[LLVMdev] [RFC] Remat Enhancements

[Jakob Stoklund Olesen]

On Feb 27, 2012, at 9:51 AM, David A. Greene wrote:

> dag at cray.com (David A. Greene) writes:
> 
>>>> The change requires that live interval analysis be able to determine
>>>> whether and instruction is a load and whether an instruction writes to
>>>> memory.
>>> 
>>> Just use MI->mayLoad(), MI->mayStore().
>> 
>> Does this also account for arithmetic instructions with memops?  These
>> interfaces didn't exist in 2.9.
> 
> This is important because if mayLoad includes arithmetic instructions
> with source memops (which I assume it will), it is unsuitable for remat
> analysis.  I don't think we want to remat general arithmetic quite yet.
> At least that's not the intent of my change.  I'll need some way to
> identify "real" loads and I don't know of any other way other than
> listing opcodes.  Ideas?

The target sets the isRematerializable bit on opcodes that are suitable for remat. That should be sufficient.

You should also check the 'canFoldAsLoad' mechanism.

/jakob