SILOptimizer: Fix bug in closure specialization with resilient build

lib/SILOptimizer/IPO/ClosureSpecializer.cpp

@@ -744,6 +744,13 @@ void ClosureSpecializer::gatherCallSites(
         if (!ApplyCallee || ApplyCallee->isExternalDeclaration())
           continue;
 
+        // Don't specialize non-fragile callees if the caller is fragile;
+        // the specialized callee will have shared linkage, and thus cannot
+        // be referenced from the fragile caller.
+        if (Caller->isFragile() &&
+            !ApplyCallee->hasValidLinkageForFragileInline())
+          continue;
+
         // Ok, we know that we can perform the optimization but not whether or
         // not the optimization is profitable. Find the index of the argument
         // corresponding to our partial apply.

test/SILOptimizer/closure_specialize_fragile.swift

@@ -0,0 +1,19 @@
+// RUN: %target-swift-frontend -Xllvm -new-mangling-for-tests %s -emit-sil -O -o - -verify | %FileCheck %s
+
+// Make sure we do not specialize resilientCallee.
+
+// CHECK-LABEL: sil [fragile] [always_inline] @_T026closure_specialize_fragile0C6CalleryyF : $@convention(thin) () -> ()
+// CHECK: function_ref @_T026closure_specialize_fragile15resilientCalleeyyyc2fn_tF : $@convention(thin) (@owned @callee_owned () -> ()) -> ()
+// CHECK: return
+
+@inline(__always) public func fragileCaller() {
+  resilientCallee {
+    print("Hi")
+  }
+}
+
+// CHECK-LABEL: sil @_T026closure_specialize_fragile15resilientCalleeyyyc2fn_tF : $@convention(thin) (@owned @callee_owned () -> ()) -> ()
+
+public func resilientCallee(fn: () -> ()) {
+  fn()
+}