https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81897
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I don't think improving the threader (which is strictly an optimization, and
might not be beneficial/desirable in many cases, if it e.g. needs copying large
amounts of code) is the way to go here. The tree-ssa-uninit.c code doesn't try
to solve this issue at all, it is about
if (cond)
v = something;
some_code;
if (cond)
use (v);
where the 2 conditions might not be identical, but the latter needs to be a
subset of the former. While in this case, it is:
if (cond)
v = something;
some_code;
if (!cond)
v = something_else;
use (v);
i.e. the use is unconditional, but the set is in the end also unconditional.
On the other side, we don't warn for:
int bar (int);
int
foo (int x)
{
int a;
if (x)
a = bar (0);
bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (1))))))))))));
bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (2))))))))))));
bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (3))))))))))));
bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (4))))))))))));
bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (5))))))))))));
bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (6))))))))))));
bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (7))))))))))));
bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (8))))))))))));
bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (9))))))))))));
if (!x)
a = bar (10);
bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (11))))))))))));
bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (12))))))))))));
bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (13))))))))))));
bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (bar (14))))))))))));
return a;
}
which simulates large amounts of code that should make the threader punt.
