Since my patch isn't the easy one liner I wanted it to be, perhaps we should concentrate on Martin's patch, which is more robust, and has testcases to boot! His patch from last week also fixes a couple other PRs.
Richard, would this be acceptable? That is, could you or Jakub review Martin's all-encompassing patch? If so, I'll drop mine. Also, could someone pontificate on whether we want to fix -Warray-bounds regressions for this release cycle? Thanks. On Wed, Jan 31, 2018 at 6:05 AM, Richard Biener <richard.guent...@gmail.com> wrote: > 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.