[lldb][test] Add tests for alignof on class with overlapping bases

[Michael137]

Follow-up to #96932

Adds XFAILed test where LLDB incorrectly infers the alignment of a derived class whose bases are overlapping due to [[no_unique_address]]. Specifically, the InferAlignment code-path of the ItaniumRecordLayoutBuilder assumes that overlapping base offsets imply a packed structure and thus sets alignment to 1. See discussion in #93809.

Also adds test where LLDB correctly infers an alignment of 1 when a packed base class is overlapping with other bases.

Lastly, there were a couple of alignof inconsistencies which I encapsulated in an XFAIL-ed packed-alignof.cpp.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Michael Buch (Michael137)

Changes

Follow-up to #96932

Adds XFAILed test where LLDB incorrectly infers the alignment of a derived class whose bases are overlapping due to [[no_unique_address]]. Specifically, the InferAlignment code-path of the ItaniumRecordLayoutBuilder assumes that overlapping base offsets imply a packed structure and thus sets alignment to 1. See discussion in #93809.

Also adds test where LLDB correctly infers an alignment of 1 when a packed base class is overlapping with other bases.

Lastly, there were a couple of alignof inconsistencies which I encapsulated in an XFAIL-ed packed-alignof.cpp.

---

Full diff: https://github.com/llvm/llvm-project/pull/97068.diff

3 Files Affected:

• (added) lldb/test/Shell/SymbolFile/DWARF/no_unique_address-base-alignment.cpp (+30)
• (added) lldb/test/Shell/SymbolFile/DWARF/packed-alignof.cpp (+41)
• (modified) lldb/test/Shell/SymbolFile/DWARF/packed.cpp (+14)

diff --git a/lldb/test/Shell/SymbolFile/DWARF/no_unique_address-base-alignment.cpp b/lldb/test/Shell/SymbolFile/DWARF/no_unique_address-base-alignment.cpp
new file mode 100644
index 0000000000000..634d461e6ff19
--- /dev/null
+++ b/lldb/test/Shell/SymbolFile/DWARF/no_unique_address-base-alignment.cpp
@@ -0,0 +1,30 @@
+// XFAIL: *
+
+// RUN: %clangxx_host -gdwarf -o %t %s
+// RUN: %lldb %t \
+// RUN:   -o "expr alignof(OverlappingDerived)" \
+// RUN:   -o "expr sizeof(OverlappingDerived)" \
+// RUN:   -o exit | FileCheck %s
+
+// CHECK:      (lldb) expr alignof(OverlappingDerived)
+// CHECK-NEXT: ${{.*}} = 4
+// CHECK:      (lldb) expr sizeof(OverlappingDerived)
+// CHECK-NEXT: ${{.*}} = 4
+
+struct Empty {};
+
+struct OverlappingBase {
+  [[no_unique_address]] Empty e;
+};
+static_assert(sizeof(OverlappingBase) == 1);
+static_assert(alignof(OverlappingBase) == 1);
+
+struct Base {
+  int mem;
+};
+
+struct OverlappingDerived : Base, OverlappingBase {};
+static_assert(alignof(OverlappingDerived) == 4);
+static_assert(sizeof(OverlappingDerived) == 4);
+
+int main() { OverlappingDerived d; }
diff --git a/lldb/test/Shell/SymbolFile/DWARF/packed-alignof.cpp b/lldb/test/Shell/SymbolFile/DWARF/packed-alignof.cpp
new file mode 100644
index 0000000000000..a15e88f0b65df
--- /dev/null
+++ b/lldb/test/Shell/SymbolFile/DWARF/packed-alignof.cpp
@@ -0,0 +1,41 @@
+// XFAIL: *
+//
+// RUN: %clangxx_host -gdwarf -o %t %s
+// RUN: %lldb %t \
+// RUN:   -o "expr alignof(base)" \
+// RUN:   -o "expr alignof(packed_base)" \
+// RUN:   -o "expr alignof(derived)" \
+// RUN:   -o "expr sizeof(derived)" \
+// RUN:   -o exit | FileCheck %s
+
+// CHECK:      (lldb) expr alignof(base)
+// CHECK-NEXT: ${{.*}} = 4
+// CHECK:      (lldb) expr alignof(packed_base)
+// CHECK-NEXT: ${{.*}} = 1
+// CHECK:      (lldb) expr alignof(derived)
+// CHECK-NEXT: ${{.*}} = 2
+// CHECK:      (lldb) expr sizeof(derived)
+// CHECK-NEXT: ${{.*}} = 16
+
+struct __attribute__((packed)) packed {
+  int x;
+  char y;
+  int z;
+} g_packed_struct;
+
+// LLDB incorrectly calculates alignof(base)
+struct foo {};
+struct base : foo { int x; };
+static_assert(alignof(base) == 4);
+
+// LLDB incorrectly calculates alignof(packed_base)
+struct __attribute__((packed)) packed_base { int x; };
+static_assert(alignof(packed_base) == 1);
+
+struct derived : packed, packed_base {
+  short s;
+} g_derived;
+static_assert(alignof(derived) == 2);
+static_assert(sizeof(derived) == 16);
+
+int main() {}
diff --git a/lldb/test/Shell/SymbolFile/DWARF/packed.cpp b/lldb/test/Shell/SymbolFile/DWARF/packed.cpp
index 640a2e0454c92..135808f46d7ea 100644
--- a/lldb/test/Shell/SymbolFile/DWARF/packed.cpp
+++ b/lldb/test/Shell/SymbolFile/DWARF/packed.cpp
@@ -4,6 +4,8 @@
 // RUN:   -o "expr sizeof(packed)" \
 // RUN:   -o "expr alignof(packed_and_aligned)" \
 // RUN:   -o "expr sizeof(packed_and_aligned)" \
+// RUN:   -o "expr alignof(derived)" \
+// RUN:   -o "expr sizeof(derived)" \
 // RUN:   -o exit | FileCheck %s
 
 // CHECK:      (lldb) expr alignof(packed)
@@ -16,6 +18,11 @@
 // CHECK:      (lldb) expr sizeof(packed_and_aligned)
 // CHECK-NEXT: ${{.*}} = 16
 
+// CHECK:      (lldb) expr alignof(derived)
+// CHECK-NEXT: ${{.*}} = 1
+// CHECK:      (lldb) expr sizeof(derived)
+// CHECK-NEXT: ${{.*}} = 13
+
 struct __attribute__((packed)) packed {
   int x;
   char y;
@@ -32,4 +39,11 @@ struct __attribute__((packed, aligned(16))) packed_and_aligned {
 static_assert(alignof(packed_and_aligned) == 16);
 static_assert(sizeof(packed_and_aligned) == 16);
 
+struct __attribute__((packed)) packed_base { int x; };
+static_assert(alignof(packed_base) == 1);
+
+struct derived : packed, packed_base {} g_derived;
+static_assert(alignof(derived) == 1);
+static_assert(sizeof(derived) == 13);
+
 int main() {}

[dwblaikie]

Might be nice to put the checks next to the static_asserts?

[Michael137]

good point, done

[Michael137]

Only test failure on buildkite is TestConcurrentVFork.py, which is unrelated. Merging