[SelectionDAG] add simplifySelect() to reduce code duplication; NFC

This should be extended to handle FP and vectors in follow-up patches.

llvm-svn: 347210

1 files changed, 2 insertions, 18 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 0f428b72d52..31589fe586b 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7236,24 +7236,8 @@ SDValue DAGCombiner::visitSELECT(SDNode *N) {
   EVT VT0 = N0.getValueType();
   SDLoc DL(N);
 
-  // select undef, N1, N2 --> N1 (if it's a constant), otherwise N2
-  if (N0.isUndef())
-    return isa<ConstantSDNode>(N1) ? N1 : N2;
-  // select, ?, undef, N2 --> N2
-  if (N1.isUndef())
-    return N2;
-  // select, ?, N1, undef --> N1
-  if (N2.isUndef())
-    return N1;
-
-  // fold (select true, X, Y) -> X
-  // fold (select false, X, Y) -> Y
-  if (auto *N0C = dyn_cast<const ConstantSDNode>(N0))
-    return N0C->isNullValue() ? N2 : N1;
-
-  // select ?, N1, N1 --> N1
-  if (N1 == N2)
-    return N1;
+  if (SDValue V = DAG.simplifySelect(N0, N1, N2))
+    return V;
 
   // fold (select X, X, Y) -> (or X, Y)
   // fold (select X, 1, Y) -> (or C, Y)