On Mon, Jul 16, 2012 at 3:55 PM, Ulrich Weigand <[email protected]> wrote:
> Richard Guenther wrote:
>> On Fri, Jul 6, 2012 at 6:36 PM, Tom de Vries <[email protected]> wrote:
>> > Bootstrapped and reg-tested (ada inclusive) on x86_64.
>> >
>> > OK for trunk?
>>
>> Ok.
>> Thanks,
>> Richard.
>>
>> > 2012-07-06 Tom de Vries <[email protected]>
>> > Richard Guenther <[email protected]>
>> >
>> > * tree-ssa-ccp.c (optimize_unreachable): New function.
>> > (execute_fold_all_builtins): Use optimize_unreachable to optimize
>> > BUILT_IN_UNREACHABLE. Don't optimize after BUILT_IN_UNREACHABLE.
>> >
>> > * gcc.dg/builtin-unreachable-6.c: New test.
>> > * gcc.dg/builtin-unreachable-5.c: New test.
>
>
> When attempting to backport this patch to our 4.7 branch, I ran into
> segmentation faults. It turns out that at least in 4.7, gsi_stmt
> crashes when passed an empty gsi (for which gsi_end_p is true);
> on mainline, gsi_stmt simply returns NULL instead.
>
> Now I understand that even on mainline, we're still supposed to check
> gsi_end_p before calling gsi_stmt. The patch below updates
> tree-ssa-ccp.c:optimize_unreachable to do that. In the backport
> this fixes the crashes.
>
> This doesn't really have any effect on behaviour on mainline. Should
> it be installed anyway?
Yes please.
> (Tested on mainline on i386-linux with no regressions.)
>
> In addition, I was wondering whether we should backport Tom's patch
> (including the fix below) to the FSF 4.7 branch: it does fix a
> (performance) regression, in the sense that the original testcase
> calling __builtin_unreachable multiple times was optimized well
> until 4.6, and is now again optimized well on mainline, but it
> generates quite bad code on 4.7 at the moment ...
I'm not sure.
Thanks,
Richard.
> Bye,
> Ulrich
>
>
> ChangeLog:
>
> * tree-ssa-ccp.c (optimize_unreachable): Check gsi_end_p
> before calling gsi_stmt.
>
> Index: gcc/tree-ssa-ccp.c
> ===================================================================
> *** gcc/tree-ssa-ccp.c (revision 189459)
> --- gcc/tree-ssa-ccp.c (working copy)
> *************** optimize_unreachable (gimple_stmt_iterat
> *** 2358,2366 ****
> FOR_EACH_EDGE (e, ei, bb->preds)
> {
> gsi = gsi_last_bb (e->src);
> ! stmt = gsi_stmt (gsi);
>
> ! if (stmt && gimple_code (stmt) == GIMPLE_COND)
> {
> if (e->flags & EDGE_TRUE_VALUE)
> gimple_cond_make_false (stmt);
> --- 2358,2368 ----
> FOR_EACH_EDGE (e, ei, bb->preds)
> {
> gsi = gsi_last_bb (e->src);
> ! if (gsi_end_p (gsi))
> ! continue;
>
> ! stmt = gsi_stmt (gsi);
> ! if (gimple_code (stmt) == GIMPLE_COND)
> {
> if (e->flags & EDGE_TRUE_VALUE)
> gimple_cond_make_false (stmt);
>
>
> --
> Dr. Ulrich Weigand
> GNU Toolchain for Linux on System z and Cell BE
> [email protected]
>
