[Bug tree-optimization/39612] [4.4/4.5 Regression] Incorrect warning issued Re variable *is* used uninitialized in this function

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2009-04-02 09:43 -------
Confirmed.  store motion transforms a loop

 for (;;)
   a[0] = 1;

to

 lsmtmp = a[0];
 for (;;)
   lsmtmp = 1;
 a[0] = lsmtmp;

introducing a load from uninitialized memory.  We don't seem to DCE/DSE this
for the tree element array but only the two element one.

The fix is to avoid the load part of load-store-motion of course.  The
warning about unused aggregates is new in 4.4 which makes this a regression.

On the a-i branch we remove the stores later.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org, rakdver at gcc dot gnu
                   |                            |dot org
             Status|UNCONFIRMED                 |NEW
          Component|c                           |tree-optimization
     Ever Confirmed|0                           |1
           Keywords|                            |missed-optimization
   Last reconfirmed|0000-00-00 00:00:00         |2009-04-02 09:43:52
               date|                            |
            Summary|Incorrect warning issued Re |[4.4/4.5 Regression]
                   |variable *is* used          |Incorrect warning issued Re
                   |uninitialized in this       |variable *is* used
                   |function                    |uninitialized in this
                   |                            |function
   Target Milestone|---                         |4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39612