[HEXAGON] Fix hvx-isel for extract_subvector op (llvm#129672)

Fixes a crash with extract_subvectors in Hexagon backend seen when the
source vector is a vector-pair and result vector is not hvx vector size.

LLVM Issue: llvm#128775
Fixes llvm#128775
---------

Co-authored-by: aankit-quic <[email protected]>

Author: 2 people

llvm/lib/Target/Hexagon/HexagonISelLoweringHVX.cpp

@@ -1265,11 +1265,15 @@ HexagonTargetLowering::extractHvxSubvectorReg(SDValue OrigOp, SDValue VecV,
   // the subvector of interest. The subvector will never overlap two single
   // vectors.
   if (isHvxPairTy(VecTy)) {
-    if (Idx * ElemWidth >= 8*HwLen)
+    unsigned SubIdx = Hexagon::vsub_lo;
+    if (Idx * ElemWidth >= 8 * HwLen) {
+      SubIdx = Hexagon::vsub_hi;
       Idx -= VecTy.getVectorNumElements() / 2;
+    }
 
-    VecV = OrigOp;
-    if (typeSplit(VecTy).first == ResTy)
+    VecTy = typeSplit(VecTy).first;
+    VecV = DAG.getTargetExtractSubreg(SubIdx, dl, VecTy, VecV);
+    if (VecTy == ResTy)
       return VecV;
   }