[LLVMdev] A. Pool Allocation under PowerPC (Mac)

[Vikram S. Adve]

On May 27, 2005, at 4:51 PM, Ricardo wrote:

> John,
>
> Thanks for the information. That comment in the source code  
> confused me and I wanted to be sure
> that the installation of all the LLVM framework in the macintosh  
> for testing the pool allocation
> was not going to be done in vain.

That hacked function (Want8ByteAlignment) is effectively disabled if  
you use the -poolalloc-disable-alignopt option.  This will force all  
poolalloc allocations to be 8-byte aligned.

I believe malloc() on MacOS actually uses 16-byte alignment but I  
think that is to ensure that data used by AltiVec code is aligned  
propertly.  If you need 16-byte alignment for any reason, you should  
be able to fix that in the function getRecommendedAlignment() in llvm- 
poolalloc/lib/PoolAllocate/Heuristics.cpp.


> "Code generation is supported for 32-bit ABI only"
>
> If that is the case then, isn't the code generated for Power PC  
> going to use 64 bit pointers? If
> so, I suppose that the Mac platform is not going to benefit too  
> much from the Automatic Pointer
> Compression. Am I correct?


Pointer compression only compresses 64 to 32-bit pointers.  I should  
also warn that (based on very recent experience) this transform is  
very limited at the moment and will silently break a lot of programs,  
example, most codes that use function pointers.

Pool allocation, however, is much more stable and works on both 32  
and 64-bit targets.

--Vikram