[LLVMdev] Shouldn't DAGCombine insert legal nodes?

[Scott Michel]

Duncan:

DAGCombine is inserting an IllegalOperation after target-specific  
instruction legalization has occurred. I'm inserting the fabs and the  
bitconvert during instruction legalization; DAGCombine is converting  
the fabs/bitconvert to an 'and' on its second (third?) pass.


-scooter

On Jan 20, 2009, at 12:24 AM, Duncan Sands wrote:

> On Tuesday 20 January 2009 07:52:37 Evan Cheng wrote:
>> Right. DAGCombine will insert *illegal* nodes before legalize.
>
> There are two stages of legalization: legalization of types,
> followed by legalization of operations.  Before type legalization
> DAGCombine is allowed to create nodes with illegal types and illegal
> operations.  After type legalization but before operation legalization
> it is allowed to create nodes with illegal operations, but all types
> must be legal.  After operation legalization it is only allowed to
> create fully legal nodes.
>
> Inside DAGCombine this is specified by two flags:
>   LegalTypes being true means that all nodes must have legal types.
>   LegalOperations being true means that all nodes must have legal
> operations (as well as types: LegalTypes will also be true).
>
> So if LegalTypes is true and nonetheless a constant with an
> illegal type is being created then that is a DAG combiner bug.
>
> Ciao,
>
> Duncan.
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