Maintain source location while replacing symbol expressions

Linking (and also other workflows) use expression replacement. Doing so
must not destroy the source location annotated to an expression. This
left us with instructions without location.

regression/goto-cc-multi-file/maintain-location/main.c

@@ -0,0 +1,11 @@
+int foo()
+{
+  return 0;
+}
+
+int main()
+{
+  int result;
+  result = foo();
+  return result;
+}

regression/goto-cc-multi-file/maintain-location/other.c

@@ -0,0 +1,6 @@
+int foo();
+
+int bar()
+{
+  return foo();
+}

regression/goto-cc-multi-file/maintain-location/test.desc

@@ -0,0 +1,9 @@
+CORE
+main.c
+other.c
+file main.c line 9 function main
+^EXIT=0$
+^SIGNAL=0$
+--
+--
+We previously lost the location attached to the call of `foo` in function main.

src/linking/linking.cpp

@@ -100,13 +100,19 @@ bool casting_replace_symbolt::replace_symbol_expr(symbol_exprt &s) const
 
   const exprt &e = it->second;
 
+  source_locationt previous_source_location{s.source_location()};
+  DATA_INVARIANT_WITH_DIAGNOSTICS(
+    previous_source_location.is_not_nil(),
+    "front-ends should construct symbol expressions with source locations",
+    s.pretty());
   if(e.type().id() != ID_array && e.type().id() != ID_code)
   {
     typet type = s.type();
     static_cast<exprt &>(s) = typecast_exprt::conditional_cast(e, type);
   }
   else
     static_cast<exprt &>(s) = e;
+  s.add_source_location() = std::move(previous_source_location);
 
   return false;
 }

src/util/replace_symbol.cpp

@@ -51,7 +51,12 @@ bool replace_symbolt::replace_symbol_expr(symbol_exprt &s) const
     s.type() == it->second.type(),
     "types to be replaced should match. s.type:\n" + s.type().pretty() +
       "\nit->second.type:\n" + it->second.type().pretty());
+  source_locationt previous_source_location{s.source_location()};
   static_cast<exprt &>(s) = it->second;
+  // back-end generated or internal symbols (like rounding mode) might not have
+  // a source location
+  if(s.source_location().is_nil() && previous_source_location.is_not_nil())
+    s.add_source_location() = std::move(previous_source_location);
 
   return false;
 }
@@ -334,7 +339,12 @@ bool unchecked_replace_symbolt::replace_symbol_expr(symbol_exprt &s) const
   if(it == expr_map.end())
     return true;
 
+  source_locationt previous_source_location{s.source_location()};
   static_cast<exprt &>(s) = it->second;
+  // back-end generated or internal symbols (like rounding mode) might not have
+  // a source location
+  if(s.source_location().is_nil() && previous_source_location.is_not_nil())
+    s.add_source_location() = std::move(previous_source_location);
 
   return false;
 }
@@ -415,7 +425,12 @@ bool address_of_aware_replace_symbolt::replace_symbol_expr(
 
   // Note s_copy is no longer a symbol_exprt due to the replace operation,
   // and after this line `s` won't be either
+  source_locationt previous_source_location{s.source_location()};
   s = s_copy;
+  // back-end generated or internal symbols (like rounding mode) might not have
+  // a source location
+  if(s.source_location().is_nil() && previous_source_location.is_not_nil())
+    s.add_source_location() = std::move(previous_source_location);
 
   return false;
 }