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| author | Josh Bleecher Snyder <josharian@gmail.com> | 2019-03-22 14:51:33 -0700 |
|---|---|---|
| committer | Josh Bleecher Snyder <josharian@gmail.com> | 2019-03-25 17:11:46 +0000 |
| commit | 24f846e21240f6d6ab2ca23fe319230b7d7f8168 (patch) | |
| tree | ec155f1507cfc0a537c56a603e6225e34d785edc /src/runtime/slice.go | |
| parent | 2034fbab5b1d11bc59cb476bc3f49ee1b344839d (diff) | |
| download | go-24f846e21240f6d6ab2ca23fe319230b7d7f8168.tar.gz go-24f846e21240f6d6ab2ca23fe319230b7d7f8168.zip | |
runtime: skip wb call in growslice when unnecessary
Instrumenting make.bash reveals that almost half (49.54%)
of the >16 million calls to growslice for
pointer-containing slices are
growing from an empty to a non-empty slice.
In that case, there is no need to call the write barrier,
which does some work before discovering that no pointers need shading.
Change-Id: Ide741468d8dee7ad43ea0bfbea6ccdf680030a0f
Reviewed-on: https://go-review.googlesource.com/c/go/+/168959
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Diffstat (limited to 'src/runtime/slice.go')
| -rw-r--r-- | src/runtime/slice.go | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/src/runtime/slice.go b/src/runtime/slice.go index 2309b1a615..dca41ff8cd 100644 --- a/src/runtime/slice.go +++ b/src/runtime/slice.go @@ -179,7 +179,7 @@ func growslice(et *_type, old slice, cap int) slice { } else { // Note: can't use rawmem (which avoids zeroing of memory), because then GC can scan uninitialized memory. p = mallocgc(capmem, et, true) - if writeBarrier.enabled { + if lenmem > 0 && writeBarrier.enabled { // Only shade the pointers in old.array since we know the destination slice p // only contains nil pointers because it has been cleared during alloc. bulkBarrierPreWriteSrcOnly(uintptr(p), uintptr(old.array), lenmem) |