i965/vec4: split d2x conversion and data gathering from one opcode to two explicit ones

When doing a 64-bit to a smaller data type size conversion, the destination should
be aligned to 64-bits. Because of that, we need to gather the data after the
actual conversion.

Until now, these two operations were done by VEC4_OPCODE_FROM_DOUBLE but
now we split them explicitely in two different instructions:
VEC4_OPCODE_FROM_DOUBLE just do the conversion and
VEC4_OPCODE_PICK_LOW_32BIT will gather the data.

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>

src/intel/compiler/brw_vec4_generator.cpp

@@ -1961,14 +1961,6 @@ generate_code(struct brw_codegen *p,
          src[0].width = BRW_WIDTH_4;
          brw_MOV(p, spread_dst, src[0]);
 
-         /* As we have set horizontal stride 1 instead of 2 in IVB/BYT, we
-          * need to fix it here to have the expected value.
-          */
-         if (devinfo->gen == 7 && !devinfo->is_haswell)
-            spread_dst = stride(dst, 8, 4, 2);
-
-         brw_MOV(p, dst, spread_dst);
-
          brw_set_default_access_mode(p, BRW_ALIGN_16);
          break;
       }

src/intel/compiler/brw_vec4_nir.cpp

@@ -1191,6 +1191,7 @@ vec4_visitor::emit_conversion_from_double(dst_reg dst, src_reg src,
    emit(VEC4_OPCODE_FROM_DOUBLE, temp2, src_reg(temp))
       ->size_written = 2 * REG_SIZE;
 
+   emit(VEC4_OPCODE_PICK_LOW_32BIT, temp2, src_reg(retype(temp2, BRW_REGISTER_TYPE_DF)));
    vec4_instruction *inst = emit(MOV(dst, src_reg(temp2)));
    inst->saturate = saturate;
 }