AST: Fix some comments

Author: slavapestov

lib/AST/ASTContext.cpp

@@ -5754,7 +5754,7 @@ ProtocolConformanceRef ProtocolConformanceRef::forAbstract(
     properties |= conformingType->getRecursiveProperties();
   auto arena = getArena(properties);
 
-  // Profile the substitution map.
+  // Form the folding set key.
   llvm::FoldingSetNodeID id;
   AbstractConformance::Profile(id, conformingType, proto);
 

lib/AST/AbstractConformance.h

@@ -10,8 +10,9 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// This file defines the AbstractConformance class, which stores an
-// abstract conformance that is stashed in a ProtocolConformanceRef.
+// This file defines the AbstractConformance class, which represents
+// the conformance of a type parameter or archetype to a protocol.
+// These are usually stashed inside a ProtocolConformanceRef.
 //
 //===----------------------------------------------------------------------===//
 #ifndef SWIFT_AST_ABSTRACT_CONFORMANCE_H
@@ -36,7 +37,7 @@ class AbstractConformance final : public llvm::FoldingSetNode {
     Profile(id, getType(), getProtocol());
   }
 
-  /// Profile the substitution map storage, for use with LLVM's FoldingSet.
+  /// Profile the storage for this conformance, for use with LLVM's FoldingSet.
   static void Profile(llvm::FoldingSetNodeID &id,
                       Type conformingType,
                       ProtocolDecl *requirement) {