SH1ADD - RISC-V instruction reference

sh1addShift left by 1 and add 
Sets t1 to t2 shifted left by 1, plus t3.
RISC-V manual: sh1add 
Forms  sh1add , ,   
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 stepping a pointer through an array of 2 byte elements
 .text
li t0, 13
li t1, 5
# t0=13, t1=5; sh1add writes 31 to t2.
sh1add t2, t0, t1