[PATCH][ADT] Add move-construction and move-assignment from SmallVectorImpl<T> to SmallVector<T,N>.

[Duncan P. N. Exon Smith]

This tests that `Constructable` was moved, but it still doesn't test
whether the heap allocation was moved (as opposed to individual
elements being moved to a new allocation).  You need something like
this to test that:

     SmallVector<int, 4> V1(8), V2;
     auto First = V1.begin();
     V2 = std::move(V1);
     EXPECT_EQ(First, V2.begin());

Of course, you only want to check this when you expect the whole
allocation to move over: when the source vector is in big mode.

> On 2015-Jan-22, at 16:43, Lang Hames <lhames at gmail.com> wrote:
> 
> Hi Guys,
> 
> Thanks for catching that - I've attached an updated patch. I'm still just testing correctness, rather than implementation specifics, but it does at least verify that it's move-constructing rather than copy-constructing now.
> 
> Cheers,
> Lang.
> 
> 
> On Thu, Jan 22, 2015 at 4:19 PM, David Blaikie <dblaikie at gmail.com> wrote:
> 
> 
> On Thu, Jan 22, 2015 at 4:17 PM, Duncan P. N. Exon Smith <dexonsmith at apple.com> wrote:
> 
> > On 2015-Jan-22, at 16:04, David Blaikie <dblaikie at gmail.com> wrote:
> >
> > This looks like it's only adding copy, not move - did I miss something?
> >
> > On Thu, Jan 22, 2015 at 3:54 PM, Lang Hames <lhames at gmail.com> wrote:
> > Hi All,
> >
> > The attached patch adds move-construction and move-assignment from SmallVectorImpl<T> to SmallVector<T, N>. It enables us to move between SmallVectors of different types, which will allow me to fix one of the most commented-upon warts from the new JIT APIs.
> >
> > Unit-test included.
> >
> > Cheers,
> > Lang.
> >
> 
> Yeah, the tests don't actually confirm that the thing was moved.  In
> particular, you want to check that whenever the source is in big-mode,
> the destination points at the same memory that the source used to (well,
> assuming that's the behaviour you want, which the naive implementation
> will give you IIUC).
> 
> There's also a "big mode -> small mode" funny state thing that'll happen
> with the naive implementation.  I'm not sure it's *wrong*, but...
> 
> Given:
> 
>     SmallVector<int, 1> InBigMode(2);
>     SmallVector<int, 2> InBigModeToo = std::move(InBigMode);
> 
> I think this will pass:
> 
>     assert(!InBigModeToo.isSmall());
> 
> This a new state -- a SmallVector can be in "big" mode with a heap
> allocation, even though its capacity would fit in its "small" mode
> stack allocation.
> 
> While weird, I don't really have a problem with it (but maybe others
> do?).  Might be worth testing a few operations in this untested state
> though.
> 
> It's probably valuable that this is the outcome - it'd be wasteful to throw away the dynamic allocation (going down to small mode) - better to keep it even though it's < small_size. So I'd be in favor of this. 
> 
> 
> <SmallVectorMoveAssignmentFromSmallVectorImpl-2.patch>