[Bug tree-optimization/22184] tree vectorizer depends on context

["irar at il dot ibm dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From irar at il dot ibm dot com  2005-07-07 07:47 -------
The problem occurs in decision whether the number of loop iterations is greater 
than zero. The (single) predecessor edge is checked for being EDGE_TRUE_VALUE 
or EDGE_FALSE_VALUE, and the corresponding predicate is used to make the 
decision. 

In the first case (single loop)  BB 0 contains predicate 'len>0', its TRUE 
successor is BB 1, and the fallthru successor of BB 1 is BB 2 - the loop. The 
condition to check is 'len <= 0', which is therefore simplified to FALSE. 

In the second case, however, the control flow is more complicated. The loop is 
in BB 6, its predecessor is BB 3, which has 2 predecessors: BB 5 (with 
predicate 'len > 0'), and BB 2 - the first loop. The first loop is also guarded 
by 'len  > 0', but this information is not propagated.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rakdver at atrey dot karlin
                   |                            |dot mff dot cuni dot cz
   Last reconfirmed|2005-06-25 18:28:42         |2005-07-07 07:47:46
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22184