[WPD] Emit vcall_visibility metadata for MicrosoftCXXABI

[tejohnson]

Summary

The MicrosoftCXXABI uses a separate mechanism for emitting vtable
type metadata, and thus didn't pick up the change from D71907
to emit the vcall_visibility metadata under -fwhole-program-vtables.

I believe this is the cause of a Windows bot failure when I committed
follow on change D71913 that required a revert. The failure occurred
in a CFI test that was expecting to not abort because it expected a
devirtualization to occur, and without the necessary vcall_visibility
metadata we would not get devirtualization.

Note in the equivalent code in CodeGenModule::EmitVTableTypeMetadata
(used by the ItaniumCXXABI), we also emit the vcall_visibility metadata
when Virtual Function Elimination is enabled. Since I am not as familiar
with the details of that optimization, I have marked that as a TODO and
am only inserting under -fwhole-program-vtables.

[tejohnson]

I fixed the test matching as I found that the names generated for the anonymous namespace comdats depend on the module identifier in some way. I changed the matching to look at the struct type embedded in the initializer, which is also more intuitive. I also moved the new MS checks to be alongside the companion Itanium checks. And I added comments noting that MSVC gets DSO (hidden) visibility by default.

[tejohnson]

Improve test

[evgeny777]

LGTM

[ayermolo]

@tejohnson I was wondering where does this @anon.{{.*}} gets set, or in general where can I find more information about it.

When I step through the code in emitVTableTypeMetadata, it's still.

@0 = private unnamed_addr constant { [2 x i8*] } { [2 x i8*] [i8* bitcast (%rtti.CompleteObjectLocator* @"??_R4A@?A0x3E47408C@@6B@" to i8*), i8* bitcast (i32 (%"struct.(anonymous namespace)::A"*)* @"?f@A@?A0x3E47408C@@UEAAHXZ" to i8*)] }, comdat($"??_7A@?A0x3E47408C@@6B@")

Thanks

[tejohnson]

In D73418#2461943, @ayermolo wrote:

@tejohnson I was wondering where does this @anon.{{.*}} gets set, or in general where can I find more information about it.

When I step through the code in emitVTableTypeMetadata, it's still.

@0 = private unnamed_addr constant { [2 x i8*] } { [2 x i8*] [i8* bitcast (%rtti.CompleteObjectLocator* @"??_R4A@?A0x3E47408C@@6B@" to i8*), i8* bitcast (i32 (%"struct.(anonymous namespace)::A"*)* @"?f@A@?A0x3E47408C@@UEAAHXZ" to i8*)] }, comdat($"??_7A@?A0x3E47408C@@6B@")

Thanks

It would be later, in LLVM, see nameUnamedGlobals in llvm/lib/Transforms/Utils/NameAnonGlobals.cpp. It is called towards the end the compile when generating bitcode for LTO, as we need everything named in order to generate summary information.

clang/lib/CodeGen/MicrosoftCXXABI.cpp

 }
 
 void MicrosoftCXXABI::emitVTableTypeMetadata(const VPtrInfo &Info,
                                              const CXXRecordDecl *RD,
                                              llvm::GlobalVariable *VTable) {
   if (!CGM.getCodeGenOpts().LTOUnit)
     return;
 
+  // TODO: Should VirtualFunctionElimination also be supported here?
+  // See similar handling in CodeGenModule::EmitVTableTypeMetadata.
+  if (CGM.getCodeGenOpts().WholeProgramVTables) {
+    llvm::GlobalObject::VCallVisibility TypeVis =
+        CGM.GetVCallVisibilityLevel(RD);
+    if (TypeVis != llvm::GlobalObject::VCallVisibilityPublic)
+      VTable->setVCallVisibilityMetadata(TypeVis);
+  }
+
   // The location of the first virtual function pointer in the virtual table,
   // aka the "address point" on Itanium. This is at offset 0 if RTTI is
   // disabled, or sizeof(void*) if RTTI is enabled.
   CharUnits AddressPoint =
       getContext().getLangOpts().RTTIData
           ? getContext().toCharUnitsFromBits(
                 getContext().getTargetInfo().getPointerWidth(0))
           : CharUnits::Zero();

clang/test/CodeGenCXX/vcall-visibility-metadata.cpp

 // RUN: %clang_cc1 -flto -flto-unit -triple x86_64-unknown-linux -emit-llvm -fvirtual-function-elimination -fwhole-program-vtables -o - %s | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-VFE
 // RUN: %clang_cc1 -flto -flto-unit -triple x86_64-unknown-linux -emit-llvm -fwhole-program-vtables -o - %s | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-NOVFE
+// RUN: %clang_cc1 -flto -flto-unit -triple x86_64-pc-windows-msvc -emit-llvm -fwhole-program-vtables -o - %s | FileCheck %s --check-prefix=CHECK-MS --check-prefix=CHECK-NOVFE
 
 // Check that in ThinLTO we also get vcall_visibility summary entries in the bitcode
 // RUN: %clang_cc1 -flto=thin -flto-unit -triple x86_64-unknown-linux -emit-llvm-bc -fwhole-program-vtables -o - %s | llvm-dis -o - | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-NOVFE --check-prefix=CHECK-SUMMARY
 
 
 // Anonymous namespace.
 namespace {
 // CHECK: @_ZTVN12_GLOBAL__N_11AE = {{.*}} !vcall_visibility [[VIS_TU:![0-9]+]]
struct __attribute__((visibility("hidden"))) G : B {
   G() {}
   virtual int f() { return 1; }
 };
 }
 void *construct_G() {
   return new G();
 }
 
+// CHECK-MS: comdat($"??_7A@?A0xE24FC2D5@@6B@"){{.*}} !vcall_visibility [[VIS_TU:![0-9]+]]
+// CHECK-MS: comdat($"??_7B@@6B@"){{.*}} !vcall_visibility [[VIS_DSO:![0-9]+]]
+// CHECK-MS: comdat($"??_7C@@6B@"){{.*}} !vcall_visibility [[VIS_DSO]]
+// CHECK-MS: comdat($"??_7E@@6B@"){{.*}} !vcall_visibility [[VIS_DSO]]
+// CHECK-MS: comdat($"??_7F@?A0xE24FC2D5@@6B@"){{.*}} !vcall_visibility [[VIS_DSO]]
+// CHECK-MS: comdat($"??_7G@?A0xE24FC2D5@@6B@"){{.*}} !vcall_visibility [[VIS_DSO]]
+// CHECK-MS-DAG: [[VIS_TU]] = !{i64 2}
+// CHECK-MS-DAG: [[VIS_DSO]] = !{i64 1}
+
 // CHECK-DAG: [[VIS_DSO]] = !{i64 1}
 // CHECK-DAG: [[VIS_TU]] = !{i64 2}
 // CHECK-VFE-DAG: !{i32 1, !"Virtual Function Elim", i32 1}
 // CHECK-NOVFE-DAG: !{i32 1, !"Virtual Function Elim", i32 0}
 
 // CHECK-SUMMARY-DAG: gv: (name: "_ZTV1B", {{.*}} vcall_visibility: 1
 // CHECK-SUMMARY-DAG: gv: (name: "_ZTVN12_GLOBAL__N_11FE", {{.*}} vcall_visibility: 0
 // CHECK-SUMMARY-DAG: gv: (name: "_ZTV1D", {{.*}} vcall_visibility: 0
 // CHECK-SUMMARY-DAG: gv: (name: "_ZTV1C", {{.*}} vcall_visibility: 0
 // CHECK-SUMMARY-DAG: gv: (name: "_ZTV1E", {{.*}} vcall_visibility: 0
 // CHECK-SUMMARY-DAG: gv: (name: "_ZTVN12_GLOBAL__N_11AE", {{.*}} vcall_visibility: 2
 // CHECK-SUMMARY-DAG: gv: (name: "_ZTVN12_GLOBAL__N_11GE", {{.*}} vcall_visibility: 1