i965/vec4/nir: support doubles in ALU operations

Basically, this involves considering the bit-size information to set
the appropriate type on both operands and destination.

v2 (Curro)
  - Don't use two temporaries (and write one of them twice ) to obtain
    the nir_alu_type.

Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Reviewed-by: Matt Turner <mattst88@gmail.com>
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp b/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
index 5c56e08..062215d 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
@@ -1050,14 +1050,17 @@
 {
    vec4_instruction *inst;
 
-   dst_reg dst = get_nir_dest(instr->dest.dest,
-                              nir_op_infos[instr->op].output_type);
+   nir_alu_type dst_type = (nir_alu_type) (nir_op_infos[instr->op].output_type |
+                                           nir_dest_bit_size(instr->dest.dest));
+   dst_reg dst = get_nir_dest(instr->dest.dest, dst_type);
    dst.writemask = instr->dest.write_mask;
 
    src_reg op[4];
    for (unsigned i = 0; i < nir_op_infos[instr->op].num_inputs; i++) {
-      op[i] = get_nir_src(instr->src[i].src,
-                          nir_op_infos[instr->op].input_types[i], 4);
+      nir_alu_type src_type = (nir_alu_type)
+         (nir_op_infos[instr->op].input_types[i] |
+          nir_src_bit_size(instr->src[i].src));
+      op[i] = get_nir_src(instr->src[i].src, src_type, 4);
       op[i].swizzle = brw_swizzle_for_nir_swizzle(instr->src[i].swizzle);
       op[i].abs = instr->src[i].abs;
       op[i].negate = instr->src[i].negate;