Remove reflect type information for unexported methods that do not
satisfy any interface in the program.
Ideally the unexported method would not appear in the method list at
all, but that is tricky because the slice is built by the compiler.
Reduces binary size:
cmd/go: 81KB (0.8%)
jujud: 258KB (0.4%)
For #6853.
Change-Id: I25ef8df6907e9ac03b18689d584ea46e7d773043
Reviewed-on: https://go-review.googlesource.com/21033
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
The type information for a method includes two variants: a func
without the receiver, and a func with the receiver as the first
parameter. The former is used as part of the dynamic interface
checks, but the latter is only returned as a type in the
reflect.Method struct.
Instead of computing it at compile time, construct it at run time
with reflect.FuncOf.
Using cl/20701 as a baseline,
cmd/go: -480KB, (4.4%)
jujud: -5.6MB, (7.8%)
For #6853.
Change-Id: I1b8c73f3ab894735f53d00cb9c0b506d84d54e92
Reviewed-on: https://go-review.googlesource.com/20709
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Remove method type information for pruned methods from any program
that does not reflect on methods. This can be a significant saving:
addr2line: -310KB (8.8%)
A future update might want to consider a more aggressive variant of
this: setting the Type and Func fields of reflect.Method to nil for
unexported methods. That would shrink cmd/go by 2% and jujud by 2.6%
but could be considered an API change. So this CL sticks to the
uncontroversial change.
For #6853.
Change-Id: I5d186d9f822dc118ee89dc572c4912a3b3c72577
Reviewed-on: https://go-review.googlesource.com/20701
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
In addition to reflect.Value.Call, exported methods can be invoked
by the Func value in the reflect.Method struct. This CL has the
compiler track what functions get access to a legitimate reflect.Method
struct by looking for interface calls to either of:
Method(int) reflect.Method
MethodByName(string) (reflect.Method, bool)
This is a little overly conservative. If a user implements a type
with one of these methods without using the underlying calls on
reflect.Type, the linker will assume the worst and include all
exported methods. But it's cheap.
No change to any of the binary sizes reported in cl/20483.
For #14740
Change-Id: Ie17786395d0453ce0384d8b240ecb043b7726137
Reviewed-on: https://go-review.googlesource.com/20489
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Today the linker keeps all methods of reachable types. This is
necessary if a program uses reflect.Value.Call. But while use of
reflection is widespread in Go for encoders and decoders, using
it to call a method is rare.
This CL looks for the use of reflect.Value.Call in a program, and
if it is absent, adopts a (reasonably conservative) method pruning
strategy as part of dead code elimination. Any method that is
directly called is kept, and any method that matches a used
interface's method signature is kept.
Whether or not a method body is kept is determined by the relocation
from its receiver's *rtype to its *rtype. A small change in the
compiler marks these relocations as R_METHOD so they can be easily
collected and manipulated by the linker.
As a bonus, this technique removes the text segment of methods that
have been inlined. Looking at the output of building cmd/objdump with
-ldflags=-v=2 shows that inlined methods like
runtime.(*traceAllocBlockPtr).ptr are removed from the program.
Relatively little work is necessary to do this. Linking two
examples, jujud and cmd/objdump show no more than +2% link time.
Binaries that do not use reflect.Call.Value drop 4 - 20% in size:
addr2line: -793KB (18%)
asm: -346KB (8%)
cgo: -490KB (10%)
compile: -564KB (4%)
dist: -736KB (17%)
fix: -404KB (12%)
link: -328KB (7%)
nm: -827KB (19%)
objdump: -712KB (16%)
pack: -327KB (14%)
yacc: -350KB (10%)
Binaries that do use reflect.Call.Value see a modest size decrease
of 2 - 6% thanks to pruning of unexported methods:
api: -151KB (3%)
cover: -222KB (4%)
doc: -106KB (2.5%)
pprof: -314KB (3%)
trace: -357KB (4%)
vet: -187KB (2.7%)
jujud: -4.4MB (5.8%)
cmd/go: -384KB (3.4%)
The trivial Hello example program goes from 2MB to 1.68MB:
package main
import "fmt"
func main() {
fmt.Println("Hello, 世界")
}
Method pruning also helps when building small binaries with
"-ldflags=-s -w". The above program goes from 1.43MB to 1.2MB.
Unfortunately the linker can only tell if reflect.Value.Call has been
statically linked, not if it is dynamically used. And while use is
rare, it is linked into a very common standard library package,
text/template. The result is programs like cmd/go, which don't use
reflect.Value.Call, see limited benefit from this CL. If binary size
is important enough it may be possible to address this in future work.
For #6853.
Change-Id: Iabe90e210e813b08c3f8fd605f841f0458973396
Reviewed-on: https://go-review.googlesource.com/20483
Reviewed-by: Russ Cox <rsc@golang.org>
