This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: if-conversion/HOT-COLD partitioning
On 24 October 2012 00:42, Steven Bosscher <stevenb.gcc@gmail.com> wrote:
> On Tue, Oct 23, 2012 at 10:29 PM, Christophe Lyon
> <christophe.lyon@linaro.org> wrote:
>> Well, both of these functions appear to check that the 2 blocks to
>> merge belong to the same partition, so it should be OK.
>
> In your first email, you said if-convert was merging two blocks from
> different partitions. can_merge_block_p() would rejected merging the
> two blocks, so merge_blocks shouldn't be called on them.
>
> IIRC cfghooks.c:merge_blocks() used to have a
> gcc_assert(can_merge_blocks(a,b)) but it's not there now. But if
> can_merge_blocks() returns false, merge_blocks should fail. Your bug
> is that merge_blocks is being called at all on those blocks from
> different partitions.
>
>
>> But not all calls to merge_blocks are guarded by if
>> (can_merge_block_p()), this is probably where the problem is?
>
> Not sure. Depends on what blocks get merged. It may be that
> if-conversion shouldn't even be attempting whatever transformation
> it's attempting. Not enough information.
>
What happens is that merge_if_block() is called with test_bb, then_bb
and else_bb in the cold section, while join_bb is in the hot one.
merge_if_block calls merge_blocks unconditionally several times (in my
case, the wrong one is merge_blocks (combo_bb, join_bb)).
Christophe.