GCC generates LEA even for a regular addition, even with -O3 and -march=native on a modern Intel x86-64 system. A simple addition of int64_t gives you:

GCC generates LEA even for a regular addition, even with -O3 and -march=native on a modern Intel x86-64 system. A simple addition of int64_t gives you: leaq (%rdi,%rsi), %rax Whereas subtracting the tag gives you: leaq -1(%rdi,%rsi), %rax So pretty much the same either way, though you do get five instruction bytes for the tag version vs. four bytes without. Here are the comparisons for multiply and divide, from "gcc -c -O3 -g -march=native" and "objdump -d": x * y: 10: 48 89 f8 mov %rdi,%rax 13: 48 0f af c6 imul %rsi,%rax (x >> 1) * (y - 1) + 1: 40: 48 d1 ff sar %rdi 43: 48 83 ee 01 sub $0x1,%rsi 47: 48 89 f8 mov %rdi,%rax 4a: 48 0f af c6 imul %rsi,%rax 4e: 48 83 c0 01 add $0x1,%rax x / y: 20: 48 89 f8 mov %rdi,%rax 23: 48 99 cqto 25: 48 f7 fe idiv %rsi (((x >> 1) / (y >> 1)) << 1) + 1: 60: 48 89 f8 mov %rdi,%rax 63: 48 d1 fe sar %rsi 66: 48 d1 f8 sar %rax 69: 48 99 cqto 6b: 48 f7 fe idiv %rsi 6e: 48 8d 44 00 01 lea 0x1(%rax,%rax,1),%rax