[CodeGen] Align rtti and vtable data

Previously the alignment on the newly created rtti/typeinfo data was largely
not set, meaning that DataLayout::getPreferredAlignment was free to overalign
it to 16 bytes. This causes unnecessary code bloat.

Differential Revision: https://reviews.llvm.org/D51416

llvm-svn: 342053

clang/lib/CodeGen/CGVTT.cpp

@@ -119,10 +119,10 @@ llvm::GlobalVariable *CodeGenVTables::GetAddrOfVTT(const CXXRecordDecl *RD) {
 
   llvm::ArrayType *ArrayType =
     llvm::ArrayType::get(CGM.Int8PtrTy, Builder.getVTTComponents().size());
+  unsigned Align = CGM.getDataLayout().getABITypeAlignment(CGM.Int8PtrTy);
 
-  llvm::GlobalVariable *GV =
-    CGM.CreateOrReplaceCXXRuntimeVariable(Name, ArrayType,
-                                          llvm::GlobalValue::ExternalLinkage);
+  llvm::GlobalVariable *GV = CGM.CreateOrReplaceCXXRuntimeVariable(
+      Name, ArrayType, llvm::GlobalValue::ExternalLinkage, Align);
   GV->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
   return GV;
 }

clang/lib/CodeGen/CGVTables.cpp

@@ -756,9 +756,11 @@ CodeGenVTables::GenerateConstructionVTable(const CXXRecordDecl *RD,
   if (Linkage == llvm::GlobalVariable::AvailableExternallyLinkage)
     Linkage = llvm::GlobalVariable::InternalLinkage;
 
+  unsigned Align = CGM.getDataLayout().getABITypeAlignment(VTType);
+
   // Create the variable that will hold the construction vtable.
   llvm::GlobalVariable *VTable =
-    CGM.CreateOrReplaceCXXRuntimeVariable(Name, VTType, Linkage);
+      CGM.CreateOrReplaceCXXRuntimeVariable(Name, VTType, Linkage, Align);
   CGM.setGVProperties(VTable, RD);
 
   // V-tables are always unnamed_addr.

clang/lib/CodeGen/CodeGenModule.cpp

@@ -3099,10 +3099,9 @@ CodeGenModule::GetAddrOfGlobal(GlobalDecl GD,
                               IsForDefinition);
 }
 
-llvm::GlobalVariable *
-CodeGenModule::CreateOrReplaceCXXRuntimeVariable(StringRef Name,
-                                      llvm::Type *Ty,
-                                      llvm::GlobalValue::LinkageTypes Linkage) {
+llvm::GlobalVariable *CodeGenModule::CreateOrReplaceCXXRuntimeVariable(
+    StringRef Name, llvm::Type *Ty, llvm::GlobalValue::LinkageTypes Linkage,
+    unsigned Alignment) {
   llvm::GlobalVariable *GV = getModule().getNamedGlobal(Name);
   llvm::GlobalVariable *OldGV = nullptr;
 
@@ -3138,6 +3137,8 @@ CodeGenModule::CreateOrReplaceCXXRuntimeVariable(StringRef Name,
       !GV->hasAvailableExternallyLinkage())
     GV->setComdat(TheModule.getOrInsertComdat(GV->getName()));
 
+  GV->setAlignment(Alignment);
+
   return GV;
 }
 

clang/lib/CodeGen/CodeGenModule.h

@@ -764,7 +764,8 @@ class CodeGenModule : public CodeGenTypeCache {
   /// bitcast to the new variable.
   llvm::GlobalVariable *
   CreateOrReplaceCXXRuntimeVariable(StringRef Name, llvm::Type *Ty,
-                                    llvm::GlobalValue::LinkageTypes Linkage);
+                                    llvm::GlobalValue::LinkageTypes Linkage,
+                                    unsigned Alignment);
 
   llvm::Function *
   CreateGlobalInitOrDestructFunction(llvm::FunctionType *ty, const Twine &name,

clang/lib/CodeGen/ItaniumCXXABI.cpp

@@ -1598,12 +1598,6 @@ void ItaniumCXXABI::emitVTableDefinitions(CodeGenVTables &CGVT,
   // Set the right visibility.
   CGM.setGVProperties(VTable, RD);
 
-  // Use pointer alignment for the vtable. Otherwise we would align them based
-  // on the size of the initializer which doesn't make sense as only single
-  // values are read.
-  unsigned PAlign = CGM.getTarget().getPointerAlign(0);
-  VTable->setAlignment(getContext().toCharUnitsFromBits(PAlign).getQuantity());
-
   // If this is the magic class __cxxabiv1::__fundamental_type_info,
   // we will emit the typeinfo for the fundamental types. This is the
   // same behaviour as GCC.
@@ -1703,8 +1697,14 @@ llvm::GlobalVariable *ItaniumCXXABI::getAddrOfVTable(const CXXRecordDecl *RD,
       CGM.getItaniumVTableContext().getVTableLayout(RD);
   llvm::Type *VTableType = CGM.getVTables().getVTableType(VTLayout);
 
+  // Use pointer alignment for the vtable. Otherwise we would align them based
+  // on the size of the initializer which doesn't make sense as only single
+  // values are read.
+  unsigned PAlign = CGM.getTarget().getPointerAlign(0);
+
   VTable = CGM.CreateOrReplaceCXXRuntimeVariable(
-      Name, VTableType, llvm::GlobalValue::ExternalLinkage);
+      Name, VTableType, llvm::GlobalValue::ExternalLinkage,
+      getContext().toCharUnitsFromBits(PAlign).getQuantity());
   VTable->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
 
   CGM.setGVProperties(VTable, RD);
@@ -2725,9 +2725,10 @@ llvm::GlobalVariable *ItaniumRTTIBuilder::GetAddrOfTypeName(
   // get the mangled name of the type.
   llvm::Constant *Init = llvm::ConstantDataArray::getString(VMContext,
                                                             Name.substr(4));
+  auto Align = CGM.getContext().getTypeAlignInChars(CGM.getContext().CharTy);
 
-  llvm::GlobalVariable *GV =
-    CGM.CreateOrReplaceCXXRuntimeVariable(Name, Init->getType(), Linkage);
+  llvm::GlobalVariable *GV = CGM.CreateOrReplaceCXXRuntimeVariable(
+      Name, Init->getType(), Linkage, Align.getQuantity());
 
   GV->setInitializer(Init);
 
@@ -3366,6 +3367,10 @@ llvm::Constant *ItaniumRTTIBuilder::BuildTypeInfo(
   if (CGM.supportsCOMDAT() && GV->isWeakForLinker())
     GV->setComdat(M.getOrInsertComdat(GV->getName()));
 
+  CharUnits Align =
+      CGM.getContext().toCharUnitsFromBits(CGM.getTarget().getPointerAlign(0));
+  GV->setAlignment(Align.getQuantity());
+
   // The Itanium ABI specifies that type_info objects must be globally
   // unique, with one exception: if the type is an incomplete class
   // type or a (possibly indirect) pointer to one.  That exception

clang/lib/CodeGen/MicrosoftCXXABI.cpp

@@ -2024,8 +2024,10 @@ MicrosoftCXXABI::getAddrOfVBTable(const VPtrInfo &VBT, const CXXRecordDecl *RD,
 
   assert(!CGM.getModule().getNamedGlobal(Name) &&
          "vbtable with this name already exists: mangling bug?");
-  llvm::GlobalVariable *GV =
-      CGM.CreateOrReplaceCXXRuntimeVariable(Name, VBTableType, Linkage);
+  CharUnits Alignment =
+      CGM.getContext().getTypeAlignInChars(CGM.getContext().IntTy);
+  llvm::GlobalVariable *GV = CGM.CreateOrReplaceCXXRuntimeVariable(
+      Name, VBTableType, Linkage, Alignment.getQuantity());
   GV->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
 
   if (RD->hasAttr<DLLImportAttr>())

clang/test/CodeGenCXX/microsoft-abi-vbtables.cpp

@@ -19,7 +19,7 @@ D d; // Force vbtable emission.
 // C: vbptr C
 //    int c
 
-// CHECK-DAG: @"??_8D@Test1@@7B01@@" = linkonce_odr unnamed_addr constant [4 x i32] [i32 0, i32 8, i32 12, i32 20]
+// CHECK-DAG: @"??_8D@Test1@@7B01@@" = linkonce_odr unnamed_addr constant [4 x i32] [i32 0, i32 8, i32 12, i32 20], comdat, align 4
 // CHECK-DAG: @"??_8D@Test1@@7BB@1@@" = {{.*}} [2 x i32] [i32 0, i32 -4]
 // CHECK-DAG: @"??_8D@Test1@@7BC@1@@" = {{.*}} [2 x i32] [i32 0, i32 -12]
 // CHECK-DAG: @"??_8C@Test1@@7B@" = {{.*}} [2 x i32] [i32 0, i32 8]

clang/test/CodeGenCXX/vtable-align.cpp

@@ -10,5 +10,8 @@ struct A {
 void A::f() {}
 
 // CHECK-32: @_ZTV1A = unnamed_addr constant { [5 x i8*] } { [5 x i8*] [i8* null, i8* bitcast ({ i8*, i8* }* @_ZTI1A to i8*), i8* bitcast (void (%struct.A*)* @_ZN1A1fEv to i8*), i8* bitcast (void (%struct.A*)* @_ZN1A1gEv to i8*), i8* bitcast (void (%struct.A*)* @_ZN1A1hEv to i8*)] }, align 4
-
+// CHECK-32: @_ZTS1A = constant [3 x i8] c"1A\00", align 1
+// CHECK-32: @_ZTI1A = constant { i8*, i8* } { i8* bitcast (i8** getelementptr inbounds (i8*, i8** @_ZTVN10__cxxabiv117__class_type_infoE, i32 2) to i8*), i8* getelementptr inbounds ([3 x i8], [3 x i8]* @_ZTS1A, i32 0, i32 0) }, align 4
 // CHECK-64: @_ZTV1A = unnamed_addr constant { [5 x i8*] } { [5 x i8*] [i8* null, i8* bitcast ({ i8*, i8* }* @_ZTI1A to i8*), i8* bitcast (void (%struct.A*)* @_ZN1A1fEv to i8*), i8* bitcast (void (%struct.A*)* @_ZN1A1gEv to i8*), i8* bitcast (void (%struct.A*)* @_ZN1A1hEv to i8*)] }, align 8
+// CHECK-64: @_ZTS1A = constant [3 x i8] c"1A\00", align 1
+// CHECK-64: @_ZTI1A = constant { i8*, i8* } { i8* bitcast (i8** getelementptr inbounds (i8*, i8** @_ZTVN10__cxxabiv117__class_type_infoE, i64 2) to i8*), i8* getelementptr inbounds ([3 x i8], [3 x i8]* @_ZTS1A, i32 0, i32 0) }, align 8

clang/test/CodeGenCXX/vtable-linkage.cpp

@@ -98,10 +98,10 @@ void use_F() {
 
 // C has no key function, so its vtable should have weak_odr linkage
 // and hidden visibility (rdar://problem/7523229).
-// CHECK-DAG: @_ZTV1C = linkonce_odr unnamed_addr constant {{.*}}, comdat,
-// CHECK-DAG: @_ZTS1C = linkonce_odr constant {{.*}}, comdat{{$}}
-// CHECK-DAG: @_ZTI1C = linkonce_odr constant {{.*}}, comdat{{$}}
-// CHECK-DAG: @_ZTT1C = linkonce_odr unnamed_addr constant {{.*}}, comdat{{$}}
+// CHECK-DAG: @_ZTV1C = linkonce_odr unnamed_addr constant {{.*}}, comdat, align 8{{$}}
+// CHECK-DAG: @_ZTS1C = linkonce_odr constant {{.*}}, comdat, align 1{{$}}
+// CHECK-DAG: @_ZTI1C = linkonce_odr constant {{.*}}, comdat, align 8{{$}}
+// CHECK-DAG: @_ZTT1C = linkonce_odr unnamed_addr constant {{.*}}, comdat, align 8{{$}}
 
 // D has a key function that is defined in this translation unit so its vtable is
 // defined in the translation unit.
@@ -120,27 +120,27 @@ void use_F() {
 // defined in this translation unit, so its vtable should have
 // weak_odr linkage.
 // CHECK-DAG: @_ZTV1EIsE = weak_odr unnamed_addr constant {{.*}}, comdat,
-// CHECK-DAG: @_ZTS1EIsE = weak_odr constant {{.*}}, comdat{{$}}
-// CHECK-DAG: @_ZTI1EIsE = weak_odr constant {{.*}}, comdat{{$}}
+// CHECK-DAG: @_ZTS1EIsE = weak_odr constant {{.*}}, comdat, align 1{{$}}
+// CHECK-DAG: @_ZTI1EIsE = weak_odr constant {{.*}}, comdat, align 8{{$}}
 
 // F<short> is an explicit template instantiation without a key
 // function, so its vtable should have weak_odr linkage
 // CHECK-DAG: @_ZTV1FIsE = weak_odr unnamed_addr constant {{.*}}, comdat,
-// CHECK-DAG: @_ZTS1FIsE = weak_odr constant {{.*}}, comdat{{$}}
-// CHECK-DAG: @_ZTI1FIsE = weak_odr constant {{.*}}, comdat{{$}}
+// CHECK-DAG: @_ZTS1FIsE = weak_odr constant {{.*}}, comdat, align 1{{$}}
+// CHECK-DAG: @_ZTI1FIsE = weak_odr constant {{.*}}, comdat, align 8{{$}}
 
 // E<long> is an implicit template instantiation with a key function
 // defined in this translation unit, so its vtable should have
 // linkonce_odr linkage.
 // CHECK-DAG: @_ZTV1EIlE = linkonce_odr unnamed_addr constant {{.*}}, comdat,
-// CHECK-DAG: @_ZTS1EIlE = linkonce_odr constant {{.*}}, comdat{{$}}
-// CHECK-DAG: @_ZTI1EIlE = linkonce_odr constant {{.*}}, comdat{{$}}
+// CHECK-DAG: @_ZTS1EIlE = linkonce_odr constant {{.*}}, comdat, align 1{{$}}
+// CHECK-DAG: @_ZTI1EIlE = linkonce_odr constant {{.*}}, comdat, align 8{{$}}
 
 // F<long> is an implicit template instantiation with no key function,
 // so its vtable should have linkonce_odr linkage.
 // CHECK-DAG: @_ZTV1FIlE = linkonce_odr unnamed_addr constant {{.*}}, comdat,
-// CHECK-DAG: @_ZTS1FIlE = linkonce_odr constant {{.*}}, comdat{{$}}
-// CHECK-DAG: @_ZTI1FIlE = linkonce_odr constant {{.*}}, comdat{{$}}
+// CHECK-DAG: @_ZTS1FIlE = linkonce_odr constant {{.*}}, comdat, align 1{{$}}
+// CHECK-DAG: @_ZTI1FIlE = linkonce_odr constant {{.*}}, comdat, align 8{{$}}
 
 // F<int> is an explicit template instantiation declaration without a
 // key function, so its vtable should have external linkage.
@@ -171,8 +171,8 @@ void use_F() {
 // F<char> is an explicit specialization without a key function, so
 // its vtable should have linkonce_odr linkage.
 // CHECK-DAG: @_ZTV1FIcE = linkonce_odr unnamed_addr constant {{.*}}, comdat,
-// CHECK-DAG: @_ZTS1FIcE = linkonce_odr constant {{.*}}, comdat{{$}}
-// CHECK-DAG: @_ZTI1FIcE = linkonce_odr constant {{.*}}, comdat{{$}}
+// CHECK-DAG: @_ZTS1FIcE = linkonce_odr constant {{.*}}, comdat, align 1{{$}}
+// CHECK-DAG: @_ZTI1FIcE = linkonce_odr constant {{.*}}, comdat, align 8{{$}}
 
 // CHECK-DAG: @_ZTV1GIiE = linkonce_odr unnamed_addr constant {{.*}}, comdat,
 template <typename T>