https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88797
--- Comment #3 from Cassio Neri <cassio.neri at gmail dot com> ---
The attached file is running example that shows that performance is damaged.
The code runs faster when test_f calls g instead of f where g is
bool g(unsigned x, unsigned y) {
if (x >= y) return false;
return f(n, r);
}
even in the case where x < y and g does call f.
Depending on #defines the example runs either f, g or both. These are the
timings:
$ g++ -O3 -o gcc_issue gcc_issue.cpp -D RUN_SIMPLE && time ./gcc_issue
Running simple function...
real 0m3.646s
user 0m3.645s
sys 0m0.000s
$ g++ -O3 -o gcc_issue gcc_issue.cpp -D RUN_COMPLEX && time ./gcc_issue
Running complex function...
real 0m1.165s
user 0m1.161s
sys 0m0.003s
$ g++ -O3 -o gcc_issue gcc_issue.cpp -D RUN_BOTH && time ./gcc_issue
Running simple function...
Running complex function...
real 0m3.059s
user 0m3.051s
sys 0m0.007s
Notice that run both is faster than running f only! This is so because then the
compiler gives up inlining and calls the (good) generated code for f in
isolation.
