[LLVMdev] Any extend

Duncan Sands baldrick at free.fr
Mon Jan 25 09:52:20 PST 2010

Hi Greg,

> 1) What causes the Initial selection DAG code to choose an any_extend 
> over a sign_extend (or zero_extend)?

because it is more efficient: the backend gets more choice in how to do
it, and at the same time it tells the optimizers that the extra bits
contain rubbish, which gives them more freedom to reason.

> 2) What does any_extend actually signify?  Presumably this indicates 
> that either a sign extend or zero extend will suffice.

Yes, or anything else.



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