[DirectX] Start documenting DXIL Resource handling

clang/docs/HLSL/HLSLIRReference.rst

@@ -11,15 +11,6 @@ Introduction
 The goal of this document is to provide a reference for all the special purpose
 IR metadata and attributes used by the HLSL code generation path.
 
-IR Metadata
-===========
-
-``hlsl.uavs``
--------------
-
-The ``hlsl.uavs`` metadata is a list of all the external global variables that
-represent UAV resources.
-
 Function Attributes
 ===================
 

clang/docs/HLSL/ResourceTypes.rst

@@ -19,16 +19,15 @@ In Clang resource types are forward declared by the ``HLSLExternalSemaSource``
 on initialization. They are then lazily completed when ``requiresCompleteType``
 is called later in Sema.
 
-Resource types are templated class declarations. The template parameter
-specifies the expected return type of resource loads, and the expected parameter
-type for stores.
-
-In Clang's AST and code generation, resource types are classes that store a
-pointer of the template parameter type. The pointer is populated from a call to
-``__builtin_hlsl_create_handle``, and treated as a pointer to an array of typed
-data through until lowering in the backend.
-
-Resource types are annotated with the ``HLSLResource`` attribute, which drives
-code generation for resource binding metadata. The ``hlsl`` metadata nodes are
-transformed in the backend to the binding information expected by the target
-runtime.
+Resource types are classes that have the "intangible" resource handle type,
+`__hlsl_resource_t`, as a member. These are generally templated class
+declarations that specify the type of data that can be loaded from or stored
+into the resource. The handle is annotated with hlsl-specific attributes
+describing properties of the resource. Member functions of a resource type are
+generally fairly simple wrappers around builtins that operate on the handle
+member.
+
+During code generation resource types are lowered to target extension types in
+IR. These types are target specific and differ between DXIL and SPIR-V
+generation, providing the necessary information for the targets to generate
+binding metadata for their respective target runtimes.