Re: [PATCH] Redesign jump threading profile updates

[Teresa Johnson <tejohnson at google dot com>]

On Wed, Oct 1, 2014 at 6:20 AM, Teresa Johnson <tejohnson@google.com> wrote:
> Sorry, yes, will try to reproduce.
> Teresa
>
> On Wed, Oct 1, 2014 at 12:03 AM, Christophe Lyon
> <christophe.lyon@linaro.org> wrote:
>> On 30 September 2014 20:20, Teresa Johnson <tejohnson@google.com> wrote:
>>> On Mon, Sep 29, 2014 at 9:33 PM, Jeff Law <law@redhat.com> wrote:
>>>> On 09/29/14 08:19, Teresa Johnson wrote:
>>>>>>
>>>>>>
>>>>>> Just an update - I found some good test cases by compiling the
>>>>>> c-torture tests with profile feedback with and without my patch. But
>>>>>> in the cases I pulled out I saw that there were still a couple profile
>>>>>> or probability insanities introduced by jump threading (albeit far
>>>>>> less than before), so I wanted to investigate before I commit. I ran
>>>>>> out of time this week and will not get to this until I get back from
>>>>>> vacation the week after next.
>>>>>
>>>>>
>>>>> Hi Jeff,
>>>>>
>>>>> I finally had a chance to get back to this and look at the remaining
>>>>> insanities in the new test cases I created. It turns out that there
>>>>> were still a few issues in the case where there were guessed
>>>>> frequencies and no profile counts. The two test cases I created do use
>>>>> FDO, and the insanities in the routines with profile counts went away
>>>>> with my patch. But the outlined copies of routines that were also
>>>>> inlined into the main routine still had estimated frequencies, and
>>>>> these still had a few issues.
>>>>>
>>>>> The problem is that the profile updates are done incrementally as we
>>>>> walk and update the paths in ssa_fix_duplicate_block_edges, including
>>>>> the block and edge counts, the block frequencies and the
>>>>> probabilities. This is very difficult to do when only operating on
>>>>> frequencies since the edge frequencies are derived from the source
>>>>> block frequency and the probability. Therefore, once the source block
>>>>> frequency is updated, the edge frequency is also affected, and it is
>>>>> really difficult to figure out what the update to the edge frequency
>>>>> (essentially the probability) is using the same incremental update
>>>>> approach. I was attempting to handle this with the routine
>>>>> deduce_freq, for example, but this turned out to have issues for
>>>>> certain types of paths. I tried a few other approaches, but they start
>>>>> looking really ugly and I didn't want to add a parallel but different
>>>>> algorithm in the case of no profile counts.
>>>>>
>>>>> So by far the simplest approach was simply to take a snapshot of the
>>>>> existing block and edge frequencies along the path before we start the
>>>>> updates in ssa_fix_duplicate_block_edges, by copying them into the
>>>>> profile count fields of those blocks and edges. Then the existing
>>>>> algorithm operates the same as when we do have counts, and can
>>>>> essentially operate incrementally on the edge frequencies since they
>>>>> live in the count field of the edge and are no longer affected anytime
>>>>> the source block is updated. Since the algorithm does update block
>>>>> frequencies and probabilities as well (based on the count updates
>>>>> performed), we can simply clear out these fake count fields at the end
>>>>> of ssa_fix_duplicate_block_edges. This takes care of the remaining
>>>>> insanities introduced by jump threading from these test cases. During
>>>>> testing I also added in some checking to ensure that the count fields
>>>>> for the whole routine were cleared properly to make sure the new
>>>>> clear_counts_path was not missing anything (checking is a little too
>>>>> heavyweight to add in normally).
>>>>>
>>>>> New patch below (also attached since my mailer sometimes eats spaces).
>>>>> The differences between the old patch and the new one:
>>>>> - removed deduce_freq (which was my least favorite part of the patch
>>>>> anyway!), and its call from recompute_probabilities, since it is no
>>>>> longer necessary.
>>>>> - two new routines freqs_to_counts_path and clear_counts_path, invoked
>>>>> from ssa_fix_duplicate_block_edges.
>>>>> - two new tests
>>>>>
>>>>> Bootstrapped and tested on x86_64-unknown-linux-gnu, ok for trunk?
>>>>>
>>>>> Thanks,
>>>>> Teresa
>>>>>
>>>>> gcc:
>>>>>
>>>>> 2014-09-29  Teresa Johnson  <tejohnson@google.com>
>>>>>
>>>>>          * tree-ssa-threadupdate.c (struct ssa_local_info_t): New
>>>>>          duplicate_blocks bitmap.
>>>>>          (remove_ctrl_stmt_and_useless_edges): Ditto.
>>>>>          (create_block_for_threading): Ditto.
>>>>>          (compute_path_counts): New function.
>>>>>          (update_profile): Ditto.
>>>>>          (recompute_probabilities): Ditto.
>>>>>          (update_joiner_offpath_counts): Ditto.
>>>>>          (freqs_to_counts_path): Ditto.
>>>>>          (clear_counts_path): Ditto.
>>>>>          (ssa_fix_duplicate_block_edges): Update profile info.
>>>>>          (ssa_create_duplicates): Pass new parameter.
>>>>>          (ssa_redirect_edges): Remove old profile update.
>>>>>          (thread_block_1): New duplicate_blocks bitmap,
>>>>>          remove old profile update.
>>>>>          (thread_single_edge): Pass new parameter.
>>>>>
>>>>> gcc/testsuite:
>>>>>
>>>>> 2014-09-29  Teresa Johnson  <tejohnson@google.com>
>>>>>
>>>>>          * testsuite/gcc.dg/tree-prof/20050826-2.c: New test.
>>>>>          * testsuite/gcc.dg/tree-prof/cmpsf-1.c: Ditto.
>>>>
>>>> Given I'd already been through this pretty thoroughly, I just gave this a
>>>> cursory review.
>>>>
>>>> clear_counts_path needs a function comment.  It's pretty obvious what it's
>>>> doing, but for completeness let's go ahead and get the obvious comment in
>>>> there.
>>>
>>> Done and committed as r215739.
>>>
>>
>> Since this commit, I can see all my builds for arm*linux* and
>> aarch64*linux* fail while building glibc:
>>
>> /tmp/3496222_18.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/tools/bin/aarch64-none-linux-gnu-gcc
>> iso-2022-cn.c -c -std=gnu99 -fgnu89-inline  -O2 -Wall -Win
>> line -Wundef -Wwrite-strings -fmerge-all-constants -frounding-math -g
>> -Wstrict-prototypes   -fPIC        -I../include
>> -I/tmp/3496222_18.tmpdir/aci-gcc-f
>> sf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/glibc-1/iconvdata
>> -I/tmp/3496222_18.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux
>> -gnu/glibc-1  -I../sysdeps/unix/sysv/linux/aarch64/nptl
>> -I../sysdeps/unix/sysv/linux/aarch64
>> -I../sysdeps/unix/sysv/linux/generic  -I../sysdeps/unix/s
>> ysv/linux/wordsize-64  -I../nptl/sysdeps/unix/sysv/linux
>> -I../nptl/sysdeps/pthread  -I../sysdeps/pthread
>> -I../sysdeps/unix/sysv/linux  -I../sysdeps/gn
>> u  -I../sysdeps/unix/inet  -I../nptl/sysdeps/unix/sysv
>> -I../sysdeps/unix/sysv  -I../nptl/sysdeps/unix  -I../sysdeps/unix
>> -I../sysdeps/posix  -I../sysd
>> eps/aarch64/fpu  -I../sysdeps/aarch64/nptl  -I../sysdeps/aarch64
>> -I../sysdeps/wordsize-64  -I../sysdeps/ieee754/ldbl-128
>> -I../sysdeps/ieee754/dbl-64/w
>> ordsize-64  -I../sysdeps/ieee754/dbl-64  -I../sysdeps/ieee754/flt-32
>> -I../sysdeps/aarch64/soft-fp  -I../sysdeps/ieee754
>> -I../sysdeps/generic  -I../npt
>> l  -I.. -I../libio -I. -nostdinc -isystem
>> /tmp/3496222_18.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/tools/lib/gcc/aarch64-none-linux-gnu/5.0.0/include
>> -i
>> system /tmp/3496222_18.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/tools/lib/gcc/aarch64-none-linux-gnu/5.0.0/include-fixed
>> -isystem /tmp/3496222_18.tmpdir
>> /aci-gcc-fsf/builds/gcc-fsf-gccsrc/sysroot-aarch64-none-linux-gnu/usr/include
>>  -D_LIBC_REENTRANT -include ../include/libc-symbols.h  -DPIC -DSHARED
>> -DNOT_IN_libc -o
>> /tmp/3496222_18.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/glibc-1/iconvdata/iso-2022-cn.os
>> -MD -MP -MF /tmp/3
>> 496222_18.tmpdir/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/glibc-1/iconvdata/iso-2022-cn.os.dt
>> -MT /tmp/3496222_18.tmpdir/aci-gcc-fsf
>> /builds/gcc-fsf-gccsrc/obj-aarch64-none-linux-gnu/glibc-1/iconvdata/iso-2022-cn.os
>>
>> In file included from iso-2022-cn.c:407:0:
>> ../iconv/skeleton.c: In function 'gconv':
>> ../iconv/skeleton.c:800:1: internal compiler error: in
>> check_probability, at basic-block.h:959
>> 0xe4e2fb find_many_sub_basic_blocks(simple_bitmap_def*)
>>         /tmp/3496222_18.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/basic-block.h:959
>> 0x6623f0 execute
>>         /tmp/3496222_18.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/cfgexpand.c:5916
>> Please submit a full bug report,
>> with preprocessed source if appropriate.
>> Please include the complete backtrace with any bug report.
>> See <http://gcc.gnu.org/bugs.html> for instructions.
>>
>> Can you have a look?

Unfortunately doesn't reproduce with x86_64, so I will build an
aarch64 cross-compiler next and give that a try. This was with the
latest glibc sources I git cloned from sourceware.org. Let me know if
I need something else.

Also, the instructions I found for configuring an aarch64 cross-compiler are:

./configure --prefix=$prefix \
    --target=aarch64-none-linux --enable-languages=c \
    --disable-threads --disable-shared --disable-libmudflap \
    --disable-libssp --disable-libgomp --disable-libquadmath

Let me know if I need to configure it differently.

Thanks,
Teresa

>>
>> Thanks,
>>
>> Christophe.
>>
>>> Thanks,
>>> Teresa
>>>
>>>>
>>>> With that fix, approved for the trunk.  Thanks for taking the time to sort
>>>> out all these issues.
>>>>
>>>> jeff
>>>>
>>>>
>>>
>>>
>>>
>>> --
>>> Teresa Johnson | Software Engineer | tejohnson@google.com | 408-460-2413
>
>
>
> --
> Teresa Johnson | Software Engineer | tejohnson@google.com | 408-460-2413



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