From 4a1535c0383254741bcddd3500081782aad11864 Mon Sep 17 00:00:00 2001 From: Hal Finkel Date: Thu, 12 Sep 2013 19:04:12 +0000 Subject: Make the PPC fast-math sqrt expansion safe at 0 In fast-math mode sqrt(x) is calculated using the fast expansion of the reciprocal of the reciprocal sqrt expansion. The reciprocal and reciprocal sqrt expansions use the associated estimate instructions along with some Newton iterations. Unfortunately, as a result, sqrt(0) was being calculated as NaN, which is not correct. Now we explicitly return a result of zero if the input is zero. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190624 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/PowerPC/PPCISelLowering.cpp | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) (limited to 'lib/Target/PowerPC/PPCISelLowering.cpp') diff --git a/lib/Target/PowerPC/PPCISelLowering.cpp b/lib/Target/PowerPC/PPCISelLowering.cpp index d341074..b4ba527 100644 --- a/lib/Target/PowerPC/PPCISelLowering.cpp +++ b/lib/Target/PowerPC/PPCISelLowering.cpp @@ -7021,8 +7021,28 @@ SDValue PPCTargetLowering::PerformDAGCombine(SDNode *N, if (RV.getNode() != 0) { DCI.AddToWorklist(RV.getNode()); RV = DAGCombineFastRecip(RV, DCI); - if (RV.getNode() != 0) + if (RV.getNode() != 0) { + // Unfortunately, RV is now NaN if the input was exactly 0. Select out + // this case and force the answer to 0. + + EVT VT = RV.getValueType(); + + SDValue Zero = DAG.getConstantFP(0.0, VT.getScalarType()); + if (VT.isVector()) { + assert(VT.getVectorNumElements() == 4 && "Unknown vector type"); + Zero = DAG.getNode(ISD::BUILD_VECTOR, dl, VT, Zero, Zero, Zero, Zero); + } + + SDValue ZeroCmp = + DAG.getSetCC(dl, getSetCCResultType(*DAG.getContext(), VT), + N->getOperand(0), Zero, ISD::SETEQ); + DCI.AddToWorklist(ZeroCmp.getNode()); + DCI.AddToWorklist(RV.getNode()); + + RV = DAG.getNode(VT.isVector() ? ISD::VSELECT : ISD::SELECT, dl, VT, + ZeroCmp, Zero, RV); return RV; + } } } -- cgit v1.1