[isa-dev] Zcmp vs expanded Zcmt
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L Peter Deutsch
Oct 18, 2022, 10:42:29 AM10/18/22
to isa...@groups.riscv.org
How important is execution speed, as opposed to code compression? If
execution speed is not a significant goal, it would get rid of the vexing
issues associated with the Zcmp opcodes to replace them with more Zcmt
entries, with one tweak. Specifically:
- cm.popret and cm.popretz can be replaced with cm.jt .
- All of the other cm.* opcodes can be replaced with cm.jalt if we use bit 0
of the address in the jump table to indicate that the return address should
be placed in x5 rather than x1, the ABI standard for millicode.
--
L Peter Deutsch :: Aladdin Enterprises :: Healdsburg, CA & Burnaby, BC
execution speed is not a significant goal, it would get rid of the vexing
issues associated with the Zcmp opcodes to replace them with more Zcmt
entries, with one tweak. Specifically:
- cm.popret and cm.popretz can be replaced with cm.jt .
- All of the other cm.* opcodes can be replaced with cm.jalt if we use bit 0
of the address in the jump table to indicate that the return address should
be placed in x5 rather than x1, the ABI standard for millicode.
--
L Peter Deutsch :: Aladdin Enterprises :: Healdsburg, CA & Burnaby, BC
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