On 6/11/2013 12:35 AM, Don Clugston wrote:
It's not a compiler bug. It's something more interesting.
I counted the number of instantiations in std.algorithm -unittest.
635 templates are instantiated, half of them only 1 to 10 times.
These ones here cover 70% of the total.
70763 isNarrowString
31279 binaryFun
24425 isInputRange
22308 Unqual
15563 startsWith
15381 isBidirectionalRange
11405 endsWith
7861 FormatSpec
7277 OriginalType
7275 to
6723 TypeTuple
5827 defaultInit
5713 from
5413 isRawStaticArray
Then, the question is, how do we get 71K different types to instantiate
isNarrowString with? There aren't nearly that many types declared in the program!
Turns our it's things like:
Zip!(Sequence!("n", Tuple!(ulong)), Sequence!("n", Tuple!(int)), Result,
Repeat!(Sequence!("n", Tuple!(int))), Repeat!(Result))
So we've got a combinatorial explosion of types happening here. I'm sure
that's true for the other massively-instantiated templates as well. If we
could avoid this, we would get an order of magnitude improvement in memory
usage and compilation time.
This is great information. 71000 instantiations of isNarrowString!! Definitely
need a hash rather than a linear list. I had no idea. You're right, though,
about figuring out a way to avoid this. isNarrowString is nothing more than:
template isNarrowString(T)
{
enum isNarrowString = (is(T : const char[]) || is(T : const wchar[])) &&
!isAggregateType!T;
}
Makes me wonder why isAggregateType is not 71000 instantiations, too?
Maybe we can avoid generating a mangled name for a template if it is an
eponymous one that evaluates to a manifest constant? This will save a ton of memory.
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