[Mesa-dev] i965: Single program flow for shaders with no control flow.

[Matt Turner]

The docs say that flipping this bit on for shaders that don't do SIMD
branching (i.e., non-uniform control flow) will save us some power.

An easy first step is turning this on when we don't see control flow.

In the future with more infrastructure in place, we can determine if
all branching conditions are uniformly constant and turn on SPF.

Hopefully this saves some power and extends battery life, but I'm not
sure how to accurately quantify this, short of printing i915_energy_uJ
before and after some workload. Even then I don't have any expectation
for how much energy the GPU would use for, say a piglit run. Is
200 ~ 300 Joules reasonable (over 220 seconds)?