[LLVMdev] DataLayout

[Rafael Espíndola]

Long term I think we should keep only the one in the module.


On 24 June 2015 at 14:42, Mehdi Amini <mehdi.amini at apple.com> wrote:
> Hi all,
>
> We have multiple DataLayout object in flight during a compilation: at least the one owned by the Module and the one owned by the TargetMachine.
> There are two issues:
> 1) What if they differ? I guess we could assert at the beginning of CodeGen.
> 2) The DataLayout has internal mutable state (a cache of StructLayout).
>
> The latter is my current concern: the cache in DataLayout is based on Type pointer which means that is has to be Context specific.
> This is fine with the DataLayout attached to the Module but not with the TargetMachine.
> The cache could live in the Context, but it is also DataLayout specific so it wouldn’t be a good fit either.
>
> I considered modifying the cache in the DataLayout to invalidate itself when queried with a new Context, however it wouldn’t work in a multi-threaded environment (or the query would have to be behind a Mutex).
>
> Another option is to remove the DataLayout from the TargetMachine, I tried it and it seems possible but awkward as well in some places where the DataLayout has to be supplied externally because TargetLoweringXX would not have it.
>
> Finally the TargetMachine could be deemed to be "context-specific”, i.e. the CodeGen infrastructure would need to be reinitialized for each new Context. That would be a strong limitation though.
>
> There may be other options?
>
> —
> Mehdi
>
>
>
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