nir/opt_preamble: Move phis for movable if's

nir/opt_preamble: Move phis for movable if's

Add infrastructure to reconstruct if's. Later in the series, this will let us
hoist loads from inside uniform if's without speculating. For now, it lets us
handle phi's in nir_opt_preamble in a straightforward way.

Results on AGX are good:

   total instructions in shared programs: 1504730 -> 1499674 (-0.34%)
   instructions in affected programs: 153673 -> 148617 (-3.29%)
   helped: 496
   HURT: 0
   Instructions are helped.

   total bytes in shared programs: 10287768 -> 10238284 (-0.48%)
   bytes in affected programs: 1113724 -> 1064240 (-4.44%)
   helped: 496
   HURT: 0
   Bytes are helped.

   total halfregs in shared programs: 452669 -> 452049 (-0.14%)
   halfregs in affected programs: 14825 -> 14205 (-4.18%)
   helped: 152
   HURT: 99
   Halfregs are helped.

   total threads in shared programs: 16469504 -> 16470784 (<.01%)
   threads in affected programs: 8960 -> 10240 (14.29%)
   helped: 10
   HURT: 0
   Threads are helped.

Results on ir3 is a bit more of a wash but still should be a win overall: The
regression in moves seems scary, but the cost model already accounts for them as
evidenced by instruction count coming out ahead.

   total instructions in shared programs: 3108750 -> 3105993 (-0.09%)
   instructions in affected programs: 317367 -> 314610 (-0.87%)
   helped: 675
   HURT: 242
   Instructions are helped.

   total nops in shared programs: 673152 -> 675048 (0.28%)
   nops in affected programs: 74551 -> 76447 (2.54%)
   helped: 353
   HURT: 347
   Inconclusive result (%-change mean confidence interval includes 0).

   total non-nops in shared programs: 2435598 -> 2430945 (-0.19%)
   non-nops in affected programs: 232664 -> 228011 (-2.00%)
   helped: 816
   HURT: 38
   Non-nops are helped.

   total mov in shared programs: 78201 -> 84011 (7.43%)
   mov in affected programs: 10726 -> 16536 (54.17%)
   helped: 60
   HURT: 781
   Mov are HURT.

   total cov in shared programs: 74964 -> 74906 (-0.08%)
   cov in affected programs: 273 -> 215 (-21.25%)
   helped: 17
   HURT: 0
   Cov are helped.

   total dwords in shared programs: 6716814 -> 6748726 (0.48%)
   dwords in affected programs: 879778 -> 911690 (3.63%)
   helped: 12
   HURT: 948
   Dwords are HURT.

   total full in shared programs: 193210 -> 193212 (<.01%)
   full in affected programs: 278 -> 280 (0.72%)
   helped: 12
   HURT: 22
   Inconclusive result (value mean confidence interval includes 0).

   total constlen in shared programs: 493632 -> 494816 (0.24%)
   constlen in affected programs: 19904 -> 21088 (5.95%)
   helped: 9
   HURT: 306
   Constlen are HURT.

   total cat0 in shared programs: 742476 -> 745046 (0.35%)
   cat0 in affected programs: 84455 -> 87025 (3.04%)
   helped: 277
   HURT: 489
   Cat0 are HURT.

   total cat1 in shared programs: 153303 -> 159059 (3.75%)
   cat1 in affected programs: 17810 -> 23566 (32.32%)
   helped: 69
   HURT: 780
   Cat1 are HURT.

   total cat2 in shared programs: 1144508 -> 1140731 (-0.33%)
   cat2 in affected programs: 121284 -> 117507 (-3.11%)
   helped: 841
   HURT: 0
   Cat2 are helped.

   total cat3 in shared programs: 942098 -> 934804 (-0.77%)
   cat3 in affected programs: 87140 -> 79846 (-8.37%)
   helped: 855
   HURT: 1
   Cat3 are helped.

   total cat4 in shared programs: 65261 -> 65249 (-0.02%)
   cat4 in affected programs: 42 -> 30 (-28.57%)
   helped: 12
   HURT: 0
   Cat4 are helped.

   total sstall in shared programs: 237311 -> 241281 (1.67%)
   sstall in affected programs: 33755 -> 37725 (11.76%)
   helped: 179
   HURT: 493
   Sstall are HURT.

   total (ss) in shared programs: 58166 -> 58795 (1.08%)
   (ss) in affected programs: 4535 -> 5164 (13.87%)
   helped: 35
   HURT: 664
   (ss) are HURT.

   total systall in shared programs: 503784 -> 503805 (<.01%)
   systall in affected programs: 3170 -> 3191 (0.66%)
   helped: 16
   HURT: 13
   Inconclusive result (value mean confidence interval includes 0).

   total (sy) in shared programs: 27261 -> 27259 (<.01%)
   (sy) in affected programs: 76 -> 74 (-2.63%)
   helped: 8
   HURT: 5
   Inconclusive result (value mean confidence interval includes 0).

   total waves in shared programs: 439848 -> 439872 (<.01%)
   waves in affected programs: 160 -> 184 (15.00%)
   helped: 12
   HURT: 0
   Waves are helped.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24011>