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internal/runtime/maps: linear scan of small map

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We still use the hash and control word, but loop over all 8 bytes
instead of doing the match operation, which ends up being slightly
faster when there is only one group.

Note that specialized variants added later will avoid hashing at all.

For #54766.

Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest-swissmap
Change-Id: I3bb353b023dd6120b6585e87d3efe2f18ac9e1ef
Reviewed-on: https://go-review.googlesource.com/c/go/+/611189
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
This commit is contained in:
Michael Pratt 2024-08-19 17:45:41 -04:00 committed by Gopher Robot
parent 77e3d8cf13
commit 808da68c1c
1 changed files with 8 additions and 4 deletions
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12
src/internal/runtime/maps/map.go
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@ -381,16 +381,20 @@ func (m *Map) getWithKeySmall(hash uintptr, key unsafe.Pointer) (unsafe.Pointer,
data: m.dirPtr,
}
match := g.ctrls().matchH2(h2(hash))
h2 := uint8(h2(hash))
ctrls := *g.ctrls()
for match != 0 {
i := match.first()
for i := uint32(0); i < abi.SwissMapGroupSlots; i++ {
c := uint8(ctrls)
ctrls >>= 8
if c != h2 {
continue
}
slotKey := g.key(i)
if m.typ.Key.Equal(key, slotKey) {
return slotKey, g.elem(i), true
}
match = match.removeFirst()
}
return nil, nil, false