[llvm-commits] [llvm] r62790 - /llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

[Chris Lattner]

On Jan 22, 2009, at 3:41 PM, Bob Wilson wrote:

>
> On Jan 22, 2009, at 3:21 PM, Chris Lattner wrote:
>> Instead of checking ZeroOrOneBooleanContent, it seems safer to me to
>> do this only if MaskedValueIsZero tells you that the high bits are
>> zero.  ZeroOrOneBooleanContent really only applies to memory (iirc)
>> not to intermediate register values.
>
> I'll take a look at MaskedValueIsZero.  I was checking the result of
> getBooleanContents based on the comment describing SELECT in <llvm/
> CodeGen/SelectionDAGNodes.h>:
>
>     // Select(COND, TRUEVAL, FALSEVAL).  If the type of the boolean
> COND is not
>     // i1 then the high bits must conform to getBooleanContents.
>
> Is that comment still accurate?

Aha, yes, you're right, the patch is safe.  Using MVIZ might be a  
slight performance optimization, but isn't necessary.  Thanks!

-Chris