C++: Move builtin function identification to its own table

cpp/ql/lib/semmle/code/cpp/Function.qll

@@ -282,9 +282,12 @@ class Function extends Declaration, ControlFlowNode, AccessHolder, @function {
    * definition, if possible.)
    */
   override Location getLocation() {
-    if exists(this.getDefinition())
-    then result = this.getDefinitionLocation()
-    else result = this.getADeclarationLocation()
+    if this instanceof BuiltInFunction
+    then result instanceof UnknownLocation // a dummy location for the built-in function
+    else
+      if exists(this.getDefinition())
+      then result = this.getDefinitionLocation()
+      else result = this.getADeclarationLocation()
   }
 
   /** Gets a child declaration of this function. */
@@ -896,17 +899,9 @@ class FunctionTemplateSpecialization extends Function {
  * A GCC built-in function. For example: `__builtin___memcpy_chk`.
  */
 class BuiltInFunction extends Function {
-  BuiltInFunction() { functions(underlyingElement(this), _, 6) }
-
-  /** Gets a dummy location for the built-in function. */
-  override Location getLocation() {
-    suppressUnusedThis(this) and
-    result instanceof UnknownLocation
-  }
+  BuiltInFunction() { builtin_functions(underlyingElement(this)) }
 }
 
-private predicate suppressUnusedThis(Function f) { any() }
-
 /**
  * A C++ user-defined literal [N4140 13.5.8].
  */

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -288,12 +288,13 @@ macro_argument_expanded(
 
 /*
 case @function.kind of
-  1 = @normal_function
+  0 = @unknown_function
+| 1 = @normal_function
 | 2 = @constructor
 | 3 = @destructor
 | 4 = @conversion_function
 | 5 = @operator
-| 6 = @builtin_function     // GCC built-in functions, e.g. __builtin___memcpy_chk
+// ... 6 = @builtin_function deprecated    // GCC built-in functions, e.g. __builtin___memcpy_chk
 | 7 = @user_defined_literal
 | 8 = @deduction_guide
 ;
@@ -305,6 +306,10 @@ functions(
     int kind: int ref
 );
 
+builtin_functions(
+    int id: @function ref
+)
+
 function_entry_point(
     int id: @function ref,
     unique int entry_point: @stmt ref