The V_MQSAD_PK_U16_U8, V_QSAD_PK_U16_U8, and V_MQSAD_U32_U8 take more than 1 pass in hardware.
For these three instructions, the destination registers must be different than all sources so that the first pass does not overwrite sources for the following passes.
See Bug 33279: https://bugs.llvm.org//show_bug.cgi?id=33279