[Bug tree-optimization/59303] [4.9 Regression] uninit-pred-8_b.c and uninit-pred-9_b.c fail after better optimizations

[xinliangli at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59303

--- Comment #5 from davidxl <xinliangli at gmail dot com> ---
Fixing this requires more powerful predicate analysis with the help of value
equivalent classes.

>From the dump:

      "Use in stmt blah (v_1);
      is guarded by :
      if (_23 != 0)"


_23 = pephitmp_22 | _8, so the use guard is

        prephitmp_22 != 0 || _8 != 0

prephitmp_22 = PHI <0(13), prephitmp_21(3), so the guard can be translated to

        prephitmp_21 != 0 || _8 != 0

prephitmp_21 = r_9(D) <= 19, so the predicate becomes

         r_9(D) <= 19 || _8 != 0


For the def:

[CHECK] Found def edge 1 in v_1 = PHI <v_14(D)(13), r_9(D)(3)>
Operand defs of phi v_1 = PHI <v_14(D)(13), r_9(D)(3)>
is guarded by :
       if (_8 != 0)
      (.OR.)
        (.NOT.) if (_8 != 0)
        (.AND.)
         if (_13 != 0)

the predicate is
       _8 != 0 || _13 != 0

where _13 = _10 | _12, 10_ = (r_9(D) <= 19), _12 = l_11(D) != 0

so the predicate is
       _8 != 0 || r_9(D) <= 19 || 1_11(D) != 0

which is the superset for the use.


Perhaps we need to do around of predicate normalization before comparison.

David