[PATCH] D56474: [ARM] [NEON] Add ROTR/ROTL lowering

[easyaspi314 (Devin) via Phabricator via llvm-commits]

easyaspi314 added a comment.

Definitely either result/writeback cycles.

                               @ Cy / Re / Wr
  vld1.8 { inpLo, inpHi }, [p] @  2 /  2 /  6
  vmla.i32 v, inp, prime2      @  4 /  9 /  9
  vshr.u32 v2, v, #19          @  1 /  3 /  6
  vsli.32 v2, v, #13           @  2 /  4 /  7
  vmul.i32 v, v2, prime1       @  4 /  9 /  9
                               @ 13 / 27 / 37



  vld1.8 { inpLo, inpHi }, [p] @  2 /  2 /  6
  vmla.i32 v, inp, prime2      @  4 /  9 /  9
  vshr.u32 tmp, v, #19         @  1 /  3 /  6
  vshl.i32 v, v, #13           @  1 /  3 /  6
  vorr v, v, tmp               @  1 /  3 /  6
  vmul.i32 v, v, prime1        @  4 /  9 /  9
                               @ 13 / 29 / 42

If we count result cycles, we get 29 cycles with `vshr`/`vshr`/`vorr`, and 27 cycles with `vshr`/`vsli`. 29/27 = 1.074. If we count writeback cycles, we get 1.135.  That checks out with the 1.10x ratio I saw in the benchmark, as it lands right in that range.


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https://reviews.llvm.org/D56474