Don't eliminate begin_access [signed] in AccessMarkerElimination

Author: meg-gupta

lib/SILOptimizer/Mandatory/AccessMarkerElimination.cpp

@@ -77,8 +77,10 @@ bool AccessMarkerElimination::shouldPreserveAccess(
   switch (enforcement) {
   case SILAccessEnforcement::Static:
   case SILAccessEnforcement::Unsafe:
-  case SILAccessEnforcement::Signed:
     return false;
+  // Signed access should be preserved until IRGen
+  case SILAccessEnforcement::Signed:
+    return true;
   case SILAccessEnforcement::Unknown:
   case SILAccessEnforcement::Dynamic:
     return Mod->getOptions().EnforceExclusivityDynamic;
@@ -100,7 +102,7 @@ AccessMarkerElimination::checkAndEliminateMarker(SILInstruction *inst) {
     if (beginAccess->isFromBuiltin())
       return inst->getIterator();
 
-    // Leave dynamic accesses in place, but delete all others.
+    // Leave dynamic and signed accesses in place, but delete all others.
     if (shouldPreserveAccess(beginAccess->getEnforcement()))
       return inst->getIterator();