As an optimization, the callers and callstack queries now avoid the
relatively costly pointer analysis in some common cases:
The callers of a function that is never address-taken can be enumerated
directly from the SSA representation.
Similarly, the callstack can be computed initially by ignoring dynamic
call edges; we run the pointer analysis only if no path is found in this
partial callgraph. As a bonus, this also causes the tool to
preferentially report all-static callpaths.
A callers query on fmt.Errorf now completes in 3 seconds instead of 8,
and a callstack query completes in 2 seconds instead of 8.
The new code is covered by the existing tests.
Change-Id: I777ea07a1cdb6cadcc2a94952f553b6b036e7382
Reviewed-on: https://go-review.googlesource.com/19496
Reviewed-by: Michael Matloob <matloob@golang.org>
