linaro-toolchain February 2011

linaro-toolchain@lists.linaro.org

27 participants
66 discussions

Representing interleaving and lane load/stores at the tree level

by Richard Sandiford

I've been spending this week playing around with various representations of the v{ld,st}{1,2,3,4}{,_lane} operations. I agree with Ira that the best representation would be to use built-in functions. One concern in the original discussion was that the optimisers might move the original MEM_REFs away from the call. I don't think that's a problem though. For loads, we can simply treat the whole of the accessed memory as an array, and pass the array by value. If we do that, then the call would just look like: __builtin_load_lanes (MEM_REF[(elem[N] *)ADDR]) (where, despite the C notation, the MEM_REF accesses the whole of elem[N]). It is of course possible in principle for the tree optimisers to replace this MEM_REF with another, equivalent, one, but that's OK semantically. It isn't possible for the optimisers to replace it with something like an SSA name, because arrays can't be stored in gimple registers. __builtin_load_lanes would then be used like this: combined_vectors = __builtin_load_lanes (...); vector1 = ...extract first vector from combined_vectors... vector2 = ...extract second vector from combined_vectors... .... So combined_vectors only exists for load and extract operations. The question then is: what type should it have? (At this point I'm just talking about types, not modes.) The main possibilities seemed to be: 1. an integer type Pros * Gimple registers can store integers. Cons * As Julian points out, GCC doesn't really support integer types that are wider than 2 HOST_WIDE_INTs. It would be good to remove that restriction, but it might be a lot of work, and it isn't something we'd want to take on as part of this project. * We're not really using the type as an integer. * The combination of the integer type and the __builtin_load_lanes array argument wouldn't be enough to determine the correct load operation. __builtin_load_lanes would need something like a vector count (N => vldN) argument as well. 2. a combined vector type Pros * Gimple registers can store vectors. Cons * For vld3, this would mean creating vector types with non-power- of-two vectors. GCC doesn't support those yet, and you get ICEs as soon as you try to use them. (Remember that this is all about types, not modes.) It _might_ be interesting to implement this support, but as above, it would be a lot of work. It also raises some semantic questions, such as: what is the alignment of the new vectors? Which leads to... * The alignment of the type would be strange. E.g. suppose we're loading N*2 uint32_ts into N vectors of 2 elements each. The types and alignments would be: N=2 uint32x4_t, alignment 16 N=3 uint32x6_t, alignment 8 (if we follow the convention for modes) N=4 uint32x8_t, alignment 32 We don't need alignments greater than 8 in our intended use; 16 and 32 are overkill. * We're not really using the type as a single vector, but as a collection of vectors. * The combination of the vector type and the __builtin_load_lanes array argument wouldn't be enough to determine the correct load operation. __builtin_load_lanes would need something like a vector count (N => vldN) argument as well. 3. an array of vectors type Pros * No support for new GCC features (large integers or non-power-of-two vectors) is needed. * The alignment of the type would be taken from the alignment of the individual vectors, which is correct. * It accurately reflects how the loaded value is going to be used. * The type uniquely identifies the correct load operation, without need for additional arguments. (This is minor.) Cons * Gimple registers can't store array values. So I think the only disadvantage of using an array of vectors is that the result can never be a gimple register. But that isn't much of a disadvantage really; the things we care about are the individual vectors, which can of course be treated as gimple registers. I think our tracking of memory values is good enough for combined_vectors to be treated as such (even though, with the back-end changes we talked about earlier, they will actually be stored in RTL registers). So how about the following functions? (Forgive the pascally syntax.) __builtin_load_lanes (REF : array N*M of X) returns array N of vector M of X maps to vldN in practice, the result would be used in assignments of the form: vectorX = ARRAY_REF <result, X> __builtin_store_lanes (VECTORS : array N of vector M of X) returns array N*M of X maps to vstN in practice, the argument would be populated by assignments of the form: vectorX = ARRAY_REF <result, X> __builtin_load_lane (REF : array N of X, VECTORS : array N of vector M of X, LANE : integer) returns array N of vector M of X maps to vldN_lane __builtin_store_lane (VECTORS : array N of vector M of X, LANE : integer) returns array N of X maps to vstN_lane Note that each operation can be expanded independently. The expansion doesn't rely on preceding or following statements. I've hacked up the prototype below as a proof of concept. It includes changes to the C parser to allow these functions to be created in the original source code. This is throw-away code though; it would never be submitted. I've also included a simple test case and the output I get from it. The output looks pretty good; there's not even the stray VMOV that I saw with the intrinsics earlier in the week. (Note that if you'd like to try this yourself, you'll need the patch I posted on Monday as well.) What do you think? Obviously this discussion needs to move to gcc@ at some point, but I wanted to make sure this was vaguely sane first. Richard

14 years, 12 months

[ACTIVITY] 21st - 26th February

by Andrew Stubbs

Temporarily took over Tech Lead of the Toolchain Working Group while Michael Hope recovers from the Christchurch earthquake. (He's fine, but unable to work.) This didn't actually require any action, in the end. Michael returned to work towards the end of the week. Forward ported, benchmarked, and posted one of Mark Shinwell's NEON patches upstream. Further benchmarking was not possible as the Panda board I was using is located in Christchurch, NZ. Merged and tested the FSF GCC 4.5 branch into Linaro GCC. There were a couple of test regressions in the fortran testsuite, so I've filed bug lp:723086. The other test results were either the same or better. Benchmarked the ARM A8 function/jump alignment patch to see what effect it has in GCC 4.6. Found no measurable improvement in EEMBC. I suggest dropping this patch. Brought the patch tracker up-to-date, and entered tracking tickets for all outstanding patches. Merged FSF trunk to Linaro GCC 4.6. Committed Jie's Thumb2 testcase fix to FSF GCC trunk. Thanks to Ramana for using his new found authority to approve it. Investigated the suitability of several of the patches for forward-porting. Corresponded with Benrd and Julian. ---- Upstream patched requiring review: * Thumb2 constants: http://gcc.gnu.org/ml/gcc-patches/2010-12/msg00652.html * Kazu's VFP testcases: http://gcc.gnu.org/ml/gcc-patches/2011-02/msg00128.html * ARM EABI half-precision functions http://gcc.gnu.org/ml/gcc-patches/2011-02/msg00874.html * ARM Thumb2 Spill Likely tweak http://gcc.gnu.org/ml/gcc-patches/2011-02/msg00880.html * NEON scheduling patch http://gcc.gnu.org/ml/gcc-patches/2011-02/msg01431.html

15 years

[ACTIVITY] Feb 21 -- Feb 27

by Chung-Lin Tang

== Last week == * Launchpad #721021 GCC ICE on ARM/XScale: identified as case of upstream PR45177; backported and pushed to Linaro. * Launchpad #709453/CS Issue #7122: Neon vmov 0.0 issues; some progress on my current WIP patch, but tests showed another 3 regressions, still on-going. * Launchpad #711819/GCC PR47719: ICE in push_minipool_fix. Ramana reminded that my patch, which added some pool range attributes, were actually removed earlier by Bernd in the fix for PR43137. Discussed and mostly concluded that we should add them back for now. Will re-submit patch with testcase to gcc-patches this week. * Coremark ARMv7-A regressions: still work in progress. == This week == * TW Public Holiday Feb.28 (Mon). * Ping some of my upstream patch submissions. * Get incompleted issues done. * Coremark regression investigation.

15 years

GCC M4 DSP support

by Christian ANDERSSON2

Hello Linaro toolchain guys, I have a few questions regarding GCC fully supporting the ARM Cortex M4, I'm especially thinking of the additional DSP instructions and if these are supported and how optimal the code being produced is? Thanks for your support, Best Regards Christian (ST-Ericsson)

15 years

[ACTIVITY] weekly status

by Ken Werner

Hi, == Investigate developer tools == * Finished latrace investigation. == PandaBoard == * The defective PandaBoard that was sent back in December is now repaired and on my desk again. It doesn't show the behaviour of #708883 and works flawlessly so far. :) == libunwind == * Did some debugging of the test-async-sig testcase to get started with libunwind. It will dead-lock if you add "--enable-debug" since libunwind does printfs in this case which are not signal safe. * Sorted out which of Zachs patches are upstream and which are not. * Started to learn about the different unwind methods that libunwind provides on ARM. Regards Ken

15 years

[ACTIVITY] 2011-02-25

by David Gilbert

== ffi == * Sent variadic patch for libffi to libffi-discuss * Worked through some suggestions from Chung-Lin, need to do some rework == string routines == * memchr & strchr patch sent for inclusion in ubuntu packages * tried sqlite's benchmarks - they don't spend too much time in the C library; although a few % in memcpy, and ~1% in memset (also seem to have found an sqlite test case failure on ARM and filed as bug 725052) == porting jam == * There wasn't much traffic on #linaro during this related to the jam * I closed bug 635850 (fastdep FTBFS) which was already fixed with an explicit fix for ARM in the changelog and bug 492336 (eglibc's tst-eintr1 failing) which seems to work now but it's not clear when it was fixed. * Looking at eglibc's test log there seem to be a bunch of others that are failing and may well be worth investigating. * bug 372121 (qemu/xargs stack/number of arguments limit) seems to work ok, however the reporter did say it was quite a fragile test; that needs more investigation to see whether the original reason has actually been fixed. == misc == * swapping notes with Peter on the PBX SD card investigation Dave

15 years

[ACTIVITY] report week 08

by Peter Maydell

RAG: Red: Amber: Green: Current Milestones: | Planned | Estimate | Actual | qemu-linaro 2011-03 | 2011-03-08 | 2011-03-08 | | Historical Milestones: finish virtio-system | 2010-08-27 | postponed | | finish testing PCI patches | 2010-10-01 | 2010-10-22 | 2010-10-18 | successful ARM qemu pull req | 2010-12-16 | 2010-12-16 | 2010-12-16 | finish qemu-cont-integration | 2011-01-25 | 2011-01-25 | handed off | first qemu-linaro release | 2011-02-08 | 2011-02-08 | 2011-02-08 | == maintain-beagle-models == * rebased qemu-linaro on upstream * checked omap_uart model for any issues with enabling the extended (non-16550A) features which the new Linux drivers need. Sent meego merge request for patchset which turns on the features, and does a little cleanup. Now in meego, qemu-linaro. == merge-correctness-fixes == * reviewed versions 5 and 6 of Christophe's vrecpe/vsqrte patchset; v6 was good and has now been committed * sent a version of "dummy cp14 debug registers" patch upstream; however I've realised it triggers a false positive in the temp-leak debugging code in target-arm/translate.c * wrote/sent a patch which moves this temp-leak debugging code into TCG proper (which I think makes it much simpler and cleaner and avoids the false positives mentioned above) * some work on the cp15 performance counter registers. I now have some code which I think is a fully architecturally valid implementation of an "implements no events" core, except that we don't implement the cycle count register. * started testing/review of Adam's VA-to-PA translation regs patch. In the course of this discovered that qemu unconditionally implements an ARM940 cp15 WFI register which clashes with these; submitted patch to add correct not-for-v6/v7 feature gating. * sent out patch fixing usermode seeks by 32 bit guest on 64 bit host (based on a diagnosis and suggested fix by Eoghan Sherry) * sent patch fixing compile error in vnc code == vexpress model == * sent a patchset for fixing the MMC card detect wiring on PBX upstream; this is needed for vexpress too * finished vexpress cleanup and cross-checking against the docs; I now have a patchset I'm happy to upstream and will post next week == other == * took part in pgp keysigning event with emdebian folks * meetings: toolchain, PDSW-tools Current qemu patch status is tracked here: https://wiki.linaro.org/PeterMaydell/QemuPatchStatus Absences: 17/18 March: QEMU Users Forum, Grenoble Holiday: 22 Apr - 2 May 9-13 May: UDS, Budapest (maybe) ~17-19 August: QEMU/KVM strand at LinuxCon NA, Vancouver

15 years

[ACTIVITY] Feb 21 - Feb 25

by Ulrich Weigand

== GDB == * Worked with Will Deacon and the Linaro kernel team to make sure HW watchpoint and Versatile Express errata fixes are included in the upcoming Linaro kernel release. * Committed GDB HW watchpoint patches to mainline, and backport to Linaro GDB. This completes work on the HW watchpoint blueprint. * Worked on fixing the GDB part of #620611 (Unable to backtrace out of vector page 0xffff0000). Posted (two versions of) mainline patch for discussion. * Worked on kernel patch for #615974 (Interrupted system call handling). Mit freundlichen Gruessen / Best Regards Ulrich Weigand -- Dr. Ulrich Weigand | Phone: +49-7031/16-3727 STSM, GNU compiler and toolchain for Linux on System z and Cell/B.E. IBM Deutschland Research & Development GmbH Vorsitzender des Aufsichtsrats: Martin Jetter | Geschäftsführung: Dirk Wittkopp Sitz der Gesellschaft: Böblingen | Registergericht: Amtsgericht Stuttgart, HRB 243294

15 years

[ACTIVITY] Weekly status

by Richard Sandiford

== This week == * Looked at the poor code generated for Neon load/store intrinsics. Looked into the history behind the treatment of VFP registers by CANNOT_CHANGE_MODE_CLASS. Peter confirmed that the restrictions apply only to VFPv1. Wrote a patch to improve the code, which partly overlapped with Julian's. * Looked at how the operations should be represented at the tree level. Experimented with various combinations of tree codes and types to see which felt right. Wrote this up in the message I sent today. == Next week == * More vectorisation. * Submit some queued patches. * Maybe some bug fixing. (I see there's a reload bug just waiting to be claimed by a lucky developer.) On holiday the following week. Richard

15 years

Re: Unavailable for a bit

by Michael Hope

Services at ex.seabright.co.nz are back up. On Tue, Feb 22, 2011 at 10:06 PM, Michael Hope <michael.hope(a)linaro.org> wrote: > Hi there. We've had an earthquake. Family and friends are fine but i'll be > unavailable for a few days. Services on ex.seabright.co.nz are down. I'll > cancel Wednesdays standup call. > > See you soon, > > -- Michael

15 years

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linaro-toolchain February 2011