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Published 20 hours ago • verified publisher icon riscv

PK* overlap with PACK* in Zbp

Open aswaterman opened this issue 3 years ago • 2 comments

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].

aswaterman avatar May 25 '21 17:05 aswaterman

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 avatar Sep 15 '21 03:09 chuanhua

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.

chuanhua avatar Sep 27 '21 03:09 chuanhua