AST: Simplify ProtocolConformance::getSubstitutions()

Author: slavapestov

lib/AST/ProtocolConformance.cpp

@@ -347,46 +347,19 @@ GenericSignature ProtocolConformance::getGenericSignature() const {
 }
 
 SubstitutionMap ProtocolConformance::getSubstitutions(ModuleDecl *M) const {
-  // Walk down to the base NormalProtocolConformance.
-  SubstitutionMap subMap;
-  const ProtocolConformance *parent = this;
-  while (!isa<RootProtocolConformance>(parent)) {
-    switch (parent->getKind()) {
-    case ProtocolConformanceKind::Normal:
-    case ProtocolConformanceKind::Self:
-    case ProtocolConformanceKind::Builtin:
-      llvm_unreachable("should have exited the loop?!");
-    case ProtocolConformanceKind::Inherited:
-      parent =
-          cast<InheritedProtocolConformance>(parent)->getInheritedConformance();
-      break;
-    case ProtocolConformanceKind::Specialized: {
-      auto SC = cast<SpecializedProtocolConformance>(parent);
-      parent = SC->getGenericConformance();
-      assert(subMap.empty() && "multiple conformance specializations?!");
-      subMap = SC->getSubstitutionMap();
-      break;
-    }
-    }
-  }
+  const ProtocolConformance *conformance = this;
 
-  // Found something; we're done!
-  if (!subMap.empty())
-    return subMap;
+  if (auto *inheritedC = dyn_cast<InheritedProtocolConformance>(conformance))
+    conformance = inheritedC->getInheritedConformance();
 
-  // If the normal conformance is for a generic type, and we didn't hit a
-  // specialized conformance, collect the substitutions from the generic type.
-  // FIXME: The AST should do this for us.
-  const NormalProtocolConformance *normalC =
-      dyn_cast<NormalProtocolConformance>(parent);
-  if (!normalC)
-    return SubstitutionMap();
+  if (auto *specializedC = dyn_cast<SpecializedProtocolConformance>(conformance))
+    return specializedC->getSubstitutionMap();
 
-  if (!normalC->getType()->isSpecialized())
-    return SubstitutionMap();
+  auto *rootC = cast<RootProtocolConformance>(conformance);
+  if (auto genericSig = rootC->getGenericSignature())
+    return genericSig->getIdentitySubstitutionMap();
 
-  auto *DC = normalC->getDeclContext();
-  return normalC->getType()->getContextSubstitutionMap(M, DC);
+  return SubstitutionMap();
 }
 
 bool RootProtocolConformance::isInvalid() const {