[Bug tree-optimization/37449] [4.4 Regression] calculix gets wrong answer for -O1 -ffast-math

[jakub at gcc dot gnu dot org]

------- Comment #13 from jakub at gcc dot gnu dot org  2008-10-14 17:35 -------
The different results between -O1 -f{,no}unsafe-math-optimizations are because
this testcase relies heavily on signed zeros, and with with fast math 0 and -0
aren't considered to make a difference, you get at least different value of tt
depending on it (for cn -1.0 it can be either pi/3 or -pi/3, depending on
whether
sqrt returned -0 or 0).  But no matter whether tt is pi/3 or -pi/3, two of the
results should be 0.5 and so the test should succeed.  But dom1 when it decides
to duplicate the bb's (once for the passed in cn, once for +-1.0) omits
unexpectedly the first conditional (i.e. set *neig = 2 if fabs (al[0] - al[1])
<  1.e-5).  It does that both when -funsafe-math-optimizations and
-fno-unsafe-math-optimizations, but given that for -funsafe-math-optimizations
tt is -pi/3, al[0] is 0.5 and al[1] is 0.5, so this is fatal, while for
non-fast math al[0] is 0.5 and al[2] is 0.5, so it doesn't care.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37449