https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71046
Bug ID: 71046
Summary: gcov time hog
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: gcov-profile
Assignee: unassigned at gcc dot gnu.org
Reporter: jakub at gcc dot gnu.org
Target Milestone: ---
struct A
{
char a1, a2, a3, a4, a5, a6, a7, a8, a9;
char b1, b2, b3, b4, b5, b6, b7, b8, b9;
char c1, c2, c3, c4, c5;
};
struct A s;
int
main ()
{
if (__builtin_expect (s.a1 < 0 || s.a1 > 200 || s.a2 < 0 || s.a2 > 200
|| s.a3 < 0 || s.a3 > 200 || s.a4 < 0 || s.a4 > 200
|| s.a5 < 0 || s.a5 > 200 || s.a6 < 0 || s.a6 > 200
|| s.a7 < 0 || s.a7 > 200 || s.a8 < 0 || s.a8 > 200
|| s.a9 < 0 || s.a9 > 200 || s.b1 < 0 || s.b1 > 200
|| s.b2 < 0 || s.b2 > 200 || s.b3 < 0 || s.b3 > 200
|| s.b4 < 0 || s.b4 > 200 || s.b5 < 0 || s.b5 > 200
|| s.b6 < 0 || s.b6 > 200 || s.b7 < 0 || s.b7 > 200
|| s.b8 < 0 || s.b8 > 200 || s.b9 < 0 || s.b9 > 200
|| s.c1 < 0 || s.c1 > 200 || s.c2 < 0 || s.c2 > 200
|| s.c3 < 0 || s.c3 > 200 || s.c4 < 0 || s.c4 > 200
|| s.c5 < 0 || s.c5 > 200, 0))
__builtin_printf ("hello\n");
return 0;
}
(reduced from Linux kernel) with
gcc -O2 -fprofile-arcs -ftest-coverage test.c
./a.out
gcov -b -c -d -a test.gcda
gets stuck in accumulate_line_counts until killed.
There are no loops in the testcase, all bbs have at most 2 successors, one bb
has 23 predecessors, most others have just one.
The comment in accumulate_line_counts says:
/* Find the loops. This uses the algorithm described in
Tiernan 'An Efficient Search Algorithm to Find the
Elementary Circuits of a Graph', CACM Dec 1970. We hold
the P array by having each block point to the arc that
connects to the previous block. The H array is implicitly
held because of the arc ordering, and the block's
previous arc pointer.
Although the algorithm is O(N^3) for highly connected
graphs, at worst we'll have O(N^2), as most blocks have
only one or two exits. Most graphs will be small.
For each loop we find, locate the arc with the smallest
transition count, and add that to the cumulative
count. Decrease flow over the cycle and remove the arc
from consideration. */
