[Bug middle-end/70992] Infinite recursion between fold_build2_stat_loc and fold_binary_loc w/ -fwrapv

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70992

--- Comment #7 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
We can simply do:
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -9387,6 +9387,11 @@ fold_binary_loc (location_t loc,
                              TREE_TYPE (arg0), arg0,
                              cst0));
        }
+     /* Adding anything to a division-by-zero makes no sense and
+        can confuse extract_muldiv and fold_plusminus_mult_expr.  */
+     else if (TREE_CODE (arg0) == TRUNC_DIV_EXPR
+          && integer_zerop (TREE_OPERAND (arg0, 1)))
+       return fold_convert_loc (loc, type, arg0);
    }

       /* Handle (A1 * C1) + (A2 * C2) with A1, A2 or C1, C2 being the same or

(In reply to Alexander Monakov from comment #6)
> We can simply fold A / 0 * B and A / 0 + B to 1 / 0 or 0 / 0.
> 
> I wonder why fold_plusminus_mult_expr puts the addition inside, that doesn't
> appear useful?

fold_plusminus_mult_expr tries to turn e.g. 2*a + a into 3*a, so that's where
the + 1 comes from.