http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55079
--- Comment #13 from Richard Biener <rguenth at gcc dot gnu.org> 2012-12-10
14:14:07 UTC ---
(In reply to comment #9)
> This is reduced testcase from gcov.c
> int a[8];
> int
> t (void)
> {
> int ix = 0;
> int k;
> int b = 0;
> int curr = 0;
> for (k = 0; k < 2; k++)
> {
> b = ix * 32;
> curr = a[ix++];
> if (!(ix <= 8))
See below.
> abort ();
>
> while (curr)
> {
> b = ix * 32;
> curr = a[ix++];
> if (!(ix <= 8))
This is a test after the fact. For ix == 8 we will still enter the
next loop iteration (GCC can't know anything about 'curr') and thus
access a[8] which is out-of-bounds.
Fixing the tests to test < 8 instead fixes the warnings.
This testcase is invalid.
> abort ();
> }
> }
> return curr + b;
> }
>
> jan@linux-e0ml:~/trunk/build/gcc> ./xgcc -B ./ -O2 -fprofile-use t.c
> -Warray-bounds -S -S -fdump-tree-cunroll-details -fdump-tree-all-details
> t.c: In function ‘t’:
> t.c:14:2: warning: incompatible implicit declaration of built-in function
> ‘abort’ [enabled by default]
> abort ();
> ^
> t.c:25:1: note: file /home/jan/trunk/build/gcc/t.gcda not found, execution
> counts estimated
> }
> ^
> t.c:19:15: warning: array subscript is above array bounds [-Warray-bounds]
> curr = a[ix++];
> ^
> t.c:19:15: warning: array subscript is above array bounds [-Warray-bounds]
>
> Obivously here unroller does not know that bv_ix is at least 1
