Adding support for R6 of MIPS architecture
sellcey at imgtec.com
Tue Feb 10 17:50:45 UTC 2015
On Fri, 2015-02-06 at 09:13 +0100, Torbjörn Granlund wrote:
> I think the old assembly code should be tweaked for r6 in a slightly
> deeper way. Two extra move instructions in a critical loop isn't OK.
> The mips code you started with is seriously out-of-date, with
> over-scheduling of load; this ought to be fixed too.
My thought was to get a working version checked in and then make
improvements after that.
> In the r6 parts which exists and are planned, are mulu and muhu
> pipelined? If they are pipelined, how close can a 2nd multiply be
> scheduled without issue stalling? What are their latency?
mulu and muhu will be pipelined (at least for high and medium end
cores), I am not entirely sure about low end cores.
> Is there a way to do 'make check' with a simulator or a remote system?
> If you are patient enough, perhaps you could find a QEMU release which
> works well enough for testing this? I recall having seen some mention
> of mipsr6 around QEMU, so presumably the QEMU folks made some attempt at
> supporting this.
The top-of-tree Qemu is pretty good these days, I use it for GCC
testing, including R6 testing.
> Finding a linux config which works with a QEMU version and config can be
> quite irksome. Often, you will need to patch QEMU's handling of one or
> two instructions.
> QEMU's mips64 emulator have been particularly buggy in the past years,
> with perhaps a dozen releases which were useless.
> I usually build MIPS code using a cross compiler on an x86 Linux box and
> that is what I did to build GMP (using --build=x86_64-unknown-linux-gnu
> --host=mips-img-linux-gnu or some other host depending on what flavor of
> MIPS I wanted to build). I was hoping I could run 'make check' on the
> x86 box and have it run tests via a simulator. That makes it easier to
> build and test multiple MIPS architectures.
> GMP provides a TEST_ENVIRONMENT environment variable which could be used
> for remote executiion.
OK, I will look into TEST_ENVIRONMENT.
> I tweaked the GMP configure script to recognize mips*-mti-* and
> mips*-img-* targets, these hosts/targets exist in GCC and binutils as
> names to use for cross compilers targeting MIPS (mti for pre-r6, img for
> Then GCC apparently abuses the GNU configure system. GMP follows the
> GNU convention cpu-system[-kernel]-os. For r6 CPUs, use either
> cpu=mips64r6 or [when pipeline-specific optimised assembly is provided]
> cpu=mipsfoo where foo describes the specific CPU.
> We need FSF paperwork to handle your patch. Are you willing to sign
> your work to the FSF? If you are employed to do programming, we need
> assignment or disclaimer from your employer too.
I'll have to work on this. The company I work for (Imagination
Technologies, which purchased MIPS) has an FSF copyright assignment on
file but it does not include GMP in the list of projects.
sellcey at imgtec.com
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