This patch improves the codegen of extractelement and insertelement for vector containing 8 elements.
Before, a dag combine transformation was generating a sequence of 8 select/cmp.
This patch changes the upper limit for this transformation and the movrel
instruction will eventually be used instead.
Extractlement/insertelement for vectors containing less than 8 elements are unchanged.
This patch is saving some instructions in these cases.
This case was identified in several game shaders.