Re: Stealing a Great Idea from the 6600

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Sujet : Re: Stealing a Great Idea from the 6600
De : mitchalsup (at) *nospam* aol.com (MitchAlsup1)
Groupes : comp.arch
Date : 27. Apr 2024, 21:37:34
Autres entêtes
Organisation : Rocksolid Light
Message-ID : <3458ae0a6b7c1f667ef232c58569b5e1@www.novabbs.org>
References : 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
User-Agent : Rocksolid Light
BGB wrote:

On 4/26/2024 1:59 PM, EricP wrote:
MitchAlsup1 wrote:
BGB wrote:
>
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
 A sign extended 16-bit offsets would cover almost all such access needs
so I really don't see the need for funny business.
 But if you really want a skewed range offset it could use something like
excess-256 encoding which zero extends the immediate then subtract 256
(or whatever) from it, to give offsets in the range -256..+65535-256.
So an immediate value of 0 equals an offset of -256.
 

Yeah, my thinking was that by the time one has 16 bits for Load/Store displacements, they could almost just go +/- 32K and call it done.

But, much smaller than this, there is an advantage to scaling the displacements.

In other news, got around to getting the RISC-V code to build in PIE mode for Doom (by using "riscv64-unknown-linux-gnu-*").

Can note that RV64 code density takes a hit in this case:
   RV64: 299K (.text)
   XG2 : 284K (.text)
Is this indicative that your ISA and RISC-V are within spitting distance of each other in terms of the number of instructions in .text ?? or not ??

So, apparently using this version of GCC and using "-fPIE" works in my favor regarding code density...

I guess a question is what FDPIC would do if GCC supported it, since this would be the closest direct analog to my own ABI.
What is FDPIC ?? Federal Deposit Processor Insurance   Corporation ??
                 Final   Dopey   Position  Independent Code ??

I guess some people are dragging their feet on FDPIC, as there is some debate as to whether or not NOMMU makes sense for RISC-V, along with its associated performance impact if used.

In my case, if I wanted to go over to simple base-relocatable images, this would technically eliminate the need for GBR reloading.

Checks:
Simple base-relocatable case actually currently generates bigger binaries, I suspect because in this case it is less space-efficient to use PC-rel vs GBR-rel.

Went and added a "pbostatic" option, which sidesteps saving and restoring GBR (making the simplifying assumption that functions will never be called from outside the current binary).

This saves roughly 4K (Doom's ".text" shrinks to 280K).
Would you be willing to compile DOOM with Brian's LLVM compiler and
show the results ??

....

Date Sujet#  Auteur
17 Apr 24 * Stealing a Great Idea from the 6600128John Savard
18 Apr 24 +* Re: Stealing a Great Idea from the 6600125MitchAlsup1
18 Apr 24 i`* Re: Stealing a Great Idea from the 6600124John Savard
18 Apr 24 i `* Re: Stealing a Great Idea from the 6600123MitchAlsup1
19 Apr 24 i  `* Re: Stealing a Great Idea from the 6600122John Savard
19 Apr 24 i   `* Re: Stealing a Great Idea from the 6600121John Savard
19 Apr 24 i    `* Re: Stealing a Great Idea from the 6600120MitchAlsup1
20 Apr 24 i     +* Re: Stealing a Great Idea from the 66002John Savard
21 Apr 24 i     i`- Re: Stealing a Great Idea from the 66001John Savard
20 Apr 24 i     `* Re: Stealing a Great Idea from the 6600117John Savard
20 Apr 24 i      `* Re: Stealing a Great Idea from the 6600116John Savard
20 Apr 24 i       `* Re: Stealing a Great Idea from the 6600115MitchAlsup1
20 Apr 24 i        +* Re: Stealing a Great Idea from the 6600105BGB
21 Apr 24 i        i`* Re: Stealing a Great Idea from the 6600104MitchAlsup1
21 Apr 24 i        i +* Re: Stealing a Great Idea from the 660063John Savard
21 Apr 24 i        i i+* Re: Stealing a Great Idea from the 660015John Savard
25 Apr 24 i        i ii`* Re: Stealing a Great Idea from the 660014Lawrence D'Oliveiro
25 Apr 24 i        i ii +* Re: Stealing a Great Idea from the 660012MitchAlsup1
25 Apr 24 i        i ii i+- Re: Stealing a Great Idea from the 66001Lawrence D'Oliveiro
30 Apr 24 i        i ii i`* Re: a bit of history, Stealing a Great Idea from the 660010John Levine
3 May 24 i        i ii i `* Re: a bit of history, Stealing a Great Idea from the 66009Anton Ertl
3 May 24 i        i ii i  +* Re: a bit of history, Stealing a Great Idea from the 66007John Levine
4 May 24 i        i ii i  i`* Re: a bit of history, Stealing a Great Idea from the 66006Thomas Koenig
4 May 24 i        i ii i  i +* Re: a bit of history, Stealing a Great Idea from the 66004John Levine
4 May 24 i        i ii i  i i`* Re: a bit of history, Stealing a Great Idea from the 66003MitchAlsup1
5 May 24 i        i ii i  i i `* Re: a bit of history, Stealing a Great Idea from the 66002Thomas Koenig
5 May 24 i        i ii i  i i  `- Re: a bit of history, Stealing a Great Idea from the 66001MitchAlsup1
28 Jul 24 i        i ii i  i `- Re: a bit of history, Stealing a Great Idea from the 66001Lawrence D'Oliveiro
3 May 24 i        i ii i  `- Re: a bit of history, Stealing a Great Idea from the 66001MitchAlsup1
25 Apr 24 i        i ii `- Re: Stealing a Great Idea from the 66001John Savard
21 Apr 24 i        i i`* Re: Stealing a Great Idea from the 660047MitchAlsup1
23 Apr 24 i        i i +* Re: Stealing a Great Idea from the 660045George Neuner
23 Apr 24 i        i i i`* Re: Stealing a Great Idea from the 660044MitchAlsup1
25 Apr 24 i        i i i `* Re: Stealing a Great Idea from the 660043George Neuner
26 Apr 24 i        i i i  `* Re: Stealing a Great Idea from the 660042BGB
26 Apr 24 i        i i i   `* Re: Stealing a Great Idea from the 660041MitchAlsup1
26 Apr 24 i        i i i    +* Re: Stealing a Great Idea from the 66002Anton Ertl
26 Apr 24 i        i i i    i`- Re: Stealing a Great Idea from the 66001MitchAlsup1
26 Apr 24 i        i i i    +* Re: Stealing a Great Idea from the 66004BGB
26 Apr 24 i        i i i    i+* Re: Stealing a Great Idea from the 66002MitchAlsup1
27 Apr 24 i        i i i    ii`- Re: Stealing a Great Idea from the 66001BGB
26 Apr 24 i        i i i    i`- Re: Stealing a Great Idea from the 66001MitchAlsup1
27 Apr 24 i        i i i    `* Re: Stealing a Great Idea from the 660034BGB
27 Apr 24 i        i i i     `* Re: Stealing a Great Idea from the 660033MitchAlsup1
28 Apr 24 i        i i i      `* Re: Stealing a Great Idea from the 660032BGB
28 Apr 24 i        i i i       `* Re: Stealing a Great Idea from the 660031MitchAlsup1
28 Apr 24 i        i i i        `* Re: Stealing a Great Idea from the 660030BGB
28 Apr 24 i        i i i         +* Re: Stealing a Great Idea from the 660024BGB
28 Apr 24 i        i i i         i`* Re: Stealing a Great Idea from the 660023BGB
28 Apr 24 i        i i i         i `* Re: Stealing a Great Idea from the 660022Thomas Koenig
28 Apr 24 i        i i i         i  `* Re: Stealing a Great Idea from the 660021BGB
28 Apr 24 i        i i i         i   `* Re: Stealing a Great Idea from the 660020BGB
28 Apr 24 i        i i i         i    +* Re: Stealing a Great Idea from the 66002Thomas Koenig
28 Apr 24 i        i i i         i    i`- Re: Stealing a Great Idea from the 66001BGB
29 Jul 24 i        i i i         i    +* Re: Stealing a Great Idea from the 660016Lawrence D'Oliveiro
29 Jul 24 i        i i i         i    i+* Re: Stealing a Great Idea from the 66006BGB
30 Jul 24 i        i i i         i    ii`* Re: Stealing a Great Idea from the 66005Lawrence D'Oliveiro
30 Jul 24 i        i i i         i    ii `* Re: Stealing a Great Idea from the 66004BGB
31 Jul 24 i        i i i         i    ii  `* Re: Stealing a Great Idea from the 66003Lawrence D'Oliveiro
31 Jul 24 i        i i i         i    ii   `* Re: Stealing a Great Idea from the 66002BGB
1 Aug 24 i        i i i         i    ii    `- Re: Stealing a Great Idea from the 66001Lawrence D'Oliveiro
29 Jul 24 i        i i i         i    i`* Re: Stealing a Great Idea from the 66009Terje Mathisen
29 Jul 24 i        i i i         i    i `* Re: Stealing a Great Idea from the 66008MitchAlsup1
30 Jul 24 i        i i i         i    i  +- Re: Stealing a Great Idea from the 66001Lawrence D'Oliveiro
30 Jul 24 i        i i i         i    i  +* Re: Stealing a Great Idea from the 66004Michael S
30 Jul 24 i        i i i         i    i  i`* Re: Stealing a Great Idea from the 66003MitchAlsup1
31 Jul 24 i        i i i         i    i  i `* Re: Stealing a Great Idea from the 66002BGB
1 Aug 24 i        i i i         i    i  i  `- Re: Stealing a Great Idea from the 66001Lawrence D'Oliveiro
1 Aug 24 i        i i i         i    i  `* Re: Stealing a Great Idea from the 66002Thomas Koenig
1 Aug 24 i        i i i         i    i   `- Re: Stealing a Great Idea from the 66001MitchAlsup1
29 Jul 24 i        i i i         i    `- Re: Stealing a Great Idea from the 66001George Neuner
28 Apr 24 i        i i i         `* Re: Stealing a Great Idea from the 66005MitchAlsup1
28 Apr 24 i        i i i          `* Re: Stealing a Great Idea from the 66004BGB
29 Apr 24 i        i i i           `* Re: Stealing a Great Idea from the 66003MitchAlsup1
29 Apr 24 i        i i i            `* Re: Stealing a Great Idea from the 66002BGB
29 Apr 24 i        i i i             `- Re: Stealing a Great Idea from the 66001Thomas Koenig
29 Apr 24 i        i i `- Re: Stealing a Great Idea from the 66001Tim Rentsch
21 Apr 24 i        i `* Re: Stealing a Great Idea from the 660040BGB
21 Apr 24 i        i  `* Re: Stealing a Great Idea from the 660039MitchAlsup1
22 Apr 24 i        i   +* Re: Stealing a Great Idea from the 66003BGB
22 Apr 24 i        i   i`* Re: Stealing a Great Idea from the 66002MitchAlsup1
22 Apr 24 i        i   i `- Re: Stealing a Great Idea from the 66001BGB
22 Apr 24 i        i   +* Re: Stealing a Great Idea from the 66002John Savard
22 Apr 24 i        i   i`- Re: Stealing a Great Idea from the 66001BGB
22 Apr 24 i        i   `* Re: Stealing a Great Idea from the 660033Terje Mathisen
22 Apr 24 i        i    +- Re: Stealing a Great Idea from the 66001BGB
13 Jun 24 i        i    `* Re: Stealing a Great Idea from the 660031Kent Dickey
13 Jun 24 i        i     +* Re: Stealing a Great Idea from the 660016Stefan Monnier
13 Jun 24 i        i     i`* Re: Stealing a Great Idea from the 660015BGB
13 Jun 24 i        i     i `* Re: Stealing a Great Idea from the 660014MitchAlsup1
14 Jun 24 i        i     i  `* Re: Stealing a Great Idea from the 660013BGB
18 Jun 24 i        i     i   `* Re: Stealing a Great Idea from the 660012MitchAlsup1
19 Jun 24 i        i     i    +* Re: Stealing a Great Idea from the 66008BGB
19 Jun 24 i        i     i    i`* Re: Stealing a Great Idea from the 66007MitchAlsup1
19 Jun 24 i        i     i    i +* Re: Stealing a Great Idea from the 66005BGB
19 Jun 24 i        i     i    i i`* Re: Stealing a Great Idea from the 66004MitchAlsup1
20 Jun 24 i        i     i    i i `* Re: Stealing a Great Idea from the 66003Thomas Koenig
20 Jun 24 i        i     i    i i  `* Re: Stealing a Great Idea from the 66002MitchAlsup1
21 Jun 24 i        i     i    i i   `- Re: Stealing a Great Idea from the 66001Thomas Koenig
20 Jun 24 i        i     i    i `- Re: Stealing a Great Idea from the 66001John Savard
19 Jun 24 i        i     i    +- Re: Stealing a Great Idea from the 66001Thomas Koenig
20 Jun 24 i        i     i    +- Re: Stealing a Great Idea from the 66001MitchAlsup1
31 Jul 24 i        i     i    `- Re: Stealing a Great Idea from the 66001Lawrence D'Oliveiro
13 Jun 24 i        i     +* Re: Stealing a Great Idea from the 660013MitchAlsup1
14 Jun 24 i        i     `- Re: Stealing a Great Idea from the 66001Terje Mathisen
22 Apr 24 i        `* Re: Stealing a Great Idea from the 66009John Savard
18 Apr 24 `* Re: Stealing a Great Idea from the 66002Lawrence D'Oliveiro

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