On 2018-01-26 22:49, Hunter Goatley wrote:
On 1/26/2018 3:28 PM, Timothe Litt wrote:
Sounds right. The -16 and -36 versions stayed with the native backend
and didn't get much attention once GEM took off. At least, I don't
recall GEM support for them.
I believe that's correct.
So, no GEM for BLISS-16, and most likely no chance of it being ported to
Alpha then. Thanks for confirming that.
All three (CMU ,BLISS, GEM) back ends used considerable creativity in
interpreting the instruction sets, and as time went on gave hand-coded
assembler a run for its money. They especially liked to do
computations with bizarre-looking address calculations. (Not all of
which ran fast on all processors.) In one case, a particularly
"clever" encoding of a test on a link-time constant broke RMS on an
unreleased VAX CPU. Interestingly, this one instruction was the ONLY
time this construct was encountered in all of VMS (including the top
dozen layered products), so waiting for the hardware spin wasn't as
bad as it might have been.
I vaguely remember hearing about that.
BLISS-32 on VAX generated some amazing optimizations. Before I got into
BLISS, I programmed almost exclusively in MACRO-32, and it was fun to
compare code I wrote to the assembly code generated by the BLISS
compiler. Several times, I encountered generated code that was a lot
more efficient than the code I wrote, which I thought was very
efficient. I learned a few MACRO tricks looking at the code generated.
It was less fun trying to understand the GEM output for Alpha. ;-)
Heh. I've had similar experiences with BLISS-16. I've learned a trick or
two looking at the code generated, and it can do some rather neat
tricks. Definitely impressive code generated. Not seen that level from
any other PDP-11 compiler.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: [email protected] || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
_______________________________________________
Simh mailing list
[email protected]
http://mailman.trailing-edge.com/mailman/listinfo/simh
