What is the bit pattern in register
$t1 after the following:
li $t0,0x12345678 sll $t1,$t0,8
$t1 will contain 0x34567800
With a shift left instruction, the bits at the left end of the the register "fall off". The bits shifted into the right end are always zero bits.
With a rotate left instruction, the bits at the left end of the the register are fed into the right end of the register. The 32-bit register always contains the same 32-bit values it started with, but they are rotated into new positions.
In the illustration, after rotating left one bit the pattern changes from 10100111 to 01001111. One more left rotate would change the pattern to 10011110.
Of course, registers have 32 bits, not the eight bits shown in the illustration.
With a rotate right instruction, bit values in the register are moved right. Bits at the right end of the register are fed back into the left end of the register.