SILOptimizer: Fix exclusivity checking crash when passing 'nil' as optional noescape closure

Author: slavapestov

lib/SIL/InstructionUtils.cpp

@@ -554,8 +554,13 @@ FindClosureResult swift::findClosureForAppliedArg(SILValue V) {
   if (auto *bbi = dyn_cast<BeginBorrowInst>(V))
     V = bbi->getOperand();
 
-  if (V->getType().getOptionalObjectType())
-    V = cast<EnumInst>(V)->getOperand();
+  if (V->getType().getOptionalObjectType()) {
+    auto *EI = dyn_cast<EnumInst>(V);
+    if (!EI || !EI->hasOperand())
+      return FindClosureResult(nullptr, false);
+
+    V = EI->getOperand();
+  }
 
   auto fnType = V->getType().getAs<SILFunctionType>();
   if (fnType->getRepresentation() == SILFunctionTypeRepresentation::Block) {

test/SILOptimizer/exclusivity_static_diagnostics.sil

@@ -878,3 +878,14 @@ bb0(%0 : $Int):
   %10 = tuple ()
   return %10 : $()
 }
+
+sil hidden @passNilToNoEscape : $@convention(thin) (Int) -> () {
+bb0( %0 : $Int):
+  %2 = alloc_box ${ var Int }
+  %3 = project_box %2 : ${ var Int }, 0
+  %4 = enum $Optional<@convention(block) @noescape () -> ()>, #Optional.none!enumelt
+  %5 = function_ref @takesInoutAndNoEscapeOptionalBlockClosure : $@convention(thin) (@inout Int, @owned Optional<@convention(block) @noescape () -> ()>) -> ()
+  %6 = apply %5(%3, %4) : $@convention(thin) (@inout Int, @owned Optional<@convention(block) @noescape () -> ()>) -> ()
+  %7 = tuple ()
+  return %7 : $()
+}