http://gcc.gnu.org/bugzilla/show_bug.cgi?id=61060
--- Comment #5 from Jan Hubicka <hubicka at ucw dot cz> ---
> I'd say the backend should better deal with this. Or we have to
> double-check (or delay) the zero-length check until after
>
> len_rtx = expand_normal (len);
>
> sth like
This looks good to me indeed. Thanks for explanation concerning TER.
>
> Index: gcc/builtins.c
> ===================================================================
> --- gcc/builtins.c (revision 209890)
> +++ gcc/builtins.c (working copy)
> @@ -3685,20 +3685,20 @@ expand_builtin_memset_args (tree dest, t
> if (expected_align < dest_align)
> expected_align = dest_align;
>
> + /* Stabilize the arguments in case we fail. */
> + dest = builtin_save_expr (dest);
> + val = builtin_save_expr (val);
> + len = builtin_save_expr (len);
> +
> + len_rtx = expand_normal (len);
> /* If the LEN parameter is zero, return DEST. */
> - if (integer_zerop (len))
> + if (len_rtx == const0_rtx)
> {
> /* Evaluate and ignore VAL in case it has side-effects. */
> expand_expr (val, const0_rtx, VOIDmode, EXPAND_NORMAL);
> return expand_expr (dest, target, mode, EXPAND_NORMAL);
> }
>
> - /* Stabilize the arguments in case we fail. */
> - dest = builtin_save_expr (dest);
> - val = builtin_save_expr (val);
> - len = builtin_save_expr (len);
> -
> - len_rtx = expand_normal (len);
> determine_block_size (len, len_rtx, &min_size, &max_size,
> &probable_max_size);
> dest_mem = get_memory_rtx (dest, len);
>
>
> probably applies to almost all builtin expansions.
>
> But I'd say the backend should be more fault-tolerant here. It can't
> simply reserve len == 0 for itself.
OK, I think I can just add early return to the expander functions then (or an
assert - still it seems more like middle-end's bug as it only wastes time even
at -O0)
Honza
