Add SDNodes for umin, umax, smin and smax.

This adds new SDNodes for signed/unsigned min/max. These nodes are built from
select/icmp pairs matched at SDAGBuilder stage.

This patch adds the nodes, as well as legalization support and sets them to
be "expand" for all targets.

NFC for now; this will be tested when I switch AArch64 to using these new
nodes.

llvm-svn: 237423
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
index 11b7d70..c06227b 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
@@ -322,6 +322,10 @@
   case ISD::ANY_EXTEND_VECTOR_INREG:
   case ISD::SIGN_EXTEND_VECTOR_INREG:
   case ISD::ZERO_EXTEND_VECTOR_INREG:
+  case ISD::SMIN:
+  case ISD::SMAX:
+  case ISD::UMIN:
+  case ISD::UMAX:
     QueryType = Node->getValueType(0);
     break;
   case ISD::FP_ROUND_INREG: