nir: Do not consider phis with incompatible dests equal

CSE tries to collapse equal instructions, and collapsing two phis with incompatible dests is illegal.

Reviewed-by: Konstantin Seurer <konstantin.seurer@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Reviewed-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Fixes: 6bdce55c ("nir: Add a basic CSE pass")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19960>

src/compiler/nir/nir_instr_set.c

@@ -707,6 +707,14 @@ nir_instrs_equal(const nir_instr *instr1, const nir_instr *instr2)
       if (phi1->instr.block != phi2->instr.block)
          return false;
 
+      /* In case of phis with no sources, the dest needs to be checked
+       * to ensure that phis with incompatible dests won't get merged
+       * during CSE. */
+      if (phi1->dest.ssa.num_components != phi2->dest.ssa.num_components)
+         return false;
+      if (phi1->dest.ssa.bit_size != phi2->dest.ssa.bit_size)
+         return false;
+
       nir_foreach_phi_src(src1, phi1) {
          nir_foreach_phi_src(src2, phi2) {
             if (src1->pred == src2->pred) {