------- Comment #7 from rguenth at gcc dot gnu dot org 2007-02-19 15:56 -------
Constant propagation propagates through the PHI in this case:
<bb 2>:
if (x_2(D) == 42) goto <L0>; else goto <L1>;
<L0>:;
y_4 = 23;
# y_1 = PHI <y_3(D)(2), 23(3)>
<L1>:;
y_5 = 23;
return 23;
so this would be the place where a warning could trigger. But it's likely
this will introduce more false positives (so the "may" form is only done
very late). The above could be warned as
"Warning: uninitialized value assumed to be 23."
it's like -Wstrict-overflow -- warn about valid optimizations of undefined
code (that is here, make it "dead"). In that sense it's a dup of the
mentioned PRs (it's treated as dead code).
So, let's make this a request for a warning for an optimization based on
the undefinedness of a value instead ;)
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|minor |enhancement
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30856
