[Concurrency] Remove the disable-region-based-isolation-with-strict-concurrency

flag.

Author: hborla

include/swift/Option/FrontendOptions.td

@@ -1371,11 +1371,6 @@ def disable_experimental_parser_round_trip : Flag<["-"],
   "disable-experimental-parser-round-trip">,
   HelpText<"Disable round trip through the new swift parser">;
 
-def disable_strict_concurrency_region_based_isolation : Flag<["-"],
-  "disable-region-based-isolation-with-strict-concurrency">,
-  HelpText<"Disable region based isolation when running with strict concurrency enabled. Only enabled with asserts">,
-  Flags<[HelpHidden]>;
-
 def disable_transferring_args_and_results_with_region_isolation : Flag<["-"],
   "disable-transferring-args-and-results-with-region-based-isolation">,
   HelpText<"Disable transferring args and results when region based isolation is enabled. Only enabled with asserts">,

lib/DriverTool/sil_opt_main.cpp

@@ -571,11 +571,6 @@ struct SILOptOptions {
       "Xcc",
       llvm::cl::desc("option to pass to clang"));
 
-  llvm::cl::opt<bool> DisableRegionBasedIsolationWithStrictConcurrency =
-      llvm::cl::opt<bool>(
-          "disable-region-based-isolation-with-strict-concurrency",
-          llvm::cl::init(false));
-
   llvm::cl::opt<std::string> SwiftVersionString = llvm::cl::opt<std::string>(
       "swift-version",
       llvm::cl::desc(
@@ -789,8 +784,7 @@ int sil_opt_main(ArrayRef<const char *> argv, void *MainAddr) {
 
   // If we have strict concurrency set as a feature and were told to turn off
   // region based isolation... do so now.
-  if (Invocation.getLangOptions().hasFeature(Feature::StrictConcurrency) &&
-      !options.DisableRegionBasedIsolationWithStrictConcurrency) {
+  if (Invocation.getLangOptions().hasFeature(Feature::StrictConcurrency)) {
     Invocation.getLangOptions().enableFeature(Feature::RegionBasedIsolation);
   }
 

lib/Frontend/CompilerInvocation.cpp

@@ -1101,16 +1101,7 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   if (Opts.StrictConcurrencyLevel == StrictConcurrency::Complete) {
     Opts.enableFeature(Feature::IsolatedDefaultValues);
     Opts.enableFeature(Feature::GlobalConcurrency);
-
-    // If asserts are enabled, allow for region based isolation to be disabled
-    // with a flag. This is intended only to be used with tests.
-    bool enableRegionIsolation = true;
-#ifndef NDEBUG
-    enableRegionIsolation =
-        !Args.hasArg(OPT_disable_strict_concurrency_region_based_isolation);
-#endif
-    if (enableRegionIsolation)
-      Opts.enableFeature(Feature::RegionBasedIsolation);
+    Opts.enableFeature(Feature::RegionBasedIsolation);
   }
 
   Opts.WarnImplicitOverrides =