On Wed, 18 Nov 2020, Prathamesh Kulkarni wrote:
> Hi,
> For the following test-case (slightly reduced from PR)
> int a, b, c;
>
> int g() {
> char i = 0;
> for (c = 0; c <= 8; c++)
> --i;
>
> while (b) {
> _Bool f = i <= 0;
> a = (a == 0) ? 0 : f / a;
> }
> }
>
> The compiler segfaults with -O1 -march=armv8.2-a+sve in ifcvt_local_dce.
>
> IIUC, the issue here is that tree-if-conv.c:predicate_rhs_code
> processes the following statement:
> iftmp.2_7 = a_lsm.10_11 != 0 ? iftmp.2_13 : 0;
> and records <iftmp.2_7, iftmp.2_13> mapping.
>
> However RPO VN eliminates iftmp.2_13:
> Removing dead stmt iftmp.2_13 = .COND_DIV (_29, _4, a_lsm.10_11, 0);
>
> and we end up replacing iftmp.2_7 with a dead ssa_name in ifcvt_local_dce:
> FOR_EACH_VEC_ELT (redundant_ssa_names, i, name_pair)
> replace_uses_by (name_pair->first, name_pair->second);
> redundant_ssa_names.release ();
>
> resulting in incorrect IR, and segfault down the line.
>
> To avoid clashing of RPO VN with redunant_ssa_names, the patch simply moves
> ifcvt_local_dce before do_rpo_vn, which avoids the segfault.
> Does that look OK ?
> (Altho I guess, doing DCE after VN is better in principle)
Yes, I'd say just moving
FOR_EACH_VEC_ELT (redundant_ssa_names, i, name_pair)
replace_uses_by (name_pair->first, name_pair->second);
redundant_ssa_names.release ();
before rpo_vn makes more sense, no?
OK with that change.
Thanks,
Richard.
> Thanks,
> Prathamesh
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imend
