Per the "MIPS Architecture Extension: nanoMIPS32 DSP TRM" rev 0.04,
MULT and MULTU opcodes:
The value of ac selects an accumulator numbered from 0 to 3.
When ac=0, this refers to the original HI/LO register pair of the
MIPS32 architecture.
In Release 6 of the MIPS Architecture, accumulators are eliminated
from MIPS32.
Ensure pre-Release 6 is restricted to HI/LO registers pair.
Fixes: 8b3698b294 ("target/mips: Add emulation of DSP ASE for nanoMIPS - part 4")
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
719f874b83