SH2ADD - RISC-V instruction reference

sh2addShift left by 2 and add 
Sets t1 to t2 shifted left by 2, plus t3.
RISC-V manual: sh2add 
Forms  sh2add , ,   
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. 
One instruction for indexing an array of words
 .text
li t0, 13
li t1, 5
# t0=13, t1=5; sh2add writes 57 to t2.
sh2add t2, t0, t1