AST: Introduce GenericSignatureImpl::getRequirementMachine()

Author: slavapestov

include/swift/AST/GenericSignature.h

@@ -33,6 +33,7 @@ namespace swift {
 class GenericSignatureBuilder;
 class ProtocolConformanceRef;
 class ProtocolType;
+class RequirementMachine;
 class SubstitutionMap;
 class GenericEnvironment;
 
@@ -303,6 +304,9 @@ class alignas(1 << TypeAlignInBits) GenericSignatureImpl final
   /// Retrieve the generic signature builder for the given generic signature.
   GenericSignatureBuilder *getGenericSignatureBuilder() const;
 
+  /// Retrieve the requirement machine for the given generic signature.
+  RequirementMachine *getRequirementMachine() const;
+
   /// Returns the generic environment that provides fresh contextual types
   /// (archetypes) that correspond to the interface types in this generic
   /// signature.

lib/AST/GenericSignature.cpp

@@ -22,6 +22,7 @@
 #include "swift/AST/GenericEnvironment.h"
 #include "swift/AST/Module.h"
 #include "swift/AST/PrettyStackTrace.h"
+#include "swift/AST/RequirementMachine.h"
 #include "swift/AST/Types.h"
 #include "swift/Basic/STLExtras.h"
 #include <functional>
@@ -166,6 +167,17 @@ GenericSignatureImpl::getGenericSignatureBuilder() const {
                                              CanGenericSignature(this));
 }
 
+RequirementMachine *
+GenericSignatureImpl::getRequirementMachine() const {
+  // The requirement machine is associated with the canonical signature.
+  if (!isCanonical())
+    return getCanonicalSignature()->getRequirementMachine();
+
+  // Requirement machines are stored on the ASTContext.
+  return getASTContext().getOrCreateRequirementMachine(
+                                             CanGenericSignature(this));
+}
+
 bool GenericSignatureImpl::isEqual(GenericSignature Other) const {
   return getCanonicalSignature() == Other.getCanonicalSignature();
 }