clang-5 vs gcc-7.2

matteo@raver:~/src/benchs$ make CFLAGS=-O3 CC=gcc-7 clean all && ./flops 2>/dev/null
rm -f dry flops *.o
gcc-7 -O3 -c dry.c -o dry1.o -Wall
gcc-7 -O3 -DPASS2 dry.c dry1.o -o dry -Wall
gcc-7 -O3 -DUNIX flops.c -o flops -Wall

   FLOPS C Program (Double Precision), V2.0 18 Dec 1992

   Module     Error        RunTime      MFLOPS
                            (usec)
     1      4.0146e-13      0.0042   3298.5546
     2     -1.4166e-13      0.0033   2117.9542
     3      4.7184e-14      0.0042   4071.8144
     4     -1.2557e-13      0.0038   3949.4349
     5     -1.3800e-13      0.0074   3910.9129
     6      3.2380e-13      0.0069   4232.5364
     7     -8.4583e-11      0.0126    954.9911
     8      3.4867e-13      0.0075   3987.1808

   Iterations      =  512000000
   NullTime (usec) =     0.0000
   MFLOPS(1)       =  2512.0259
   MFLOPS(2)       =  1980.5484
   MFLOPS(3)       =  3134.8066
   MFLOPS(4)       =  4071.7976

matteo@raver:~/src/benchs$ make CFLAGS=-O3 CC=clang-5.0 clean all && ./flops 2>/dev/null
rm -f dry flops *.o
clang-5.0 -O3 -c dry.c -o dry1.o -Wall
clang-5.0 -O3 -DPASS2 dry.c dry1.o -o dry -Wall
clang-5.0 -O3 -DUNIX flops.c -o flops -Wall

   FLOPS C Program (Double Precision), V2.0 18 Dec 1992

   Module     Error        RunTime      MFLOPS
                            (usec)
     1      4.0146e-13      0.0042   3367.1505
     2     -1.4166e-13      0.0033   2130.9994
     3      4.7184e-14      0.0040   4300.4378
     4     -1.2557e-13      0.0038   3989.6560
     5     -1.3800e-13      0.0058   4985.2671
     6      3.2380e-13      0.0056   5217.1212
     7     -8.4583e-11      0.0083   1443.7413
     8      3.4867e-13      0.0072   4143.1468

   Iterations      =  512000000
   NullTime (usec) =     0.0000
   MFLOPS(1)       =  2551.8586
   MFLOPS(2)       =  2690.5826
   MFLOPS(3)       =  3762.9836
   MFLOPS(4)       =  4436.3620

matteo@raver:~/src/benchs$