On Friday, 12 June 2015 at 11:06:43 UTC, Dicebot wrote:
The legendary allocator package by Andrei Alexandrescu has
arrived at your doorsteps and kindly asks to let it into Phobos
Sorry for being late, I wanted to restate an idea that could be
crucial for optimizations.
https://github.com/D-Programming-Language/druntime/pull/1183#issuecomment-77065554
This reminds me of the fact, that the IAllocator interface
(std.allocator) should also have a strongly pure allocate
function. This might allow the compiler to optimize allocations
even with a dynamic dispatch allocator, because it assumes that
an allocation doesn't have a side-effect and always returns
"fresh" unaliased memory.
Chandler Carruth was talking about this problem at the last
CppCon.
https://www.youtube.com/watch?v=fHNmRkzxHWs&t=3950
https://www.youtube.com/watch?v=fHNmRkzxHWs&t=4037
Now putting pure onto the allocate function of IAllocator would
be a very harsh constraint for any implementation. So maybe we
could employ a compiler hack, marking any IAllocator.allocate
implementation as pure.
This optimization is really important, b/c it allows the compiler
to ellide allocations when it can compute something using a
temporary buffer.
It'd probably require a magic free as well, so that the compiler
knows the lifetime and sees that data isn't escaped.
