[Bug sanitizer/82072] sanitizer does not detect an overflow from LLONG_MIN

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82072

--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
This should fix the two issues above: 

--- a/gcc/convert.c
+++ b/gcc/convert.c
@@ -434,6 +434,12 @@ do_narrow (location_t loc,
     typex = lang_hooks.types.type_for_size (TYPE_PRECISION (typex),
                        TYPE_UNSIGNED (typex));

+  /* The type demotion below might cause doing unsigned arithmetic
+     instead of signed, and thus hide overflow bugs.  */
+  if (!TYPE_UNSIGNED (typex)
+      && sanitize_flags_p (SANITIZE_SI_OVERFLOW))
+    return NULL_TREE;
+
   /* But now perhaps TYPEX is as wide as INPREC.
      In that case, do nothing special here.
      (Otherwise would recurse infinitely in convert.  */
@@ -895,7 +901,12 @@ convert_to_integer_1 (tree type, tree expr, bool dofold)
                            TYPE_UNSIGNED (typex));

          if (!TYPE_UNSIGNED (typex))
-       typex = unsigned_type_for (typex);
+       {
+         /* Using unsigned arithmetic may hide overflow bugs.  */
+         if (sanitize_flags_p (SANITIZE_SI_OVERFLOW))
+           break;
+         typex = unsigned_type_for (typex);
+       }
          return convert (type,
                  fold_build1 (ex_form, typex,
                       convert (typex,