AST: Simplify SubstitutionMap::lookupSubstitution()

Author: slavapestov

include/swift/AST/SubstitutionMap.h

@@ -277,7 +277,7 @@ class SubstitutionMap {
   /// Note that this only finds replacements for maps that are directly
   /// stored inside the map. In most cases, you should call Type::subst()
   /// instead, since that will resolve member types also.
-  Type lookupSubstitution(CanSubstitutableType type) const;
+  Type lookupSubstitution(GenericTypeParamType *type) const;
 };
 
 inline llvm::raw_ostream &operator<<(llvm::raw_ostream &OS,

lib/AST/GenericEnvironment.cpp

@@ -739,10 +739,7 @@ GenericEnvironment::mapElementTypeIntoPackContext(Type type) const {
   QueryInterfaceTypeSubstitutions mapIntoContext(this);
   return type.subst(
       [&](SubstitutableType *type) {
-        auto *genericParam = type->getAs<GenericTypeParamType>();
-        if (!genericParam)
-          return Type();
-
+        auto *genericParam = cast<GenericTypeParamType>(type);
         if (genericParam->getDepth() == elementDepth) {
           genericParam = members[genericParam->getIndex()];
           assert(genericParam->isParameterPack());
@@ -772,7 +769,7 @@ class BuildForwardingSubstitutions {
 
 Type BuildForwardingSubstitutions::operator()(SubstitutableType *type) const {
   if (auto resultType = Query(type)) {
-    auto param = type->castTo<GenericTypeParamType>();
+    auto param = cast<GenericTypeParamType>(type);
     if (!param->isParameterPack())
       return resultType;
     if (resultType->is<PackType>())

lib/AST/SubstitutionMap.cpp

@@ -154,10 +154,7 @@ SubstitutionMap SubstitutionMap::get(GenericSignature genericSig,
     return SubstitutionMap();
 
   return SubstitutionMap::get(genericSig,
-           [&](SubstitutableType *type) -> Type {
-             return substitutions.lookupSubstitution(
-                cast<SubstitutableType>(type->getCanonicalType()));
-           },
+           QuerySubstitutionMap{substitutions},
            LookUpConformanceInSubstitutionMap(substitutions));
 }
 
@@ -213,29 +210,13 @@ SubstitutionMap SubstitutionMap::get(GenericSignature genericSig,
   return SubstitutionMap(genericSig, replacementTypes, conformances);
 }
 
-Type SubstitutionMap::lookupSubstitution(CanSubstitutableType type) const {
+Type SubstitutionMap::lookupSubstitution(GenericTypeParamType *genericParam) const {
   if (empty())
     return Type();
 
-  // If we have an archetype, map out of the context so we can compute a
-  // conformance access path.
-  if (auto archetype = dyn_cast<ArchetypeType>(type)) {
-    // Only consider root archetypes.
-    if (!archetype->isRoot())
-      return Type();
-
-    if (!isa<PrimaryArchetypeType>(archetype) &&
-        !isa<PackArchetypeType>(archetype))
-      return Type();
-
-    type = cast<GenericTypeParamType>(
-      archetype->getInterfaceType()->getCanonicalType());
-  }
-
   // Find the index of the replacement type based on the generic parameter we
   // have.
   GenericSignature genericSig = getGenericSignature();
-  auto genericParam = cast<GenericTypeParamType>(type);
   auto genericParams = genericSig.getGenericParams();
   auto replacementIndex =
     GenericParamKey(genericParam).findIndexIn(genericParams);

lib/AST/TypeSubstitution.cpp

@@ -55,8 +55,7 @@ Type QueryTypeSubstitutionMap::operator()(SubstitutableType *type) const {
 }
 
 Type QuerySubstitutionMap::operator()(SubstitutableType *type) const {
-  auto key = cast<SubstitutableType>(type->getCanonicalType());
-  return subMap.lookupSubstitution(key);
+  return subMap.lookupSubstitution(cast<GenericTypeParamType>(type));
 }
 
 FunctionType *