alt Hacker NewsYou would normally use the “LDR Rd, =expr” pseudo-instruction form [1]. For immediates not directly constructible, it puts a copy of the immediate value in a PC-relative memory location, then does a PC-relative load into register.
So that would turn the whole sequence of “add constant to SP” into 2 executable instructions, 1 for constructing immediate and 1 for adding for a total of 8 bytes, and a 4 byte data area for the 17-bit immediate for a total of 12 bytes of binary which is 3 executable instructions worth.
[1] https://developer.arm.com/documentation/dui0801/l/A64-Data-T...
I've usually seen compilers handle large constants with MOV/MOVK sequences (encoding 16 bits of data per 32-bit instruction) instead of loading them from memory. Loading from memory was more common on 32-bit ARM.