Improve OutBuffer's allocation strategy

[andralex]

While tracking dmd's memory usage I noticed there are very many calls to OutBuffer::enlarge, which in turn makes a ton of calls to realloc:

1999520 calls to allocation functions with 1.07GB peak consumption from
Outbuffer::enlarge(unsigned long)

Turns out the vast majority of these calls are with buf is null and many others deal with small sizes, unnecessarily making realloc roundtrips.

This improves the strategy to special-case frequent cases and to double the allocated size for small buffers. The result for the same build:

1247003 calls to allocation functions with 773.87MB peak consumption from
Outbuffer::enlarge(unsigned long)

I also took the liberty to make a bunch of functions private. I have no idea why that works because some are actually used from client code. Why is that the case?

[dlang-bot]

Thanks for your pull request, @andralex!

Bugzilla references

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Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#12519"

[ibuclaw]

src/dmd/backend/cv8.d(141): Error: no property `writen` for type `dmd.backend.outbuf.Outbuffer*`
src/dmd/backend/cv8.d(142): Error: no property `writeByte` for type `dmd.backend.outbuf.Outbuffer*`

Not sure why it compiled for you locally, but private should not have been added to any of the member functions.

[John-Colvin]

Great find! 👍

[andralex]

src/dmd/backend/cv8.d(141): Error: no property `writen` for type `dmd.backend.outbuf.Outbuffer*`
src/dmd/backend/cv8.d(142): Error: no property `writeByte` for type `dmd.backend.outbuf.Outbuffer*`

Not sure why it compiled for you locally, but private should not have been added to any of the member functions.

Heh, that explains a lot. I was building using the makefile and it seems dependencies are not tracked properly, Now I touch **/*.d before building... will get back.

[andralex]

I took the liberty to remove some cruft as well. private is such an awesome tool.

[ibuclaw]

@WalterBright ?