[SelectionDAG] Add constant buildvector support to isKnownNeverZero

This allows us to use SelectionDAG::isKnownNeverZero in DAGCombiner::visitREM (visitSDIVLike/visitUDIVLike handle the checking for constants).

llvm-svn: 336779

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -3297,10 +3297,7 @@ SDValue DAGCombiner::visitREM(SDNode *N) {
   // by skipping the simplification if isIntDivCheap().  When div is not cheap,
   // combine will not return a DIVREM.  Regardless, checking cheapness here
   // makes sense since the simplification results in fatter code.
-  // TODO: replace matchUnaryPredicate with SelectionDAG::isKnownNeverZero(N1).
-  if (ISD::matchUnaryPredicate(
-          N1, [](ConstantSDNode *C) { return !C->isNullValue(); }) &&
-      !TLI.isIntDivCheap(VT, Attr)) {
+  if (DAG.isKnownNeverZero(N1) && !TLI.isIntDivCheap(VT, Attr)) {
     SDValue OptimizedDiv =
         isSigned ? visitSDIVLike(N0, N1, N) : visitUDIVLike(N0, N1, N);
     if (OptimizedDiv.getNode() && OptimizedDiv.getOpcode() != ISD::UDIVREM &&

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -3626,12 +3626,18 @@ bool SelectionDAG::isKnownNeverZero(SDValue Op) const {
   assert(!Op.getValueType().isFloatingPoint() &&
          "Floating point types unsupported - use isKnownNeverZeroFloat");
 
+  // If the value is a constant, we can obviously see if it is a zero or not.
+  if (ISD::matchUnaryPredicate(
+          Op, [](ConstantSDNode *C) { return !C->isNullValue(); }))
+    return true;
+
   // TODO: Recognize more cases here.
   switch (Op.getOpcode()) {
   default: break;
   case ISD::OR:
-    if (const ConstantSDNode *C = dyn_cast<ConstantSDNode>(Op.getOperand(1)))
-      return !C->isNullValue();
+    if (isKnownNeverZero(Op.getOperand(1)) ||
+        isKnownNeverZero(Op.getOperand(0)))
+      return true;
     break;
   }