[LLVMdev] Shouldn't DAGCombine insert legal nodes?

[Scott Michel]

Evan:

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


-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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