i965/vec4: Allow CSE on uniform-vec4 expansion MOVs.

i965/vec4: Allow CSE on uniform-vec4 expansion MOVs.

Three source instructions cannot directly source a packed vec4 (<0,4,1>
regioning) like vec4 uniforms, so we emit a MOV that expands the vec4 to
both halves of a register.

If these uniform values are used by multiple three-source instructions,
we'll emit multiple expansion moves, which we cannot combine in CSE
(because CSE emits moves itself).

So emit a virtual instruction that we can CSE.

Sometimes we demote a uniform to to a pull constant after emitting an
expansion move for it. In that case, recognize in opt_algebraic that if
the .file of the new instruction is GRF then it's just a real move that
we can copy propagate and such.

total instructions in shared programs: 5822418 -> 5812335 (-0.17%)
instructions in affected programs:     351841 -> 341758 (-2.87%)

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