Re: Why I've Dropped In

On 6/11/2025 12:56 AM, Thomas Koenig wrote:

quadibloc <quadibloc@gmail.com> schrieb:
 

Since the basis of the ISA is a RISC-like ISA,

 [...]
 

3) Use only four base registers instead of eight.
4) Use only three index registers instead of seven.
5) Use only six index registers instead of seven, and use only four base
registers instead of eight when indexing is used.

 Having different classes of base and index registers is very
un-RISCy, and not generally a good idea.  General purpose registers
is one of the great things that the /360 got right, as the VAX
later did, and the 68000 didn't.
 

Agreed.
Ideally, one has an ISA where nearly all registers are the same:
   No distinction between base/index/data registers;
   No distinction between integer and floating point registers;
   No distinction between general registers and SIMD registers;
   ...
Though, there are tradeoffs. For example, SPRs can be, by definition, not the same as GPRs. Say, if you have an SP or LR, almost by definition, you will not be using it as a GPR.
So, if ZR/LR/SP/GP are "not GPR", this is fine.
Pretty much everything else is best served by being a GPR or suitably GPR like.
...