
+// CHECK: define void @_ZN1A1fEv({{.*}}) unnamed_addr
+// CHECK: declare void @_ZN1A1gEv({{.*}}) unnamed_addr
+// CHECK: declare void @_ZN1AD1Ev({{.*}}) unnamed_addr
+// CHECK: declare void @_ZN1AD0Ev({{.*}}) unnamed_addr

cfe/trunk/test/CodeGenCXX/vtt-layout.cpp

 }
 
 // CHECK: @_ZTTN5Test11BE = unnamed_addr constant [1 x i8*] [i8* bitcast (i8** getelementptr inbounds ([4 x i8*], [4 x i8*]* @_ZTVN5Test11BE, i64 0, i64 3) to i8*)]
 // CHECK: @_ZTVN5Test51AE = unnamed_addr constant [4 x i8*] [i8* null, i8* bitcast ({ i8*, i8* }* @_ZTIN5Test51AE to i8*), i8* bitcast (void ()* @__cxa_pure_virtual to i8*), i8* bitcast (void (%"struct.Test5::A"*)* @_ZN5Test51A6anchorEv to i8*)]
 // CHECK: @_ZTVN5Test61AE = unnamed_addr constant [4 x i8*] [i8* null, i8* bitcast ({ i8*, i8* }* @_ZTIN5Test61AE to i8*), i8* bitcast (void ()* @__cxa_deleted_virtual to i8*), i8* bitcast (void (%"struct.Test6::A"*)* @_ZN5Test61A6anchorEv to i8*)]
 // CHECK: @_ZTTN5Test21CE = linkonce_odr unnamed_addr constant [2 x i8*] [i8* bitcast (i8** getelementptr inbounds ([5 x i8*], [5 x i8*]* @_ZTVN5Test21CE, i64 0, i64 4) to i8*), i8* bitcast (i8** getelementptr inbounds ([5 x i8*], [5 x i8*]* @_ZTVN5Test21CE, i64 0, i64 4) to i8*)] 
 // CHECK: @_ZTTN5Test31DE = linkonce_odr unnamed_addr constant [13 x i8*] [i8* bitcast (i8** getelementptr inbounds ([19 x i8*], [19 x i8*]* @_ZTVN5Test31DE, i64 0, i64 5) to i8*), i8* bitcast (i8** getelementptr inbounds ([7 x i8*], [7 x i8*]* @_ZTCN5Test31DE0_NS_2C1E, i64 0, i64 3) to i8*), i8* bitcast (i8** getelementptr inbounds ([7 x i8*], [7 x i8*]* @_ZTCN5Test31DE0_NS_2C1E, i64 0, i64 6) to i8*), i8* bitcast (i8** getelementptr inbounds ([14 x i8*], [14 x i8*]* @_ZTCN5Test31DE16_NS_2C2E, i64 0, i64 6) to i8*), i8* bitcast (i8** getelementptr inbounds ([14 x i8*], [14 x i8*]* @_ZTCN5Test31DE16_NS_2C2E, i64 0, i64 6) to i8*), i8* bitcast (i8** getelementptr inbounds ([14 x i8*], [14 x i8*]* @_ZTCN5Test31DE16_NS_2C2E, i64 0, i64 10) to i8*), i8* bitcast (i8** getelementptr inbounds ([14 x i8*], [14 x i8*]* @_ZTCN5Test31DE16_NS_2C2E, i64 0, i64 13) to i8*), i8* bitcast (i8** getelementptr inbounds ([19 x i8*], [19 x i8*]* @_ZTVN5Test31DE, i64 0, i64 15) to i8*), i8* bitcast (i8** getelementptr inbounds ([19 x i8*], [19 x i8*]* @_ZTVN5Test31DE, i64 0, i64 11) to i8*), i8* bitcast (i8** getelementptr inbounds ([19 x i8*], [19 x i8*]* @_ZTVN5Test31DE, i64 0, i64 11) to i8*), i8* bitcast (i8** getelementptr inbounds ([19 x i8*], [19 x i8*]* @_ZTVN5Test31DE, i64 1, i64 0) to i8*), i8* bitcast (i8** getelementptr inbounds ([7 x i8*], [7 x i8*]* @_ZTCN5Test31DE64_NS_2V2E, i64 0, i64 3) to i8*), i8* bitcast (i8** getelementptr inbounds ([7 x i8*], [7 x i8*]* @_ZTCN5Test31DE64_NS_2V2E, i64 0, i64 6) to i8*)] 
 // CHECK: @_ZTTN5Test41DE = linkonce_odr unnamed_addr constant [19 x i8*] [i8* bitcast (i8** getelementptr inbounds ([25 x i8*], [25 x i8*]* @_ZTVN5Test41DE, i64 0, i64 6) to i8*), i8* bitcast (i8** getelementptr inbounds ([11 x i8*], [11 x i8*]* @_ZTCN5Test41DE0_NS_2C1E, i64 0, i64 4) to i8*), i8* bitcast (i8** getelementptr inbounds ([11 x i8*], [11 x i8*]* @_ZTCN5Test41DE0_NS_2C1E, i64 0, i64 7) to i8*), i8* bitcast (i8** getelementptr inbounds ([11 x i8*], [11 x i8*]* @_ZTCN5Test41DE0_NS_2C1E, i64 0, i64 10) to i8*), i8* bitcast (i8** getelementptr inbounds ([19 x i8*], [19 x i8*]* @_ZTCN5Test41DE16_NS_2C2E, i64 0, i64 7) to i8*), i8* bitcast (i8** getelementptr inbounds ([19 x i8*], [19 x i8*]* @_ZTCN5Test41DE16_NS_2C2E, i64 0, i64 7) to i8*), i8* bitcast (i8** getelementptr inbounds ([19 x i8*], [19 x i8*]* @_ZTCN5Test41DE16_NS_2C2E, i64 0, i64 12) to i8*), i8* bitcast (i8** getelementptr inbounds ([19 x i8*], [19 x i8*]* @_ZTCN5Test41DE16_NS_2C2E, i64 0, i64 15) to i8*), i8* bitcast (i8** getelementptr inbounds ([19 x i8*], [19 x i8*]* @_ZTCN5Test41DE16_NS_2C2E, i64 0, i64 18) to i8*), i8* bitcast (i8** getelementptr inbounds ([25 x i8*], [25 x i8*]* @_ZTVN5Test41DE, i64 0, i64 17) to i8*), i8* bitcast (i8** getelementptr inbounds ([25 x i8*], [25 x i8*]* @_ZTVN5Test41DE, i64 0, i64 20) to i8*), i8* bitcast (i8** getelementptr inbounds ([25 x i8*], [25 x i8*]* @_ZTVN5Test41DE, i64 0, i64 13) to i8*), i8* bitcast (i8** getelementptr inbounds ([25 x i8*], [25 x i8*]* @_ZTVN5Test41DE, i64 0, i64 13) to i8*), i8* bitcast (i8** getelementptr inbounds ([25 x i8*], [25 x i8*]* @_ZTVN5Test41DE, i64 1, i64 0) to i8*), i8* bitcast (i8** getelementptr inbounds ([7 x i8*], [7 x i8*]* @_ZTCN5Test41DE40_NS_2V1E, i64 0, i64 3) to i8*), i8* bitcast (i8** getelementptr inbounds ([7 x i8*], [7 x i8*]* @_ZTCN5Test41DE40_NS_2V1E, i64 0, i64 6) to i8*), i8* bitcast (i8** getelementptr inbounds ([11 x i8*], [11 x i8*]* @_ZTCN5Test41DE72_NS_2V2E, i64 0, i64 4) to i8*), i8* bitcast (i8** getelementptr inbounds ([11 x i8*], [11 x i8*]* @_ZTCN5Test41DE72_NS_2V2E, i64 0, i64 7) to i8*), i8* bitcast (i8** getelementptr inbounds ([11 x i8*], [11 x i8*]* @_ZTCN5Test41DE72_NS_2V2E, i64 0, i64 10) to i8*)] 
+// CHECK: declare void @__cxa_pure_virtual() unnamed_addr
+// CHECK: declare void @__cxa_deleted_virtual() unnamed_addr