Re: Submission of pa8000 changes?

[Jeffrey A Law <law at cygnus dot com>]

  In message <3662B680.B6E559C5@americasm01.nt.com>you write:
  > Yeah.  I got no improvement at all.  I was more doing it to provide a
  > hook for those with more knowledge to work on it.  What I typically find
  > is that double performance is acceptable but single float is
  > significantly worse.
That's interesting.  Certainly worth looking at if you can identify the hot
loops for the poorly performing single precision code.

  > How do you go about making gcc avoid the fmpyadd and fmpysub
  > instructions for just the 8000?
Well, we're going to need a couple switches.  One which says to tune code
for the PA8000, the other which says to generate PA8000 instructions.

We've been using -msched=<blah> to control tuning of code for a particular
processor variant in the PA port.  So you'd need to have the compiler grok
-msched=8000.

-mpa-risc-2-0 would be used to enable PA2.0 ISA instructions like the fused
multiply/add family of instructions.

Then you can test pa_cpu to see if you're supposed to be tuning code for
the PA8000.  Then you make the call to the function which generates those
insns conditional on not tuning code for the PA8000.  See pa_reorg.

  > If we wanted to include the fused
  > multiply-add instructions, it appears that all the output would have to
  > be converted to pa2.0 opcodes, which includes revising gas.  Does this
  > sound about right?
Yes.  Some of the BFD infrastructure is already in place.  You'd need to 
add new entries to the opcode table and tweak the assembler & disassembler
appropriately.

jeff