[3.1] IRGen: Don't try to emit non-global variables of imported inline c functions

lib/IRGen/GenClangDecl.cpp

@@ -50,9 +50,18 @@ void IRGenModule::emitClangDecl(const clang::Decl *decl) {
   stack.push_back(decl);
 
   ClangDeclRefFinder refFinder([&](const clang::DeclRefExpr *DRE) {
-    const clang::ValueDecl *D = DRE->getDecl();
-    if (!D->hasLinkage() || D->isExternallyVisible())
-      return;
+    const clang::Decl *D = DRE->getDecl();
+    // Check that this is a file-level declaration and not inside a function.
+    // If it's a member of a file-level decl, like a C++ static member variable,
+    // we want to add the entire file-level declaration because Clang doesn't
+    // expect to see members directly here.
+    for (auto *DC = D->getDeclContext();; DC = DC->getParent()) {
+      if (DC->isFunctionOrMethod())
+        return;
+      if (DC->isFileContext())
+        break;
+      D = cast<const clang::Decl>(DC);
+    }
     if (!GlobalClangDecls.insert(D->getCanonicalDecl()).second)
       return;
     stack.push_back(D);

test/IRGen/Inputs/c_functions.h

@@ -2,3 +2,10 @@
 
 void overloaded(void) __attribute__((overloadable));
 void overloaded(int) __attribute__((overloadable));
+
+extern void use(const char *);
+
+static inline void test_my_log() {
+  __attribute__((internal_linkage)) static const char fmt[] = "foobar";
+  use(fmt);
+}

test/IRGen/c_functions.swift

@@ -9,4 +9,6 @@ func testOverloaded() {
   overloaded()
   // CHECK: call void @_Z10overloadedi(i32{{( signext)?}} 42)
   overloaded(42)
+  // CHECK: call void @{{.*}}test_my_log
+  test_my_log()
 } // CHECK: {{^}$}}