365594ad59
Instead of comparing if the number of elements will not fit into memory check if the memory size of the slices backing memory is higher then the memory limit. This avoids a division or maxElems lookup. With et.size > 0: uintptr(newcap) > maxSliceCap(et.size) -> uintptr(int(capmem / et.size)) > _MaxMem / et.size -> capmem / et.size > _MaxMem / et.size -> capmem > _MaxMem Note that due to integer division from capmem > _MaxMem it does not follow that uintptr(newcap) > maxSliceCap(et.size). Consolidated runtime GrowSlice benchmarks by using sub-benchmarks and added more struct sizes to show performance improvement when division is avoided for element sizes larger than 32 bytes. AMD64: GrowSlice/Byte 38.9ns ± 2% 38.9ns ± 1% ~ (p=0.974 n=20+20) GrowSlice/Int 58.3ns ± 3% 58.0ns ± 2% ~ (p=0.154 n=20+19) GrowSlice/Ptr 95.7ns ± 2% 95.1ns ± 2% -0.60% (p=0.034 n=20+20) GrowSlice/Struct/24 95.4ns ± 1% 93.9ns ± 1% -1.54% (p=0.000 n=19+19) GrowSlice/Struct/32 110ns ± 1% 108ns ± 1% -1.76% (p=0.000 n=19+20) GrowSlice/Struct/40 138ns ± 1% 128ns ± 1% -7.09% (p=0.000 n=20+20) Change-Id: I1c37857c74ea809da373e668791caffb6a5cbbd3 Reviewed-on: https://go-review.googlesource.com/53471 Run-TryBot: Martin Möhrmann <moehrmann@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Keith Randall <khr@golang.org> |
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