[DebugInfo] Add num_extra_inhabitants to debug info (llvm#112590)

An extra inhabitant is a bit pattern that does not represent a valid
value for instances of a given type. The number of extra inhabitants is
the number of those bit configurations.

This is used by Swift to save space when composing types. For example,
because Bool only needs 2 bit patterns to represent all of its values
(true and false), an Optional<Bool> only occupies 1 byte in memory by
using a bit configuration that is unused by Bool. Which bit patterns are
unused are part of the ABI of the language.

Since Swift generics are not monomorphized, by using dynamic libraries
you can have generic types whose size, alignment, etc, are known only
at runtime (which is why this feature is needed).

This patch adds num_extra_inhabitants to LLVM-IR debug info and in DWARF
as an Apple extension.

(cherry picked from commit f6617d6)

Author: augusto2112

lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserSwiftDescriptorFinder.cpp

@@ -318,7 +318,7 @@ DWARFASTParserSwift::getBuiltinTypeDescriptor(
   unsigned stride = ((byte_size + alignment - 1) & ~(alignment - 1));
 
   auto num_extra_inhabitants =
-      die.GetAttributeValueAsUnsigned(DW_AT_APPLE_num_extra_inhabitants, 0);
+      die.GetAttributeValueAsUnsigned(DW_AT_LLVM_num_extra_inhabitants, 0);
 
   auto is_bitwise_takable = true; // TODO: encode it in DWARF
 

llvm/include/llvm/BinaryFormat/Dwarf.def

@@ -617,6 +617,7 @@ HANDLE_DW_AT(0x3e07, LLVM_apinotes, 0, APPLE)
 HANDLE_DW_AT(0x3e08, LLVM_ptrauth_isa_pointer, 0, LLVM)
 HANDLE_DW_AT(0x3e09, LLVM_ptrauth_authenticates_null_values, 0, LLVM)
 HANDLE_DW_AT(0x3e0a, LLVM_ptrauth_authentication_mode, 0, LLVM)
+HANDLE_DW_AT(0x3e0b, LLVM_num_extra_inhabitants, 0, LLVM)
 
 // Apple extensions.
 HANDLE_DW_AT(0x3fe1, APPLE_optimized, 0, APPLE)
@@ -635,7 +636,6 @@ HANDLE_DW_AT(0x3fed, APPLE_property, 0, APPLE)
 HANDLE_DW_AT(0x3fee, APPLE_objc_direct, 0, APPLE)
 HANDLE_DW_AT(0x3fef, APPLE_sdk, 0, APPLE)
 HANDLE_DW_AT(0x3ff0, APPLE_origin, 0, APPLE)
-HANDLE_DW_AT(0x3ff1, APPLE_num_extra_inhabitants, 0, APPLE)
 
 // Attribute form encodings.
 HANDLE_DW_FORM(0x01, addr, 2, DWARF)

llvm/include/llvm/IR/DIBuilder.h

@@ -227,7 +227,7 @@ namespace llvm {
     /// \param Flags       Optional DWARF attributes, e.g., DW_AT_endianity.
     /// \param NumExtraInhabitants The number of extra inhabitants of the type.
     /// An extra inhabitant is a bit pattern that does not represent a valid
-    /// value for objects of a given type.
+    /// value for instances of a given type. This is used by the Swift language.
     DIBasicType *createBasicType(StringRef Name, uint64_t SizeInBits,
                                  unsigned Encoding,
                                  DINode::DIFlags Flags = DINode::FlagZero,
@@ -493,7 +493,7 @@ namespace llvm {
     /// template parameters have been substituted in.
     /// \param NumExtraInhabitants The number of extra inhabitants of the type.
     /// An extra inhabitant is a bit pattern that does not represent a valid
-    /// value for objects of a given type.
+    /// value for instances of a given type.
     DICompositeType *createStructType(
         DIScope *Scope, StringRef Name, DIFile *File, unsigned LineNumber,
         uint64_t SizeInBits, uint32_t AlignInBits, DINode::DIFlags Flags,

llvm/include/llvm/IR/DebugInfoMetadata.h

@@ -739,10 +739,12 @@ class DIType : public DIScope {
 
   /// Change fields in place.
   void mutate(unsigned Tag, unsigned Line, uint64_t SizeInBits,
-              uint32_t AlignInBits, uint64_t OffsetInBits, uint32_t NumExtraInhabitants, DIFlags Flags) {
+              uint32_t AlignInBits, uint64_t OffsetInBits,
+              uint32_t NumExtraInhabitants, DIFlags Flags) {
     assert(isDistinct() && "Only distinct nodes can mutate");
     setTag(Tag);
-    init(Line, SizeInBits, AlignInBits, OffsetInBits, NumExtraInhabitants, Flags);
+    init(Line, SizeInBits, AlignInBits, OffsetInBits, NumExtraInhabitants,
+         Flags);
   }
 
 public:
@@ -838,8 +840,7 @@ class DIBasicType : public DIType {
                               StringRef Name, uint64_t SizeInBits,
                               uint32_t AlignInBits, unsigned Encoding,
                               uint32_t NumExtraInhabitants, DIFlags Flags,
-                              StorageType Storage,
-                              bool ShouldCreate = true) {
+                              StorageType Storage, bool ShouldCreate = true) {
     return getImpl(Context, Tag, getCanonicalMDString(Context, Name),
                    SizeInBits, AlignInBits, Encoding, NumExtraInhabitants,
                    Flags, Storage, ShouldCreate);
@@ -865,6 +866,14 @@ class DIBasicType : public DIType {
   DEFINE_MDNODE_GET(DIBasicType,
                     (unsigned Tag, MDString *Name, uint64_t SizeInBits),
                     (Tag, Name, SizeInBits, 0, 0, 0, FlagZero))
+  DEFINE_MDNODE_GET(DIBasicType,
+                    (unsigned Tag, StringRef Name, uint64_t SizeInBits,
+                     uint32_t AlignInBits, unsigned Encoding, DIFlags Flags),
+                    (Tag, Name, SizeInBits, AlignInBits, Encoding, 0, Flags))
+  DEFINE_MDNODE_GET(DIBasicType,
+                    (unsigned Tag, MDString *Name, uint64_t SizeInBits,
+                     uint32_t AlignInBits, unsigned Encoding, DIFlags Flags),
+                    (Tag, Name, SizeInBits, AlignInBits, Encoding, 0, Flags))
   DEFINE_MDNODE_GET(DIBasicType,
                     (unsigned Tag, StringRef Name, uint64_t SizeInBits,
                      uint32_t AlignInBits, unsigned Encoding,
@@ -1033,8 +1042,7 @@ class DIDerivedType : public DIType {
                 std::optional<PtrAuthData> PtrAuthData, DIFlags Flags,
                 ArrayRef<Metadata *> Ops)
       : DIType(C, DIDerivedTypeKind, Storage, Tag, Line, SizeInBits,
-               AlignInBits, OffsetInBits, /*NumExtraInhabitants=*/0, Flags,
-               Ops),
+               AlignInBits, OffsetInBits, /*NumExtraInhabitants=*/0, Flags, Ops),
         DWARFAddressSpace(DWARFAddressSpace) {
     if (PtrAuthData)
       SubclassData32 = PtrAuthData->RawData;

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

@@ -737,7 +737,7 @@ void DwarfUnit::constructTypeDIE(DIE &Buffer, const DIBasicType *BTy) {
     addUInt(Buffer, dwarf::DW_AT_endianity, std::nullopt, dwarf::DW_END_little);
 
   if (uint32_t NumExtraInhabitants = BTy->getNumExtraInhabitants())
-    addUInt(Buffer, dwarf::DW_AT_APPLE_num_extra_inhabitants, std::nullopt,
+    addUInt(Buffer, dwarf::DW_AT_LLVM_num_extra_inhabitants, std::nullopt,
             NumExtraInhabitants);
 }
 
@@ -1100,10 +1100,9 @@ void DwarfUnit::constructTypeDIE(DIE &Buffer, const DICompositeType *CTy) {
               AlignInBytes);
 
     if (uint32_t NumExtraInhabitants = CTy->getNumExtraInhabitants())
-      addUInt(Buffer, dwarf::DW_AT_APPLE_num_extra_inhabitants,
-            std::nullopt, NumExtraInhabitants);
-
-  } 
+      addUInt(Buffer, dwarf::DW_AT_LLVM_num_extra_inhabitants, std::nullopt,
+              NumExtraInhabitants);
+  }
 }
 
 void DwarfUnit::constructTemplateTypeParameterDIE(

llvm/lib/IR/DebugInfoMetadata.cpp

@@ -664,8 +664,7 @@ DIBasicType *DIBasicType::getImpl(LLVMContext &Context, unsigned Tag,
                                   MDString *Name, uint64_t SizeInBits,
                                   uint32_t AlignInBits, unsigned Encoding,
                                   uint32_t NumExtraInhabitants, DIFlags Flags,
-                                  StorageType Storage,
-                                  bool ShouldCreate) {
+                                  StorageType Storage, bool ShouldCreate) {
   assert(isCanonical(Name) && "Expected canonical MDString");
   DEFINE_GETIMPL_LOOKUP(DIBasicType, (Tag, Name, SizeInBits, AlignInBits,
                                       Encoding, NumExtraInhabitants, Flags));

llvm/test/Assembler/debug-info.ll

@@ -1,8 +1,8 @@
 ; RUN: llvm-as < %s | llvm-dis | llvm-as | llvm-dis | FileCheck %s
 ; RUN: verify-uselistorder %s
 
-; CHECK: !named = !{!0, !0, !1, !2, !3, !4, !5, !6, !7, !8, !8, !9, !10, !11, !12, !13, !14, !15, !16, !17, !18, !19, !20, !21, !22, !23, !24, !25, !26, !27, !27, !28, !29, !30, !31, !32, !33, !34, !35, !36, !37, !38, !39, !40, !41, !42, !43}
-!named = !{!0, !1, !2, !3, !4, !5, !6, !7, !8, !9, !10, !11, !12, !13, !14, !15, !16, !17, !18, !19, !20, !21, !22, !23, !24, !25, !26, !27, !28, !29, !30, !31, !32, !33, !34, !35, !36, !37, !38, !39, !40, !41, !42, !43, !44, !45, !46}
+; CHECK: !named = !{!0, !0, !1, !2, !3, !4, !5, !6, !7, !8, !8, !9, !10, !11, !12, !13, !14, !15, !16, !17, !18, !19, !20, !21, !22, !23, !24, !25, !26, !27, !27, !28, !29, !30, !31, !32, !33, !34, !35, !36, !37, !38, !39, !40, !41, !42, !43, !44, !45}
+!named = !{!0, !1, !2, !3, !4, !5, !6, !7, !8, !9, !10, !11, !12, !13, !14, !15, !16, !17, !18, !19, !20, !21, !22, !23, !24, !25, !26, !27, !28, !29, !30, !31, !32, !33, !34, !35, !36, !37, !38, !39, !40, !41, !42, !43, !44, !45, !46, !47, !48}
 
 ; CHECK:      !0 = !DISubrange(count: 3, lowerBound: 0)
 ; CHECK-NEXT: !1 = !DISubrange(count: 3, lowerBound: 4)
@@ -111,3 +111,9 @@
 
 ; CHECK: !DIDerivedType(tag: DW_TAG_LLVM_ptrauth_type, baseType: !13, ptrAuthKey: 2, ptrAuthIsAddressDiscriminated: true, ptrAuthExtraDiscriminator: 1234, ptrAuthIsaPointer: true, ptrAuthAuthenticatesNullValues: true)
 !46 = !DIDerivedType(tag: DW_TAG_LLVM_ptrauth_type, baseType: !15, ptrAuthKey: 2, ptrAuthIsAddressDiscriminated: true, ptrAuthExtraDiscriminator: 1234, ptrAuthIsaPointer: true, ptrAuthAuthenticatesNullValues: true)
+
+; CHECK: !DIBasicType(name: "ExtraInhabitantBasicType", size: 1, encoding: DW_ATE_unsigned, num_extra_inhabitants: 254)
+!47 = !DIBasicType(name: "ExtraInhabitantBasicType", size: 1, encoding: DW_ATE_unsigned, num_extra_inhabitants: 254)
+
+;CHECK: !DICompositeType(tag: DW_TAG_structure_type, name: "ExtraInhabitantCompositeType", file: !10, size: 64, num_extra_inhabitants: 66, identifier: "MangledExtraInhabitantCompositeType")
+!48 = !DICompositeType(tag: DW_TAG_structure_type, name: "ExtraInhabitantCompositeType", file: !12, size: 64, num_extra_inhabitants: 66, identifier: "MangledExtraInhabitantCompositeType")

llvm/test/DebugInfo/AArch64/num_extra_inhabitants.ll

@@ -2,29 +2,40 @@
 ; RUN:   | llvm-dwarfdump - | FileCheck %s
 
 ; CHECK: DW_TAG_base_type
-; CHECK: DW_AT_APPLE_num_extra_inhabitants	(0xfe)
+; CHECK: DW_AT_name ("ExtraInhabitantBasicType")
+; CHECK: DW_AT_LLVM_num_extra_inhabitants (0xfe)
 
 ; CHECK: DW_TAG_structure_type
-; CHECK: DW_AT_APPLE_num_extra_inhabitants	(0x42)
+; CHECK: DW_AT_name ("ExtraInhabitantCompositeType")
+; CHECK: DW_AT_LLVM_num_extra_inhabitants (0x42)
+
+; CHECK: DW_TAG_structure_type
+; CHECK: DW_AT_name ("NoExtraInhabitantType")
+; CHECK-NOT: DW_AT_LLVM_num_extra_inhabitants
+
 target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
 
-@p = common global i8* null, align 8, !dbg !0
-@q = common global i8* null, align 8, !dbg !8
+@p = common global i8* null, align 8, !dbg !100
+@q = common global i8* null, align 8, !dbg !102
+@r = common global i8* null, align 8, !dbg !105
 
 !llvm.dbg.cu = !{!2}
 !llvm.module.flags = !{!6, !7}
 
-!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
-!1 = distinct !DIGlobalVariable(name: "p", scope: !2, file: !3, line: 1, type: !10, isLocal: false, isDefinition: true)
 !2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, emissionKind: FullDebug, globals: !5)
 !3 = !DIFile(filename: "/tmp/p.c", directory: "/")
 !4 = !{}
-!5 = !{!0, !8}
+!5 = !{!100, !102, !105}
 !6 = !{i32 2, !"Dwarf Version", i32 4}
 !7 = !{i32 2, !"Debug Info Version", i32 3}
 
-!8 = !DIGlobalVariableExpression(var: !9, expr: !DIExpression())
-!9 = distinct !DIGlobalVariable(name: "q", scope: !2, file: !3, line: 1, type: !11, isLocal: false, isDefinition: true)
 !10 = !DIBasicType(name: "ExtraInhabitantBasicType", size: 1, encoding: DW_ATE_unsigned, num_extra_inhabitants: 254)
 !11 = !DICompositeType(tag: DW_TAG_structure_type, name: "ExtraInhabitantCompositeType", file: !3, size: 64, num_extra_inhabitants: 66, identifier: "MangledExtraInhabitantCompositeType")
+!12 = !DICompositeType(tag: DW_TAG_structure_type, name: "NoExtraInhabitantType", file: !3, size: 64, identifier: "MangledNoExtraInhabitantType")
 
+!100 = !DIGlobalVariableExpression(var: !101, expr: !DIExpression())
+!101 = distinct !DIGlobalVariable(name: "p", scope: !2, file: !3, line: 1, type: !10, isLocal: false, isDefinition: true)
+!102 = !DIGlobalVariableExpression(var: !103, expr: !DIExpression())
+!103 = distinct !DIGlobalVariable(name: "q", scope: !2, file: !3, line: 1, type: !11, isLocal: false, isDefinition: true)
+!104 = distinct !DIGlobalVariable(name: "r", scope: !2, file: !3, line: 1, type: !12, isLocal: false, isDefinition: true)
+!105 = !DIGlobalVariableExpression(var: !104, expr: !DIExpression())

llvm/unittests/IR/MetadataTest.cpp

@@ -1787,17 +1787,16 @@ TEST_F(DIBasicTypeTest, get) {
                                 26, 7, 100, DINode::FlagZero));
 
   EXPECT_NE(N, DIBasicType::get(Context, dwarf::DW_TAG_unspecified_type,
-                                "special", 33, 26, 7,100, DINode::FlagZero));
-  EXPECT_NE(N,
-            DIBasicType::get(Context, dwarf::DW_TAG_base_type, "s", 33, 26, 7, 100,
-                              DINode::FlagZero));
+                                "special", 33, 26, 7, 100, DINode::FlagZero));
+  EXPECT_NE(N, DIBasicType::get(Context, dwarf::DW_TAG_base_type, "s", 33, 26,
+                                7, 100, DINode::FlagZero));
   EXPECT_NE(N, DIBasicType::get(Context, dwarf::DW_TAG_base_type, "special", 32,
                                 26, 7, 100, DINode::FlagZero));
   EXPECT_NE(N, DIBasicType::get(Context, dwarf::DW_TAG_base_type, "special", 33,
                                 25, 7, 100, DINode::FlagZero));
 
   EXPECT_NE(N, DIBasicType::get(Context, dwarf::DW_TAG_base_type, "special", 33,
-                             26, 7, 99, DINode::FlagZero));
+                                26, 7, 99, DINode::FlagZero));
   EXPECT_NE(N, DIBasicType::get(Context, dwarf::DW_TAG_base_type, "special", 33,
                                 26, 6, 100, DINode::FlagZero));
   EXPECT_NE(N, DIBasicType::get(Context, dwarf::DW_TAG_base_type, "special", 33,