Sujet : Re: Stealing a Great Idea from the 6600
De : mitchalsup (at) *nospam* aol.com (MitchAlsup1)
Groupes : comp.archDate : 26. Apr 2024, 14:25:03
Autres entêtes
Organisation : Rocksolid Light
Message-ID : <ff78aaa73101509100f09f190838a2a7@www.novabbs.org>
References : 1 2 3 4 5 6 7 8 9 10 11 12
User-Agent : Rocksolid Light
BGB wrote:
On 4/25/2024 4:01 PM, George Neuner wrote:
On Tue, 23 Apr 2024 17:58:41 +0000, mitchalsup@aol.com (MitchAlsup1)
wrote:
>
Agreed in the sense that negative displacements exist.
However, can note that positive displacements tend to be significantly more common than negative ones. Whether or not it makes sense to have a negative displacement, depending mostly on the probability of greater than half of the missed displacements being negative.
From what I can tell, this seems to be:
~ 10 bits, scaled.
~ 13 bits, unscaled.
So, say, an ISA like RISC-V might have had a slightly hit rate with unsigned displacements than with signed displacements, but if one added 1 or 2 bits, signed would have still been a clear winner (or, with 1 or 2 fewer bits, unsigned a clear winner).
I ended up going with signed displacements for XG2, but it was pretty close to break-even in this case (when expanding from the 9-bit unsigned displacements in Baseline).
Granted, all signed or all-unsigned might be better from an ISA design consistency POV.
If one had 16-bit displacements, then unscaled displacements would make sense; otherwise scaled displacements seem like a win (misaligned displacements being much less common than aligned displacements).
What we need is ~16-bit displacements where 82½%-91¼% are positive.
How does one use a frame pointer without negative displacements ??
[FP+disp] accesses callee save registers
[FP-disp] accesses local stack variables and descriptors
[SP+disp] accesses argument and result values
But, admittedly, main reason I went with unscaled for GBR-rel and PC-rel Load/Store, was because using scaled displacements here would have required more relocation types (nevermind if the hit rate for unscaled 9-bit displacements is "pretty weak").
Though, did end up later adding specialized Scaled GBR-Rel Load/Store ops (to improve code density), so it might have been better in retrospect had I instead just went the "keep it scaled and add more reloc types to compensate" option.
....
YMMV.
Date | Sujet | # | | Auteur |
17 Apr 24 | Stealing a Great Idea from the 6600 | 128 | | John Savard |
18 Apr 24 | Re: Stealing a Great Idea from the 6600 | 125 | | MitchAlsup1 |
18 Apr 24 | Re: Stealing a Great Idea from the 6600 | 124 | | John Savard |
18 Apr 24 | Re: Stealing a Great Idea from the 6600 | 123 | | MitchAlsup1 |
19 Apr 24 | Re: Stealing a Great Idea from the 6600 | 122 | | John Savard |
19 Apr 24 | Re: Stealing a Great Idea from the 6600 | 121 | | John Savard |
19 Apr 24 | Re: Stealing a Great Idea from the 6600 | 120 | | MitchAlsup1 |
20 Apr 24 | Re: Stealing a Great Idea from the 6600 | 2 | | John Savard |
21 Apr 24 | Re: Stealing a Great Idea from the 6600 | 1 | | John Savard |
20 Apr 24 | Re: Stealing a Great Idea from the 6600 | 117 | | John Savard |
20 Apr 24 | Re: Stealing a Great Idea from the 6600 | 116 | | John Savard |
20 Apr 24 | Re: Stealing a Great Idea from the 6600 | 115 | | MitchAlsup1 |
20 Apr 24 | Re: Stealing a Great Idea from the 6600 | 105 | | BGB |
21 Apr 24 | Re: Stealing a Great Idea from the 6600 | 104 | | MitchAlsup1 |
21 Apr 24 | Re: Stealing a Great Idea from the 6600 | 63 | | John Savard |
21 Apr 24 | Re: Stealing a Great Idea from the 6600 | 15 | | John Savard |
25 Apr 24 | Re: Stealing a Great Idea from the 6600 | 14 | | Lawrence D'Oliveiro |
25 Apr 24 | Re: Stealing a Great Idea from the 6600 | 12 | | MitchAlsup1 |
25 Apr 24 | Re: Stealing a Great Idea from the 6600 | 1 | | Lawrence D'Oliveiro |
30 Apr 24 | Re: a bit of history, Stealing a Great Idea from the 6600 | 10 | | John Levine |
3 May 24 | Re: a bit of history, Stealing a Great Idea from the 6600 | 9 | | Anton Ertl |
3 May 24 | Re: a bit of history, Stealing a Great Idea from the 6600 | 7 | | John Levine |
4 May 24 | Re: a bit of history, Stealing a Great Idea from the 6600 | 6 | | Thomas Koenig |
4 May 24 | Re: a bit of history, Stealing a Great Idea from the 6600 | 4 | | John Levine |
4 May 24 | Re: a bit of history, Stealing a Great Idea from the 6600 | 3 | | MitchAlsup1 |
5 May 24 | Re: a bit of history, Stealing a Great Idea from the 6600 | 2 | | Thomas Koenig |
5 May 24 | Re: a bit of history, Stealing a Great Idea from the 6600 | 1 | | MitchAlsup1 |
28 Jul 24 | Re: a bit of history, Stealing a Great Idea from the 6600 | 1 | | Lawrence D'Oliveiro |
3 May 24 | Re: a bit of history, Stealing a Great Idea from the 6600 | 1 | | MitchAlsup1 |
25 Apr 24 | Re: Stealing a Great Idea from the 6600 | 1 | | John Savard |
21 Apr 24 | Re: Stealing a Great Idea from the 6600 | 47 | | MitchAlsup1 |
23 Apr 24 | Re: Stealing a Great Idea from the 6600 | 45 | | George Neuner |
23 Apr 24 | Re: Stealing a Great Idea from the 6600 | 44 | | MitchAlsup1 |
25 Apr 24 | Re: Stealing a Great Idea from the 6600 | 43 | | George Neuner |
26 Apr 24 | Re: Stealing a Great Idea from the 6600 | 42 | | BGB |
26 Apr 24 | Re: Stealing a Great Idea from the 6600 | 41 | | MitchAlsup1 |
26 Apr 24 | Re: Stealing a Great Idea from the 6600 | 2 | | Anton Ertl |
26 Apr 24 | Re: Stealing a Great Idea from the 6600 | 1 | | MitchAlsup1 |
26 Apr 24 | Re: Stealing a Great Idea from the 6600 | 4 | | BGB |
26 Apr 24 | Re: Stealing a Great Idea from the 6600 | 2 | | MitchAlsup1 |
27 Apr 24 | Re: Stealing a Great Idea from the 6600 | 1 | | BGB |
26 Apr 24 | Re: Stealing a Great Idea from the 6600 | 1 | | MitchAlsup1 |
27 Apr 24 | Re: Stealing a Great Idea from the 6600 | 34 | | BGB |
27 Apr 24 | Re: Stealing a Great Idea from the 6600 | 33 | | MitchAlsup1 |
28 Apr 24 | Re: Stealing a Great Idea from the 6600 | 32 | | BGB |
28 Apr 24 | Re: Stealing a Great Idea from the 6600 | 31 | | MitchAlsup1 |
28 Apr 24 | Re: Stealing a Great Idea from the 6600 | 30 | | BGB |
28 Apr 24 | Re: Stealing a Great Idea from the 6600 | 24 | | BGB |
28 Apr 24 | Re: Stealing a Great Idea from the 6600 | 23 | | BGB |
28 Apr 24 | Re: Stealing a Great Idea from the 6600 | 22 | | Thomas Koenig |
28 Apr 24 | Re: Stealing a Great Idea from the 6600 | 21 | | BGB |
28 Apr 24 | Re: Stealing a Great Idea from the 6600 | 20 | | BGB |
28 Apr 24 | Re: Stealing a Great Idea from the 6600 | 2 | | Thomas Koenig |
28 Apr 24 | Re: Stealing a Great Idea from the 6600 | 1 | | BGB |
29 Jul 24 | Re: Stealing a Great Idea from the 6600 | 16 | | Lawrence D'Oliveiro |
29 Jul 24 | Re: Stealing a Great Idea from the 6600 | 6 | | BGB |
30 Jul 24 | Re: Stealing a Great Idea from the 6600 | 5 | | Lawrence D'Oliveiro |
30 Jul 24 | Re: Stealing a Great Idea from the 6600 | 4 | | BGB |
31 Jul 24 | Re: Stealing a Great Idea from the 6600 | 3 | | Lawrence D'Oliveiro |
31 Jul 24 | Re: Stealing a Great Idea from the 6600 | 2 | | BGB |
1 Aug 24 | Re: Stealing a Great Idea from the 6600 | 1 | | Lawrence D'Oliveiro |
29 Jul 24 | Re: Stealing a Great Idea from the 6600 | 9 | | Terje Mathisen |
29 Jul 24 | Re: Stealing a Great Idea from the 6600 | 8 | | MitchAlsup1 |
30 Jul 24 | Re: Stealing a Great Idea from the 6600 | 1 | | Lawrence D'Oliveiro |
30 Jul 24 | Re: Stealing a Great Idea from the 6600 | 4 | | Michael S |
30 Jul 24 | Re: Stealing a Great Idea from the 6600 | 3 | | MitchAlsup1 |
31 Jul 24 | Re: Stealing a Great Idea from the 6600 | 2 | | BGB |
1 Aug 24 | Re: Stealing a Great Idea from the 6600 | 1 | | Lawrence D'Oliveiro |
1 Aug 24 | Re: Stealing a Great Idea from the 6600 | 2 | | Thomas Koenig |
1 Aug 24 | Re: Stealing a Great Idea from the 6600 | 1 | | MitchAlsup1 |
29 Jul 24 | Re: Stealing a Great Idea from the 6600 | 1 | | George Neuner |
28 Apr 24 | Re: Stealing a Great Idea from the 6600 | 5 | | MitchAlsup1 |
28 Apr 24 | Re: Stealing a Great Idea from the 6600 | 4 | | BGB |
29 Apr 24 | Re: Stealing a Great Idea from the 6600 | 3 | | MitchAlsup1 |
29 Apr 24 | Re: Stealing a Great Idea from the 6600 | 2 | | BGB |
29 Apr 24 | Re: Stealing a Great Idea from the 6600 | 1 | | Thomas Koenig |
29 Apr 24 | Re: Stealing a Great Idea from the 6600 | 1 | | Tim Rentsch |
21 Apr 24 | Re: Stealing a Great Idea from the 6600 | 40 | | BGB |
21 Apr 24 | Re: Stealing a Great Idea from the 6600 | 39 | | MitchAlsup1 |
22 Apr 24 | Re: Stealing a Great Idea from the 6600 | 3 | | BGB |
22 Apr 24 | Re: Stealing a Great Idea from the 6600 | 2 | | MitchAlsup1 |
22 Apr 24 | Re: Stealing a Great Idea from the 6600 | 1 | | BGB |
22 Apr 24 | Re: Stealing a Great Idea from the 6600 | 2 | | John Savard |
22 Apr 24 | Re: Stealing a Great Idea from the 6600 | 1 | | BGB |
22 Apr 24 | Re: Stealing a Great Idea from the 6600 | 33 | | Terje Mathisen |
22 Apr 24 | Re: Stealing a Great Idea from the 6600 | 1 | | BGB |
13 Jun 24 | Re: Stealing a Great Idea from the 6600 | 31 | | Kent Dickey |
13 Jun 24 | Re: Stealing a Great Idea from the 6600 | 16 | | Stefan Monnier |
13 Jun 24 | Re: Stealing a Great Idea from the 6600 | 15 | | BGB |
13 Jun 24 | Re: Stealing a Great Idea from the 6600 | 14 | | MitchAlsup1 |
14 Jun 24 | Re: Stealing a Great Idea from the 6600 | 13 | | BGB |
18 Jun 24 | Re: Stealing a Great Idea from the 6600 | 12 | | MitchAlsup1 |
19 Jun 24 | Re: Stealing a Great Idea from the 6600 | 8 | | BGB |
19 Jun 24 | Re: Stealing a Great Idea from the 6600 | 7 | | MitchAlsup1 |
19 Jun 24 | Re: Stealing a Great Idea from the 6600 | 5 | | BGB |
19 Jun 24 | Re: Stealing a Great Idea from the 6600 | 4 | | MitchAlsup1 |
20 Jun 24 | Re: Stealing a Great Idea from the 6600 | 3 | | Thomas Koenig |
20 Jun 24 | Re: Stealing a Great Idea from the 6600 | 2 | | MitchAlsup1 |
21 Jun 24 | Re: Stealing a Great Idea from the 6600 | 1 | | Thomas Koenig |
20 Jun 24 | Re: Stealing a Great Idea from the 6600 | 1 | | John Savard |
19 Jun 24 | Re: Stealing a Great Idea from the 6600 | 1 | | Thomas Koenig |
20 Jun 24 | Re: Stealing a Great Idea from the 6600 | 1 | | MitchAlsup1 |
31 Jul 24 | Re: Stealing a Great Idea from the 6600 | 1 | | Lawrence D'Oliveiro |
13 Jun 24 | Re: Stealing a Great Idea from the 6600 | 13 | | MitchAlsup1 |
14 Jun 24 | Re: Stealing a Great Idea from the 6600 | 1 | | Terje Mathisen |
22 Apr 24 | Re: Stealing a Great Idea from the 6600 | 9 | | John Savard |
18 Apr 24 | Re: Stealing a Great Idea from the 6600 | 2 | | Lawrence D'Oliveiro |