MULW - RISC-V instruction reference

mulwMultiply word (32-bit) RV64 only
Multiplies the low 32 bits of t2 and t3 and sign-extends the low 32 bits of the product into t1 (RV64 only).
RISC-V manual: mulw 
Forms  mulw , ,   
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. 
This example runs on RV64.
 .text
li t0, 13
li t1, 5
# t0=13, t1=5; mulw writes 65 to t2.
mulw t2, t0, t1