nir: Add a small pass to rematerialize derefs per-block

This pass re-materializes deref instructions on a per-block basis to
ensure that every use of a deref occurs in the same block as the
instruction which uses it.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Cc: "18.2" <mesa-stable@lists.freedesktop.org>

src/compiler/nir/nir.h

@@ -3012,6 +3012,7 @@ bool nir_convert_from_ssa(nir_shader *shader, bool phi_webs_only);
 
 bool nir_lower_phis_to_regs_block(nir_block *block);
 bool nir_lower_ssa_defs_to_regs_block(nir_block *block);
+bool nir_rematerialize_derefs_in_use_blocks_impl(nir_function_impl *impl);
 
 bool nir_opt_algebraic(nir_shader *shader);
 bool nir_opt_algebraic_before_ffma(nir_shader *shader);