The 3DNow! instruction pmulhrw is decoded as 'pfmulhrw' in objdump -d. While it's an 3DNow! instruction, pmulhrw actually is an SIMD integer instruction and both the AMD official documents and gcc builtin/intrinsics refer to pmulhrw instead of pfmulhrw.
Fixed by http://sourceware.org/ml/binutils/2007-05/msg00178.html