nv50/ir/nir: convert 8/16 bit src to 32 bit for {i,u}2f64

Converting signed and unsigned integers from 8/16 bit sources to a 64 bit
floating point destination (i2f64 / u2f64) isn't possible, hence convert
the source to 32 bit first.

Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18109>

src/nouveau/codegen/nv50_ir_from_nir.cpp

@@ -3291,6 +3291,15 @@ Converter::lowerBitSizeCB(const nir_instr *instr, void *data)
 
       return 0;
    }
+   case nir_op_i2f64:
+   case nir_op_u2f64: {
+      DataType stype = instance->getSTypes(alu)[0];
+
+      if (isIntType(stype) && (typeSizeof(stype) <= 2))
+         return 32;
+
+      return 0;
+   }
    default:
       return 0;
    }