https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59124
Georg Müller <georgmueller at gmx dot net> changed:
What |Removed |Added
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CC| |georgmueller at gmx dot net
--- Comment #12 from Georg Müller <georgmueller at gmx dot net> ---
gcc --version
gcc (GCC) 5.0.1 20150413 (Red Hat 5.0.1-0.1)
When compiling the first example with -fopt-info, I see the following
difference between -O2 -funroll-loops and -O3:
gcc -Wall -Wextra -fopt-info -O2 -c 1.c -funroll-loops
1.c:11:5: note: loop turned into non-loop; it never loops.
1.c:11:5: note: loop with 6 iterations completely unrolled
1.c:10:3: note: loop turned into non-loop; it never loops.
1.c:10:3: note: loop with 5 iterations completely unrolled
gcc -Wall -Wextra -fopt-info -O3 -c 1.c -funroll-loops
1.c:11:5: note: loop turned into non-loop; it never loops.
1.c:11:5: note: loop with 7 iterations completely unrolled
1.c: In function 'foo':
1.c:12:23: warning: array subscript is above array bounds [-Warray-bounds]
bar[j - 1] = baz[j - 1];
^
1.c:12:23: warning: array subscript is above array bounds [-Warray-bounds]
1.c:10:3: note: loop turned into non-loop; it never loops.
1.c:10:3: note: loop with 5 iterations completely unrolled
So, -O2 unrolls 6 and 5 iterations, while -O3 unrolls 7 and 5.
