[PATCH] D73418: [WPD] Emit vcall_visibility metadata for MicrosoftCXXABI

[Teresa Johnson via Phabricator via cfe-commits]

tejohnson created this revision.
tejohnson added a reviewer: evgeny777.
Herald added a subscriber: Prazek.
Herald added a project: clang.

The MicrosoftCXXABI uses a separate mechanism for emitting vtable
type metadata, and thus didn't pick up the change from D71907 <https://reviews.llvm.org/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 <https://reviews.llvm.org/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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73418

Files:
  clang/lib/CodeGen/MicrosoftCXXABI.cpp
  clang/test/CodeGenCXX/vcall-visibility-metadata.cpp


Index: clang/test/CodeGenCXX/vcall-visibility-metadata.cpp
===================================================================
--- clang/test/CodeGenCXX/vcall-visibility-metadata.cpp
+++ clang/test/CodeGenCXX/vcall-visibility-metadata.cpp
@@ -1,5 +1,6 @@
 // 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
@@ -87,6 +88,15 @@
   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}
Index: clang/lib/CodeGen/MicrosoftCXXABI.cpp
===================================================================
--- clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -1621,6 +1621,15 @@
   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.


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