Add a comment to the InProcessThinBackend class and improve the other new class comments.

Author: bd1976bris

llvm/lib/LTO/LTO.cpp

@@ -1435,8 +1435,8 @@ Error ThinBackendProc::emitFiles(
 }
 
 namespace {
-// Base class for ThinLTO backends that perform code generation and insert the
-// generated files back into the link.
+/// Base class for ThinLTO backends that perform code generation and insert the
+/// generated files back into the link.
 class CGThinBackend : public ThinBackendProc {
 protected:
   AddStreamFn AddStream;
@@ -1464,6 +1464,8 @@ class CGThinBackend : public ThinBackendProc {
   }
 };
 
+/// This backend performs code generation by scheduling a job to run on
+/// an in-process thread when invoked for each task.
 class InProcessThinBackend : public CGThinBackend {
 protected:
   FileCache Cache;
@@ -2184,12 +2186,12 @@ std::vector<int> lto::generateModulesOrdering(ArrayRef<BitcodeModule *> R) {
 }
 
 namespace {
-// For this out-of-process backend no codegen is done when invoked for each
-// task. Instead we generate the required information (e.g. the summary index
-// shard, import list, etc..) to allow for the codegen to be performed
-// externally (similar to WriteIndexesThinBackend). This backend's `wait`
-// function then invokes an external distributor process to do backend
-// compilations.
+/// This out-of-process backend does not perform code generation when invoked
+/// for each task. Instead, it generates the necessary information (e.g., the
+/// summary index shard, import list, etc.) to enable code generation to be
+/// performed externally, similar to WriteIndexesThinBackend. The backend's
+/// `wait` function then invokes an external distributor process to carry out
+/// the backend compilations.
 class OutOfProcessThinBackend : public CGThinBackend {
   using SString = SmallString<128>;