StackPromotion: prevent resilient classes from being stack promoted.

Usually resilient classes cannot be promoted anyway, because their initializers are not visible and let the object appear to escape.
But in some rare situations this check is needed.

rdar://121558570

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/StackPromotion.swift

@@ -68,6 +68,12 @@ private func tryPromoteAlloc(_ allocRef: AllocRefInstBase,
     return false
   }
 
+  // Usually resilient classes cannot be promoted anyway, because their initializers are
+  // not visible and let the object appear to escape.
+  if allocRef.type.nominal.isResilient(in: allocRef.parentFunction) {
+    return false
+  }
+
   // The most important check: does the object escape the current function?
   if allocRef.isEscaping(context) {
     return false

test/SILOptimizer/resilience_and_stack_promotion.sil

@@ -0,0 +1,39 @@
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-frontend -parse-as-library -emit-module -o %t/Module.swiftmodule -module-name=Module %S/Inputs/public_class.swift -O
+// RUN: %target-swift-frontend -parse-as-library -emit-module -o %t/Resilient.swiftmodule -module-name=Resilient %S/Inputs/public_class.swift -O -enable-library-evolution
+
+// RUN: %target-sil-opt -stack-promotion -I %t %s | %FileCheck %s
+
+// REQUIRES: swift_in_compiler
+
+sil_stage canonical
+
+import Builtin
+import Swift
+import SwiftShims
+
+import Module
+import Resilient
+
+// CHECK-LABEL: sil @promote_non_resilient :
+// CHECK:         alloc_ref [stack] $Base
+// CHECK:       } // end sil function 'promote_non_resilient'
+sil @promote_non_resilient : $@convention(thin) () -> () {
+bb0:
+  %0 = alloc_ref $Module.Base
+  strong_release %0 : $Module.Base
+  %2 = tuple ()
+  return %2 : $()
+}
+
+// CHECK-LABEL: sil @dont_promote_resilient :
+// CHECK:         alloc_ref $Base
+// CHECK:       } // end sil function 'dont_promote_resilient'
+sil @dont_promote_resilient : $@convention(thin) () -> () {
+bb0:
+  %0 = alloc_ref $Resilient.Base
+  strong_release %0 : $Resilient.Base
+  %2 = tuple ()
+  return %2 : $()
+}