nir/loop_analyze: consider movs/vecs free

They are free more likely than not.

Foz-DB Navi31:
Totals from 462 (0.58% of 80251) affected shaders:
Instrs: 1464013 -> 1868466 (+27.63%)
CodeSize: 8476352 -> 10745544 (+26.77%)
VGPRs: 27412 -> 27560 (+0.54%)
SpillSGPRs: 0 -> 16 (+inf%)
SpillVGPRs: 83 -> 76 (-8.43%)
Scratch: 6072832 -> 6071808 (-0.02%)
Latency: 19282476 -> 19552323 (+1.40%); split: -0.11%, +1.51%
InvThroughput: 2198357 -> 2258490 (+2.74%); split: -0.47%, +3.21%
VClause: 32986 -> 43491 (+31.85%)
SClause: 72760 -> 126112 (+73.33%)
Copies: 165286 -> 223368 (+35.14%)
Branches: 60530 -> 79743 (+31.74%); split: -0.03%, +31.77%
PreSGPRs: 24885 -> 25077 (+0.77%)
PreVGPRs: 23004 -> 22494 (-2.22%); split: -2.26%, +0.04%
VALU: 760978 -> 898136 (+18.02%)
SALU: 187786 -> 252995 (+34.73%); split: -0.03%, +34.75%
VMEM: 58469 -> 69164 (+18.29%); split: -0.07%, +18.36%
SMEM: 87926 -> 158175 (+79.90%); split: -0.00%, +79.90%
VOPD: 580 -> 732 (+26.21%); split: +31.38%, -5.17%

Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35686>

src/compiler/nir/nir_loop_analyze.c

@@ -108,6 +108,9 @@ instr_cost(loop_info_state *state, nir_instr *instr,
 
       if (can_constant_fold)
          return 0;
+   } else if (nir_op_is_vec_or_mov(alu->op)) {
+      /* movs and vecs are likely free. */
+      return 0;
    }
 
    if (alu->op == nir_op_flrp) {