Fix to msvc::no_unique_address causing assert when used with __declspec(empty_bases)

[amykhuang]

no_unique_address makes it possible for a class to be empty and have non-zero virtual size, so just remove this assert.

Bug: #74442

[llvmbot]

@llvm/pr-subscribers-clang

Author: Amy Huang (amykhuang)

Changes

no_unique_address makes it possible for a class to be empty and have non-zero virtual size, so just remove this assert.

Bug: #74442

---

Full diff: https://github.com/llvm/llvm-project/pull/74776.diff

2 Files Affected:

• (modified) clang/lib/AST/RecordLayoutBuilder.cpp (+2-2)
• (modified) clang/test/Layout/ms-x86-declspec-empty_bases.cpp (+60)

diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index f1f2275da44dc..73b248ffe5899 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -2936,8 +2936,8 @@ void MicrosoftRecordLayoutBuilder::layoutNonVirtualBase(
   }
 
   if (!FoundBase) {
-    if (MDCUsesEBO && BaseDecl->isEmpty()) {
-      assert(BaseLayout.getNonVirtualSize() == CharUnits::Zero());
+    if (MDCUsesEBO && BaseDecl->isEmpty() &&
+        (BaseLayout.getNonVirtualSize() == CharUnits::Zero())) {
       BaseOffset = CharUnits::Zero();
     } else {
       // Otherwise, lay the base out at the end of the MDC.
diff --git a/clang/test/Layout/ms-x86-declspec-empty_bases.cpp b/clang/test/Layout/ms-x86-declspec-empty_bases.cpp
index cc13a980cb5db..4738ce5720f75 100644
--- a/clang/test/Layout/ms-x86-declspec-empty_bases.cpp
+++ b/clang/test/Layout/ms-x86-declspec-empty_bases.cpp
@@ -264,3 +264,63 @@ int _ = sizeof(G);
 // CHECK-NEXT:            | [sizeof=12, align=4,
 // CHECK-NEXT:            |  nvsize=12, nvalign=4]
 }
+
+namespace test5 {
+
+struct A {
+  int a;
+};
+struct B {
+  int b;
+};
+struct C {};
+struct __declspec(align(16)) D {};
+struct E {
+  [[msvc::no_unique_address]] C c;
+};
+struct __declspec(empty_bases) X : A, D, B, C, E {
+};
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test5::A
+// CHECK-NEXT:          0 |   int a
+// CHECK-NEXT:            | [sizeof=4, align=4,
+// CHECK-NEXT:            |  nvsize=4, nvalign=4]
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test5::D (empty)
+// CHECK-NEXT:            | [sizeof=16, align=16,
+// CHECK-NEXT:            |  nvsize=0, nvalign=16]
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test5::B
+// CHECK-NEXT:          0 |   int b
+// CHECK-NEXT:            | [sizeof=4, align=4,
+// CHECK-NEXT:            |  nvsize=4, nvalign=4]
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test5::C (empty)
+// CHECK-NEXT:            | [sizeof=1, align=1,
+// CHECK-NEXT:            |  nvsize=0, nvalign=1]
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test5::E (empty)
+// CHECK-NEXT:          0 |   struct test5::C c (empty)
+// CHECK-NEXT:            | [sizeof=1, align=1,
+// CHECK-NEXT:            |  nvsize=1, nvalign=1]
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test5::X
+// CHECK-NEXT:          0 |   struct test5::A (base)
+// CHECK-NEXT:          0 |     int a
+// CHECK-NEXT:          0 |   struct test5::D (base) (empty)
+// CHECK-NEXT:          0 |   struct test5::C (base) (empty)
+// CHECK-NEXT:          4 |   struct test5::B (base)
+// CHECK-NEXT:          4 |     int b
+// CHECK-NEXT:          8 |   struct test5::E (base) (empty)
+// CHECK-NEXT:          8 |     struct test5::C c (empty)
+// CHECK-NEXT:            | [sizeof=16, align=16,
+// CHECK-NEXT:            |  nvsize=16, nvalign=16]
+
+int _ = sizeof(X);
+}

[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff c6805ea44af3bfd57e6b46f2d65ec6b0d0d6c64a c3dedfd535f037fb54a8e04640f9332e655a9a7d -- clang/lib/AST/RecordLayoutBuilder.cpp clang/test/Layout/ms-x86-declspec-empty_bases.cpp

View the diff from clang-format here.

diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index 73b248ffe5..4af8770db2 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -2267,9 +2267,12 @@ ItaniumRecordLayoutBuilder::updateExternalFieldOffset(const FieldDecl *Field,
 /// \returns diagnostic %select index.
 static unsigned getPaddingDiagFromTagKind(TagTypeKind Tag) {
   switch (Tag) {
-  case TTK_Struct: return 0;
-  case TTK_Interface: return 1;
-  case TTK_Class: return 2;
+  case TTK_Struct:
+    return 0;
+  case TTK_Interface:
+    return 1;
+  case TTK_Class:
+    return 2;
   default: llvm_unreachable("Invalid tag kind for field padding diagnostic!");
   }
 }
@@ -2300,15 +2303,13 @@ void ItaniumRecordLayoutBuilder::CheckFieldPadding(
     if (D->getIdentifier())
       Diag(D->getLocation(), diag::warn_padded_struct_field)
           << getPaddingDiagFromTagKind(D->getParent()->getTagKind())
-          << Context.getTypeDeclType(D->getParent())
-          << PadSize
+          << Context.getTypeDeclType(D->getParent()) << PadSize
           << (InBits ? 1 : 0) // (byte|bit)
           << D->getIdentifier();
     else
       Diag(D->getLocation(), diag::warn_padded_struct_anon_field)
           << getPaddingDiagFromTagKind(D->getParent()->getTagKind())
-          << Context.getTypeDeclType(D->getParent())
-          << PadSize
+          << Context.getTypeDeclType(D->getParent()) << PadSize
           << (InBits ? 1 : 0); // (byte|bit)
  }
  if (isPacked && Offset != UnpackedOffset) {

[zmodem]

lgtm, thanks for fixing!