Similar effects on a Haswell-era Xeon 1240v3:

    $ perf stat -r 10 -e cycles,instructions ./loop t
    
     Performance counter stats for './loop t' (10 runs):
    
         2,631,020,892 cycles                    #    0.000 GHz                      ( +-  0.34% )
         2,403,261,796 instructions              #    0.91  insns per cycle          ( +-  0.00% )
    
           0.713682287 seconds time elapsed                                          ( +-  0.39% )
    
    $ perf stat -r 10 -e cycles,instructions ./loop c
    
     Performance counter stats for './loop c' (10 runs):
    
         2,237,200,035 cycles                    #    0.000 GHz                      ( +-  0.31% )
         3,202,823,909 instructions              #    1.43  insns per cycle          ( +-  0.00% )
    
           0.606741377 seconds time elapsed                                          ( +-  0.29% )