Dependence graph: entry points may have additional control dependencies

The first instruction of a function can reasonably have control
dependencies other than that of the function call. Pointer18 is such an
example, because there is a back edge to the beginning of the main
function.

Author: tautschnig

regression/cbmc/Pointer18/full-slice.desc

@@ -0,0 +1,8 @@
+CORE
+main.c
+--unwind 1 --no-unwinding-assertions --pointer-check --full-slice
+^EXIT=0$
+^SIGNAL=0$
+^VERIFICATION SUCCESSFUL$
+--
+^warning: ignoring

src/analyses/dependence_graph.cpp

@@ -224,23 +224,13 @@ void dep_graph_domaint::transform(
 
   // We do not propagate control dependencies on function calls, i.e., only the
   // entry point of a function should have a control dependency on the call
-  if(!control_deps.empty())
-  {
-    const goto_programt::const_targett &dep = *control_deps.begin();
-    if(dep->is_function_call())
-    {
-      INVARIANT(
-        std::all_of(
-          std::next(control_deps.begin()),
-          control_deps.end(),
-          [](const goto_programt::const_targett &d) {
-            return d->is_function_call();
-          }),
-        "All entries must be function calls");
-
-      control_deps.clear();
-    }
-  }
+  depst filtered_control_deps;
+  std::copy_if(
+    control_deps.begin(),
+    control_deps.end(),
+    std::inserter(filtered_control_deps, filtered_control_deps.end()),
+    [](goto_programt::const_targett dep) { return !dep->is_function_call(); });
+  control_deps = std::move(filtered_control_deps);
 
   // propagate control dependencies across function calls
   if(from->is_function_call())