[LLVMdev] Removing std::vector from APIs (was Re: Mutating the elements of a ConstantArray)

[Jay Foad]

> 3. Any comments on the patch itself?
>
> The one major thing to be aware of is that it isn't safe to use &V[0] when V
> is an empty std::vector

Oh dear. That's a bit of a flaw in the plan. I suppose the solution is
to switch to SmallVector whenever this might be a problem.

I'm a bit concerned that any new &empty[0] problems that are
introduced will go unnoticed. With GNU libstdc++ they aren't diagnosed
unless you build with -D_GLIBCXX_DEBUG (or ENABLE_EXPENSIVE_CHECKS=1).

For now I'm testing with ENABLE_EXPENSIVE_CHECKS=1, and it is indeed
catching lots of errors!

> (though it is safe for smallvector).

DR 464 proposes a new data() method. I'd suggest implementing that in
SmallVector, instead of relying on the relaxed checking in
operator[]().

http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#464

GNU libstdc++'s vector already has this data() method, but I suppose
we can't rely on in it being in std::vector in general.

> One minor thing is that StructType::get(NULL, 0) looks somewhat strange to
> me.  How about adding a zero-argument version of "get" that returns the
> empty struct?  That would allow code to use StructType::get().

OK, I've done this for both StructType and FunctionType.

I'll post some patches on llvm-commits.

Thanks,
Jay.