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cmd/compile/internal/gc: don't let the argument to Fields.Set escape

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Apply Robert's optimisation from CL 21241 to Type.Fields. The results
are less impressive, possibly because of the makeup of the test data.

name      old time/op    new time/op    delta
Template     365ms ± 5%     365ms ± 3%    ~     (p=0.888 n=20+16)
Unicode      182ms ±10%     180ms ± 9%    ~     (p=0.883 n=20+20)
GoTypes      1.14s ± 2%     1.13s ± 3%    ~     (p=0.096 n=20+20)
Compiler     5.74s ± 1%     5.76s ± 2%    ~     (p=0.369 n=20+20)

name      old alloc/op   new alloc/op   delta
Template    56.8MB ± 0%    56.7MB ± 0%  -0.15%  (p=0.000 n=19+20)
Unicode     38.3MB ± 0%    38.3MB ± 0%  -0.02%  (p=0.006 n=20+19)
GoTypes      180MB ± 0%     180MB ± 0%  -0.13%  (p=0.000 n=20+20)
Compiler     805MB ± 0%     804MB ± 0%  -0.05%  (p=0.000 n=20+20)

name      old allocs/op  new allocs/op  delta
Template      485k ± 0%      482k ± 0%  -0.54%  (p=0.000 n=19+20)
Unicode       377k ± 0%      377k ± 0%  -0.05%  (p=0.005 n=20+20)
GoTypes      1.37M ± 0%     1.36M ± 0%  -0.53%  (p=0.000 n=20+19)
Compiler     5.42M ± 0%     5.41M ± 0%  -0.21%  (p=0.000 n=20+20)

Change-Id: I6782659fadd605ce9931bf5c737c7058b96a29eb
Reviewed-on: https://go-review.googlesource.com/21296
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Dave Cheney 2016-03-30 20:37:51 +11:00
parent 225b223e47
commit ea5091fcd7
1 changed files with 6 additions and 3 deletions
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9
src/cmd/compile/internal/gc/type.go
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@ -209,10 +209,13 @@ func (f *Fields) Slice() []*Field {
// Set sets f to a slice.
// This takes ownership of the slice.
func (f *Fields) Set(s []*Field) {
if len(s) != 0 {
f.s = &s
} else {
if len(s) == 0 {
f.s = nil
} else {
// Copy s and take address of t rather than s to avoid
// allocation in the case where len(s) == 0.
t := s
f.s = &t
}
}