S_CODE_END pads the space after a shader's last instruction. When the code
after the final S_ENDPGM ends in a backward branch, the linear decoder walks
straight into that padding and failed with an unknown SOPP opcode 0x1F, which
stopped the session.
The decoder now names 0x1F and ends the program there, unless a forward branch
still targets code beyond it -- in which case the padding really would be
inside the program and the decode still fails.
kuba