Do not allow Any to satisfy more specific same-type constraints.

lib/Sema/CSSimplify.cpp

@@ -1885,19 +1885,6 @@ ConstraintSystem::matchTypes(Type type1, Type type2, TypeMatchKind kind,
   // we hit commit_to_conversions below, but we have to add a token restriction
   // to ensure we wrap the metatype value in a metatype erasure.
   if (concrete && type2->isExistentialType()) {
-
-    // If we're binding to an empty existential, we need to make sure that the
-    // conversion is valid.
-    if (kind == TypeMatchKind::BindType &&
-        type2->isEmptyExistentialComposition()) {
-
-      conversionsOrFixes.push_back(ConversionRestrictionKind::Existential);
-      addConstraint(ConstraintKind::SelfObjectOfProtocol,
-                    type1, type2, getConstraintLocator(locator));
-
-      return SolutionKind::Solved;
-    }
-
     if (kind == TypeMatchKind::ConformsTo) {
       conversionsOrFixes.push_back(ConversionRestrictionKind::
                                    MetatypeToExistentialMetatype);

test/Constraints/generics.swift

@@ -236,3 +236,20 @@ Whatever.foo(a: 23) // expected-error {{generic parameter 'A' could not be infer
 // <rdar://problem/21718955> Swift useless error: cannot invoke 'foo' with no arguments
 Whatever.bar()  // expected-error {{generic parameter 'A' could not be inferred}}
 
+// <rdar://problem/27515965> Type checker doesn't enforce same-type constraint if associated type is Any
+protocol P27515965 {
+  associatedtype R
+  func f() -> R
+}
+
+struct S27515965 : P27515965 {
+  func f() -> Any { return self }
+}
+
+struct V27515965 {
+  init<T : P27515965>(_ tp: T) where T.R == Float {}
+}
+
+func test(x: S27515965) -> V27515965 {
+  return V27515965(x) // expected-error {{generic parameter 'T' could not be inferred}}
+}