i965: Properly handle integer types in opt_vector_float().

i965: Properly handle integer types in opt_vector_float().

Previously, opt_vector_float() always interpreted MOV sources as
floating point, and always created a MOV with a F-type destination.

This meant that we could mess up sequences of integer loads, such as:

   mov vgrf6.0.x:D, 0D
   mov vgrf6.0.y:D, 1D
   mov vgrf6.0.z:D, 2D
   mov vgrf6.0.w:D, 3D

Here, integer 0/1/2/3 become approximately 0.0f, so we generated:

   mov vgrf6.0:F, [0F, 0F, 0F, 0F]

which is clearly wrong.  We can properly handle this by converting
integer values to float (rather than bitcasting), and emitting a type
converting MOV:

   mov vgrf6.0:D, [0F, 1F, 2F, 3F]

To do this, see first see if the integer values (converted to float)
are representable.  If so, we use a D-type MOV.  If not, we then try
the floating point values and an F-type MOV.  We make zero not impose
type restrictions.  This is important because 0D would imply a D-type
MOV, but is often used in sequences such as MOV 0D, MOV 0x3f800000D,
where we want to use an F-type MOV.

Fixes about 54 dEQP-GLES2 failures with the vec4 VS backend.  This
recently became visible due to changes in opt_vector_float() which
made it optimize more cases, but it was a pre-existing bug.

Apparently it also manages to turn more integer loads into VFs,
producing the following shader-db statistics on Haswell:

total instructions in shared programs: 7084195 -> 7082191 (-0.03%)
instructions in affected programs: 246027 -> 244023 (-0.81%)
helped: 1937

total cycles in shared programs: 65669642 -> 65651968 (-0.03%)
cycles in affected programs: 531064 -> 513390 (-3.33%)
helped: 1177

v2: Handle the type of zero better.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>