Non constant size and offset in DWARF (#141106)

In Ada, a record type can have a non-constant size, and a field can
appear at a non-constant bit offset in a record.

To support this, this patch changes DIType to record the size and offset
using metadata, rather than plain integers. In addition to a constant
offset, both DIVariable and DIExpression are now supported here.

One thing of note in this patch is the choice of how exactly to
represent a non-constant bit offset, with the difficulty being that
DWARF 5 does not support this. DWARF 3 did have a way to support a
non-constant byte offset, combined with a constant bit offset within the
byte, but this was deprecated in DWARF 4 and removed from DWARF 5.

This patch takes a simple approach: a DWARF extension allowing the use
of an expression with DW_AT_data_bit_offset. There is a corresponding
DWARF issue, see https://dwarfstd.org/issues/250501.1.html. The main
reason for this approach is that it keeps API simplicity: just a single
value is needed, rather than having separate data describing the byte
offset and the bit within the byte.

1 files changed, 50 insertions, 51 deletions

diff --git a/llvm/lib/IR/DebugInfoMetadata.cpp b/llvm/lib/IR/DebugInfoMetadata.cpp
index 473114b..44b0f0d 100644
--- a/llvm/lib/IR/DebugInfoMetadata.cpp
+++ b/llvm/lib/IR/DebugInfoMetadata.cpp
@@ -825,25 +825,23 @@ DIGenericSubrange::BoundType DIGenericSubrange::getStride() const {
 }
 
 DISubrangeType::DISubrangeType(LLVMContext &C, StorageType Storage,
-                               unsigned Line, uint64_t SizeInBits,
-                               uint32_t AlignInBits, DIFlags Flags,
-                               ArrayRef<Metadata *> Ops)
+                               unsigned Line, uint32_t AlignInBits,
+                               DIFlags Flags, ArrayRef<Metadata *> Ops)
     : DIType(C, DISubrangeTypeKind, Storage, dwarf::DW_TAG_subrange_type, Line,
-             SizeInBits, AlignInBits, 0, 0, Flags, Ops) {}
+             AlignInBits, 0, Flags, Ops) {}
 
 DISubrangeType *DISubrangeType::getImpl(
     LLVMContext &Context, MDString *Name, Metadata *File, unsigned Line,
-    Metadata *Scope, uint64_t SizeInBits, uint32_t AlignInBits, DIFlags Flags,
+    Metadata *Scope, Metadata *SizeInBits, uint32_t AlignInBits, DIFlags Flags,
     Metadata *BaseType, Metadata *LowerBound, Metadata *UpperBound,
     Metadata *Stride, Metadata *Bias, StorageType Storage, bool ShouldCreate) {
   assert(isCanonical(Name) && "Expected canonical MDString");
   DEFINE_GETIMPL_LOOKUP(DISubrangeType, (Name, File, Line, Scope, SizeInBits,
                                          AlignInBits, Flags, BaseType,
                                          LowerBound, UpperBound, Stride, Bias));
-  Metadata *Ops[] = {File,       Scope,      Name,   BaseType,
-                     LowerBound, UpperBound, Stride, Bias};
-  DEFINE_GETIMPL_STORE(DISubrangeType, (Line, SizeInBits, AlignInBits, Flags),
-                       Ops);
+  Metadata *Ops[] = {File,     Scope,      Name,       SizeInBits, nullptr,
+                     BaseType, LowerBound, UpperBound, Stride,     Bias};
+  DEFINE_GETIMPL_STORE(DISubrangeType, (Line, AlignInBits, Flags), Ops);
 }
 
 DISubrangeType::BoundType
@@ -883,18 +881,17 @@ DIEnumerator *DIEnumerator::getImpl(LLVMContext &Context, const APInt &Value,
 }
 
 DIBasicType *DIBasicType::getImpl(LLVMContext &Context, unsigned Tag,
-                                  MDString *Name, uint64_t SizeInBits,
+                                  MDString *Name, Metadata *SizeInBits,
                                   uint32_t AlignInBits, unsigned Encoding,
                                   uint32_t NumExtraInhabitants, DIFlags Flags,
                                   StorageType Storage, bool ShouldCreate) {
   assert(isCanonical(Name) && "Expected canonical MDString");
   DEFINE_GETIMPL_LOOKUP(DIBasicType, (Tag, Name, SizeInBits, AlignInBits,
                                       Encoding, NumExtraInhabitants, Flags));
-  Metadata *Ops[] = {nullptr, nullptr, Name};
-  DEFINE_GETIMPL_STORE(
-      DIBasicType,
-      (Tag, SizeInBits, AlignInBits, Encoding, NumExtraInhabitants, Flags),
-      Ops);
+  Metadata *Ops[] = {nullptr, nullptr, Name, SizeInBits, nullptr};
+  DEFINE_GETIMPL_STORE(DIBasicType,
+                       (Tag, AlignInBits, Encoding, NumExtraInhabitants, Flags),
+                       Ops);
 }
 
 std::optional<DIBasicType::Signedness> DIBasicType::getSignedness() const {
@@ -914,18 +911,18 @@ std::optional<DIBasicType::Signedness> DIBasicType::getSignedness() const {
 
 DIFixedPointType *
 DIFixedPointType::getImpl(LLVMContext &Context, unsigned Tag, MDString *Name,
-                          uint64_t SizeInBits, uint32_t AlignInBits,
+                          Metadata *SizeInBits, uint32_t AlignInBits,
                           unsigned Encoding, DIFlags Flags, unsigned Kind,
                           int Factor, APInt Numerator, APInt Denominator,
                           StorageType Storage, bool ShouldCreate) {
   DEFINE_GETIMPL_LOOKUP(DIFixedPointType,
                         (Tag, Name, SizeInBits, AlignInBits, Encoding, Flags,
                          Kind, Factor, Numerator, Denominator));
-  Metadata *Ops[] = {nullptr, nullptr, Name};
-  DEFINE_GETIMPL_STORE(DIFixedPointType,
-                       (Tag, SizeInBits, AlignInBits, Encoding, Flags, Kind,
-                        Factor, Numerator, Denominator),
-                       Ops);
+  Metadata *Ops[] = {nullptr, nullptr, Name, SizeInBits, nullptr};
+  DEFINE_GETIMPL_STORE(
+      DIFixedPointType,
+      (Tag, AlignInBits, Encoding, Flags, Kind, Factor, Numerator, Denominator),
+      Ops);
 }
 
 bool DIFixedPointType::isSigned() const {
@@ -957,17 +954,17 @@ DIStringType *DIStringType::getImpl(LLVMContext &Context, unsigned Tag,
                                     MDString *Name, Metadata *StringLength,
                                     Metadata *StringLengthExp,
                                     Metadata *StringLocationExp,
-                                    uint64_t SizeInBits, uint32_t AlignInBits,
+                                    Metadata *SizeInBits, uint32_t AlignInBits,
                                     unsigned Encoding, StorageType Storage,
                                     bool ShouldCreate) {
   assert(isCanonical(Name) && "Expected canonical MDString");
   DEFINE_GETIMPL_LOOKUP(DIStringType,
                         (Tag, Name, StringLength, StringLengthExp,
                          StringLocationExp, SizeInBits, AlignInBits, Encoding));
-  Metadata *Ops[] = {nullptr,      nullptr,         Name,
-                     StringLength, StringLengthExp, StringLocationExp};
-  DEFINE_GETIMPL_STORE(DIStringType, (Tag, SizeInBits, AlignInBits, Encoding),
-                       Ops);
+  Metadata *Ops[] = {nullptr,         nullptr,          Name,
+                     SizeInBits,      nullptr,          StringLength,
+                     StringLengthExp, StringLocationExp};
+  DEFINE_GETIMPL_STORE(DIStringType, (Tag, AlignInBits, Encoding), Ops);
 }
 DIType *DIDerivedType::getClassType() const {
   assert(getTag() == dwarf::DW_TAG_ptr_to_member_type);
@@ -1004,8 +1001,8 @@ Constant *DIDerivedType::getDiscriminantValue() const {
 
 DIDerivedType *DIDerivedType::getImpl(
     LLVMContext &Context, unsigned Tag, MDString *Name, Metadata *File,
-    unsigned Line, Metadata *Scope, Metadata *BaseType, uint64_t SizeInBits,
-    uint32_t AlignInBits, uint64_t OffsetInBits,
+    unsigned Line, Metadata *Scope, Metadata *BaseType, Metadata *SizeInBits,
+    uint32_t AlignInBits, Metadata *OffsetInBits,
     std::optional<unsigned> DWARFAddressSpace,
     std::optional<PtrAuthData> PtrAuthData, DIFlags Flags, Metadata *ExtraData,
     Metadata *Annotations, StorageType Storage, bool ShouldCreate) {
@@ -1014,11 +1011,11 @@ DIDerivedType *DIDerivedType::getImpl(
                         (Tag, Name, File, Line, Scope, BaseType, SizeInBits,
                          AlignInBits, OffsetInBits, DWARFAddressSpace,
                          PtrAuthData, Flags, ExtraData, Annotations));
-  Metadata *Ops[] = {File, Scope, Name, BaseType, ExtraData, Annotations};
-  DEFINE_GETIMPL_STORE(DIDerivedType,
-                       (Tag, Line, SizeInBits, AlignInBits, OffsetInBits,
-                        DWARFAddressSpace, PtrAuthData, Flags),
-                       Ops);
+  Metadata *Ops[] = {File,         Scope,    Name,      SizeInBits,
+                     OffsetInBits, BaseType, ExtraData, Annotations};
+  DEFINE_GETIMPL_STORE(
+      DIDerivedType,
+      (Tag, Line, AlignInBits, DWARFAddressSpace, PtrAuthData, Flags), Ops);
 }
 
 std::optional<DIDerivedType::PtrAuthData>
@@ -1030,8 +1027,8 @@ DIDerivedType::getPtrAuthData() const {
 
 DICompositeType *DICompositeType::getImpl(
     LLVMContext &Context, unsigned Tag, MDString *Name, Metadata *File,
-    unsigned Line, Metadata *Scope, Metadata *BaseType, uint64_t SizeInBits,
-    uint32_t AlignInBits, uint64_t OffsetInBits, DIFlags Flags,
+    unsigned Line, Metadata *Scope, Metadata *BaseType, Metadata *SizeInBits,
+    uint32_t AlignInBits, Metadata *OffsetInBits, DIFlags Flags,
     Metadata *Elements, unsigned RuntimeLang, std::optional<uint32_t> EnumKind,
     Metadata *VTableHolder, Metadata *TemplateParams, MDString *Identifier,
     Metadata *Discriminator, Metadata *DataLocation, Metadata *Associated,
@@ -1047,20 +1044,21 @@ DICompositeType *DICompositeType::getImpl(
        OffsetInBits, Flags, Elements, RuntimeLang, VTableHolder, TemplateParams,
        Identifier, Discriminator, DataLocation, Associated, Allocated, Rank,
        Annotations, Specification, NumExtraInhabitants, BitStride));
-  Metadata *Ops[] = {File,          Scope,        Name,           BaseType,
-                     Elements,      VTableHolder, TemplateParams, Identifier,
-                     Discriminator, DataLocation, Associated,     Allocated,
-                     Rank,          Annotations,  Specification,  BitStride};
+  Metadata *Ops[] = {File,           Scope,      Name,          SizeInBits,
+                     OffsetInBits,   BaseType,   Elements,      VTableHolder,
+                     TemplateParams, Identifier, Discriminator, DataLocation,
+                     Associated,     Allocated,  Rank,          Annotations,
+                     Specification,  BitStride};
   DEFINE_GETIMPL_STORE(DICompositeType,
-                       (Tag, Line, RuntimeLang, SizeInBits, AlignInBits,
-                        OffsetInBits, NumExtraInhabitants, EnumKind, Flags),
+                       (Tag, Line, RuntimeLang, AlignInBits,
+                        NumExtraInhabitants, EnumKind, Flags),
                        Ops);
 }
 
 DICompositeType *DICompositeType::buildODRType(
     LLVMContext &Context, MDString &Identifier, unsigned Tag, MDString *Name,
     Metadata *File, unsigned Line, Metadata *Scope, Metadata *BaseType,
-    uint64_t SizeInBits, uint32_t AlignInBits, uint64_t OffsetInBits,
+    Metadata *SizeInBits, uint32_t AlignInBits, Metadata *OffsetInBits,
     Metadata *Specification, uint32_t NumExtraInhabitants, DIFlags Flags,
     Metadata *Elements, unsigned RuntimeLang, std::optional<uint32_t> EnumKind,
     Metadata *VTableHolder, Metadata *TemplateParams, Metadata *Discriminator,
@@ -1086,12 +1084,13 @@ DICompositeType *DICompositeType::buildODRType(
     return CT;
 
   // Mutate CT in place.  Keep this in sync with getImpl.
-  CT->mutate(Tag, Line, RuntimeLang, SizeInBits, AlignInBits, OffsetInBits,
-             NumExtraInhabitants, EnumKind, Flags);
-  Metadata *Ops[] = {File,          Scope,        Name,           BaseType,
-                     Elements,      VTableHolder, TemplateParams, &Identifier,
-                     Discriminator, DataLocation, Associated,     Allocated,
-                     Rank,          Annotations,  Specification,  BitStride};
+  CT->mutate(Tag, Line, RuntimeLang, AlignInBits, NumExtraInhabitants, EnumKind,
+             Flags);
+  Metadata *Ops[] = {File,           Scope,       Name,          SizeInBits,
+                     OffsetInBits,   BaseType,    Elements,      VTableHolder,
+                     TemplateParams, &Identifier, Discriminator, DataLocation,
+                     Associated,     Allocated,   Rank,          Annotations,
+                     Specification,  BitStride};
   assert((std::end(Ops) - std::begin(Ops)) == (int)CT->getNumOperands() &&
          "Mismatched number of operands");
   for (unsigned I = 0, E = CT->getNumOperands(); I != E; ++I)
@@ -1103,7 +1102,7 @@ DICompositeType *DICompositeType::buildODRType(
 DICompositeType *DICompositeType::getODRType(
     LLVMContext &Context, MDString &Identifier, unsigned Tag, MDString *Name,
     Metadata *File, unsigned Line, Metadata *Scope, Metadata *BaseType,
-    uint64_t SizeInBits, uint32_t AlignInBits, uint64_t OffsetInBits,
+    Metadata *SizeInBits, uint32_t AlignInBits, Metadata *OffsetInBits,
     Metadata *Specification, uint32_t NumExtraInhabitants, DIFlags Flags,
     Metadata *Elements, unsigned RuntimeLang, std::optional<uint32_t> EnumKind,
     Metadata *VTableHolder, Metadata *TemplateParams, Metadata *Discriminator,
@@ -1138,7 +1137,7 @@ DISubroutineType::DISubroutineType(LLVMContext &C, StorageType Storage,
                                    DIFlags Flags, uint8_t CC,
                                    ArrayRef<Metadata *> Ops)
     : DIType(C, DISubroutineTypeKind, Storage, dwarf::DW_TAG_subroutine_type, 0,
-             0, 0, 0, 0, Flags, Ops),
+             0, 0, Flags, Ops),
       CC(CC) {}
 
 DISubroutineType *DISubroutineType::getImpl(LLVMContext &Context, DIFlags Flags,
@@ -1146,7 +1145,7 @@ DISubroutineType *DISubroutineType::getImpl(LLVMContext &Context, DIFlags Flags,
                                             StorageType Storage,
                                             bool ShouldCreate) {
   DEFINE_GETIMPL_LOOKUP(DISubroutineType, (Flags, CC, TypeArray));
-  Metadata *Ops[] = {nullptr, nullptr, nullptr, TypeArray};
+  Metadata *Ops[] = {nullptr, nullptr, nullptr, nullptr, nullptr, TypeArray};
   DEFINE_GETIMPL_STORE(DISubroutineType, (Flags, CC), Ops);
 }