diff options
Diffstat (limited to 'src/internal/runtime/maps/table.go')
| -rw-r--r-- | src/internal/runtime/maps/table.go | 33 |
1 files changed, 29 insertions, 4 deletions
diff --git a/src/internal/runtime/maps/table.go b/src/internal/runtime/maps/table.go index a8160befd2..0535be0fc1 100644 --- a/src/internal/runtime/maps/table.go +++ b/src/internal/runtime/maps/table.go @@ -604,12 +604,37 @@ func (t *table) Clear(typ *abi.MapType) { if t.used == 0 && t.growthLeft == mgl { // no current entries and no tombstones return } - for i := uint64(0); i <= t.groups.lengthMask; i++ { - g := t.groups.group(typ, i) - if g.ctrls().anyFull() { + // We only want to do the work of clearing slots + // if they are full. But we also don't want to do too + // much work to figure out whether a slot is full or not, + // especially if clearing a slot is cheap. + // 1) We decide group-by-group instead of slot-by-slot. + // If any slot in a group is full, we zero the whole group. + // 2) If groups are unlikely to be empty, don't bother + // testing for it. + // 3) If groups are 50%/50% likely to be empty, also don't + // bother testing, as it confuses the branch predictor. See #75097. + // 4) But if a group is really large, do the test anyway, as + // clearing is expensive. + fullTest := uint64(t.used)*4 <= t.groups.lengthMask // less than ~0.25 entries per group -> >3/4 empty groups + if typ.SlotSize > 32 { + // For large slots, it is always worth doing the test first. + fullTest = true + } + if fullTest { + for i := uint64(0); i <= t.groups.lengthMask; i++ { + g := t.groups.group(typ, i) + if g.ctrls().anyFull() { + typedmemclr(typ.Group, g.data) + } + g.ctrls().setEmpty() + } + } else { + for i := uint64(0); i <= t.groups.lengthMask; i++ { + g := t.groups.group(typ, i) typedmemclr(typ.Group, g.data) + g.ctrls().setEmpty() } - g.ctrls().setEmpty() } t.used = 0 t.growthLeft = mgl |