On Tue, Jan 30, 2018 at 11:11 PM, Aldy Hernandez <al...@redhat.com> wrote:
> Hi!
>
> [Note: Jakub has mentioned that missing -Warray-bounds regressions should be
> punted to GCC 9. I think this particular one is easy pickings, but if this
> and/or the rest of the -Warray-bounds regressions should be marked as GCC 9
> material, please let me know so we can adjust all relevant PRs.]
>
> This is a -Warray-bounds regression that happens because the IL now has an
> MEM_REF instead on ARRAY_REF.
>
> Previously we had an ARRAY_REF we could diagnose:
>
> D.2720_5 = "12345678"[1073741824];
>
> But now this is represented as:
>
> _1 = MEM[(const char *)"12345678" + 1073741824B];
>
> I think we can just allow check_array_bounds() to handle MEM_REF's and
> everything should just work.
>
> The attached patch fixes both regressions mentioned in the PR.
>
> Tested on x86-64 Linux.
>
> OK?
This doesn't look correct. You lump MEM_REF handling together with
ADDR_EXPR handling but for the above case you want to diagnose
_dereferences_ not address-taking.
For the dereference case you need to amend the ARRAY_REF case, for example
via
Index: gcc/tree-vrp.c
===================================================================
--- gcc/tree-vrp.c (revision 257181)
+++ gcc/tree-vrp.c (working copy)
@@ -5012,6 +5012,13 @@ check_array_bounds (tree *tp, int *walk_
if (TREE_CODE (t) == ARRAY_REF)
vrp_prop->check_array_ref (location, t, false /*ignore_off_by_one*/);
+ else if (TREE_CODE (t) == MEM_REF
+ && TREE_CODE (TREE_OPERAND (t, 0)) == ADDR_EXPR
+ && TREE_CODE (TREE_OPERAND (TREE_OPERAND (t, 0), 0)) == STRING_CST)
+ {
+ call factored part of check_array_ref passing in STRING_CST and offset
+ }
+
else if (TREE_CODE (t) == ADDR_EXPR)
{
vrp_prop->search_for_addr_array (t, location);
note your patch will fail to warn for "1"[1] because taking that
address is valid but not
dereferencing it.
Richard.
