ADDIW - RISC-V instruction reference

addiwAdd immediate word (32-bit) RV64 only
Adds a signed 12-bit immediate to the low 32 bits of t2 and sign-extends the sum into t1 (RV64 only).
RISC-V manual: addiw 
Forms  addiw , ,   
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. 
imm12 A signed 12-bit immediate, -2048 to 2047. 
This example runs on RV64.
 .text
li t0, 2147483647
# t0=2147483647, immediate 1; addiw writes -2147483648 (0xFFFFFFFF80000000) to t2.
addiw t2, t0, 1