Adding support for R6 of MIPS architecture

[Torbjörn Granlund]

Steve Ellcey <sellcey at imgtec.com> writes:

  OK, so what I did was to create a mips32r6 directory under mips32 and a
  mips64r6 directory under mips64 and put copies of the routines that had
  to be changed for r6 in those directories.  I have done test builds for
  various MIPS targets and verified that the non-r6 code has not changed.
  For the new r6 stuff I have verified that it all builds but I haven't
  tested the changes with 'make check'.
  
Nice contribution!

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The mips code you started with is seriously out-of-date, with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.

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?

  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.

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.

  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
  r6).
  
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.


Torbjörn
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