Update ConditionForwarding for @guaranteed forwarding phi support

Author: meg-gupta

lib/SILOptimizer/Transforms/ConditionForwarding.cpp

@@ -202,6 +202,14 @@ bool ConditionForwarding::tryOptimize(SwitchEnumInst *SEI) {
     if (!EI)
       return false;
 
+    if (getFunction()->hasOwnership() && EI->hasOperand()) {
+      auto some = EI->getOperand();
+      if (some->getOwnershipKind() == OwnershipKind::Guaranteed &&
+          isa<SILFunctionArgument>(some)) {
+        return false;
+      }
+    }
+
     if (CommonBranchBlock && PredPred != CommonBranchBlock)
       return false;
     CommonBranchBlock = PredPred;

test/SILOptimizer/conditionforwarding_nontrivial_ossa.sil

@@ -71,7 +71,8 @@ bb6:
   return %r : $()
 }
 
-// Currently, this is not optimized away because memory behavior of begin_borrow is conservative
+// Currently, this is not optimized away because enum has @guaranteed function argument, which 
+// will need a borrow scope before being forwarded
 // CHECK-LABEL: sil [ossa] @simple_forwarding2 :
 // CHECK: switch_enum
 // CHECK-LABEL: } // end sil function 'simple_forwarding2'