From cc78bb5ebf77b09d6771cf2769cfcb20f2f10033 Mon Sep 17 00:00:00 2001
From: Doug Gregor <dgregor@apple.com>
Date: Wed, 12 Nov 2025 11:37:19 -0800
Subject: [PATCH] [Multi-threaded IRGen] Ensure that autolink info gets into
 each object file

When performing multi-threaded IRGen, all of the link libraries used
for autolinking went (only) into the first object file. If the object
files were then placed in a static archive, the autolinking would only
kick in if clients that link the static library reference something in
the first object file. This causes link failures.

Make sure that we put the autolink information into each of the object
files we create when doing multi-threaded IRGen.

Fixes the rest of rdar://162400654.
---
 lib/IRGen/IRGen.cpp                   |  4 +--
 test/IRGen/autolink_multithread.swift | 35 +++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 3 deletions(-)
 create mode 100644 test/IRGen/autolink_multithread.swift

diff --git a/lib/IRGen/IRGen.cpp b/lib/IRGen/IRGen.cpp
index f1a07b1fdb0df..7fa848208dd6e 100644
--- a/lib/IRGen/IRGen.cpp
+++ b/lib/IRGen/IRGen.cpp
@@ -1740,9 +1740,7 @@ static void performParallelIRGeneration(IRGenDescriptor desc) {
 
     (void)layoutStringsEnabled(*IGM, /*diagnose*/ true);
 
-    // Only need to do this once.
-    if (!IGMcreated)
-      IGM->addLinkLibraries();
+    IGM->addLinkLibraries();
     IGMcreated = true;
   }
 
diff --git a/test/IRGen/autolink_multithread.swift b/test/IRGen/autolink_multithread.swift
new file mode 100644
index 0000000000000..b4e7a2b4bab31
--- /dev/null
+++ b/test/IRGen/autolink_multithread.swift
@@ -0,0 +1,35 @@
+// This test checks that we produce autolink entries into the expected places
+// when performing multi-threaded IR generation.
+
+// RUN: %empty-directory(%t/src)
+// RUN: split-file %s %t/src
+
+// RUN: %target-swift-frontend -emit-module -o %t -module-name empty -module-link-name empty %S/../Inputs/empty.swift
+
+// RUN: %target-swift-frontend -emit-ir %t/src/A.swift %t/src/B.swift -I %t -Fsystem %S/Inputs/Frameworks -o %t/A.ll -o %t/B.ll -num-threads 2 -O -g -module-name test
+// RUN: %FileCheck --check-prefix=CHECK-A %s <%t/A.ll
+// RUN: %FileCheck --check-prefix=CHECK-B %s <%t/B.ll
+
+// Linux uses a different autolinking mechanism, based on
+// swift-autolink-extract. This file tests the Darwin mechanism.
+// UNSUPPORTED: autolink-extract
+// REQUIRES: OS=macosx
+
+
+//--- A.swift
+import empty
+
+public func f() -> String { "hello" }
+
+// CHECK-A: !llvm.linker.options = !{
+// CHECK-A: !{{[0-9]+}} = !{!{{"-lempty"|"/DEFAULTLIB:empty.lib"}}}
+
+//--- B.swift
+import LinkFramework
+
+public func useLibrarySym() {
+  let _ = LinkFramework.IComeFromLinkFramework
+}
+
+// CHECK-B: !llvm.linker.options = !{
+// CHECK-B: !{{[0-9]+}} = !{!"-framework", !"LinkFramework"}