[X86] Don't form masked instructions if the operation has an additional user.

This will cause the operation to be repeated in both a mask and another masked
or unmasked form. This can a wasted of execution resources.

Differential Revision: https://reviews.llvm.org/D60940

Author: topperc

llvm/lib/Target/X86/X86ISelDAGToDAG.cpp

@@ -259,6 +259,8 @@ namespace {
                           SDValue &Index, SDValue &Disp,
                           SDValue &Segment);
 
+    bool isProfitableToFormMaskedOp(SDNode *N) const;
+
     /// Implement addressing mode selection for inline asm expressions.
     bool SelectInlineAsmMemoryOperand(const SDValue &Op,
                                       unsigned ConstraintID,
@@ -722,6 +724,20 @@ X86DAGToDAGISel::IsProfitableToFold(SDValue N, SDNode *U, SDNode *Root) const {
   return true;
 }
 
+// Indicates it is profitable to form an AVX512 masked operation. Returning
+// false will favor a masked register-register masked move or vblendm and the
+// operation will be selected separately.
+bool X86DAGToDAGISel::isProfitableToFormMaskedOp(SDNode *N) const {
+  assert(
+      (N->getOpcode() == ISD::VSELECT || N->getOpcode() == X86ISD::SELECTS) &&
+      "Unexpected opcode!");
+
+  // If the operation has additional users, the operation will be duplicated.
+  // Check the use count to prevent that.
+  // FIXME: Are there cheap opcodes we might want to duplicate?
+  return N->getOperand(1).hasOneUse();
+}
+
 /// Replace the original chain operand of the call with
 /// load's chain operand and move load below the call's chain operand.
 static void moveBelowOrigChain(SelectionDAG *CurDAG, SDValue Load,