Eduardo Lima Mitev authored Aug 05, 2019 and Rob Clark committed Oct 18, 2019

The pass should run once at the end of shader compilation, for a4xx
onwards. It iterates texture sampling instructions and mark those
eligibile for pre-dispatch by changing the tex op from 'tex' to
'tex_prefetch'. An instruction is eligibile if:

* The coordinate is a vector where all its components come from a
  shader input.
* The order of the components match exactly that of the input (no
  swizzles).
* The instruction is in the 'main' function, and in the outer
  most-block.

The first two restrictions were arrived to empirically, so more
testing could tighten or loosen it.

The 3rd restriction is there to allow moving the instructions
eligible for pre-dispatch to the beginning of the shader, so
that we don't block the registers holding the result for too
long.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>