[llvm-commits] CVS: llvm/lib/Target/X86/X86InstrFPStack.td X86InstrInfo.cpp X86InstrInfo.h X86InstrInfo.td X86InstrMMX.td X86InstrSSE.td

[Chris Lattner]

On Jun 19, 2007, at 9:38 AM, Evan Cheng wrote:

>>> If we are really concerned about the speed, then I agree the hybrid
>>> approach is the best. Sorry about the confusion.
>>
>> Speed is something to consider, but I don't think it should override
>> maintainability.
>>
>>> Not to mention I had already considered the "trivial
>>> rematerialization"
>>> scheme to be temporary.
>>
>> Okay, how do you think this should work going forward?
>
> Trivial remat will go away when proper remat is implemented. All
> instructions without side-effect will be rematerializable if their
> operands are available so all these will go away. Not that proper
> remat is coming anytime soon though.

Ok.  How do you intend to capture the "without side-effects" part?

It seems that simple remat works for things that:

1. have no side effects
2. have no register inputs

Is there another condition?

If so, simple remat can check #2 today, just by itself looking at the  
machineinstr.  Given that, it comes down to how we want to represent #1.

-Chris