SILGen: Don't emit property descriptors for ~Escapable types.

Key paths can't reference them, so we don't need to refer to them resiliently.
Fixes rdar://151628396.

Author: jckarter

lib/SIL/IR/SIL.cpp

@@ -344,7 +344,7 @@ static bool isUnsupportedKeyPathValueType(Type ty) {
   // They would also need a new ABI that's yet to be implemented in order to
   // be properly supported, so let's suppress the descriptor for now if either
   // the container or storage type of the declaration is non-copyable.
-  if (ty->isNoncopyable())
+  if (ty->isNoncopyable() || !ty->isEscapable())
     return true;
 
   return false;
@@ -356,7 +356,7 @@ bool AbstractStorageDecl::exportsPropertyDescriptor() const {
 
   if (!isStatic()) {
     if (auto contextTy = getDeclContext()->getDeclaredTypeInContext()) {
-      if (contextTy->isNoncopyable()) {
+      if (contextTy->isNoncopyable() || !contextTy->isEscapable()) {
         return false;
       }
     }

test/SILOptimizer/lifetime_dependence/verify_library_diagnostics.swift

@@ -29,16 +29,8 @@ public struct NEImmortal: ~Escapable {
 
 class C {}
 
-// Test diagnostics on keypath getter.
-//
-// rdar://150073405 ([SILGen] support synthesized _modify on top of borrowed getters with library evolution)
-//
-// This produces the error:
-// <unknown>:0: error: unexpected error produced: lifetime-dependent value returned by generated thunk
-// '$s4test17ImplicitAccessorsV10neComputedAA10NEImmortalVvpACTK'
-//
-// Since this error has no source file, we can't verify the diagnostic!
-/*
+// Test that we don't implicitly try to create a keypath getter, since
+// ~Escapable types are not yet supported by keypaths.
 public struct ImplicitAccessors {
   let c: C
 
@@ -50,7 +42,6 @@ public struct ImplicitAccessors {
     }
   }
 }
- */
 
 public struct NoncopyableImplicitAccessors : ~Copyable & ~Escapable {
   public var ne: NE