[LLVMdev] Shouldn't DAGCombine insert legal nodes?

[Evan Cheng]

On Jan 20, 2009, at 8:50 AM, Scott Michel wrote:

> Evan:
>
> And after legalize too. DAGCombine gets run after legalization. :-)

Yes? It nows if it's run after legalization. Like Duncan said, if it's  
inserting illegal nodes after legalization, then it's a bug.

Evan

>
>
>
> -scooter
>
> On Jan 19, 2009, at 10:52 PM, Evan Cheng wrote:
>
>> Right. DAGCombine will insert *illegal* nodes before legalize.
>>
>> Evan
>>
>> On Jan 19, 2009, at 8:17 PM, Eli Friedman wrote:
>>
>>> On Mon, Jan 19, 2009 at 6:36 PM, Scott Michel <scottm at aero.org>
>>> wrote:
>>>> I just ran across something interesting: DAGCombine inserts a 64- 
>>>> bit
>>>> constant as the result of converting a (bitconvert (fabs val)) to a
>>>> (and (bitconvert val), i64const).
>>>>
>>>> The problem: i64 constants have to be legalized for the CellSPU
>>>> platform. DAGCombine is doing the right thing but it's not doing  
>>>> the
>>>> right thing for CellSPU and it's damed difficult to work around  
>>>> this
>>>> "feature". Moreover, the way all of SelectionDAGLegalize and
>>>> DAGCombne's code is written, it's particularly difficult to "re-
>>>> legalize" nodes unless one more legalization pass is invoked after
>>>> DAGCombine.
>>>
>>> I don't think DAGCombine should be doing a transform like that
>>> post-legalize; if it is, it's probably a bug.
>>>
>>> -Eli
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