| commit | 22c16b4b92f10baf42a3db5de439a70f49101a89 | [log] [tgz] |
|---|---|---|
| author | Dmitry Vyukov <dvyukov@google.com> | Fri Jan 16 23:30:35 2015 +0300 |
| committer | Dmitry Vyukov <dvyukov@google.com> | Wed Jan 28 17:37:55 2015 +0000 |
| tree | 9f9c12c64cf66b6fb5a9f6a74bed7da1508e1912 | |
| parent | 1b87f01239de499654b390a41a7f8e2b453789dc [diff] |
cmd/gc: ignore re-slicing in escape analysis
Escape analysis treats everything assigned to OIND/ODOTPTR as escaping.
As the result b escapes in the following code:
func (b *Buffer) Foo() {
n, m := ...
b.buf = b.buf[n:m]
}
This change recognizes such assignments and ignores them.
Update issue #9043.
Update issue #7921.
There are two similar cases in std lib that benefit from this optimization.
First is in archive/zip:
type readBuf []byte
func (b *readBuf) uint32() uint32 {
v := binary.LittleEndian.Uint32(*b)
*b = (*b)[4:]
return v
}
Second is in time:
type data struct {
p []byte
error bool
}
func (d *data) read(n int) []byte {
if len(d.p) < n {
d.p = nil
d.error = true
return nil
}
p := d.p[0:n]
d.p = d.p[n:]
return p
}
benchmark old ns/op new ns/op delta
BenchmarkCompressedZipGarbage 32431724 32217851 -0.66%
benchmark old allocs new allocs delta
BenchmarkCompressedZipGarbage 153 143 -6.54%
Change-Id: Ia6cd32744e02e36d6d8c19f402f8451101711626
Reviewed-on: https://go-review.googlesource.com/3162
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
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