MULHU: RISC-V instruction reference

mulhuMultiply high (unsigned × unsigned) 
Multiplies the second register by the third, both unsigned, and stores the high register-width bits of the product in the first.
RISC-V manual: mulhu 
Used in Arithmetic, logic and bitsRISC-V assembly
 
Forms  mulhu , ,   
Operands t1 Any integer register, x0 to x31, or its named alias, such as zero, t0 or t6. 
t2 An integer register. It may be the same register as t1. 
t3 An integer register. It may be the same register as t1. 
 .text
li t0, -1
li t1, 2
# t0=0xFFFFFFFF and t1=2; the unsigned high product is 1; mulhu writes 1 to t2.
mulhu t2, t0, t1