DAGCombine: Remove redundant NaN checks around ISD::FSQRT

This folds:

(select (setcc x, -0.0, *lt), NaN, (fsqrt x)) -> ( fsqrt x)

llvm-svn: 235333

1 files changed, 35 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index e218e22459b..c32c21d1f9c 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -5190,6 +5190,9 @@ SDValue DAGCombiner::visitVSELECT(SDNode *N) {
     }
   }
 
+  if (SimplifySelectOps(N, N1, N2))
+    return SDValue(N, 0);  // Don't revisit N.
+
   // If the VSELECT result requires splitting and the mask is provided by a
   // SETCC, then split both nodes and its operands before legalization. This
   // prevents the type legalizer from unrolling SETCC into scalar comparisons
@@ -12545,6 +12548,38 @@ SDValue DAGCombiner::SimplifySelect(SDLoc DL, SDValue N0,
 bool DAGCombiner::SimplifySelectOps(SDNode *TheSelect, SDValue LHS,
                                     SDValue RHS) {
 
+  // fold (select (setcc x, -0.0, *lt), NaN, (fsqrt x))
+  // The select + setcc is redundant, because fsqrt returns NaN for X < -0.
+  if (const ConstantFPSDNode *NaN = isConstOrConstSplatFP(LHS)) {
+    if (NaN->isNaN() && RHS.getOpcode() == ISD::FSQRT) {
+      // We have: (select (setcc ?, ?, ?), NaN, (fsqrt ?))
+      SDValue Sqrt = RHS;
+      ISD::CondCode CC;
+      SDValue CmpLHS;
+      const ConstantFPSDNode *NegZero = nullptr;
+
+      if (TheSelect->getOpcode() == ISD::SELECT_CC) {
+        CC = dyn_cast<CondCodeSDNode>(TheSelect->getOperand(4))->get();
+        CmpLHS = TheSelect->getOperand(0);
+        NegZero = isConstOrConstSplatFP(TheSelect->getOperand(1));
+      } else {
+        // SELECT or VSELECT
+        SDValue Cmp = TheSelect->getOperand(0);
+        if (Cmp.getOpcode() == ISD::SETCC) {
+          CC = dyn_cast<CondCodeSDNode>(Cmp.getOperand(2))->get();
+          CmpLHS = Cmp.getOperand(0);
+          NegZero = isConstOrConstSplatFP(Cmp.getOperand(1));
+        }
+      }
+      if (NegZero && NegZero->isNegative() && NegZero->isZero() &&
+          Sqrt.getOperand(0) == CmpLHS && (CC == ISD::SETOLT ||
+          CC == ISD::SETULT || CC == ISD::SETLT)) {
+        // We have: (select (setcc x, -0.0, *lt), NaN, (fsqrt x))
+        CombineTo(TheSelect, Sqrt);
+        return true;
+      }
+    }
+  }
   // Cannot simplify select with vector condition
   if (TheSelect->getOperand(0).getValueType().isVector()) return false;