[CodeGen][X86] Expand UADDSAT to NOT+UMIN+ADD

Followup to D56636, this time handling the UADDSAT case by expanding
uadd.sat(a, b) to umin(a, ~b) + b.

Differential Revision: https://reviews.llvm.org/D56869

llvm-svn: 352409

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 5d8f3851980..a07b2594153 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -5287,6 +5287,12 @@ SDValue TargetLowering::expandAddSubSat(SDNode *Node, SelectionDAG &DAG) const {
     return DAG.getNode(ISD::SUB, dl, VT, Max, RHS);
   }
 
+  if (Opcode == ISD::UADDSAT && isOperationLegalOrCustom(ISD::UMIN, VT)) {
+    SDValue InvRHS = DAG.getNOT(dl, RHS, VT);
+    SDValue Min = DAG.getNode(ISD::UMIN, dl, VT, LHS, InvRHS);
+    return DAG.getNode(ISD::ADD, dl, VT, Min, RHS);
+  }
+
   if (VT.isVector()) {
     // TODO: Consider not scalarizing here.
     return SDValue();