Re: [PATCH] Fix PR target/59233 (ICE on *-apple-darwin* with -m32 exposed by -freorder-blocks-and-partition)

[Teresa Johnson <tejohnson at google dot com>]

On Thu, Nov 21, 2013 at 3:31 PM, Steven Bosscher <stevenb.gcc@gmail.com> wrote:
> On Thu, Nov 21, 2013 at 8:57 PM, Teresa Johnson wrote:
>> There are two problems I am fixing here (see
>> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59233 for full analysis).
>>
>> The first is the original ICE in crossjump optimization, which was
>> exposed by enabling -freorder-blocks-and-partition which was
>> conservatively preventing some upstream block combining optimizations.
>> The issue is that the block ended in a NOTE_INSN_DELETED, which
>> old_insns_match_p could not handle. I am fixing this by passing
>> old_insns_match_p the last instruction in the block that it knows how
>> to handle.
>>
>> The second issue this exposed was that we were unnecessarily marking
>> landing pad branches EDGE_PRESERVE since
>> flag_reorder_blocks_and_partition was on, even though this was -Os and
>> we will gate partitioning off.
>
> So we keep an edge to a landing pad... Why is this a problem?

It just seems silly to limit optimization unnecessarily when we can
deduce that we won't actually attempt partitioning.

>
>
>>         * bb-reorder.c (do_partition_blocks): New function.
>>         (gate_handle_partition_blocks): Call do_partition_blocks.
>>         * bb-reorder.h (do_partition_blocks): Declare.
>>         * except.c (dw2_build_landing_pads): Call do_partition_blocks.
>
> Exporting this gate function from bb-reorder.c shouldn't be necessary.
> Better fix this at the root, in except.c.

How would we do that? I didn't want to clone the logic that determines
whether we will partition, so I thought outlining the checks from the
gate function and exporting them would be cleaner. But I am open to
suggestions.

>
>
>>         * cfgcleanup.c (outgoing_edges_match): Walk up past note instructions
>>         not understood by old_insns_match_p.
>
> This part is OK.

Ok, let me get this part in first, since it will address the ICE.

Thanks,
Teresa

>
> Ciao!
> Steven



-- 
Teresa Johnson | Software Engineer | tejohnson@google.com | 408-460-2413