Re: sim/mips patch: add support for more NEC VR targets

[Andrew Cagney <ac131313@redhat.com>]

>   :function:::int:check_mf_cycles:hilo_history *history, signed64 time, const char *new
>   {
> +   /* There are no timing requirements in vr5500 code.  */
> +   if (MIPS_MACH (SD) == bfd_mach_mips5500)
> +     return 1;
>     if (history->mf.timestamp + 3 > time)
>       {
>         sim_engine_abort (SD, CPU, CIA, "HILO: %s: %s at 0x%08lx too close to MF at 0x%08lx\n",

Just this,

Add:

	function:::int:check_mf_cycles:hilo_history *history, signed64 time, 
const char *new
	*vr5500
	{
	  return 1;
	}

and then tag the old function with the other CPU variants.

that way
	if (MIPS_MACH (SD) == bfd_mach_mips5500)
is not needed and the compiler can (if configured with sufficient 
inlining) eliminate the entire function call.

This post:

http://sources.redhat.com/ml/gdb-patches/2002-11/msg00512.html
> We have had very bad experiences with trying to make a single function
> serve two different ABI's in the past.  (mips_push_arguments seems to
> have been cleaned up since I last looked; it was a real mess.)  So
> while using things like 'REGISTER_SIZE' and
> 'S390_STACK_PARAMETER_ALIGNMENT' are clearly a good idea, for the sake
> of the other stuff I'd like to see a separate 's390x_push_arguments'
> function written that does things right for the s390x's ABI.  The
> helper functions like `is_simple_arg' should be duplicated, rather
> than testing GDB_TARGET_IS_ESAME.

Gives the thrust of the rationale.  Namely, its better to, from the 
start, have separate independant functions and not confuse things by 
adding more and more if(ISA/ABI) specific gunk.  As JimB noted, the MIPS 
is the not so shining example of how to do things (i.e., how things can 
go wrong).

For the sim, the original gencode tried to be smart and combine isa 
variants.  Given the age of the code, the number of CPU variants, and 
the number of developers making changes (the two are comparable and both 
are large!), it ended to end up with a total mess.  Someone trying to 
add one ISA would [always, I'm pretty sure it was] broke the other ISAs 
(only discovered months later) by either also adding instructions to 
other ISAs or, worse, removing/changing existing instructions.  Ulgh!

IGEN and MIPS.IGEN gave up.

Instead, the developer gets to spend a few minutes adding an ISA 
selector to every relevant instruction.  That's in the noise when 
compared to the amount of time that needs to be spent auding the 
instruction set looking for where the vendor has an instruction variant 
that deviates from the official spec (how many mul/adds are there?).  In 
the case of a variant, the instruction can cloned, taged and changed 
with the absolute certaintity that it won't break any other instruction, 
because none of the other instructions / ISAs are affected.

So, while this might sux from an asthetic point of view, it definitly 
doesn't sux from the point of view of being able to confidently, quickly 
and reliably update the simulator.

(cgd, does this answer your question?)
Andrew