[Bug middle-end/56574] False possibly uninitialized variable warning

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56574

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic, wrong-code
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-03-11
     Ever Confirmed|0                           |1

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> 2013-03-11 10:43:45 UTC ---
ISO C99 6.5.13 says that 'value' is not evaluated when !flag is false.  But
clearly we are not considering the "side-effect" of using an uninitialized
variable when deciding to output straight-line code sequences.

Affected are at least gimple SSA if-combine and eventually fold and
gimplification (I didn't check them).

Ok, for this testcase it is fold that ends up producing a TRUTH_AND_EXPR.

For SSA if-combine we should only linearize the code if all inner block
SSA (or memory - ugh) uses in

  if (...)
   {
     <here>
     if (...)
      {
...

have a dominating definition.