This is achieved by means of creating a variable storing zero,
loading every array element, comparing if the non-constant index
matches the index of that element at runtime, and in that case
store the corresponding element in the variable.
This seems to be the same strategy that the native compiler uses.
This is simply unnecessary and wastes time.
As part of this, simply remove the "all" directive. Only for a couple of tests
is it even potentially interesting to validate all pixels (e.g.
nointerpolation.shader_test), and for those "all" is replaced with an explicit
(0, 0, 640, 480) rect.
In all other cases we just probe (0, 0).
