Bubble sort slower with -O3 than -O2 with GCC

I made a bubble sort implementation in C, and was testing its performance when I noticed that the -O3 flag made it run even slower than no flags at all! Meanwhile -O2 was making it run a lot faster as expected. Without optimisations: time ./sort 30000 ./sort 30000 1.82s user 0.00s system 99% cpu 1.816 total -O2: time ./sort 30000 ./sort 30000 1.00s user 0.00s system 99% cpu 1.005 total -O3: time .