6ed4661807
match: m = make([]T, x); copy(m, s) for pointer free T and x==len(s) rewrite to: m = mallocgc(x*elemsize(T), nil, false); memmove(&m, &s, x*elemsize(T)) otherwise rewrite to: m = makeslicecopy([]T, x, s) This avoids memclear and shading of pointers in the newly created slice before the copy. With this CL "s" is only be allowed to bev a variable and not a more complex expression. This restriction could be lifted in future versions of this optimization when it can be proven that "s" is not referencing "m". Triggers 450 times during make.bash.. Reduces go binary size by ~8 kbyte. name old time/op new time/op delta MakeSliceCopy/mallocmove/Byte 71.1ns ± 1% 65.8ns ± 0% -7.49% (p=0.000 n=10+9) MakeSliceCopy/mallocmove/Int 71.2ns ± 1% 66.0ns ± 0% -7.27% (p=0.000 n=10+8) MakeSliceCopy/mallocmove/Ptr 104ns ± 4% 99ns ± 1% -5.13% (p=0.000 n=10+10) MakeSliceCopy/makecopy/Byte 70.3ns ± 0% 68.0ns ± 0% -3.22% (p=0.000 n=10+9) MakeSliceCopy/makecopy/Int 70.3ns ± 0% 68.5ns ± 1% -2.59% (p=0.000 n=9+10) MakeSliceCopy/makecopy/Ptr 102ns ± 0% 99ns ± 1% -2.97% (p=0.000 n=9+9) MakeSliceCopy/nilappend/Byte 75.4ns ± 0% 74.9ns ± 2% -0.63% (p=0.015 n=9+9) MakeSliceCopy/nilappend/Int 75.6ns ± 0% 76.4ns ± 3% ~ (p=0.245 n=9+10) MakeSliceCopy/nilappend/Ptr 107ns ± 0% 108ns ± 1% +0.93% (p=0.005 n=9+10) Fixes #26252 Change-Id: Iec553dd1fef6ded16197216a472351c8799a8e71 Reviewed-on: https://go-review.googlesource.com/c/go/+/146719 Reviewed-by: Keith Randall <khr@golang.org> Run-TryBot: Martin Möhrmann <moehrmann@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org>
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