Add test to cover callback/internal linkage/addresstaken case.

Author: Prabhuk

clang/test/CodeGen/call-graph-section-callback.cpp

@@ -0,0 +1,29 @@
+// Tests that callback function whose address is taken is attached Type ID metadata
+// as it is a potential indirect call target.
+
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -fexperimental-call-graph-section \
+// RUN: -emit-llvm -o %t %s
+// RUN: FileCheck %s < %t
+
+////////////////////////////////////////////////////////////////////////////////
+typedef void (*CallbackFn)(int);
+
+// Callback function with "internal" linkage.
+// CHECK-DAG: define internal void @_ZL10myCallbacki({{.*}} !type [[F_CALLBACK:![0-9]+]]
+static void myCallback(int value) 
+{
+    volatile int sink = value;
+    (void)sink;
+}
+
+int takeCallbackAddress() {
+    // Take the address of the callback explicitly (address-taken function)
+    CallbackFn cb = &myCallback;
+    // Store the address in a volatile pointer to keep it observable
+    volatile void* addr = (void*)cb;
+    (void)addr;
+
+    return 0;
+}
+
+// CHECK-DAG: [[F_CALLBACK]]   = !{i64 0, !"_ZTSFviE.generalized"}