[dev.ssa] cmd/compile: cache sparse sets in Config
Move the cached sparse sets to the Config. I tested make.bash with
pre-allocating sets of size 150 and not caching very small sets, but the
difference between this implementation (no min size, no preallocation)
and a min size with preallocation was fairly negligible:
Number of sparse sets allocated:
Cached in Config w/none preallocated no min size 3684 *this CL*
Cached in Config w/three preallocated no min size 3370
Cached in Config w/three preallocated min size=150 3370
Cached in Config w/none preallocated min size=150 15947
Cached in Func, w/no min 96996 *previous code*
Change-Id: I7f9de8a7cae192648a7413bfb18a6690fad34375
Reviewed-on: https://go-review.googlesource.com/19152 Reviewed-by: Keith Randall <khr@golang.org>