ClosureLifetimeFixup: Don't insert dealloc_stack at unreachable

Author: aschwaighofer

lib/SILOptimizer/Mandatory/ClosureLifetimeFixup.cpp

@@ -297,6 +297,9 @@ static bool tryRewriteToPartialApplyStack(
   // Insert destroys of arguments after the apply and the dealloc_stack.
   if (auto *Apply = dyn_cast<ApplyInst>(singleApplyUser)) {
     auto InsertPt = std::next(SILBasicBlock::iterator(Apply));
+    // Don't insert dealloc_stacks at unreachable.
+    if (isa<UnreachableInst>(*InsertPt))
+      return true;
     SILBuilderWithScope B3(InsertPt);
     B3.createDeallocStack(loc, newPA);
     insertDestroyOfCapturedArguments(newPA, B3);
@@ -684,6 +687,7 @@ class ClosureLifetimeFixup : public SILFunctionTransform {
 
     bool checkStackNesting = false;
     bool modifiedCFG = false;
+
     if (fixupClosureLifetimes(*getFunction(), checkStackNesting)) {
       if (checkStackNesting){
         StackNesting SN;

test/SILOptimizer/closure_lifetime_fixup.swift

@@ -99,3 +99,8 @@ public func dontCrash<In, Out>(test: Bool, body: @escaping ((In) -> Out, In) ->
 public func to_stack_of_convert_function(p: UnsafeMutableRawPointer?) {
   _ = p.map(String.init(describing:))
 }
+
+
+public func no_dealloc_stack_before_unreachable(_ message: String, fileName: StaticString = #file, lineNumber: Int = #line) -> Never  {
+  Swift.fatalError(message, file: fileName, line: UInt(lineNumber))
+}