P0840R2: support for [[no_unique_address]] attribute
Summary:
Add support for the C++2a [[no_unique_address]] attribute for targets using the Itanium C++ ABI.
This depends on D63371.
Reviewers: rjmccall, aaron.ballman
Subscribers: dschuff, aheejin, cfe-commits
Tags: #clang
Differential Revision: https://reviews.llvm.org/D63451
llvm-svn: 363976
diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index 3b1c5bf..a41b420 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -1846,15 +1846,32 @@
return LV;
}
+AggValueSlot::Overlap_t
+CodeGenFunction::overlapForFieldInit(const FieldDecl *FD) {
+ if (!FD->hasAttr<NoUniqueAddressAttr>() || !FD->getType()->isRecordType())
+ return AggValueSlot::DoesNotOverlap;
+
+ // If the field lies entirely within the enclosing class's nvsize, its tail
+ // padding cannot overlap any already-initialized object. (The only subobjects
+ // with greater addresses that might already be initialized are vbases.)
+ const RecordDecl *ClassRD = FD->getParent();
+ const ASTRecordLayout &Layout = getContext().getASTRecordLayout(ClassRD);
+ if (Layout.getFieldOffset(FD->getFieldIndex()) +
+ getContext().getTypeSize(FD->getType()) <=
+ (uint64_t)getContext().toBits(Layout.getNonVirtualSize()))
+ return AggValueSlot::DoesNotOverlap;
+
+ // The tail padding may contain values we need to preserve.
+ return AggValueSlot::MayOverlap;
+}
+
AggValueSlot::Overlap_t CodeGenFunction::overlapForBaseInit(
const CXXRecordDecl *RD, const CXXRecordDecl *BaseRD, bool IsVirtual) {
- // Virtual bases are initialized first, in address order, so there's never
- // any overlap during their initialization.
- //
- // FIXME: Under P0840, this is no longer true: the tail padding of a vbase
- // of a field could be reused by a vbase of a containing class.
+ // If the most-derived object is a field declared with [[no_unique_address]],
+ // the tail padding of any virtual base could be reused for other subobjects
+ // of that field's class.
if (IsVirtual)
- return AggValueSlot::DoesNotOverlap;
+ return AggValueSlot::MayOverlap;
// If the base class is laid out entirely within the nvsize of the derived
// class, its tail padding cannot yet be initialized, so we can issue