i965/fs: Fix the inline nir_op_pack_double optimization

We can only do the optimization if the source *is* SSA.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Cc: "13.0 17.0" <mesa-stable@lists.freedesktop.org>
(cherry picked from commit a4393bd97fe62e8299273bae769201c5c9c816ea)

Squashed with commit:

i965/fs: Remove the inline pack_double_2x32 optimization

It's broken in a number of ways.  In particular, a bunch of the
conditions are backwards so it doesn't actually detect what it's
supposed to detect.  Since it's been broken, it hasn't actually been
helping anything so just deleting it isn't a regression.

This (and removing another optimization) were done on master in commit
b07381161777ba5d5f4a1d713f7655bcaede4139.

Cc: "Kenneth Grunke" <kenneth@whitecape.org>
Cc: "Mark Janes" <mark.a.janes@intel.com>

[Emil Velikov: patch is a backport of the below "cherry pick"]
Fixes: a4393bd97fe ("i965/fs: Fix the inline nir_op_pack_double optimization")

(cherry picked from commit b07381161777ba5d5f4a1d713f7655bcaede4139)
diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
index 8f745df..ff29711 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
@@ -1166,35 +1166,6 @@
       break;
 
    case nir_op_pack_double_2x32_split:
-      /* Optimize the common case where we are re-packing a double with
-       * the result of a previous double unpack. In this case we can take the
-       * 32-bit value to use in the re-pack from the original double and bypass
-       * the unpack operation.
-       */
-      for (int i = 0; i < 2; i++) {
-         if (instr->src[i].src.is_ssa)
-            continue;
-
-         const nir_instr *parent_instr = instr->src[i].src.ssa->parent_instr;
-         if (parent_instr->type == nir_instr_type_alu)
-            continue;
-
-         const nir_alu_instr *alu_parent = nir_instr_as_alu(parent_instr);
-         if (alu_parent->op == nir_op_unpack_double_2x32_split_x ||
-             alu_parent->op == nir_op_unpack_double_2x32_split_y)
-            continue;
-
-         if (!alu_parent->src[0].src.is_ssa)
-            continue;
-
-         op[i] = get_nir_src(alu_parent->src[0].src);
-         op[i] = offset(retype(op[i], BRW_REGISTER_TYPE_DF), bld,
-                        alu_parent->src[0].swizzle[channel]);
-         if (alu_parent->op == nir_op_unpack_double_2x32_split_y)
-            op[i] = subscript(op[i], BRW_REGISTER_TYPE_UD, 1);
-         else
-            op[i] = subscript(op[i], BRW_REGISTER_TYPE_UD, 0);
-      }
       bld.emit(FS_OPCODE_PACK, result, op[0], op[1]);
       break;