i965/fs: optimize unpack double

When we are actually unpacking from a double that we have previously
packed from its 32-bit components we can bypass the pack operation
and source from its arguments directly.

v2 (Sam):
- Fix line overflow (Topi)
- Bail if the parent instruction's source is not SSA (Connor)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
1 file changed