[DAG] Move isNullConstantOrUndef helper to SelectionDAGNodes.h to allow other future uses. NFC.

Author: RKSimon

llvm/include/llvm/CodeGen/SelectionDAGNodes.h

@@ -1754,6 +1754,9 @@ class ConstantFPSDNode : public SDNode {
 /// Returns true if \p V is a constant integer zero.
 bool isNullConstant(SDValue V);
 
+/// Returns true if \p V is a constant integer zero or an UNDEF node.
+bool isNullConstantOrUndef(SDValue V);
+
 /// Returns true if \p V is an FP constant with a value of positive zero.
 bool isNullFPConstant(SDValue V);
 

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -11753,6 +11753,10 @@ bool llvm::isNullConstant(SDValue V) {
   return Const != nullptr && Const->isZero();
 }
 
+bool llvm::isNullConstantOrUndef(SDValue V) {
+  return V.isUndef() || isNullConstant(V);
+}
+
 bool llvm::isNullFPConstant(SDValue V) {
   ConstantFPSDNode *Const = dyn_cast<ConstantFPSDNode>(V);
   return Const != nullptr && Const->isZero() && !Const->isNegative();

llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.h

@@ -24,10 +24,6 @@ using namespace llvm;
 
 namespace {
 
-static inline bool isNullConstantOrUndef(SDValue V) {
-  return V.isUndef() || isNullConstant(V);
-}
-
 static inline bool getConstantValue(SDValue N, uint32_t &Out) {
   // This is only used for packed vectors, where using 0 for undef should
   // always be good.