demonstrate left shifting on risc-v - cf. https://stackoverflow.com/questions/57949406/rotating-bits-in-risc-v/58018098?noredirect=1#comment106365159_58018098

riscv-shift-example.txt

    Code / Registers:                   x5                  x6     x7   x29     x30
addi x30,  x0, 0x123                     ?                   ?      ?     ?   0x123
andi x29, x30, 0x00f                                                    0x3
slli  x6, x29, 60                           0x3000000000000000
srli  x7, x30, 4                                                 0x12
add   x5,  x6, x7       0x3000000000000012

when eliminating the andi instruction, it yields exactly the same result in x6 and of course in x5:

    Code / Registers:                   x5                  x6     x7   x29     x30
addi x30,  x0, 0x123                     ?                   ?      ?     ?   0x123
slli  x6, x30, 60                           0x3000000000000000
srli  x7, x30, 4                                                 0x12
add   x5,  x6, x7       0x3000000000000012

That means the masking step is superfluous, because the left shift would shift out all the masked bits anyways.
Q.E.D.