+/*!
+ * Emit the instruction sequence for i64/i32 -> i128 sign extend. The basic
+ * algorithm is to duplicate the sign bit using rotmai to generate at
+ * least one byte full of sign bits. Then propagate the "sign-byte" into
+ * the leftmost words and the i64/i32 into the rightmost words using shufb.
+ *
+ * @param Op The sext operand
+ * @param DAG The current DAG
+ * @return The SDValue with the entire instruction sequence
+ */
+static SDValue LowerSIGN_EXTEND(SDValue Op, SelectionDAG &DAG)
+{
+ DebugLoc dl = Op.getDebugLoc();
+
+ // Type to extend to
+ MVT OpVT = Op.getValueType().getSimpleVT();
+
+ // Type to extend from
+ SDValue Op0 = Op.getOperand(0);
+ MVT Op0VT = Op0.getValueType().getSimpleVT();
+
+ // The type to extend to needs to be a i128 and
+ // the type to extend from needs to be i64 or i32.
+ assert((OpVT == MVT::i128 && (Op0VT == MVT::i64 || Op0VT == MVT::i32)) &&
+ "LowerSIGN_EXTEND: input and/or output operand have wrong size");
+
+ // Create shuffle mask
+ unsigned mask1 = 0x10101010; // byte 0 - 3 and 4 - 7
+ unsigned mask2 = Op0VT == MVT::i64 ? 0x00010203 : 0x10101010; // byte 8 - 11
+ unsigned mask3 = Op0VT == MVT::i64 ? 0x04050607 : 0x00010203; // byte 12 - 15
+ SDValue shufMask = DAG.getNode(ISD::BUILD_VECTOR, dl, MVT::v4i32,
+ DAG.getConstant(mask1, MVT::i32),
+ DAG.getConstant(mask1, MVT::i32),
+ DAG.getConstant(mask2, MVT::i32),
+ DAG.getConstant(mask3, MVT::i32));
+
+ // Word wise arithmetic right shift to generate at least one byte
+ // that contains sign bits.
+ MVT mvt = Op0VT == MVT::i64 ? MVT::v2i64 : MVT::v4i32;
+ SDValue sraVal = DAG.getNode(ISD::SRA,
+ dl,
+ mvt,
+ DAG.getNode(SPUISD::PREFSLOT2VEC, dl, mvt, Op0, Op0),
+ DAG.getConstant(31, MVT::i32));
+
+ // Shuffle bytes - Copy the sign bits into the upper 64 bits
+ // and the input value into the lower 64 bits.
+ SDValue extShuffle = DAG.getNode(SPUISD::SHUFB, dl, mvt,
+ DAG.getNode(ISD::ANY_EXTEND, dl, MVT::i128, Op0), sraVal, shufMask);
+
+ return DAG.getNode(ISD::BIT_CONVERT, dl, MVT::i128, extShuffle);
+}
+