llvm dev - Aug 2010 - [LLVMdev] [Patch] Fix for ExpandShiftWithUnknownAmountBit when shift amount is zero

Hello,

A while back I submitted a patch for this function. The patch, added in revision
90482, left the case of a shift by zero undefined. Attached is another patch to
deal with that condition.

Thanks,
Javier
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On Aug 24, 2010, at 5:58 PM, Martinez, Javier E wrote:
> Hello,
>  
> A while back I submitted a patch for this function. The patch, added in
revision 90482, left the case of a shift by zero undefined. Attached is another
patch to deal with that condition.
>  
Hi Javier,

This patch seems ok, but it will pessimize all of the existing targets, which
produce an undefined result on overflow instead of performing an undefined
operation.  Does your target really produce undefined behavior on this
condition, or does it just produce an undefined result?

If you really need to get this in, please add a new TargetLowering hook (along
the same lines of getShiftAmountTy() which would return an enum indicating the
behavior on overflow.  The legalize code can then use this hook to determine if
it needs to generate the extra code.

Thanks!

-Chris

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