From 6988b03c133f4107e73713aaad7753359bee922e Mon Sep 17 00:00:00 2001
From: Erik Eckstein <eeckstein@apple.com>
Date: Tue, 21 Oct 2025 08:09:55 +0200
Subject: [PATCH] ClosureSpecialization: don't crash for recursive functions

Don't support self-recursive functions because that would result in mapping troubles when cloning.
---
 .../ClosureSpecialization.swift               |  5 +++-
 test/SILOptimizer/closure_specialization.sil  | 25 +++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/ClosureSpecialization.swift b/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/ClosureSpecialization.swift
index aabfc62369030..b57244b98737a 100644
--- a/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/ClosureSpecialization.swift
+++ b/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/ClosureSpecialization.swift
@@ -242,7 +242,10 @@ private func isCalleeSpecializable(of apply: ApplySite) -> Bool {
      // might no longer have 'self' as the last parameter.
      //
      // TODO: Keep the self argument the last when appending arguments.
-     !callee.mayBindDynamicSelf
+     !callee.mayBindDynamicSelf,
+
+     // Don't support self-recursive functions because that would result in duplicate mapping of values when cloning.
+     callee != apply.parentFunction
   {
     return true
   }
diff --git a/test/SILOptimizer/closure_specialization.sil b/test/SILOptimizer/closure_specialization.sil
index 5c3d776b2d01d..7ea1372b7edb3 100644
--- a/test/SILOptimizer/closure_specialization.sil
+++ b/test/SILOptimizer/closure_specialization.sil
@@ -947,3 +947,28 @@ bb0(%nc : @owned $NC):
   %11 = tuple ()
   return %11 : $()
 }
+
+sil @closure_with_closure : $@convention(thin) (@guaranteed @callee_guaranteed () -> ()) -> ()
+
+// Just make sure the pass is not crashing.
+sil [ossa] @test_recursion : $@convention(thin) (@guaranteed @callee_guaranteed () -> ()) -> () {
+bb0(%0 : @guaranteed $@callee_guaranteed () -> ()):
+  %2 = apply %0() : $@callee_guaranteed () -> ()
+  cond_br undef, bb1, bb2
+
+bb1:
+  %5 = function_ref @closure_with_closure : $@convention(thin) (@guaranteed @callee_guaranteed () -> ()) -> ()
+  %6 = copy_value %0
+  %7 = partial_apply [callee_guaranteed] %5(%6) : $@convention(thin) (@guaranteed @callee_guaranteed () -> ()) -> ()
+  %8 = function_ref @test_recursion : $@convention(thin) (@guaranteed @callee_guaranteed () -> ()) -> ()
+  %9 = apply %8(%7) : $@convention(thin) (@guaranteed @callee_guaranteed () -> ()) -> ()
+  destroy_value %7
+  br bb3
+
+bb2:
+  br bb3
+
+bb3:
+  %13 = tuple ()
+  return %13
+}