go/parser will by default resolve objects as per the go/ast.Object type,
which is then used by gofmt's rewrite and simplify flags.
However, none of that is needed if neither of the flags is set,
so we can avoid the work entirely for a nice speed-up.

	benchcmd -n 8 GofmtSrcCmd gofmt -l ~/tip/src/cmd

	name         old time/op         new time/op         delta
	GofmtSrcCmd          957ms ± 7%          908ms ± 7%  -5.12%  (p=0.028 n=8+8)

	name         old user-time/op    new user-time/op    delta
	GofmtSrcCmd          11.2s ± 1%          10.4s ± 1%  -7.23%  (p=0.001 n=7+7)

	name         old sys-time/op     new sys-time/op     delta
	GofmtSrcCmd          325ms ±29%          286ms ±22%    ~     (p=0.065 n=8+8)

	name         old peak-RSS-bytes  new peak-RSS-bytes  delta
	GofmtSrcCmd          295MB ±17%          276MB ±15%    ~     (p=0.328 n=8+8)

See #46485.

Change-Id: Iad1ae294953710c233f7837d7eb02e23d11c6185
Reviewed-on: https://go-review.googlesource.com/c/go/+/401454
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

Just like https://golang.org/cl/401454 removed the work from gofmt for a
nice ~5% speed-up in the default case, we can also use the option in the
equivalent go/format for programs which use it rather than gofmt,
as go/format makes no use of objects either.

No benchmark numbers as we already measured the ~5% speed-up with gofmt
in the other CL linked above.

See #46485.

Change-Id: Icbf98e6d46a616081314e2faa13f1dfade3bbaef
Reviewed-on: https://go-review.googlesource.com/c/go/+/401474
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

The "simplify" feature used go/ast's object tracking in only one place -
to replace s[a:len(s)] with s[a:].
Using go/ast.Object did allow us to not simplify code like:

	len := func(s []int) int { ... }
	s = s[a:len(s)]

The existing code already noted the limitation with that approach,
such as "len" being redeclared in a different file in the same package.
Since go/ast's object tracking is file-based and very basic,
it wouldn't work with edge cases like those.

The reasoning is that redeclaring len and abusing it that way is
extremely unlikely, and hasn't been a problem in about a decade now.
I reason that the same applies to len being redeclared in the same file,
so we should be able to safely remove the use of go/ast.Object here.

Per https://go.dev/cl/401454, this makes "gofmt -s" about 5% faster.
If we ever wanted to truly get rid of false positive simplifications,
I imagine we'd want to reimplement the feature under go/analysis,
which is able to fully typecheck packages and suggest edits.
That seems unnecessary at this point, but we can always course correct
in the presumably unlikely scenario that users start reporting bugs.

See #46485.
For #52463.

Change-Id: I77fc97adceafde8f0fe6887ace83ae325bfa7416
Reviewed-on: https://go-review.googlesource.com/c/go/+/401875
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

None of cgo, "go test", nor srcimporter make use of go/ast's object
resolution via go/ast.Object. As such, we can skip that work during
parse time, which should save some CPU time.

We don't have any benchmark numbers, as none of the three packages have
any usable benchmarks, but we measured gofmt to be about 5% faster
thanks to this tweak in https://go.dev/cl/401454.
These three packages are quite different to gofmt, but one can expect
similar speed-ups in the 1-5% range.

Two notable exceptions, which do make use of go/ast.Object, are cmd/fix
and cmd/doc - we do not modify those here.

See #46485.

Change-Id: Ie3e65600d4790641c4e4d6f1c379be477fa02cee
Reviewed-on: https://go-review.googlesource.com/c/go/+/401455
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>