More reponses to review comments by @gribozavr.

One larger change is that we're now also running this test in C as well
as C++.

Author: martinboehme

test/Interop/C/function/Inputs/emit-called-function.h

@@ -0,0 +1,23 @@
+#ifdef __cplusplus
+#define INLINE inline
+#else
+// When compiling as C, make the functions `static inline`. This is the flavor
+// of inline functions for which we require the behavior checked by this test.
+// Non-static C inline functions don't require Swift to emit LLVM IR for them
+// because the idea is that there will we one `.c` file that declares them
+// `extern inline`, causing an out-of-line definition to be emitted to the
+// corresponding .o file.
+#define INLINE static inline
+#endif
+
+INLINE int notCalled() {
+  return 42;
+}
+
+INLINE int calledTransitively() {
+  return 42;
+}
+
+INLINE int calledFromSwift() {
+  return calledTransitively();
+}

test/Interop/Cxx/function/Inputs/module.modulemap renamed to test/Interop/C/function/Inputs/module.modulemap

@@ -0,0 +1,19 @@
+// Test that we emit LLVM IR for inline functions that are called directly or
+// transitively from Swift.
+//
+// Test that we don't emit LLVM IR for inline functions that are not called from
+// Swift.
+
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend %s -I %S/Inputs -Xcc -std=c99 -emit-ir -o - | %FileCheck %s -check-prefix C99 --implicit-check-not notCalled
+// RUN: %target-swift-frontend %s -I %S/Inputs -enable-cxx-interop -emit-ir -o - | %FileCheck %s -check-prefix CXX --implicit-check-not notCalled
+
+import EmitCalledFunction
+
+// C99-DAG: define internal i32 @calledFromSwift() #{{[0-9]+}} {
+// C99-DAG: define internal i32 @calledTransitively() #{{[0-9]+}} {
+
+// CXX-DAG: define linkonce_odr i32 @_Z15calledFromSwiftv() #{{[0-9]+}} comdat {
+// CXX-DAG: define linkonce_odr i32 @_Z18calledTransitivelyv() #{{[0-9]+}} comdat {
+
+calledFromSwift()