[PATCH] D136944: [AMDGPU] Enable `s_sendmsg_rtn` selection with `+gfx11-insts`

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added a comment.

In D136944#3899931 <https://reviews.llvm.org/D136944#3899931>, @foad wrote:

>> There's 3 different ways instructions can be illegal
>
> What are they?



1. Instruction doesn't exist for the subtarget, but is encodable. For example, all instructions added in CI aren't available for SI, but are encodable since nothing changed there.
2. Instruction does not exist for the subtarget, but the opcode was recycled into something else. This is the case for when v_mad_mix* was replaced with v_fma_mix* between gfx900 and gfx906
3. The instruction doesn't exist on the subtarget, and also isn't encodable. This is what happened with the image instructions for MI-200


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