Refactor the code that checks that all operands of a node are UNDEFs.

Add a micro-optimization to getNode of CONCAT_VECTORS when both operands are undefs.
Can't find a testcase for this because VECTOR_SHUFFLE already handles undef operands, but Duncan suggested that we add this.

Together with Michael Kuperstein <michael.m.kuperstein@intel.com>



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160229 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 21 insertions, 0 deletions

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index a8dce2176f..3947648e6a 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -219,6 +219,22 @@ bool ISD::isScalarToVector(const SDNode *N) {
   return true;
 }
 
+/// allOperandsUndef - Return true if the node has at least one operand
+/// and all operands of the specified node are ISD::UNDEF.
+bool ISD::allOperandsUndef(const SDNode *N) {
+  // Return false if the node has no operands.
+  // This is "logically inconsistent" with the definition of "all" but
+  // is probably the desired behavior.
+  if (N->getNumOperands() == 0)
+    return false;
+
+  for (unsigned i = 0, e = N->getNumOperands(); i != e ; ++i)
+    if (N->getOperand(i).getOpcode() != ISD::UNDEF)
+      return false;
+
+  return true;
+}
+
 /// getSetCCSwappedOperands - Return the operation corresponding to (Y op X)
 /// when given the operation for (X op Y).
 ISD::CondCode ISD::getSetCCSwappedOperands(ISD::CondCode Operation) {
@@ -2674,6 +2690,11 @@ SDValue SelectionDAG::getNode(unsigned Opcode, DebugLoc DL, EVT VT,
     if (N1 == N2) return N1;
     break;
   case ISD::CONCAT_VECTORS:
+    // Concat of UNDEFs is UNDEF.
+    if (N1.getOpcode() == ISD::UNDEF &&
+        N2.getOpcode() == ISD::UNDEF)
+      return getUNDEF(VT);
+
     // A CONCAT_VECTOR with all operands BUILD_VECTOR can be simplified to
     // one big BUILD_VECTOR.
     if (N1.getOpcode() == ISD::BUILD_VECTOR &&