[embedded] Fix calling convention on embedded runtime APIs (switch @_silgen_name for @_cdecl)

test/embedded/lto-multiple-object-files.swift

@@ -0,0 +1,56 @@
+// Regression test for a runtime failure that used to happen under some very specific conditions: (1) LTO, (2) Swift
+// compiler is used with -num-threads to emit multiple .o files even in WMO mode, (3) the first listed source file
+// contains no code that would trigger the use of swift_initStaticObject runtime function (e.g. no array literals), (4)
+// another source file does use swift_initStaticObject that doesn't get optimized away (e.g. an array literal in a
+// never-inline function, but not an empty array). In that case, we used to have a mismatching calling convention on
+// swift_initStaticObject that the LTO pipeline would conclude is invalid IR and replace it with an unconditional trap.
+
+// RUN: %empty-directory(%t)
+// RUN: %{python} %utils/split_file.py -o %t %s
+
+// RUN: %target-swift-frontend -Osize -lto=llvm-full %t/MyFile1.swift %t/MyFile2.swift -enable-experimental-feature Embedded -emit-bc -num-threads 2 -o %t/MyFile1.o -o %t/MyFile2.o
+// RUN: %target-clang -Oz %t/MyFile1.o %t/MyFile2.o -o %t/a.out
+// RUN: %target-run %t/a.out | %FileCheck %s
+
+// REQUIRES: swift_in_compiler
+// REQUIRES: executable_test
+// REQUIRES: OS=macosx
+
+// For LTO, the linker dlopen()'s the libLTO library, which is a scenario that
+// ASan cannot work in ("Interceptors are not working, AddressSanitizer is
+// loaded too late").
+// REQUIRES: no_asan
+
+// BEGIN MyFile1.swift
+
+public func foo() {
+  print("foo")
+}
+
+// BEGIN MyFile2.swift
+
+public func bar() {
+  print("bar")
+}
+
+@inline(never)
+public func baz(array: [Int]) -> ([Int], [Int]) {
+  let x = [1, 2, 3]
+  let y = [3, 4, 5]
+  return (x, y)
+}
+
+@main
+struct Main {
+  static func main() {
+    foo()
+    let (x, y) = baz(array: Array<Int>.init(repeating: 0, count: 8))
+    let c = x.count + y.count
+    print(c)
+    bar()
+  }
+}
+
+// CHECK: foo
+// CHECK-NEXT: 6
+// CHECK-NEXT: bar