1480361 - Tweak handling of removed entries in HashTable::lookup()

Status: RESOLVED FIXED

(Core :: MFBT, enhancement)

Description

[Nicholas Nethercote [inactive]]

There are two improvements here.

- When we're just doing a lookup (i.e. aCollisionBit==0), we don't need to
  do any special handling of removed entries. (Inlining means that the removed
  entry code is entirely removed for lookups.)

- When we're doing an insertion (i.e. aCollisionBit==sCollisionBit), we now
  stop adding collision markings once we find a removed entry, because they're
  unnecessary after that point.

This change brings the code in alignment with PLDHashTable::SearchTable().

Comment 1

[Nicholas Nethercote [inactive]]

Attachment: Tweak handling of removed entries in HashTable::lookup()

Comment 2

[Luke Wagner [:luke]]

Comment on attachment 8996954 [details] [diff] [review]
Tweak handling of removed entries in HashTable::lookup()

Review of attachment 8996954 [details] [diff] [review]:
-----------------------------------------------------------------

Nice find!

Comment 3

[Nicholas Nethercote [inactive]]

Attachment: Introduce HashTable::LookupReason

Again inspired by PLDHashTable, this makes things a bit clearer than passing 0
or sCollisionBit.

It also guarantees more strongly that we'll end up with appropriately
specialized code for the Add vs. NonAdd cases. (That guarantee isn't currently
needed because the compiler inlines things sufficiently anyway, but it can't
hurt.)

Comment 4

[Luke Wagner [:luke]]

Comment on attachment 8997177 [details] [diff] [review]
Introduce HashTable::LookupReason

Review of attachment 8997177 [details] [diff] [review]:
-----------------------------------------------------------------

Yes, much clearer, thanks.

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/d9baec9cf420
Tweak handling of removed entries in HashTable::lookup(). r=luke
https://hg.mozilla.org/integration/mozilla-inbound/rev/6c0410ddd1f6
Introduce HashTable::LookupReason. r=luke

Comment 6

[Dorel Luca [:dluca]]

https://hg.mozilla.org/mozilla-central/rev/d9baec9cf420
https://hg.mozilla.org/mozilla-central/rev/6c0410ddd1f6