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

flag.

(cherry picked from commit de78fd4)

Author: hborla

include/swift/Option/FrontendOptions.td

@@ -1352,11 +1352,6 @@ 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

@@ -535,10 +535,6 @@ 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));
 };
 
 /// Regular expression corresponding to the value given in one of the
@@ -706,8 +702,7 @@ int sil_opt_main(ArrayRef<const char *> argv, void *MainAddr) {
   if (options.StrictConcurrencyLevel.hasArgStr()) {
     Invocation.getLangOptions().StrictConcurrencyLevel =
         options.StrictConcurrencyLevel;
-    if (options.StrictConcurrencyLevel == StrictConcurrency::Complete &&
-        !options.DisableRegionBasedIsolationWithStrictConcurrency) {
+    if (options.StrictConcurrencyLevel == StrictConcurrency::Complete) {
       Invocation.getLangOptions().enableFeature(Feature::RegionBasedIsolation);
     }
   }

lib/Frontend/CompilerInvocation.cpp

@@ -1098,16 +1098,7 @@ 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 =