[Mesa-dev] Reducing GLSL compiler optimization time

[Eric Anholt]

With the conversion of texenvprogram to producing GLSL IR, all those
nice little optimization passes end up slowing down our
combinatorial-explosion ff tests pretty significantly.  This patch
series reduces glean texCombine runtime overall by 20% on my gen6
system.  The lowest-hanging fruit at this point looks like the
register allocator setup, which I think a 1-entry cache would cut down
pretty easily.

Surprisingly enough, making the refcount visitor use a hash table
didn't pay off in reducing its couple of percent, as the cost of
alloc/free of the hash table was too high.  This branch is present as
glsl-refcount-ht of my tree if you might have a workload where it
helps -- it was a non-statistically-significant change here.