Merge pull request swiftlang#39404 from lorentey/force-cx16-on-linux

Author: lorentey

lib/ClangImporter/ClangImporter.cpp

@@ -781,6 +781,12 @@ importer::addCommonInvocationArguments(
     invocationArgStrs.push_back("-march=z13");
   }
 
+  if (triple.getArch() == llvm::Triple::x86_64) {
+    // Enable double wide atomic intrinsics on every x86_64 target.
+    // (This is the default on Darwin, but not so on other platforms.)
+    invocationArgStrs.push_back("-mcx16");
+  }
+
   if (!importerOpts.Optimization.empty()) {
     invocationArgStrs.push_back(importerOpts.Optimization);
   }

test/IRGen/cx16.swift

@@ -0,0 +1,12 @@
+// RUN: %target-swift-frontend -target x86_64-unknown-linux-gnu -disable-legacy-type-info -parse-stdlib -disable-objc-interop %s -module-name main -emit-ir -o - | %FileCheck %s
+// RUN: %target-swift-frontend -target x86_64-unknown-windows-msvc -disable-legacy-type-info -parse-stdlib -disable-objc-interop %s -module-name main -emit-ir -o - | %FileCheck %s
+// RUN: %target-swift-frontend -target x86_64-unknown-freebsd -disable-legacy-type-info -parse-stdlib -disable-objc-interop %s -module-name main -emit-ir -o - | %FileCheck %s
+// RUN: %target-swift-frontend -target x86_64-apple-macosx10.9 -disable-legacy-type-info -parse-stdlib -module-name main %s -emit-ir -o - | %FileCheck %s
+
+// REQUIRES: CODEGENERATOR=X86
+
+public func test() {
+}
+
+// We expect double-wide atomic intrinsics to always be available on x86_64.
+// CHECK: "target-features"="{{.*}}+cx16,