[LLVMdev] Use of flags in selection dags

Bagel bagel99 at gmail.com
Thu Mar 20 09:39:57 PDT 2008

Duncan Sands wrote:
>> Can someone tell me, or point me to documentation, that explains the use 
>> of "flags" in the selection DAG?    I figured out that, if one is 
>> present, it must be the last operand.  But when are "flags" used and why?
> Please give details of the context, such as the kind of node you are looking at.
> Thanks,
> Duncan.
I'm looking at this in general as one would when writing patterns for a 
new machine. It appears that flags are used in patterns that use or set 
condition codes. Is this because the condition code register is not 
modelled or is it more that the dags can't handle two outputs. I just 
want to know what the rules are on when and how to use "flags".


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