cmd/compile/internal/pgo: use slices for in/out edges
Currently in the pprof Graph, a Node's in/out edges are
represented as maps, keyed by the source/destination Nodes. For a
Node it usually has a very small number of edges, so linear search
would be generally faster than map operations. Use slices and
linear search instead.
Change-Id: I5ab06be0c019373cd3a845b9f3282731372e9c4c
Reviewed-on: https://go-review.googlesource.com/c/go/+/447802 Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>