PR37275 packed attribute should not apply to base classes
Clang incorrectly applied the packed attribute to base classes. Per GCC's
documentation and as can be observed from its behavior, packed only applies to
members, not base classes.
This change is conditioned behind -fclang-abi-compat so that an ABI break can
be avoided by users if desired.
Differential Revision: https://reviews.llvm.org/D46218
llvm-svn: 331136
diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index 390c8e0..47e696a 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -967,7 +967,7 @@
void ItaniumRecordLayoutBuilder::EnsureVTablePointerAlignment(
CharUnits UnpackedBaseAlign) {
- CharUnits BaseAlign = (Packed) ? CharUnits::One() : UnpackedBaseAlign;
+ CharUnits BaseAlign = Packed ? CharUnits::One() : UnpackedBaseAlign;
// The maximum field alignment overrides base align.
if (!MaxFieldAlignment.isZero()) {
@@ -1175,9 +1175,14 @@
HasExternalLayout = External.getExternalVBaseOffset(Base->Class, Offset);
}
+ // Clang <= 6 incorrectly applied the 'packed' attribute to base classes.
+ // Per GCC's documentation, it only applies to non-static data members.
CharUnits UnpackedBaseAlign = Layout.getNonVirtualAlignment();
- CharUnits BaseAlign = (Packed) ? CharUnits::One() : UnpackedBaseAlign;
-
+ CharUnits BaseAlign = (Packed && Context.getLangOpts().getClangABICompat() <=
+ LangOptions::ClangABI::Ver6)
+ ? CharUnits::One()
+ : UnpackedBaseAlign;
+
// If we have an empty base class, try to place it at offset 0.
if (Base->Class->isEmpty() &&
(!HasExternalLayout || Offset == CharUnits::Zero()) &&