[semantic-arc-opts] Make sure to only run this pass when optimization is enabled even though it is running during the mandatory passes (for now).

The idea is that eventually down the line we will split this pass into a
mandatory/performance parts once ownership SSA is eliminated after the
guaranteed passes run. For now though, just run this when optimization is
enabled.

This pass only runs on the stdlib/overlays so far so there shouldn't have been
any slow downs in non-stdlib -Onone builds.

Author: gottesmm

lib/SILOptimizer/PassManager/PassPipeline.cpp

@@ -92,7 +92,14 @@ static void addMandatoryOptPipeline(SILPassPipelinePlan &P,
   P.addAllocBoxToStack();
   P.addNoReturnFolding();
   addDefiniteInitialization(P);
-  if (Options.EnableMandatorySemanticARCOpts) {
+  // Only run semantic arc opts if we are optimizing and if mandatory semantic
+  // arc opts is explicitly enabled.
+  //
+  // NOTE: Eventually this pass will be split into a mandatory/more aggressive
+  // pass. This will happen when OSSA is no longer eliminated before the
+  // optimizer pipeline is run implying we can put a pass that requires OSSA
+  // there.
+  if (Options.EnableMandatorySemanticARCOpts && Options.shouldOptimize()) {
     P.addSemanticARCOpts();
   }
   P.addClosureLifetimeFixup();