Re: Oops (Concertina II Going Around in Circles)

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Sujet : Re: Oops (Concertina II Going Around in Circles)
De : anton (at) *nospam* mips.complang.tuwien.ac.at (Anton Ertl)
Groupes : comp.arch
Date : 11. May 2024, 18:48:51
Autres entêtes
Organisation : Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID : <2024May11.194851@mips.complang.tuwien.ac.at>
References : 1 2
User-Agent : xrn 10.11
jgd@cix.co.uk (John Dallman) writes:
Also, teaching development tools about vast instruction sets is likely to
demonstrate the RISC lesson again: compilers only use the simple parts.

That needs some elaboration.  There are several potential reasons for
that:

1) The compiler writers found it too hard to use the complex
instructions or addressing modes.  For some kinds of instructions that
is the case (e.g, for the AES instructions in Intel and AMD CPUs), but
at least these days such instructions are there for use in libraries
written in assembly language/with intrinsics.

2) Some instructions are slower than a sequence of simpler
instructions, so compilers will avoid them even if they would
otherwise use them.  That has been reported by both the IBM 801
project about some S/370 instructions and by the Berkeley RISC project
about the VAX.  I don't remember any reports about addressing modes
with that problem.

3) Some instructions or addressing modes can be selected by compilers
and are beneficial when they are used, but they are selected rarely
because they fit the needs of the compiled program rarely.

IIRC the RISC papers mentioned mainly 2), with a little bit of 3).

- anton
--
'Anyone trying for "industrial quality" ISA should avoid undefined behavior.'
  Mitch Alsup, <c17fcd89-f024-40e7-a594-88a85ac10d20o@googlegroups.com>

Date Sujet#  Auteur
25 Apr 24 * Oops (Concertina II Going Around in Circles)53John Savard
25 Apr 24 +* Re: Oops (Concertina II Going Around in Circles)44MitchAlsup1
25 Apr 24 i+* Re: Oops (Concertina II Going Around in Circles)2John Savard
25 Apr 24 ii`- Re: Oops (Concertina II Going Around in Circles)1John Savard
25 Apr 24 i+- Re: Oops (Concertina II Going Around in Circles)1BGB
8 May 24 i`* Re: Oops (Concertina II Going Around in Circles)40John Savard
8 May 24 i +* Re: Oops (Concertina II Going Around in Circles)3John Savard
8 May 24 i i`* Re: Oops (Concertina II Going Around in Circles)2MitchAlsup1
9 May 24 i i `- Re: Oops (Concertina II Going Around in Circles)1John Savard
8 May 24 i +- Re: Oops (Concertina II Going Around in Circles)1John Savard
8 May 24 i `* Re: Oops (Concertina II Going Around in Circles)35MitchAlsup1
9 May 24 i  +* Re: Oops (Concertina II Going Around in Circles)6John Savard
9 May 24 i  i+* Re: Oops (Concertina II Going Around in Circles)3MitchAlsup1
9 May 24 i  ii`* Re: Oops (Concertina II Going Around in Circles)2John Savard
9 May 24 i  ii `- Re: Oops (Concertina II Going Around in Circles)1Thomas Koenig
9 May 24 i  i`* Re: Oops (Concertina II Going Around in Circles)2MitchAlsup1
10 May 24 i  i `- Re: Oops (Concertina II Going Around in Circles)1MitchAlsup1
9 May 24 i  `* Re: Oops (Concertina II Going Around in Circles)28John Savard
9 May 24 i   `* Re: Oops (Concertina II Going Around in Circles)27John Savard
9 May 24 i    `* Re: Oops (Concertina II Going Around in Circles)26John Savard
9 May 24 i     `* Re: Oops (Concertina II Going Around in Circles)25John Savard
9 May 24 i      `* Re: Oops (Concertina II Going Around in Circles)24John Dallman
9 May 24 i       +* Re: Oops (Concertina II Going Around in Circles)21John Savard
10 May 24 i       i`* Re: Oops (Concertina II Going Around in Circles)20John Dallman
10 May 24 i       i +* Re: Oops (Concertina II Going Around in Circles)13John Savard
10 May 24 i       i i+* Re: Oops (Concertina II Going Around in Circles)10MitchAlsup1
10 May 24 i       i ii`* Re: Oops (Concertina II Going Around in Circles)9John Savard
10 May 24 i       i ii +* Re: Oops (Concertina II Going Around in Circles)6MitchAlsup1
11 May 24 i       i ii i+* Re: Oops (Concertina II Going Around in Circles)4John Savard
11 May 24 i       i ii ii+- Re: Oops (Concertina II Going Around in Circles)1John Savard
11 May 24 i       i ii ii`* Re: Oops (Concertina II Going Around in Circles)2MitchAlsup1
11 May 24 i       i ii ii `- Re: Oops (Concertina II Going Around in Circles)1John Savard
11 May 24 i       i ii i`- Re: Oops (Concertina II Going Around in Circles)1John Savard
11 May 24 i       i ii `* Re: Oops (Concertina II Going Around in Circles)2Thomas Koenig
11 May 24 i       i ii  `- Re: Oops (Concertina II Going Around in Circles)1John Savard
10 May 24 i       i i`* Re: Oops (Concertina II Going Around in Circles)2John Dallman
10 May 24 i       i i `- Re: Oops (Concertina II Going Around in Circles)1BGB
10 May 24 i       i +- Re: Oops (Concertina II Going Around in Circles)1BGB
11 May 24 i       i `* Re: Oops (Concertina II Going Around in Circles)5Anton Ertl
11 May 24 i       i  `* Re: Oops (Concertina II Going Around in Circles)4MitchAlsup1
12 May 24 i       i   `* Compiler use of instructions (was: Oops)3Anton Ertl
12 May 24 i       i    `* Re: Compiler use of instructions (was: Oops)2John Levine
13 May 24 i       i     `- Re: Compiler use of instructions1MitchAlsup1
12 May 24 i       `* Re: Oops (Concertina II Going Around in Circles)2John Savard
12 May 24 i        `- Re: Oops (Concertina II Going Around in Circles)1Thomas Koenig
5 May 24 +* Re: Oops (Concertina II Going Around in Circles)6John Savard
6 May 24 i+* Re: Oops (Concertina II Going Around in Circles)3John Savard
7 May 24 ii`* Re: Oops (Concertina II Going Around in Circles)2John Savard
8 May 24 ii `- Re: Oops (Concertina II Going Around in Circles)1John Savard
6 May 24 i`* Re: Oops (Concertina II Going Around in Circles)2John Savard
6 May 24 i `- Re: Oops (Concertina II Going Around in Circles)1MitchAlsup1
12 May 24 `* Re: Oops (Concertina II Going Around in Circles)2John Savard
12 May 24  `- Re: Oops (Concertina II Going Around in Circles)1John Savard

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