[6.1] IRGen: Fix anonymous context descriptors of alwaysEmitIntoClient functions

Explanation: Relative references from context descriptors to types outside of the
current module need to use indirect relative references. If direct
relative references are used instead linking will fail.

Scope: This situation can occurr with alwaysEmitIntoClient functions
returning opaque types combined with availability and the use of
-enable-anonymous-context-mangled-names (which is enabled at Onone).

Reviewer: John M.

Original PR: #78017

Risk: Low. Should only affect cases that would have previously failed to
link.

rdar://140356479

(cherry picked from commit d31e4a5)

Author: aschwaighofer

lib/IRGen/GenDecl.cpp

@@ -809,6 +809,12 @@ IRGenModule::getAddrOfContextDescriptorForParent(DeclContext *parent,
 
   case DeclContextKind::GenericTypeDecl:
     if (auto nomTy = dyn_cast<NominalTypeDecl>(parent)) {
+      if (nomTy->getDeclContext()->getParentModule() != getSwiftModule() &&
+          fromAnonymousContext) {
+        // Can't emit a direct reference.
+        auto entity = LinkEntity::forNominalTypeDescriptor(nomTy);
+        return getAddrOfLLVMVariableOrGOTEquivalent(entity);
+      }
       return {getAddrOfTypeContextDescriptor(nomTy, DontRequireMetadata),
               ConstantReference::Direct};
     }

test/IRGen/anonymous_context_descriptors.swift

@@ -0,0 +1,79 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend                           \
+// RUN:     %t/C.swift                                   \
+// RUN:     -emit-module                                 \
+// RUN:     -enable-library-evolution                    \
+// RUN:     -module-name C                               \
+// RUN:     -emit-module-path %t/C.swiftmodule
+
+// RUN: %target-swift-frontend                           \
+// RUN:     %t/A.swift                                   \
+// RUN:     -enable-anonymous-context-mangled-names      \
+// RUN:     -I %t -emit-ir | %FileCheck %s
+
+// REQUIRES: PTRSIZE=64
+// REQUIRES: OS=macosx || OS=ios
+// UNSUPPORTED: CPU=arm64e
+
+//--- A.swift
+import C
+public func callStuff()  {
+  var x: any P = Empty()
+  if #available(iOS 17.3, macOS 14.3, *) {
+    x = MyBuilder.f(Empty())
+    x = MyBuilder.h(Empty())
+  }
+  print(x)
+}
+
+// Make sure that when we generate an anoynmous context descriptor its parent
+// relative reference to another module uses an indirect relative reference.
+
+// CHECK: @"$s1C9MyBuilderVMn" = external global %swift.type_descriptor
+// CHECK: @"got.$s1C9MyBuilderVMn" = private unnamed_addr constant ptr @"$s1C9MyBuilderVMn"
+// CHECK: @"$s1C9MyBuilderV1fyQrAA1P_pFZMXX" = linkonce_odr hidden constant <{ i32, i32, i32 }> <{ i32 {{[0-9]+}}, i32 add (i32 trunc (i64 sub (i64 ptrtoint (ptr @"got.$s1C9MyBuilderVMn"
+// CHECK: @"$s1C9MyBuilderV1hyQrAA1P_pFZMXX" = linkonce_odr hidden constant <{ i32, i32, i32 }> <{ i32 {{[0-9]+}}, i32 add (i32 trunc (i64 sub (i64 ptrtoint (ptr @"got.$s1C9MyBuilderVMn"
+
+//--- C.swift
+public protocol P {
+  func g()
+}
+
+public struct Empty : P {
+  public init() {}
+  public func g() {}
+}
+
+@available(iOS 17.3, macOS 14.3, *)
+public struct S : P {
+  public init<T: P>(_ c: T) {}
+
+  public func g() {
+    print("g")
+  }
+}
+
+public struct MyBuilder {
+  @_alwaysEmitIntoClient
+  @available(iOS 17.3, macOS 14.3, *)
+  public static func f(_ content: any P) -> some P {
+    if #unavailable(iOS 17.3, macOS 14.3) {
+      return Empty()
+    }
+    return S(content)
+  }
+}
+
+
+extension MyBuilder {
+  @_alwaysEmitIntoClient
+  @available(iOS 17.3, macOS 14.3, *)
+  public static func h(_ content: any P) -> some P {
+    if #unavailable(iOS 17.3, macOS 14.3) {
+      return Empty()
+    }
+    return S(content)
+  }
+}