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/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index a2a4bca..17bb9e9 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -3879,12 +3879,27 @@
return EmitLValueForField(LambdaLV, Field);
}
+/// Get the address of a zero-sized field within a record. The resulting
+/// address doesn't necessarily have the right type.
+static Address emitAddrOfZeroSizeField(CodeGenFunction &CGF, Address Base,
+ const FieldDecl *Field) {
+ CharUnits Offset = CGF.getContext().toCharUnitsFromBits(
+ CGF.getContext().getFieldOffset(Field));
+ if (Offset.isZero())
+ return Base;
+ Base = CGF.Builder.CreateElementBitCast(Base, CGF.Int8Ty);
+ return CGF.Builder.CreateConstInBoundsByteGEP(Base, Offset);
+}
+
/// Drill down to the storage of a field without walking into
/// reference types.
///
/// The resulting address doesn't necessarily have the right type.
static Address emitAddrOfFieldStorage(CodeGenFunction &CGF, Address base,
const FieldDecl *field) {
+ if (field->isZeroSize(CGF.getContext()))
+ return emitAddrOfZeroSizeField(CGF, base, field);
+
const RecordDecl *rec = field->getParent();
unsigned idx =
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
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());
}
diff --git a/clang/lib/CodeGen/CGOpenMPRuntime.cpp b/clang/lib/CodeGen/CGOpenMPRuntime.cpp
index 602c9a2..ee5f399 100644
--- a/clang/lib/CodeGen/CGOpenMPRuntime.cpp
+++ b/clang/lib/CodeGen/CGOpenMPRuntime.cpp
@@ -7811,7 +7811,7 @@
for (const auto *Field : RD->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(CGF.getContext())) {
unsigned FieldIndex = RL.getLLVMFieldNo(Field);
RecordLayout[FieldIndex] = Field;
}
diff --git a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
index b5102bb..4de64a3 100644
--- a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
+++ b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
@@ -347,18 +347,21 @@
void CGRecordLowering::accumulateFields() {
for (RecordDecl::field_iterator Field = D->field_begin(),
FieldEnd = D->field_end();
- Field != FieldEnd;)
+ Field != FieldEnd;) {
if (Field->isBitField()) {
RecordDecl::field_iterator Start = Field;
// Iterate to gather the list of bitfields.
for (++Field; Field != FieldEnd && Field->isBitField(); ++Field);
accumulateBitFields(Start, Field);
- } else {
+ } else if (!Field->isZeroSize(Context)) {
Members.push_back(MemberInfo(
bitsToCharUnits(getFieldBitOffset(*Field)), MemberInfo::Field,
getStorageType(*Field), *Field));
++Field;
+ } else {
+ ++Field;
}
+ }
}
void
@@ -590,10 +593,17 @@
if (!Member->Data && Member->Kind != MemberInfo::Scissor)
continue;
if (Member->Offset < Tail) {
- assert(Prior->Kind == MemberInfo::Field && !Prior->FD &&
+ assert(Prior->Kind == MemberInfo::Field &&
"Only storage fields have tail padding!");
- Prior->Data = getByteArrayType(bitsToCharUnits(llvm::alignTo(
- cast<llvm::IntegerType>(Prior->Data)->getIntegerBitWidth(), 8)));
+ if (!Prior->FD || Prior->FD->isBitField())
+ Prior->Data = getByteArrayType(bitsToCharUnits(llvm::alignTo(
+ cast<llvm::IntegerType>(Prior->Data)->getIntegerBitWidth(), 8)));
+ else {
+ assert(Prior->FD->hasAttr<NoUniqueAddressAttr>() &&
+ "should not have reused this field's tail padding");
+ Prior->Data = getByteArrayType(
+ Context.getTypeInfoDataSizeInChars(Prior->FD->getType()).first);
+ }
}
if (Member->Data)
Prior = Member;
@@ -797,6 +807,10 @@
for (unsigned i = 0, e = AST_RL.getFieldCount(); i != e; ++i, ++it) {
const FieldDecl *FD = *it;
+ // Ignore zero-sized fields.
+ if (FD->isZeroSize(getContext()))
+ continue;
+
// For non-bit-fields, just check that the LLVM struct offset matches the
// AST offset.
if (!FD->isBitField()) {
@@ -810,10 +824,6 @@
if (!FD->getDeclName())
continue;
- // Don't inspect zero-length bitfields.
- if (FD->isZeroLengthBitField(getContext()))
- continue;
-
const CGBitFieldInfo &Info = RL->getBitFieldInfo(FD);
llvm::Type *ElementTy = ST->getTypeAtIndex(RL->getLLVMFieldNo(FD));
diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index e95a07c..efb68c56 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -2322,14 +2322,7 @@
}
/// Determine whether a field initialization may overlap some other object.
- AggValueSlot::Overlap_t overlapForFieldInit(const FieldDecl *FD) {
- // FIXME: These cases can result in overlap as a result of P0840R0's
- // [[no_unique_address]] attribute. We can still infer NoOverlap in the
- // presence of that attribute if the field is within the nvsize of its
- // containing class, because non-virtual subobjects are initialized in
- // address order.
- return AggValueSlot::DoesNotOverlap;
- }
+ AggValueSlot::Overlap_t overlapForFieldInit(const FieldDecl *FD);
/// Determine whether a base class initialization may overlap some other
/// object.