PK* overlap with PACK* in Zbp

riscv / riscv-p-spec

RISC-V Packed SIMD Extension

https://jira.riscv.org/browse/RVG-129

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PK* overlap with PACK* in Zbp #56

Open aswaterman opened 3 years ago

aswaterman commented 3 years ago

PKBB16/PKBB32/PKTT16/PKTT32 overlap PACK[U][W] in Zbp.

Zbp is not yet frozen, but a subset is frozen: Zbb includes zext.h, which maps to pack[w] rd, rs1, x0.

My recommendation is to retain the Zbp encodings for PACK[U][W]. We then delete the corresponding PKBB16/PKBB32/PKTT16/PKTT32 instructions from P, then add PACK[U][W] to P.

Finally, we should consider changing the encoding of PKBT16/PKBT32/PKTB16/PKTB32 to be more similar to the encoding of PACK[U][W].

chuanhua commented 3 years ago

Release v0.9.7 (0560ad6) adds pack to replace pkbb16 in RV32 and pkbb32 in RV64. Release v0.9.7 (0560ad6) adds packu to replace pktt16 in RV32 and pktt32 in RV64.

chuanhua commented 3 years ago

Some usability issues are mentioned in #94. I think the comments there are worth considering for how to handle instruction overlaps if the overlaps only happen either for RV32 or RV64, but not both.