PerformanceDiagnostics: diagnose dynamic casts

Dynamic casts need metadata and therefore cannot be used in embedded swift.
Fixes an internal IRGen error.

Author: eeckstein

include/swift/AST/DiagnosticsSIL.def

@@ -390,6 +390,8 @@ ERROR(embedded_swift_metatype,none,
       "cannot use metatype in embedded Swift", ())
 ERROR(embedded_swift_keypath,none,
       "cannot use key path in embedded Swift", ())
+ERROR(embedded_swift_dynamic_cast,none,
+      "cannot do dynamic casting in embedded Swift", ())
 ERROR(embedded_swift_allocating_type,none,
       "cannot use allocating type %0 in -no-allocations mode", (Type))
 ERROR(embedded_swift_allocating,none,

lib/SILOptimizer/Mandatory/PerformanceDiagnostics.cpp

@@ -526,6 +526,10 @@ bool PerformanceDiagnostics::visitInst(SILInstruction *inst,
         diagnose(loc, diag::embedded_swift_keypath);
         return true;
       }
+      if (isa<CheckedCastAddrBranchInst>(inst) || isa<UnconditionalCheckedCastAddrInst>(inst)) {
+        diagnose(loc, diag::embedded_swift_dynamic_cast);
+        return true;
+      }
       if (!allowedMetadataUseInEmbeddedSwift(inst)) {
         PrettyStackTracePerformanceDiagnostics stackTrace("metatype", inst);
         if (impactType) {

test/embedded/metatypes.swift

@@ -11,3 +11,13 @@ public func test() -> Int {
   sink(t: metatype)
   return 42
 }
+
+func castToExistential<T>(x: T) {
+  if x is any FixedWidthInteger {    // expected-error {{cannot do dynamic casting in embedded Swift}}
+  }
+}
+
+func callCastToExistential() {
+  castToExistential(x: 42)    // expected-note {{called from here}}
+}
+