C++: Support __builtin_bit_cast builtin

Author: jketema

cpp/ql/lib/semmle/code/cpp/exprs/BuiltInOperations.qll

@@ -1023,3 +1023,18 @@ class BuiltInOperationHasUniqueObjectRepresentations extends BuiltInOperation,
 
   override string getAPrimaryQlClass() { result = "BuiltInOperationHasUniqueObjectRepresentations" }
 }
+
+/**
+ * A C/C++ `__builtin_bit_cast` built-in operation (used by some implementations
+ * of `std::bit_cast`).
+ *
+ * Performs a bit cast from a value to a type.
+ * ```
+ * __builtin_bit_cast(Type, value);
+ * ```
+ */
+class BuiltInBitCast extends BuiltInOperation, @builtinbitcast {
+  override string toString() { result = "__builtin_bit_cast" }
+
+  override string getAPrimaryQlClass() { result = "BuiltInBitCast" }
+}

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -1653,6 +1653,7 @@ case @expr.kind of
 | 330 = @isassignable
 | 331 = @isaggregate
 | 332 = @hasuniqueobjectrepresentations
+| 333 = @builtinbitcast
 ;
 
 @var_args_expr = @vastartexpr
@@ -1717,6 +1718,7 @@ case @expr.kind of
             | @isassignable
             | @isaggregate
             | @hasuniqueobjectrepresentations
+            | @builtinbitcast
             ;
 
 new_allocated_type(

cpp/ql/test/library-tests/builtins/edg/edg.c

@@ -1,4 +1,4 @@
-
+// semmle-extractor-options: --clang
 struct mystruct {
     int f1;
     int f2;
@@ -13,3 +13,6 @@ void f(void) {
     int i2 = edg_offsetof(struct mystruct,f2);
 }
 
+void g(void) {
+    double f = __builtin_bit_cast(double,42l);
+}

cpp/ql/test/library-tests/builtins/edg/expr.expected

@@ -13,3 +13,6 @@
 | edg.c:13:14:13:45 | (size_t)... | 0 | 0 |
 | edg.c:13:14:13:45 | __INTADDR__ | 1 | 1 |
 | edg.c:13:43:13:44 | f2 | 0 | 0 |
+| edg.c:17:16:17:45 | __builtin_bit_cast | 1 | 1 |
+| edg.c:17:16:17:45 | double | 0 | 0 |
+| edg.c:17:42:17:44 | 42 | 1 | 1 |