http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50693
--- Comment #15 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-10-11
14:34:47 UTC ---
Note that it doesn't handle memset though, and the convoluted loop wouldn't be
easy to detect either.
size_t i = 0;
bool loop_cond = i < n;
while (loop_cond) {
goto copy_block;
loop_back:
loop_cond = i < n;
}
goto end;
copy_block:
v->chars[i] = c;
i++;
goto loop_back;
end:
v->chars[n] = '\0';
return v;
is simply trying to be too clever. I can't even understand that source ;)
What probably causes this is that we don't merge the blocks
# i_29 = PHI <i_10(3), 0(2)>
copy_block:
D.3506_7 = v_20->chars;
D.3507_8 = D.3506_7 + i_29;
*D.3507_8 = c_9(D);
i_10 = i_29 + 1;
goto <bb 3> (loop_back);
loop_back:
loop_cond_11 = i_10 < n_3(D);
if (loop_cond_11 != 0)
goto <bb 4> (copy_block);
else
goto <bb 5> (end);
even though it's a fallthru edge. We don't do this to preserve user labels
for debugging (and mind, no code-gen differences between -g0 vs. -g).
