[CAS] Add LLVMCAS library with InMemoryCAS implementation

llvm/docs/ContentAddressableStorage.md

@@ -2,11 +2,11 @@
 
 ## Introduction to CAS
 
-Content Addressable Storage, or `CAS`, is a storage system where it assigns
+Content Addressable Storage, or `CAS`, is a storage system that assigns
 unique addresses to the data stored. It is very useful for data deduplicaton
 and creating unique identifiers.
 
-Unlike other kinds of storage system like a file system, CAS is immutable. It
+Unlike other kinds of storage systems like file systems, CAS is immutable. It
 is more reliable to model a computation by representing the inputs and outputs
 of the computation using objects stored in CAS.
 
@@ -24,7 +24,7 @@ struct CASObject {
 }
 ```
 
-With this abstraction, it is possible to compose CASObjects into a DAG that is
+With this abstraction, it is possible to compose `CASObject`s into a DAG that is
 capable of representing complicated data structures, while still allowing data
 deduplication. Note you can compare two DAGs by just comparing the CASObject
 hash of two root nodes.

llvm/docs/Reference.rst

@@ -242,5 +242,9 @@ Additional Topics
    A description of uniformity analysis in the presence of irreducible
    control flow, and its implementation.
 
+:doc:`MLGO`
+   Facilities for ML-Guided Optimization, such as collecting IR corpora from a
+   build, interfacing with ML models, an exposing features for training.
+
 :doc:`ContentAddressableStorage`
    A reference guide for using LLVM's CAS library.

llvm/include/llvm/CAS/BuiltinCASContext.h

@@ -54,6 +54,7 @@ namespace llvm::cas::builtin {
 using HasherT = BLAKE3;
 using HashType = decltype(HasherT::hash(std::declval<ArrayRef<uint8_t> &>()));
 
+/// CASContext for LLVM builtin CAS using BLAKE3 hash type.
 class BuiltinCASContext : public CASContext {
   void printIDImpl(raw_ostream &OS, const CASID &ID) const final;
   void anchor() override;

llvm/include/llvm/CAS/BuiltinObjectHasher.h

@@ -14,6 +14,7 @@
 
 namespace llvm::cas {
 
+/// Hasher for stored objects in builtin CAS.
 template <class HasherT> class BuiltinObjectHasher {
 public:
   using HashT = decltype(HasherT::hash(std::declval<ArrayRef<uint8_t> &>()));

llvm/lib/CAS/BuiltinCAS.h

@@ -17,6 +17,7 @@ namespace llvm::cas {
 class ActionCache;
 namespace builtin {
 
+/// Common base class for builtin CAS implementations using the same CASContext.
 class BuiltinCAS : public ObjectStore {
 public:
   BuiltinCAS() : ObjectStore(BuiltinCASContext::getDefaultContext()) {}

llvm/lib/CAS/InMemoryCAS.cpp

@@ -33,6 +33,7 @@ using InMemoryIndexT =
 /// their hash.
 using InMemoryIndexValueT = InMemoryIndexT::value_type;
 
+/// Builtin InMemory CAS that stores CAS object in the memory.
 class InMemoryObject {
 public:
   enum class Kind {