1 files changed, 3 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
index b6f74aea41a..693ac68e30b 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
@@ -224,6 +224,9 @@ SDValue VectorLegalizer::LegalizeOp(SDValue Op) {
 }
 
 SDValue VectorLegalizer::PromoteVectorOp(SDValue Op) {
+  // Vector "promotion" is basically just bitcasting and doing the operation
+  // in a different type.  For example, x86 promotes ISD::AND on v2i32 to
+  // v1i64.
   MVT VT = Op.getValueType();
   assert(Op.getNode()->getNumValues() == 1 &&
          "Can't promote a vector with multiple results!");