Conversation
lenary@types.pl

Sam

If NOP does nothing, why does the program counter change?

I think Architects and ISA designers should have more courage to say NOP means NOP, without this program counter funny business.

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dysfun@social.treehouse.systems

gaytabase

Reply to @lenary@types.pl

@lenary it doesn't do nothing, it performs no operation. subtle difference

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lenary@types.pl

Sam

Reply to @dysfun@social.treehouse.systems

@dysfun it's performing an operation on my program counter, tyvm, and i don't want it to

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palmer

Palmer Dabbelt

Reply to @lenary@types.pl
@lenary @dysfun the RISC-V specs used to say this ;)
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lenary@types.pl

Sam

Reply to @palmer

@palmer @dysfun I thought the RISC-V spec's attitude was "who needs NOP when you've got mov x0..."

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palmer

Palmer Dabbelt

Reply to @lenary@types.pl
@lenary @dysfun we've got everything: x0, NOP, hints, MOPs ...
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ahfrom@fedi.ahfrom.synology.me

Asta Halkjær From

Reply to @lenary@types.pl
@lenary @palmer @dysfun

> The NOP instruction does not change any user-visible state, except for advancing the pc. NOP is encoded as ADDI x0, x0, 0
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lenary@types.pl

Sam

Reply to @palmer

@palmer @dysfun ... pushes *and* pops

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lenary@types.pl

Sam

Reply to @ahfrom@fedi.ahfrom.synology.me

@ahfrom oh yeah, I forgot that RISC-V doesn't actually have MOV, it just has ADDI. Oops. So everything's an ADDI, even when nothing is happening.

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seancribbs@hachyderm.io

Sean Cribbs 🌻

Reply to @lenary@types.pl

@lenary obviously you've never written a bunch of NOPs to time the on/off of blinkenlights

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lenary@types.pl

Sam

Reply to @seancribbs@hachyderm.io

@seancribbs I'm not sure you understood my toot :)

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