[PATCH] ADT: Remove misaligned pointeres from DenseMapInfo

[Alexey Samsonov]

On Thu, Jan 8, 2015 at 4:38 PM, Chandler Carruth <chandlerc at google.com>
wrote:

>
> On Thu, Jan 8, 2015 at 3:59 PM, Duncan P. N. Exon Smith <
> dexonsmith at apple.com> wrote:
>
>> > On 2015-Jan-08, at 15:56, Chandler Carruth <chandlerc at google.com>
>> wrote:
>> >
>> > After arguing about this for like an hour with Richard, David, and
>> Alexey, I think we have a better path forward...
>> >
>> > Much as you suggest, the key is nuking the upcast in the asserts build.
>> But we can fix a number of other things in the process. For example, it is
>> really annoying that we construct ValueHandle objects for the empty and
>> tombstone keys. Instead, it would be better if we could not construct an
>> object at all, and it turns out there is a nice way to do this.
>>
>> Colour me interested...
>>
>> > Unfortunately, it requires some refactoring to DenseMap and
>> DenseMapInfo to expose this freedom. I'm going to do that refactoring
>> (which seems like generally good cleanup), and then we can look at a more
>> direct way of fixing the bug here.
>>
>> SGTM!
>
>
> Bleh. Never mind. Doesn't work. Removing the PointerIntPair still helps,
> and I'll submit the obvious patch to do that shortly.
>
> We add a private constructor to AssertingVH that accepts a raw Value* (and
> in NDEBUG, store a raw Value*), sinking all the casting into methods. We
> ensure the ValueHandleBase can also be constructed for a raw Value* with no
> casting. Then we hand in DenseMapInfo<Value *>::getEmptyKey() and
> DenseMapInfo<Value *>::getTombstoneKey(). No need to do any other funny
> business I think.
>

Alright, see http://reviews.llvm.org/D6903


>
> At some point, I would really like to also get rid of the shifts in
> DenseMapInfo<T*>, but I don't think we need to solve that problem today.
>
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>


-- 
Alexey Samsonov
vonosmas at gmail.com
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