The llvm.hexagon.M2.mpy.acc.lh.s1 intrinsic; known as __builtin_HEXAGON_M2_mpy_acc_lh_s1 in GCC.
See Implementation
The llvm.hexagon.M2.mpy.acc.lh.s1 intrinsic; known as __builtin_HEXAGON_M2_mpy_acc_lh_s1 in GCC.