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cmd/compile: optimize append(x, make([]T, y)...) slice extension

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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>
This commit is contained in:
Martin Möhrmann 2018-04-26 18:30:11 +02:00
parent 87412a1430
commit a8a60ac2a7
11 changed files with 295 additions and 26 deletions
Download patch file Download diff file Expand all files Collapse all files

16
src/runtime/slice.go
View file

@ -44,6 +44,14 @@ func maxSliceCap(elemsize uintptr) uintptr {
return maxAlloc / elemsize
}
func panicmakeslicelen() {
panic(errorString("makeslice: len out of range"))
}
func panicmakeslicecap() {
panic(errorString("makeslice: cap out of range"))
}
func makeslice(et *_type, len, cap int) slice {
// NOTE: The len > maxElements check here is not strictly necessary,
// but it produces a 'len out of range' error instead of a 'cap out of range' error
@ -52,11 +60,11 @@ func makeslice(et *_type, len, cap int) slice {
// See issue 4085.
maxElements := maxSliceCap(et.size)
if len < 0 || uintptr(len) > maxElements {
panic(errorString("makeslice: len out of range"))
panicmakeslicelen()
}
if cap < len || uintptr(cap) > maxElements {
panic(errorString("makeslice: cap out of range"))
panicmakeslicecap()
}
p := mallocgc(et.size*uintptr(cap), et, true)
@ -66,12 +74,12 @@ func makeslice(et *_type, len, cap int) slice {
func makeslice64(et *_type, len64, cap64 int64) slice {
len := int(len64)
if int64(len) != len64 {
panic(errorString("makeslice: len out of range"))
panicmakeslicelen()
}
cap := int(cap64)
if int64(cap) != cap64 {
panic(errorString("makeslice: cap out of range"))
panicmakeslicecap()
}
return makeslice(et, len, cap)