[DebugInfo] Add num_extra_inhabitants to debug info (#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.

1 files changed, 9 insertions, 7 deletions

diff --git a/llvm/lib/Bitcode/Reader/MetadataLoader.cpp b/llvm/lib/Bitcode/Reader/MetadataLoader.cpp
index ada1597..8ca46a4 100644
--- a/llvm/lib/Bitcode/Reader/MetadataLoader.cpp
+++ b/llvm/lib/Bitcode/Reader/MetadataLoader.cpp
@@ -1525,18 +1525,19 @@ Error MetadataLoader::MetadataLoaderImpl::parseOneMetadata(
     break;
   }
   case bitc::METADATA_BASIC_TYPE: {
-    if (Record.size() < 6 || Record.size() > 7)
+    if (Record.size() < 6 || Record.size() > 8)
       return error("Invalid record");
 
     IsDistinct = Record[0];
     DINode::DIFlags Flags = (Record.size() > 6)
                                 ? static_cast<DINode::DIFlags>(Record[6])
                                 : DINode::FlagZero;
+    uint32_t NumExtraInhabitants = (Record.size() > 7) ? Record[7] : 0;
 
     MetadataList.assignValue(
         GET_OR_DISTINCT(DIBasicType,
                         (Context, Record[1], getMDString(Record[2]), Record[3],
-                         Record[4], Record[5], Flags)),
+                         Record[4], Record[5], NumExtraInhabitants, Flags)),
         NextMetadataNo);
     NextMetadataNo++;
     break;
@@ -1599,7 +1600,7 @@ Error MetadataLoader::MetadataLoaderImpl::parseOneMetadata(
     break;
   }
   case bitc::METADATA_COMPOSITE_TYPE: {
-    if (Record.size() < 16 || Record.size() > 22)
+    if (Record.size() < 16 || Record.size() > 23)
       return error("Invalid record");
 
     // If we have a UUID and this is not a forward declaration, lookup the
@@ -1617,6 +1618,7 @@ Error MetadataLoader::MetadataLoaderImpl::parseOneMetadata(
       return error("Alignment value is too large");
     uint32_t AlignInBits = Record[8];
     uint64_t OffsetInBits = 0;
+    uint32_t NumExtraInhabitants = (Record.size() > 22) ? Record[22] : 0;
     DINode::DIFlags Flags = static_cast<DINode::DIFlags>(Record[10]);
     Metadata *Elements = nullptr;
     unsigned RuntimeLang = Record[12];
@@ -1681,9 +1683,9 @@ Error MetadataLoader::MetadataLoaderImpl::parseOneMetadata(
     if (Identifier)
       CT = DICompositeType::buildODRType(
           Context, *Identifier, Tag, Name, File, Line, Scope, BaseType,
-          SizeInBits, AlignInBits, OffsetInBits, Flags, Elements, RuntimeLang,
-          VTableHolder, TemplateParams, Discriminator, DataLocation, Associated,
-          Allocated, Rank, Annotations);
+          SizeInBits, AlignInBits, OffsetInBits, NumExtraInhabitants, Flags,
+          Elements, RuntimeLang, VTableHolder, TemplateParams, Discriminator,
+          DataLocation, Associated, Allocated, Rank, Annotations);
 
     // Create a node if we didn't get a lazy ODR type.
     if (!CT)
@@ -1692,7 +1694,7 @@ Error MetadataLoader::MetadataLoaderImpl::parseOneMetadata(
                             SizeInBits, AlignInBits, OffsetInBits, Flags,
                             Elements, RuntimeLang, VTableHolder, TemplateParams,
                             Identifier, Discriminator, DataLocation, Associated,
-                            Allocated, Rank, Annotations));
+                            Allocated, Rank, Annotations, NumExtraInhabitants));
     if (!IsNotUsedInTypeRef && Identifier)
       MetadataList.addTypeRef(*Identifier, *cast<DICompositeType>(CT));