[PATCH] D98936: [RISCV] DAG nodes and pseudo instructions for CSR access

[Jessica Clarke via Phabricator via llvm-commits]

jrtc27 added a comment.

In D98936#2661228 <https://reviews.llvm.org/D98936#2661228>, @asb wrote:

> In D98936#2642039 <https://reviews.llvm.org/D98936#2642039>, @jrtc27 wrote:
>
>> Are there ever any cases where you _wouldn't_ want a CSR-specific pseudo in order to have control over the scheduling of it specifically? This feels a bit like a middle-ground that's the worst of both worlds to me.
>
> Hi @jrtc27 - could you please elaborate a little on the concern that the approach in this path might be the worst of both worlds? I'm not sure I fully follow. Thanks.

If you want to have different scheduling for different CSRs, do you not need per-CSR pseudos in order to express that? This diff is ostensibly to allow for that in future, but is at a much coarser read/write/swap granularity, so doesn't really get you much over and above just scheduling CSRRW itself as a whole, just adds more complexity for little gain. IMO any CSRs we need scheduling info for should just get their own dedicated read/write/swap pseudos as and when they're needed.


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