[LLVMdev] Making a CopyToReg/CopyFromReg into a zext/sext?

[Matt Arsenault]

On 01/27/2015 12:28 PM, Ryan Taylor wrote:
> Thanks for getting back to me.
>
> So those nodes record if the type has already been expanded from a 
> narrower type. Can you elaborate how I could use these to help? Again, 
> I'm pretty unfamiliar with the SDNodes.
>
> Thanks.
What is the problem you are trying to solve? These should allow 
SimplifyDemandedBits type optimizations understand that your copy 
implicitly extended the source



>
> On Tue, Jan 27, 2015 at 3:22 PM, Matt Arsenault 
> <Matthew.Arsenault at amd.com <mailto:Matthew.Arsenault at amd.com>> wrote:
>
>     On 01/27/2015 12:16 PM, Ryan Taylor wrote:
>>     I have a CopyToReg that is copying from different size types,
>>     what's the best way to change that to a zext or sext node based
>>     on signed or unsigned?
>>
>>     I'm fairly unfamiliar with SelectionDAG process (outside of the
>>     docs on llvm website).
>>
>>     It seems like I should be able to insert a custom hook using the
>>     register class to identify the type, potentially in
>>     ISelDAGToDag.cpp or is there a better place for this to be done?
>>
>>     Thanks.
>>
>
>     It sounds to me like you are looking for the AssertSext /
>     AssertZext nodes
>
>     -Matt
>
>

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