[RFC] PatternMatch for SelectionDAG

[Christian König]

Am 21.07.2013 07:24, schrieb Nadav Rotem:
> David,
>
> I am really happy to see that you are working on this. As part of the 
> discussions on replacing SelectionDAG with something new, a few people 
> mentioned that it would be much easier to migrate to a new 
> infrastructure if the patterns were written in patterns such as the 
> ones that you are proposing.  I like your approach. I look forward to 
> seeing the complete patch.
>

Completely agreeing on this, I was already wondering why matching 
SelectionDAG nodes looked so conventional while matching LLVM IR has a 
rather elegant solution.

Please leave me a notice if you have a complete solution,
Christian.

>>
>> I have a simple implementation attached, it matches on SDValue types 
>> and provides a convenience overload for SDNodes.
>>
>> Currently, it uses similar names to PattternMatch.h (match, m_And, etc.).
>> I don't really care about the names but I figured to start with 
>> something familiar. They shouldn't conflict because they would both 
>> exist in their own namespaces.
>>
>> The effect is pretty nice on some DAGCombiner code:
>>
>>    // (or (and X, C1), (and Y, C2))  -> (and (or X, Y), C3) if possible.
>>    if (N0.getOpcode() == ISD::AND &&
>>        N1.getOpcode() == ISD::AND &&
>>        N0.getOperand(1).getOpcode() == ISD::Constant &&
>>        N1.getOperand(1).getOpcode() == ISD::Constant &&
>>        // Don't increase # computations.
>>        (N0.getNode()->hasOneUse() || N1.getNode()->hasOneUse())) {
>>      const APInt &LHSMask =
>>  cast<ConstantSDNode>(N0.getOperand(1))->getAPIntValue();
>>      const APInt &RHSMask =
>>  cast<ConstantSDNode>(N1.getOperand(1))->getAPIntValue();
>>
>> becomes:
>>    const APInt *LHSMask, *RHSMask;
>>    if (match(N0, m_And(m_Value(), m_APInt(LHSMask))) &&
>>        match(N1, m_And(m_Value(), m_APInt(RHSMask))) &&
>>        // Don't increase # computations.
>>        (match(N0, m_OneUse()) || match(N1, m_OneUse()))) {
>>
>> Note that the attached implementation is pretty incomplete, I just 
>> wanted a proof of concept before I run off and flesh it out further.
>>
>> Thanks
>>
>> -- 
>> David Majnemer
>> <ns.h>_______________________________________________
>> llvm-commits mailing list
>> llvm-commits at cs.uiuc.edu <mailto:llvm-commits at cs.uiuc.edu>
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20130721/3572b8e4/attachment.html>