For the record, the thing I half-remembered on the call was:
http://gcc.gnu.org/ml/gcc-patches/2009-08/msg00697.html
and:
http://gcc.gnu.org/ml/gcc-patches/2009-09/msg02112.html
The problem is that all __sync operations besides __sync_lock_test_and_set
and __sync_lock_release are defined to be full barriers. Using something
like __sync_val_compare_and_swap for __arch_compare_and_exchange_val_*_acq
and __arch_compare_and_exchange_val_*_rel may on some architectures be too
heavyweight, since those macros only need acquire/after and release/before
barriers. See in particular:
http://gcc.gnu.org/ml/gcc-patches/2009-08/msg00928.html
from the first thread, where the feeling was that the future wasn't
these __sync builtins, but the new C and C++ atomic memory support.
Probably already known, sorry. I just wasn't sure that trying to
convert everyone (not just ARM) to __sync_* was necessarily going
to go down well.
Richard
== Last Week ==
* Reached the point with understanding libunwind where I can begin
writing patches for parsing unwind information out of .ARM.exidx and
.ARM.extab ELF sections.
== This Week ==
* Begin writing support for ARM-specific unwind information to libunwind.
--
Zach Welch
CodeSourcery
zwelch(a)codesourcery.com
(650) 331-3385 x743
== Linaro GCC ==
* Continued looking at big-endian/quad-vector patch: attempted to
figure out the proper semantics for vec_extract in big endian mode
(about 1 day). Put on hold temporarily to work on lp675347, QT failing
to build due to constraint failure in inline asm statements used for
atomic operations: found the patch which introduced the failure, and
suggested a workaround to the OP. Came up with a plausible-looking
patch, and started testing it, after spending some time trying to
figure out why ARM Linux mainline doesn't build at present. Patch sent
upstream.
Hi Richard,
As per the discussion at this mornings call; I've reread the TRM and I
agree with you about the LSLS being the same speed as the TST. (1 cycle)
However as we agreed, the uxtb does look like 2 cycles v the AND 1 cycle.
On the space v perf theme, one thing that would be interesting to know is
whether there are any icache/issue stage limitations;
i.e. if I have a stream of 32-bit Thumb-2 instructions that are all listed
as 1 cycle and are all in i-cache, can they be fetched
and issued fast enough, or is there a performance advantage to short
instructions?
Dave
LP:663939 - Thumb2 constants
* Continued testing, found a few bugs. Tidied a few bits up.
* Wrote some new testcases to go with the patch.
LP:618684 - ICE
* Begun looking at this one. So far I can't reproduce it. I have a
debuggable native toolchain building, but it'd been delayed by hardware
issues.
In the course of testing I discovered that the ARM FSF config wasn't
testing the right thing, so begun work on a new, more appropriate FSF
build/test config for Linaro work.
Also found the the SD card rootfs in my IGEPv2 board was corrupted. I've
restored it from backup, and now it's working once more.
== Linaro and upstream GCC ==
* Linaro launchpad issues:
- LP #672833, x64-64 varargs regression: after testing pushed bzr branch
for merging.
- LP #634738, inefficient low bit extraction: some discussion with Yao.
- LP #618684, ICE when building ziproxy: looked into and quickly found
not reproducible anymore of Linaro 4.5 trunk.
* Worked on some GCC bugzilla PRs:
- PR44557, ICE in Thumb-1 secondary reload: this should be fixed by a
change of the scratch operand constraint of "reload_inhi" from "r" to
"l". Interesting to note that this was from the
merged-arm-thumb-backend-branch merge, from about 10 years ago.
- PR46508: libffi fails to build on VFP asm instructions, seems to need
a '.fpu vfp' directive. Probably missed earlier because my toolchain was
configured with --with-fpu=vfp.
- PR45416: 4.6 code generation regression on ARM, after expand from SSA
changes. Looking at this currently.
== This week ==
* Look at Linaro issues with higher priority.
* Continue working on GCC PRs.
== Linaro GCC ==
* Merge ldm/stm patch to Linaro 4.5 tree.
Found two regressions on the last minute of proposing merge request in
pass ce3. Revert one of ldm/stm patches about ifcvt. Complete testcase
in branch.
* Try Richard E.'s "TST to LSLS transformation" patch on cortex-a9 with
FFMPEG. No speed improvements.
* Various Linaro GCC Bug fixing.
** LP:634738
Follow the fix to GCC PR40697, and create a new patch, which emits
extzv or shift rather than loading constants in some cases. Tested on
FSF GCC trunk, and no regression. However, found a regression by eyes
in pr44999.c, in which, ubfx (4byte) is generated, rather than uxth
(2byte). uxth is produced by combiner from ashift and lshiftrt. During
reading arm.c, find that constant handling in thumb2 should be improved
to some extent.
** LP:633243
Re-implement regrename improvement, as Eric B. suggested in
gcc-patches. Spend some time on understanding API in GCC related to
hard-reg. Tested on x86_64-linux. No regression.
** LP:638935
Update my tree to FSF trunk, and find RTL seq for fldm/fstm peephole
disappears due to fix to PR45722. Extend arm-ldmstm.ml to support vfp.
Peephole and RTL patterns for vfp are done. Will revise
arm.c:{load,store}_multiple_sequence to accept vfp data.
Fix a bug in ldm/stm peephole when starting offset is negative.
== This week ==
* LP:634738: Figure out how uxth is produced by combiner.
* LP:633243: Test it on ARM.
* LP:638935: Revise {load,store}_multiple_sequence to accept vfp data.
--
Yao (齐尧)
Re my recent email "Upstream GCC feature freeze", I think we're agreed
that we need to create a branch that tracks GCC 4.6 development, but has
our own performance improvements included. The question is where to host it?
Option 1: Launchpad/bzr
Pros:
* We need no permission to do it
* The branch will naturally evolve into our 4.6 release series in time.
* The 3-way merge works well (if slowly)
* We can include patches that we have no intention of posting upstream
ever
* Our patch tracker will Just Work.
* Merge requests will be available.
Cons:
* Bzr ;)
* It's hidden away from the view of most GCC developers
Option 2: GCC SVN branch
Pros:
* We can work in the open, submitting patches via gcc-patches, as usual
* The final merge to GCC trunk (come stage 1) will be eased, a little
Cons:
* We can't really apply anything we want just for ourselves
* we may end up maintaining an LP branch shadowing the svn branch
* When we do want to do 4.6 in LP, we'll have to backport all our
patches from 4.7, and this may no longer be straightforward.
* Write permissions not clear.
* Although I think you can just go ahead and do it?
OK, so I'm sure I've missed some big ones. Please discuss! ;)
I think the big question here is, when will we start wanting to make
(unstable/experimental) Linaro GCC 4.6 releases? If we want to do it
early, then we'll have no choice but to have an LP branch to release from.
Andrew
Like everyone from Toolchain WG I will share my activites in last week:
1. cross compilers for archive
- discussed with doko about dropping update-alternatives use
- wrote gcc-defaults-armel-cross 1.4 which does proper symlinks for cross
compilers
- wrote gcc-4.5-armel-cross 1.41 which removes update-alternatives support
- wrote gcc-4.4-armel-cross 1.37 which removes update-alternatives support
- wrote armel-cross-toolchain-base 1.53 which has all updates which I had
- sent all of them to Steve for review
Status of changes:
- default version of armel cross compiler will be 4.5 like it is in Natty
- both 4.4 and 4.5 will be provided as it is for native
- any traces of update-alternatives use should be removed
Needs to be done:
- adding conflicts on older cross compilers to gcc-defaults-armel-cross
Order of upload to archive:
- armel-cross-toolchain-base
- gcc-4.5-armel-cross
- gcc-4.4-armel-cross
- gcc-defaults-armel-cross
2. Checked few old bugs do they still apply:
- Bugs #646729, #637454, #671455 are done with armel-cross-toolchain-base 1.52
(landed in maverick-proposed)
Regards,
--
JID: hrw(a)jabber.org
Website: http://marcin.juszkiewicz.com.pl/
LinkedIn: http://www.linkedin.com/in/marcinjuszkiewicz
Short week.
Finally got external hard drive for my beagle - makes it sanely possible to
natively build things.
Got eglibc cross built (Thanks to Wookey for pointing me in the right
direction with the magic incantation of dpkg-buildpackage -aarmel
--target=binary) and
easily rebuilding . I have a version with the neon version of my memset
built into it - it doesn't seem to make a noticeable difference to my
ghostscript benchmark
though.
Panda's aren't likely to turn up until mid December; arranging borrowing
an A9 is turning out to be difficult, but it looks like we should be able to
get access to
the one in the London datacentre - although it has a disc problem at the
moment.
I did manage to get a colleague to try my tests on his own Toshiba AC-10
(Tegra-2 - no Neon); the
graphs had approximately the same shape as my previous Panda tests. Memchr
looked pretty
good on there.
Also trying to look at the sign off I need for various libc access.
Dave
