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Changes the compiler to recognize the slice extension pattern
append(x, make([]T, y)...)
and replace it with growslice and an optional memclr to avoid an allocation for make([]T, y).
Memclr is not called in case growslice already allocated a new cleared backing array
when T contains pointers.
amd64:
name old time/op new time/op delta
ExtendSlice/IntSlice 103ns ± 4% 57ns ± 4% -44.55% (p=0.000 n=18+18)
ExtendSlice/PointerSlice 155ns ± 3% 77ns ± 3% -49.93% (p=0.000 n=20+20)
ExtendSlice/NoGrow 50.2ns ± 3% 5.2ns ± 2% -89.67% (p=0.000 n=18+18)
name old alloc/op new alloc/op delta
ExtendSlice/IntSlice 64.0B ± 0% 32.0B ± 0% -50.00% (p=0.000 n=20+20)
ExtendSlice/PointerSlice 64.0B ± 0% 32.0B ± 0% -50.00% (p=0.000 n=20+20)
ExtendSlice/NoGrow 32.0B ± 0% 0.0B -100.00% (p=0.000 n=20+20)
name old allocs/op new allocs/op delta
ExtendSlice/IntSlice 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.000 n=20+20)
ExtendSlice/PointerSlice 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.000 n=20+20)
ExtendSlice/NoGrow 1.00 ± 0% 0.00 -100.00% (p=0.000 n=20+20)
Fixes #21266
Change-Id: Idc3077665f63cbe89762b590c5967a864fd1c07f
Reviewed-on: https://go-review.googlesource.com/109517
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
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