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/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
index e94fc67..16ccd05 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -675,11 +675,12 @@
++FieldNo;
// If this is a union, skip all the fields that aren't being initialized.
- if (RD->isUnion() && ILE->getInitializedFieldInUnion() != Field)
+ if (RD->isUnion() &&
+ !declaresSameEntity(ILE->getInitializedFieldInUnion(), Field))
continue;
- // Don't emit anonymous bitfields, they just affect layout.
- if (Field->isUnnamedBitfield())
+ // Don't emit anonymous bitfields or zero-sized fields.
+ if (Field->isUnnamedBitfield() || Field->isZeroSize(CGM.getContext()))
continue;
// Get the initializer. A struct can include fields without initializers,
@@ -720,6 +721,10 @@
if (!AppendField(Field, Layout.getFieldOffset(FieldNo), EltInit,
AllowOverwrite))
return false;
+ // After emitting a non-empty field with [[no_unique_address]], we may
+ // need to overwrite its tail padding.
+ if (Field->hasAttr<NoUniqueAddressAttr>())
+ AllowOverwrite = true;
} else {
// Otherwise we have a bitfield.
if (auto *CI = dyn_cast<llvm::ConstantInt>(EltInit)) {
@@ -793,14 +798,15 @@
unsigned FieldNo = 0;
uint64_t OffsetBits = CGM.getContext().toBits(Offset);
+ bool AllowOverwrite = false;
for (RecordDecl::field_iterator Field = RD->field_begin(),
FieldEnd = RD->field_end(); Field != FieldEnd; ++Field, ++FieldNo) {
// If this is a union, skip all the fields that aren't being initialized.
if (RD->isUnion() && !declaresSameEntity(Val.getUnionField(), *Field))
continue;
- // Don't emit anonymous bitfields, they just affect layout.
- if (Field->isUnnamedBitfield())
+ // Don't emit anonymous bitfields or zero-sized fields.
+ if (Field->isUnnamedBitfield() || Field->isZeroSize(CGM.getContext()))
continue;
// Emit the value of the initializer.
@@ -814,12 +820,16 @@
if (!Field->isBitField()) {
// Handle non-bitfield members.
if (!AppendField(*Field, Layout.getFieldOffset(FieldNo) + OffsetBits,
- EltInit))
+ EltInit, AllowOverwrite))
return false;
+ // After emitting a non-empty field with [[no_unique_address]], we may
+ // need to overwrite its tail padding.
+ if (Field->hasAttr<NoUniqueAddressAttr>())
+ AllowOverwrite = true;
} else {
// Otherwise we have a bitfield.
if (!AppendBitField(*Field, Layout.getFieldOffset(FieldNo) + OffsetBits,
- cast<llvm::ConstantInt>(EltInit)))
+ cast<llvm::ConstantInt>(EltInit), AllowOverwrite))
return false;
}
}
@@ -2216,7 +2226,7 @@
for (const auto *Field : record->fields()) {
// Fill in non-bitfields. (Bitfields always use a zero pattern, which we
// will fill in later.)
- if (!Field->isBitField()) {
+ if (!Field->isBitField() && !Field->isZeroSize(CGM.getContext())) {
unsigned fieldIndex = layout.getLLVMFieldNo(Field);
elements[fieldIndex] = CGM.EmitNullConstant(Field->getType());
}