aco: be more careful combining additions that could wrap into loads/stores

aco: be more careful combining additions that could wrap into loads/stores

SMEM does the addition with 64-bits, not 32. So if the original code
relied on wrapping around (for example, for subtraction), it would break.

Apparently swizzled MUBUF accesses also have issues with combining
additions that could overflow. Normal MUBUF accesses seem fine.

fossil-db (Navi):
Totals from 27219 (20.02% of 135946) affected shaders:
CodeSize: 128303256 -> 131062756 (+2.15%); split: -0.00%, +2.15%
Instrs: 24818911 -> 25280558 (+1.86%); split: -0.01%, +1.87%
VMEM: 162311926 -> 177226874 (+9.19%); split: +9.36%, -0.17%
SMEM: 18182559 -> 20218734 (+11.20%); split: +11.53%, -0.34%
VClause: 423635 -> 424398 (+0.18%); split: -0.02%, +0.20%
SClause: 865384 -> 1104986 (+27.69%); split: -0.00%, +27.69%

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/2748
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/2720>