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[RFC ARM] Use vcvt.f32.s32 with immediate bits to do fixed to floating point conversions.

by Ramana Radhakrishnan

Hi, So one of the things Michael pointed out in today's call was that the ARM backend doesn't generate vcvt.f32.s<type> where you have an idiom conversion from fixed to floating point as in the example below. I've chosen to implement this in the following manner in the backend using these interfaces from real.c . The reason I've chosen to not allow this transformation in case flag_rounding_math is true is because this instruction always ends up rounding using round-to-nearest rather than obeying whats in the FPSCR and thus is not safe for programs that want to dynamically set their rounding modes. The benefits are quite obvious in that we eliminate a load from the constant pool and a floating point multiply and thus essentially shaving off a floating point multiply + Load latency off these sequences. This instruction can only write the output into the same register as the input register which is why I've modelled it as below by tying op1 into op0. If there's a simpler way of using the interfaces into real.c then I'm all ears ? Thoughts ? I believe such idioms are used in libav from where the original report appears to have come and thus it's a worthwhile gain where we can have it. Any other places where folks might have noticed this. I will post upstream as well once I finish testing this patch. I'm posting this here to get some feedback as well to let anyone who is really really keen about trying this out have a go given I'm out tomorrow. ( I took a quick look at the short -> f32 case as well but the fact remains that loads either zero or sign extend anyway so there's probably not much gain in modelling that right away and the win really is in getting rid of that fp mul and the constant pool load. There's probably some gain in going from i64-> f64 as well so those patterns need to be written up at some point for completeness ) cheers Ramana 2011-10-04 Ramana Radhakrishnan <ramana.radhakrishnan(a)linaro.org> * config/arm/arm.c (vfp3_const_double_for_fract_bits): Define. * config/arm/arm-protos.h (vfp3_const_double_for_fract_bits): Declare. * config/arm/constraints.md ("Dt"): New constraint. * config/arm/predicates.md (const_double_vcvt_power_of_two_reciprocal): New. * config/arm/vfp.md (*arm_combine_vcvt_f32_s32): New. (*arm_combine_vcvt_f32_u32): New. For the following testcases I see the code as follows with -mfloat-abi=hard -mfpu=vfpv3 and -mcpu=cortex-a9 float foo (int i) { float v = (float)i / (1 << 11); return v; } float foa_unsigned (unsigned int i) { float v = (float)i / (1 << 5); return v; } After patch . foo: @ args = 0, pretend = 0, frame = 0 @ frame_needed = 0, uses_anonymous_args = 0 @ link register save eliminated. fmsr s0, r0 @ int vcvt.f32.s32 s0, s0, #11 bx lr .size foo, .-foo .align 2 .global foa_unsigned .type foa_unsigned, %function foa_unsigned: @ args = 0, pretend = 0, frame = 0 @ frame_needed = 0, uses_anonymous_args = 0 @ link register save eliminated. fmsr s0, r0 @ int vcvt.f32.u32 s0, s0, #5 bx lr .size foa_unsigned, .-foa_unsigned .align 2 .global foo1 .type foo1, %function rather than .type foo, %function foo: @ args = 0, pretend = 0, frame = 0 @ frame_needed = 0, uses_anonymous_args = 0 @ link register save eliminated. fmsr s15, r0 @ int fsitos s0, s15 flds s15, .L2 fmuls s0, s0, s15 bx lr .L3: .align 2 .L2: .word 973078528 .size foo, .-foo .align 2 .global foa_unsigned .type foa_unsigned, %function foa_unsigned: @ args = 0, pretend = 0, frame = 0 @ frame_needed = 0, uses_anonymous_args = 0 @ link register save eliminated. fmsr s15, r0 @ int fuitos s0, s15 flds s15, .L5 fmuls s0, s0, s15 bx lr .L6: .align 2 .L5: .word 1023410176

14 years, 1 month

[ACTIVITY] 26th - 30th September

by Andrew Stubbs

* Vacation Monday, Tuesday, and Wednesday. * GCC Continued work on my constant reuse optimizations. Disappointingly, I've found that there are very few optimization opportunities in EEMBC (ARM/Thumb V7-A), although it's not difficult to write testcases that the optimization could improve. I also discovered that the data-flow chains don't work exactly how I thought (with respect to if-then-else cases) so I need to do a little more work. Pinged the native tuning patches; they're still waiting for upstream review. Still can't get the generic tuning work done as the CodeSourcery panda boards appear to be still offline.

14 years, 1 month

[ACTIVITY] Weekly status

by Revital Eres

Committed to mainline the patch to support instructions with auto-inc operations in SMS after addressing Ayal's comments. The patch contains two parts; one of them fixes a bug revealed during bootstrapping with the patch and SMS flags. http://gcc.gnu.org/ml/gcc-patches/2011-09/msg01988.html http://gcc.gnu.org/ml/gcc-patches/2011-09/msg01987.html Looking at estimating register pressure with SMS: based on previous discussion with Richard the current approach is to try and use the register pressure estimation in loop invariant pass.

14 years, 1 month

undefined reference to __aeabi_unwind_cpp_pr0

by AJ ONeal

I'm compiling an application built with TI's DVSDK 3 *[0]. /home/user/ti/dvsdk/dvsdk_3_01_00_10/linuxutils_2_25_02_08/packages/ti/sdo/linuxutils/cmem/lib/cmem.a470MV(cmem.o470MV):(.ARM.exidx+0x0): undefined reference to `__aeabi_unwind_cpp_pr0' arm-linux-gnueabi-gcc --version arm-linux-gnueabi-gcc (Ubuntu/Linaro 4.5.2-5ubuntu2~ppa1) 4.5.2 arm-linux-gnueabi-ld --version GNU ld (GNU Binutils for Ubuntu) 2.21.0.20110302 More full output is here (but it isn't particularly helpful due to TI's RTSC make system's black-magic) https://gist.github.com/925674 FYI: the MV in cmem.a470MV stands for MontaVista. This name is hard-coded somewhere even though it's not being linked against a MontaVista system. I believe the 470 means that it should work with ARMv4 through ARMv7, but I'm not positive. My googling suggest that this is a toolchain bug and that the best way around the issue is to create a file which defines the function as a void dummy and include it. http://www.codesourcery.com/archives/arm-gnu/msg03604.html http://comments.gmane.org/gmane.comp.boot-loaders.u-boot/78649 http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=__aeabi_unwind_cpp_pr0 I have a script that I'll post shortly with instructions as to how to setup TI's DVSDK with Linaro AJ ONeal [0] I'm not using the latest DVSDK version 4 because the paths and such are so hard-coded for the 2009q3 version of codesourcery on ubuntu 10.04 LTS that I don't know where to start fixing it.

14 years, 1 month

[ACTIVITY] Week ending 30th September 2011.

by Ramana Radhakrishnan

===Progress=== * Patch review week. * Looked at bootstrap issue for a while but Richard Sandiford picked it up and sorted it out (Thanks Richard). * Fun and games with some paperwork. * Some backporting and testing patches. (50099 and 50186) underway. === Plans === * Clear out some of the old patches (POST_MODIFY_DISP for vfp, BRANCH_COST ) and finish on auto-inc-dec patch from last week. * Away for 1 day next week. Meetings: * 1-1s * TCWG calls Absences. * 5th October -Out of Office. * 13th - 14th October - Internal training. * 31st Oct - 4th Nov - Linaro Summit Orlando. * 08 Nov - 11 Nov - Tentatively booked * Dec 19 - 31st Dec - Tentatively booked

14 years, 1 month

[ACTIVITY] report week 39

by Peter Maydell

(short week: 3 days) RAG: Red: Amber: Green: Current Milestones: || || Planned || Estimate || Actual || ||add-omap3-networking || 2011-10-13 || 2011-10-13 || || ||a15-systemmode-planning || 2011-10-13 || 2011-10-13 || 2011-09-22 || ||a15-usermode-support || 2011-11-10 || 2011-11-10 || || ||upstream-omap3-cleanup || 2011-11-10 || 2011-11-10 || || Historical Milestones: ||qemu-linaro 2011-04 || 2011-04-21 || 2011-04-21 || 2011-04-21 || ||qemu-linaro 2011-05 || 2011-05-19 || 2011-05-19 || n/a || ||close out 1105 blueprints || 2011-05-28 || 2011-05-28 || 2011-05-19 || ||complete 1111 planning || 2011-05-28 || 2011-05-28 || 2011-05-27 || ||qemu-linaro-2011-06 || 2011-06-16 || 2011-06-16 || 2011-06-16 || ||qemu-linaro-2011-07 || 2011-07-21 || 2011-07-21 || 2011-07-21 || ||qemu-linaro 2011-08 || 2011-08-18 || 2011-08-18 || 2011-08-18 || ||qemu-linaro 2011-09 || 2011-09-15 || 2011-09-15 || 2011-09-15 || == a15-usermode-support == * completed the implementation and testing of fused-mac instructions; posted patch series with these and udiv/sdiv == other == * lightning talk for pdsw doughnut session Current qemu patch status is tracked here: https://wiki.linaro.org/PeterMaydell/QemuPatchStatus

14 years, 1 month

[ACTIVITY] Weekly status

by Richard Sandiford

== This week == * Applied patch for doing NEON high/low extraction using subregs. Ramana pointed out that we do the same thing for insertion, so I wrote a patch to handle that too. Both now merged into Linaro sources. * Looked at ARM bootstrap problem on trunk. Turned out to be an aliasing problem. Submitted and applied patch. * Reworked part of my SMS register-scheduling patch after feedback from Ayal. Submitted new version upstream. * Got SPEC2006 running on the powerpc boxes and tested one part of my -fsched-pressure patch. Bit of a mixed bag. h264ref was one of the worst sufferers, which was a bit worrying. I think I'll need to make a third change too. To recap, there are two pieces now: 1) Make -fsched-pressure honour the DFA 2) Make -fsched-pressure allow values that are live across a loop to be spilled. I naively hoped that (1) would be OK on its own, but h264 shows that the current -fsched-pressure code is very conservative when it comes to large blocks. It only considers register deaths once there is a single remaining use; if there are two unscheduled uses, it assumes that the register remains live for the rest of the block. So the problem that (1) was fixing was that -fsched-pressure was too optimistic in terms of what it could schedule in a cycle. But with that fixed, we seem to have too many sources of pessimism... Richard

14 years, 1 month

[ACTIVITY] Sep 26 - Sep 30

by Ulrich Weigand

== GDB == * Worked on support for cross-platform core file generation. * Followed up on patch to support disabling address space randomization in gdbserver. == GCC == * Followed up on patch for PR 50305. 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

14 years, 1 month

[ACTIVITY] w39

by Asa Sandahl

* Working on croos-compiling Firefox. Getting dependencies in place and setting up the configuration file (.mozconfig). I have had the strategy to fix one dependency at a time, picking prebuilt packages or building my self. Michael told me at yesterday's meeting about multistrap, that could possibly be used for fixing all dependencies at once. I will look into that next week. * During this process I have also spent some time reading up on cross compilation in general and also on autoconf and the GNU build system. Best Regards Åsa

14 years, 1 month

[ACTIVITY] 2011-09-28

by David Gilbert

== String routines == * Got eglibc testing setup happy at last - Note that -O3 builds generally seem to give a few more errors that are probably worth looking at - -march=armv6 -mthumb hit some non-thumb1 instructions (normally non-lo registers), again worth looking at - Cross testing to Qemu user mode often stalls, mostly on nptl tests that abort/fail when run in system/natively * Sent new version of eglibc/memchr patch upstream * Now have working newlib test setup and reference set - next step is to try adding my memchr there == Other == * Testing a QEmu patch with Peter * Looking at bug 861296 (difference in mmap layouts) * Adding a few suggestions to the set of cpu hotplug tests. * Dealing with the Manchester lab cold. Short week; back on Monday Dave

14 years, 1 month

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