s_sethalt with SIMM16[0] clear is a no-op; s_sethalt 1, s_sendmsghalt, a reached s_code_end, s_rfe_b64, the ds_gws_* instructions and ds_ordered_count throw with the reason at translation. Linear decoding stops at s_code_end like at s_endpgm, so code padded with s_code_end after a final backward branch decodes. Encodings from LLVM SOPInstructions.td and DSInstructions.td, checked against the gfx10 MC tests; semantics from the RDNA 2 ISA guide.
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