1 files changed, 16 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 4120e79e667..cde38e479ac 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7176,6 +7176,22 @@ SDValue DAGCombiner::visitTRUNCATE(SDNode *N) {
     }
   }
 
+  // Fold truncate of a bitcast of a vector to an extract of the low vector
+  // element.
+  //
+  // e.g. trunc (i64 (bitcast v2i32:x)) -> extract_vector_elt v2i32:x, 0
+  if (N0.getOpcode() == ISD::BITCAST && !VT.isVector()) {
+    SDValue VecSrc = N0.getOperand(0);
+    EVT SrcVT = VecSrc.getValueType();
+    if (SrcVT.isVector() && SrcVT.getScalarType() == VT) {
+      SDLoc SL(N);
+
+      EVT IdxVT = TLI.getVectorIdxTy(DAG.getDataLayout());
+      return DAG.getNode(ISD::EXTRACT_VECTOR_ELT, SL, VT,
+                         VecSrc, DAG.getConstant(0, SL, IdxVT));
+    }
+  }
+
   // Simplify the operands using demanded-bits information.
   if (!VT.isVector() &&
       SimplifyDemandedBits(SDValue(N, 0)))