From: Luke Kenneth Casson Leighton Date: Fri, 3 Mar 2023 10:32:45 +0000 (+0000) Subject: ls003: now 5 instructions being proposed. X-Git-Tag: opf_rfc_ls001_v3~200 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=0970139d9d2848364c8019a2262b57758107fd78;p=libreriscv.git ls003: now 5 instructions being proposed. shorten the words in the observations section to fit onto 1st page --- diff --git a/openpower/sv/rfc/ls003.mdwn b/openpower/sv/rfc/ls003.mdwn index 0ab082c0f..af41f94d2 100644 --- a/openpower/sv/rfc/ls003.mdwn +++ b/openpower/sv/rfc/ls003.mdwn @@ -46,7 +46,7 @@ Instructions added **Impact on processor**: ``` - Addition of four new GPR-based instructions + Addition of five new GPR-based instructions ``` **Impact on software**: @@ -76,14 +76,12 @@ Instructions added **Notes and Observations**: -TODO: address Jacob's comments: https://libre-soc.org/irclog/%23libre-soc.2022-10-28.log.html#t2022-10-28T18:00:27 - -1. It is not practical to add Rc=1 variants as VA-Form is used and +1. It is not practical to add Rc=1 variants when VA-Form is used and there is a **pair** of results produced. 2. An overflow variant (XER.OV set) of `divmod2du` would be valuable but VA-Form EXT004 is under severe pressure. 3. Both `maddhdu` and `divmod2du` instructions have been present in Intel x86 - for several decades. Likewise, variants of `dsld` and `dsrd`. + for several decades. Likewise, `dsld` and `dsrd`. 4. None of these instruction is present in VSX: these are 128/64 whereas VSX is 128/128. 5. `maddedu` and `divmod2du` are full inverses of each other, including @@ -91,11 +89,10 @@ TODO: address Jacob's comments: https://libre-soc.org/irclog/%23libre-soc.2022-1 6. These are all 3-in 2-out instructions. If Power ISA did not already have LD/ST-with-update instructions and instructions with `RAp` and `RTp` then these instructions would not be proposed. -7. `maddedus` is the first scalar signed/unsigned multiply instruction, the - only other signed/unsigned multiply instruction is `vmsummbm`, which has the - drawbacks that it is rather specialist, only working on bytes, - requires VSX/VMX, and isn't very suited for big-integer multiplication or - other general integer arithmetic. +7. `maddedus` is the first Scalar signed/unsigned multiply instruction. The + only other signed/unsigned multiply instruction is the + specialist `vmsummbm` (bytes only), requires VSX, + and is unsuited for big-integer or other general arithmetic. **Changes**