strimo378 created this revision.
strimo378 added a project: clang.
Herald added subscribers: jeroen.dobbelaere, kosarev.
Herald added a project: All.
strimo378 requested review of this revision.
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Hi all,
this is my first contribution to the LLVM project.
The patch adds support for generating the tbaa.struct metadata for structs
containing bitfields. The current implementation does not support bitfields and
even generates wrong tbaa.struct metadata ... see
https://github.com/llvm/llvm-project/issues/59328 .
The patch is not yet finished. I need some help to create an appropriate test
case. My first test case looks like that
struct a {
int : 8;
int b1 : 4;
int b2 : 8;
};
a i1,i2;
void c() { i1 = i2; }
and should generate the following metadata
call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 4 bitcast (%struct.a* @i1 to
i8*), i8* align 4 bitcast (%struct.a* @i2 to i8*), i64 4, i1 false),
!tbaa.struct !3
...
!3 = !{i64 1, i64 2, !4}
Furthermore, I am unsure what Type should be used for adding bitfields to
tbaa.struct. The original type or char? The current implementation uses the
original type (if not alias).
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D139267
Files:
clang/lib/CodeGen/CodeGenTBAA.cpp
clang/lib/CodeGen/CodeGenTBAA.h
Index: clang/lib/CodeGen/CodeGenTBAA.h
===================================================================
--- clang/lib/CodeGen/CodeGenTBAA.h
+++ clang/lib/CodeGen/CodeGenTBAA.h
@@ -146,6 +146,12 @@
/// considered to be equivalent to it.
llvm::MDNode *getChar();
+ /// AddCollectedField - Add one collected field to Fields vector
+ void
+ AddCollectedField(SmallVectorImpl<llvm::MDBuilder::TBAAStructField> &Fields,
+ uint64_t Offset, uint64_t Size, QualType QTy, bool
MayAlias,
+ bool FuseOverlapping);
+
/// CollectFields - Collect information about the fields of a type for
/// !tbaa.struct metadata formation. Return false for an unsupported type.
bool CollectFields(uint64_t BaseOffset,
Index: clang/lib/CodeGen/CodeGenTBAA.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenTBAA.cpp
+++ clang/lib/CodeGen/CodeGenTBAA.cpp
@@ -272,13 +272,28 @@
Size);
}
+void CodeGenTBAA::AddCollectedField(
+ SmallVectorImpl<llvm::MDBuilder::TBAAStructField> &Fields, uint64_t Offset,
+ uint64_t Size, QualType QTy, bool MayAlias, bool FuseOverlapping) {
+
+ // Fuse fields that overlap in their byte position (e.g. caused by bitfields)
+ if (FuseOverlapping && !Fields.empty() && Offset < Fields.back().Offset +
Fields.back().Size) {
+ Fields.back().Size = Fields.back().Offset - Offset + Size;
+ return;
+ }
+
+ llvm::MDNode *TBAAType = MayAlias ? getChar() : getTypeInfo(QTy);
+ llvm::MDNode *TBAATag = getAccessTagInfo(TBAAAccessInfo(TBAAType, Size));
+ Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size, TBAATag));
+}
+
bool
CodeGenTBAA::CollectFields(uint64_t BaseOffset,
QualType QTy,
SmallVectorImpl<llvm::MDBuilder::TBAAStructField> &
Fields,
bool MayAlias) {
- /* Things not handled yet include: C++ base classes, bitfields, */
+ /* Things not handled yet include: C++ base classes */
if (const RecordType *TTy = QTy->getAs<RecordType>()) {
const RecordDecl *RD = TTy->getDecl()->getDefinition();
@@ -300,19 +315,25 @@
uint64_t Offset = BaseOffset +
Layout.getFieldOffset(idx) / Context.getCharWidth();
QualType FieldQTy = i->getType();
- if (!CollectFields(Offset, FieldQTy, Fields,
- MayAlias || TypeHasMayAlias(FieldQTy)))
- return false;
+ bool FieldMayAlias = MayAlias || TypeHasMayAlias(FieldQTy);
+ if ((*i)->isBitField()) {
+ uint64_t EndOffset =
+ BaseOffset +
+ (Layout.getFieldOffset(idx) + (*i)->getBitWidthValue(Context) - 1)
/
+ Context.getCharWidth();
+
+ AddCollectedField(Fields, Offset, EndOffset - Offset + 1, QTy,
FieldMayAlias, true);
+ } else {
+ if (!CollectFields(Offset, FieldQTy, Fields, FieldMayAlias))
+ return false;
+ }
}
return true;
}
/* Otherwise, treat whatever it is as a field. */
- uint64_t Offset = BaseOffset;
uint64_t Size = Context.getTypeSizeInChars(QTy).getQuantity();
- llvm::MDNode *TBAAType = MayAlias ? getChar() : getTypeInfo(QTy);
- llvm::MDNode *TBAATag = getAccessTagInfo(TBAAAccessInfo(TBAAType, Size));
- Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size, TBAATag));
+ AddCollectedField(Fields, BaseOffset, Size, QTy, MayAlias, false);
return true;
}
Index: clang/lib/CodeGen/CodeGenTBAA.h
===================================================================
--- clang/lib/CodeGen/CodeGenTBAA.h
+++ clang/lib/CodeGen/CodeGenTBAA.h
@@ -146,6 +146,12 @@
/// considered to be equivalent to it.
llvm::MDNode *getChar();
+ /// AddCollectedField - Add one collected field to Fields vector
+ void
+ AddCollectedField(SmallVectorImpl<llvm::MDBuilder::TBAAStructField> &Fields,
+ uint64_t Offset, uint64_t Size, QualType QTy, bool MayAlias,
+ bool FuseOverlapping);
+
/// CollectFields - Collect information about the fields of a type for
/// !tbaa.struct metadata formation. Return false for an unsupported type.
bool CollectFields(uint64_t BaseOffset,
Index: clang/lib/CodeGen/CodeGenTBAA.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenTBAA.cpp
+++ clang/lib/CodeGen/CodeGenTBAA.cpp
@@ -272,13 +272,28 @@
Size);
}
+void CodeGenTBAA::AddCollectedField(
+ SmallVectorImpl<llvm::MDBuilder::TBAAStructField> &Fields, uint64_t Offset,
+ uint64_t Size, QualType QTy, bool MayAlias, bool FuseOverlapping) {
+
+ // Fuse fields that overlap in their byte position (e.g. caused by bitfields)
+ if (FuseOverlapping && !Fields.empty() && Offset < Fields.back().Offset + Fields.back().Size) {
+ Fields.back().Size = Fields.back().Offset - Offset + Size;
+ return;
+ }
+
+ llvm::MDNode *TBAAType = MayAlias ? getChar() : getTypeInfo(QTy);
+ llvm::MDNode *TBAATag = getAccessTagInfo(TBAAAccessInfo(TBAAType, Size));
+ Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size, TBAATag));
+}
+
bool
CodeGenTBAA::CollectFields(uint64_t BaseOffset,
QualType QTy,
SmallVectorImpl<llvm::MDBuilder::TBAAStructField> &
Fields,
bool MayAlias) {
- /* Things not handled yet include: C++ base classes, bitfields, */
+ /* Things not handled yet include: C++ base classes */
if (const RecordType *TTy = QTy->getAs<RecordType>()) {
const RecordDecl *RD = TTy->getDecl()->getDefinition();
@@ -300,19 +315,25 @@
uint64_t Offset = BaseOffset +
Layout.getFieldOffset(idx) / Context.getCharWidth();
QualType FieldQTy = i->getType();
- if (!CollectFields(Offset, FieldQTy, Fields,
- MayAlias || TypeHasMayAlias(FieldQTy)))
- return false;
+ bool FieldMayAlias = MayAlias || TypeHasMayAlias(FieldQTy);
+ if ((*i)->isBitField()) {
+ uint64_t EndOffset =
+ BaseOffset +
+ (Layout.getFieldOffset(idx) + (*i)->getBitWidthValue(Context) - 1) /
+ Context.getCharWidth();
+
+ AddCollectedField(Fields, Offset, EndOffset - Offset + 1, QTy, FieldMayAlias, true);
+ } else {
+ if (!CollectFields(Offset, FieldQTy, Fields, FieldMayAlias))
+ return false;
+ }
}
return true;
}
/* Otherwise, treat whatever it is as a field. */
- uint64_t Offset = BaseOffset;
uint64_t Size = Context.getTypeSizeInChars(QTy).getQuantity();
- llvm::MDNode *TBAAType = MayAlias ? getChar() : getTypeInfo(QTy);
- llvm::MDNode *TBAATag = getAccessTagInfo(TBAAAccessInfo(TBAAType, Size));
- Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size, TBAATag));
+ AddCollectedField(Fields, BaseOffset, Size, QTy, MayAlias, false);
return true;
}
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