commit 1e1ec013b916a41f3dffeb3699ee9dfc44bc5470
author Josh Bleecher Snyder <josharian@gmail.com> Wed Feb 28 17:01:09 2018 -0800
committer Alan Donovan <adonovan@google.com> Tue May 01 18:10:48 2018 +0000
tree 7fb46757d09675104e8c30dfb519629267914380
parent c47212f6f0f9f75a23516f7a938ff23dd00dc110

cmd/guru: optimize global pkglevel referrer queries

Global, package-level queries can be done without typechecking.
This makes it significantly cheaper.

Instead of typechecking, consider all packages that directly
import the query package. In each of those packages, filter out:

* files that don't contain the query name
* files that don't import the query package

Fully parse the remaining files and look for selector expressions
matching the query package and name.

There are a few twists (dot imports, the query package, xtests).
They are described, along with how they are handled,
in the large comment at the beginning of globalReferrersPkgLevel.

On my machine and GOPATH, this reduces typical time
needed to find referrers to encoding/json.MarshalIndent
from (roughly)

real	0m39.946s
user	2m27.844s
sys	0m54.774s

to (roughly)

real	0m5.687s
user	0m15.793s
sys	0m16.001s

The processing of packages could be parallelized;
that is left for a future change, to ease reviewing.

Benefits from that will be limited;
building the reverse import graph accounts for 73%
of the runtime, and that is dominated by syscalls.

Optimization idea from Alan Donovan.

This work supported by Sourcegraph.

Change-Id: Ib19e25fcdcb27673fb03d7300dba2a53198901ad
Reviewed-on: https://go-review.googlesource.com/97800
Reviewed-by: Alan Donovan <adonovan@google.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>