i965/fs: Fix vgrf0 live interval when no interpolation was done.

When you've got a simple solid-color shader that doesn't generate
pixel_x/y interpolation, we were deciding that the first vgrf was both the
undefined pixel_x and pixel_y, and extending its live interval to avoid
the stride problem.  That tricked other optimization that tries to see if
a particular instruction is the last use of a variable.

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