[llvm-commits] [llvm] r61401 - in /llvm/trunk: lib/CodeGen/SelectionDAG/DAGCombiner.cpp test/CodeGen/X86/2008-12-23-dagcombine-6.ll

[Dale Johannesen]

On Dec 23, 2008, at 3:14 PMPST, Chris Lattner wrote:

>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=61401&view=rev
>> Log:
>> Add another permutation where we should get rid of a-a.
>
>> @@ -1177,13 +1177,20 @@
>>    return N0.getOperand(1);
>>  // fold (A+B)-B -> A
>>  if (N0.getOpcode() == ISD::ADD && N0.getOperand(1) == N1)
>> -    return N0.getOperand(0);
>> -  // fold ((A+(B-C))-B) -> A-C
>> +    return N0.getOperand(0);
>> +  // fold ((A+(B+-C))-B) -> A+-C
>
> I don't see why you'd ever way to match on A + (-B).  Shouldn't dag
> combine independently fold this into A-B?

That should be read "plus or minus".