[AST] Teach SpecializedProtocolConformance to profile its substitutions.

Otherwise, we could theoretically get collisions, although they are
quite unlikely to matter in practice.

Author: DougGregor

include/swift/AST/ProtocolConformance.h

@@ -589,17 +589,16 @@ class SpecializedProtocolConformance : public ProtocolConformance,
   }
 
   void Profile(llvm::FoldingSetNodeID &ID) {
-    Profile(ID, getType(), getGenericConformance());
+    Profile(ID, getType(), getGenericConformance(),
+            getGenericSubstitutions());
   }
 
   static void Profile(llvm::FoldingSetNodeID &ID, Type type,
-                      ProtocolConformance *genericConformance) {
-    // FIXME: Consider profiling substitutions here. They could differ in
-    // some crazy cases that also require major diagnostic work, where the
-    // substitutions involve conformances of the same type to the same
-    // protocol drawn from different imported modules.
+                      ProtocolConformance *genericConformance,
+                      SubstitutionList subs) {
     ID.AddPointer(type.getPointer());
     ID.AddPointer(genericConformance);
+    profileSubstitutionList(ID, subs);
   }
 
   static bool classof(const ProtocolConformance *conformance) {

include/swift/AST/SubstitutionList.h

@@ -21,6 +21,11 @@
 
 #include "swift/AST/Substitution.h"
 #include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/FoldingSet.h"
+
+namespace llvm {
+class FoldingSetNodeID;
+} // end namespace llvm
 
 namespace swift {
 
@@ -41,6 +46,10 @@ void dump(SubstitutionList subs);
 SubstitutionList
 getCanonicalSubstitutionList(SubstitutionList subs,
                              SmallVectorImpl<Substitution> &canSubs);
+
+/// Profile the substitution list for use in a folding set.
+void profileSubstitutionList(llvm::FoldingSetNodeID &id, SubstitutionList subs);
+
 } // end namespace swift
 
 #endif

lib/AST/ASTContext.cpp

@@ -1528,7 +1528,7 @@ ASTContext::getSpecializedConformance(Type type,
                                       ProtocolConformance *generic,
                                       SubstitutionList substitutions) {
   llvm::FoldingSetNodeID id;
-  SpecializedProtocolConformance::Profile(id, type, generic);
+  SpecializedProtocolConformance::Profile(id, type, generic, substitutions);
 
   // Figure out which arena this conformance should go into.
   AllocationArena arena = getArena(type->getRecursiveProperties());

lib/AST/SubstitutionList.cpp

@@ -17,5 +17,17 @@
 //===----------------------------------------------------------------------===//
 
 #include "swift/AST/SubstitutionList.h"
+#include "swift/AST/ProtocolConformanceRef.h"
+#include "llvm/ADT/FoldingSet.h"
 
 using namespace swift;
+
+void swift::profileSubstitutionList(llvm::FoldingSetNodeID &id,
+                                    SubstitutionList subs) {
+  id.AddInteger(subs.size());
+  for (auto &sub : subs) {
+    id.AddPointer(sub.getReplacement().getPointer());
+    for (auto conformance : sub.getConformances())
+      id.AddPointer(conformance.getOpaqueValue());
+  }
+}

lib/AST/Type.cpp

@@ -4060,11 +4060,7 @@ bool TypeBase::usesNativeReferenceCounting(ResilienceExpansion resilience) {
 void SILBoxType::Profile(llvm::FoldingSetNodeID &id, SILLayout *Layout,
                          SubstitutionList Args) {
   id.AddPointer(Layout);
-  for (auto &arg : Args) {
-    id.AddPointer(arg.getReplacement().getPointer());
-    for (auto conformance : arg.getConformances())
-      id.AddPointer(conformance.getOpaqueValue());
-  }
+  profileSubstitutionList(id, Args);
 }
 
 SILBoxType::SILBoxType(ASTContext &C,