Simplification: check for isolated conformances when simplifying metatype casts

rdar://147417762

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyCheckedCast.swift

@@ -81,7 +81,9 @@ private extension UnconditionalCheckedCastInst {
       return
     }
     let conformance = sourceFormalType.instanceTypeOfMetatype.checkConformance(to: proto)
-    guard conformance.isValid else {
+    guard conformance.isValid,
+          conformance.matchesActorIsolation(in: parentFunction)
+    else {
       return
     }
 

test/SILOptimizer/simplify_unconditional_check_cast.sil

@@ -1,7 +1,11 @@
-// RUN: %target-sil-opt -enable-sil-verify-all %s -simplification -simplify-instruction=unconditional_checked_cast | %FileCheck %s
+// RUN: %target-sil-opt -enable-sil-verify-all %s -simplification -simplify-instruction=unconditional_checked_cast -enable-experimental-feature IsolatedConformances | %FileCheck %s
+
+// REQUIRES: swift_feature_IsolatedConformances
+// REQUIRES: concurrency
 
 import Swift
 import Builtin
+import _Concurrency
 
 protocol P {}
 protocol PC: AnyObject {}
@@ -12,6 +16,8 @@ struct T {}
 
 class C {}
 
+struct X : @MainActor P {}
+
 // CHECK-LABEL: sil [ossa] @test_conforming_struct :
 // CHECK:         %1 = init_existential_metatype %0, $@thick any P.Type
 // CHECK-NEXT:    return %1
@@ -52,3 +58,14 @@ bb0(%0 : $@thick S.Type):
   %1 = unconditional_checked_cast %0 to Int.Type
   return %1
 }
+
+// CHECK-LABEL: sil [ossa] @test_isolated_conformance :
+// CHECK:         %1 = unconditional_checked_cast %0
+// CHECK-NEXT:    return %1
+// CHECK:       } // end sil function 'test_isolated_conformance'
+sil [ossa] @test_isolated_conformance : $@convention(thin) (@thick X.Type) -> @thick any P.Type {
+bb0(%0 : $@thick X.Type):
+  %1 = unconditional_checked_cast %0 to any P.Type
+  return %1
+}
+