r209297 - Make the parent-map use significantly less memory.

[Jordan Rose]

On May 21, 2014, at 9:19 , Manuel Klimek <klimek at google.com> wrote:

> On Wed, May 21, 2014 at 6:10 PM, Jordan Rose <jordan_rose at apple.com> wrote:
> You might want to bump up the size of the SmallVector too. Right now you're dynamically allocating a SmallVector<T, 1>, and immediately putting two things into it. Alternately, you could use a std::vector, which has a smaller sizeof itself.
> 
> I tried the various combinations, and it didn't make a difference, so I went for making the code the simplest, which was reusing the ParentVector typedef.
> If we change the ParentVector to a SmallVector<T, 2> we'll also use that for getParents() which mostly returns a single element.
>  

SmallVector's already too big to fit in registers, so adding another two words to it won't really hurt any uses on the stack, will it?

Alternately you could wrap up your PointerUnion in something similar to TinyPtrVector, but that's probably more complexity than is really necessary here.

Jordan

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