[Simh] VAX emulation issues on Raspberry Pi

[Timothe Litt]

On 31-Jul-18 10:08, Paul Koning wrote:
>
>> On Jul 31, 2018, at 9:33 AM, Robert Armstrong <bob at jfcl.com> wrote:
>>
>> FWIW, this may also say something about the quality of the code
>> generation in gcc for ARM vs x86 processors, or it may even say
>> something about the relative efficiency of those two architectures. 
> One thing worth doing is to use the latest gcc.  Code generation keeps improving, and it's likely that architectures such as ARM see significant benefits in newer releases.
>
> 	

Bob's SimH shows:

Compiler: GCC 6.3.0 20170516

The latest gcc is 8.1.0.

It's a bit of a pain to build (I did it recently), but less so than in
years past.

On a Pi, it will take quite a while.  Be sure to use the latest
dependencies - gmp, mpc, mpfr.  And put in some place like /usr/local -
you don't want to replace the system compiler.

Read http://gcc.gnu.org/wiki/InstallingGCC &
https://gcc.gnu.org/install/index.html.

I haven't played with isl - it may help, or it may expose new issues.

You may be better off building a cross-compiler & building on a fast x86
or other platform if you have one.  Besides computes, I/O on the PI can
be pretty slow - USB is not a high-performance bus.  Especially if  you
need a bunch of hubs.

You also may need the latest binutils - if not for the build, for using
the compiler.  Somewhere between the version I used previously and the
new one, the object file format was enhanced incompatibly.

ARM is a RISCish architecture, x86 is a very CISC one, burdened with a
lot of backward compatibility.  Under the hood, it uses a lot of clever
optimizations.  Both are moving targets, as are their compilers.  (GCC
isn't the only choice.  Don't forget to try ICC if you want Intel's take
on optimized code for their CPUs.  And Clang is coming along.)  Don't
open the religious war over "relative efficiency"; the only thing that
matters is whether code that you care about has performance that you
deem adequate.

Have fun.

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