Do the legality checks first

Author: davemgreen

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -17281,12 +17281,12 @@ SDValue DAGCombiner::visitFREM(SDNode *N) {
 
   // Lower frem N0, N1 => x - trunc(N0 / N1) * N1, providing N1 is an integer
   // power of 2.
-  if (DAG.isKnownToBeAPowerOfTwoFP(N1) &&
-      (Flags.hasNoSignedZeros() || DAG.isKnownNonNegativeFP(N0)) &&
-      !TLI.isOperationLegal(ISD::FREM, VT) &&
+  if (!TLI.isOperationLegal(ISD::FREM, VT) &&
       TLI.isOperationLegalOrCustom(ISD::FMUL, VT) &&
       TLI.isOperationLegalOrCustom(ISD::FDIV, VT) &&
-      TLI.isOperationLegalOrCustom(ISD::FTRUNC, VT)) {
+      TLI.isOperationLegalOrCustom(ISD::FTRUNC, VT) &&
+      DAG.isKnownToBeAPowerOfTwoFP(N1) &&
+      (Flags.hasNoSignedZeros() || DAG.isKnownNonNegativeFP(N0))) {
     SDValue Div = DAG.getNode(ISD::FDIV, DL, VT, N0, N1);
     SDValue Rnd = DAG.getNode(ISD::FTRUNC, DL, VT, Div);
     SDValue Mul = DAG.getNode(ISD::FMUL, DL, VT, Rnd, N1);