Nicholas Nethercote 01e442a7dd Bug 1400193 (part 2) - Shrink PLDHashTable. r=froydnj. ...

This patch reduces sizeof(PLDHashTable) as follows.

- 64-bit: from 40 bytes to 32
- 32-bit: from 28 bytes to 20

It does this by doing the following.

- It moves mGeneration from EntryStore to PLDHashTable, to avoid unnecessary
  padding on 64-bit. This requires tweaking EntryStore::Set() as explained in a
  comment.

- It also shrinks mGeneration from uint32_t to uint16_t, saving 2 bytes of
  data.

- It shrinks mEntrySize from uint32_t to uint8_t, to cut 3 bytes of data.

- It shrinks mHashShift from int16_t to uint8_t, trimming another byte of data,
  and moves it, saving another 2 bytes of padding.

And it reorders the fields so the word-sized ones are at the start, which makes
it easier to imagine the memory layout.

The patch also adds a test, and fixes some misordered function arguments in
existing tests.

2017-09-15 20:04:29 +10:00

22 KiB

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