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...; CNV += OV; > else > CNV -= OV; > > perhaps something here is not quite right. I suspect that the first snippet (where OV is inverted) is wrong because ARM implementation of getPreIndexedAddressParts inverts Offset for pre-decrement case, both for ARM and Thumb2, in getARMIndexedAddressParts and getT2IndexedAddressParts, respectively, in a calls to: Offset = DAG.getConstant(-RHSC, RHS->getValueType(0)); ^^^^^ here! So you don't need to invert it one more time in DAGCombiner::CombineToPreIndexedLoadStore. Dmitry

----- Original Message ----- > From: "Dmitry Antipov" <antipov at dev.rtsoft.ru> > To: "Hal Finkel" <hfinkel at anl.gov> > Cc: "Renato Golin" <renato.golin at linaro.org>, llvmdev at cs.uiuc.edu > Sent: Thursday, April 4, 2013 3:22:05 AM > Subject: Is r174746 broken on ARM? > > Hello Hal, > > I have a strong suspicion

Hello Hal, I have a strong suspicion that your constant folding optimization introduced at r174746 is broken on ARM. There is a bug about it: http://llvm.org/bugs/show_bug.cgi?id=15581 There is no such issue with 3.2, and reverting r174746 on top of r178740 also fixes the problem. I'm trying to fix it myself, but still have no good ideas; so it would be great to have an advice from you.