Produce specialized conformances to AnyObject for bound generic types.

Fixes rdar://31910351 (SR-4750)

Author: swiftix

lib/AST/ProtocolConformance.cpp

@@ -159,7 +159,13 @@ ProtocolConformanceRef::subst(Type origType,
     SmallVector<ProtocolConformance *, 1> lookupResults;
     classDecl->lookupConformance(classDecl->getParentModule(), proto,
                                  lookupResults);
-    return ProtocolConformanceRef(lookupResults.front());
+    auto *conf = lookupResults.front();
+    auto subMap = substType->getContextSubstitutionMap(
+        conf->getDeclContext()->getParentModule(), conf->getDeclContext());
+    if (!subMap.empty())
+      conf = substType->getASTContext().getSpecializedConformance(substType,
+                                                                  conf, subMap);
+    return ProtocolConformanceRef(conf);
   }
 
   llvm_unreachable("Invalid conformance substitution");

lib/AST/SubstitutionMap.cpp

@@ -116,7 +116,9 @@ Type SubstitutionMap::lookupSubstitution(CanSubstitutableType type) const {
   auto genericParam = cast<GenericTypeParamType>(type);
   auto mutableThis = const_cast<SubstitutionMap *>(this);
   auto replacementTypes = mutableThis->getReplacementTypes();
-  auto genericParams = getGenericSignature()->getGenericParams();
+  auto genericSig = getGenericSignature();
+  assert(genericSig);
+  auto genericParams = genericSig->getGenericParams();
   auto replacementIndex =
     GenericParamKey(genericParam).findIndexIn(genericParams);
 
@@ -133,7 +135,6 @@ Type SubstitutionMap::lookupSubstitution(CanSubstitutableType type) const {
   // The generic parameter may have been made concrete by the generic signature,
   // substitute into the concrete type.
   ModuleDecl &anyModule = *genericParam->getASTContext().getStdlibModule();
-  auto genericSig = getGenericSignature();
   if (auto concreteType = genericSig->getConcreteType(genericParam, anyModule)){
     // Set the replacement type to an error, to block infinite recursion.
     replacementType = ErrorType::get(concreteType);

test/SILOptimizer/specialized_anyobject_conformance.swift

@@ -0,0 +1,23 @@
+// RUN: %target-swift-frontend  -O -sil-inline-threshold 0 -emit-sil -primary-file %s | %FileCheck %s
+
+// rdar://problem/31910351
+
+// Check that swift compiler does not crash on this input.
+
+public protocol P {
+  func use<T:AnyObject>(_ t: T)
+}
+
+public class C<T> {
+}
+
+public func callee(_ t: C<Int32>?, _ p: P) {
+  // This call results in a creation of a specialized conformance of C<Int32> to AnyObject.
+  p.use(t!)
+}
+
+// CHECK-LABEL: sil @_T033specialized_anyobject_conformance7caller1yAA1P_p1p_tF : $@convention(thin) (@in P) -> ()
+public func caller1(p: P) {
+  callee(C<Int32>(), p)
+}
+